大样本恒星演化研究组知识库

Context. Type lax supernovae (SNe lax) are proposed as one new sub-class of SNe Ia since they present sufficiently distinct observational properties from the bulk of SNe Ia. Observationally, SNe lax have been estimated to account for similar to 5%-30% of the total SN Ia rate, and most SNe lax have been discovered in late-type galaxies. In addition, observations constrain the progenitor systems of some SN Iax progenitors that have ages of <80 Myr. Although the identity of the progenitors of SNe lax is unclear, the weak deflagration explosions of Chandrasekhar-mass (Ch-mass) carbon/oxygen white dwarfs (C/O WDs) seem to provide a viable physical scenario. Aims. Comparing theoretical predictions from binary population synthesis (BPS) calculations with observations of SNe lax, we put constraints on the single-degenerate (SD) Ch-mass model as a possible SN lax progenitor. Methods. Based on the SD Ch-mass model, the SN rates and delay times are predicted by combining binary evolution calculations for the progenitor systems into a BPS model. Moreover, with current X-ray observations of SNe lax, we constrain the pre-explosion mass-loss rates of stellar progenitor systems by using two analytic models. Results. From our calculations, the long delay times of greater than or similar to 3 Gyr and low SN rates of similar to 3 x 10(-5) yr(-1) are found in the red-gaint donor channel, indicating that this channel is unlikely to produce SNe lax. With our standard models, we predict that the Galactic SN lax rate from the main-sequence (helium-star) donor scenario is similar to 1.5 x 10(-3) yr-1 (similar to 3 x 10(-4) yr(-1)). The total rate of these two models is consistent with the observed SN lax rate. The short delay times in the helium-star donor channel (<100 Myr) support the young host environments of SNe lax. However, the relatively long delay times in the main-sequence donor channel (similar to 250 Myr-1 Gyr) are less favourable for the observational constraints on the ages of SN Iax progenitors. Finally, with current X-ray observations for SNe lax, we set an upper limit on the pre-SN mass-loss rate at M less than or similar to a few x 10(-4) M-circle dot yr(-1) (for a wind velocity of v(omega) = 100 km s(-1)). Conclusions. The delay times in the SD Ch-mass model do not account for a significant number of SNe lax being located in late-type, star-forming galaxies. However, at least one SN Iax event (SN 2008ge) is hosted by an SO galaxy with no signs of star formation. Current X-ray observations for SNe lax cannot rule out the SD Ch-mass model. Taking all these into account and considering the uncertainty of the observed rate for SN Iax events, we suggest that some SNe lax may be produced from weak deflagrations of Ch-mass C/O WDs in SD progenitor systems, especially in the helium-star donor channel. This is consistent with recent analysis of HST observations, which suggests that the SN Iax SN2012Z had a progenitor system which contained a helium-star companion. However, this SD deflagration model is still unlikely to be the most common progenitor scenario for SNe lax.