1 Introduction

October Ursa Majorids (OUM) is a new meteor stream whose weak (but clear) manifestation was reported by Japanese observers within their video network observations on Oct.14–16, 2006 (Uehara et al. 2006). Meteors of the stream radiated from a position R.A. = 144.8° and Dec. = 64.5°, with the geocentric velocity V g  = 54.1 km s−1. Simultaneously observed meteors yield the mean orbit (read: average of individual meteors elements) of the stream with parameters a = 5.9 AU, q = 0.979 AU, e = 0.875, ω = 163.7°, Ω = 202.1°, and i = 99.7° (J2000.0). With respect to the renewed meteor stream nomenclature rules (Task Group for Meteor Shower Nomenclature, IAU Commission 22), we will use a correct name for this stream: October Ursae Majorids (OUM).

In a searching for past displays of OUM, we examined sources of meteor orbits and meteor phenomena (second section). In third section, we are looking for an admissible type of a parent body which could either fit orbital characteristics of the new meteor shower or, in assumed specific circumstances resulted in formation of the meteoroid stream. All data we used are in Equinox (J2000.0).

2 Survey of Common Sources

2.1 Established Showers in a Vicinity of OUM

In a search for coincidental streams, we firstly had look at the summary tables published by Jenniskens (2006), which besides of his own results encompass a compilation of meteor streams from many authors. The tables list basic orbital data of cometary and suspected asteroidal streams, their major apparition peaks, as well as bibliographic sources of the data.

Working list of cometary meteor showers therein (Table 7), presents two streams exactly in the time of the OUM apparition. Daytime phi-Virginids (DFV, #240, ecliptic helion source) have its peak on Oct. 15 at the solar longitude \(\lambda_{\odot}\) = 202.0° while the gamma-Puppids (GPU, #239) peak on Oct. 16 at the solar longitude \(\lambda_{\odot}\) = 202.7°. DFV is a broad daytime stream and GPU do not match Oct. Ursae Majorids radiant at all (Dec. = −44.0°). There are two other well-known showers in a week intervals before and after the OUM: Oct. Draconids (DRA, #9) on Oct. 8 (\(\lambda_{\odot}\) = 195.1°) and Oct. Ursae Minorids (OUI, #241) on Oct. 21 at \(\lambda_{\odot}\) = 208.0°. Having in mind some analogy with OUM detection, we shouldn’t omit recent case of the October Camelopardalids (OCT, #281) on Oct. 5, 2005 (Jenniskens 2005).

In the Working list of possible asteroidal meteor showers therein (Table 9), we identified a single shower in the mid of October with a few members only—delta-Cygnids (DCY, #282). Again, radiant coordinates differ more than allowed, and both do not fulfill the coordinates of the OUM.

Besides of highlighted streams, there are many minor meteor showers with low or irregular activity in a period from mid of September to the end of October (corresponding solar longitudes \(\lambda_{\odot}\) = ∼170°–220°). We point out that OUMa displayed on a background of approaching Orionids, as well as ongoing long-lasting Taurid meteor complex, in 2006. As mentioned by Uehara et al. (2006) already, if we should search for the OUMa pattern we have to do it over a miscellaneous background activity. Therein, a percentage of detected OUMa meteors was at the level up to 9%, the lowest among above mentioned streams in the period Oct. 10–20, considering other minor streams activity as sporadic. We ascertained in this survey that no hitherto known meteoroid stream could be associated with the OUMa, as none has suitable orbital and/or geophysical parameters.

2.2 A Search for Ancient OUMa Activity

Jenniskens (2006) presents historic meteor phenomena reports in his Table 1, also, originally collected by many authors. Looking at the solar longitudes, there are listed two timely lagged sightings around 202°: on Oct. 9.7, 1798 at \(\lambda_{\odot}\) = 199.4°, and second one identified with Orionids in year 288 (\(\lambda_{\odot}\) = 206.1° and 207.5°), visible in two subsequent days (September 25.3 and 26.7). Next are records on September 25.7, 930, September 23.7, 585, and Sep. 27.0, 903, at the solar longitudes 201.9°, 202.4°, and 203.2°, all identified as Orionids. Description of sightings from Oct. 9, 1798, (\(\lambda_{\odot}\) = 199.4°)—Stars flew all around, next few nights too—evoke a hope. It should mean solar longitudes close to the OUMa.

Table 1 An appearance time and orbital parameters of listed meteors, and their D-criterion value
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2.3 An Inspection of the IMO Video Database

In examination of the IMO Video Meteor Database we refer to precise complete analysis by Molau (2006). Along with used analysis procedure description, he lists detected meteor showers in his Table 2. There, among known showers have been identified six sporadic sources (N/S Apex, N/S Toroidal, Helion, Antihelion). Based on radiant coordinates and velocity we tried to find some sign of regular stream, in the list. But, among a cluster of mainly sporadic and known sources in September and October data, no fitting candidate was found. As to video observations, noteworthy is that Trigo-Rodríguez et al. (2007) detected no OUMa activity either by the all-sky cameras or by the video cameras patrol.

Table 2 A geophysical and physical data on listed meteors
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2.4 A Search for Past and Recent Activity of OUMa in Radio Observations

In a search for past activity of the OUMa, radio observations are very proper. However, Orionids dominate in the second half of October, thus common radio campaigns start a little later as we need. From the same reason, the forward-scatter system with baseline Bologna-Modra operated on Oct. 13–28, 2002, and Oct. 14–28, 2003, with only accident overlapping of investigated OUMa activity period. Unfortunately, our moderate noisy data do not provided any clue. However, a dedicated analysis of observations from continually working radar systems around the world (where a radiant is above horizon, currently e.g., CMOR) could help reveal recent activity of OUMa, especially its presence in 2006. A more challenging is searching for 2006 display of the OUMa among the radio forward-scattering meteor data of the Global-MS-Net. Yrjölä and Jenniskens (1998) proved that in course of continuous observation by the same forward-scatter system, there is possible to detect an activity of zenithal hourly rate as low as 3–4 meteors, if the activity is insulated or on steady background. For example, recent video detection of Oct. Camelopardalids display in 2005 (Jenniskens 2005; only 10 days before OUMa and shifted ∼20° in R.A. and ∼15° in Dec. off OUM radiant) was confirmed by proper use of this source. Our opinion is that including of the observability function (Hines 1955, 1958) into an identification procedure wouldn’t be successful among coincidental minor meteor streams and rising Orionids rate.

2.5 A Search Among Precise Meteor Orbits

The most precise source for searching of possible OUMa related meteors is the IAU MDC database of photographic meteor orbits (Lindblad et al. 2005). Currently, the database contains homogenized orbital elements of 4,581 meteors along with geophysical data (radiant coordinates, geocentric and heliocentric velocities, beginning/end heights of meteors, photometric masses). In a course of the renewed search for the bolide meteor showers (Gajdoš and Porubčan 2005; Gajdoš 2005), we supplemented the MDC database with a few tens (state to March 31, 2006) of meteor orbits from unpublished database of the Interplanetary Section, Astronomical Institute AS CR in Ondřejov (Spurný 2007, Personal communication). The meteor orbits bear labels Onxxx. The whole working data set is in equinox (J2000.0).

Due to initial knowledge on the OUMa activity, we handled broader interval of solar longitudes to catch material for analysis. We involved the iteration procedure used by Porubčan and Gavajdová (1994) which is based on D-criterion by Southworth and Hawkins (1963). We had look for meteors fitting the mean orbit of OUMa with the limit value of D-criterion D SH  ≤ 0.20. The searching revealed a few meteor orbits similar to the OUMa, only. An explanation we see in high inclined retrograde orbit of the OUMa. In a triplet with the OUMa mean orbit appeared two meteor orbits labeled 022K1, 331J1, having appropriate values of D-criterion. Noteworthy, when mutual pairs of the three orbits are taken into consideration, latter two orbits fit better each other than 022K1 with the OUMa (Table 1 gives this value of D). In parenthesis, we add D value of 331J1 orbit from triplet. For the sake of completeness, other photographic orbits were subjected to an inspection. It resulted in three more high inclined orbits throughout investigated period (On012, 100E1, 037E2). Each of them is matter of our interest.

The tables above contain relevant meteors data taken into consideration: designation, apparition date and orbital parameters (perihelion distance, semimajor axis, eccentricity, and angular elements) are in the Table 1, as well as radiant coordinates, geocentric velocity, beginning/ending heights of meteors, their magnitudes and photometric masses, are in the Table 2, respectively. One bolide has an additional datum on type of the meteoroid. Tables list four meteor orbits from the IAU MDC database, the mean orbit of OUMa, and the orbit of the fireball “Velvary” (our working label On012).

If we omit a, e elements of 100E1, in first look there seems fairly compact group of three orbits in mid of October (022K1, OUMa, 100E1), and “wings” in late September (On012) and October (037E2). Bolide 100E1 apparently outstands with a hyperbolic orbit, whilst other parameters fit well. This orbit comes out from Ondřejov photographic program (Ceplecha and Rajchl 1965) and in the original version it had the parabolic eccentricity value. In consistent IAU MDC database (Lindblad et al. 2005) it has recalculated high hyperbolic eccentricity e = 1.457. This and original values indicate difficulties in meteor orbit processing. Due to less favorite circumstances (e.g., small number of photographic images for elaboration, unfavourable position of a bolide, small number of breaks on bolide trail, etc.) some parameters could embody more uncertainty. This feature of the IAU MDC database is pointed out by Hajduková (1994), in her searching for hyperbolic interplanetary particles, and generalized in Hajduková and Hajduk (2006). They demonstrated that the number of hyperbolic meteors found within meteor showers increases with a velocity approaching the hyperbolic limit of particular shower. As well known, in a process of some orbital parameters reduction, the meteor velocity determination is crucial. Thus, providing of an elliptical orbit we verified a case of 100E1. Putting its parameters a, e equal to those ones of the OUMa mean orbit, we examined theirs similarity. D-criterion value of such a hypothetic orbit in a triplet with OUMa and 022K1 was as low as 0.013 (see Table 1, in square brackets). Apparently, besides of elements a, e, orbit and geophysical parameters of bolide 100E1 show a high level of similarity with OUMa characteristics.

In the Fig. 1, beginning (Hb) and ending (He) heights of meteors are compared. Uehara et al. (2006) gave no maximum brightness height for listed meteors, thus we omitted it in both tables for IAU MDC meteors, too. Single plumb lines depict meteors used for OUMa mean orbit calculation. Lines with begin/end squares are from both IAU MDC/Ondřejov meteor databases. Reported OUMa meteors are of an unified display, with a slight tendency of their beginning heights increasing toward brighter meteors. Uehara et al. (2006) list visual magnitudes with errors ±1m as observed from more stations (we plot the arithmetic mean of individual magnitudes), while IAU MDC meteors bear photographic magnitudes. Both magnitudes differ, but considering generally accepted dependence we assume a larger photometrical mass for brighter meteoroids. Other meteors seems to have a comparable (331J1, 037E2, On012, 100E1) or lower (022K1) beginning heights. But, these data were taken by different cameras with different sensitivity what results in undervalued beginning (low) and overvalued (high) terminal heights. Both plotted groups of meteors (OUMa + IAU MDC) do not overlap a limit of ∼130 km at which a thermal ablation of meteoroid start to dominate. Koten et al. (2004) pointed out that the beginning height increases with increasing photometric mass. This feature was reported for generally fainter meteors of several cometary meteor showers, and also for brighter meteors (Spurný et al. 2000). Due to similar behavior of plotted meteors, we suggest their common physical characteristics. Based on the two papers, and presented meteoroid type II/IIIa (Ceplecha 1988) of meteor On012 (Table 2), we may conclude that discussed meteoroids had a cometary origin.

Fig. 1
figure 1

Beginning and ending heights of investigated meteors

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3 Searching for Possible Parent Body

An other approach to the subject is plain search for a possible parent body based on simple similarity of orbits. A high inclination was a first indication. For the sake of completeness, we browsed groups of near-Earth bodies. In the recent NEA population (as to Nov. 12, 2007) in the JPL webpage (http://neo.jpl.nasa.gov) exist objects with inclination up to 72°, only, and single object (2007 VA85) with retrograde orbit (∼133°), probably a dormand comet. Another search produced a cluster of about twenty cometary orbits fulfilling wider criteria: i ∼ 100° ± 20°, and ω ∼ 165° ± 30°, and Ω ∼ 200° ± 20°. We applied the code for calculation of theoretical meteoroid stream radiant by Neslušan et al. (1998) to finding out a meteor producing orbit. At the same time we got a minimal distance of the comet/Earth orbits. Although a number of examined orbits approach the Earth’s one very close (e.g., C/1907 G1 less than 0.003 AU), no OUMa fitting radiant occurred, whereas more of them are of southern declination. More meaningful entry is distance of the comet orbit nodes from the orbit of the Earth. These data provided the Catalogue of cometary orbits (Marsden and Williams 2005). We checked the minimal distance of individual comets from the Earth at the time of the comet passage. Of investigated set, fairly close encounters experienced single-apparition comets C/1014 C1 (0.0407 AU) and C/1132 T1 (0.0447 AU). Considering orbital elements and geometrical conditions of cometary approach, we found, say, prototypes of possible parent comet of the OUMa meteoroid stream. Besides of above mentioned, they are C/1683 O1, C/1848 U1, C/1975 T2, C/1999 J3. The comet C/1975 T2 (Suzuki-Saigusa-Mori) has orbital period of about 446 years. This fact would be attractive in an assumption of meteor stream formation by regular activity of a long-period comet (e.g., April Lyrids and comet C/1861 G1 with period 415 years). In such a case, an unexpected 2006 display of OUMa we could interpret as a collision of the Earth with a filament of the stream.

4 Conclusions

We searched a display of reported OUMa meteor shower in a list of known meteor showers and among ancient records, as well as in the IMO video database. Besides of one indistinct record from Oct. 9, 1798, we found no obvious signs of OUMa activity in the past, in individual sources. We concluded that search for OUMa in the Global-MS-Net archive would be unsuccessful, even with using of the observability function. The IAU MDC database of photographic orbits provides us with several orbits similar to that of the OUMa mean orbit. We believe that meteoroids 331J1 and 022K1 are past members of assumed OUMa meteoroid stream, and also 100E1 is potential. The OUMa are of cometary origin. We suggest their parent body being a long-period, high inclined comet (nearly-isotropic, coming from the Oort cloud). The OUMa display like an irregular swarm, possibly with some filaments.

We think that along with independent confirmation, a dedicated inspection of CMOR data could help to reveal more details on the OUMa 2006 display. Anyway, aimed radar/video/photographic observations starting at begin of October would be suitable to monitoring of OUMa activity, in 2007 and after.