Different Kinds of “Novae” I. Super Novae Type Ia: No hydrogen, CO WD deflagration --> detonation Type Ia: No hydrogen, CO WD deflagration --> detonation SNe Ia progenitor unclear: SD and DD models SNe Ia progenitor unclear: SD and DD models Type II: Core collapse of (M >~ 8 M_sun) progenitor Type II: Core collapse of (M >~ 8 M_sun) progenitor II. Classical & Recurrent Novae Thermonuclear runaway of accreted gas on WD surface Thermonuclear runaway of accreted gas on WD surface Possible channel to SNe Ia??? Possible channel to SNe Ia??? III. Dwarf Novae (Not Relevant Here) L peak ~ 10 L sun (gravitational potential energy) L peak ~ 10 L sun (gravitational potential energy) E tot ~ ergs E tot ~ ergs

SNe Ia: Observed Facts General properties: Homogeneous (small correlated variations) Rise time: ~2-3 weeks Decay time: ~ several months Expansion velocities ~10,000 km/s NO Hydrogen in spectra (almost always!) Si, Ca, Mg (abs early); Fe (em late) Seen in all galaxy types including ellipticals ([some] progenitors must have long lifetimes) SNe Ia in ellipticals generally less luminous

SN 2002ic: A SNe Ia with Hydrogen! Hamuy et al. (2003) Kotak et al. (2004)

Proposed SNe Ia progenitors: Single Degenerate (SD) Symbiotic Binaries (WD + RG) Recurrent Novae (WD + MS) SSS (> 10^-7 M_sun yr^-1?, but see Starrfield et al. 2004) Helium Star + WD binary Hydrogen or Helium Accretion? Double Degenerate (DD) Binary WDs (>= Chandra mass) Binary WDs (subChandra) Importance of Mass Ratio (e.g. van Kerkwijk et al. 2010)?

Challenges of SD and DD Models Single Degenerate: ONeMg WD --> Accretion Induced Collapse (e- captures onto 24Mg) Require CO WD (max mass ~1.1 M_sun from stellar evolution). How to build up ~0.3 M_sun of material? i.e, How to avoid H flashes? Are there enough binaries (constraints from active SSS population)? H problem Delay Time problems (Chris) Double Degenerate: Will merger lead to detonation? May require q~1 Enough progenitors? (constraints from the SSS population)

From D. Townsley -- KITP 2009

Basic Nova Properties Material builds up on the WD surface and slowly becomes degenerate (if dM/dt sufficiently low, i.e. ~< M_sun per year). TNR on surface of WD leads to a nova eruption Luminous! M V ~ -6 to -10 Peak luminosity & fade rate depend mainly on M WD, but also on T WD, dM/dt (and stellar population?) All novae are recurrent at intervals of ~ ~10 5 yr.

Classical Nova Ignition Masses Ignition masses depend not only on M WD, but also on T WD and hence dM/dt. For a given dM/dt, the higher M WD, the less material is accreted prior to the TNR. The higher dM/dt, the hotter the WD, the hotter the WD (for a given WD mass) the less material is accreted prior to the TNR.  ownsley & Bildsten (2005)

Summary: Outstanding Nova & SN Ia Questions 1) In the single degenerate scenario, can the mass of a CO WD grow by the accretion of solar composition gas? (i.e., do H flashes blow off all accreted material?) 2) What are the likely candidate binary systems that are able to build up a ~1 M_sun CO WD (max mass from evolution?) to Chandra mass IF helium must be accreted? 3) If a 1 M_sun CO core accretes a layer of He at dM/dt ~ 10^-7 M_sun/yr, does the He burn steadily to C? (Starrfield et al 2004 say “yes” if the WD is hot enough) If not, can the (sub-Chandra) core detonate?, and if it does, what would the spectrum of the explosion look like? 4) What is the physics of binary WD coalescence: Can more (or less!) than a Chandra mass deflagrate, producing super (Sub) Chandra SNe Ia explosions?... or... 4a) Are WD mergers in super-Chandra binaries inefficient, resulting in generally lower Ni^56 yields and fainter SNe 1a? (ellipticals)