Accretes Hydrogen-rich Material Research Articles

A SUPER-EDDINGTON WIND SCENARIO FOR THE PROGENITORS OF TYPE Ia SUPERNOVAE

The accretion of hydrogen-rich material onto carbon-oxygen white dwarfs (CO WDs) is crucial for understanding type Ia supernova (SN Ia) from the single-degenerate model, but this process has not been well understood due to the numerical difficulties in treating H and He flashes during the accretion. For the CO WD masses from 0.5 to $1.378\,{M}_\odot$ and accretion rates in the range from $10^{-8}$ to $10^{-5}\,{M}_\odot\,\mbox{yr}^{-1}$, we simulated the accretion of solar-composition material onto CO WDs using the state-of-the-art stellar evolution code of {\sc MESA}. For comparison with the steady-state models (e.g \citet{nskh07}), we firstly ignored the contribution from nuclear burning to the luminosity when determining the Eddington accretion rate and found that the properties of H burning in our accreting CO WD models are similar to those from the steady-state models, except that the critical accretion rates at which the WDs turn into red giants or H-shell flashes occur on their surfaces are slightly higher than those from the steady-state models. However, the super-Eddington wind is triggered at much lower accretion rates, than previously thought, when the contribution of nuclear burning to the total luminosity is included. This super-Eddington wind naturally prevents the CO WDs with high accretion rates from becoming red giants, thus presenting an alternative to the optically thick wind proposed by \cite{hkn96}. Furthermore, the super-Eddington wind works in low-metallicity environments, which may explain SNe Ia observed at high redshifts.

WD+MS Systems as Progenitors of Type Ia Supernovae with Different Metallicities

Abstract The single-degenerate model for the progenitors of type Ia supernovae (SNe Ia) is one of the two most popular models, in which a carbon–oxygen white dwarf accretes hydrogen-rich material from its companion, increases its mass to the Chandrasekhar mass limit, and then explodes as a SN Ia. Incorporating the prescription of Hachisu et al. (1999a, ApJ, 519, 314) for the accretion efficiency into Eggleton’s stellar evolution code and assuming that the prescription is valid for all metallicities, we carried out a detailed binary evolution study with different metallicities. We showed the initial and final parameter space for SNe Ia in a (log$ P$–$M_{\rm 2}$) plane. The positions of some famous recurrent novae in the (log$ P$–$M_{2}$) plane, as well as a supersoft X-ray source (SSS), RX J0513.9$-$6951 are well explained by our model, and our model can also explain the space velocity and mass of Tycho G, which is now suggested to be a companion star of Tycho’s supernova. Our study indicates that a SSS, V Sge, is a potential progenitor of supernovae, like SN 2002ic, if the delayed dynamical-instability model in Han and Podsiadlowski (2006, MNRAS, 368, 1095) is appropriate.

WD+MS systems as the progenitor of SNe Ia

The single-degenerate (SD) channel for the progenitors of type Ia supernovae (SNe Ia) is one of the most popular channels, in which a carbon–oxygen white dwarf (CO WD) accretes hydrogen-rich material from its companion, increases its mass to the Chandrasekhar mass limit, and then explodes as a SN Ia. We show the initial and final parameter space for SNe Ia in a ( $\log P^{\mathrm{i}},M_{2}^{\mathrm{i}}$ ) plane and find that the positions of some famous recurrent novae, as well as a supersoft X-ray source (SSS), RX J0513.9-6951, are well explained by our model. The model can also explain the space velocity and mass of Tycho G, which is now suggested to be the companion star of Tycho’s supernova. Our study indicates that the SSS, V Sge, might be the potential progenitor of supernovae like SN 2002ic if the delayed dynamical-instability model due to Han and Podsiadlowski (Mon. Not. R. Astron. Soc. 368:1095, 2006) is appropriate. Following the work of Meng et al. (Mon. Not. R. Astron. Soc. 395:2103, 2009a), we found that the SD model (WD+MS) with an optically thick wind can explain the birth rate of supernovae like SN 2006X and reproduce the distribution of the color excess of SNe Ia. The model also predicts that at least 75% of all SNe Ia may show a polarization signal in their spectra.

Color excesses of type Ia supernovae from the single-degenerate channel model

The single degenerate model is the most widely accepted progenitor model of type Ia supernovae (SNe Ia), in which a carbon-oxygen white dwarf (CO WD) accretes hydrogen-rich material from a main sequence or a slightly evolved star (WD+MS) to increase its mass, and explodes when its mass approaches the Chandrasekhar mass limit. During the mass transfer phase between the two components, an optically thick wind may occur and the material lost as wind may exist as circumstellar material (CSM). Searching for the CSM around a progenitor star is helpful for discriminating different progenitor models of SNe Ia. In addition, the CSM is a source of color excess. The purpose of this paper is to study the color excess produced from the single-degenerate progenitor model with an optically thick wind, and reproduce the distribution of color excesses of SNe Ia. Meng et al. systemically carried out binary evolution calculations of the WD +MS systems for various metallicities and showed the parameters of the systems before Roche lobe overflow and at the moment of supernova explosion in Meng & Yang. With the results of Meng et al., we calculate the color excesses of SNe Ia at maximum light via a simple analytic method. We reproduce the distribution of color excesses of SNe Ia by our binary population synthesis approach if the velocity of the optically thick wind is taken to be an order of magnitude of 10 km s−1. However, if the wind velocity is larger than 100 km s−1, the reproduction is bad.

A single-degenerate channel for the progenitors of Type Ia supernovae with different metallicities

A single-degenerate channel for the progenitors of Type Ia supernovae (SNe Ia) is currently accepted, in which a carbon-oxygen white dwarf (CO WD) accretes hydrogen-rich material from its companion, increases its mass to the Chandrasekhar mass limit and then explodes as a SN Ia. Incorporating the prescription of Hachisu et al. for the accretion efficiency into Eggleton's stellar evolution code, and assuming that the prescription is valid for all metallicities, we performed binary stellar evolution calculations for more than 25 000 close WD binaries with metallicities Z = 0.06, 0.05, 0.04, 0.03, 0.02, 0.01, 0.004, 0.001, 0.0003 and 0.0001. For our calculations, the companions are assumed to be unevolved or slightly evolved stars (WD + MS). As a result, the initial parameter spaces for SNe Ia at various Z are presented in the orbital period-secondary mass (log P(i), M(2)(i)) plane. Our study shows that both the initial mass of the secondary and the initial orbital period increase with metallicity. Thus, the minimum mass of the CO WD for SNe Ia decreases with metallicity Z. The difference in the minimum mass may be as large as 0.24M(circle dot) for different Z. Adopting the results above, we studied the birth rate of SNe Ia for various Z via a binary population synthesis approach. If a single starburst is assumed, SNe Ia occur systemically earlier and the peak value of the birth rate is larger for a high Z. The Galactic birth rate from the WD + MS channel is lower than ( but comparable to) that inferred from observations. Our study indicates that supernovae like SN2002ic will not occur in extremely low-metallicity environments, if the delayed dynamical-instability model is appropriate.

The single degenerate channel for the progenitors of Type Ia supernovae

AbstractWe have carried out a detailed study of the single-degenerate channel for the progenitors of type Ia supernovae (SNe Ia). In the model, a carbon-oxygen white dwarf (CO WD) accretes hydrogen-rich material from an unevolved or a slightly evolved non-degenerate companion to increase its mass to Chandrasekhar mass limit. Incorporating the prescription of Hachisuet al. (1999a) for the accretion efficiency into Eggleton's stellar evolution code and assuming that the prescription is valid for all metallicities, we performed binary stellar evolution calculations for more than 25,000 close WD binary systems with various metallicities. The initial parameter spaces for SNe Ia are presented in an orbital period-secondary mass (logPi,M2i) plane for eachZ.Adopting the results above, we studied the birth rate of SNe Ia for variousZvia binary population synthesis. From the study, we see that for a highZ, SNe Ia occur systemically earlier and the peak value of the birth rate is larger if a single starburst is assumed. The Galactic birth rate from the channel is lower than (but comparable to) that inferred from observations.We also showed the distributions of the parameters of the binary systems at the moment of supernova explosion and the distributions of the properties of companions after supernova explosion. The former provides physics input to simulate the interaction between supernova ejecta and its companion, and the latter is helpful for searching the companions in supernova remnants.

Nova Ejecta Abundances Resulting from Multi-Cycle Evolutionary Calculations

The theory of nova outbursts invokes accretion of hydrogen-rich material by a white dwarf (WD) in a close binary system, due to Roche lobe overflow of a red dwarf companion, leading to periodic outbursts — powered by thermonuclear runaways — that result in mass ejection. Observed characteristics of novae are reproduced by varying the values of three basic and independent parameters: the accreting white dwarf’s mass, its core temperature, and the mass transfer rate. In a recent study (Prialnik & Kovetz 1995) we have carried out a systematic investigation of nova outbursts on WD progenitors composed of C and O in equal mass fractions, concluding that the entire range of observed nova characteristics could be accounted for. A subset of 34 out of 64 evolutionary sequences (obtained with different parameter combinations) reproduced classical novae, and here we focus on the break-up of the heavy element abundances in the ejecta of these models, in comparison with observations, based on a recent analysis of observed nova abundances by Livio & Truran (1994).

22Na and 26Al production in nova outbursts

The consequences of accretion of hydrogen rich material onto ONeMg white dwarfs with masses of 1.0, 1.25, and 1.35 M ⊙ are examined. Our results demonstrate that novae produce both 22na and 26Al in astrophysically interesting amounts. Hot hydrogen burning on ONeMg white dwarfs can produce as much as 2% of the ejected material as 26Al and 3% as 22Na. The largest amount of 22Na is produced by the highest mass ONeMg white dwarf nova systems which are predicted to be the fastest and most luminous of all types of nova. The largest amount of 26Al is produced in the lowest mass white dwarfs, which according to our evolutionary calculations, should eject the largest amount of material. In support of this prediction, the observations of QU Vul, a slow ONeMg nova, indicate that it has ejected about 10 −3 M ⊙. However, such a large amount of ejected mass is inconsistent with a typical ONeMg white dwarf mass > 1.25 M ⊙.