Superoutbursts of selected new SU UMa-type and WZ Sge-type stars .

1. Superoutbursts of selected new SU UMa-type and WZ Sge-type stars. • N.A. Katysheva 1, S.Yu Shugarov1,2, D. Chochol2 • Sternberg State Astronomical Institute, Universitetskij Prosp. 13, 119992, Moscow, Russia • 2) Astronomical Institute of the Slovak Academy of Sciences, 059 60 Tatranská Lomnica, The Slovak Republic SU UMa-type close binaries consist of a red dwarf filling up the Roche lobe and a white dwarf surrounded by an accretion disk. Remarkable feature of SU UMa-type and WZ Sge-type stars are superhumps. The early superhumps appear near the maximum magnitude of superoutburst of WZ-Sge type stars and have periods almost identical to the orbital one. They can be explained by a two-armed spiral pattern of tidal dissipation, generated by the 2:1 resonance. The common, or ordinary superhumps, with a single peak profile, appear during the plateau of superoutburst of SU UMa-type and WZ Sge-type stars. Their periods are a few percent longer than the orbital period. They can be explained by the thermal tidal instability model of an accretion disk (Osaki, 1989; Whitehurst, 1988). The presence of the tidal 3:1 resonance results in the formation of an eccentric outer ring with apsidal precession longer than the orbital one. The beating of both periods cause periodic superhumps. The late superhumps appear several days after the rapid decline from the plateau of a superoutburst and may continue for several hundred cycles after the end of superoutburst. According to Kato et al. (2008), the late superhumps originate in the precessing eccentric disk near the tidal truncation. The eccentric disk slowly expands during the superoutburst decline and finally reaches the tidal truncation, where the period is stabilized. We present the results of our observations of selected new SU UMa- and WZ Sge-type stars which have been in outbursts during 2007–2009 years. SU UMa- and WZ Sge-type stars are a subclass of dwarf novae binaries with very short orbital periods, at the average of about 1.5 – 2 hours. The photometric observations of such systems, as SDSS J081207.63+131824.4, OT J080714.2+113812, V632 Cyg, etc. have been carried out with telescopes of the SAI and AISAS. We investigated photometric behaviour of SU UMa- and WZ Sge-type stars during their superoutbursts. WZ Sge-type dwarf novae SU UMa is a subclass of dwarf novae binaries (consisting of the red and white dwarfs) with very short orbital periods, at the average of about 1.5 – 2 hours. The superoutbursts with superhumps are the one of the main features of SU UMa-type DNe. The period of superhumps exceeds the orbital one on 1-3%. The WZ Sge-type objects are the most extreme subgroup of SU UMa-type DNe with a long (several years) superoutbursts recurrence time. Their orbital periods are the shortest ones observed in SU UMa-type stars. Some of them exhibit a complex post-superoutburst rise of brightness called rebrightening(s), rarely seen in other SU UMa-type DNe. One of the most remarkable signatures of WZ Sge-type objects is a presence of ”early superhumps” during the earliest stages of superoutbursts. This feature is also referred to as orbital superhumps or outburst orbital humps. Early superhumps have a period extremely close to the binary period and commonly show a double–humped profile, in contrast to the ordinary superhumps of SU UMa-type dwarf novae. Early superhumps are the most discriminative feature of the WZ Sge-type objects, and have not been detected in other DNe. Observations. We present the photometric observations of four new SU UMa stars: SDSS J081207.63+131824.4, V632 Cyg, OT J080714.2+113812 and OT J213701.8+ 071446, experienced their superoutbursts in 2007 – 2009 yrs and four new WZ Sge-type binaries – V455 And (2007 yr) , dwarf nova in Tri (2008 yr), V466 And (2008 yr), and dwarf nova in Leo (2010). Our CCD observations were taken with the Ap-47camera (0.6m Zeiss-reflector) and the Pictor-416 camera (0.5m Maksutov telescope) at the Crimean Laboratory of theSAI and the ST-10XME camera (0.5m reflector) at the AISAS Observatory in Stará Lesná (Slovakia). V632 Cyg. Wenzel (1989) mentioned three outbursts in JD 2429244, 571 and 794 found by Hoffmeister & Rohlfs. Superoutburst of 2008 began in November, 12 (VSNET dN-alerts 5999-6001). We observed it in Nov.12–25. A classical saw-like superhump light curve is present in Fig.1. Fig. 1. The del BVR light curve summed with the superhump period 0.06564 d. V466 And discovery and classification V466 And was discovered as an optical transient by K. Itagaki (Yamaoka et al., 2008) on a CCD image taken on September 1.6 UT, 2008 (JD 2454711.1). Our observations were provided in Crimea, Stará Lesná and Mt. Terskol. The overall light curves are plotted in Fig. 5. Fig. 5. The RC ,V light curves, B−V and V −RC colour indices curves of V466 And from Sept. 1 to Nov. 18, 2008. (from Chochol et al., 2010). SDSS J081207.63+131824.4 This object is from Sloan Sky Service (Szkody et al., 2007). The 2008 superoutburst detected by K. Itagaki The mean superhump period was 0.08432 d (Kato et al., 2009). We observed this system from the13th to the 19th of October during the a fading of brightness. So it is possible a decrease of superhump period, Fig.2. The orbital period is near the low edge of “a period gap”. OT J213701.8+71446 The beginning of superoutburst – 08.11.2008. Our observations were taken during the superoutburst decline. There is a hint on the second hump between the phases 0.2 and 0.8. The orbital period is inside ”the period gap”. Fig. 4. The del BVR light curve of J0812 folded with the superhump period 0.09743 d. Fig. 2. The del BVR light curve of J0812 folded with superhump period 0.08416 d. Fig. 6. Evolution of superhumps during the super- Outburst of V466 And. OT J080714.2+113812 This object was discovered by K. Itagaki (vsnet-alert 9721, 9731). The object was soon confirmed to exhibit superhumps. The outburst was associated with an unusual rebrightening following a one-day dip near the termination of the superoutburst (see Kato et al., 2009). The mean superhump period was 0.060818 d. The superhump period is small and close to the WZ Sge-type stars. Scattering of data is large. Fig. 3. The del BVR light curve of J0812 folded with the superhump period 0.06083 d. Nova 2010 in Leo The object CSS100217:104411+211307 = OT J104411.4+211307 was discovered on February 16, 2010. The object reached 12.5 mag at maximum. At quiescence it was ~19 mag. We began to observe on February 17, 2010. On Fig7. the overall V-light curve and color-indices curves U-B, B-V, V-Rс V-Iс are presented. Fig. 7. The overall light curves (Chochol et al., 2011). Nova 2008 in Triangulum On October 26, 2008, Maehara (VSNET) reported an outburst of tCatalina transient in Tri (Drake et al., 2009). The Early superhumps with the period 0.0531 d and ordinary superhumps with the period 0.0537 d were discovered by Shugarov et al. (2008). References Chochol D. et al., 2010, Contrib. Astr.. Obs. Skalna. Pleso,40, 19. Chochol D. et al., 2011, in press Drake A.J.etal. 2009, ApJ, 696, 870 Kato T., Maehara H., Monard B., 2008, PASJ, 60, L23 Kato T. et al., 2009, PASJ, 61S, 395 Osaki Y., 1989, PASJ, 41, 1005 Shugarov S., Volkov I., Chochol D., IBVS, 5862, 1 Szkody P. et al., 2007, AJ, 134, 185 Wenzel W., 1989, IBVS, 13405, 1 Whitehurst, R.: 1988, MNRAS, 232, 35 VSNET dN-alerts, campaigns (Kato T.,etal. ) 17th European White Dwarf Workshop, Tübingen, Germany, August 16-20, 2010