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[vsnet-alert 831] more on outburst of DV UMa

   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://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

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