RX J0640-24: an SU UMa-type candidate

P. Schmeer reported an outburst of the ROSAT selected cataclysmic variable RX J0640-24 on January 6. R. Fried (Braeside Observatory) confirms the outburst and reports an instrumental unfiltered magnitude of 11.8 for January 7.185 UT. A minor brightening was observed with the same instrument on 1999 December 14. The only previously known outburst was recorded on an ESO B plate (mag about 11) (vsnet-alert 3956). M. Uemura and T. Kato performed a time-series observation on January 7 and , in 1.3-hour continuous run, detected a modulation with an amplitude of about 0.3mag, which might be attributed to a superhump (vsnet-alert 3959, vsnet-alert 3968). In the next night they found it rapidly faded (vsnet-alert 3970). The possible superhump-like feature observed in the January 7 data seems to have decayed on January 8 data. However, there looks like some evidence of modulations with a likely period less than an hour. During the 3.4-hour run, the object showed little trend of the continuing rapid fading. This precludes the possible explanation of the January 7 variation as the effect of extinction. The rapid rate of decline (~1 mag/day between Jan. 6 and 8) suggests that the object can be a short-period system (e.g. SU UMa stars) (vsnet-alert 3980).

On February 22, RX J0640-24 is again reported to undergo an outburst at 12.0mag and 11.5mag by R. Stubbings and A. Pearce, respectively (vsnet-alert 4255, vsnet-alert 4257). The outburst again terminated rapidly (vsnet-alert 4270, vsnet-obs 26500).

As reported by R. Stubbings and B. Monard in vsnet-outburst messages, RX J0640-24 experienced the other outburst (11.1mag) on May 13 (vsnet-campaign 49). W. Walker reported the possible structure in his two hours light curve on 19 May, but the amplitude is not more than 0.15 magnitudes (vsnet-campaign 97). This presumable superoutburst of RX J0640-24 entered the rapid decline stage on 24 May (vsnet-campaign 131, 104). The rate of decline, the duration of the plateau phase, the rate of rapid decline are all characteristic to those of superoutbursts.

Light Curve and General Information of This Object