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Title: Pulsations and outbursts of luminous blue variables

Abstract

We propose an outburst mechanism for the most luminous stars in our and other galaxies. These million solar luminosity stars, with masses (after earlier mass loss) of between 20 and maybe 70 solar masses, are pulsationally unstable for both radial and low-degree nonradial modes. Some of these modes are ``strange,`` meaning mostly that the pulsations are concentrated near the stellar surface and have very rapid growth rates in linear theory. The pulsation driving is by both the high iron line opacity (near 150,000 K) and the helium opacity (near 30,000 K) kappa effects. Periods range from 5 to 40 days. Depending on the composition, pulsations periodically produce luminosities above the Eddington limit for deep layers. The radiative luminosity creates an outward push that readily eases the very low gamma envelope to very large outburst radii. A key point is that a super-Eddington luminosity cannot be taken up by the sluggish convection rapidly enough to prevent an outward acceleration of much of the envelope. As the helium abundance in the envelope stellar material increases by ordinary wind mass loss and the luminous blue variable outbursts, the opacity in the deep pulsation driving layers decreases. This makes the current Eddington luminosity evenmore » higher so that pulsations can then no longer give radiative luminosities exceeding the limit. For the lower mass and luminosity luminous blue variables there is considerably less iron line opacity driving, and pulsations are almost all caused by the helium ionization kappa effect.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Assistant Secretary for Management and Administration, Washington, DC (United States)
OSTI Identifier:
626048
Report Number(s):
LA-UR-97-4190; CONF-9706195-
ON: DE98002651; TRN: AD-a340 003
DOE Contract Number:  
W-7405-ENG-36
Resource Type:
Conference
Resource Relation:
Conference: Workshop: a half century of stellar pulsation interpretations - a tribute to Arthur N. Cox, Los Alamos, NM (United States), 16-20 Jun 1997; Other Information: PBD: Jun 1997
Country of Publication:
United States
Language:
English
Subject:
66 PHYSICS; MASS; IRON; IONIZATION; HELIUM; OPACITY; LUMINOSITY; VARIABLE STARS; BLUE STELLAR OBJECTS; EDDINGTON THEORY; STAR EVOLUTION; PULSATING VARIABLE STARS

Citation Formats

Cox, A N, Guzik, J A, Soukup, M S, and Despain, K M. Pulsations and outbursts of luminous blue variables. United States: N. p., 1997. Web.
Cox, A N, Guzik, J A, Soukup, M S, & Despain, K M. Pulsations and outbursts of luminous blue variables. United States.
Cox, A N, Guzik, J A, Soukup, M S, and Despain, K M. 1997. "Pulsations and outbursts of luminous blue variables". United States. https://www.osti.gov/servlets/purl/626048.
@article{osti_626048,
title = {Pulsations and outbursts of luminous blue variables},
author = {Cox, A N and Guzik, J A and Soukup, M S and Despain, K M},
abstractNote = {We propose an outburst mechanism for the most luminous stars in our and other galaxies. These million solar luminosity stars, with masses (after earlier mass loss) of between 20 and maybe 70 solar masses, are pulsationally unstable for both radial and low-degree nonradial modes. Some of these modes are ``strange,`` meaning mostly that the pulsations are concentrated near the stellar surface and have very rapid growth rates in linear theory. The pulsation driving is by both the high iron line opacity (near 150,000 K) and the helium opacity (near 30,000 K) kappa effects. Periods range from 5 to 40 days. Depending on the composition, pulsations periodically produce luminosities above the Eddington limit for deep layers. The radiative luminosity creates an outward push that readily eases the very low gamma envelope to very large outburst radii. A key point is that a super-Eddington luminosity cannot be taken up by the sluggish convection rapidly enough to prevent an outward acceleration of much of the envelope. As the helium abundance in the envelope stellar material increases by ordinary wind mass loss and the luminous blue variable outbursts, the opacity in the deep pulsation driving layers decreases. This makes the current Eddington luminosity even higher so that pulsations can then no longer give radiative luminosities exceeding the limit. For the lower mass and luminosity luminous blue variables there is considerably less iron line opacity driving, and pulsations are almost all caused by the helium ionization kappa effect.},
doi = {},
url = {https://www.osti.gov/biblio/626048}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Jun 01 00:00:00 EDT 1997},
month = {Sun Jun 01 00:00:00 EDT 1997}
}

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