Wind properties of variable B supergiants. Evidence of pulsations connected with mass-loss episodes

Abstract

Variable B supergiants (BSGs) constitute a heterogeneous group of stars with complex photometric and spectroscopic behaviours. They exhibit mass-loss variations and experience different types of oscillation modes, and there is growing evidence that variable stellar winds and photospheric pulsations are closely related. To discuss the wind properties and variability of evolved B-type stars, we derive new stellar and wind parameters for a sample of 19 Galactic BSGs by fitting theoretical line profiles of H, He, and Si to the observed ones and compare them with previous determinations. The mass-loss rate of three stars has been obtained for the first time. All stars follow the known empirical wind momentum-luminosity relationships, and the late BSGs show the trend of the mid BSGs. We find an empirical relationship that associates the amplitude of mass-loss variations with photometric/spectroscopic variability on timescales of tens of days. We find that stars located on the cool side of the bi-stability jump show a decrease in the terminal and escape velocities ratio, while their corresponding mass-loss rates are similar to or lower than the values found for stars on the hot side. Particularly, for those variable stars a decrease in the terminal and escape velocities ratio is accompanied by a decrease in the mass-loss rate. Our results also suggest that radial pulsation modes with periods longer than 6 days might be responsible for the wind variability in the mid/late-type BSGs. These radial modes might be identified with strange modes, which are known to facilitate (enhanced) mass loss. On the other hand, we propose that the wind behaviour of stars on the cool side of the bi-stability jump could fit with predictions of the delta-slow hydrodynamics solution for radiation-driven winds with highly variable ionization.

References in corpus (8)

• Mass loss from hot massive stars
• Effects of gravitational darkening on the determination of fundamental parameters in fast rotating B-type stars
• Estimating distances from parallaxes. III. Distances of two million stars in the Gaia DR1 catalogue
• Quantitative studies of the optical and UV spectra of Galactic early B supergiants I. Fundamental parameters
• Most Detects G- and P-Modes in the B Supergiant HD 163899 (B2Ib/II)
• Nitrogen enrichment, boron depletion and magnetic fields in slowly-rotating B-type dwarfs
• The IACOB project: IV. New predictions for high-degree non-radial mode instability domains in massive stars and connection with macroturbulent broadening
• The variable stellar wind of Rigel probed at high spatial and spectral resolution

Cited by in corpus (4)

• Theoretical wind clumping predictions of OB supergiants from line-driven instability simulations across the bi-stability jump
• Stochastic light variations in hot stars from wind instability: Finding photometric signatures and testing against the TESS data
• High-resolution spectroscopy of the high velocity hot post-AGB star IRAS 18379-1707 (LS 5112)
• GG Carinae: Discovery of orbital phase dependent 1.583-day periodicities in the B[e] supergiant binary