On Stellar Models with Double Energy-Sources

Minoru Nishida
1960 Progress of theoretical physics  
To investigate the characteristics of stellar models having double energy-sources, three sample models (M=1.2Me.) consisting of the following regions were constructed using the newest rate of the eN-cycle: (1) hydrogen-rich envelope, (2) radiative helium region and (3) convective helium core. A model for which the mass fraction of the helium regions is 0.6 shifts towards the left of the RR Lyrae gap in the HR-diagram from the red giant region, in which the corresponding model of Hoyle and
more » ... of Hoyle and Schwarzschild lies. This result shows that the properties of such models are very sensitive to the rates of both the hydrogen-and helium-burning. § 1. Introduction Calculations have been made by Morton l ) on the effect on the main sequence of transfer of control of the CN-cycle from N 14 (p, r) 0 15 to C 12 (p, r) N 13 • His results indicate a sideward shift of the main sequence on the mass-luminosity diagram. This shift would be of the order of the observational spread in the width of the main sequence, and he has concluded that the absence of such a shift is an evidence for the absence of a level in the critical region of 0 15 just above 7.30 Mev. Recently, Hebbard and Povh 2 )** have found a new level of 0 15 with an excitation energy of 7.17 Mev, hence it is established that the N 14 (p, r) 0 15 reaction is off-resonant at stellar energies. A few years ago, several authors 3 -4 ) investigated the structure of population II stars in the helium-burning phase. Their results showed that the horizontal branch in the HR-diagram of the globular clusters corresponds to the stars in this phase. In their calculation, however, they used the old rate of the CN-cycle which was the most reasonable at that time and which was one hundred times larger than the newest correct value. On the other hand, it has been shown by Hayashi et al. 5 ) that in the case of massive stars the properties of the stellar models with double energy-sources are very sensitive to the rates of both the hydrogen-and helium-burning. One may expect that such a tendency will appear also in the case of population II stars at the helium-burning stage. The purpose of this paper is to reconstruct the models in the helium-burning phase by using the newest rate of the eN-cycle.
doi:10.1143/ptp.23.896 fatcat:rfkcd6eitrarxhdklj2xec23ky