(CCD image by Daisaku Nogami, Hida Observatory)
As reported by Christopher Jones (vsnet-outburst 5622), [Poyner's report] the suspected large-amplitude SU UMa-type dwarf nova GO Com is undergoing a bright outbust (mag 13.0-13.9, depending on observers). The most recent confirmed outburst was in 1998 April. The only likely superoutburst recorded in this decade was in 1995 August (Kato et al. 1995, IBVS 4228), which apparently showed a precursor outburst and a rebrightening. The 1995 outburst was not sufficiently followed to determine the superhump period because of the short visibility. We must also note that GO Com was once considered as a WZ Sge-type candidate; this also needs to be tested.
The present outburst is as bright as the 1995 one, and the present excellent visibility will certainly allow us to make first-time detailed time-series photometry! Please observe GO Com as the first priority target.
Initial observations reported to VSNET: YYYYMMDD(UT) mag observer 20030527.128 <147 (Mike Simonsen) 20030529.894 <148 (Pavol A. Dubovsky) 20030531.962 <148 (Gary Poyner) 20030601.214 <148 (Mike Simonsen) 20030602.917 134: (Hazel McGee) 20030602.947 139 (Gary Poyner) 20030602.948 133 (Hazel McGee) 20030602.950 130 (Christopher P. Jones) 20030602.959 130 (Christopher P. Jones) 20030603.008 130 (Christopher P. Jones) 20030603.274 137 (Mike Linnolt)GO Com is located at: 12:56:37.10 +26:36:43.7 (J2000.0)
Dear colleagues,
Out time-resolved unfiltered photomety carried out at Hida observatory in Jun 3.539-3.725 (UT) revealed that GO Com is monotonously fading at a rate of about 1.0 mag/day, although we can see some hint of modulations with an amplitude ~0.03 mag. Whle this decline rate suggests that the present outburst is a normal outburst, it may be a precursor of the long-awaited superoutburst. Follow-up observations are highly encouraged!
Best regards, Daisaku Nogami
As a follow up observation from Central Asia: Analysis of 255 images Exposure 60 seconds, unfiltered GO Com, JD=794.15-794.37 Fade of 0.2 magnitude in five hours. Tom Krajci Tashkent, Uzbekistan
===================================================================== On June 4, the object finally eveolved into a genuine superoutburst!! =====================================================================
On June 4.906 UT GO Com was back at mag 13.
Regards, Patrick
Based on unfiltered CCD images, GO Com, JD=795.15-795.36, has well developed superhumps 0.4 mag. amplitude! Period is approx. 1.5 hours based on visual inspection of data.
Tom Krajci Tashkent, Uzbekistan
As reported by Tom Krajci, GO Com is now displaying flashing superhumps, finally confirming the SU UMa-type nature of this object. The object is now by 0.3-0.4 mag brighter than its precursor outburst starting on June 3. The Kyoto team (observer: M. Uemura and R. Ishioka) also succeeded in obtaining full data last night, which just precedes Krajci's observation.
The preliminary superhump period on June 4 observation is 0.0635(4) d, which generally confirms Krajci's report. The mean superhump profile is presented at:
Fully grown superhumps are clearly seen!
We have tried to reanalyze the June 2 observations to further investigate the growing stage of the superhumps, but the signal is not yet evident (although the result is still preliminary), at least not so evident as in T Leo 1993 superoutburst).
In any case, we *very* strongly encourage further intensive observations to fully cover the present, long-awaited rare superoutburst of this object!
Dear Colleagues,
We have received new data from Bill Yeung (new member!) and Lew Cook. All the data up to now (will be presented later on the webpage) show very prominent, fully grown superhumps. The best superhump period up to now is 0.06327(11) d. Although this period is too long for a typical WZ Sge-type star, the (apprently) long outburst interval would require additional mechanism other than usual SU UMa-type dwarf novae. Please keep observing as much as you can!
Regards, Taichi Kato VSNET Collaboration team
We have received further data from Nakajima-san, Nogami-san (Hida Observatory, reported earlier), Tom Krajci. Sano-san also commnicated the report of successful observation. From all the reported and analyzed observations, we have obtained a refined superhump period of 0.06326(5) d. The superhump signal is very strong. In addition to these superhumps, there is a hint of low-amplitude (~0.03 mag) qausi-periodic oscillations with periods of 6-7 min. This feature was most prominent in June 5 data. This appearance of QPOs dueing the early stage of a superoutburst reminds us of "super-QPOs", which are long-period QPOs with high coherence seen only during a limited stage of an superoutburst.
http://www.kusastro.kyoto-u.ac.jp/vsnet/DNe/superqpo.html
Literature: Kato et al. (1992) PASJ 44, L215
Kato (2002) PASJ 54, 87
Although this phenomenon has a period similar to other QPOs in
(outbursting) dwarf novae, I consider that the mechanism of excitation
would be different, since the appearance of this phenomenon is closely
associated with a specific stage of a superoutburst. In any case,
the bright new, somewhat peculiar, SU UMa star GO Com would provide
deep insight into the physics of SU UMa-type stars, superhumps and
QPOs. Please continue observing this object as the top priority target
for the evening to midnight.
Regards, Taichi Kato VSNET Collaboration team
Dear Colleagues,
We have received further data from Donn Starkey. The combination of all the data now marginally show the decrease in the superhump period, which is not inconsistent with the superhump period (the superhump period of GO Com lies close to the borderline of negative-postive superhump Pdot distribution). However, the data may also suggest that the early 10 superhump cycles had a different period evolution from that in the later stage. In any case, we are witnessing the early development of the superhumps, as is also suggested from the presence of what can be understood as "super-QPOs".
We have updated the figure of the superhump profile on the VSNET web page. Please reload the figure.
Regards, Taichi Kato VSNET Collaboration team
We have received new data from Tonny Vanmunster, Lew Cook, Yasuo Sano-san, Torii-san and GETS team observing at Gunma Astronomical Observatory (two nights), and preliminary data from Bill Yeung. There are four nights data taken at Kyoto.
The overall analysis of the data clearly indicates that the period change was an early stepwise one, as recently observed in UV Gem and NSV 10934. The superhump timings since late June 5 (UT) have been well expressed by a single period of 0.06268 d. We consider that this period would better represent the superhump period of GO Com. Compared to this period, the period observed on the first night was longer by 1.5%, which is almost comparable to the typical fractional superhump period excess(!). Although we need a full period analysis with fully analyzed data sets, this period change already signifies the unusual nature of this dwarf nova -- which may be somehow related to the probably unusual outburst characteristics. Further observations are strongly encouraged!
We have also posted two images (from Starkey and Nogami-san) on the VSNET GO Com page. Enjoy these images for this rare superoutburst!
Regards, Taichi Kato VSNET Collaboration team
GO Com: superhump period increase! (beat phenomenon?)
Dear Colleagues,
We have received new data from Nakajima-san, Tonny Vanmunster (2 nights), Brian Martin, Tom Krajci, and Tanabe-san (VSNET Okayama station) and the OUS team. Surprisingly, the superhump period of GO Com increased during the past one night! Such a sudden change in the superhump period is rarely seen during the superoutburst plateau stage.
The period change may be alternately interpreted as the effect of a "beat phenomenon" between the superhump period and orbital period (the best example in an non-eclipsing SU UMa/WZ Sge star being RZ Leo: Ishioka et al. 2001 PASJ 53, 905, see also http://www.kusastro.kyoto-u.ac.jp/vsnet/DNe/rzleo.html). One may remember the strong effect of beat phenomenon during the 2001 superoutburst of WZ Sge, see http://www.kusastro.kyoto-u.ac.jp/vsnet/DNe/wzsge01.html). There is also a hint of beat phenomenon in the mean magnitude and the superhump amplitude.
If the second interpretation is correct, the estimated fractional superhump excess is about 2.5%, which is not unusual for an SU UMa-type dwarf nova with this superhump period. In any case, the superhump evolution of GO Com has not been monotonous. We therefore strongly encourage observations as continously and thoroughly as possible during the entire superoutburst and the subsequent post-superoutburst stage!
Regards, Taichi Kato VSNET Collaboration team
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