X Per and V725 Tau: infrared variations on timescales longer than fifteen years

作者：Taranova O G^*; Shenavrin V I

来源：Astronomy Reports, 2017, 61(11): 983-995.

DOI：10.1134/S1063772917100080

The results of infrared observations of the two Be stars X Per and V725 Tau, which are the optical components of X-ray binary systems, obtained in 1994-2016 are presented. The observations cover Be-star phases as well as shell phases. The data analysis shows that the radiation observed from the binaries at 1.25, 3.5, and 5 mu m can be explained as the combined radiation from the optical components and variable sources (shells/disks) that emit as blackbodies (BBs). Emission from a source with the color temperature T (c) similar to 1000-1500 K was detected for X Per at lambda ae 3.5 mu m. The highest IR-brightness variation amplitudes for X Per were 0.9-1.2 (m) (JHK magnitudes) and similar to 1.45 (m) (LM magnitudes); for V725 Tau, they were 1.1-1.4 (m) and similar to 1.7 (m) (L magnitudes). The parameters of the optical components and interstellar extinction during the Be phases were estimated: the color excesswasE(B-V) = 0.65 +/- 0.08 (m) and 0.77 +/- 0.03 (m) for X Per and V725 Tau, respectively. Light from the variable sources (disks/shells) was distinguished and their color temperatures, radii, and luminosities estimated for different observation epochs in a BB model. The variations of the binaries' IR brightness and colors are shown to be due to changing parameters of the variable sources. The mean color temperature of the cool source (disk/shell) and the mean radius and mean luminosity of X Per are 9500 +/- 2630 K, (35 +/- 10) R (aS (TM)), and (9100 +/- 540) L (aS (TM)). For V725 Tau, these parameters are 6200 +/- 940 K, (27 +/- 6) R (aS (TM)), and (980 +/- 420) L (aS (TM)). The 1.25-5 mu m radiation from X Per at different epochs can be represented as a sum of contributions from at least three sources: the optical component and two objects emitting as BBs. To reproduce the 1.25-3.5 mu m radiation from V725 Tau, two components are sufficient: the optical component and a single variable BB object. For both binary systems, orbital variations of the IR brightness can be noted near the Be-star phase. The amplitudes of the J-band variations of X Per and V725 Tau are about 0.3 (m) and 0.1 (m) , respectively.

• 出版日期2017-11