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Different Kinds of “Novae”

Different Kinds of “Novae”. I. Super Novae Type Ia: No hydrogen , CO WD deflagration --> detonation SNe Ia progenitor unclear: SD and DD models Type II: Core collapse of (M >~ 8 M_sun) progenitor II. Classical & Recurrent Novae

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Different Kinds of “Novae”

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  1. Different Kinds of “Novae” I. Super Novae • Type Ia: No hydrogen, CO WD deflagration --> detonation SNe Ia progenitor unclear: SD and DD models • Type II: Core collapse of (M >~ 8 M_sun) progenitor II.Classical & Recurrent Novae • Thermonuclear runaway of accreted gas on WD surface • Possible channel to SNe Ia??? III. Dwarf Novae (Not Relevant Here) • Lpeak ~ 10 Lsun (gravitational potential energy) • Etot ~ 1040 ergs

  2. 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

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

  4. 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)?

  5. 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)

  6. From D. Townsley -- KITP 2009

  7. Basic Nova Properties • Material builds up on the WD surface and slowly becomes degenerate (if dM/dt sufficiently low, i.e. ~< 10-7 M_sun per year). • TNR on surface of WD leads to a nova eruption • Luminous! MV~ -6 to -10 • Peak luminosity & fade rate depend mainly on MWD, but also on TWD, dM/dt (and stellar population?) • All novae are recurrent at intervals of ~101 - ~105 yr.

  8. Classical Nova Ignition Masses • Ignition masses depend not only on MWD, but also on TWD and hence dM/dt. • For a given dM/dt, the higher MWD, 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. Townsley & Bildsten (2005)

  9. 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)

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