Variability of Galactic blue supergiants observed with TESS

Abstract

Blue supergiants (BSGs) mediate between the main sequence and the late stages of massive stars, which makes them valuable for assessing the physics that drives the stars across the diverse evolutionary channels. By exploring correlations between the parameters of BSGs and their variability properties, we aim to improve the constraints on the models of the evolved star structure and on the physics of the post-main-sequence evolution. We conducted a variability study of 41 BSGs with known spectroscopic parameters in the Galaxy using photometry from the Transiting Exoplanet Survey Satellite. We described the time domain of the stars by means of three statistical measures and extracted frequencies via iterative pre-whitening. Alongside, we investigated the stochastic low-frequency (SLF) variability, which manifests itself in all amplitude spectra. We report a positive correlation between the amplitude of variability and the stellar luminosity. For log(L/L${}_{\odot }\lesssim 5$), stars display frequencies that match the rotational one, suggesting that variability is driven by surface spots and/or features embedded in the wind. For log(L/L${}_{\odot }\gtrsim 5$), variables of the $\alpha$ Cyg class manifest themselves with their diverse and/or time-variant properties. Moreover, we report a positive correlation between the SLF variability amplitude and $T_{\mathrm{eff}}$, indicating an influential role that the stellar age plays on the emergence of the background signal beyond the main sequence. Positive, though weak, correlation is observed between the intrinsic brightness and the SLF variability amplitude, similar to the findings in the Large Magellanic Cloud, which suggests an in common excitation mechanism that depends only mildly on metallicity. Exceptionally, the $\alpha$ Cyg variables display a suppressed SLF variability that prompts to the interior changes that the evolving stars undergo.

26 pages (incl. appendices), 10 figures in the main text. The appendices include 6 figures, 4 tables. Accepted for publication in A&A

References in corpus (26)

• The Transiting Exoplanet Survey Satellite
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• A Grid of NLTE Line-Blanketed Model Atmospheres of Early B-type Stars
• Low-frequency gravity waves in blue supergiants revealed by high-precision space photometry
• The spectroscopic Hertzsprung-Russell diagram
• The spectroscopic Hertzsprung-Russell diagram of Galactic massive stars
• The impact of mass-loss on the evolution and pre-supernova properties of red supergiants
• Statistical properties of a sample of periodically variable B-type supergiants - Evidence for opacity-driven gravity-mode oscillations
• Most Detects G- and P-Modes in the B Supergiant HD 163899 (B2Ib/II)
• Variability of OB stars from TESS southern Sectors 1-13 and high-resolution IACOB and OWN spectroscopy
• Three-Dimensional Simulations of Massive Stars: I. Wave Generation and Propagation
• Photometric detection of internal gravity waves in upper main-sequence stars. II. Combined TESS photometry and high-resolution spectroscopy
• The Araucaria Project: the Local Group Galaxy WLM--Distance and metallicity from quantitative spectroscopy of blue Supergiants
• The Araucaria Project. VLT spectra of blue supergiants in WLM: classification and first abundances
• Diverse Variability of O and B Stars Revealed from 2-minute Cadence Light Curves in Sectors 1 and 2 of the TESS Mission: Selection of an Asteroseismic Sample
• Low-frequency variability in massive stars: Core generation or surface phenomenon?
• Discovery of $\beta$ Cep pulsations in the eclipsing binary V453 Cygni
• The puzzling new class of variable stars in NGC 3766 : old friend pulsators?
• New mass-loss rates of B supergiants from global wind models
• Stochastic light variations in hot stars from wind instability: Finding photometric signatures and testing against the TESS data
• Red noise and pulsations in evolved massive stars
• Revisiting the evolved hypergiants in the Magellanic Clouds
• Clumpiness: Time-domain classification of red-giant evolutionary states
• Three-Dimensional Simulations of Massive Stars: II. Age Dependence
• A Transparent Window into Early-Type Stellar Variability
• The variable stellar wind of Rigel probed at high spatial and spectral resolution