Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1972
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1972ap%26ss..15..353b&link_type=abstract
Astrophysics and Space Science, Volume 15, Issue 3, pp.353-374
Astronomy and Astrophysics
Astrophysics
47
Scientific paper
The evolution of massive stars is investigated in the phases of hydrogen and helium burning, taking into account the mass-loss due to light pressure in optically thick media. The evolution in the stage of hydrogen burning near the Main Sequence occurs without mass loss. The large inverse density gradient appears in the outer layers of a 30 M&sun; star after it goes into the domain of red super-giants in the helium-burning stage. This effect appears as a consequence of an excess of luminosity of the star the ciritical one in sufficiently extensive outer layer, where convection is not so effective. In this way, the conditions for outflow of matter are formed. The sequence of selfconsistent models is constructed, with the core in hydrostatic equilibrium and hydrodynamically outflowing envelope. The amount of mass loss is not a given parameter, but it is found during the calculations as a characteristic number of the problem. The amount of mass loss is very high, of the order of ≈0.5M &sun; yr, the velocity of the flow is ≈20 km s-1. The star loses about 7.2M &sun; during 15 yr. The amount of mass loss must rapidly decrease or finish altogether when matter near the hydrogen-burning layer begins to flow out, and a transformation of stellar structure must occur. The evolution of a 9M &sun; star is calculated. The density in the envelope of this star is sufficiently large and the outer convective zone, which develops on the red giant stage, prevents the outflow of matter. The intensive mass outflow from such star can take place at the carbon burning, or heavier element burning stages. The formation of infrared stars and Wolf-Rayet stars can be possibly explained by such a mechanism of mass loss, so that the infrared stage must precede the Wolf-Rayet stage.
Bisnovatyi-Kogan Gennadi S.
Nadyozhin D. K.
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