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Getting started: How a supersonic stellar wind is initiated from a hydrostatic surface

Published online by Cambridge University Press:  30 November 2022

Stan Owocki Open the ORCID record for Stan Owocki [Opens in a new window]
Stan Owocki*
Affiliation:
Department of Physics & Astronomy, Bartol Research Institute, University of Delaware, Newark, DE 19716 USA email: [email protected]
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Abstract

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Most of a star’s mass is bound in a hydrostatic equilibrium in which pressure balances gravity. But if at some near-surface layer additional outward forces overcome gravity, this can transition to a supersonic, outflowing wind, with the sonic point, where the outward force cancels gravity, marking the division between hydrostatic atmosphere and wind outflow. This talk will review general issues with such transonic initiation of a stellar wind outflow, and how this helps set the wind mass loss rate. The main discussion contrasts the flow initiation in four prominent classes of steady-state winds: (1) the pressure-driven coronal wind of the sun and other cool stars; (2) line-driven winds from OB stars; (3) a two-stage initiation model for the much denser winds from Wolf-Rayet (WR) stars; and (4) the slow “overflow” mass loss from highly evolved giant stars. A follow on discussion briefly reviews eruptive mass loss, with particular focus on the giant eruption of η Carinae.

Keywords

Sun: solar windstars: early-typestars: mass lossstars: Wolf-Rayetstars: AGB
Type
Contributed Paper
Information
Proceedings of the International Astronomical Union , Volume 16 , Symposium S366: The Origin of Outflows in Evolved Stars , November 2020 , pp. 1 - 14
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Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
© The Author(s), 2022. Published by Cambridge University Press on behalf of International Astronomical Union

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