Short-term variability and mass loss in Be stars II. Physical taxonomy of photometric variability observed by the Kepler spacecraft

Abstract

Context: [abbreviated] Aims: Kepler data of three known Be stars are re-visited to establish their pulsational nature and assess the properties of additional, non-pulsational variations. The three program stars turned out to be one inactive Be star, one active, continuously outbursting Be star, and one Be star transiting from a non-outbursting into an outbursting phase, thus forming an excellent sample to distill properties of Be stars in the various phases of their life-cycle. Methods: [abbreviated] Results: The short-term photometric variability of Be stars must be disentangled into a stellar and a circumstellar part. The stellar part is on the whole not different from what is seen in non-Be stars. However, some of the observed phenomena might be to be due to resonant mode coupling, a mechanism not typically considered for B-type stars. Short-term circumstellar variability comes in the form of either a group of relatively well-defined, short-lived frequencies during outbursts, which are called Štefl frequencies, and broad bumps in the power spectra, indicating aperiodic variability on a time scale similar to typical low-order $g$-mode pulsation frequencies, rather than true periodicity. Conclusions: From a stellar pulsation perspective, Be stars are rapidly rotating SPB stars, that is they pulsate in low order $g$-modes, even if the rapid rotation can project the observed frequencies into the traditional high-order $p$-mode regime above about 4 c/d. However, when a circumstellar disk is present, Be star power spectra are complicated by both cyclic, or periodic, and aperiodic circumstellar phenomena, possibly even dominating the power spectrum.

arXiv commentAccepted by Astronomy and Astrophysics

References in corpus (23)

• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• Kepler Mission Design, Realized Photometric Performance, and Early Science
• The CoRoT satellite in flight : description and performance
• Classical Be Stars: Rapidly Rotating B Stars with Viscous Keplerian Decretion Disks
• Revised Stellar Properties of Kepler Targets for the Quarter 1-16 Transit Detection Run
• Rotation and differential rotation of active Kepler stars
• Rotation periods of 12 000 main-sequence Kepler stars: Dependence on stellar spectral type and comparison with v sin i observations
• BRITE-Constellation: nanosatellites for precision photometry of bright stars
• Deep MMT Transit Survey of the Open Cluster M37 II: Variable Stars
• Kepler observations of variability in B-type stars
• A unifying explanation of complex frequency spectra of gamma Dor, SPB and Be stars: combination frequencies and highly non-sinusoidal light curves
• Dynamical Evolution of Viscous Disks around Be Stars. I: photometry
• CoRoT's view of newly discovered B-star pulsators: results for 358 candidate B pulsators from the initial run's exoplanet field data
• Short-term variability and mass loss in Be stars I. BRITE satellite photometry of $\eta$ and $\mu$ Centauri
• The Observational Signatures of Convectively Excited Internal Gravity Modes in Main Sequence Stars
• Solar-like oscillations in a massive star
• The Classificiation of Kepler B star Variables
• Impact of rotation on stochastic excitation of gravity and gravito-inertial waves in stars
• MOST detects SPBe pulsations in HD 127756 & HD 217543: Asteroseismic rotation rates independent of vsini
• Seismic modelling of the $\beta$Cep star HD\,180642 (V1449\,Aql)
• Disk-Loss and Disk-Renewal Phases in Classical Be Stars II. Contrasting with Stable and Variable Disks
• Angular momentum transport by stochastically excited oscillations in rapidly rotating massive stars
• Chaos in large-amplitude pulsators: application to the beta Cep star HD180642

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• The life cycles of Be viscous decretion discs: fundamental disc parameters of 54 SMC Be stars
• Photometric Variability of the Be Star Population
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• Short-term variability and mass loss in Be stars III. BRITE and SMEI satellite photometry of 28 Cygni
• Outbursts and Disk Variability in Be Stars
• TESS observations of Be stars: a new interpretation
• Detection of nonlinear resonances among gravity modes of slowly pulsating B stars: results from five iterative prewhitening strategies
• TESS lightcurves of gamma-Cas stars
• Short-term variability and mass loss in Be stars IV. Two groups of closely spaced, approximately equidistant frequencies in three decades of space photometry of $\nu$ Puppis (B7-8 IIIe)
• The accelerating rotation of the magnetic He-weak star HD 142990
• TESS observations of Be stars: general characteristics and the impulsive magnetic rotator model
• Short-term variability and mass loss in Be stars VI. Frequency groups in $\gamma$ Cas detected by TESS
• Let there be more variability in two gamma Cas stars
• A new look into putative duplicity and pulsations of the Be star $\beta$ CMi
• Fast time optical variability in Be/X-ray binaries. Pulsation and rotation
• A survey for variable young stars with small telescopes: VI -- Analysis of the outbursting Be stars NSW284, Gaia19eyy, and VES263
• HD 42477: coupled r modes, g modes and a p mode in an A0Vnne star
• An observer's view on the future of asteroseismology
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