TY - JOUR

T1 - BINARIES γ CAS ANALOGS: OPTICAL AND X-RAY VARIABILITY

AU - Kholtygin, A.F.

AU - Ryspaeva, E.B.

AU - Dodin, A.V.

AU - Tsiopa, O.A.

N1 - Export Date: 19 February 2026; Cited By: 0; Correspondence Address: A.F. Kholtygin; St. Petersburg State University, St. Petersburg, 198504, Russian Federation; email: afkholtygin@gmail.com

PY - 2025

Y1 - 2025

N2 - γ Cas analogs constitute a small group of Be stars characterized by unusual X-ray spectra and high X-ray luminosities, LX ∼ 1031 –1033 erg s−1. This is 2–3 orders of magnitude higher than for typical Be stars, yet lower than that observed in massive X-ray binaries with Be components. Compared to classical Be stars, these objects exhibit unusually hard X-ray spectra. In the present paper, we present results from the analysis of the spectral and photometric variability of binary γ Cas analogs in both optical and X-ray bands. Notably, the periods of regular optical and X-ray variability appear to be similar. This suggests that at least part of the X-ray emission arises from interactions between local magnetic fields of the Be stars and the magnetic fields of their decretion disks. X-ray flares are expected to result from the reconnection of magnetic field lines. For the stars BZ Cru and π Aqr, several thousand flare events were identified in the X-ray light curves obtained with the XMM-Newton satellite. Moreover, regular variations in X-ray brightness with periods of 50–90 seconds have been detected for the γ Cas analogs HD 45314, HD 45995, NGC 6649 9, and V558 Lyr. These periods may correspond to the rotation periods of white dwarfs in binary Be+WD systems. We propose that the hard component of X-ray emission from γ Cas stars is generated via the accretion of disk material onto a rapidly rotating white dwarf. © 2025, Azerbaijan National Academy of Sciences. All rights reserved.

AB - γ Cas analogs constitute a small group of Be stars characterized by unusual X-ray spectra and high X-ray luminosities, LX ∼ 1031 –1033 erg s−1. This is 2–3 orders of magnitude higher than for typical Be stars, yet lower than that observed in massive X-ray binaries with Be components. Compared to classical Be stars, these objects exhibit unusually hard X-ray spectra. In the present paper, we present results from the analysis of the spectral and photometric variability of binary γ Cas analogs in both optical and X-ray bands. Notably, the periods of regular optical and X-ray variability appear to be similar. This suggests that at least part of the X-ray emission arises from interactions between local magnetic fields of the Be stars and the magnetic fields of their decretion disks. X-ray flares are expected to result from the reconnection of magnetic field lines. For the stars BZ Cru and π Aqr, several thousand flare events were identified in the X-ray light curves obtained with the XMM-Newton satellite. Moreover, regular variations in X-ray brightness with periods of 50–90 seconds have been detected for the γ Cas analogs HD 45314, HD 45995, NGC 6649 9, and V558 Lyr. These periods may correspond to the rotation periods of white dwarfs in binary Be+WD systems. We propose that the hard component of X-ray emission from γ Cas stars is generated via the accretion of disk material onto a rapidly rotating white dwarf. © 2025, Azerbaijan National Academy of Sciences. All rights reserved.

KW - stars: binaries: individual: γ Cas-stars

KW - stars: emission-line, Be

U2 - 10.59849/2078-4163.2025.2.10

DO - 10.59849/2078-4163.2025.2.10

M3 - статья

VL - 20

SP - 10

EP - 14

JO - Azerbaijan Astronomical Journal

JF - Azerbaijan Astronomical Journal

SN - 2078-4163

IS - 2

ER -