The evolution of intermediate-mass protostars. II - Influence of the accretion flow

Abstract

The growth of spherical protostars that condense from diffuse interstellar clouds is considered, with emphasis on the internal structure of protostars in the intermediate-mass range 2-10 solar masses. Three evolutionary sequences, one with a previous mass accretion rate of 0.00001 solar mass/yr, and the others with 0.00003 and 0.0001 solar mass/yr. The stellar birthline constructed with M-dot of 0.00001 solar mass/yr and either set of boundary conditions shows good agreement with the observed distribution of premain-sequence stars in the H-R diagram. It is proposed that all stars with less than about 10 solar masses form with an accretion rate of this order of magnitude, and from molecular cloud cores with similar density and temperature structures. It is speculated that high-mass stars, i.e., those with no visible premain-sequence phase, form with accretion rates no larger than about 0.0001 solar mass/yr.