Mathematics – Logic
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011acasn..52...89w&link_type=abstract
Acta Astronomica Sinica, vol. 52, no.1, p. 89-90
Mathematics
Logic
Binaries: Close, Stars: Evolution, Supernovae: General, White Dwarfs
Scientific paper
Type Ia supernovae (SNe Ia) are good cosmological distance indicators due to their high luminosities and remarkable uniformity, and thus are used for determining cosmological parameters. However, several key issues related to the nature of their progenitor systems are still not well understood. In this thesis, the progenitors of SNe Ia and the related objects are systematically investigated. Some main results are obtained as follows: (1) Recent observations implicate that about half of SNe Ia explode soon after starburst, with delay times less than 100 Myr, but previous models do not predict the young populations of SNe Ia. The WD + He model is proposed to solve this mystery. In this model, a carbon-oxygen WD (CO WD) accretes material from a He main sequence (MS) star or a He subgiant to increase its mass to the Chandrasekhar mass limit. It is found that this scenario can explain SNe Ia with short delay times (<100 Myr). (2) The progenitor model of SNe Ia with long delay times is systematically studied. It is found that SNe Ia from the WD + MS and WD + RG channels can contribute to the old populations (>1 Gyr) of SNe Ia, in which the WD + MS channel may be the main contributor. (3) It is found that the Galactic SN Ia birthrate from the double-degenerate (DD) model is close to those inferred from observations, while the birthrate from the single-degenerate (SD) model (including the contribution from the WD + MS, WD + RG and WD+He star channels) accounts for only about 1/2~2/3 of the observations. In these SD models, the WD + He star channel produces 14% of all SNe Ia, which constitutes the weak bimodality suggested by recent observations. (4) The companions in these SD models would survive after SN explosion. However, there has been no conclusive proof yet that any individual object is the surviving companion of a SN Ia. We show the distributions of many properties of the surviving companion stars of these SD models at the moment of SN explosion in the Galaxy. The properties can be verified by future observations. (5) Hypervelocity stars (HVSs) belong to one type of mysterious objects and their formation is still unclear. The surviving companions from the WD + He star channel have high spatial velocities (>400 km/s) after SN explosion, which could be an alternative origin for HVSs, especially for HVSs such as US 708. (6) The existence of a population of single low-mass WDs (LMWDs) (<0.45 M&sun;) is supported by some observations at present. However, its formation is still a puzzle. It is found that the surviving companions of the old SNe Ia have low masses, which could explain the formation of the population of single LMWDs.
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