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[vsolj-alert 500] DV UMa rare outburst

DV UMa rare outburst

　食のあるSU UMa型、DV UMaがアウトバーストしています。（第一発見はKinnunen
　のやや不確かな観測で、昨晩の観測で確認されました）。確認されている最も
　最近のアウトバーストは1997年４月のもので、これはスーパーアウトバースト
　でした。その前が1995年2-3月で、これはノーマルアウトバースト。いずれも
　深い食が観測されています。

　以下はvsnet-alertに投稿した情報です。

DV UMa eclipse ephemeris

  Based on ephemeris [vsnet-alert 832]
(http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-alert/msg00832.html)

  Min.HJD = 2446854.7487 + 0.085852614 E     (1),

  YYMMDD hh:mm:ss (UT, Geocentric)
 -----------------
  991207 01:08:56
  991207 03:12:33
  991207 05:16:10
  991207 07:19:47
  991207 09:23:24
  991207 11:27:02
  991207 13:30:39
  991207 15:34:16
  991207 17:37:53
  991207 19:41:30
  991207 21:45:07
  991207 23:48:44

  991208 01:52:21
  991208 03:55:58
  991208 05:59:36
  991208 08:03:13
  991208 10:06:50
  991208 12:10:27
  991208 14:14:04
  991208 16:17:41
  991208 18:21:18
  991208 20:24:55
  991208 22:28:33

  991209 00:32:10
  991209 02:35:47
  991209 04:39:24
  991209 06:43:01
  991209 08:46:38
  991209 10:50:15
  991209 12:53:52
  991209 14:57:30
  991209 17:01:07
  991209 19:04:44
  991209 21:08:21
  991209 23:11:58

  991210 01:15:35
  991210 03:19:12
  991210 05:22:50
  991210 07:26:27
  991210 09:30:04
  991210 11:33:41
  991210 13:37:18
  991210 15:40:55
  991210 17:44:32
  991210 19:48:09
  991210 21:51:47
  991210 23:55:24

  991211 01:59:01
  991211 04:02:38
  991211 06:06:15
  991211 08:09:52
  991211 10:13:29
  991211 12:17:07
  991211 14:20:44
  991211 16:24:21
  991211 18:27:58
  991211 20:31:35
  991211 22:35:12

  991212 00:38:49
  991212 02:42:27
  991212 04:46:04
  991212 06:49:41
  991212 08:53:18
  991212 10:56:55
  991212 13:00:32
  991212 15:04:09
  991212 17:07:47
  991212 19:11:24
  991212 21:15:01
  991212 23:18:38

  991213 01:22:15
  991213 03:25:52
  991213 05:29:30
  991213 07:33:07
  991213 09:36:44
  991213 11:40:21
  991213 13:43:58
  991213 15:47:35
  991213 17:51:12
  991213 19:54:50
  991213 21:58:27

  991214 00:02:04
  991214 02:05:41
  991214 04:09:18
  991214 06:12:55
  991214 08:16:33
  991214 10:20:10
  991214 12:23:47
  991214 14:27:24
  991214 16:31:01
  991214 18:34:38
  991214 20:38:16
  991214 22:41:53

  991215 00:45:30
  991215 02:49:07
  991215 04:52:44
  991215 06:56:21
  991215 08:59:59
  991215 11:03:36
  991215 13:07:13
  991215 15:10:50
  991215 17:14:27
  991215 19:18:04
  991215 21:21:42
  991215 23:25:19

  991216 01:28:56
  991216 03:32:33
  991216 05:36:10
  991216 07:39:47
  991216 09:43:25
  991216 11:47:02
  991216 13:50:39
  991216 15:54:16
  991216 17:57:53
  991216 20:01:31
  991216 22:05:08

 ====================================================================
  ** Previous vsnet-alert messages -- a brief history of DV UMa **
 ====================================================================

 see also   http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/DNe/dvuma.html

  (CVC 28, 1995)

DV UMa = US 943 [UGSU:, 15.4v - 20.6v]
======================================

Tonny Vanmunster, Landen, Belgium has detected an outburst of this
very important and poorly studied dwarf nova type cataclysmic 
variable. The observation has been confirmed both by Gary Poyner,
Birmingham, UK and Eric Broens, Mol, Belgium, as follows :

1995 02 22.845 UT, [14.4  (T. Vanmunster, 0.35-m refl., seq: GSC);
     02 26.826 UT,  14.6  (T. Vanmunster, 0.35-m refl., seq: TA);
     02 26.840 UT,  14.7  (G. Poyner, 0.40-m refl., seq: TA);
     02 26.846 UT,  14.7  (E. Broens, 0.35-m refl., seq: TA);

Only very few outbursts of the object have been reported : 1933, 
January 23; 1946, February 4; 1953, February 13 and 1987, April 30.
DV UMa is discussed in a number of publications on cataclysmic
variables. We identified references in following professional
journals :

  Howell, S., et al., 1987, PASP, 99, 126-129
  Hameury, J.M., et al., 1991, A&A, 248, 525-530
  Szkody, P., Howell, S., 1993, ApJ, 403, 743-751
  Howell, S., Szkody, P., 1990, ApJ, 356, 623-629
  Howell, S., Mason, K., et al., 1988, MNRAS, 233, 79-86
  Mukai, K., et al., 1990, MNRAS, 245, 385-391
  
Please remark that TA Sequence 881223 shows the object on the wrong
location. A correct identification and sequence appeared afterwards
as TA 941025. Both Poyner and Vanmunster noticed during the present 
outburst, that DV UMa appears somewhat to the SE of the indicated 
position.


Tonny Vanmunster

(vsnet-alert 48,
 http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-alert/msg00048.html)

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

From: stars@personal.eunet.fi (Timo Kinnunen)
Subject: [vsnet-alert 828] 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.

(vsnet-alert 831)

   For more information, refer to the VSNET page:

   http://vsnet.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

From: VANMUNSTER Tonny <tvm@lms.be>
Subject: [vsnet-obs 5494] DV UMa - New SU UMa type dwarf nova

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

From: Daisaku Nogami <nogami@kusastro.kyoto-u.ac.jp>
Subject: [vsnet-alert 842] Superhumps in DV UMa

Dear colleagues,

We (Ouda Team) have detected superhumps with a quite large
amplitude (~0.6 mag!) in DV UMa during the last night 5-hr
run.  The preliminary period analysis with the PDM method
give the best estimated period of 0.090 (+- 0.002) day.

Best regards,
Daisaku Nogami

(end quote)

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