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We report on a large survey for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY - SPY).
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We report on a large survey for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (SN Ia Progenitor surveY - SPY). About 560 white dwarfs were checked for radial velocity variations until now. Ninety new DDs have been discovered, including short period systems with masses close to the Chandrasekhar mass.
The double-degenerate (DD) model, involving the merging of massive double carbon-oxygen white dwarfs (CO WDs) driven by gravitational wave radiation, is one of the classical pathways for the formation of type Ia supernovae (SNe Ia). Recently, it has been proposed that the WD+He subgiant channel has a significant contribution to the production of massive double WDs, in which the primary WD accumulates mass by accreting He-rich matter from a He subgiant. We evolved about 1800 CO WD+He star systems and obtained a large and dense grid for producing SNe Ia through the DD model. We then performed a series of binary population synthesis simulations for the DD model, in which the WD+He subgiant channel is calculated by interpolations in this grid. According to our standard model, the Galactic birthrate of SNe Ia is about 2.4*10^{-3} yr^{-1} for the WD+He subgiant channel of the DD model; the total birthrate is about 3.7*10^{-3} yr^{-1} for all channels, reproducing that of observations. Previous theoretical models still have deficit with the observed SNe Ia with delay times <1 Gyr and >8 Gyr. After considering the WD+He subgiant channel, we found that the delay time distributions is comparable with the observed results. Additionally, some recent studies proposed that the violent WD mergers are more likely to produce SNe Ia based on the DD model. We estimated that the violent mergers through the DD model may only contribute to about 16% of all SNe Ia.
Double white dwarf binaries with merger timescales smaller than the Hubble time and with a total mass near the Chandrasekhar limit (i.e. classical Chandrasekhar population) or with high-mass primaries (i.e. sub-Chandrasekhar population) are potential supernova type Ia (SNIa) progenitors. However, we have not yet unambiguously confirmed the existence of these objects observationally, a fact that has been often used to criticise the relevance of double white dwarfs for producing SNIa. We analyse whether this lack of detections is due to observational effects. To that end we simulate the double white dwarf binary population in the Galaxy and obtain synthetic spectra for the SNIa progenitors. We demonstrate that their identification, based on the detection of Halpha double-lined profiles arising from the two white dwarfs in the synthetic spectra, is extremely challenging due to their intrinsic faintness. This translates into an observational probability of finding double white dwarf SNIa progenitors in the Galaxy of (2.1+-1.0)x10^{-5} and (0.8+-0.4)x10^{-5} for the classical Chandrasekhar and the sub-Chandrasekhar progenitor populations, respectively. Eclipsing double white dwarf SNIa progenitors are found to suffer from the same observational effect. The next generation of large-aperture telescopes are expected to help in increasing the probability for detection by ~1 order of magnitude. However, it is only with forthcoming observations such as those provided by LISA that we expect to unambiguously confirm or disprove the existence of double white dwarf SNIa progenitors and to test their importance for producing SNIa.
We report on systematic radial velocity surveys for white dwarf - white dwarf binaries (double degenerates - DDs) including SPY (ESO Supernovae Ia progenitor survey) recently carried out at the VLT. A large sample of DD will allow us to put strong constrains on the phases of close binary evolution of the progenitor systems and to perform an observational test of the DD scenario for supernovae of type Ia. We explain how parameters of the binaries can be derived from various methods. Results for a sample of DDs are presented and discussed.
The origin of the progenitors of type Ia supernovae (SNe Ia) is still uncertain. The core-degenerate (CD) scenario has been proposed as an alternative way for the production of SNe Ia. In this scenario, SNe Ia are formed at the final stage of common-envelope evolution from a merger of a carbon-oxygen white dwarf (CO WD) with the CO core of an asymptotic giant branch companion. However, the birthrates of SNe Ia from this scenario are still not well determined. In this work, we performed a detailed investigation on the CD scenario based on a binary population synthesis approach. The SN Ia delay times from this scenario are basically in the range of 90Myr-2500Myr, mainly contributing to the observed SNe Ia with short and intermediate delay times although this scenario can also produce some old SNe Ia. Meanwhile, our work indicates that the Galactic birthrates of SNe Ia from this scenario are no more than 20% of total SNe Ia due to more careful treatment of mass transfer. Although the SN Ia birthrates in the present work are lower than those in Ilkov & Soker, the CD scenario cannot be ruled out as a viable mechanism for the formation of SNe Ia. Especially, SNe Ia with circumstellar material from this scenario contribute to 0.7-10% of total SNe Ia, which means that the CD scenario can reproduce the observed birthrates of SNe Ia like PTF 11kx. We also found that SNe Ia happen systemically earlier for a high value of metallicity and their birthrates increase with metallicity.
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