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Diversity of Type Ia SNe: Challenges and Opportunities.
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Challenges and Opportunities
Until the final explosion of an accreting WD as a Type Ia supernovae, the brightest manifestations of mass transfer are thermonuclear ignitions of accreted Hydrogen and Helium. The current and upcoming transient and SNe surveys are bound to reveal new populations and puzzles.
Townsley and L. B., 2004, Ap. J., 600, 390 (Theoretical overview)
Townsley and L.B., 2005, Ap. J., 628, 395 (Classical Novae)
Scannapieco and L.B., 2005, Ap. J., 629, L85 (Type Ia SN Rates)
L.B., Townsley, Deloye & Nelemans 2006, Ap. J., 640, 466 (AM CVn)
Shen and L. B. 2007, Ap J, 660, 1444 (Stable H/He Burning)
L.B., Shen, Weinberg & Nelemans 2007, Ap J., 662, L95 (Faint .Ia SN)
Piro and L.B., 2008, Ap J., 673, 1009 (Simmering and 56Ni in Ia)
Shen and L.B., 2008, submitted to Ap J (Unstable H burning)
L.B. 2008, in preparation (Survey Expectations)
Stars with < 6-8 solar masses make a Carbon/Oxygen white dwarf of mass 0.5-1.0 with radius ~ Earth and central density >106 gr/cm3PN image from HST
Kalirai et al ‘07
Ring Nebulae (M 57)
1.05 or so
Kalirai et al ‘07
Stellar Lifetime (Myr)
Young White Dwarf
500 100 50
~1% of white dwarfs are in binaries where accretion occurs, releasing gravitational energy
Donor star can be H/He or pure He
Whereas nuclear fusion of H=>He or He=>C releases
This contrast is further enhanced when the white dwarf stores fuel and burns it rapidly, making these binaries detectable in distant galaxies during thermonuclear events.
White Dwarf of Carbon/Oxygen
In 1011 solar masses of old stars (e.g. Elliptical galaxy), two WDs are made per year. The observed rates for thermonuclear events are:
M87 in Virgo
Predicted rates are:
Helium novae every ~250 years, one large He explosion (.Ia; Bildsten et al. ‘07) every ~5,000 years. Double WD mergers every 200 years
The ‘standard’ story (Nomoto, Thielemann & Yokoi ‘84) is 12C ignition in the core leading to a full explosion, implying that:
Townsley & Bildsten 2005
Supersoft Sources: Burn H Stably (van den Heuvel et al 1992), or weakly unstable
Cataclysmic Variables (CVs): undergo unstable burning, leading to Classical Novae. Accumulated mass appears to leave, observed CN rate reveals population.
The fate of 1 in 2000 white dwarfs in our galactic disk.But none yet seen in other galaxies.GP COM
These are the brightest Sources for Space-Based
Gravitational Wave Detectors (e.g. LISA)
L. B., Shen, Weinberg & Nelemans ‘07
*Thanks to Chris Stubbs for the name
The sub-luminous Ia’s fit within the continuum of the Phillip’s relation, extending down by nearly 2.5 mags.
Garnavich et al ‘00
Sloan Digital Sky Survey (Dilday et al 2008)
Current survey (V=22.5, 258 deg2) will find 7 .Ia per year at -17, and 0.5 per year at -15. Total duration = 9 months…. so maybe one in sample
Medium deep survey (V=24, 50 deg2) gets10 .Ia per year at -17, and 1 per year at -15
Palomar Transient Factory (2008)
Large Synoptic Survey Telescope (LSST) is a proposed 8.4-meter, 10 square-degree-field telescope that will provide V=24 imaging across the entire sky every night.
Cerra Pachon, Chile.
Daily survey 1/2 sky would ~1000 .Ia’s per year.
Kulkarni et al (2007)
The boxes plot the volume rate * duration for Type Ia (30 d), Type IIp (100 d), .Ia (5 d), M85-OT (60 d), CN (30 d), and last thermal pulses (2 years)
Bildsten, in prep.
SNLS (24.3, 4 deg2)
1 per exposure (SDSS & PS1)
Observed trends in Ia properties with galaxy type (no evidence yet for metallicity effects) will hopefully identify progenitors:
Brightest (e.g. 1991T) events occur preferentially in young stellar environments (hence mostly spiral and irregular galaxies)
Sub-luminous (and peculiar, eg. 1991bg) Ia’s dramatically prefer old stellar populations . . (Elliptical and S0 Galaxies)
Rates track BOTH the stellar mass and the star formation rate
The odd 2002cx-likes are only seen in star forming galaxies
Ia’s are clearly the result of old and young stellar populations and motivated our (Scannapieco & LB, 2005) simple explanation for the observed cosmic Ia rate. Sullivan et al. (2007) used CFHT SNLS data to go much further!
Neill et al (2007) astroph-0701161 Dilday et al. astroph 0801.3297
The Type Ia rate was higher in the past by at least a
factor of 3, pointing to rapid channels of explosion.
Clear puzzles remain in connecting accreting WDs to their exploding Type Ia counterparts
Clearly much more to learn about thermonuclear events on accreting white dwarfs!!