Rare superoutburst of
DV UMa Rare superoutburst of
DV UMa
DV UMa appears to be in outburst: Apr 08.85 at 13.9.
Observer Timo Kinnunen,
Espoo, Finland
Instr. 44.5 cm f/4.5 refl.
(from CVC 132, also vsnet-alert 830)
DV UMa [UGSU, 15.4v - 20.6v] ============================
Timo Kinnunen, Finland and Tonny Vanmunster, Belgium independently report a visual outburst detection of this most interesting dwarf nova (part of the TA/BAA VSS Recurrent Objects programme). The available observations are :
1997 Apr 07.877 UT, <15.2 (G. Poyner, visual);
Apr 07.890 UT, <14.8 (T. Vanmunster, visual);
Apr 08.85 UT, 13.9 (T. Kinnunen, visual);
Apr 08.931 UT, 14.0 (T. Vanmunster);
DV UMa was last seen in outburst on Feb 26, 1995 by Vanmunster [CVC 28]. During that outburst, time-series photometry by the Ouda team at Kyoto University, Japan revealed superhumps with a period of 0.08585 +/- 0.00001 day, a value that is significantly different from the published Porb (0.08579 day). [CVC 29]. Accurate astrometry by Nick James, Chelmsford, UK gave following position of DV UMa : RA = 9h46m36s.64, decl = +44g46'44".8 (J2000.0). This is 2" W and 4" N of the position in 'A Catalog and Atlas of Cataclysmic Variables' [Downes, R.A., Shara, M.M., 1993, PASP, 105, 127-245].
DV UMa was discovered by Usher et al. (1981) as an ultraviolet excess object. The object was subsequently identified as an eclipsing cataclysmic variable by Howell et al. (1988). Their photometric observations showed deep eclipses (1.5 mag or more) with an orbital period of 0.08597 day. Eclipses lasted about 0.15 Porb ~ slightly shorter than 20 min.
Comment to CVC 132 (vsnet-alert 830) by Tonny Vanmunster. The Ouda team did not observe superhumps during the 1995 outburst. The denoted period of 0.08585 +/- 0.00001 day actually corresponds to the orbital (eclipse) period. Extract from the vsnet-alert log:
(vsnet-alert 48, 1995 Feb. 27)
> DV UMa > > The object was discovered by Usher et al. (1981) as an ultraviolet excess > object. Following magnitude estimates from the archival plates were given. > (Some of them have been already listed in CVC 28 by T. Vanmunster) > > 1933 Jan 23 15.3+/-0.6 Feb 24 14:+/-1 > 1938 Mar 25 <17.75 Nov 27 <17.75 > 1939 Apr 15 18.4+/-0.3 > 1945 Mar 7 <17.4 > 1946 Feb 4 14.8+/-0.4 Feb 4 14.5+/-0.4 > Feb 7 15.2+/-0.7 > 1947 Mar 12 <16.7 > 1948 Feb 9 18.7+/-0.4 Dec 4 <16.7 > 1949 Mar 20 15.5+/-0.3 > 1950 Mar 9 <16.0 > 1952 Feb 29 <16.0 > 1953 Feb 13 14.2+/-0.12 > 1976 Jan 29 18.9+/-0.3 > 1978 Feb 1 19.8+/-0.4 Feb 2 19.8+/-0.3 > Feb 3 19.5+/-0.3 Dec 5 18.7+/-0.4 > 1980 Apr 17 19.3+/-0.3 Apr 17 18.5+/-0.3 > Apr 17 18.7+/-0.3 > > The object was subsequently idetified as an eclipsing cataclysmic > variable by Howell et al. (1988). Their photometric observations showed > deep eclipses (1.5 mag or more) with an orbital period of 0.08597 day. > The quiescent magnitude outside eclipses was V=19.3, and V=18.6 at maximum > of orbital humps. The eclipses lasted about 0.15 Porb ~ slightly shorter > than 20 min. > The orbital period (just below the period gap!) strongly suggests that > the object is an SU UMa-type dwarf nova with deep eclipses, the second > known in the northern hemisphere (the first one is well-known HT Cas). > Since no outbrust has been reported since the discovery, the persent > outburst provides not only the long-awaited opportunity to examine the > eclipses of this interesting dwarf nova during outburst, but also the > long-awaited detection of superhumps if the present outburst is a super- > outburst. The historical outburst in 1946 looks like a superoutburst. > The magnitude reported by Vanmunster & Poyner rivals that of the 1946 > outburst. Therefore there would be a good chance that the present > outburst is also a superoutburst. > > One thing should be mentioned concerning the outburst frequency > (or the duty cycle). Howell et al. (1988) examined 15 Harvard plates > and detected DV UMa brighter than 16 mag in seven occasions. Similar > frequency could be found in the estimates by Usher et al. (1981). > Such high frequency of outbursts seem to have never observed in recent > years, as Vanmunster and Poyner have already pointed out. We have also > a number of CCD photometry of this system, but an outburst was never met. > Has anything occurred in this system which has modified the outburst > frequency? Anyway, all sorts of observations are most emergently > needed during the current rare event in order to reveal the nature of > this object. > > Congratulations to T. Vanmunster and G. Poyner on their excellent work! > > Regards, > Taichi Kato
(vsnet-alert 56, 1995 Mar. 3)
> Dear vsnet-alert members, > > As D. Nogami has already announced, the Ouda team successfully obtained > V-band photometry of additional three eclipses of DV UMa, an SU UMa candidate > currently in rapid decline from a short (normal) outburst. > > The averaged magnitudes of DV UMa outside eclipses on these four nights > are given below. > > mid-UT DV-comp SD N band V-mag > ------------------------------------ ----- > 950227.510 2.852 0.070 82 V 15.0 > 950228.712 3.608 0.166 19 V 15.7 > 950301.432 3.849 0.159 31 V 15.9 > 950302.623 4.953 0.191 58 V 17.1 > > comparison: GSC V=12.1 star > > A preliminary analysis of the eclipse light curves has yielded > following mid-eclipse times and eclipse depths. This table also contains > the eclipse times on Feb. 27 for convenience. The eclipse times were > not calculated for Feb. 28 and Mar. 1 observations due to the very poor > photometric condition. Note that the asymmetry of the eclipse light > curves may have resulted a certain offset from the mid-eclipse times of > the white dwarf. > > mid-eclipse (JD-Geo) depth(V) > > 2449775.9651 1.6 > 776.0509 1.7 > 776.1365 1.9 > 776.2224 2.0 > > 2449779.0557 5.1: (low S/N) > 779.1413 >3.4 (eclipse center was missed) > 779.2273 4.1 > > On Mar. 3, DV UMa reached V = 21.7+/-0.5 at eclipse minimum. > > A least-sqares fit to the observed times of eclipse yieded a period > of 0.08585 +/- 0.00001 day (again internal error only), which is two sigma > longer than that obtained from Feb. 27 observations, but is still > significantly shorter than the published orbital period of 0.08597 day. > More observations (esp. in quiescence) are clearly needed whether this > discrepancy is caused by any asymmetric feature in the outbursting > disk, or by the error in the orbital period. > > We hope these eclipse times and period determination would be of any > help in scheduling the further observations. > > Regards, > Taichi Kato
For more information, refer to the VSNET page:
http://www.kusastro.kyoto-u.ac.jp/vsnet/DNe/dvuma.html
The suggested classification of SU UMa-type thus still needs to be confirmed. Congratulations to Timo Kinnunen and Tonny Vanmunster on their discovery of this rare phenomenon, and wishing for potential collaborations between world-wide CCD observers!
Regards,
Taichi Kato
I have tried to refine the eclipse ephemeris of DV UMa using the following available mid-eclipse times.
HJD-2400000 source ----------------------------------------- 46854.7485 Howell et al. (MNRAS 233, 79) 46854.8339 " 46854.9195 " 46855.6944 " 46855.7798 " 46855.8660 " 46855.9517 " 46856.4646 " 46856.5503 " 46856.6370 " 46857.4963 " 46857.5815 " 49775.9696 Nogami et al. (vsnet-alert 56) 49776.0554 " 49776.1410 " 49776.2269 " 49779.0601 " 49779.1457 " 49779.2317 " 50079.289 Kato (unpublished) The best fit ephemeris is Min.HJD = 2446854.7487 + 0.085852614 E (1), which expresses all the observed times within an error of 0.002 day. The second best (viable) solution is Min.HJD = 2446854.7483 + 0.085877839 E (2) Using the equation (1), predicted times of eclipses on Apr. 9 and 10 would become: YYMMDD hh:mm:ss (UT Geo) 970409 00:36:14 970409 02:39:53 970409 04:43:31 970409 06:47:09 970409 08:50:47 970409 10:54:26 970409 12:58:04 970409 15:01:42 970409 17:05:20 970409 19:08:59 970409 21:12:37 970409 23:16:15 970410 01:19:53 970410 03:23:32 970410 05:27:10 970410 07:30:48 970410 09:34:26 970410 11:38:05 970410 13:41:43 970410 15:45:21 970410 17:48:59 970410 19:52:38 970410 21:56:16The equation (2) predicts eclipses 1h 18m later.
Hope this would help, and someone could confirm or reject this prediction.
Regards,
Taichi Kato
Detection of superhumps! Dear Colleagues,
I performed unfiltered time series photometry on DV UMa at CBA Belgium Observatory last night (April 9/10, 1997), during 4.8 hours.
The resulting light curve shows three eclipses and very prominent superhumps. These observations thus establish DV UMa as a new member of the UGSU-type dwarf novae.
I will determine an exact superhump period value shortly, using the PDM method. A rough inspection of the data already yields a value of 0.0837 d.
I will also shortly calculate the mid-eclipse times, allowing me to check the eclipse timing ephemeris published by Taichi Kato in an earlier VSNET message.
Best regards,
Tonny Vanmunster
CBA Belgium
Hi all,
I just analysed a set of DV UMa time series photometry data, obtained on April 9/10 at the Centers for Backyard Astrophysics of Dave Skillman and myself. I wanted to comment on the two DV UMa mid-eclipse formulae given by T. Kato in VSNET-ALERT 832.
The best fit ephemeris clearly is the first one
Min.HJD = 2446854.7487 + 0.085852614 E (1),
The eclipses we observed apparently fit within the 0.002 day error mentioned by Taichi.
Best regards,
Tonny Vanmunster
CBA Belgium Observatory
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