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Variable Winds in Early-B Hypergiants

Published online by Cambridge University Press:  12 April 2016

Bernhard Wolf  and
Thomas Rivinius
Bernhard Wolf
Affiliation:
Landessternwarte Königstuhl, D-69117 Heidelberg, Germany
Thomas Rivinius
Affiliation:
Landessternwarte Königstuhl, D-69117 Heidelberg, Germany

Abstract

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Early-B hypergiants belong to the most luminous stars in the Universe. They are characterized by high mass-loss rates (Ṁ ≈ 10−5Mʘyr−1) and low terminal wind velocities (v∞ʘ400 kms−1) implying very dense winds. They represent a short-lived evolutionary phase and are of particular interest for evolutionary theories of massive stars with mass loss. Due to their high luminosity they play a key role in connection with the “wind momentum - luminosity relation”. Among the main interesting characteristics of early-B hypergiants are the various kinds of photometric and spectroscopic variations. In several recent campaigns our group has performed extensive high dispersion spectroscopy of galactic early-B hypergiants with our fiber-fed echelle spectrograph FLASH/HEROS at the ESO-50 cm telescope. The main outcome was that their dense winds behave hydrodynamically differently to the less luminous supergiants of comparable spectral type. Outwardly accelerated propagating discrete absorption components of the P Cyg-type lines are the typical features rather than rotationally modulated line profile variations. These discrete absorptions could be traced in different spectral lines from photospheric velocities up to 75% of the terminal velocity. The stellar absorption lines show a pulsation-like radial velocity variability pattern lasting up to two weeks as the typical time scale. The radius variations connected with this pulsation-like motions are correlated with the emission height of the P Cyg-type profiles.

Type
Section III Variable Winds
Information
International Astronomical Union Colloquium , Volume 169: Variable and Non-spherical Stellar Winds in Luminous Hot Stars , 1999 , pp. 222 - 229
Copyright
Copyright © Springer-Verlag 1999

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