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P Cygni Type Stars: Evolution and Physical Processes

Published online by Cambridge University Press:  04 August 2017

Henny J. G. L. M. Lamers
Henny J. G. L. M. Lamers*
Affiliation:
Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, Colorado 80309 USA

Abstract

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The class of P Cygni Type (PCT) stars is defined and the brightest members in our galaxy, LMC, M31 and M33 are identified. They are located near the upper luminosity limit in the HRD in the range of 8500 ≤ Teff ≤ 27,000 K and −11.0 ≤ Mbol ≤ −7.8. We suggest that all PCT stars are S Dor variables, and that the reverse may also be true. The basic parameters of the PCT stars are derived and compared with those of normal supergiants: the effective gravity is a factor 3 to 10 lower, the mass loss rate is a factor 3 to 10 higher, the terminal velocity is about a factor 10 lower. This results in a wind density which is a factor 30 higher and thus produces the P Cygni lines in the visual spectrum. The history and the physical processes in the star P Cygni are discussed. The photometric variability and the shell ejections on a timescale of about a month are probably due to non-radial pulsations. The acceleration of the wind is due to radiation pressure by numerous (∼103) metal lines in the Balmer continuum. This can also explain the S Dor type of variability. The proposed mechanism will automatically lead to a P Cygni phase in the evolution of the most massive stars and to the existence of an upper limit in the HR diagram. The expected lifetime of the PCT phase is about 104 to 105 years. Some unresolved problems and recommendations for future research are discussed.

Type
Session 3. Luminous Blue Variables
Information
Symposium - International Astronomical Union , Volume 116: Luminous Stars and Associations in Galaxies , 1986 , pp. 157 - 182
Copyright
Copyright © Reidel 1986 

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