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Although Type Ia supernovae(SNe Ia) play an important role in the study of cosmology, their progenitors are still poorly understood. Thermonuclear explosions from the helium double-detonation sub-Chandrasekhar mass model have been considered as an alternative method for producing SNe Ia. By adopting the assumption that a double detonation occurs when a He layer with a critical ignition mass accumulates on the surface of a carbon–oxygen white dwarf(CO WD), we perform detailed binary evolution calculations for the He double-detonation model, in which a He layer from a He star accumulates on a CO WD. According to these calculations, we obtain the initial parameter spaces for SNe Ia in the orbital period and secondary mass plane for various initial WD masses. We implement these results into a detailed binary population synthesis approach to calculate SN Ia birthrates and delay times. From this model,the SN Ia birthrate in our Galaxy is ~0.4- 1.6 × 10-3yr-1. This indicates that the double-detonation model only produces part of the SNe Ia. The delay times from this model are ~ 70- 710 Myr, which contribute to the young population of SNe Ia in the observations. We found that the CO WD + sdB star system CD-30 11223 could produce an SN Ia via the double-detonation model in its future evolution. 相似文献
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Roger W. Stump 《The Professional geographer》1987,39(4):438-449
This study examines the hypothesis that the determinants of denominational switching vary regionally among white American Protestants. Data for the analysis are taken from the National Opinion Research Center's General Social Survey for 1974 through 1984. Using logistic regression, the analysis compares the determinants of switching among respondents residing in the nine Census regions of the U.S. Results reveal significant regional differences in the determinants of switching, especially in the effects of conversion, childhood affiliation and interdenominational marriage. 相似文献
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D. Koester 《Astronomy and Astrophysics Review》2002,11(1):33-66
Summary. During the last decade white dwarfs have become important as tools in many areas beyond traditional stellar physics: from
the age determination of the stars in the solar neighborhood to the dating of open clusters and the distance determination
of globular clusters. They are primary candidates for the MACHO microlensing events, possibly for a stellar component of the
dark halo, and for the supernova Ia progenitors. The recent developments in these areas are reviewed, but some highlights
from more “mature” areas such as stellar parameters, mass distributions, magnetic, and pulsating white dwarfs are also summarized
briefly.
Received 5 October 2001 / Published online 11 January 2002 相似文献