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UBV photometry of V934 Her in the X-ray outburst

ATel #6497; N. V. Metlova (SAI, Crimean Station), V. P. Goranskij (SAI, Moscow University)
on 25 Sep 2014; 17:33 UT
Credential Certification: Vitaly Goranskij (goray@sai.msu.ru)

Subjects: X-ray, Binary, Neutron Star, Star, Variables, Pulsar

After Swift detection of the X-ray outburst in the system of M2 III giant with a neutron star V934 Her (4U 1700+24, HD 154791) on 18 Sep 2014 (ATel #6482), we perform its optical photometry at the Sternberg Astronomical Institute Crimean Station using 60 cm telescope and Lyuty's photoelectric UBV photometer. Five observations were taken between 2014 Sep 21.715 and 21.742 UT, and the following average UBV magnitudes were found: 11.238 +/-0.028; 9.292 +/-0.009; 7.682 +/-0.011. Previous observation relating to the period of X-ray activity started around 5 Feb 2014 and described in ATel #6482 was made on 2014 May 2.887 UT, UBV values then were as follows (11.243; 9.270; 11.243). We have a series of 467 observations in 302 nights taken with the same device since 1997 in the quiet state (Astrophys. Bull. V.67, p.73, 2012). Photometric observations confirm 404-day spectroscopic orbital period by Galloway et al. (ApJ V.580, p.1065, 2002) but give some larger value of 415+/-14 days with the largest amplitude in the U band of 0.108 mag. Besides orbital light variations, the intrinsic variability of M giant was observed, and it was interpreted as its non-radial pulsations. The phase of our last observation calculated using 415-day period and the periastron epoch MJD 49090 determined by Galloway et all. is 0.87. U- and B-band brightness measured on Sep 21 corresponds to the lowest level of brightness observed earlier in this orbital phase. Also May 2 measurements cannot be distinguished from other data by higher brightness. So we confirm that X-ray outburst is not accompanied by any photometric changes in near-UV and optical wavelengths. Additionally, these observations show that the photometric orbital wave is not connected to X-ray heating or reprocessing of X-ray radiation in the atmosphere of M type giant.

Orbital UBV light curves of V934 Her