Izumi Hachisu

A SINGLE DEGENERATE PROGENITOR MODEL FOR TYPE Ia SUPERNOVAE HIGHLY EXCEEDING THE CHANDRASEKHAR MASS LIMIT

Recent observations of Type Ia supernovae (SNe Ia) suggest that some of the progenitor white dwarfs (WDs) had masses up to 2.4-2.8 M{sub Sun }, highly exceeding the Chandrasekhar mass limit. We present a new single degenerate model for SN Ia progenitors, in which the WD mass possibly reaches 2.3-2.7 M{sub Sun }. Three binary evolution processes are incorporated: optically thick winds from mass-accreting WDs, mass stripping from the binary companion star by the WD winds, and WDs being supported by differential rotation. The WD mass can increase by accretion up to 2.3 (2.7) M{sub Sun} from the initial value of 1.1 (1.2) M{sub Sun }, consistent with high-luminosity SNe Ia, such as SN 2003fg, SN 2006gz, SN 2007if, and SN 2009dc. There are three characteristic mass ranges of exploding WDs. In the extreme massive case, differentially rotating WDs explode as an SN Ia soon after the WD mass exceeds 2.4 M{sub Sun} because of a secular instability at T/|W| {approx} 0.14. For the mid-mass range of M{sub WD} = 1.5-2.4 M{sub Sun }, it takes some time (spinning-down time) until carbon is ignited to induce an SN Ia explosion after the WD mass has reached maximum, because it needsmorexa0» a loss or redistribution of angular momentum. For the lower mass case of rigidly rotating WDs, M{sub WD} = 1.38-1.5 M{sub Sun }, the spinning-down time depends on the timescale of angular momentum loss from the WD. The difference in the spinning-down time may produce the prompt and tardy components. We also suggest that the very bright super-Chandrasekhar mass SNe Ia are born in a low-metallicity environment.«xa0less

SHORTEST RECURRENCE PERIODS OF NOVAE

Stimulated by the recent discovery of the 1 yr recurrence period nova M31N 2008-12a, we examined the shortest recurrence periods of hydrogen shell flashes on mass-accreting white dwarfs (WDs). We discuss the mechanism that yields a finite minimum recurrence period for a given WD mass. Calculating the unstable flashes for various WD masses and mass accretion rates, we identified a shortest recurrence period of about two months for a non-rotating 1.38 M ☉ WD with a mass accretion rate of 3.6 × 10–7 M ☉ yr–1. A 1 yr recurrence period is realized for very massive ( 1.3 M ☉) WDs with very high accretion rates ( 1.5 × 10–7 M ☉ yr–1). We revised our stability limit of hydrogen shell burning, which will be useful for binary evolution calculations toward Type Ia supernovae.

Hydrodynamical Evolution of Merging Carbon-Oxygen White Dwarfs: Their Pre-supernova Structure and Observational Counterparts

We perform smoothed particle hydrodynamics (SPH) simulations for merging binary carbon-oxygen (CO) white dwarfs (WDs) with masses of

A remarkable recurrent nova in M 31: The predicted 2014 outburst in X-rays with Swift

1.1

The critical mass ratio of double white dwarf binaries for violent merger-induced Type Ia supernova explosions

and

AN X-RAY AND OPTICAL LIGHT CURVE MODEL OF THE ECLIPSING SYMBIOTIC BINARY SMC3

1.0

THE UBV COLOR EVOLUTION OF CLASSICAL NOVAE. II. COLOR–MAGNITUDE DIAGRAM

M_odot

Evolution of the Symbiotic Nova PU Vul?Outbursting White Dwarf, Nebulae, and Pulsating Red Giant Companion

, until the merger remnant reaches a dynamically steady state. Using these results, we assess whether the binary could induce a thermonuclear explosion, and whether the explosion could be observed as a type Ia supernova (SN Ia). We investigate three explosion mechanisms: a helium-ignition following the dynamical merger (`helium-ignited violent merger model), a carbon-ignition (`carbon-ignited violent merger model), and an explosion following the formation of the Chandrasekhar mass WD (`Chandrasekhar mass model). An explosion of the helium-ignited violent merger model is possible, while we predict that the resulting SN ejecta are highly asymmetric since its companion star is fully intact at the time of the explosion. The carbon-ignited violent merger model can also lead to an explosion. However, the envelope of the exploding WD spreads out to

FINAL EVOLUTION AND DELAYED EXPLOSIONS OF SPINNING WHITE DWARFS IN SINGLE DEGENERATE MODELS FOR TYPE Ia SUPERNOVAE

sim 0.1R_odot