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Single Low-mass WDs

Single Low-mass WDs. Reference: arXiv0811.2633 Xu Xiaojie 2008/12/18. Outline. SN Ia & its companion remnants Low mass white dwarfs Possible evolution path towards LMWDs Questions. SNe Ia. Used as standard light of the universe

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Single Low-mass WDs

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  1. Single Low-mass WDs Reference: arXiv0811.2633 Xu Xiaojie 2008/12/18

  2. Outline • SN Ia & its companion remnants • Low mass white dwarfs • Possible evolution path towards LMWDs • Questions

  3. SNe Ia • Used as standard light of the universe • Explosion of a WD reaching certain mass (usually chandrasekhar/sub~ mass limit) • Single degenerate model/double degenerate model • Detection of circumstellar material ejected 50 yrs before the explosion of SN 2006X • Non-degenerated companion after explosion? No conclusive proof, but…

  4. WD’s Motion • Oppenheimer 2001 Hansen 2003

  5. Mass of WDs • Single stars evolution1 M_s ZAMS=0.55 M_s WDat present, WDs with mass <0.4—0.5 WD requiring removing of their envelope • BinariesReaching much lower WD mass, e.g. LMXBs The P_orb---M_wd relation

  6. Single LMWDs • Maxted et al., 2000

  7. A Very Low Mass WD • WD LP 400-22 ,Kawka et al., 2006

  8. Impossible Paths to Single LMWDs • Single: High Z population? down to 0.4M_s WDs • Binaries:A core-collapse SN, system unbounded?(Primary mass too high to become a LMWD)A WD+MS star with a CB disk?(The initial WD has to be a LMWD, too)AIC NS + kick? (kick velocity may not high)WD mergers?

  9. SD SNe Ia Populations • Formation channelsSupersoft: WD + MS starRed giant: WD + RG star Example: RS Oph, 456d Orbit, ~1.38 WD (?) • Remnant massBurst takes 15% mass from a MS or subgiant companion and all envelope from a RG companionRemnant WD mass related to companion core mass

  10. Orbits & Runaway Velocity • Space velocity of the remnant related to the orbital period at explosion • For RG donors, P related to companion core mass (Rappaport et al., 1995)

  11. Single UCWDs as SN Ia LMWDs • Single Ultra-cool WDs (T<4000K)

  12. New Samples of UCWDs • Harris et al., 2008

  13. Discussion • Super soft channel still important • For RG donors, final P below 100d? • Mass distribution of LMWDs

  14. Questions • Those LMWDs with high space velocities

  15. Questions • Equations? (Rappaport 1995, Tauris 1999)

  16. Questions • Evolving to SN Ia: with an unstable disk?Enable SNe Ia with a less massive donor star • Less massive WD left: down to about 0.2M_sor, in a tighter orbit: <2days • Possible evolution path to those LMWDs with higher velocity or with extremely low mass, like LP 400-22 (7 WDs <0.2 M_s). • Possible help from Irradiation (strong enough?)

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