Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003astl...29..522f&link_type=abstract
Astronomy Letters, vol. 29, p. 522-529 (2003)
Astronomy and Astrophysics
Astronomy
7
Scientific paper
We present the results of our hydrodynamic calculations of radial pulsations in helium stars with masses 1 M_solar < M < 10 M_solar, luminosity-to-mass ratios 1 x 10^3 L_solar/M_solar < L/M < 2 x 10^4 L_solar/M_solar, and effective temperatures 2 x 10^4 K < T_eff < 10^5 K for mass fractions of helium Y=0.98 and heavy elements Z=0.02. We show that the lower boundary of the pulsation-instability region corresponds to L/M ~ 10^3 L_solar/M_solar and that the instability region for L/M < 5 x 10^3 L_solar/M_solar is bounded by effective temperatures T_eff < 3 x 10^4 K. As the luminosity rises, the instability boundary moves into the left part of the Hertzsprung-Russell diagram and radial pulsations can arise in stars with effective temperatures T_eff < 10^5 K at L/M > 7 x 10^3 L_solar/M_solar. The velocity amplitude for the outer boundary of the hydrodynamic model increases with L/M and lies within the range 200 < Delta U < 700 km/s for the models under consideration. The periodic shock waves that accompany radial pulsations cause a significant change of the gas-density distribution in the stellar atmosphere, which is described by a dynamic scale height comparable to the stellar radius. The dynamic instability boundary that corresponds to the separation of the outer stellar atmospheric layers at a superparabolic velocity is roughly determined by a luminosity-to-mass ratio L/M ~ 3 x 10^4 L_solar/M_solar.
Fadeyev Yu A.
Novikova M. F.
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