RZ Leo: Extremely rare outburst on December

As reported by R. Stubbings in [vsnet-alert 5437], the possible WZ Sge type dwarf nova RZ Leo experienced an extremely rare outburst (12.1mag) on December 20. The magnitude (12.1v) is probably the brightest one except for the original discovery at mpg=11.5 (vsnet-campaign 584, 589). The rare outburst of RZ Leo has been confirmed by T. Kinnunen, at mv=12.2 on December 21.21 UT (vsnet-campaign 591, vsnet-campaign-dn 327).

(CCD image taken at Kyoto University by R. Ishioka, M. Uemura, H. Iwamatsu, T. Kato, and K. Matsumoto)

T. Vanmunster detected periodic modulations in a light curve on December 20/21 (vsnet-alert 5446). Gary W. Billings presented a light curve and its data on December 20/21 at his web site (vsnet-campaign 611). Combined with G. W. Billings's data, the early Kyoto data shows periodicity of 0.07631 d which is extraordinally close to the photometric period (0.0756 +/- 0.0012 d, Mennieckent et al., 1999, Astron. Astrophys. 352, 239). The observed early hump profile is also peculiar in contrast to "usual" superhumps in SU UMa stars. The humps show a complex structure, similar to "early superhumps" observed in other WZ Sge-type stars (vsnet-campaign 598, 599, 600, 617). T. Vanmunster analyzed his 3 nights data and reported 0.0755 d period which is consistent with the results by the Kyoto team (vsnet-campaign 602).

(Phase-averaged superhump light curve on Dec. 22, taken at Kyoto University)

The light curve obtained by the Kyoto team on December 23 revealed "true" superhumps was evolving with an amplitude of ~0.3mag (vsnet-campaign 603). G. Masi showed a light curve and a CCD image on December 23 at his web site (vsnet-campaign 604, vsnet-campaign-dn 341), which shows superhumps with some secondary features whose period is about 0.08d and amplitude is about 0.2mag (vsnet-campaign-dn 341). Combined with S. Kiyota, G. Masi, and the Kyoto data, the data on December 23 showed a 0.0813 d period (vsnet-campaign 606). A preliminary period analysis of the combined data by the Kyoto and S. Kiyota on December 24 yields the the decrease of the superhump period to 0.079 d (vsnet-campaign 612). B. Warner and P. Woudt have observed RZ Leo for three nights at the South African Astronomical Observatory. They report that they saw low amplitude humps on the first two nights, but that last night there was a full superhump with an amplitude of about 0.35 mag (vsnet-campaign 609, 610). On December 25, S. Kiyota's and the Kyoto data showed superhumps are still very prominently present, with narrower peaks than before. The amplitude of superhumps still amounts to 0.35 mag. (vsnet-campaign 623). The VSNET collaboration team revealed the combined data (December 23-26) has yielded a superhump period of 0.07851 d, which is slightly shorter than the previous determination. This may suggest a shortening of the superhump period. On December 26, superhumps have became narrower, more resembling those of usual SU UMa type stars. Secondary superhump maxima (small notches) were visible both (vsnet-campaign 626). T. Vanmunster reported that his data combined with J. Pietz's one revealed a fairly simple superhump signal at 0.0785 +- 0.0002 d. This yields a fractional period excess of 3.3%, which is a rather standard excess value. (vsnet-campaign 630). T. Kato suggested there seem to be a wavy pattern with a period of 2-3 d in the averaged light curve. The amplitude of superhumps seems to vary with this period. This is likely caused by the beat phenomenon between the superhump period and the orbital period, a natural consequence of a high-inclination system as suggested by earlier quiescent observations. (vsnet-campaign 633). J. Pietz presented light curves at: http://home.t-online.de/home/Jochen.Pietz/rzleo1.gif and http://home.t-online.de/home/Jochen.Pietz/rzleo2.gif (vsnet-campaign 354). A. Oksanen presented observations at: [vsnte-campaign 634].

(Fully grown superhumps on Dec. 23, taken Kyoto University and S. Kiyota)

(Further evolution of superhumps on Dec. 26, taken Kyoto University and S. Kiyota)

Light Curve and General Information of This Object