High-Luminosity, Fully Convective Contracting Sun. II
1962; Institute of Physics; Volume: 67; Linguagem: Inglês
10.1086/108834
ISSN1538-3881
Autores Tópico(s)Astronomy and Astrophysical Research
ResumoModels described in the accompanying paper (p. 575) have many interesting properties. For R/R > 57, the absolute value of the gravitational potential energy is less than the sum of the thermal, ionization, and dissociation energies of the material. Hence such models are purely formal and would be in the region of instability against gravitational collapse. Deuterium burning was not taken explicitly into account, but it would occur at approximately R/R = 10. If the primitive sun had the terrestrial ratio of deuterium to hydrogen, then with L;L 28 the contraction would be halted for only about 3 X 10 yr. During the further contraction the bottom of the outer convection zone goes through a temperature maximum of 3.5 X 1060K. This would lead to considerable depletion of lithium throughout the sun. The Helmholtz-Kelvin contraction time from R/R0 -57 to R$R -1.7 is only 106 yr (not including deuterium burning). The sun should reach the main sequence in about 2 x 100 yr. These results were calculated for the convective mixing length equal to the pressure scale height. It is probable that the mixing length should be greater than this, and in such a case we find the luminosity to be increased. Hence these contraction times are probably upper limits. From these results it is clear that we must expect the high-luminosity stages of the contraction to have a considerable influence on conditions in a primitive solar nebula from which planets have presumably condensed, but the sun may well have reached the main sequence long before the development of the planets was completed.
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