CATACLYSMIC VARIABLES FROM SDSS. VII. THE SEVENTH YEAR (2006)^*

Of the 39 entries in Table 1, 13 are CVs that were found prior to SDSS spectra. These include the novalike Leo5 (1H1025+220; SDSSJ1029) and eight dwarf novae: Boo1 (SDSSJ1504), AK Cnc (SDSSJ0855), GY Cnc (SDSSJ0909), GO Com (SDSSJ1256), NY Ser (SDSSJ1513), QW Ser (SDSSJ1526), IY UMa (SDSSJ1043), and HS1340+1524 (SDSSJ1343). Leo5 was previously identified as a CV candidate during the follow-up of HEAO-1 sources, and spectroscopically confirmed by Munari & Zwitter (1998). Boo1 was discovered as a faint emission line star by Filippenko et al. (1985), who tentatively classified the object as a dwarf nova, even though no outburst was observed, and no follow-up observations have been obtained so far. AK Cnc was determined to be a dwarf novae by Wenzel (1993) with an orbital period of 97.3 mm determined by Arenas & Mennickent (1998). GY Cnc was identified as an eclipsing dwarf nova with P_orb = 252.6 minutes; an updated ephemeris is given by Feline et al. (2005). GO Com has been long known as a dwarf nova (Brun & Petit 1957), and had P_orb = 95 minutes determined by Howell et al. (1995b). NY Ser was identified as a CV in the Palomar-Green Survey (Green et al. 1986), and a short outburst cycle was noted by Iida et al. (1995). Nogami et al. (1998) measured a superhump period of 153 minutes, making NY Ser the first SU UMa type dwarf nova in the period gap between 2 and 3 hr where few CVs are found (Warner 1995). Patterson et al. (2003) determined the orbital period as 140.4 minutes. QW Ser was identified as a dwarf nova by Takamizawa (1998), and P_orb = 107.3 minutes was determined by Patterson et al. (2003). IY UMa is another eclipsing dwarf nova with an P_orb = 106.4 minutes (Uemura et al. 2000), for an updated ephemeris see Steeghs et al. (2003). HS1340+1524 (SDSSJ1343) is a dwarf nova with infrequent short outbursts, and P_orb = 92.7 minutes (Aungwerojwit et al. 2006).

Finally, there are four previously known polars among the SDSS CVs presented here. Two of them were observed in a low state: ST LMi (SDSSJ1105), one of the few polars identified in the optical (Shore et al. 1982) with P_orb = 113.9 minutes (Schmidt et al. 1983; Cropper 1985); and EU UMa (SDSSJ1149), discovered with ROSAT (Mittaz et al. 1992) with P_orb = 90 minutes (Howell et al. 1995a). The two other polars were observed by SDSS during high states, MR Ser (SDSSJ1552), identified in the PG survey (Liebert et al. 1982) with P_orb = 113.5 minutes (Schwope et al. 1991), and RXS J161008.0+035222 (SDSSJ1610), identified as a ROSAT polar by Schwope et al. (2000, 2002), with recent polarimetry published by Rodrigues et al. (2006) which refined the orbital period to 109.5 minutes.

Table 1 also includes four polars that we found since Paper VI which have detailed information recently published (Schmidt et al. 2007, 2008); we include them in the table for completeness: SDSSJ0921, SDSSJ1031, SDSSJ1059, and SDSSJ1333. Of these, SDSSJ1031 and SDSSJ1059 belong to the group of extremely low mass transfer rate polars, while the rest are normal polars with high and low states of accretion. Note that the magnitudes listed for SDSSJ0921 and SDSSJ1333 in Schmidt et al. 2008 are in juxtaposed order in their table (the magnitudes are actually in the order of g, i, r, u, z instead of u, g, r, i, z as labeled.

Previous work on SDSS systems has shown that those with deep central absorption in the Balmer lines typically have high inclination and show photometric eclipses. Two systems, SDSSJ1057 and SDSSJ1524 (Figure 1), show this central absorption, and are promising candidates for having deep eclipses of the white dwarf by the secondary star.

While CVs can be generally identified by their emission line spectrum, the identification of a dwarf nova requires that an outburst is apparent. This can be apparent from a difference in the SDSS photometry versus the spectra (which are obtained at different times) or as large differences in magnitude in past USNO or DSS catalogs or in other non-SDSS observations. The known dwarf nova QW Ser (SDSSJ1526) was caught at outburst in the SDSS spectra (Figure 1) while the photometry (Table 1) is consistent with its normal quiescent magnitude near 18.

SDSSJ1005. A report of an outburst of this object by Brady & Pietz (2009) recently appeared in the vsnet,¹⁰ thus providing a classification for this system. Subsequent searches of ASAS-3 data as reported by Kato (2009) showed previous outbursts near 12.5 mag in 2003 and 2006.

Our follow-up APO time-resolved spectra during quiescence in 2007 produced consistent results from the Hα and Hβ emission lines. The period obtained from both lines is near 113 minutes and the K amplitude is low (Figure 2 and Table 4). While further data over several nights will be needed to pin this down precisely, it is apparent that this is likely a low inclination, short period system that is near the lower edge of the period gap. The preliminary superhump period reported by Brady and Pietz is identical to our spectroscopic period within the accuracy reported.

Zoom In Zoom Out Reset image size

SDSSJ1619. The SDSS photometry (Table 1) and spectrum (Figure 1) show a typical CV at quiescence, with an optical magnitude near 18.5 and Balmer emission lines with a flat decrement. However, our follow-up APO spectra (Table 2 and Figure 3) show a much brighter source (near magnitude 15.5) with strong He ii 4686 emission as well as weaker Balmer emission flanked by broad absorption. The APO spectra are typical of dwarf novae at outburst, where the increased accretion at outburst results in the high excitation He line and an optically thick accretion disk which produces the broad absorption. Thus, we can narrow the classification of this object to that of dwarf nova. Our time-resolved APO data covered close to 2 hr of observation, but our measurements of the Hα, Hβ, and He ii emission components did not reveal any periodic radial velocity variation outside of random variability that was less than 20 km s⁻¹. Thus, either this system has a low inclination, a long period, or the emission lines at outburst are too distorted by the underlying absorption to extract the underlying orbital motion. Further observations during quiescence are needed to determine its orbital period.

Zoom In Zoom Out Reset image size

SDSSJ1627. A superoutburst has recently been detected by Shears et al. (2008), who determined a superhump period of P_sh = 156.8 minutes. Since the superhump period is usually only a few percent different from the orbital period (Warner 1995), this system appears to be one of the few in the 2–3 orbital period gap.

The He ii 4686 line is a strong indicator of a polar or of high accretion. All of the polars mentioned in Section 3.1 show this line (except for the two with extremely low accretion rates). In addition to these known polars, Figure 1 reveals three other systems with unusually strong He II4686.

SDSSJ1549. This object has a very peculiar spectrum, showing a strong continuum, weak Balmer emission but very strong He ii. The SDSS spectrum is very similar to that of UMa 6 (SDSSJ0932) shown in Paper V. UMa 6 has a very long orbital period for a CV (10 hr¹¹) and a deep optical eclipse (Hilton et al. 2009). Our 2.5 hr of APO time-resolved spectroscopy (Table 2) showed 40 km s⁻¹ variability in both Hα and He ii but no simple sinusoidal motion consistent with an orbital radial velocity. Thus, this system will require much longer monitoring to ascertain its nature.

SDSSJ0938. The spectrum of SDSSJ0938 looks typical for a polar (Figure 1) in a high state of accretion. It is virtually identical to the known polar SDSSJ1610 also in Figure 1. Spectropolarimetry will be able to provide definitive information on this issue. While our APO observations (Table 2) were not long enough to obtain an orbital period, a smooth, large amplitude (70 km s⁻¹) variation throughout the 65 minutes is consistent with a polar with a period that is below 2 hr.

SDSSJ0935. While this object has stronger He ii than Hβ emission (Figure 1 and Table 3), the spectral appearance is different than for the above two objects. The continuum is very strong and the emission lines are broad and weak. This spectrum appears more like an old nova than a system containing a magnetic white dwarf (Warner 1995).

The ability of SDSS to obtain spectra of CVs that are fainter than previous surveys has resulted in discovering many systems that have low accretion rates, hence accretion disks which do not overwhelm the light of the underlying stars. In these cases, the white dwarfs are revealed through their broad absorption lines flanking the Balmer emission and, if the secondary star is a late main-sequence object, it is evident by TiO features in the red. From Figure 1, it is apparent that SDSSJ1005, SDSSJ1057, and SDSSJ1605 show the white dwarf, while SDSSJ0230, SDSSJ1059, SDSSJ1105, and SDSSJ1544 show an M star (SDSSJ1105 and SDSSJ1059 are known polars with no accretion disk) and SDSSJ0805 appears to show a K star (albeit of somewhat later type than the K stars in SDSSJ0615 and SDSSJ0805 found in Paper VI).

The spectra of systems with accretion disks can show a large range in variety (Warner 1995). Figure 1 shows five systems with strong, blue continua: SDSSJ0758, SDSSJ0901, SDSSJ0935 (already mentioned in Section 3.4), SDSSJ1054, and SDSSJ1513. Most of these are likely to be novalikes with large accretion rates. SDSSJ1054 may be questionable as it could be just a white dwarf and a faint active but non-interacting M star. Two spectra taken 26 days apart exist in the SDSS archive for this object and they show minor differences in the structure of the Balmer emission and absorption lines which could be due to a close binary, so we have left this in the list. Follow-up spectroscopy will determine the correct classification. The systems with weaker continua and stronger emission lines are likely candidates for short orbital period systems with lower mass transfer. For our follow-up APO spectra, we generally concentrated on these latter systems due to the way observing time is scheduled in half-nights.

SDSSJ1557. This object has strong, broad Balmer emission lines that are typical for dwarf novae systems. Our 2.5 hr of time-resolved spectra revealed a sinusoidal modulation with a period near 2 hr, which is the lower end of the period gap (Table 4 and Figure 4). The amplitude is typical for dwarf novae. The object will need to be followed photometrically to detect an outburst and confirm this as a dwarf nova.

Zoom In Zoom Out Reset image size

SDSSJ0812. Follow-up 3.5 hr of time-resolved spectra of this CV that was first reported in Paper V show a high-amplitude radial velocity curve with a period near 3.7 hr, close to the length of the data set (Table 4 and Figure 5). This object thus appears to be above the period gap and has a higher accretion rate than the majority of SDSS CVs that have periods less than 2 hr.

Zoom In Zoom Out Reset image size

SDSSJ1006. This system from Paper VI was targeted for follow-up spectra as it shows strong emission lines plus TiO bands from its secondary star. However, 100 minutes of spectra do not reveal a clear sinusoidal variation. There is a jump in velocities in both Hα and Hβ from red to blue (with no change in comparison lamps taken near these times) and there is a decline in flux in the spectra at this time. These properties could be an indication of an eclipse, so additional data on this object could produce interesting results.

Ten of the objects in Table 1 have been detected with the ROSAT All Sky Survey (RASS; Voges et al. 1999, 2000). The exposure times and count rates are listed in Table 5. Among the 10 detections are the known polars EU UMa, MR Ser, and RXJ1610+03 and the dwarf novae GY Cnc, GO Com, QW Ser, and HS1340+15. Several of the sources are only in the faint source catalog with marginal detections (no error is listed for the faint detection of SDSSJ1005). The lack of detection of the other polars such as ST LMi and the LARPS detailed in Schmidt et al. (2007, 2008) are indications of states of very low mass transfer for these systems. On the other hand, the detection of SDSSJ0938 lends further support for this object being a possible polar. As in UMa 6, the strong He ii present in SDSSJ1549 is not correlated with X-ray emission.