Evolution and the period-luminosity relation for red supergiants in the Magellanic Clouds

Abstract

Excitation of radial pulsations in red supergiants of Magellanic Clouds is investigated using the stellar evolution calculations and the self-consistent solution of the equations of radiation hydrodynamics and turbulent convection. The stars with initial masses 6M_odot<=M_zams<=28 M_odot and the initial chemical composition X=0.7, 0.004<=Z<=0.008 are shown to be unstable against fundamental mode oscillations with periods from 17 to 1200 days as they become helium burning red supergiants. The period-luminosity relation slightly depends on the mass loss rate varying with a factor of three, whereas its dependence on the metal abundance is delta M_bol=0.89 delta log Z. In comparison with galactic red supergiants (Z=0.02) the low metal abundances in red supergiants of Magellanic Clouds are responsible for their higher effective temperatures and substantially narrower ranges of evolutionary stellar radius change during helium burning. Therefore on the period-mass diagram the red supergiants of Magellanic Clouds are located within the strip with width of delta log M = 0.09, so that the uncertainty of mass evaluation of the red supergiant with the known pulsational period is nearly 25%.