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Understanding the Evolution of Low-Mass White Dwarfs and Their Role in Type Ia Supernovae

This paper delves into the characteristics and evolutionary pathways of low-mass white dwarfs (LMWDs), focusing on their connection to Type Ia supernovae (SNe Ia). It discusses the formation channels, including single degenerate and double degenerate models, and the implications of their companion stars. The study examines circumstellar material from SNe Ia events, as well as the orbital dynamics influencing the space velocities of LMWDs. Additionally, it highlights the significance of ultra-cool white dwarfs and poses critical questions for future research in this area.

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Understanding the Evolution of Low-Mass White Dwarfs and Their Role in Type Ia Supernovae

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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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