[vsnet-alert 156] rare outburst of GO Com

[tkato@kusastro.kyoto-u.ac.jp]

Forwarded message from vsnet-obs:

>From: tvanmuns@innet.be (Tonny Vanmunster)

Dear colleagues,

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*  OUTBURST OF GO Com [UGWZ:, 13.1p - 20p]  *
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1995 Jul 16.951 UT, 13.3 (T. Vanmunster, 0.35-m refl, seq: GSC);

Confirmation is urgently needed !


In IBVS 3489, T. Kato and R. Hirata describe CCD photometry of
GO Com, and report quasi-periodic modulation with an amplitude
of 0.5 mag, and a "periodicity" of 33 min. The same paper
mentions a major outburst of GO Com, observed on May 30, 1989 
(mv 13.2) by Watanabe and Kato. As far as we could trace, this
constitutes the last reported positive observation of GO Com !

Another publication on GO Com (PASP, 102, 758-772, 1990), by
Steve Howell, Paula Szkody a.o., mentions that GO Com has been
seen in outburst at least three times. They further describe
photometric observations showing approx. 0.5 mag flickering on
top of a determined 95-min period (assumed to be the orbital
period). The 95-min period, although seen with high confidence,
may simply be flickering.

It finally is interesting to note that GO Com is classified as 
a TOAD (Tremendous Outburst Amplitude Dwarf Nova) by S. Howell.

We would very much appreciate receiving further information,
and observations, of this intriguing object !

Best regards,
Tonny Vanmunster

========================================================================
The following is a part of a draft which will be submitted to the
VSOLJ Bulletin.  As far as I know, this is the only documented recent
outburst of GO Com.

  Outburst Observation of GO Comae Berenices in 1989

  GO Com was discovered by Kowal (1977) as an eruptive object on a Palomar
plate taken on 1977 July 1.213.  The variable was confirmed to be coincide
with a suspected variable star CSV 1959 = SVS 382 (Belyavskij 1933).
On the other hand, Usher (1981) independently discovered a very blue star
of B=18.1 during the survey of the north galactic pole region.  This star
(US 31) was identified with GO Com.  The extreme color (U-B = -1.5) suggests
an extreme nature of this object.  Vogt and Bateson (1982) classified this
variable as a WZ Sge-type dwarf nova because of its large outburst amplitude
and low outburst frequency.

  During the course of monitoring dwarf novae since 1986, we were able to
catch this dwarf nova in outburst probably for the first time since
discovery.  The observations are as follows.

   [not completed yet, but we have at least four positive observations]

  The object attained a maximal magnitude of mv=13.2, which was followed
by a rapid decline by about 1 mag in one day.  This rapid decline suggests
a normal outburst of SU UMa stars.  Since this observation in 1989, no
definite outbursts have been recorded until June, 1995 (see also Vanmunter
and Howell 1995).  Despite the seasonal gaps in monitoring this object, the
extreme low outburst frequency of this dwarf nova seems to be established.
Apparent absence of long outbursts, infrequent short outbursts and possible
excursion to a low state (mp ~ 20) may suggest a relationship to BZ UMa.
Intensive observations during the next outburst, systematic searches for
historical outbursts and determination of the physical parameters are
recommended.

References:

Belyavskij 1933, Perem. Zvezdy 4, 234
Kowal 1977, IAU Circ. 2562
Usher 1981, ApJ Suppl. 46, 117
Vanmunster T., Howell S. B. 1995, in "Outburst Activity Data on Selected
    Cataclysmic Variables"
Vogt N., Bateson F. M. 1982, Astron. Astrophys. Suppl. 48, 383

Regards,
Taichi Kato

In addition to this, there is at least one spectroscopic observation
during quiescence by Mukai et al.  The spectrum shows strong hydrogen
emission lines.

PS. I will soon leave here in order to attend to the East Asian Meeting
    on Astronomy.  Looking forward to hearing fruitful results on the
    current outburst.

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