ABSTRACT
We present multiband photometry of 185 type-Ia supernovae (SNe Ia), with over 11,500 observations. These were acquired between 2001 and 2008 at the F. L. Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics (CfA). This sample contains the largest number of homogeneously observed and reduced nearby SNe Ia (z ≲ 0.08) published to date. It more than doubles the nearby sample, bringing SN Ia cosmology to the point where systematic uncertainties dominate. Our natural system photometry has a precision of ≲0.02 mag in BVRIr'i' and ≲0.04 mag in U for points brighter than 17.5 mag. We also estimate a systematic uncertainty of 0.03 mag in our SN Ia standard system BVRIr'i' photometry and 0.07 mag for U. Comparisons of our standard system photometry with published SN Ia light curves and comparison stars, where available for the same SN, reveal agreement at the level of a few hundredths mag in most cases. We find that 1991bg-like SNe Ia are sufficiently distinct from other SNe Ia in their color and light-curve-shape/luminosity relation that they should be treated separately in light-curve/distance fitter training samples. The CfA3 sample will contribute to the development of better light-curve/distance fitters, particularly in the few dozen cases where near-infrared photometry has been obtained and, together, can help disentangle host-galaxy reddening from intrinsic supernova color, reducing the systematic uncertainty in SN Ia distances due to dust.
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1. INTRODUCTION
SNe Ia are standardizable candles (σ ≲ 0.2 mag after correction for light-curve shape) and have been used to measure the expansion history of the universe (e.g., Phillips 1993; Riess et al. 1996; Hamuy et al. 1996a; Goldhaber et al. 2001; Jha et al. 2007), giving rise to the startling conclusion that the universe is accelerating (e.g., Riess et al. 1998; Perlmutter et al. 1999).
Some 30 years prior to the discovery of the accelerating universe, Kowal (1968) found a dispersion of ∼0.6 mag in the SN Ia redshift–magnitude relation. Reasons for the high dispersion are that many of the objects in his sample were not in the Hubble flow, corrections for light-curve shape and absorption were not made, and not all objects were SNe Ia. He predicted that SNe Ia might become distance estimators with better than 10% precision and enable measurement of the curvature of the Hubble diagram at greater redshifts. Nearly 20 years later, Norgaard-Nielsen et al. (1989) made a valiant attempt to measure SNe Ia at z ∼ 0.3, using methods similar to modern SN searches. They had the right idea but their telescope and detector were too small and they only reported one SN Ia in two years of searching. The advent of significantly larger detectors, mounted on larger telescopes, provided the higher discovery rates needed and was one of the main factors in the discovery of the accelerating universe.
SN Ia studies can be divided into two broad groups: low redshift and high redshift. For our purposes, the dividing line between the two groups is at z ≈ 0.15. Low-redshift SNe Ia are easier to study to higher precision and can generally be observed over a greater range in phase. They map out the recent expansion of the universe and can be used to study the local bulk flows and peculiar velocities of galaxies in the nearby universe (e.g., Tammann & Leibundgut 1990; Riess et al. 1995; Jha et al. 2007; Neill et al. 2007; Haugbolle et al. 2007). They also serve as the template against which the high-redshift SNe Ia are compared. Having, and understanding, a nearby sample that fills out the phase space of SN Ia properties is vital to the use of SNe Ia as precise distance indicators at greater redshifts. High-redshift SNe Ia allow measurements of the change in the expansion rate of the universe over time as well as in any presumed underlying models, such as dark energy. Up to a point, more data at both high and low redshift decrease the statistical uncertainty in the derived cosmological parameters. It can also help refine our understanding of possible systematic uncertainties such as host-galaxy reddening and intrinsic color variation of SNe Ia.
On the nearby front, the Calan-Tololo survey produced the first large, multiband, CCD sample of SN Ia photometry, publishing 29 light curves (Hamuy et al. 1996b). This was followed by 22 BVRI SN Ia light curves from the CfA in 1999 (Riess et al. 1999) and a further 44 UBVRI in 2006 (Jha et al. 2006, hereafter, J06) (these two samples will be referred to as CfA1 and CfA2, respectively). Additionally, Krisciunas and his collaborators have published a significant number (Krisciunas et al. 2000, 2001, 2003, 2004a, 2004b, 2006), the European Supernova Collaboration has published photometry of several nearby SNe Ia (see Stanishev et al. 2007, and references therein), and Kowalski et al. (2008) recently published eight nearby SNe Ia.
Other groups that are working on significant nearby samples are KAIT,25 in conjunction with the LOTOSS/LOSS SN searches, CSP (Hamuy et al. 2006) and the Nearby Supernova Factory (Aldering et al. 2002). The 2004 Sloan Digital Sky Survey (SDSS) SN Survey (Sako et al. 2005) found 16 spectroscopically confirmed SNe Ia as a preparation run for the SDSS-II SN Survey (Frieman et al. 2008). In its first two years, SDSS-II observed over 300 spectroscopically confirmed and ∼100 photometrically identified SNe Ia in ugriz and in the redshift range 0.05 < z < 0.35. This survey has good control of systematics in their photometry and will be very useful in calculating SN rates in the nearby to intermediate redshift range. Dilday et al. (2008) present a calculation of nearby SN Ia rates based on 17 SNe Ia at z ⩽ 0.12 from the 2005 season of SDSS-II.
Systematic differences often exist between different groups' photometry of the same SN Ia at low redshift, typically at the level of a few hundredths mag and sometimes larger. These differences are mainly due to difficulties in transforming to the standard system and, to a lesser extent, the use of different photometry pipelines. A large, homogeneously observed and reduced nearby sample does not internally suffer from these two problems and can help reduce systematic uncertainties in dark energy measurements. However, there is still the issue of ensuring that the nearby and faraway samples are photometrically consistent.
The goal of our research was to produce a large sample of homogeneously observed and reduced SN Ia light curves that fills out the sampling of the whole range of SN Ia properties and can be used to reduce the statistical and systematic uncertainties in SN Ia cosmology. Here, we publish 185 multiband optical SN Ia light curves, with data taken between the years 2001 and 2008. This is the third sample of nearby CfA SN Ia photometry (CfA3 sample). This is the largest set of nearby SN Ia photometry to date, more than doubling the literature sample. It consists of over 11,500 observations. For comparison, the CfA1 and CfA2 samples consist of 1210 and 2190 observations.
A better understanding of the nature and range of SN Ia properties improves their use as standardizable candles and may reveal that certain subsamples are more useful than others. We intentionally built up the sample of slow (more luminous) and fast (less luminous) decliners. The slow decliners are particularly helpful for improving SN Ia cosmology since they are found more often at high redshift. The study of peculiar SNe Ia also deepens our understanding of what physical mechanisms might be at work and large samples are more likely to include rare types. One such object that the CfA Supernova Group26 observed was SN 2006gz (Hicken et al. 2007; Maeda et al. 2009), a very slow-declining and bright SN Ia that may have come from a double-degenerate merger and/or a Super-Chandrasekhar progenitor. With the larger sample, light-curve fitters can be trained better and a proper prediction error can be calculated by excluding individual objects (or groups of objects) from the training sample one at a time. Mandel et al. (2009) has developed the machinery for this in the near infrared and will be including the optical bands shortly. Combining the optical and near-infrared photometry should help disentangle host-galaxy reddening from intrinsic SN Ia color.
The impact of adding additional nearby SNe Ia can be seen in Kowalski et al. (2008), who take 49 nearby and 250 faraway SNe Ia from the literature and add eight of their own, using the light-curve fitter SALT (Guy et al. 2005). These additional eight reduce the statistical uncertainty on the dark energy parameter, w, by a factor of 1.04, when the intrinsic or additional uncertainty of ∼0.1 mag that they discuss is added. If the intrinsic uncertainty is not added then their eight reduce the statistical uncertainty in w by a factor of 1.07. The application of the CfA3 data set to studying dark energy is presented in Hicken et al. (2009, hereafter H09), where 90 of the 185 objects presented here pass the quality cuts (on such things as redshift and phase of first observation) of Kowalski et al. (2008). These 90 are added to their "Union" set to form the "Constitution" set (a more perfect union) with a total of 157 nearby and 250 faraway objects. The Constitution set produces a value of 1 + w = 0.013+0.066−0.068(0.11 syst), consistent with the cosmological constant. The uncertainty on w for the Constitution set is found to be 1.2–1.3 times smaller than the comparable Union value (1.3 when the ∼0.1 mag intrinsic uncertainty is included and 1.2 when it is not), in line with approximate statistical expectations. The systematic uncertainty is estimated to be ∼65% larger than the statistical uncertainty. The other fitters, SALT2 (Guy et al. 2007), MLCS2k2 (Jha et al. 2007) with RV = 3.1 and MLCS2k2 with RV = 1.7 were found to reduce the statistical uncertainty by a factor of ∼1.2–1.3, slightly less than the rough statistical expectation. The addition of the CfA3 sample achieves its goal of reducing the statistical uncertainty of w. Both the good and the bad news is that systematic errors are now the main limit for making further progress in better understanding dark energy with SNe Ia! Improvements in systematic uncertainties are needed to maximize the contributions of future SN Ia surveys, such as the Joint Dark Energy Mission, that aim to place tight constraints on the time dependence of dark energy.
In this paper, we first show that the CfA3 sample is consistent with previous nearby samples in its color and host-galaxy reddening distributions. By design, the CfA3 sample has a wider distribution of light-curve shapes than earlier work since we gave the fast and slow decliners higher priority in deciding which objects to follow most thoroughly. However, the range of decline rates covered is the same. We also show that the agreement of our photometry with that of other groups, for the same objects, is as good as the agreement between other groups, typically at the level of a few hundredths mag. These facts give us confidence that the CfA3 sample can be used by current light-curve fitters developed primarily from the Calan-Tololo, CfA1, and CfA2 surveys. We invite people to combine the CfA3 sample with previous samples to retrain existing fitters or invent new ones. The CfA3 sample itself was not part of the training sample for any of the light-curve fitters in H09 and so the good agreement found there of the CfA3 results with previous samples is encouraging.
The CfA3 sample shares many of its methods with ESSENCE (Miknaitis et al. 2007). The same data-reduction pipeline was used, minimizing the introduction of systematic effects due to different reduction methods. The CfA3 sample also helps reduce the systematic uncertainty in w because it was reduced and mostly observed in a homogeneous fashion (the use of two different cameras and changing from RI filters to r'i' being the exceptions to completely homogeneous observation).
In conjunction with this optical photometry, the CfA Supernova Group has taken spectra (Matheson et al. 2008; S. Blondin et al. 2009, in preparation) of many of these SNe using the FAST spectrograph (Fabricant et al. 1998) and, starting in 2004, began the use of the PAIRITEL near-infrared telescope27 to acquire valuable JHK-band data for the brighter SN Ia in the sample. These near-infrared SN Ia light curves stand on their own as standard candles (Wood-Vasey et al. 2008) and, when combined with the optical data, will help clarify the properties of host-galaxy dust and intrinsic color variation of SNe Ia (A. Friedman et al. 2009, in preparation). This should help decrease the systematic uncertainties due to these intertwined phenomena.
In Section 2, we describe our observing strategy, explain our data reduction choices, and present the CfA3 light curves. We also show that our photometry is internally consistent and agrees well externally (to a few hundredths mag, roughly) in cases where others have published light curves for the same objects. Typical uncertainties in our V-band SN photometry are 0.015 mag around maximum light. We estimate a systematic uncertainty of 0.03 mag in BVRIr'i' and 0.07 mag in U. In Section 3, we examine the decline rates, intrinsic colors, and intrinsic absolute magnitudes. We confirm many of the relations seen before. The one main new insight is that the fast decliners have a range in intrinsic magnitude of 1.0–1.5 mag, with the 1991bg-like objects significantly fainter and not forming part of the otherwise tight locus of SN Ia points, suggesting that they should be treated separately in light-curve fitter training samples. We present our conclusions in Section 4.
The CfA3 light curves, comparison star magnitudes, and passbands can be found at our Web site28 and are archived with the journal. Luminosity distances from H09 can also be found at our Web site.
2. DATA AND REDUCTION
The instruments, data acquisition, and data reduction are described here. The data reduction consists of three stages: reduction, calibration, and host-galaxy subtraction (where necessary). The reduction and subtraction stages are carried out by a version of the ESSENCE and SuperMACHO pipeline (Miknaitis et al. 2007; Rest et al. 2005; Garg et al. 2007), modified for use on the CfA3 data. The calibration was carried out very similarly to the calibration in the CfA1 and CfA2 samples. We made use of differential photometry by calibrating the field or comparison stars surrounding the SN on photometric nights and then measuring the flux of the SN relative to the comparison stars in each image, on both photometric and nonphotometric nights. In most cases, the underlying host-galaxy light had to be subtracted, using reference images taken after the SN had faded.
2.1. Instruments
The 1.2 m telescope at the F. L. Whipple Observatory (FLWO) was used to obtain the photometry presented here. The 4Shooter 2 × 2 CCD mosaic29 was employed up until 2004 August for 64 objects of the CfA3 sample. From 2004 September to 2005 July, the 2 × 1 CCD mosaic Minicam30 was used to observe five SNe Ia. The single-chip CCD Keplercam31 was used for the remaining 116 SNe Ia beginning in 2005 September.
The 4Shooter camera uses four thinned, backside-illuminated, antireflective coated Loral 2048 × 2048 CCD detectors. Our 4Shooter observations were always on chip three (read out by a single amplifier) in the bin-by-2 mode such that the binned pixel scale is 0674 pixel−1 and the field of view was 115 × 115. The typical image quality was 15 to 3'' FWHM. The Minicam chips are thinned, backside-illuminated Marconi (ex-EEV) 2248 × 4640 CCD detectors with two long-rectangular shaped amplifiers per chip. In the bin-by-2 mode, the pixel scale is 0600 pixel−1. Our observations were always on amplifier three with an approximate field of view of 51 × 231. The Keplercam uses a Fairchild "CCD 486." It is read out by four amplifiers, each covering a region of 2048 × 2048 pixels. Our observations were always on amplifier 2. In the bin-by-2 mode, the pixel scale is 0672 pixel−1, resulting in an amplifier-2 field of view of approximately 115 × 115.
All three instruments have good response in the red while the 4Shooter was superior in the near ultraviolet. The 4Shooter had a significant number of bad pixels that required masking, the Minicam had few and the Keplercam had virtually none. A bad-pixel mask was not required or used for the Minicam and Keplercam. The Johnson UBV passbands were used with all three detectors. The Krons–Cousins RI passbands were used on the 4Shooter. In order to cooperate better with other FLWO observing programs, SDSS r'i' filters were used on the Minicam and Keplercam. The "Harris" set of BVRI filters and a U filter with a CuSO4 cell for red blocking were used for all CfA3 4Shooter observations. The same UBV filters, and SDSS r'i' filters were used on the Minicam and Keplercam. The U filter broke in 2007 January and was replaced in 2007 June. A liquid leak was discovered in the CuSO4 cell of the U filter in 2007 November and after repair and testing it was installed in 2008 February. These problems with the U filter account for missing U-band photometry in 2007–2008.
The 64 4Shooter objects are all observed with the same camera and filters and reduced with the same pipeline, constituting one homogeneously observed and reduced sample. The 116 Keplercam objects also represent a homogeneously observed and reduced sample. The use of three different cameras and changing from RI filters to r'i' limits us from calling the entire CfA3 sample homogeneously observed and reduced. However, its acquisition and reduction can be called quasi homogeneous, since the UBV filters were used on all three cameras, the detector responses are similar, and the same reduction pipeline was used.
2.2. Observations
Nearby SNe are discovered by both amateur and professional astronomers. Many of the discoverers promptly report their findings to the SN community via email. The IAU's Central Bureau for Astronomical Telegrams, the IAU Circulars and The Astronomer's Telegram are commonly used to disseminate information. Usually the initial discovery does not include spectroscopic confirmation and typing. The CfA Supernova Group depends on these discoveries, north of declination −20°, for the SN it studies. The CfA3 discovery data are displayed in Table 1. Roughly two thirds of the CfA3 sample were discovered by professional observers. Roughly one third was discovered by amateurs, demonstrating their valuable contribution to nearby SN science. In first place, KAIT/LOTOSS/LOSS discovered 46% of the CfA3 sample. In second place, the Puckett Observatory Supernova Search32 discovered 18%. Most of these search surveys had typical limiting magnitudes of 19.5 mag. SDSS-II is the most obvious exception.
Table 1. SN Ia Discovery Data
SN Ia | Galaxy | Discovery Date (yyyy mm dd) | Position | CBET/IAUC | Discoverer |
---|---|---|---|---|---|
2001C | Anon Gal | 2001 01 04 | 06:59:36.138 +59:31:01.21 | IAUC 7555 | Puckett, Sehgal |
2001G | MCG +08-17-43 | 2001 01 08 | 09:09:33.215 +50:16:50.83 | IAUC 7560 | Armstrong |
2001N | NGC 3327 | 2001 01 21 | 10:39:58.060 +24:05:25.68 | IAUC 7568 | Chornock |
2001V | NGC 3987 | 2001 02 19 | 11:57:24.910 +25:12:09.49 | IAUC 7585 | Berlind |
2001ah | UGC 6211 | 2001 03 27 | 11:10:29.838 +55:09:39.03 | IAUC 7603 | Puckett, Peoples |
2001ay | IC 4423 | 2001 04 18 | 14:26:16.943 +26:14:55.24 | IAUC 7611 | LOTOSS |
2001az | UGC 10483 | 2001 04 27 | 16:34:27.476 +76:01:46.34 | IAUC 7614 | Puckett, Peoples |
2001bf | MCG +04-42-22 | 2001 05 03 | 18:01:34.059 +26:15:01.82 | IAUC 7620 | Armstrong |
2001cp | UGC 10738 | 2001 06 19 | 17:11:02.600 +05:50:27.04 | IAUC 7645 | LOTOSS |
2001da | NGC 7780 | 2001 07 09 | 23:53:32.741 +08:07:02.20 | IAUC 7658 | LOTOSS |
2001eh | UGC 1162 | 2001 09 09 | 01:38:12.056 +41:39:18.95 | IAUC 7712 | Armstrong |
2001en | NGC 523 | 2001 09 26 | 01:25:22.856 +34:01:30.06 | IAUC 7724 | LOTOSS; BAO |
2001ep | NGC 1699 | 2001 10 03 | 04:57:00.349 −04:45:40.04 | IAUC 7727 | LOTOSS |
2001fe | UGC 5129 | 2001 11 02 | 09:37:57.021 +25:29:40.84 | IAUC 7742 | Armstrong |
2001fh | Anon Gal | 2001 11 03 | 21:20:42.538 +44:23:53.14 | IAUC 7744 | LOTOSS |
2001gb | IC 582 | 2001 11 20 | 09:59:00.960 +17:49:12.32 | IAUC 7758 | LOTOSS |
2001gc | UGC 3375 | 2001 11 21 | 05:55:26.111 +51:54:34.22 | IAUC 7759 | LOTOSS |
2001ic | NGC 7503 | 2001 12 07 | 23:10:43.298 +07:34:10.25 | IAUC 7770 | LOTOSS |
2001ie | UGC 5542 | 2001 12 09 | 10:16:50.954 +60:16:53.32 | IAUC 7771 | Bincoletto |
2002G | Anon Gal | 2002 01 18 | 13:07:55.285 +34:05:07.09 | IAUC 7797 | LOTOSS |
2002ar | NGC 3746 | 2002 02 03 | 11:37:43.863 +22:00:34.47 | IAUC 7819 | LOTOSS |
2002bf | Anon Gal | 2002 02 22 | 10:15:42.314 +55:40:07.35 | IAUC 7836 | LOTOSS |
2002bo | NGC 3190 | 2002 03 09 | 10:18:06.515 +21:49:41.63 | IAUC 7847 | Cacella; Hirose |
2002bz | MCG +05-34-33 | 2002 04 03 | 14:24:40.524 +26:37:35.29 | IAUC 7866 | Puckett, Gauthier |
2002cd | NGC 6916 | 2002 04 08 | 20:23:34.402 +58:20:47.30 | IAUC 7871 | Armstrong |
2002ck | UGC 10030 | 2002 04 23 | 15:47:00.762 −00:59:24.92 | IAUC 7884 | LOTOSS |
2002cr | NGC 5468 | 2002 05 01 | 14:06:37.652 −05:26:21.34 | IAUC 7890 | Kushida |
2002de | NGC 6104 | 2002 06 01 | 16:16:30.334 +35:42:30.09 | IAUC 7914 | LOTOSS |
2002dj | NGC 5018 | 2002 06 12 | 13:13:00.414 −19:31:08.56 | IAUC 7918 | LOTOSS |
2002do | MCG +07-41-1 | 2002 06 17 | 19:56:12.853 +40:26:10.47 | IAUC 7923 | LOTOSS |
2002dp | NGC 7678 | 2002 06 18 | 23:28:30.103 +22:25:38.05 | IAUC 7924 | Klotz |
2002es | UGC 2708 | 2002 08 23 | 03:23:47.196 +40:33:53.56 | IAUC 7959 | LOTOSS |
2002eu | Anon Gal | 2002 08 30 | 01:49:43.549 +32:37:42.31 | IAUC 7963 | LOTOSS |
2002fb | NGC 759 | 2002 09 06 | 01:57:48.869 +36:20:26.00 | IAUC 7967 | LOTOSS |
2002fk | NGC 1309 | 2002 09 17 | 03:22:05.706 −15:24:02.99 | IAUC 7973 | Kushida; BAO |
2002ha | NGC 6962 | 2002 10 21 | 20:47:18.592 +00:18:45.36 | IAUC 7997 | LOTOSS |
2002hd | MCG −01-23-8 | 2002 10 24 | 08:54:03.366 −07:11:21.48 | IAUC 7999 | LOTOSS |
2002he | UGC 4322 | 2002 10 28 | 08:19:58.804 +62:49:13.71 | IAUC 8002 | LOTOSS |
2002hu | MCG +06-6-12 | 2002 11 07 | 02:18:20.027 +37:27:58.58 | IAUC 8012 | Boles |
2002hw | UGC 52 | 2002 11 09 | 00:06:49.025 +08:37:48.64 | IAUC 8014 | LOTOSS |
2002jy | NGC 477 | 2002 12 17 | 01:21:16.231 +40:29:55.27 | IAUC 8035 | Arbour; Vanmunster |
2002kf | Anon Gal | 2002 12 27 | 06:37:15.283 +49:51:10.87 | IAUC 8040 | Brady |
2003D | MCG −01-25-9 | 2003 01 06 | 09:38:53.551 −04:51:05.61 | IAUC 8043 | Puckett, Langoussis |
2003K | IC 1129 | 2003 01 11 | 15:32:01.832 +68:14:36.12 | IAUC 8048 | Puckett, Langoussis |
2003U | NGC 6365 | 2003 01 27 | 17:22:45.626 +62:09:50.67 | IAUC 8059 | Boles |
2003W | UGC 5234 | 2003 01 28 | 09:46:49.496 +16:02:37.77 | IAUC 8061 | LOTOSS |
2003ae | Anon Gal | 2003 01 23 | 09:28:22.570 +27:26:41.29 | IAUC 8066 | NEAT/Wood-Vasey et al. |
2003ai | IC 4062 | 2003 02 08 | 13:00:58.699 +39:51:24.66 | IAUC 8068 | LOTOSS |
2003cg | NGC 3169 | 2003 03 21 | 10:14:16.016 +03:28:02.01 | IAUC 8097 | Itagaki; Arbour |
2003ch | UGC 3787 | 2003 03 21 | 07:17:57.890 +09:41:34.84 | IAUC 8097 | LOTOSS |
2003cq | NGC 3978 | 2003 03 30 | 11:56:14.156 +60:31:19.67 | IAUC 8103 | Arbour |
2003du | UGC 9391 | 2003 04 22 | 14:34:35.728 +59:20:03.93 | IAUC 8121 | LOTOSS |
2003fa | Anon Gal | 2003 06 01 | 17:44:07.733 +40:52:51.08 | IAUC 8140 | LOTOSS |
2003hu | Anon Gal | 2003 09 06 | 19:11:31.121 +77:53:34.91 | IAUC 8196 | Armstrong |
2003ic | MCG −02-2-86 | 2003 09 16 | 00:41:50.334 −09:18:19.11 | IAUC 8201 | LOTOSS |
2003it | UGC 40 | 2003 10 13 | 00:05:48.523 +27:27:08.62 | IAUC 8225 | Puckett, Cox |
2003iv | MCG +02-8-14 | 2003 10 17 | 02:50:07.244 +12:50:45.29 | IAUC 8226 | LOTOSS |
2003kc | MCG +05-23-37 | 2003 11 21 | 09:46:34.293 +30:39:19.27 | IAUC 8242 | LOSS |
2003kf | MCG −02-16-2 | 2003 11 27 | 06:04:35.484 −12:37:42.87 | IAUC 8245 | LOSS |
2004K | ESO 579-G22 | 2004 01 19 | 14:23:39.802 −19:26:50.13 | IAUC 8273 | LOSS |
2004L | MCG +03-27-38 | 2004 01 21 | 10:27:04.125 +16:01:07.80 | IAUC 8274 | LOSS |
2004ap | Anon Gal | 2004 03 08 | 10:05:43.813 +10:16:16.68 | IAUC 8300 | LOSS |
2004as | Anon Gal | 2004 03 11 | 11:25:39.185 +22:49:49.05 | IAUC 8302 | LOSS |
2004bg | UGC 6363 | 2004 04 07 | 11:21:01.542 +21:20:22.95 | IAUC 8317 | Armstrong |
2004ef | UGC 12158 | 2004 09 04 | 22:42:10.021 +19:59:39.89 | IAUC 8399 | Boles; Armstrong |
2004fu | NGC 6949 | 2004 11 04 | 20:35:11.608 +64:48:26.41 | IAUC 8428 | Arbour |
2005M | NGC 2930 | 2005 01 19 | 09:37:32.356 +23:12:02.20 | IAUC 8470 | Puckett, George |
2005am | NGC 2811 | 2005 02 22 | 09:16:13.087 −16:18:15.97 | IAUC 8490 | Martin |
2005cf | MCG −01-39-3 | 2005 05 28 | 15:21:32.225 −07:24:47.66 | CBET 158 | LOSS |
2005dv | NGC 5283 | 2005 09 04 | 13:41:04.478 +67:40:19.53 | CBET 217 | Dainese, Dimai |
2005el | NGC 1819 | 2005 09 25 | 05:11:48.744 +05:11:39.19 | CBET 233 | LOSS |
2005eq | MCG −01-9-6 | 2005 09 30 | 03:08:49.357 −07:02:00.24 | IAUC 8608 | LOSS |
2005eu | Anon Gal | 2005 10 04 | 02:27:43.239 +28:10:36.71 | CBET 242 | LOSS |
2005ew | Anon Gal | 2005 10 04 | 03:39:23.747 +35:02:49.38 | CBET 244 | Nearby SN Factory |
2005hc | MCG +00-6-3 | 2005 10 12 | 01:56:47.950 −00:12:49.42 | CBET 259 | SDSS-II |
2005hf | Anon Gal | 2005 10 25 | 01:27:05.991 +19:07:00.83 | IAUC 8622 | Quimby et al. |
2005hj | Anon Gal | 2005 10 26 | 01:26:48.397 −01:14:17.30 | CBET 266 | Quimby et al. |
2005hk | UGC 272 | 2005 10 30 | 00:27:50.879 −01:11:53.32 | IAUC 8625 | SDSS-II; LOSS |
2005iq | MCG −03-1-8 | 2005 11 05 | 23:58:32.422 −18:42:32.97 | IAUC 8628 | LOSS |
2005ir | Anon Gal | 2005 10 28 | 01:16:43.796 +00:47:40.89 | CBET 277 | SDSS II; Quimby et al. |
2005kc | NGC 7311 | 2005 11 09 | 22:34:07.308 +05:34:06.04 | IAUC 8629 | Puckett, Sostero |
2005ke | NGC 1371 | 2005 11 13 | 03:35:04.356 −24:56:38.93 | IAUC 8630 | LOSS |
2005ki | NGC 3332 | 2005 11 18 | 10:40:28.219 +09:12:08.21 | IAUC 8632 | LOSS |
2005ls | MCG +07-7-1 | 2005 12 09 | 02:54:15.914 +42:43:29.15 | IAUC 8643 | Armstrong |
2005lu | MCG −03-07-40 | 2005 12 11 | 02:36:03.753 −17:15:49.50 | IAUC 8645 | LOSS |
2005lz | UGC 1666 | 2005 12 24 | 02:10:49.727 +34:58:57.84 | CBET 329 | Puckett, Gagliano |
2005mc | UGC 4414 | 2005 12 23 | 08:27:06.277 +21:38:46.61 | CBET 331 | THCA Supernova Survey |
2005ms | UGC 4614 | 2005 12 27 | 08:49:14.320 +36:07:46.72 | CBET 343 | Puckett, Kroes |
2005mz | NGC 1275 | 2005 12 31 | 03:19:49.910 +41:30:18.86 | CBET 347 | Newton, Peoples, Puckett |
2005na | UGC 3634 | 2005 12 31 | 07:01:36.659 +14:07:58.75 | CBET 350 | Newton, Ceravolo, Puckett |
2006B | UGC 12538 | 2006 01 08 | 23:21:09.803 +33:24:00.74 | CBET 356 | Puckett, Sostero |
2006D | MCG −01-33-34 | 2006 01 11 | 12:52:33.871 −09:46:30.56 | CBET 362 | Colesanti, et al. |
2006H | Anon Gal | 2006 01 15 | 03:26:01.533 +40:41:41.69 | CBET 367 | Puckett, Sostero |
2006N | MCG +11-8-12 | 2006 01 21 | 06:08:31.268 +64:43:24.82 | CBET 375 | Armstrong |
2006S | UGC 7934 | 2006 01 26 | 12:45:39.033 +35:05:12.16 | CBET 379 | Puckett, Gagliano |
2006X | NGC 4321 | 2006 02 04 | 12:22:53.911 +15:48:31.65 | IAUC 8667 | Suzuki; Migliardi |
2006ac | NGC 4619 | 2006 02 09 | 12:41:44.894 +35:04:07.93 | IAUC 8669 | LOSS |
2006ah | Anon Gal | 2006 02 09 | 13:46:13.540 −09:07:51.92 | CBET 402 | Nearby SN Factory |
2006ak | Anon Gal | 2006 02 17 | 11:09:32.640 +28:37:51.63 | CBET 408 | Tyurina, Lipunov et al. |
2006al | Anon Gal | 2006 02 19 | 10:39:28.238 +05:11:00.39 | IAUC 8677 | Holmes, Devore |
2006an | Anon Gal | 2006 02 21 | 12:14:38.749 +12:13:47.75 | CBET 413 | Quimby, Castro |
2006ar | MCG +11-13-36 | 2006 03 05 | 10:37:30.616 +65:00:57.78 | CBET 420 | Boles |
2006ax | NGC 3663 | 2006 03 20 | 11:24:03.432 −12:17:29.52 | CBET 435 | LOSS |
2006az | NGC 4172 | 2006 03 23 | 12:12:14.650 +56:10:47.11 | IAUC 8691 | Newton, Cox, Puckett |
2006bb | UGC 4468 | 2006 03 25 | 08:33:31.096 +41:31:04.20 | CBET 444 | Puckett, Gagliano |
2006bd | UGC 6609 | 2006 03 26 | 11:38:28.420 +20:31:34.45 | CBET 448 | Puckett, Cox |
2006bk | MCG +06-23-20 | 2006 04 03 | 15:04:33.606 +35:57:50.53 | CBET 462 | Boles |
2006bq | NGC 6685 | 2006 04 23 | 18:39:58.941 +39:58:56.34 | CBET 479 | Puckett, Pelloni |
2006br | NGC 5185 | 2006 04 25 | 13:30:01.716 +13:24:56.61 | CBET 482 | Puckett, Sostero |
2006bt | Anon Gal | 2006 04 26 | 15:56:30.526 +20:02:45.34 | CBET 485 | LOSS |
2006bu | Anon Gal | 2006 04 27 | 13:52:47.736 +05:18:48.41 | CBET 490 | Holmes, Devore, Graves |
2006bw | Anon Gal | 2006 04 27 | 14:33:56.806 +03:47:55.82 | CBET 497 | LOSS |
2006bz | Anon Gal | 2006 05 04 | 13:00:43.362 +27:57:41.28 | IAUC 8707 | LOSS |
2006cc | UGC 10244 | 2006 05 06 | 16:09:56.460 +43:07:35.89 | CBET 505 | LOSS |
2006cf | UGC 6015 | 2006 05 11 | 10:54:02.585 +46:01:36.44 | IAUC 8710 | LOSS; Puckett, Toth |
2006cg | Anon Gal | 2006 05 06 | 13:05:02.382 +28:44:25.11 | CBET 509 | Quimby, Mondol |
2006cj | Anon Gal | 2006 05 17 | 12:59:24.519 +28:20:51.36 | CBET 515 | Quimby, Mondol, Castro |
2006cm | UGC 11723 | 2006 05 24 | 21:20:17.423 −01:41:02.08 | CBET 521 | Puckett, Langoussis |
2006cp | UGC 7357 | 2006 05 28 | 12:19:14.890 +22:25:37.89 | CBET 524 | LOSS |
2006cq | IC 4239 | 2006 05 29 | 13:24:25.040 +30:57:22.32 | CBET 527 | Newton, Briggs, Puckett |
2006cs | MCG +06-30-79 | 2006 06 03 | 13:45:33.879 +35:36:36.58 | CBET 536 | LOSS |
2006cz | MCG −01-38-2 | 2006 06 14 | 14:48:36.643 −04:44:30.91 | IAUC 8721 | LOSS |
2006ef | NGC 809 | 2006 08 18 | 02:04:19.529 −08:43:42.50 | CBET 597 | LOSS |
2006ej | NGC 191 | 2006 08 23 | 00:38:59.812 −09:00:57.43 | CBET 603 | LOSS |
2006em | NGC 911 | 2006 08 25 | 02:25:44.313 +41:56:31.55 | CBET 605 | LOSS |
2006en | MCG +05-54-41 | 2006 08 26 | 23:10:05.053 +30:13:23.82 | CBET 606 | Puckett, Peoples |
2006et | NGC 232 | 2006 09 03 | 00:42:45.779 −23:33:29.80 | CBET 616 | Itagaki |
2006eu | MCG +08-36-16 | 2006 09 03 | 20:02:51.147 +49:19:02.18 | CBET 618 | LOSS |
2006ev | UGC 11758 | 2006 09 12 | 21:30:59.329 +13:59:21.30 | IAUC 8747 | Ory |
2006gj | UGC 2650 | 2006 09 18 | 03:17:35.718 −01:41:30.18 | CBET 631 | Puckett, Toth |
2006gr | UGC 12071 | 2006 08 21 | 22:32:22.677 +30:49:43.80 | CBET 638 | LOSS |
2006gt | Anon Gal | 2006 09 18 | 00:56:17.318 −01:37:46.66 | CBET 641 | Quimby, Mondol |
2006ha | IC 1461 | 2006 09 27 | 22:58:34.280 +15:10:25.53 | CBET 649 | LOSS |
2006hb | MCG −04-12-34 | 2006 09 27 | 05:02:01.302 −21:07:55.18 | CBET 649 | LOSS |
2006hn | UGC 6154 | 2006 09 28 | 11:07:18.439 +76:41:50.52 | CBET 653 | Sehgal, Gagliano, Puckett |
2006is | Anon Gal | 2006 09 18 | 05:17:34.372 −23:46:54.67 | CBET 659 | LOSS |
2006je | IC 1735 | 2006 10 15 | 01:50:53.264 +33:05:53.27 | CBET 675 | LOSS |
2006ke | UGC 3365 | 2006 10 19 | 05:52:37.391 +66:49:00.78 | CBET 682 | LOSS |
2006kf | UGC 2829 | 2006 10 21 | 03:41:50.472 +08:09:24.93 | CBET 686 | LOSS |
2006le | UGC 3218 | 2006 10 26 | 05:00:41.934 +62:15:18.98 | CBET 700 | LOSS |
2006lf | UGC 3108 | 2006 10 26 | 04:38:29.511 +44:02:01.82 | CBET 704 | LOSS |
2006mo | MCG +06-02-17 | 2006 11 01 | 00:46:38.479 +36:19:57.70 | CBET 719 | LOSS |
2006mp | MCG +08-31-29 | 2006 11 03 | 17:12:00.194 +46:33:21.54 | CBET 720 | Puckett, Gagliano |
2006mq | ESO 494-G26 | 2006 10 22 | 08:06:12.378 −27:33:45.38 | CBET 721 | LOSS |
2006nz | Anon Gal | 2006 11 08 | 00:56:29.206 −01:13:35.90 | CBET 743 | SDSS-II |
2006oa | Anon Gal | 2006 11 11 | 21:23:42.939 −00:50:36.50 | CBET 743 | SDSS-II |
2006ob | Anon Gal | 2006 11 13 | 01:51:48.133 +00:15:48.46 | CBET 743 | SDSS-II |
2006on | Anon Gal | 2006 11 11 | 21:55:58.482 −01:04:12.79 | CBET 745 | SDSS-II |
2006or | NGC 3891 | 2006 11 18 | 11:48:03.469 +30:21:23.02 | CBET 749 | Puckett, Kroes |
2006os | UGC 2384 | 2006 11 21 | 02:55:00.998 +16:00:35.26 | CBET 751 | Quimby, Castro |
2006ot | ESO 544-G31 | 2006 11 22 | 02:15:04.800 −20:45:58.97 | CBET 754 | LOSS (Joubert, Li) |
2006qo | UGC 4133 | 2006 11 29 | 08:00:08.422 +56:22:07.25 | CBET 763 | Joubert, Li (LOSS) |
2006sr | UGC 14 | 2006 12 12 | 00:03:35.024 +23:11:45.67 | IAUC 8784 | Rich |
2006td | Anon Gal | 2006 12 24 | 01:58:15.761 +36:20:57.76 | CBET 787 | Kloehr |
2006te | Anon Gal | 2006 12 28 | 08:11:42.963 +41:33:16.80 | CBET 791 | Trondal, Luckas, Schwartz |
2007F | UGC 8162 | 2007 01 11 | 13:03:15.059 +50:37:07.53 | CBET 803 | Puckett, Gagliano |
2007H | Anon Gal | 2007 01 10 | 08:35:02.009 −08:20:16.00 | CBET 806 | Joubert, Li (LOSS) |
2007N | MCG −01-33-12 | 2007 01 21 | 12:49:01.212 −09:27:10.77 | CBET 818 | Lee, Li (LOSS) |
2007O | UGC 9612 | 2007 01 21 | 14:56:05.161 +45:24:17.37 | CBET 818 | Lee, Li (LOSS) |
2007R | UGC 4008 | 2007 01 26 | 07:46:37.513 +44:47:22.51 | CBET 823 | Puckett, Gray |
2007S | UGC 5378 | 2007 01 29 | 10:00:31.237 +04:24:25.26 | CBET 825 | Puckett, Gorelli |
2007ae | UGC 10704 | 2007 02 19 | 17:01:52.067 +79:01:54.26 | CBET 856 | Nissinen, Hentunen |
2007af | NGC 5584 | 2007 03 01 | 14:22:21.064 −00:23:37.92 | CBET 863 | Itagaki |
2007ai | MCG −04-38-4 | 2007 03 06 | 16:12:53.740 −21:37:48.57 | CBET 870 | Li (LOSS) |
2007al | Anon Gal | 2007 03 10 | 09:59:18.467 −19:28:25.39 | CBET 875 | Madison, Li (LOSS) |
2007ap | MCG +03-41-3 | 2007 03 13 | 15:56:23.035 +16:30:57.92 | CBET 883 | Puckett, Kroes |
2007ar | MCG +10-19-62 | 2007 03 12 | 13:21:01.797 +58:33:02.80 | CBET 886 | Duszanowicz |
2007au | UGC 3725 | 2007 03 18 | 07:11:46.095 +49:51:13.08 | CBET 895 | Lee, Li (LOSS) |
2007ax | NGC 2577 | 2007 03 21 | 08:22:43.242 +22:33:16.91 | CBET 904 | Arbour |
2007ba | UGC 9798 | 2007 03 29 | 15:16:42.581 +07:23:47.91 | CBET 911 | Winslow, Li (LOSS) |
2007bc | UGC 6332 | 2007 04 04 | 11:19:14.566 +20:48:32.26 | CBET 913 | Prasad, Li (LOSS) |
2007bd | UGC 4455 | 2007 04 04 | 08:31:33.375 −01:11:57.73 | CBET 914 | Prasad, Li (LOSS) |
2007bm | NGC 3672 | 2007 04 20 | 11:25:02.309 −09:47:53.96 | CBET 936 | Martin |
2007bz | IC 3918 | 2007 04 22 | 12:56:53.764 +22:22:23.12 | CBET 941 | Nearby SN Factory |
2007ca | MCG −02-34-61 | 2007 04 25 | 13:31:05.840 −15:06:06.52 | CBET 945 | Prasad, Li |
2007cg | ESO 508-G75 | 2007 05 11 | 13:25:33.588 −24:39:08.29 | CBET 960 | Thrasher, Li (LOSS) |
2007ci | NGC 3873 | 2007 05 15 | 11:45:45.851 +19:46:13.74 | CBET 966 | Puckett, Crowley |
2007co | MCG +05-43-16 | 2007 06 04 | 18:23:03.599 +29:53:49.39 | CBET 977 | Nicolas |
2007cp | IC 807 | 2007 06 13 | 12:42:12.748 −17:24:07.45 | CBET 980 | Khandrika, Li (LOSS) |
2007cq | Anon Gal | 2007 06 21 | 22:14:40.423 +05:04:48.57 | CBET 983 | Orff, Newton |
2007qe | Anon Gal | 2007 11 13 | 23:54:12.958 +27:24:33.02 | CBET 1138 | Yuan et al. (ROTSE) |
2007sr | NGC 4038 | 2007 12 18 | 12:01:52.800 −18:58:21.83 | CBET 1172 | Drake et al. |
2008L | NGC 1259 | 2008 01 14 | 03:17:16.596 +41:22:56.23 | CBET 1212 | Fujita |
2008af | UGC 9640 | 2008 02 09 | 14:59:28.493 +16:39:11.77 | CBET 1248 | Boles |
2008bf | NGC 4055 | 2008 03 18 | 12:04:02.877 +20:14:42.29 | CBET 1307 | Parisky (LOSS) |
Notes. Positions are a weighted mean of our measured SN positions, usually in R/r' but occasionally from V when insufficient R/r' data were available. These are generally an improvement over the positions reported by the discoverer.
The CfA Supernova Group rapidly responds to new objects, acquiring spectra and optical and JHK light curves. This allows for a deeper investigation into individual SN. For the CfA3 sample, we would sometimes initiate photometric observations of untyped SN candidates, depending on their brightness and any additional properties provided in the email circulars, such as color or when the last nondetection of the SN candidate was made. If the SN candidate was brighter than 18–18.5 mag and north of −20° then we would take spectra with the FAST spectrograph. Our efforts have contributed roughly 40% of the reported identifications of SN type over the last six years. We did not follow any SN that had peak magnitudes fainter than ∼18.5 mag, making this the effective limiting magnitude for the CfA3 sample. However, this does not mean we observed every SN brighter than ∼18.5 mag.
With the information on type, age and any peculiar features in hand, either from our own spectra or from others' reports, a decision on whether to begin or continue observing the SN candidate was made. As one of our goals was to fill out the sampling across the whole range of SNe Ia (to provide a more complete training set for light-curve fitters), highest priority was given to SNe Ia that were young, slow-declining, fast-declining, or otherwise peculiar. Another reason to prioritize slow decliners is that these are preferentially found at high redshift. Our program also observes core collapse SNe and high priority was given to stripped-envelope SNe IIb/Ib/c. Lower priority was given to SNe II and older SNe Ia. If a SN Ia was found to be older than ∼14 days after B-band maximum at the time of our first observation then it was usually removed from our list.
We emphasize that the CfA3 sample distribution is not representative of the abundances of SN Ia type or host galaxies. Objects announced during the bright phase of the moon were also less likely to be included since spectroscopic identification was less likely to be obtained. The Keplercam and Minicam were usually mounted on the telescope at all phases of the moon while the 4Shooter was often taken off for several days around full moon. Our preference for young and more extreme events makes the CfA3 sample distribution less representative of the underlying population but does ensure that the wide range is being amply sampled. Finally, the limiting magnitude of both the searches and our follow up mean that highly reddened or intrinsically less-luminous SNe Ia are only observed in a small volume: they are severely under-represented in this sample compared to the cosmic rate.
In Figure 1, we plot redshift histograms of the CfA3 and OLD samples. The OLD sample is the nearby SN Ia sample as compiled in Jha et al. (2007). The CfA3 sample is primarily in the 0.02 < zCMB < 0.04 region, where zCMB is the redshift in the cosmic microwave background (CMB) reference frame. The OLD sample is primarily below zCMB ≈ 0.03. Above zCMB = 0.01, the median CfA3 and OLD redshifts are, respectively, 0.027 and 0.025. Figure 2 shows the time of first observation, relative to B-band maximum light, with median values of −0.8 and −1.5 for CfA3 and OLD, respectively. The OLD sample has a higher percentage with very early observations. Respectively, the CfA3 and OLD samples have 48 and 47 objects with the time of first observation beginning sooner than 5 days before maximum, and 90 and 76 objects beginning before maximum.
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Standard image High-resolution imageThe MLCS2k2 (Jha et al. 2007) light-curve parameter, Δ, is roughly a measure of the relative V-band brightness compared to the Δ = 0 model light curve. Negative Δ means greater intrinsic luminosity and broader light curves and positive Δ means fainter luminosity and narrower light curves. Figure 3 shows the CfA3 distribution of Δ versus redshift above zCMB = 0.01. The whole range of Δ is present out to zCMB ≈ 0.03 and then the magnitude limits of discovery, spectroscopic identification, and photometric-follow-up decisions discriminate against fainter objects which are not present in our sample at higher redshifts. The roughly diagonal slope in the right edge of the Δ-versus-redshift distribution is consistent with a limiting peak magnitude of ∼18.5 mag in the CfA3 objects.
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Standard image High-resolution imageThe FLWO 1.2 m telescope has its time allocated to a specific observing program each night with the requirement that roughly 10% of the night be devoted to other programs' observations. From 2001 to summer, 2005, our typical time allocation was one night per month with a few months of multiple nights to acquire calibration and host-galaxy reference images. Nightly requests of two SNe to other observers were typical during this period. Beginning in the fall of 2005, two changes significantly increased both the number of SNe we observed and the sampling per object. Instead of a single night per month, we received roughly seven nights per month. Additionally, several other observing programs made significant numbers of SN observations for us in time they could not use. The most notable group was the CfA component of the Kepler Mission.33 We tried to observe new, high-priority SNe every one or two nights until ∼10 days past maximum light and less frequently thereafter. Weather and competing targets sometimes reduced the actual cadence. Secondary standards from Landolt (1992) and Smith et al. (2002) were observed on photometric nights and reference images for host-galaxy subtraction were obtained after the SN had faded sufficiently, usually a year after maximum light. Figure 4 shows a histogram of the number of nights observed for each SN in the CfA3 sample. The mean number is 15 and the median is 12. The number of objects with 20-or-more nights of observation is 45 and the number with 10-or-more nights is 121.
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Standard image High-resolution image2.3. Pipeline: Reduction Stage
In this stage, raw images are processed to the point where all their star-like objects have had their flux measured, but not yet calibrated. Images first undergo bias subtraction and flat fielding. Dome-screen flats were used for BVRIr'i' while twilight flats were used for U. The 4Shooter images had their bad pixels masked out while the Minicam and Keplercam images did not require this. The small, but non-negligible, I-band fringes on the 4Shooter were removed to the extent possible by subtracting fringe frames created from several nights of I-band images. The i'-band fringes on the Minicam and Keplercam were much smaller in amplitude, making fringe correction unnecessary.
The cosmic-ray removal algorithm, la_cosmic (van Dokkum 2001), in the form of the IDL code, la_cosmic.pro, by Joshua Bloom, was then applied to the flat-fielded images to remove most of the cosmic rays. It uses a two-dimensional Laplacian algorithm to detect cosmic rays. Although removing the cosmic rays did not have a significant effect on the photometry and reference-image subtraction, this step was applied to each image.
A linear astrometric solution was calculated for each image. We used astrometric solutions based on an external astrometric catalog for a handful of good-seeing images of a single field. We then ran SWarp (Bertin et al. 2002) on these images to properly scale and align them, and center them on the SN position. DoPHOT (Schechter et al. 1993) was used to get the field star positions to make an "internal" astrometric catalog from our own images. We then reran these same images through these same stages with the internal astrometric catalog and recalculated the field star positions to make our final internal astrometric catalog. This was done for each SN field.
The UCAC2 catalog (Zacharias et al. 2004) was our preferred external catalog but it does not extend above declinations of roughly +45°. Where the UCAC2 catalog was sparsely populated, we used either the USNO-B1.0 (Monet et al. 2003) or USNO-A2.0 catalogs (Monet et al. 1998). UCAC2 has an accuracy of around 003 while USNO-B1.0 and USNO-A2.0 have poorer accuracies of roughly 020 and 025, respectively. The resulting average standard deviation and relative accuracy of the star coordinates in our internal astrometric catalogs did not depend significantly on which external catalog was used. The absolute accuracy of our internal catalogs will be better in those that used UCAC2 for the initial solution but our positions will generally be better than those reported at discovery. Since we are primarily interested in relative accuracy, though, all our internal astrometric catalogs are adequate. The typical standard deviation of a star's position in our internal astrometric catalogs is 006.
We then used our internal astrometric catalogs to create a linear astrometric solution for all of the flat-fielded images. A linear solution was adequate for the small field of view of the 1.2 m images. The astrometric solution was used in SWarp to align the images to a common pixel system so that host-galaxy reference images can be subtracted. DoPHOT was run on the SWarped images to calculate fluxes for all stellar-shaped objects.
DoPHOT uses a parameterized point-spread function (PSF) model. A range of functions can be effectively chosen by setting different values of the DoPHOT PSF-shape parameters α and β. With the PSF function set, DoPHOT first fits for a single PSF shape and size over the whole image. The high signal-to-noise ratio (S/N) stars most heavily influence the best-fit PSF in DoPHOT. Then it fits this PSF to each star-like detection, calculating a best-fit position, sky value and flux amplitude. It is important that the PSF model be capable of fitting the actual PSF shape of the data. We found that an order-2 Moffat fit our stars' PSF well while the default, truncated Gaussian underestimated the flux in the wings of the stars.
A mismatched PSF function will do a better job of fitting low-S/N stars than of fitting high-S/N stars (since low-S/N data is less constraining), possibly introducing relative inaccuracies between the faint and bright stars. We compared our DoPHOT truncated-Gaussian-PSF magnitudes with aperture-photometry magnitudes and found that the DoPHOT magnitudes differed from the aperture-photometry magnitudes by about 0.01–0.02 mag per mag. The fainter stars were being interpreted as fainter relative to the aperture photometry magnitudes than were the bright stars. When we used the well matching, order-2 Moffat function for our PSF, this effect was drastically diminished.
In Section 2.5, we describe the calibration process to generate photometric catalogs for the comparison stars in the SN fields. To calculate a photometric zero point for each SN image, we took a weighted mean of the differences between our catalog magnitudes (in the natural system) and the DoPHOT measurements of the comparison stars. In the cases where the SN is sufficiently distant from any underlying structure (such as host-galaxy light or neighboring stars) the DoPHOT magnitudes of the SN can be combined with their respective image zero points to produce a calibrated light curve in the natural system.
2.4. Pipeline: Host-Galaxy Subtraction
Most of the SNe in our sample required host-galaxy subtraction. Reference images were acquired on clear nights with good seeing and little or no moon so as to maximize their S/N. We also took reference images of SNe that did not need host subtraction as a way to test the host-subtraction process.
Accurately subtracting the reference image from the SN image which was obtained under different seeing conditions requires a convolution kernel that can transform the PSF of one image to the PSF of the other. The convolution kernel is calculated using the algorithm of Alard & Lupton (1998) and Alard (2000) with slight improvements as in Becker et al. (2004) and Miknaitis et al. (2007). The two images are each divided into stamps and substamps and the best-fit convolution kernel is determined. The image with a narrower PSF is convolved to the other image. Usually the reference image was convolved but sometimes the SN image was. The SN flux in the difference image is measured with the DoPHOT PSF from the stars of the (wider) unconvolved image.
All of the reference images for the Keplercam SN Ia were obtained with the Keplercam, resulting in "same-camera" subtractions. Some of the reference images for the 4Shooter and Minicam SN Ia were taken with the Keplercam, resulting in "cross-camera" subtractions. The responsivity of the different cameras are similar enough in a given passband so there is no problem in using the Keplercam reference images for 4Shooter and Minicam SN images. The flux normalization for the difference image can be chosen from either the SN image or the reference image. In the case of the same-camera subtractions, we chose to use the flux normalization from the reference image so that this would be used for every observation of that SN in a given band. In the cross-camera subtractions, the flux normalization from the SN image was used in order to stay in the natural system of the camera in which the SN data were observed. If the unconvolved image happens to be the one chosen for the flux normalization of the difference image then its zero-point magnitude can be directly applied to the DoPHOT SN magnitude to achieve the calibrated natural-system SN magnitude. If the zero point of the image-that-got-convolved is used for the flux normalization then the flux of the SN in the difference image must be divided by the normalization (sum) of the convolution kernel to preserve the pre-convolution flux scale.
Noise maps are propagated for both images and are used to calculate a noise map for the difference image. Information from the noise image is combined with the DoPHOT uncertainty and calibration uncertainty to produce the uncertainty of the natural system SN measurement.
2.5. Calibration
On photometric nights, we observed one or two fields of secondary standards every hour, over a range in air mass that matched the SN observations. For the UBVRI bands used on the 4Shooter, we used secondary standards from Landolt (1992). Smith et al. (2002) establish the photometric system for the SDSS passbands, u'g'r'i'z'. They use many of the fields from Landolt (1992) but much fewer stars. For the Minicam and Keplercam, where we are using UBVr'i', we chose our secondary standards from Smith et al. (2002) to ensure that we have stars with r'i' calibration and used the UBV magnitudes from Landolt (1992).
We performed aperture photometry on the Landolt/Smith standard stars and on our SN-field comparison stars using the NOAO/DIGIPHOT/APPHOT package in IRAF (Tody 1993). The comparison stars were chosen so that they were reasonably well isolated and usually detected in all bands. A few sparse fields required also using stars that only had good detections in BVRI/r'i' but not in U. An aperture with radius of 15 pixels was used on both the standard and comparison stars. An aperture correction was calculated from one or two bright, isolated, good curve-of-growth stars by subtracting the 6-pixel-radius-aperture magnitude from the 15-pixel-radius-aperture magnitude and applied to all of the stars in the field.
A photometric transformation solution for a given night was calculated from our Landolt/Smith stars using system of Equations (1). A linear dependence on air mass and color was sufficient for our intended level of final V-band comparison star precision (∼0.015 mag). Higher-order terms were found to be consistent with zero and so we did not use them.
The terms on the left side of the equations are the instrumental colors except for the V-band term. The first term on the right side of each equation is the zero point, followed by the air mass coefficients, α, times the air mass, x. The V-band equation is unique in that it directly relates the instrumental magnitude v to the standard system magnitude and color, V and B−V. The other four equations only relate the instrumental and standard-system colors to each other. The final term on the right of the four color equations multiplies the standard-system color of the standard stars by a coefficient, β, to convert the standard-system color into the "calibrated" natural-system color.
Having solved for the zero point, air mass, and color coefficients by using the Landolt/Smith standards, this photometric solution was then applied to the comparison star measurements, producing tertiary standards that were used to calibrate the SN measurements.
Our goal was to observe each SN field on multiple photometric nights to ensure more accurate calibration. Sometimes this was not possible, but even in those cases SN fields that produced consistent, multiple-night calibration were observed on the same night, making us sufficiently confident that the SN fields with a single night of calibration were accurate. The uncertainties of the comparison stars include the measurement uncertainties, the standard deviation of measurements from multiple nights (for single nights, an appropriate error floor was used instead), and the uncertainty of the transformation to the standard system. The typical uncertainty of our V-band comparison star measurements is 0.015 mag. The average color coefficients are presented in Table 2.
Table 2. Photometric Color Terms
Detector/Filters | Color Term | Value | Nights |
---|---|---|---|
Keplercam/UBVr'i' | (u − b)/(U − B) | 1.0279 ± 0.0069 | 20 |
Keplercam/UBVr'i' | (b − v)/(B − V) | 0.9212 ± 0.0029 | 37 |
Keplercam/UBVr'i' | (v − V)/(B − V) | 0.0185 ± 0.0023 | 37 |
Keplercam/UBVr'i' | (v − r)/(V − r') | 1.0508 ± 0.0029 | 37 |
Keplercam/UBVr'i' | (v − i)/(V − i') | 1.0185 ± 0.0020 | 37 |
Minicam/UBVr'i' | (u − b)/(U − B) | 1.0060 ± 0.0153 | 4 |
Minicam/UBVr'i' | (b − v)/(B − V) | 0.9000 ± 0.0095 | 4 |
Minicam/UBVr'i' | (v − V)/(B − V) | 0.0380 ± 0.0030 | 4 |
Minicam/UBVr'i' | (v − r)/(V − r') | 1.0903 ± 0.0140 | 4 |
Minicam/UBVr'i' | (v − i)/(V − i') | 1.0375 ± 0.0088 | 4 |
4Shooter/UBVRI | (u − b)/(U − B) | 0.9912 ± 0.0078 | 16 |
4Shooter/UBVRI | (b − v)/(B − V) | 0.8928 ± 0.0019 | 16 |
4Shooter/UBVRI | (v − V)/(B − V) | 0.0336 ± 0.0020 | 16 |
4Shooter/UBVRI | (v − r)/(V − R) | 1.0855 ± 0.0058 | 16 |
4Shooter/UBVRI | (v − i)/(V − I) | 1.0166 ± 0.0067 | 16 |
Notes. Lower-case ubvri refer to the instrumental magnitudes while UBVRIr'i' refer to the standard magnitudes. All color terms implicitly contain an additive constant. For example, for the Keplercam: (v − V) = 0.0185(B − V) + const; (u − b) = 1.0279(U − B) + const.
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We also synthesized natural system BVr'i' passbands for the Keplercam by combining the primary and secondary mirror reflectivities (taken as the square of the measured reflectivity of the primary), the measured filter transmissions, and the measured Keplercam quantum efficiencies. No atmospheric component is included. We present these passbands as normalized photon sensitivities. A U-band filter transmission curve and the Minicam quantum efficiency were not available so passbands were not made for Keplercam U or any of the Minicam bands. The 4Shooter BVRI passbands can be found in J06 as the "4Shooter/Harris" combination and we point out that they are presented as normalized energy sensitivities. To convert to normalized photon sensitivities, the passbands should be divided by wavelength and renormalized. See Figure 5 for a visual representation of the Keplercam BVRI passbands. Our light curves were produced in the natural system and then converted to the standard system by using the color terms in Table 2. The light curves and comparison stars, both natural and standard system versions, can be found at our Web site34 and are archived with the journal. The Keplercam BVr'i' passbands can also be found at these two locations. "Stub" examples of these tables are seen in Tables 3–7. The natural system passbands and photometry can be used together to avoid the uncertainty of using star-derived color terms but we do not pursue this here. Figure 6 shows nine of our better light curves.
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Standard image High-resolution imageTable 3. Standard System Comparison Star Photometry
Star | R.A. (J2000) | Decl. (J2000) | V | dV | NV | U−B | ± | NU | B−V | ± | NB | V − r' | ± | V − i' | pm | ||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
2006D | |||||||||||||||||
01 | 12 52 50.385 | −09 42 37.78 | 17.684 | 0.037 | 2 | 1.325 | 0.219 | 2 | 1.058 | 0.061 | 2 | 0.572 | 0.061 | 2 | 1.119 | 0.067 | 2 |
02 | 12 52 46.717 | −09 50 32.12 | 15.245 | 0.016 | 2 | 0.424 | 0.042 | 2 | 0.701 | 0.015 | 2 | 0.244 | 0.009 | 2 | 0.460 | 0.009 | 2 |
03 | 12 52 40.799 | −09 48 43.84 | 16.548 | 0.017 | 2 | −0.029 | 0.051 | 2 | 0.469 | 0.016 | 2 | 0.164 | 0.016 | 2 | 0.316 | 0.013 | 2 |
04 | 12 52 38.144 | −09 45 40.33 | 17.002 | 0.014 | 2 | 1.475 | 0.278 | 2 | 1.371 | 0.087 | 2 | 0.651 | 0.022 | 2 | 1.809 | 0.022 | 2 |
05 | 12 52 37.397 | −09 42 12.02 | 16.492 | 0.022 | 2 | 0.047 | 0.057 | 2 | 0.521 | 0.018 | 2 | 0.179 | 0.014 | 2 | 0.355 | 0.010 | 2 |
Only a portion of this table is shown here to demonstrate its form and content. A machine-readable version of the full table is available.
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Table 4. Natural (Instrumental) System Comparison Star Photometry
Star | R.A. (J2000) | Decl. (J2000) | V | dV | NV | U−B | ± | NU | B−V | ± | NB | V − r' | ± | V − i' | pm | ||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
2006D | |||||||||||||||||
01 | 12 52 50.385 | −09 42 37.78 | 17.7039 | 0.0375 | 2 | 1.3624 | 0.2186 | 2 | 1.0871 | 0.0610 | 2 | 0.5881 | 0.0611 | 2 | 1.1504 | 0.0668 | 2 |
02 | 12 52 46.717 | −09 50 32.12 | 15.2575 | 0.0156 | 2 | 0.4356 | 0.0422 | 2 | 0.7210 | 0.0150 | 2 | 0.2511 | 0.0094 | 2 | 0.4724 | 0.0090 | 2 |
03 | 12 52 40.799 | −09 48 43.84 | 16.5570 | 0.0166 | 2 | −0.0301 | 0.0510 | 2 | 0.4820 | 0.0156 | 2 | 0.1681 | 0.0163 | 2 | 0.3249 | 0.0125 | 2 |
04 | 12 52 38.144 | −09 45 40.33 | 17.0275 | 0.0139 | 2 | 1.5162 | 0.2784 | 2 | 1.4091 | 0.0874 | 2 | 0.6696 | 0.0218 | 2 | 1.8589 | 0.0217 | 2 |
05 | 12 52 37.397 | −09 42 12.02 | 16.5020 | 0.0220 | 2 | 0.0479 | 0.0573 | 2 | 0.5355 | 0.0182 | 2 | 0.1841 | 0.0139 | 2 | 0.3654 | 0.0098 | 2 |
Only a portion of this table is shown here to demonstrate its form and content. A machine-readable version of the full table is available.
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Table 5. Standard System SN Light Curves
Filter | MJD | StdMag | dMag |
---|---|---|---|
sn06D | |||
1 | 53753.51876 | 14.434 | 0.033 |
1 | 53757.43733 | 14.224 | 0.025 |
1 | 53764.45479 | 14.935 | 0.026 |
1 | 53764.45843 | 14.962 | 0.026 |
1 | 53765.43324 | 15.056 | 0.026 |
1 | 53765.43685 | 15.048 | 0.025 |
Notes. Filter codes: UBVRIr'i' are 1, 2, 3, 4, 5, 13, and 14, respectively.
Only a portion of this table is shown here to demonstrate its form and content. A machine-readable version of the full table is available.
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Table 6. Natural (Instrumental) System SN Light Curves
Filter | MJD | InstMag | dMag |
---|---|---|---|
sn06D | |||
1 | 53753.51876 | 14.429 | 0.033 |
1 | 53757.43733 | 14.216 | 0.025 |
1 | 53764.45479 | 14.916 | 0.026 |
1 | 53764.45843 | 14.944 | 0.026 |
1 | 53765.43324 | 15.036 | 0.026 |
1 | 53765.43685 | 15.027 | 0.025 |
Notes. Filter codes: UBVRIr'i' are 1, 2, 3, 4, 5, 13, and 14, respectively.
Only a portion of this table is shown here to demonstrate its form and content. A machine-readable version of the full table is available.
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Table 7. Keplercam BVr'i' Passbands
Wavelength (nm) | Passband (B band) |
---|---|
345 | 0.000 |
350 | 0.005 |
355 | 0.035 |
360 | 0.116 |
365 | 0.234 |
370 | 0.360 |
Notes. Photon sensitivity passbands are the product of detector QE, filter transmission, primary mirror reflectivity, and secondary mirror reflectivity (approximated as the primary mirror reflectivity). No atmospheric term has been applied.
Only a portion of this table is shown here to demonstrate its form and content. A machine-readable version of the full table is available.
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Standard image High-resolution image2.6. Internal Consistency Checks
By choosing an appropriate shape for the PSF of the comparison stars we ensured accurate flux measurements for well-isolated stars. This also applies to cases where the SN is well isolated, allowing for two tests of the image-subtraction process: comparing the unsubtracted light curve with the light curve produced by subtracting a reference image taken with the same camera; doing the same procedure but with a reference image taken with a different camera. A third test involves comparing the light curve produced by subtracting a same-camera reference image with the light curve produced by subtracting a reference image from a different camera. As described below, we have done these tests and find internal consistency at about the 0.01 mag level in most cases, when the SN is brighter than 17 mag.
2.6.1. Same-Camera Subtracted Versus Unsubtracted Light Curves
SN 2007af was very bright compared to its underlying galaxy background and the subtracted and unsubtracted light curves agree to better than 0.01 mag for most points, as seen in Figure 7, showing that the subtraction stage of the pipeline works well. The comparison plots also contain the weighted mean (WM) and χ2 (Chi2) of the differences.
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Standard image High-resolution imageSN 2006X allows two comparisons. Since it was fairly bright compared to its underlying galaxy light, the subtracted and unsubtracted light curves can be compared, especially in i', where dust extinction is the least and the PSF is the narrowest. Figure 8 shows that the unsubtracted light curve is slightly brighter at bright times, due to the small amount of underlying galaxy flux. Nonetheless, most points agree to better than 0.01 mag. At faint times, this galaxy flux becomes more significant. However, the agreement at bright times is a good indication that the subtraction stage is working well.
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Standard image High-resolution imageThese two examples, plus several others that we do not present, show that the reference-image subtraction process itself does not introduce any significant offset into the final SN photometry.
2.6.2. Cross-Camera Subtracted Versus Unsubtracted Light Curves
Many of the 4Shooter and Minicam SN Ia reference images were acquired with the Keplercam and so it was important to see that the cross-camera subtraction works well. SN 2004et was a bright SN type II on a fairly smooth host-galaxy background. The SN data were taken on the Minicam while the reference image was acquired on the Keplercam. Figure 9 shows that the cross-camera subtracted and the unsubtracted V-band light curves agree within the uncertainties. At bright times, about two-thirds of the points agree to better than 0.01 mag. The largest discrepancy is 0.03 mag. At faint times, the galaxy light begins to contribute more, and the unsubtracted light curve more is roughly 0.015 mag brighter with a scatter of 0.02 mag but when the SN is bright, the cross-camera subtraction does not introduce any systematic error.
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Standard image High-resolution image2.6.3. Cross-Camera Subtraction Versus Same-Camera Subtraction
The SN data for SN 2002jy were obtained with the 4Shooter while reference images were obtained with both the 4Shooter and the Keplercam. There is excellent agreement between the BVRI same-camera and the cross-camera subtracted light curves, with typical agreement at the 0.01 mag level or better. The 4Shooter U-band reference image was of inferior quality and could not be used. The scatter is much smaller than the error bars because the only difference in the two light curves is the reference images, while the data images are the same. The R-band comparison is shown in Figure 10, with all the points agreeing to better than 0.01 mag. The slight differences in the light curves may be due to slight flux and seeing differences in the two reference images. Other factors include poorer 4Shooter cosmetic properties and different responsivities between the cameras. We also found good agreement in other SNe, bolstering our confidence that the cross-camera subtraction process was reliable.
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Standard image High-resolution image2.7. External Consistency Checks
Comparisons with published photometry are made to check for consistency in comparison star calibration and SN Ia light curves. Differences in instruments, reduction techniques, and comparison star calibration are some of the factors leading to disagreements in the photometry from different telescopes of the same SN Ia. Typical disagreement of SN Ia photometry is roughly 0.02–0.05 mag in BVR around maximum light with larger discrepancies more common at later times and in U and I at all times. J06 present photometry comparisons from different groups for several SNe Ia and find typical agreement of several hundredths mag in most cases but worse in others.
SN 1999ee is an example where data was taken by two different telescopes on the same mountain and reduced in the exact same fashion with the same comparison star magnitudes (Stritzinger et al. 2002). The only difference was in the two telescopes/detectors. The differences in the two UBVRI light curves near maximum light were −0.14, −0.01, −0.04, +0.04, and −0.03 mag, respectively, and slightly larger a month later. S-corrections integrate the convolution of the natural system passband and SN spectrum and subtract the convolution of the standard system passband and SN spectrum. Because of the nonstellar spectra of SNe Ia, especially at later times, they can be used instead of star-derived color terms to more accurately place the SN photometry on the standard (or some other) system. S-corrections were applied, resulting in partial improvement for some bands and worsening in R, leading to the conclusion that accurate passbands must be determined if S-corrections are to be of use. Similarly to SN 1999ee, Suntzeff (2000) discusses the disagreement in the photometry of SN 1998bu from two telescopes that he reduced in the same manner with the same comparison stars. He finds a color difference between the two telescopes of δ(B − V) = 0.12 mag at late times, when the second telescope began observing. He finds that S-corrections would be able to correct this.
As another case, Krisciunas et al. (2003) applies S-corrections to SN 2001el. These are on the order of a few hundredths mag. Most S-corrections in the literature are roughly in the range 0.0 to ±0.1 mag. In general, S-corrections can be large or small, depending on the mismatch between the natural system and standard system passbands and the spectral properties of the SN. SN 2005cf (Wang et al. 2009) is an example where the disagreement between different telescope's light curves is still 0.02–0.03 mag after S-corrections. This shows that differences of a few hundredths mag can occur even when many, but not all, of the systematic differences are not present and great care is taken in acquiring and processing the data.
As a check on our photometry pipeline, in Section 2.7.1, we first run the raw data of 17 SNe Ia from J06 through our photometry pipeline and compare the results. The J06 photometry pipeline mainly differs from the CfA3 pipeline in the reference image subtraction software. Then, for six objects from the literature, in Sections 2.7.2–2.7.7, we compare our CfA3 comparison stars and light curves with the published values. Of particular worth are the cases where values are presented from two or more telescopes. Overall, we find good consistency between our comparison star calibration and light curves in comparison to those from other groups for the same objects. This is of great importance when combining multiple data sets together to calculate dark energy properties. For purposes of comparing two sources of SN photometry, we define "excellent" agreement for all bands (except U) as better than 0.02 mag difference, "good" as 0.02–0.04 mag, "adequate" as 0.04–0.06, and "poor" as greater than 0.06. For U, these values are doubled. These labels will be used in the following sections as a way of giving a measure of the agreement. Applying one of these labels to a light-curve comparison should be understood to apply to each point. For example, two light curves with excellent agreement would have no points disagreeing by more than 0.02 mag. Mostly good agreement would mean most of the points differ by no more than 0.04 mag. These labels are consistent with typical differences in published photometry of the same SN Ia from different groups, using different instruments (see above).
2.7.1. Running J06 Data Through CfA3 Pipeline
To test our photometry pipeline, we ran the 4Shooter BVRI raw data for 17 SNe Ia from J06 through our pipeline and compared the results with those obtained by J06, whose reduction methods differed from ours in some ways. The main difference was in the reference image subtraction software. J06 used the ISIS subtraction package (Alard & Lupton 1998) as modified by B. Schmidt. We think that our more modern subtraction software is an improvement but this needs an empirical test. Another difference was our use of DoPHOT while J06 used aperture photometry. We note that we did not correct for fringing on the I-band images for these 17 objects (not to be confused with the fact that we did for the CfA3 I-band images). Running the U-band data through successfully requires more effort and does not add to determining the consistency of the J06 photometry pipeline with ours so we did not do it. The agreement was typically good or excellent around maximum light with typically good or adequate agreement at later times. A weighted mean of the difference between the two light curves was computed for each SN in each band. The average of these weighted means was 0.001 ± 0.019 mag for all bands while in each separate band they were 0.010 ± 0.015 mag in B, 0.005 ± 0.011 mag in V, 0.001 ± 0.011 mag in R, and −0.012 ± 0.029 mag in I. The larger disagreement in I is possibly due to our lack of fringe correction for these comparison objects. The two pipelines agree at ≲0.01 mag in each band. These differences make clear the advantages of using one large sample that has been reduced by the same pipeline. It also illustrates the advantage that the CfA3 sample has since one of the significant high-z samples, ESSENCE, uses the same pipeline. That each band's offset is consistent with zero is important since no significant, net offset is being introduced relative to the CfA2 photometry, much of which was used to train the various light-curve fitters that are used in H09. We later will adopt 0.01 mag as the systematic uncertainty for our pipeline. As a representative example (neither the best nor the worst), we show the BV light-curve comparisons of SN 1999gh in Figures 11 and 12.
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Standard image High-resolution image2.7.2. SN 2003du
SN 2003du has four sets of photometry: CfA3 provides one and Stanishev et al. (2007), Leonard et al. (2005), and Anupama et al. (2005) provide the other three. We will refer to these as CfA3, STAN, LEO, and ANU. Our comparison stars agree to better than 0.02 mag with STAN in BVI, with LEO in BVRI, and with ANU in I. ANU is fainter in BV, by several hundredths magnitude compared to the other three. STAN is the most discrepant in R. In U, CfA3 is fainter than STAN, but within the uncertainty. CfA3 pairings with the other groups are in as good or better agreement than most of the other non-CfA3 pairings.
The agreement of the CfA3 light curve is mostly excellent with STAN in V, as seen in Figure 13, and it is good in BRI, with a few points brighter by about 0.1 mag at late times in I. STAN and LEO have good agreement in R but STAN is systematically brighter in BV by a few hundredths and in I by 0.06 mag. CfA3 has good and excellent agreement with LEO in R and B but is brighter by about 0.03 mag in V and 0.07 mag in I. ANU is fainter than CfA3 by around 0.04–0.05 mag in BV around max, in rough agreement with the offset in the three comparison stars in common, but agrees better at late time. CfA3 and ANU have good agreement in RI. It is interesting to note that most of the STAN values we compare with were from various telescopes and S-corrected, suggesting that the CfA3 color-term transformations do a decent job of converting to the standard passbands.
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Standard image High-resolution image2.7.3. SN 2002bo
Krisciunas et al. (2004b; KRIS) and Benetti et al. (2004; BEN) present optical light curves of SN 2002bo. In looking at the five comparison stars in common, those of KRIS are brighter than those of BEN by several hundredths mag. BEN only presents BVRI data while CfA3 and KRIS also present U-band data. For the three comparison stars in common between KRIS and CfA3, excellent agreement is found in VRI, while KRIS is fainter by about 0.03 mag in B and 0.02 mag in U, with a large scatter in U. CfA3 agrees excellently with BEN in B. CfA3 is brighter than BEN in VRI by 0.03 to 0.05 mag, but KRIS is even brighter, compared to BEN. Overall, in the bands presented by all three groups, CfA3 and KRIS agree best in VRI while CfA3 and BEN agree best in B.
KRIS presents both S-corrected light curves and color-term-corrected light curves. We find that our light curves agree slightly better with the S-corrected BV light curves. The B difference, CfA3−KRIS, is 0.026 ± 0.021 and in V it is 0.004 ± 0.031. In R, there is little difference in which KRIS light curve we compare to. The agreement is good except for one poor point. In I, there is one KRIS point—their minimum point between the two I-band peaks—that seems excessively low compared to the shape of the neighboring points and so we consider this to be a bad point and not really worth comparing. It differs from ours by about 0.25 mag. Besides this point, our points around the first peak have good agreement with the S-corrected KRIS version and good-to-adequate agreement with the un-S-corrected version. There are two other KRIS I points at later times where the un-S-corrected points are fainter than CfA3 by about 0.1 mag but the (same) S-corrected points are only ∼0.02 and 0.04 mag fainter. Finally, in U, both KRIS light curves are narrower and fainter than the CfA3 and there is very poor agreement—it is difficult to say which is right but the CfA3 light curve has a smoother shape and smaller error bars so it may be better.
KRIS and BEN generally have good-to-adequate agreement with a few poor points. The bad KRIS I-band point mentioned above is about 0.35 mag fainter than BEN, confirming that it is likely an aberrant point. Similarly, BEN and CfA3 have good-to-adequate agreement with a few poor points.
2.7.4. SN 2002bf
Leonard et al. (2005; LEO) present BVRI photometry of SN 2002bf. We only have two comparison stars in common but they are consistent with zero difference in all bands except for one of the stars in I, where the LEO star is fainter by slightly more than the 1σ level. As LEO note, the SN is only 41 from its host galaxy's center, resulting in subtraction difficulties. As a result, both CfA3 and LEO light curves are somewhat choppy and several points have large error bars. The agreement in photometry is good to excellent in the two brightest B points and in the brightest V point, with adequate-to-poor agreement in most of the other V points. The CfA3 light curves are mostly fainter in R, and in B after the two brightest points. In I, there are some phases of good agreement and some of large disagreement (∼0.2 mag).
2.7.5. SN 2005hk
Phillips et al. (2007) present optical comparison star photometry and light curves for SN 2005hk from four different sources: CSP, CTIO, KAIT, and SDSS. We make no comparison with SDSS since their values are in ri and not in r'i'. We compare the CfA3 comparison stars with the other telescopes' values where the stars and passbands are the same. In BV, CfA3, CSP, and CTIO all agree within 0.01 mag in the mean while KAIT is most different from the other three but still in good-to-excellent agreement. In U, CfA3 and KAIT show the best agreement (0.01 mag) and CfA3 and CTIO differ by ∼0.03 mag. The CfA3 comparison star photometry was calibrated on three nights, with excellent agreement, showing internal consistency. The excellent agreement with CSP and CTIO and the good-to-excellent agreement with KAIT suggest that our comparison star calibration is reliably on the standard system.
Phillips et al. (2007) compare the BV KAIT and CSP light curves of SN 2005hk. The KAIT light curve is not reference-image subtracted and this is probably the largest source of the discrepancies of several hundredths mag after S-correction. The CSP light curve used a g' SDSS reference image for B and a g' + r' reference image for V so this might be a small source of inaccuracy. They also compare the CSP and SDSS light curves in ri. S-corrections bring the two data sets into better agreement with some scatter at the level of a couple hundredths left over.
The CfA3 V light curve shows good-to-excellent agreement, and excellent agreement in the mean, with CSP. The CfA3 B light curve mostly shows good-to-excellent agreement with CSP, with a few poorly agreeing points, mostly at late times. The CfA3 r'i' light curves are about 0.03 mag fainter, with a few poorly agreeing points at later times. Possible sources of disagreement are the reference images used, passband differences, and no S-corrections for the CfA3 light curves.
2.7.6. SN 2005am and SN 2005cf
Li et al. (2006) present UBV comparison star calibration of SN 2005am and 2005cf. Using the stars in common for SN 2005am, CfA3 is in excellent agreement with Li in the mean in U (∼0 mag), but with a scatter of 0.08 mag. CfA3 is fainter by about 0.03 and 0.02 mag in B and V, respectively, but consistent with zero difference. No comparisons of the SN 2005am light curves are made since the Li light curve is not reference-image subtracted and the CfA3 light curve is. There are three UBV comparison stars in common for SN 2005cf and there is excellent agreement in each band: less than 0.01 mag mean difference for BV and less than 0.025 mag in U.
2.7.7. SN 2006X
We compare our UBV comparison stars and light curves with those from Wang et al. (2008), who present data from KAIT, CTIO, and the Teramo-Normale Telescope (TNT). The comparison stars in common differ in UBV, respectively, as follows: −0.043 ± 0.116, 0.008 ± 0.041, −0.013 ± 0.032.
The CfA3 B-band light curve agrees excellently in the mean with the composite light curve from Wang et al. (2008) but several of the individual points are only in adequate or poor agreement. In V band, CfA3 has excellent agreement with KAIT and CTIO in eight points, adequate in another, and poor (0.07–0.09 mag) in three more. TNT is systematically fainter than CfA3 by about 0.06 mag. The TNT data are the most discrepant of any of the four groups.
2.7.8. External Comparisons Summary
Our external comparisons show that our light curves are consistent with those from other groups at about the same level that other groups' light curves are consistent with each other, typically at the "good" level of a few hundredths mag. This is important so that multiple nearby samples can be combined, both for training light-curve fitters and for calculating cosmological results. The reduction pipeline and the calibration to the standard system are usually the largest sources of systematic uncertainty between groups and so we emphasize the value of one large, homogeneously observed and reduced sample. The CfA3 sample fits the bill, with the slight exception of the three cameras used, and the change from RI filters on the 4Shooter to r'i' on the later cameras. The CfA3-4Shooter subsample, with 64 objects, and the CfA3-Keplercam subsample, with 116 objects, each individually qualify as large, homogeneously observed and reduced samples since they were each observed with one telescope, one camera, and one set of filters.
2.8. Systematic Uncertainty
The uncertainties of our comparison star photometry take into account both statistical uncertainty and the uncertainty in the photometric transformation and so no systematic error needs to be added. However, in calculating the differential photometry zero point to be added to the SN and its uncertainty (by calculating the weighted mean of the difference of the instrumental and calibrated magnitudes of the comparison stars) the individual star errors are treated as if they were purely statistical. The zero-point error is roughly equal to the typical individual comparison star uncertainty divided by the square root of the number of stars. This usually lowers the differential-photometry zero-point uncertainty below the amount of systematic uncertainty contained in the individual comparison star values and so our SN photometry uncertainties can be considered accurate in the natural system. A systematic uncertainty, on the order of the photometric transformation uncertainty (including photometric zero point and color term uncertainties), should be added when comparing CfA3 standard system SN photometry with that of other groups. We estimate this systematic uncertainty to be 0.02 mag in BVRIr'i' and 0.06 mag in U. This uncertainty was not added to the comparisons of literature and CfA3 SN Ia light curves above.
The other main source of systematic uncertainty for the CfA3 light curves comes from the photometry pipeline. The CfA3 photometry pipeline does propagate all the uncertainties of the various stages to the final SN measurement and are reliable in comparing with other CfA3 pipeline measurements. However, there may be differences compared to other photometry pipelines. Based on the differences in the CfA3 and J06 BVRI photometry of the 17 SNe Ia seen in Section 2.7.1 (≲0.01 mag) and an estimated reference-image flux zero-point uncertainty of 0.005 mag, we attribute a systematic uncertainty of 0.01 mag to our pipeline photometry in BVRIr'i'. For U, we estimate this to be 0.02 mag.
Adding the photometric transformation and CfA3 pipeline systematics in quadrature gives a total systematic uncertainty of roughly 0.03 mag in BVRIr'i' and 0.07 mag in U. The U measurements should be used with caution. We emphasize that this level of systematic uncertainty is typical of the literature SN Ia photometry as well and has the potential to lead to systematic errors in derived cosmological quantities, such as the dark energy equation of state parameter, w. If there is a 0.03 mag offset from the true distance modulus in the nearby sample then this would roughly give rise to an error in w of ∼0.06–0.08, roughly the same size as current statistical uncertainties in w (H09). Using a homogeneously observed and reduced sample can reduce this systematic uncertainty.
As in H09, the "OLD" sample refers to the list of SNe Ia from Jha et al. (2007). For 0.01 ⩽ zCMB ⩽ 0.15, the four different light-curve fitters, SALT, MLCS2k2 (RV = 1.7), MLCS2k2 (RV = 3.1), and SALT2, produce CfA3 Hubble residuals that are fainter on average than the OLD sample by 0.017 ± 0.027, 0.018 ± 0.027, 0.038 ± 0.027, and 0.056 ± 0.032 mag, respectively. The average of these (∼0.03 ± 0.03 mag) is similar to our systematic uncertainty estimate, but consistent with no offset. Part of the difference in mean residuals is probably due to slightly different SN Ia populations being sampled, and how the light-curve/distance fitters interacts with them. Another part is possibly due to some sort of systematic difference in photometry. It should be noted that the standard deviation of the Hubble residuals is similar between the CfA3 and OLD samples, suggesting that the CfA3 photometry is about as intrinsically consistent as the OLD sample, although other effects contribute to this as well.
3. SN I LIGHT-CURVE PROPERTIES
We examine some of the SN Ia light-curve properties of the CfA3 and OLD samples. In H09, the CfA3 and OLD samples are fit with MLCS2k2, using the Galactic value of RV = 3.1 and RV = 1.7 (see Conley et al. 2007 for additional discussion). RV = 3.1 leads to an overestimate in the host extinction while RV = 1.7, chosen to remove the trend in Hubble residuals versus AV for the CfA3 sample, does not. We believe that RV = 1.7 MLCS2k2 extinction estimates are closer to reality so we choose here to use the light-curve shape parameter, Δ, and the calculated host-galaxy extinction, AV, from the RV = 1.7 MLCS2k2 fits. A nearby Hubble diagram is presented in Figure 14 with the CfA3 points in red and the OLD points in black. This plot includes objects with a large range of extinction (AV < 1.5) and light-curve shape (−0.4 ⩽ Δ ⩽ 1.6), including the less-luminous, 1991bg-like objects. The scatter for the CfA3+OLD sample is 0.20 mag, similar to the scatter of CfA3 and OLD separately.
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Standard image High-resolution imageWe also take well sampled light curves from the CfA3 and OLD samples that have data before maximum light in B as measured by MLCS2k2 and measure properties directly from them, thus eliminating any dependency on a model or template light curve (see Tables 8 and 9). K-corrections are applied and Milky Way reddening (Schlegel et al. 1998) and time-dilation are removed, placing these in the rest frame but without any host-galaxy reddening correction. A high-order polynomial (typically order 5 to provide enough flexibility to match the light-curve shape before and after maximum) is fit to the rest-frame UBV light curves, smoothly passing through a large majority of the light-curve points, well inside the error bars, with only a few outliers in the more jagged light curves.
Table 8. Direct-Fit and MLCS2k2 Light-Curve Properties
SN | zCMB | mU | mB | mV | (B − V)Bmax | (U − B)Bmax | AV | EBV | EUB |
---|---|---|---|---|---|---|---|---|---|
80N | 0.0055 | 12.10(0.06) | 12.40(0.03) | 12.38(0.03) | −0.02(0.05) | −0.29(0.07) | 0.2110(0.0510) | 0.1241(0.0300) | 0.0881(0.0213) |
81B | 0.0072 | 11.62(0.10) | 11.93(0.04) | 11.89(0.05) | 0.01(0.06) | −0.25(0.11) | 0.2300(0.0630) | 0.1353(0.0371) | 0.0961(0.0263) |
81D | 0.0055 | 12.28(0.16) | 12.49(0.09) | 12.34(0.05) | 0.11(0.10) | −0.15(0.18) | 0.3390(0.1520) | 0.1994(0.0894) | 0.1416(0.0635) |
86G | 0.0027 | 12.58(0.10) | 12.03(0.08) | 11.11(0.06) | 0.88(0.09) | 0.64(0.10) | 1.2210(0.0860) | 0.7182(0.0506) | 0.5099(0.0359) |
89B | 0.0035 | 12.20(0.07) | 12.23(0.09) | 11.88(0.05) | 0.32(0.10) | 0.04(0.11) | 0.8590(0.0810) | 0.5053(0.0476) | 0.3588(0.0338) |
90N | 0.0043 | ... | 12.67(0.05) | 12.65(0.04) | 0.01(0.06) | ... | 0.2210(0.0510) | 0.1300(0.0300) | 0.0923(0.0213) |
90af | 0.0502 | ... | 17.77(0.04) | 17.76(0.04) | −0.01(0.06) | ... | 0.0730(0.0640) | 0.0429(0.0376) | 0.0305(0.0267) |
91T | 0.0069 | 11.16(0.03) | 11.60(0.02) | 11.45(0.02) | 0.12(0.03) | −0.45(0.04) | 0.3020(0.0390) | 0.1776(0.0229) | 0.1261(0.0163) |
91bg | 0.0046 | ... | 14.60(0.05) | 13.85(0.04) | 0.71(0.06) | ... | 0.0960(0.0570) | 0.0565(0.0335) | 0.0401(0.0238) |
92A | 0.0059 | 12.36(0.07) | 12.53(0.02) | 12.48(0.01) | 0.02(0.02) | −0.16(0.07) | 0.0140(0.0140) | 0.0082(0.0082) | 0.0058(0.0058) |
92ag | 0.0259 | ... | 16.20(0.08) | 16.16(0.06) | 0.03(0.08) | ... | 0.3120(0.0810) | 0.1835(0.0476) | 0.1303(0.0338) |
92al | 0.0141 | ... | 14.45(0.04) | 14.55(0.04) | −0.10(0.05) | ... | 0.0330(0.0270) | 0.0194(0.0159) | 0.0138(0.0113) |
92bc | 0.0198 | ... | 15.08(0.04) | 15.16(0.04) | −0.08(0.05) | ... | 0.0120(0.0120) | 0.0071(0.0071) | 0.0050(0.0050) |
92bh | 0.0451 | ... | 17.59(0.04) | 17.54(0.04) | 0.02(0.06) | ... | 0.1830(0.0790) | 0.1076(0.0465) | 0.0764(0.0330) |
92bo | 0.0181 | ... | 15.69(0.04) | 15.74(0.04) | −0.07(0.06) | ... | 0.0340(0.0290) | 0.0200(0.0171) | 0.0142(0.0121) |
92bp | 0.0789 | ... | 18.30(0.07) | 18.41(0.06) | −0.11(0.09) | ... | 0.0360(0.0310) | 0.0212(0.0182) | 0.0151(0.0129) |
93H | 0.0248 | ... | 16.71(0.05) | 16.51(0.04) | 0.13(0.06) | ... | 0.0290(0.0260) | 0.0171(0.0153) | 0.0121(0.0109) |
93O | 0.0519 | ... | 17.58(0.05) | 17.72(0.05) | −0.18(0.07) | ... | 0.0480(0.0340) | 0.0282(0.0200) | 0.0200(0.0142) |
93ag | 0.0500 | ... | 17.82(0.09) | 17.78(0.07) | 0.02(0.10) | ... | 0.1020(0.0660) | 0.0600(0.0388) | 0.0426(0.0275) |
94D | 0.0031 | 11.14(0.09) | 11.78(0.04) | 11.82(0.02) | −0.04(0.04) | −0.62(0.10) | 0.0090(0.0090) | 0.0053(0.0053) | 0.0038(0.0038) |
94S | 0.0160 | ... | 14.76(0.05) | 14.78(0.06) | −0.02(0.08) | ... | 0.0470(0.0340) | 0.0276(0.0200) | 0.0196(0.0142) |
94T | 0.0357 | ... | 17.32(0.03) | 17.14(0.04) | 0.18(0.05) | ... | 0.0530(0.0420) | 0.0312(0.0247) | 0.0222(0.0175) |
94ae | 0.0055 | ... | 12.95(0.06) | 12.99(0.03) | −0.04(0.07) | ... | 0.0490(0.0320) | 0.0288(0.0188) | 0.0204(0.0133) |
95D | 0.0077 | ... | 13.17(0.06) | 13.25(0.05) | −0.10(0.07) | ... | 0.0680(0.0440) | 0.0400(0.0259) | 0.0284(0.0184) |
95E | 0.0117 | ... | 16.68(0.05) | 15.97(0.05) | 0.70(0.07) | ... | 1.4600(0.0640) | 0.8588(0.0376) | 0.6097(0.0267) |
95ac | 0.0488 | ... | 17.06(0.04) | 17.13(0.04) | −0.11(0.06) | ... | 0.1060(0.0550) | 0.0624(0.0324) | 0.0443(0.0230) |
95ak | 0.0220 | ... | 16.00(0.06) | 15.94(0.06) | 0.03(0.08) | ... | 0.2590(0.0720) | 0.1524(0.0424) | 0.1082(0.0301) |
95al | 0.0059 | 12.72(0.10) | 13.33(0.05) | 13.19(0.05) | 0.13(0.07) | −0.57(0.11) | 0.1770(0.0490) | 0.1041(0.0288) | 0.0739(0.0204) |
95bd | 0.0144 | ... | 15.20(0.33) | 14.91(0.25) | 0.27(0.33) | ... | 0.4620(0.1590) | 0.2718(0.0935) | 0.1930(0.0664) |
96X | 0.0078 | 12.36(0.06) | 12.98(0.05) | 13.02(0.04) | −0.05(0.05) | −0.48(0.06) | 0.0310(0.0240) | 0.0182(0.0141) | 0.0129(0.0100) |
96bo | 0.0163 | ... | 15.83(0.05) | 15.50(0.04) | 0.31(0.06) | ... | 0.6260(0.0710) | 0.3682(0.0418) | 0.2614(0.0297) |
97E | 0.0133 | 14.77(0.10) | 15.12(0.08) | 15.07(0.07) | 0.03(0.09) | −0.32(0.10) | 0.0850(0.0510) | 0.0500(0.0300) | 0.0355(0.0213) |
97bp | 0.0094 | 13.81(0.05) | 13.91(0.03) | 13.73(0.03) | 0.10(0.04) | −0.06(0.05) | 0.4790(0.0480) | 0.2818(0.0282) | 0.2001(0.0200) |
97br | 0.0080 | 13.04(0.09) | 13.63(0.12) | 13.42(0.08) | 0.16(0.13) | −0.54(0.13) | 0.5490(0.0540) | 0.3229(0.0318) | 0.2293(0.0226) |
97dg | 0.0297 | 16.33(0.3) | 16.85(0.06) | 16.86(0.04) | −0.03(0.06) | −0.47(0.08) | 0.0920(0.0520) | 0.0541(0.0306) | 0.0384(0.0217) |
98aq | 0.0045 | 11.62(0.03) | 12.31(0.02) | 12.43(0.02) | −0.12(0.03) | −0.65(0.04) | 0.0110(0.0110) | 0.0065(0.0065) | 0.0046(0.0046) |
98bp | 0.0102 | 15.20(0.08) | 15.28(0.05) | 15.05(0.04) | 0.16(0.06) | −0.06(0.08) | 0.0250(0.0200) | 0.0147(0.0118) | 0.0104(0.0084) |
98bu | 0.0040 | 11.78(0.04) | 12.12(0.02) | 11.78(0.02) | 0.32(0.02) | −0.29(0.04) | 0.6310(0.0400) | 0.3712(0.0235) | 0.2636(0.0167) |
98de | 0.0156 | ... | 17.30(0.05) | 16.66(0.04) | 0.60(0.05) | ... | 0.1420(0.0610) | 0.0835(0.0359) | 0.0593(0.0255) |
98es | 0.0096 | 13.26(0.06) | 13.83(0.04) | 13.75(0.07) | 0.08(0.07) | −0.54(0.06) | 0.2070(0.0420) | 0.1218(0.0247) | 0.0865(0.0175) |
99aa | 0.0153 | 14.17(0.06) | 14.72(0.03) | 14.77(0.02) | −0.06(0.03) | −0.53(0.06) | 0.0250(0.0210) | 0.0147(0.0124) | 0.0104(0.0088) |
99ac | 0.0098 | 13.77(0.06) | 14.09(0.04) | 14.05(0.03) | −0.01(0.05) | −0.27(0.06) | 0.2440(0.0420) | 0.1435(0.0247) | 0.1019(0.0175) |
99aw | 0.0392 | ... | 16.73(0.04) | 16.74(0.03) | −0.01(0.04) | ... | 0.0210(0.0160) | 0.0124(0.0094) | 0.0088(0.0067) |
99by | 0.0028 | 13.73(0.02) | 13.54(0.06) | 13.10(0.02) | 0.40(0.06) | 0.20(0.06) | 0.0300(0.0220) | 0.0176(0.0129) | 0.0125(0.0092) |
99cc | 0.0315 | 16.44(0.05) | 16.76(0.02) | 16.75(0.02) | −0.01(0.03) | −0.31(0.06) | 0.0640(0.0490) | 0.0376(0.0288) | 0.0267(0.0204) |
99cl | 0.0087 | 15.51(0.07) | 14.87(0.04) | 13.72(0.04) | 1.12(0.05) | 0.66(0.08) | 2.1980(0.0660) | 1.2929(0.0388) | 0.9180(0.0275) |
99da | 0.0125 | ... | 16.65(0.04) | 16.06(0.04) | 0.52(0.05) | ... | 0.0660(0.0490) | 0.0388(0.0288) | 0.0275(0.0204) |
99dk | 0.0139 | 14.54(0.09) | 14.81(0.05) | 14.76(0.04) | 0.05(0.05) | −0.24(0.10) | 0.2520(0.0580) | 0.1482(0.0341) | 0.1052(0.0242) |
99dq | 0.0135 | 13.88(0.10) | 14.42(0.08) | 14.34(0.06) | 0.07(0.08) | −0.48(0.10) | 0.2990(0.0510) | 0.1759(0.0300) | 0.1249(0.0213) |
99ee | 0.0106 | 14.65(0.03) | 14.85(0.02) | 14.56(0.02) | 0.27(0.03) | −0.18(0.03) | 0.6430(0.0410) | 0.3782(0.0241) | 0.2685(0.0171) |
99ek | 0.0176 | ... | 15.61(0.37) | 15.49(0.28) | 0.10(0.37) | ... | 0.3120(0.1560) | 0.1835(0.0918) | 0.1303(0.0652) |
99gp | 0.0260 | 15.40(0.06) | 15.99(0.05) | 15.97(0.03) | −0.00(0.05) | −0.54(0.07) | 0.1490(0.0440) | 0.0876(0.0259) | 0.0622(0.0184) |
00E | 0.0042 | ... | 12.86(0.24) | 12.68(0.19) | 0.17(0.24) | ... | 0.4660(0.1220) | 0.2741(0.0718) | 0.1946(0.0510) |
00cf | 0.0365 | ... | 17.08(0.03) | 17.11(0.03) | −0.05(0.04) | ... | 0.0860(0.0550) | 0.0506(0.0324) | 0.0359(0.0230) |
00cn | 0.0232 | 16.40(0.09) | 16.57(0.05) | 16.40(0.03) | 0.10(0.06) | −0.16(0.10) | 0.0710(0.0600) | 0.0418(0.0353) | 0.0297(0.0251) |
00dk | 0.0164 | 14.99(0.07) | 15.34(0.05) | 15.33(0.04) | −0.02(0.06) | −0.29(0.07) | 0.0170(0.0150) | 0.0100(0.0088) | 0.0071(0.0062) |
01ba | 0.0305 | ... | 16.18(0.05) | 16.31(0.05) | −0.15(0.06) | ... | 0.0250(0.0210) | 0.0147(0.0124) | 0.0104(0.0088) |
01bt | 0.0144 | ... | 15.26(0.05) | 15.09(0.04) | 0.14(0.05) | ... | 0.4260(0.0630) | 0.2506(0.0371) | 0.1779(0.0263) |
01cz | 0.0163 | ... | 15.05(0.06) | 14.95(0.05) | 0.09(0.07) | ... | 0.2000(0.0700) | 0.1176(0.0412) | 0.0835(0.0293) |
01el | 0.0037 | 12.56(0.04) | 12.75(0.03) | 12.70(0.01) | 0.03(0.03) | −0.16(0.05) | 0.5000(0.0440) | 0.2941(0.0259) | 0.2088(0.0184) |
01ep | 0.0129 | 14.52(0.04) | 14.87(0.04) | 14.81(0.03) | 0.03(0.05) | −0.31(0.05) | 0.2590(0.0540) | 0.1524(0.0318) | 0.1082(0.0226) |
01fe | 0.0143 | 14.02(0.10) | 14.68(0.04) | 14.65(0.03) | 0.02(0.05) | −0.60(0.09) | 0.0990(0.0490) | 0.0582(0.0288) | 0.0413(0.0204) |
01fh | 0.0114 | 13.87(0.59) | 14.19(0.50) | 14.31(0.38) | −0.15(0.50) | −0.25(0.59) | 0.0770(0.0620) | 0.0453(0.0365) | 0.0322(0.0259) |
01V | 0.0162 | 14.01(0.09) | 14.64(0.08) | 14.61(0.05) | −0.00(0.10) | −0.60(0.12) | 0.1710(0.0410) | 0.1006(0.0241) | 0.0714(0.0171) |
02bo | 0.0054 | ... | 13.94(0.08) | 13.59(0.07) | 0.34(0.11) | ... | 0.9080(0.0500) | 0.5341(0.0294) | 0.3792(0.0209) |
02cd | 0.0097 | 15.57(0.32) | 15.53(0.27) | 14.93(0.22) | 0.57(0.28) | 0.06(0.31) | 1.0260(0.1320) | 0.6035(0.0776) | 0.4285(0.0551) |
02cr | 0.0103 | ... | 14.16(0.04) | 14.23(0.04) | −0.07(0.05) | ... | 0.1220(0.0630) | 0.0718(0.0371) | 0.0510(0.0263) |
02cx | 0.0250 | ... | 17.54(0.10) | 17.34(0.08) | 0.17(0.13) | ... | 0.7030(0.0680) | 0.4135(0.0400) | 0.2936(0.0284) |
02de | 0.0281 | 16.32(0.06) | 16.66(0.03) | 16.52(0.02) | 0.13(0.04) | −0.31(0.06) | 0.3820(0.0840) | 0.2247(0.0494) | 0.1595(0.0351) |
02dj | 0.0104 | ... | 13.98(0.07) | 13.83(0.06) | 0.10(0.08) | ... | 0.3420(0.0780) | 0.2012(0.0459) | 0.1429(0.0326) |
02dp | 0.0105 | 14.16(0.06) | 14.60(0.05) | 14.47(0.05) | 0.10(0.07) | −0.39(0.07) | 0.2680(0.0900) | 0.1576(0.0529) | 0.1119(0.0376) |
02er | 0.0085 | 13.91(0.13) | 14.24(0.11) | 14.10(0.09) | 0.12(0.11) | −0.33(0.13) | 0.2270(0.0740) | 0.1335(0.0435) | 0.0948(0.0309) |
02fk | 0.0070 | ... | 13.11(0.05) | 13.23(0.04) | −0.12(0.06) | ... | 0.0340(0.0230) | 0.0200(0.0135) | 0.0142(0.0096) |
02ha | 0.0134 | ... | 14.69(0.08) | 14.77(0.07) | −0.09(0.09) | ... | 0.0420(0.0320) | 0.0247(0.0188) | 0.0175(0.0133) |
02hu | 0.0382 | 16.08(0.05) | 16.58(0.04) | 16.70(0.03) | −0.12(0.05) | −0.48(0.06) | 0.0360(0.0300) | 0.0212(0.0176) | 0.0151(0.0125) |
03W | 0.0211 | 15.60(0.08) | 15.85(0.04) | 15.71(0.05) | 0.12(0.06) | −0.15(0.08) | 0.3300(0.0500) | 0.1941(0.0294) | 0.1378(0.0209) |
03cg | 0.0053 | 16.38(0.05) | 15.79(0.05) | 14.56(0.02) | 1.23(0.05) | 0.66(0.06) | 2.2090(0.0530) | 1.2994(0.0312) | 0.9226(0.0222) |
03du | 0.0066 | 13.07(0.16) | 13.43(0.06) | 13.54(0.02) | −0.12(0.07) | −0.35(0.19) | 0.0320(0.0220) | 0.0188(0.0129) | 0.0133(0.0092) |
03iv | 0.0335 | 16.57(0.15) | 16.97(0.09) | 17.01(0.08) | −0.10(0.10) | −0.37(0.15) | 0.0230(0.0240) | 0.0135(0.0141) | 0.0096(0.0100) |
03kf | 0.0077 | 12.93(0.25) | 13.28(0.21) | 13.25(0.16) | 0.02(0.21) | −0.27(0.25) | 0.1140(0.0800) | 0.0671(0.0471) | 0.0476(0.0334) |
04as | 0.0321 | ... | 16.93(0.15) | 16.91(0.03) | 0.01(0.15) | ... | 0.3030(0.0580) | 0.1782(0.0341) | 0.1265(0.0242) |
05am | 0.0095 | ... | 13.62(0.04) | 13.60(0.03) | 0.01(0.05) | −0.27(0.06) | 0.0370(0.0330) | 0.0218(0.0194) | 0.0155(0.0138) |
05cf | 0.0070 | 12.84(0.08) | 13.24(0.07) | 13.28(0.05) | −0.05(0.07) | −0.38(0.08) | 0.2080(0.0700) | 0.1224(0.0412) | 0.0869(0.0293) |
05el | 0.0148 | 14.28(0.10) | 14.84(0.08) | 14.88(0.06) | −0.05(0.08) | −0.53(0.10) | 0.0120(0.0130) | 0.0071(0.0076) | 0.0050(0.0054) |
05eq | 0.0284 | 15.77(0.08) | 16.28(0.06) | 16.25(0.05) | 0.03(0.07) | −0.47(0.09) | 0.1040(0.0470) | 0.0612(0.0276) | 0.0435(0.0196) |
05eu | 0.0341 | ... | ... | 16.39(0.08) | ... | ... | 0.0520(0.0380) | 0.0306(0.0224) | 0.0217(0.0159) |
05hc | 0.0450 | 16.93(0.06) | 17.31(0.04) | 17.41(0.04) | −0.12(0.06) | −0.38(0.07) | 0.1150(0.0520) | 0.0676(0.0306) | 0.0480(0.0217) |
05hk | 0.0118 | 15.44(0.03) | 15.84(0.05) | 15.71(0.02) | 0.04(0.05) | −0.27(0.06) | 0.8100(0.0440) | 0.4765(0.0259) | 0.3383(0.0184) |
05iq | 0.0330 | 16.30(0.19) | 16.80(0.07) | 16.88(0.03) | −0.10(0.07) | −0.48(0.20) | 0.0310(0.0260) | 0.0182(0.0153) | 0.0129(0.0109) |
05kc | 0.0138 | 15.49(0.11) | 15.58(0.09) | 15.38(0.07) | 0.20(0.14) | −0.09(0.20) | 0.6240(0.0740) | 0.3671(0.0435) | 0.2606(0.0309) |
05ke | 0.0045 | 15.15(0.04) | 14.88(0.05) | 14.14(0.04) | 0.66(0.07) | 0.34(0.06) | 0.0680(0.0400) | 0.0400(0.0235) | 0.0284(0.0167) |
05ki | 0.0208 | 14.96(0.12) | 15.56(0.07) | 15.66(0.02) | −0.10(0.07) | −0.55(0.14) | 0.0180(0.0150) | 0.0106(0.0088) | 0.0075(0.0062) |
05lz | 0.0402 | 17.33(0.10) | 17.55(0.07) | 17.59(0.06) | −0.04(0.08) | −0.22(0.11) | 0.1730(0.0680) | 0.1018(0.0400) | 0.0723(0.0284) |
05mc | 0.0261 | 17.14(0.06) | 17.21(0.04) | 17.00(0.04) | 0.17(0.05) | −0.04(0.06) | 0.0770(0.0510) | 0.0453(0.0300) | 0.0322(0.0213) |
05ms | 0.0259 | 15.70(0.04) | 16.13(0.03) | 16.17(0.03) | −0.08(0.04) | −0.43(0.05) | 0.0700(0.0400) | 0.0412(0.0235) | 0.0293(0.0167) |
05mz | 0.0170 | 16.32(0.13) | 16.37(0.11) | 16.06(0.09) | 0.24(0.11) | 0.07(0.14) | 0.2660(0.0890) | 0.1565(0.0524) | 0.1111(0.0372) |
06ac | 0.0236 | 15.83(0.05) | 16.19(0.03) | 16.06(0.03) | 0.11(0.04) | −0.35(0.06) | 0.1040(0.0470) | 0.0612(0.0276) | 0.0435(0.0196) |
06ar | 0.0229 | ... | 16.46(0.03) | 16.33(0.03) | 0.11(0.04) | ... | 0.1960(0.1240) | 0.1153(0.0729) | 0.0819(0.0518) |
06ax | 0.0180 | 14.47(0.05) | 15.01(0.04) | 15.08(0.03) | −0.08(0.04) | −0.50(0.06) | 0.0380(0.0290) | 0.0224(0.0171) | 0.0159(0.0121) |
06az | 0.0316 | 15.87(0.06) | 16.45(0.03) | 16.55(0.03) | −0.13(0.04) | −0.52(0.06) | 0.0120(0.0120) | 0.0071(0.0071) | 0.0050(0.0050) |
06br | 0.0255 | ... | 19.08(0.07) | 18.09(0.04) | 0.99(0.08) | ... | 1.7010(0.1020) | 1.0006(0.0600) | 0.7104(0.0426) |
06bt | 0.0325 | ... | 16.91(0.04) | 16.77(0.03) | 0.12(0.04) | ... | 0.4280(0.0530) | 0.2518(0.0312) | 0.1788(0.0222) |
06bz | 0.0277 | ... | 18.33(0.08) | 17.63(0.03) | 0.61(0.05) | ... | 0.1820(0.1150) | 0.1071(0.0676) | 0.0760(0.0480) |
06cc | 0.0328 | 17.60(0.06) | 17.81(0.03) | 17.45(0.02) | 0.35(0.04) | −0.14(0.07) | 0.8120(0.0510) | 0.4776(0.0300) | 0.3391(0.0213) |
06cm | 0.0152 | ... | 18.05(0.05) | 16.96(0.04) | 1.07(0.06) | ... | 1.8290(0.0790) | 1.0759(0.0465) | 0.7639(0.0330) |
06cp | 0.0233 | ... | 15.89(0.14) | 15.87(0.09) | 0.02(0.05) | ... | 0.4400(0.0640) | 0.2588(0.0376) | 0.1837(0.0267) |
06D | 0.0097 | 13.90(0.05) | 14.13(0.04) | 14.06(0.04) | 0.05(0.05) | −0.20(0.06) | 0.0760(0.0420) | 0.0447(0.0247) | 0.0317(0.0175) |
06gj | 0.0277 | ... | 17.67(0.08) | 17.28(0.07) | 0.34(0.10) | ... | 0.4820(0.1260) | 0.2835(0.0741) | 0.2013(0.0526) |
06gr | 0.0335 | 16.59(0.09) | 16.91(0.07) | 16.87(0.05) | 0.03(0.08) | −0.28(0.10) | 0.3040(0.0520) | 0.1788(0.0306) | 0.1269(0.0217) |
06kf | 0.0208 | ... | ... | 15.90(0.12) | ... | ... | 0.0240(0.0240) | 0.0141(0.0141) | 0.0100(0.0100) |
06le | 0.0173 | 14.26(0.32) | 14.78(0.27) | 14.85(0.21) | −0.09(0.27) | −0.50(0.31) | 0.0760(0.0600) | 0.0447(0.0353) | 0.0317(0.0251) |
06lf | 0.0130 | ... | 13.70(0.63) | 13.88(0.49) | −0.18(0.63) | ... | 0.0950(0.0740) | 0.0559(0.0435) | 0.0397(0.0309) |
06mp | 0.0229 | ... | 15.96(0.03) | 15.93(0.04) | −0.00(0.04) | ... | 0.1660(0.0680) | 0.0976(0.0400) | 0.0693(0.0284) |
06N | 0.0143 | ... | 15.08(0.07) | 15.09(0.05) | −0.03(0.07) | −0.43(0.08) | 0.0270(0.0230) | 0.0159(0.0135) | 0.0113(0.0096) |
06nz | 0.0372 | ... | 18.11(0.06) | 17.73(0.05) | 0.29(0.08) | ... | 0.0940(0.0780) | 0.0553(0.0459) | 0.0393(0.0326) |
06oa | 0.0589 | 17.46(0.08) | 17.84(0.06) | 17.85(0.06) | −0.02(0.08) | −0.30(0.10) | 0.1860(0.0670) | 0.1094(0.0394) | 0.0777(0.0280) |
06ob | 0.0582 | 17.78(0.08) | 18.20(0.05) | 18.17(0.04) | −0.02(0.06) | −0.21(0.09) | 0.0210(0.0210) | 0.0124(0.0124) | 0.0088(0.0088) |
06qo | 0.0300 | ... | 16.81(0.04) | 16.64(0.04) | 0.17(0.06) | ... | 0.4530(0.0630) | 0.2665(0.0371) | 0.1892(0.0263) |
06S | 0.0329 | 16.34(0.05) | 16.79(0.02) | 16.75(0.02) | −0.00(0.03) | −0.43(0.05) | 0.2680(0.0460) | 0.1576(0.0271) | 0.1119(0.0192) |
06sr | 0.0232 | ... | 16.14(0.07) | 16.11(0.05) | 0.02(0.07) | ... | 0.0850(0.0530) | 0.0500(0.0312) | 0.0355(0.0222) |
06td | 0.0150 | ... | 15.72(0.06) | 15.60(0.05) | 0.11(0.06) | ... | 0.1710(0.0790) | 0.1006(0.0465) | 0.0714(0.0330) |
06X | 0.0063 | 16.28(0.07) | 15.28(0.04) | 13.97(0.02) | 1.26(0.05) | 1.00(0.09) | 2.4960(0.0430) | 1.4682(0.0253) | 1.0424(0.0180) |
07af | 0.0063 | ... | 13.13(0.03) | 13.10(0.02) | 0.02(0.03) | ... | 0.2150(0.0540) | 0.1265(0.0318) | 0.0898(0.0226) |
07au | 0.0202 | ... | 16.46(0.06) | 16.32(0.07) | 0.12(0.09) | ... | 0.0490(0.0390) | 0.0288(0.0229) | 0.0204(0.0163) |
07bc | 0.0219 | ... | 15.82(0.04) | 15.92(0.03) | −0.11(0.05) | ... | 0.0840(0.0590) | 0.0494(0.0347) | 0.0351(0.0246) |
07bd | 0.0320 | ... | 16.53(0.03) | 16.58(0.03) | −0.06(0.04) | ... | 0.0430(0.0330) | 0.0253(0.0194) | 0.0180(0.0138) |
07ca | 0.0152 | ... | 15.95(0.05) | 15.65(0.04) | 0.29(0.05) | ... | 0.5800(0.0690) | 0.3412(0.0406) | 0.2423(0.0288) |
07ci | 0.0191 | ... | ... | 15.86(0.02) | ... | ... | 0.0740(0.0630) | 0.0435(0.0371) | 0.0309(0.0263) |
07co | 0.0266 | 16.39(0.10) | 16.43(0.08) | 16.38(0.06) | 0.03(0.08) | −0.02(0.10) | 0.3920(0.0690) | 0.2306(0.0406) | 0.1637(0.0288) |
07cq | 0.0247 | ... | 15.82(0.07) | 15.79(0.06) | 0.01(0.08) | ... | 0.1090(0.0590) | 0.0641(0.0347) | 0.0455(0.0246) |
07F | 0.0242 | ... | 15.87(0.03) | 15.91(0.02) | −0.04(0.04) | ... | 0.0470(0.0380) | 0.0276(0.0224) | 0.0196(0.0159) |
07qe | 0.0244 | ... | 16.01(0.04) | 15.99(0.03) | −0.01(0.05) | ... | 0.1480(0.0590) | 0.0871(0.0347) | 0.0618(0.0246) |
07S | 0.0137 | ... | 15.82(0.03) | 15.40(0.03) | 0.39(0.04) | ... | 0.8330(0.0540) | 0.4900(0.0318) | 0.3479(0.0226) |
08bf | 0.0253 | 15.29(0.08) | 15.72(0.04) | 15.68(0.04) | 0.04(0.05) | −0.40(0.09) | 0.1020(0.0490) | 0.0600(0.0288) | 0.0426(0.0204) |
Notes. The peak magnitudes, mU, mB, and mV, are measured at the time of maximum light in each band while (B − V)Bmax and (U − B)Bmax are measured at the time of maximum light in B. For these measurements, the light curves were K-corrected, corrected for Milky Way extinction, and corrected for time dilation. The host-galaxy extinction, AV, is from MLCS2k2 (RV = 1.7) and has not been removed from the peak magnitudes listed. The host-galaxy color excesses, EBV and EUB, are derived from AV.
Table 9. Δm15, Δ, and Time Between Points at Maximum Light
SN | Δm15(U) | Δm15(B) | Δm15(V) | Δ | Δt(U) | Δt(B) | Δt(V) |
---|---|---|---|---|---|---|---|
80N | ... | 1.28(0.05) | 0.73(0.05) | −0.0400(0.0780) | 2.02 | 2.02 | 0.98 |
81B | 1.39(0.18) | 1.10(0.06) | 0.73(0.09) | −0.1360(0.0700) | 0.66 | 0.36 | 3.50 |
81D | 1.34(0.32) | 1.32(0.18) | 0.86(0.13) | 0.2900(0.2230) | 1.00 | 5.99 | 5.99 |
86G | 2.05(0.24) | 1.65(0.09) | 1.01(0.09) | 1.2030(0.0640) | 5.09 | 0.99 | 3.94 |
89B | 1.24(0.10) | 1.02(0.13) | 0.64(0.19) | 0.0030(0.1150) | 0.99 | 3.99 | 3.99 |
90N | ... | 1.04(0.13) | 0.62(0.11) | −0.2990(0.0560) | ... | 7.90 | 7.02 |
90af | ... | 1.63(0.06) | 0.89(0.07) | 0.5070(0.1190) | ... | 0.99 | 1.90 |
91T | 1.37(0.04) | 0.80(0.03) | 0.62(0.05) | −0.3510(0.0360) | 1.00 | 1.00 | 3.05 |
91bg | ... | 1.87(0.08) | 1.41(0.07) | 1.4350(0.0480) | ... | 0.99 | 0.15 |
92A | 1.44(0.14) | 1.36(0.03) | 0.83(0.02) | 0.4130(0.0550) | 7.04 | 0.96 | 1.11 |
92ag | ... | 1.10(0.09) | 0.60(0.08) | 0.0500(0.0860) | ... | 0.98 | 1.05 |
92al | ... | 1.10(0.08) | 0.61(0.08) | −0.0640(0.0610) | ... | 3.78 | 3.78 |
92bc | ... | 0.82(0.08) | 0.61(0.08) | −0.2530(0.0440) | ... | 3.85 | 3.85 |
92bh | ... | ... | ... | −0.1700(0.0860) | ... | 2.81 | 2.81 |
92bo | ... | ... | ... | 0.5800(0.0790) | ... | 4.02 | 2.94 |
92bp | ... | 1.34(0.15) | 0.58(0.13) | 0.0090(0.0990) | ... | 6.48 | 6.48 |
93H | ... | 1.76(0.09) | 1.02(0.07) | 0.8740(0.0960) | ... | 1.11 | 0.87 |
93O | ... | 1.23(0.07) | 0.71(0.08) | −0.0300(0.0720) | ... | 2.13 | 3.61 |
93ag | ... | ... | ... | −0.0190(0.0940) | ... | 6.67 | 6.67 |
94D | 1.71(0.12) | 1.35(0.07) | 0.81(0.05) | 0.3610(0.0490) | 0.81 | 0.65 | 0.49 |
94S | ... | ... | 0.68(0.09) | −0.1730(0.0780) | ... | 1.97 | 1.97 |
94T | ... | 1.36(0.05) | 0.87(0.06) | 0.7460(0.1060) | ... | 0.87 | 0.87 |
94ae | ... | 0.98(0.15) | 0.64(0.04) | −0.2360(0.0440) | ... | 7.96 | 0.99 |
95D | ... | 1.02(0.07) | 0.65(0.07) | −0.2290(0.0480) | ... | 1.98 | 2.02 |
95E | ... | 1.11(0.11) | 0.61(0.08) | −0.0930(0.0660) | ... | 2.87 | 2.87 |
95ac | ... | 0.77(0.07) | 0.58(0.08) | −0.3160(0.0520) | ... | 2.78 | 3.83 |
95ak | ... | ... | 0.86(0.07) | 0.1300(0.0800) | ... | 1.01 | 0.86 |
95al | 0.89(0.17) | 0.84(0.09) | 0.56(0.06) | −0.2750(0.0490) | 3.97 | 3.98 | 1.00 |
95bd | ... | 0.94(0.34) | 0.74(0.25) | −0.3270(0.0490) | ... | 5.97 | 0.98 |
96X | 1.37(0.10) | 1.29(0.06) | 0.81(0.04) | 0.0660(0.0560) | 0.99 | 1.09 | 1.00 |
96bo | ... | 1.23(0.06) | 0.70(0.07) | −0.0350(0.0780) | ... | 1.96 | 3.93 |
97E | 1.64(0.11) | 1.41(0.09) | 0.79(0.09) | 0.3120(0.0860) | 1.07 | 1.86 | 3.94 |
97bp | ... | 1.16(0.06) | 0.71(0.04) | −0.2850(0.0560) | 1.00 | 0.98 | 2.05 |
97br | 1.21(0.10) | 1.08(0.17) | 0.65(0.12) | −0.3760(0.0390) | 1.90 | 6.79 | 5.96 |
97dg | ... | ... | ... | −0.0180(0.0840) | 9.0 | 9.0 | 9.0 |
98aq | 1.23(0.05) | 1.03(0.03) | 0.66(0.03) | −0.1220(0.0380) | 2.01 | 1.03 | 0.94 |
98bp | 2.36(0.10) | 1.96(0.08) | 1.12(0.04) | 1.2540(0.0470) | 2.98 | 2.98 | 1.04 |
98bu | 1.16(0.05) | 1.04(0.03) | 0.75(0.03) | −0.0660(0.0470) | 0.91 | 0.82 | 0.82 |
98de | ... | 1.99(0.12) | 1.27(0.06) | 1.5170(0.0420) | ... | 0.98 | 1.02 |
98es | ... | 0.81(0.07) | 0.59(0.14) | −0.3300(0.0370) | 1.03 | 0.89 | 7.99 |
99aa | ... | 0.80(0.06) | 0.58(0.03) | −0.3460(0.0320) | 4.82 | 2.02 | 0.86 |
99ac | ... | 1.33(0.06) | ... | −0.1440(0.0470) | 4.02 | 0.98 | 1.97 |
99aw | ... | 0.79(0.08) | 0.62(0.06) | −0.4580(0.0420) | ... | 4.72 | 1.18 |
99by | ... | 1.98(0.08) | 1.26(0.03) | 1.4650(0.0320) | 0.99 | 0.97 | 1.00 |
99cc | ... | ... | ... | 0.2880(0.0940) | 4.91 | 0.81 | 0.98 |
99cl | ... | ... | ... | −0.0160(0.0860) | 1.98 | 1.95 | 2.99 |
99da | ... | 1.92(0.11) | 1.15(0.10) | 1.4870(0.0430) | ... | 1.84 | 2.08 |
99dk | 1.93(0.21) | 1.19(0.05) | 0.64(0.05) | −0.3060(0.0530) | 7.89 | 1.24 | 1.24 |
99dq | ... | 0.86(0.11) | 0.55(0.08) | −0.3590(0.0340) | 1.01 | 0.95 | 0.94 |
99ee | 1.23(0.06) | 0.90(0.03) | 0.65(0.03) | −0.2780(0.0370) | 2.94 | 0.95 | 0.87 |
99ek | ... | 1.21(0.37) | 0.72(0.28) | 0.0560(0.0780) | ... | 2.03 | 0.85 |
99gp | 1.05(0.08) | 0.80(0.07) | 0.55(0.04) | −0.4150(0.0350) | 1.86 | 2.85 | 0.91 |
00E | ... | 0.94(0.25) | 0.66(0.19) | −0.2270(0.0630) | ... | 4.96 | 3.94 |
00cf | ... | 1.47(0.05) | 0.77(0.04) | −0.0050(0.0790) | ... | 1.13 | 1.13 |
00cn | ... | ... | ... | 0.7240(0.0840) | 5.95 | 5.95 | 0.92 |
00dk | 1.86(0.08) | ... | ... | 0.5110(0.0660) | 0.91 | 1.84 | 4.91 |
01ba | ... | 0.95(0.05) | 0.59(0.07) | −0.1640(0.0580) | ... | 0.98 | 2.90 |
01bt | ... | 1.26(0.07) | 0.70(0.06) | 0.0410(0.0690) | ... | 2.83 | 3.01 |
01cz | ... | 0.93(0.08) | 0.62(0.06) | −0.1240(0.0610) | ... | 2.89 | 1.97 |
01el | 1.55(0.07) | 1.15(0.07) | 0.63(0.02) | −0.1150(0.0530) | 4.03 | 4.02 | 1.02 |
01ep | ... | ... | ... | 0.0460(0.0810) | 0.84 | 3.97 | 3.98 |
01fe | ... | ... | ... | −0.1690(0.0670) | 6.88 | 5.88 | 4.03 |
01fh | ... | ... | ... | 0.6320(0.1240) | 0.97 | 3.01 | 2.93 |
01V | 1.01(0.18) | 0.65(0.15) | 0.53(0.13) | −0.3300(0.0430) | 8.70 | 7.74 | 7.74 |
02bo | ... | ... | ... | −0.1060(0.0640) | ... | ... | - |
02cd | 1.06(0.33) | 0.98(0.27) | ... | −0.3210(0.0560) | 3.95 | 3.96 | ... |
02cr | ... | 1.26(0.11) | 0.66(0.11) | 0.0090(0.0830) | ... | 6.83 | 6.82 |
02cx | ... | 1.32(0.14) | 0.79(0.13) | −0.5320(0.0580) | ... | 5.86 | 6.87 |
02de | ... | ... | ... | −0.2240(0.1430) | 2.00 | 2.94 | 2.94 |
02dj | ... | ... | ... | −0.2000(0.1200) | ... | 1.96 | 7.94 |
02dp | ... | 1.12(0.06) | ... | 0.0230(0.1350) | 1.97 | 1.97 | 6.86 |
02er | 1.87(0.13) | 1.28(0.12) | 0.73(0.10) | 0.2700(0.0780) | 0.99 | 1.03 | 1.94 |
02fk | ... | ... | 0.65(0.10) | −0.0620(0.0560) | ... | 6.98 | 6.02 |
02ha | ... | 1.34(0.15) | 0.78(0.15) | 0.1270(0.0790) | ... | 8.84 | 8.84 |
02hu | 1.32(0.09) | 1.04(0.07) | 0.53(0.07) | −0.2460(0.0550) | 3.84 | 3.85 | 3.84 |
03W | 1.35(0.10) | 1.16(0.04) | 0.71(0.14) | −0.0710(0.0590) | 1.04 | 0.94 | 8.90 |
03cg | ... | ... | 0.68(0.05) | 0.0230(0.0740) | 3.08 | 5.91 | 2.84 |
03du | ... | ... | ... | −0.1680(0.0450) | 6.94 | 2.86 | 2.86 |
03iv | ... | ... | ... | 0.2780(0.1060) | ... | 1.97 | 4.80 |
03kf | 0.94(0.28) | 0.97(0.23) | 0.70(0.19) | −0.1710(0.0550) | 9.02 | 6.10 | 6.11 |
04as | ... | ... | 0.64(0.06) | −0.1840(0.0700) | ... | ... | 2.81 |
05am | ... | 1.73(0.05) | 0.89(0.05) | 0.4000(0.0910) | ... | 1.01 | 0.95 |
05cf | 1.30(0.09) | 1.06(0.08) | 0.61(0.06) | −0.1470(0.0810) | 3.05 | 3.03 | 1.00 |
05el | 1.65(0.17) | 1.23(0.11) | 0.79(0.10) | 0.2100(0.0600) | 8.84 | 4.85 | 4.85 |
05eq | 1.18(0.13) | 0.86(0.11) | 0.49(0.10) | −0.3090(0.0450) | 5.78 | 5.79 | 5.78 |
05eu | ... | ... | 0.67(0.15) | −0.3190(0.0560) | ... | ... | 7.89 |
05hc | 1.49(0.15) | 0.97(0.05) | 0.53(0.10) | −0.1250(0.0750) | 1.04 | 0.86 | 5.69 |
05hk | 1.72(0.06) | 1.47(0.14) | 0.83(0.03) | −0.3100(0.0460) | 0.88 | 8.87 | 0.91 |
05iq | 1.88(0.31) | 1.05(0.10) | 0.68(0.04) | 0.1370(0.0730) | 5.84 | 4.72 | 0.89 |
05kc | ... | 1.24(0.19) | 0.66(0.14) | 0.0360(0.0820) | 2.88 | 1.93 | 1.93 |
05ke | 1.77(0.06) | 1.66(0.14) | 1.15(0.13) | 1.5510(0.0330) | 0.01 | 8.86 | 7.86 |
05ki | ... | ... | ... | 0.2850(0.0660) | 8.80 | 8.80 | 1.02 |
05lz | ... | 1.35(0.19) | 0.59(0.09) | 0.2170(0.1030) | 3.02 | 3.02 | 3.02 |
05mc | 1.96(0.36) | 1.87(0.11) | 1.04(0.07) | 0.9350(0.0710) | 1.02 | 3.92 | 3.91 |
05ms | ... | 0.79(0.07) | 0.56(0.04) | −0.1590(0.0520) | 3.90 | 3.91 | 1.83 |
05mz | ... | 1.96(0.14) | 1.33(0.11) | 1.3640(0.0670) | 1.98 | 1.94 | 3.97 |
06ac | 1.46(0.08) | 1.08(0.07) | 0.66(0.08) | 0.1610(0.0790) | 1.91 | 3.86 | 4.97 |
06ar | ... | ... | ... | 0.4280(0.2430) | ... | 3.93 | 2.85 |
06ax | 1.39(0.10) | 1.08(0.05) | 0.63(0.05) | −0.1620(0.0480) | 4.93 | 1.95 | 1.94 |
06az | 1.52(0.11) | 1.30(0.06) | 0.73(0.05) | 0.1540(0.0560) | 4.83 | 2.08 | 1.91 |
06br | ... | 1.47(0.20) | 0.89(0.08) | 0.0450(0.1500) | ... | 0.89 | 0.90 |
06bt | ... | 1.09(0.06) | 0.54(0.04) | −0.3250(0.0520) | ... | 1.04 | 0.98 |
06bz | ... | 2.09(0.16) | 1.41(0.06) | 1.5020(0.0820) | ... | 0.92 | 1.08 |
06cc | 1.07(0.15) | 1.01(0.05) | 0.72(0.06) | −0.2260(0.0580) | 3.75 | 0.96 | 2.81 |
06cm | ... | 0.99(0.13) | 0.79(0.07) | −0.0520(0.0870) | ... | 0.94 | 1.97 |
06cp | ... | ... | ... | −0.1720(0.0870) | ... | 4.84 | 4.84 |
06D | 1.85(0.08) | 1.35(0.07) | 0.84(0.11) | 0.4230(0.0770) | 3.88 | 3.88 | 6.96 |
06gj | ... | 1.39(0.17) | 0.96(0.15) | 0.5820(0.1590) | ... | 8.71 | 8.71 |
06gr | ... | 0.95(0.13) | 0.57(0.08) | −0.3050(0.0460) | 1.85 | 6.91 | 3.93 |
06kf | ... | ... | 0.77(0.12) | 0.6280(0.0970) | ... | ... | 0.87 |
06le | 1.04(0.33) | 0.85(0.27) | 0.59(0.22) | −0.2720(0.0440) | 2.01 | 4.02 | 4.03 |
06lf | ... | 1.35(0.62) | 0.71(0.49) | 0.2920(0.0790) | ... | 6.06 | 6.06 |
06mp | ... | ... | ... | −0.1210(0.0580) | ... | 1.92 | 5.87 |
06N | ... | 1.57(0.07) | 0.90(0.06) | 0.4230(0.0700) | ... | 1.85 | 1.85 |
06nz | ... | ... | 1.18(0.14) | 1.1150(0.1180) | ... | 7.58 | 7.57 |
06oa | ... | 0.98(0.18) | 0.60(0.14) | −0.2520(0.1000) | 0.93 | 5.67 | 3.77 |
06ob | ... | 1.70(0.12) | 1.15(0.11) | 0.5410(0.0780) | 1.03 | 1.80 | 1.94 |
06qo | ... | 1.02(0.10) | 0.61(0.10) | −0.1820(0.0550) | ... | 5.74 | 5.75 |
06S | ... | 0.91(0.04) | 0.60(0.05) | −0.1980(0.0530) | 2.01 | 0.93 | 2.82 |
06sr | ... | 1.26(0.09) | 0.72(0.08) | 0.1870(0.0860) | ... | 3.87 | 3.88 |
06td | ... | 1.48(0.12) | 0.76(0.10) | 0.3900(0.1380) | ... | 0.99 | 0.98 |
06X | ... | 1.10(0.12) | 0.69(0.03) | −0.1020(0.0570) | ... | 7.04 | 1.01 |
07af | ... | 1.20(0.05) | 0.65(0.03) | −0.0400(0.0520) | ... | 2.04 | 0.94 |
07au | ... | 1.95(0.11) | 0.94(0.08) | 1.0840(0.0580) | ... | 5.88 | 0.97 |
07bc | ... | 1.35(0.07) | 0.67(0.04) | 0.2850(0.0900) | ... | 2.92 | 0.91 |
07bd | ... | ... | ... | 0.2900(0.0970) | ... | 3.93 | 3.93 |
07ca | ... | ... | ... | −0.2140(0.0570) | ... | 2.92 | 2.93 |
07ci | ... | ... | 0.86(0.03) | 0.8830(0.0780) | ... | ... | 0.99 |
07co | 1.28(0.22) | 1.14(0.09) | 0.70(0.07) | −0.0410(0.0780) | 2.69 | 1.16 | 1.01 |
07cq | ... | 1.17(0.18) | 0.61(0.07) | 0.0520(0.0710) | ... | 0.85 | 2.00 |
07F | ... | 0.93(0.07) | 0.58(0.06) | −0.1400(0.0510) | ... | 3.84 | 3.84 |
07qe | ... | 0.98(0.05) | 0.59(0.06) | −0.2570(0.0490) | ... | 1.93 | 2.94 |
07S | ... | 0.88(0.08) | 0.62(0.08) | −0.3230(0.0400) | ... | 4.83 | 4.83 |
08bf | ... | 1.01(0.09) | 0.59(0.08) | −0.1790(0.0640) | 2.06 | 4.91 | 4.92 |
Notes. Δt is the time between the closest point before and the closest point after maximum light. Δ is the light-curve shape parameter from MLCS2k2 with RV = 1.7.
3.1. UBV Decline Rates, Δm15
Where possible, the time of maximum and the magnitude at that time are measured in each of the UBV bands from the polynomial fits just described. The U and V values are also measured at the time of B maximum, where possible, to give the color at maximum light. To measure the peak magnitude for a light curve in a given band, we require a point before and after maximum, with a separation of no more than Δt = 9.2 days. Most of the light curves have much smaller separations but we want to measure the peak color for as many light curves as possible. We choose to use this wider separation limit because the peak magnitude calculations are fairly insensitive to the calculated time of maximum, as seen by removing points from light curves with many points around maximum and recalculating the peak magnitude. The uncertainty of each peak magnitude is taken to be the average of the uncertainties of the nearest points, one before and one after, plus 0.005Δt, added in quadrature.
We also measure the decline rate, Δm15, in UBV from the polynomial fits to the light curves. For this measurement, we also require that there be a point before and after t = +15 days, with a separation no greater than 12.2 days. The uncertainty in Δm15 is approximated by summing (in quadrature) the uncertainty at peak and the uncertainty at t = +15 days. The magnitude at t = +15 days is sensitive to the time of maximum and we estimate its uncertainty to be the sum in quadrature of the average uncertainty of the surrounding points and the product of the slope of the light curve at t = +15 days times the uncertainty in tmax. The slope of the light curve is roughly 0.1 mag per day since a typical SN Ia declines ∼1 mag in 15 days with most of that decline coming over the last 10 days. The uncertainty in tmax is estimated to be roughly 0.15 times the separation in time between the two surrounding points, determined by removing points from well sampled light curves and noting the effect.
Because we are mostly concerned with looking for trends in the plots, we choose to include the light curves with larger separations and lower precision measurements. For more precise purposes we advise the reader to have caution in using the peak magnitude and Δm15 values derived from light curves with time separations between the two points near maximum of greater than 6 days. The time separations are listed in Table 9 for this purpose. We note that only 13.7% of the peak magnitudes and 12.5% of the Δm15 values come from light curves with separations of more than 6 days.
3.2. Decline Rates, Colors at Maximum Light, and Δ
In Figure 15, the 15 day decline rates in U and V are plotted against that of B. There is a fairly tight cluster of points, with a few outliers, in the bottom-left (slower decline) portion of the V-versus-B panel with the fast decliners in B showing a wide range of V decline rates in the upper-right portion. The fastest V decliners (Δm15(V)>1.2) are all 1991bg-like SNe Ia (which can be identified as such by strong Ti II lines in their spectra). A linear relation between B and V decline rates cannot describe the data well. A quadratic relation does a better job. The upper panel shows a roughly linear relation between the U and B decline rates, with a larger amount of scatter than in the V-versus-B comparison. This same qualitative effect was seen in the stretch relations of J06.
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Standard image High-resolution imageThe U−B and B−V colors at B maximum, directly measured from the light curves with Milky Way reddening correction but no host-galaxy reddening correction, are plotted in the top panel of Figure 16. In the bottom panel, they are corrected for the host-galaxy reddening as measured by MLCS2k2 (RV = 1.7), and mostly form a tight cluster with −0.2 < (B − V)max < 0.1 and −0.7 < (U − B)max < 0.0. This behavior is similar to that seen in J06.
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Standard image High-resolution imageIn Figure 17, the MLCS2k2 light-curve shape and luminosity parameter, Δ, is plotted against the directly measured Δm15(B). There is a linear correlation for the slow and moderate decliners. The fast decliners have a wide range in Δ.
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Standard image High-resolution imageIn Figure 18, the host-galaxy corrected peak colors are plotted versus Δ and Δm15(B). Immediately standing out is the large range of red intrinsic (B − V)max colors among the fast decliners, similar to what was found by Garnavich et al. (2004). The redder fast decliners are all 1991bg-like objects while many of the relatively bluer (though still red) fast decliners are the more intermediate 1986G-like objects. The (B − V)max versus Δ panel does suggest three interesting (though arbitrary) groupings of points. The slow and normal decliners form one group, with typical peak color of (B − V)max ∼ −0.1. The moderately high-Δ objects, including 1986G-like and some seemingly spectroscopically "normal" objects, form a second grouping with a typical color of 0.1. Finally, the 1991bg-like objects have a typical (B − V)max color of 0.5. Another way of grouping the objects in this plot is by their slope in color versus Δ. Those with Δ < 0.1 have a flat slope while those with 0.1 < Δ < 1.3 have a slightly positive slope and those with Δ>1.4 have a very steep slope. The 1991bg-like objects are clearly distinct in B−V color at maximum.
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Standard image High-resolution image3.3. Histograms of Color, Extinction, and Δ
Our intention is to use light-curve fitters that were trained on objects from the OLD sample, apply it to the CfA3 sample, and use the combined OLD+CfA3 sample to infer useful cosmological properties. To compare how similar the OLD and the CfA3 samples are, we take the nearby SN Ia with zCMB ⩾ 0.01. We plot a histogram of the directly measured, intrinsic peak color, (B − V)max, corrected for host reddening (see Figure 19). There are 44 CfA3 and 48 Old objects and their distributions are fairly close—the two-sample Kolmogorov–Smirnov (KS) test gives a probability of 87% that they come from the same distribution.
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Standard image High-resolution imageA histogram of AV, as measured by MLCS2k2, is shown in Figure 20. There are 133 CfA3 and 70 OLD objects, all with zCMB ⩾ 0.01 and with good MLCS2k2 fits. Their distributions are quite similar—the KS test gives a probability of 74% that they are from the same distribution.
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Standard image High-resolution imageFinally, in Figure 21, a histogram of Δ for the two samples is shown. In part, due to our prioritization of fast and slow decliners in our observing strategy, CfA3 has a wider distribution, most noticeably in the most-negative end and in the range around Δ = 0.2. The increased number of highly negative Δ SN Ia is especially helpful for dark energy studies where these brighter objects are preferentially found due to magnitude-limited high-z searches. In H09, the three high-redshift samples used (ESSENCE, SNLS, and Higher-Z) do not have any objects with Δ>0.75. The KS test gives a probability of 9.4% that the two samples are from the same distribution. This should not be interpreted as an intrinsic difference in the underlying populations from which the CfA3 and OLD samples were drawn but, rather, as evidence of different selection effects, mostly related to which objects were chosen to be observed. Of the 133 CfA3 and 70 OLD SNe Ia at zCMB ⩾ 0.01, 42 CfA3 and 28 OLD SNe Ia have Δm15(B) values and they are more similar in their light-curve shape distributions, producing KS-test probabilities of 70% for arising from the same Δm15(B) population and 53% for arising from the same Δ population. An exact match in Δm15(B) and Δ KS probabilities should not be expected since Δm15(B) and Δ are not perfectly correlated.
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Standard image High-resolution image3.4. Intrinsic Absolute Magnitude
Using a lambda cold dark matter (ΛCDM) universe with (Ωm = 0.3, ΩΛ = 0.7, h = 0.7), we calculate distance moduli based on the CMB redshifts for all the CfA3 and OLD SNe Ia with zCMB ⩾ 0.01 and good MLCS2k2 (RV = 1.7) fits for which we could also directly measure the peak UBV magnitudes. We subtract off the distance moduli in the top panels of Figures 22–24 to show the absolute magnitudes before correction for host-galaxy extinction. In the bottom panels, we also subtract off the MLCS2k2-calculated host extinction to give a good estimate of the intrinsic absolute magnitudes of our sample.
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Standard image High-resolution imageThe two most noticeable things are that the extinction correction does a good job of reducing the scatter and that Δ is more tightly correlated with intrinsic absolute magnitude than is Δm15(B). Part of this may be due to the larger uncertainties in our Δm15(B) measurements.
Focusing on the lower right panel of Figure 22, there appears to be a linear relation between B-band intrinsic absolute magnitude and Δ, out to Δ ≈ 1.2. In V, the three faint and high-Δ objects are 1991bg-like objects. We also note that if the z = 0.01 cut were not made that there would be several more 1991bg-like objects from our direct light-curve measurements with Δ ≈ 1.5 and MB ≈ −17, confirming the faint and separate nature of 1991bg-like SNe Ia. In order to include these, MLCS2k2 uses a positive term in Δ but this comes at the expense of underestimating the luminosity of the SN Ia in the range 0.7 < Δ < 1.2 (see Figure 23 where the solid line shows the dependence of intrinsic absolute magnitude versus Δ for the MLCS2k2 model light curves). It may be better to avoid 1991bg-like objects altogether for use in the light-curve-shape/magnitude relation, or to at least treat them separately. Removing them can be accomplished by spectroscopic identification of 1991bg-like features or by simply removing all objects above a certain Δ and/or intrinsic peak color.
4. CONCLUSION
The goal of our research was to produce a large sample of nearby SN Ia light curves that would better sample the whole range of SN Ia and serve to reduce the statistical and systematic uncertainties in dark energy calculations using SNe Ia.
We have presented 185 nearby CfA3 SN Ia light curves, adding a significant number of fast and slow decliners. We have shown that the photometry is internally consistent, and that it is externally consistent at roughly the same level as seen in other nearby SN Ia photometry. The intrinsic properties of SNe Ia have been explored in UBV, confirming previous studies. One of the most important findings is that (B − V)max and the peak intrinsic magnitude in B and V do not correlate well with light-curve shape among the fast decliners (see Figures 18, 22, and 23). However, when the 1991bg-like objects are removed, the remaining fast decliners still seem to be well correlated with color and intrinsic absolute magnitude. This suggests that 1991bg-like SN Ia should be excluded from light-curve/distance fitter training samples and from dark energy studies. We believe that this will improve the performance of fitters, like MLCS2k2, that have used them in their training samples.
The CfA3 sample is an important contribution to dark energy studies because it is the largest homogeneously reduced nearby sample, doubling the cosmologically useful sample. The addition of the CfA3 sample to the literature SN Ia and its effects on the dark energy calculations are explored in H09. H09 show that the statistical uncertainty in w is reduced by a factor of 1.2–1.3 by adding the CfA3 sample. The CfA3 sample lowers the statistical uncertainty on static dark energy measurements to the point where systematic uncertainties begin to dominate. The CfA3 sample can be used to lower systematic uncertainties in dark energy studies in two ways. First, either the complete sample or the CfA3-Keplercam subsample can be used as a stand-alone nearby sample that reduces or eliminates the uncertainties that arise from different reduction pipelines, filters, cameras, and comparison-star calibration among nearby SNe Ia. Second, it will be very useful for retraining light-curve fitters and making them more precise. The two CfA3 subsamples, CfA3-Keplercam and CfA3-4Shooter, are the largest and second-largest homogeneously observed and reduced nearby samples to date. A large fraction of the CfA3 objects have spectra. A few dozen CfA3 objects also have near-infrared photometry and will help disentangle host-galaxy reddening from intrinsic SN Ia color. This will lead to a large decrease in the systematic uncertainty associated with host-galaxy dust absorption. Other large optical samples will soon be published too, with dozens of objects overlapping the CfA3 sample, providing a good opportunity to search for systematic errors and better combine data sets from different groups. We plan on publishing another 70–100 SN Ia light curves (CfA4 sample) when the host-galaxy reference images are obtained and the comparison star calibration is completed. These have been observed and reduced in the same way as the CfA3-Keplercam subsample and when added together will number roughly 200.
Future nearby SN Ia studies should focus on reducing their statistical and systematic photometric uncertainties by obtaining higher S/N measurements and improved understanding of their passbands and SN Ia calibration. The goal of 1% SN Ia photometry should be pursued so that more precise SN Ia measurements can produce tighter limits on both static and especially dynamic models of dark energy. The largest hurdles to achieving 1% photometry are in understanding atmospheric transmission and instrumental passbands. Efforts along the lines of Stubbs & Tonry (2006) should be pursued and improved. Use of calibrated photodiodes and monochromatic light allows for a precise determination of the system's transmission function. The pixel-by-pixel CCD response can be precisely determined by taking monochromatic flat fields at a sufficiently sampled range of wavelengths and measuring the intensity of this light with the calibrated photodiode. Additionally, improved treatment of host-galaxy contamination of SN light should be developed, through improved image-subtraction software and/or improved galaxy+SN models that measure both without image subtraction.
We thank the staff at FLWO for their dedicated work in maintaining the 1.2 m telescope and instruments. This work has been supported, in part, by NSF grant AST0606772 to Harvard University. A.R. thanks the Goldberg Fellowship Program for its support.
Facility: FLWO: 1.2 m
Footnotes
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