The February 2003 outburst of KS UMa

The February 2003 outburst of KS UMa was first reported by Belgian variable star observer Eddy Muyllaert on 2003, February 18.840 UT. The night before, the object definitely was still fainter than mag 14.6 (observation by Gary Poyner). 
I started an unfiltered CCD photometry session on this target, at CBA Belgium Observatory, during the night of the outburst detection. My session took place under good atmospheric conditions and lasted for about 3.4 hours. No obvious modulations are visible in the resulting light curve (see below), suggesting that the present outburst is either a normal outburst or a superoutburst caught in its very initial development stage.



The next night (2003, February 19/20) was clear again over Belgium, and allowed me to monitor the object for 4.6 hours under good conditions. This time, the light curve was telling a completely different story (see below), with strong superhumps being present, and therefore classifying the present outburst as a genuine superoutburst. Using the PDM technique, I derived a superhump period of 0.0719 +/- 0.0010 d. This Psh value is slightly higher than the value of 0.0697 d that I reported in 1998 (CVC 161, vsnet-alert 1448; CVC 162, vsnet-alert 1450), at the moment I detected the UGSU-type nature of KS UMa. D. Nogami (vsnet-alert 1452) also reported a Psh value of 0.069 d.


The next nights were clear again, allowing me to continue the photometry sessions on KS UMa. The resulting light curves are listed below.

Here's some interesting notes, extracted from "VSNET Weekly Campaign Summary" (vsnet-campaign 1372) regarding the KS UMa superoutburst :

"As reported by E. Muyllaert and G. Poyner on Feb. 18, the SU UMa-type dwarf nova, KS UMa is now in outburst (12.7, 12.9mag;vsnet-campaign-dn 3447). There was no clear modulations in the light curve obtained by T. Vanmunster on Feb. 18/19 (vsnet-campaign-dn 3449). A subsequent observation by K. Nakajima showed a weak (~0.05 mag) signal, which may be attributed to early-stage superhumps (vsnet-campaign-dn 3454). T. Vanmunster then detected clear superhumps with an amplitude of 0.21 mag on February 19/20 (vsnet-campaign-dn 3455, 3459). Using the combined data, T. Kato reported that the superhump period of the early superoutburst phase was 0.07068(7) d, which is substantially longer than the previously reported periods (vsnet-campaign-dn 3460). On Feb. 22, T. Kato reported that, although there was a slight tendency of a period decrease during this period, no striking period change as recorded in UV Gem was observed (vsnet-campaign-dn 3464).
A. Olech et al., the Ostrowik team, performed time-series
observation on Feb. 21/22 and 22/24 and reported a period of 0.0699 +/- 0.0002 days (vsnet-campaign-dn 3465, 3476). T. Kato revised the superhump period to be 0.07026(2) d on Feb. 23. The rate of period change dot(P)/P was around -3*10(^4). While the baseline was still short, if confirmed, this negative period derivative is one of the most pronounced among moderate-period SU UMa-type dwarf novae (vsnet-campaign-dn 3467). In the late Feb. 23 - early Feb. 24 data, the main superhump maxima became weaker, while other peaks became stronger. The profile then become very complex, which resembles that of superhumps during the rapid decline stage. However, the present stage is too early for such a rapid decline, neither observations show such a rapid trend (vsnet-campaign-dn 3484). The superoutburst is now ongoing (vsnet-campaign-dn 3448, 3453,
3456, 3463, 3479)."






Copyright © 2003 - Tonny Vanmunster.