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Title: On the behaviour of stellar winds that exceed the photon-tiring limit
Authors: van Marle, Allard Jan ×
Owocki, Stanley
Shaviv, Nir #
Issue Date: Apr-2009
Publisher: Priestley and Weale
Series Title: Monthly Notices of the Royal Astronomical Society vol:394 issue:2 pages:595-604
Article number: 10.1111/j.1365-2966.2008.14366.x
Abstract: Stars can produce steady-state winds through radiative driving as long as the mechanical
luminosity of the wind does not exceed the radiative luminosity at its base. This upper bound
on the mass-loss rate is known as the photon-tiring limit. Once above this limit, the radiation
field is unable to lift all the material out of the gravitational potential of the star, such that only
part of it can escape and reach infinity. The rest stalls and falls back towards the stellar surface,
making a steady-statewind impossible. Photon-tiring is not an issue for line-driven winds since
they cannot achieve sufficiently high mass-loss rates. It can, however, become important if
the star exceeds the Eddington limit and continuum interaction becomes the dominant driving
mechanism.
This paper investigates the time-dependent behaviour of stellar winds that exceed the photontiring
limit, using one-dimensional numerical simulations of a porosity-moderated, continuumdriven
stellar wind. We find that the regions close to the star show a hierarchical pattern of
high-density shells moving back and forth, unable to escape the gravitational potential of the
star. At larger distances, the flow eventually becomes uniformly outward, though still quite
variable. Typically, these winds have a very high density but a terminal flow speed well below
the escape speed at the stellar surface. Since most of the radiative luminosity of the star is
used to drive the stellar wind, such stars would appear much dimmer than expected from the
super-Eddington energy generation at their core. The visible luminosity typically constitutes
less than half of the total energy flow and can become as low as 10 per cent or less for those
stars that exceed the photon-tiring limit by a large margin.
ISSN: 0035-8711
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Plasma-astrophysics Section
× corresponding author
# (joint) last author

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