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

Authors :
Taranova, O.
Shenavrin, V.
Source :
Astronomy Reports; Nov2017, Vol. 61 Issue 11, p983-995, 13p
Publication Year :
2017

Abstract

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 μm 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 ~1000−1500 K was detected for X Per at λ ≥ 3.5 μm. The highest IR-brightness variation amplitudes for X Per were 0.9−1.2 (JHK magnitudes) and ~1.45 (LM magnitudes); for V725 Tau, they were 1.1−1.4 and ~1.7 ( L magnitudes). The parameters of the optical components and interstellar extinction during the Be phases were estimated: the color excesswas E( B− V) = 0.65±0.08 and 0.77 ± 0.03 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 , and (9100± 540) L . For V725 Tau, these parameters are 6200 ± 940 K, (27 ± 6) R , and (980 ± 420) L . The 1.25-5 μm 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 μm 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 and 0.1, respectively. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
10637729
Volume :
61
Issue :
11
Database :
Complementary Index
Journal :
Astronomy Reports
Publication Type :
Academic Journal
Accession number :
126307719
Full Text :
https://doi.org/10.1134/S1063772917100080