Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apjs...95..517b&link_type=abstract
Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 95, no. 2, p. 517-534
Astronomy and Astrophysics
Astrophysics
72
Massive Stars, Pre-Main Sequence Stars, Star Formation, Stellar Mass Accretion, Stellar Models, Hertzsprung-Russell Diagram, Mathematical Models, Opacity, Stellar Interiors, Stellar Mass, Stellar Oscillations
Scientific paper
Pre-main sequence evolutionary tracks of massive stars have been calculated under the canonical theory and the mass accretion paradigm. The canonical tracks for 15, 20, 25, 30, 45, and 60 solar mass stars have been calculated with both Cox-Stewart (1970) and the Rogers & Iglesias (1992a, b) opacities. Stellar models less massive than about 30 solar mass develop cores only during the onset of central hydrogen burning. Because of the increasing importance of radiation pressure, stars more massive than 30 solar mass develop convective cores before the onset of hydrogen burning. A generalized Naur-Osterbrock (1953) criterion has been used to understand the development of the convective core. It is estimated that stars more massive than approximately = 95 solar mass evolving canonically to the main sequence will have a convective core throughout the whole pre-main-sequence phase. The canonical 30 solar mass model has been evolved through the main-sequence phase using the mass-loss algorithm of de Jager, Nieuwenhuijzen, & van de Hucht (1988). The pre-main-sequence evolution has also been calculated under the accretion paradigm: beginning with a collapsed core, mass was accreted until a final stellar mass was reached. The accretion sequence was calculated up to the final mass of 45 solar mass. The locus where massive stars first become optically visible, the upper stellar birth line, was determined from these models. It is pointed out that the upper mass limit of stable stars must be determined by the formation environment of the star rather than the onset of nuclearly energized pulsation instability, since the increasingly large chemical inhomogeneity that develops as a massive star accretes matter evolving along the upper stellar birth line will stabilize nuclearly driven pulsations.
Beech Martin
Mitalas R.
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