Short-term variability and mass loss in Be stars V. Space photometry and ground-based spectroscopy of $\gamma$ Cas

Abstract

Context. Be stars are physically complex systems that continue to challenge theory to understand their rapid rotation, complex variability and decretion disks. $\gamma$ Cassiopeiae ($\gamma$ Cas) is one such star but is even more curious because of its unexplained hard thermal X-ray emission. Aims. We aim to examine the optical variability of $\gamma$ Cas and thereby to shed more light on its puzzling behaviour. Methods. Three hundred twenty-one archival H$\alpha$ spectra from 2006 to 2017 are analysed to search for frequencies corresponding to the 203.5 day orbit of the companion. Space photometry from the SMEI satellite from 2003 to 2011 and the BRITE-Constellation of nano-satellites between 2015 and 2019 is investigated in the period range from a couple of hours to a few days. Results. The orbital period of the companion of 203.5 days is confirmed with independent measurements from the structure of the H$\alpha$ line emission. A strong blue/red asymmetry in the amplitude distribution across the H$\alpha$ emission line could hint at a spiral structure in the decretion disk. With the space photometry, the known frequency of 0.82 d${}^{-1}$ is confirmed in data from the early 2000s. A higher frequency of 2.48 d${}^{-1}$ is present in the data from 2015 to 2019 and possibly also in the early 2000s. A third frequency at 1.25 d${}^{-1}$ is proposed to exist in both SMEI and BRITE data. The only explanation covering all three rapid variations seems to be nonradial pulsation. The two higher frequencies are incompatible with rotation.

arXiv comment13 pages, 12 figures. Accepted for publication in A&A

References in corpus (32)

• The SIMBAD astronomical database
• Mass loss from hot massive stars
• Classical Be Stars: Rapidly Rotating B Stars with Viscous Keplerian Decretion Disks
• The rotation rates of massive stars: the role of binary interaction through tides, mass transfer and mergers
• Enhanced Angular Momentum Transport in Accretion Disks
• X-Ray Spectroscopy of Stars
• Effects of gravitational darkening on the determination of fundamental parameters in fast rotating B-type stars
• BRITE-Constellation: nanosatellites for precision photometry of bright stars
• Evolution towards the critical limit and the origin of Be stars
• Viscous Effects on the Interaction between the Coplanar Decretion Disc and the Neutron Star in Be/X-Ray Binaries
• FM stars: A Fourier view of pulsating binary stars, a new technique for measuring radial velocities photometrically
• Mass and angular momentum loss via decretion disks
• Populations of rotating stars II. Rapid rotators and their link to Be-type stars
• CoRoT's view of newly discovered B-star pulsators: results for 358 candidate B pulsators from the initial run's exoplanet field data
• The life cycles of Be viscous decretion discs: fundamental disc parameters of 54 SMC Be stars
• An asteroseismic study of the O9V star HD 46202 from CoRoT space-based photometry
• The first determination of the viscosity parameter in the circumstellar disk of a Be Star
• Photometric Variability of the Be Star Population
• The BRITE Constellation nanosatellite mission: Testing, commissioning and operations
• First spectro-interferometric survey of Be stars I. Observations and constraints on the disks geometry and kinematics
• Be discs in binary systems I. Coplanar orbits
• Hot stars observed by XMM-Newton II. A survey of Oe and Be stars
• The life cycles of Be viscous decretion discs: The case of ω CMa
• gamma Cas stars: Normal Be stars with disks impacted by the wind of a helium-star companion?
• BRITE-Constellation: Data processing and photometry
• Be discs in coplanar circular binaries: Phase-locked variations of emission lines
• Short-term variability and mass loss in Be stars III. BRITE and SMEI satellite photometry of 28 Cygni
• Rotational and Cyclical Variability in gamma Cassiopeia
• Rotational and Cyclical Variability in gamma Cassiopeiae. II. Fifteen Seasons
• An investigation of the photometric variability of confirmed and candidate Galactic Be stars using ASAS-3 data
• Variations of the amplitudes of oscillation of the Be star Achernar
• Ultraviolet Activity as indicator of Small-scale Magnetic Fields in gamma Cassiopeiae

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• V1294 Aql = HD 184279: A bad boy among Be stars or an important clue to the Be phenomenon?
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