The June 2003 superoutburst of GO Com

On June 2, 2003, Hazel McGee (UK) reported her visual detection of a rare and bright outburst of the large-amplitude cataclysmic variable GO Com. This object was discovered by Kowal as an eruptive object on a Palomar plate taken on July 1.213, 1977. The variable was confirmed to be identical to the suspected variable star CSV 1959 = SVS 382 (Belyavskij 1933). In 1981, Usher independently discovered a very blue star of B=18.1, during his survey of the North galactic pole region, that afterwards was identified to be GO Com. Vogt and Bateson (1982) classified GO Com as a UGWZ-type dwarf nova, based on its large outburst amplitude and low outburst frequency.

GO Com had not been seen in outburst anymore since April 1998. Before that date, GO Com was reported to be in outburst on 1997, Feb 07 [CVC 128] and on 1996, Mar 26 [CVC 89]. The latter was a faint, normal outburst. GO Com underwent a very remarkable series of outbursts in July/August 1995. In less than one month, 3 separate outbursts were observed :

- The first outburst of GO Com was detected on July 16, 1995 (T. Vanmunster) [CVC 47]. I estimated the object at mag. 13.3. Due to the low altitute of GO Com at the moment of outburst detection, no confirmative observations were received.

- Hungarian amateur Laszlo Szentasko detected the second outburst of GO Com. His observation (mag. 13.3) was made on July 30, 1995 [CVC 51]. 

- It is still unclear how the exact relationship between het first and second outburst of GO Com should be interpreted. Likely, the first outburst was a normal one, triggering the second (super?)outburst ? To make things even more complicated, another outburst was reported, about two weeks later. This third one was detected by Daisaku Nogami and Taichi Kato, Ouda Team, Kyoto University, Japan on August 13, 1995 [CVC 52], when they observed GO Com at mag. 15-15.5.   

Due to the bad visibility of GO Com in 1995, this outburst did not allow detailed CCD photometry to study the outbursting characteristics cq. detect superhumps. 

Final confirmation of the SU UMa-type nature of GO Com came on June 5, 2003, when Tom Krajci (CBA Uzbekistan)  announced the detection of superhumps with an amplitude of 0.3 - 0.4 mag. By that time, the object had just left the precursor outburst stage, and entered into the superoutburst stage.

GO Com is now the subject of an intensive CCD monitoring campaign (VSNET, CBA), resulting in excellent coverage of each stage of the outburst. For a detailed analysis of the CBA observations of GO Com, click here. An initial superhump period determination by Tachi Kato [vsnet-campaign-dn 3738] results in a value of 0.06327(11) d. This is well in agreement with photometric quiescence observations of GO Com by Steve Howell, Paula Szkody a.o. (PASP, 102, 758-772, 1990), on the basis of which they determined a 95-min period, assumed to be the orbital period. 

I here report my own observations, obtained at CBA Belgium Observatory, using the 0.35-m f.6.3 telescope and unfiltered ST-7 CCD.

I first observed GO Com in the night of June 5/6, 2003, under good atmospheric conditions. The variable was monitored for 4.1 hours, and the resulting light curve is shown below. Superhumps with a 0.25-mag amplitude are obvious, and result in a superhump period (determined using the PDM technique) of 0.0635 +/- 0.0003 d. 


On June 06/07, 2003, I had another unfiltered CCD run on GO Com. Sky conditions were not really good (quite hazy), and the session was limited to 2.5 hours. The unfiltered mag of GO Com was about 13.6. The resulting light curve (see below) shows the presence of superhumps with an amplitude of 0.24 mag. 

Another clear night (2003, June 07/08) over CBA Belgium Observatory
resulted in a 4.0 hours unfiltered CCD session of GO Com. The unfiltered mag of GO Com was about 13.7 (0.1 mag fainter than yesterday). The resulting light curve is shown below. Although it still clearly shows superhumps, their amplitude definitely has become smaller compared to previous nights (it is now about 0.16 mag). The trend of decline (0.1 mag in 5 hours), reported by Tom Krajci (CBA New Mexico) in vsnet-campaign-dn 3755, is confirmed by my observations, but seems to have slowed down a bit.






Copyright © 2003 - Tonny Vanmunster.