Abrupt change of the light curve of classical nova V723 Casстатья

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[1] Abrupt change of the light curve of classical nova v723 cas / V. P. Goranskij, N. V. Metlova, A. V. Zharova et al. // The Astronomer’s Telegram. — 2015. — no. 7985. — P. 1–1. V723 Cas was detected as a supersoft X-ray source first on 2006 Jan 31 (Ness et al., 2006, IAUC # 8676) and last on 2012 Dec 3 (Ness et al. 2015, AsAp 578, 39). Goranskij et al. (2007, AstrBull 62, 125) reported the temperature rise to 280000 K and the appearance of the strong [Fe X] 6374 Å line on 2003 Aug 2 what suggests that the SSS phase had begun before the X-ray detection. The SSS phase was accompanied by a strict periodic light variability with the increasing amplitude treated as an orbital one. Maximum amplitude of 2.0 mag in the B band was reached in 2005. The shape of the orbital light curve and its amplitude were not variable in the intensity scale, provided that the general decay trend was removed. We continued photometric monitoring of V723 Cas up-to-date, and improved the period of the variability using the O-C method to 0.6932672 (±0.0000004) day, Min JD hel.= 2453628.5275 (±0.0050). The recent CCD BV(RI)c photometry was carried out with the 50 cm Maksutov meniscus telescope of the SAI Crimean Station between 2015 Aug 7 and 27. We found that the amplitude of the variability decreased abruptly by about 4.5 times if compared with the previous season of 2014 and was equal to 0.3 mag in all the bands. At the same time, the star remains at the light level higher than the pre-outburst one by 2.6 mag in the B band, and by 2.0 mag in the R band. Additionally, we carried out spectroscopic observations of V723 Cas with the Russian 6 meter telescope BTA and SCORPIO focal reducer. The spectrum was taken on 2015 Aug 18.956 UT with the exposure 1800 s, the spectral range 3700-7190 Å, and the resolution 14 Å. In this spectrum, we identified series of Balmer and He II lines, C III+N III blend at 4640 Å, C IV 5805 Å, [Ca V]+[Fe VII] blend at 6087 Å, [Fe VII] 4942, 5158, 5276, 5721 Å, all the lines are in emission. Hbeta/HeII 4686 A flux ratio is about 0.40 what suggests a high temperature of an ionizing source. [Fe X] 6374 Å line has disappeared without a trace. These changes may signify the finish of a long SSS phase in V723 Cas. X ray observations are encouraged.

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