■ [dwarf nova] J2138+26: a rapid fading stopped
J2138+26 is a new WZ Sge-type dwarf nova, discovered by Dae-Am Yi on May 7 (CBET 2273). The superoutburst entered a rapid fading stage on May 30 (vsnet-alert 12013). The object is suggested to be similar to GW Lib, another WZ Sge star outbursting in 2007, in terms of a low inclination angle and apparent brightness.
We have monitored this object with standard optical and near-infrared imaging and high-speed photometry with a time-resolution of 1 sec. The upper figure shows the V and J-band light curves we obtained. The V-J color during the superoutburst is quite similar to that observed in GW Lib (V-J~-0.2 -- +0.1). The rapid fading was confirmed in our observation on 31 May. At the same time, the V-J color increased to ~0.8, which is also analogous to GW Lib at the same phase. The lower figure shows the result of our high-speed photometry on 31 May. The rapid fading trend seems to be stopped, and small humps with an amplitude of ~0.1 mag can be seen. In the case of GW Lib, the rapid fading was not stopped like J2138+26, and continued until it reached V~15 and V-J~1.5.
The termination of the rapid fading implies that the object could experience a rebrightening in the next couple of days.
■ [dwarf nova] Reanalysis of OT J104411.4+211307
We performed the reanalysis of the dwarf nova OT J104411.1+211307 (=CSS100217). The flux distribution in our reanalysis are well similar to that of a typical dwarf nova undergoing an outburst. We can confirm that there is an weak emission in the center of the H alpha absorption.
■ [dwarf nova] V455 And: high-speed photometry on 100117
We performed high-speed photometry of the dwarf nova, V455 And on 17 Jan 2010 with a time-resolution of 2 s. V455 And experienced a WZ Sge-type superoutburst in 2007. This object is also known as an intermediate polar, whose spin period of the white dwarf is 67 s. The figures show our preliminary results: the light curve (the upper panel) and power spectrum (the lower panel) in 17 Jan. The features of the light curve and power spectrum are almost same as those observed on 23 Sep 2009. The object is still slightly brighter than the quiescent state observed before the 2007 superoutburst. We will continue the observation of this object to find a possible change in the structure of the power spectrum.
■ [dwarf nova] V455 And: high-speed photometry
We performed high-speed photometry of the dwarf nova, V455 And on 23 Sep with a time-resolution of 5 sec. The upper and lower panel show the light curve and power spectrum, respectively. In the light curve, the vertical dotted lines indicate the orbital period of V455 And (~4865 s). As can be seen in the power spectrum, a sharp spike at 0.01484 Hz (67.39 s) is present, which is probably a spin period of the white dwarf. Another noteworthy feature is a signal around 0.003516 Hz (~284.4 s). The overall feature of the light curve is analogous to that observed before the outburst (Araujo-Betancor et al. 2005)
■ [IP][dwarf nova] HT Cam: high-speed photometry
HT Cam is an intermediate polar, occationally showing a quite short (<1 day) outburst, like dwarf novae. An outburst of the object was reported on 17 Apr. We performed high-speed photometry with a time-resolution of 1 sec. Preliminary light curves are shown in the above figure. The figure also includes our result during the last outburst in Feb. 2008. On 17 Apr, the object was almost at maximum of the outburst. We can see possible 200-300-s periodic modulations seem to be rapidly evolving. Compared with the light curve on 7 Feb. 2008, the light curve on 17 Apr. 2009 might exhibit shorter time-scale variations. On 18 Apr, longer time-scale modulations were apparently dominant. No signal of white-dwarf pluses (514 s) was detected in all light curves we obtained.