(vsnet-alert, Mar. 26)
outburst of GO Com and S10932
Makoto Iida (VSOLJ) communicates that both GO Com and S10932 are detected in outburst on his CCD frames taken on Mar. 26. Follow-up observations are strongly encouraged.
More detailed information will follow.
CCD image of S10932, showing an eclipse caught during the present outburst
CCD image of GO Com by Iida
Forwarded message from vsnet-obs:
>From: firstname.lastname@example.org (Tonny Vanmunster)
********************************************* * OUTBURST OF GO Com [UGWZ:, 13.1p - 20p] * ********************************************* 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 !
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.
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
In addition to this, there is at least one spectroscopic observation during quiescence by Mukai et al. The spectrum shows strong hydrogen emission lines.
Our V-band CCD observation shows GO Com is definitely undergoing its unpredicted second outburst. GO Com was fainter than GSC 12.8 star by 0.79 mag on July 31.445 UT. We will try to follow this object to see if the present outburst is a short one like previously observed ones.
Taichi Kato & Ouda team
(vsnet-alert 180, 1995 Aug. 3)
Our CCD observation tonight shows GO Com is still in outburst, in contrast to a short one just preceding. First ever observed superoutburst?? We are trying to obtain continuous photometry, but the observing window will be very short due to trees west to the observatory and changable weather in the early evening. We would appreciate anyone's efforts in following this object just a few hours. (Last night we were interfered by the clouds.)
Taichi Kato & Ouda team
(vsnet-alert 187, 1995 Aug. 4)
As notified earlier, dwarf nova GO Com is undergoing a long-lasting post-outburst brightening. Nightly averaged magnitudes obtained at Ouda Station (Kyoto University) are:
mid-UT V-C S.D. N band -------------------------------- 950731.445 0.786 0.099 9 V 950801.447 0.719 0.141 5 V 950803.467 1.037 0.046 34 V V=13.8 C = GSC 12.8 (125636.64 +263142.9 J2000.0)
The present rate of decline (~0.1 mag/day) seems to be characteristic to a superoutburst. Although very preliminary, Aug. 3 data seems to suggest existence of variation of ~0.1 mag. A broad maximum possibly occurred around Aug. 3.473 UT (superhump?), but not conclusive because of the short duration (~40min) of the observing run and the bright sky background.
Taichi Kato & Ouda team
(vsnet-alert 195, 1995 Aug. 13)
We caught another unexpected outburst in GO Com! The current magnitude estimated from CCD images is 15-15.5 on Aug. 13.44(UT). It is an week after the end of the previous outburst. What are going on in GO Com!
Daisaku Nogami and Taichi Kato
paper on the 1995 outburst
The 1997 Feb. outburst
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