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Gravitational Waves and Underluminous Supernovae Explosions from ELM White Dwarfs

This UNT Physics Colloquium discusses the properties and survey results of extremely low mass white dwarfs (ELM WDs), including their potential as progenitors for underluminous supernovae and sources of gravitational waves.

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Gravitational Waves and Underluminous Supernovae Explosions from ELM White Dwarfs

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  1. Alex Gianninas December 3rd, 2013 UNT PhysicsColloquium Gravitational Waves and Underluminous Supernovae Explosions from ELM White Dwarfs

  2. Collaborators • University of Oklahoma • Mukremin Kilic, Sara Barber, Paul Canton • SmithsonianAstrophysicalObservatory • Warren Brown, Scott Kenyon • University of Warwick • JJ Hermes • Université de Montréal • Patrick Dufour, Pierre Bergeron UNT Colloquium

  3. White DwarfProperties • M ~ 0.6 M • R ~ 0.01 R ~ 1 R •  ~ 106  • log g ~ 8.0 (log g= 4.4) • Teff ~ 150,000  3000 K • No H burning  WDs cool over several Gyrs UNT Colloquium

  4. He Internal Structure of WDs C/O H He Non-DA (DO, DB, DQ, DZ) C/O C/O DA Hot DQ UNT Colloquium

  5. Gianninas et al. (2011) BinaryEvolution UNT Colloquium

  6. These “friends” are binary companions that stripped a significant amount of material from the progenitor, preventing the ignition of He burning, giving birth to an extremely low mass (ELM) WD • ELM WDs are found almost exclusively in short-period binaries (P < 1 day) • Many will merge in less than a Hubble time! UNT Colloquium

  7. Internal Structure of WDs H H He He C/O DA ELM DA UNT Colloquium

  8. ELM Survey • Targeted search for Extremely Low Mass WDs • M < 0.25 M • Motivation: • Progenitors of Type Iasupernovae • Progenitors of underluminous supernovae (.Ia, Bildsten et al. 2007) • Progenitors of AM CVn systems (Kilic et al., 2013) • Pulsar companions • Nearest systems are important sources of gravitational waves UNT Colloquium

  9. ELM Survey: Target Selection • Hypervelocity Survey (Warren Brown, SAO): search for B type stars leaving the Galaxy, colors similar to ELM WDs  15% of targets are in fact ELM WDs • Spectroscopy from the Sloan Digital Sky Survey (SDSS) • SDSS colors (u-g, g-r) UNT Colloquium

  10. ELM Survey: Target Selection Brown et al. (2010) UNT Colloquium

  11. ELM Survey: Target Selection Brown et al. (2012) UNT Colloquium

  12. ELM Survey: Observations • MMT (6.5m), FLWO (1.5m), KPNO 4m • Radial velocity follow-up to confirm the binary nature of each candidate • Once confirmed, we seek to improve our orbital solution by better sampling all phases of the orbit UNT Colloquium

  13. ELM Survey: Success Rate • Before ELM Survey: • Only 6 known merger systems • Shortest known period is P = 1.5 hr • ELM Survey has found 8 systems with P < 1.5 hr and 3 with P < 1 hr UNT Colloquium

  14. Orbital Solutions Orbital solutions provide period (P) and velocity semi-amplitude (K) Brown et al. (2013) UNT Colloquium

  15. Orbital Parameters • Mass Function  Lower limit on M2 • Merger time  Upper limit on  UNT Colloquium

  16. ELM Survey: Results • Super-Chandrasekhar mass systems not necessarily Type Ia progenitors • Mass ratio is important • 0.2 + 1.2 M systems → Stable mass transfer system (AM CVn, .Ia SN) • Can be WD+NS binaries Brown et al. (2013) UNT Colloquium

  17. Progenitors of AM CVn(cataclysmic variables, novae) • Massive Companion • Pulsars? No detections with Chandra • Will undergo stable mass transfer • Result: AM CVn Kilic et al. (2013) UNT Colloquium

  18. Masses & Radii • Model dependent and model independent measurements • Model dependent: two ingredients • Precise measurements of the atmospheric parameters (Teff and log g) • Evolutionary models • Model independent: • Eclipses • Ellipsoidal variations (tidal distortion) UNT Colloquium

  19. Hydrogen Balmer lines(model spectra) UNT Colloquium

  20. Spectroscopic Fits UNT Colloquium

  21. New Model Atmospheres • New regime in surface gravity (log g < 7.0) • New grid of models (down to log g = 4.5) computed with the atmosphere code of P. Bergeron (UdeM) • Need to include higher Balmer lines (up to H12) in the fits since lines are still present in WDs with log g < 7.0 UNT Colloquium

  22. UNT Colloquium

  23. Latest Evolutionary Models H-shell flash Althaus et al. (2013) UNT Colloquium

  24. Evolutionary Models • Statistical approach to calculate masses and ages • Mean weighted by the time spent at each point in Teff- log g plane • Still much uncertainty Althaus et al. (2013) UNT Colloquium

  25. Results for ELM sample ∆ Pulsating □ Non-pulsating UNT Colloquium

  26. ZZ Ceti Instability Strip • Non-Pulsating • Pulsating UNT Colloquium

  27. Results for ELM sample ∆ Pulsating □ Non-pulsating UNT Colloquium

  28. 1stPulsating ELM WD: J1840 Hermes et al. (2012) UNT Colloquium

  29. J1112 et J1518 Hermes et al. (2012) UNT Colloquium

  30. J1614 et J2228 Hermes et al. (2013) UNT Colloquium

  31. Pulsating ELM WDs • Currently 5 known pulsating ELM WDs • Van Grootel et al. (2013): first exploration of pulsations models appropriate for ELM WDs • Equivalent properties to ZZ Ceti stars at lower mass • Additional evidence that these are indeed bona fide WDs UNT Colloquium

  32. Extended Instability Strip Van Grootel et al. (2013) UNT Colloquium

  33. Results for ELM sample • ∆ Pulsating • □ Non-pulsating • Ca lines • He lines UNT Colloquium

  34. UNT Colloquium

  35. ALL ELM WDs with log g < 6.0 have Ca lines! UNT Colloquium

  36. Ca abundances UNT Colloquium

  37. He abundances UNT Colloquium

  38. J074511.56+194926.5 (J0745) UNT Colloquium

  39. J0745 : A whole lot of metals! Gianninas et al. (2013, submitted) UNT Colloquium

  40. J0745: An Extreme DAZ ELM WD • Teff = 8380 K • log g = 6.21 • Abundances log Ca/H = -5.8 log Mg/H = -3.9 log Cr/H = -6.1 log Ti/H = -5.6 log Fe/H = -4.5 All nearly solar! Gianninas et al. (2013, submitted) UNT Colloquium

  41. Origin of metals • For more massive DAZ WDs  circumstellar debris disks… circumbinary disks for ELM WDs? • Radiative levitation? • Recent H-shell flash? Optically thick Dotted i = 30° Dashed-dotted i = 60° Rin= 1.3 R Rout = 1.4 – 5.0 R UNT Colloquium

  42. PSR J1816+4510 • Kaplan et al. (2013) • ELM WD pulsar companion • Teff = 16,000 K • log g = 4.90 • Hypothesis: result of a recent H-shell flash UNT Colloquium

  43. HST (COS) Yes! 10 orbits Keck (HIRES) TBD… UNT Colloquium

  44. UNT Colloquium

  45. J065133.34+284423.4 (J0651) • ‘‘Poster child” for ELM WDs • Shortest period ELM WD binary  P = 12.75 min! • Eclipsing! • After initial discovery, photometric follow-up at McDonald, APO, Gemini North and GTC UNT Colloquium

  46. Light Curves Direct detection of orbital decay! UNT Colloquium Hermes et al. (2013)

  47. O-C Diagram UNT Colloquium Hermes et al. (2013)

  48. J0651: Rotation Rate • Isolated WDs : slow rotators ( < 10’s of km/s), measured with Ca line profile • Evolution in compact binaries and interactions with companions  could ELM WDs be fast rotators? • Tidal forces  synchronized orbits • For J0651 = 200 km/s Berger et al. (2005) UNT Colloquium

  49. Rossiter-McLaughlin Effect Winn et al. (2005) UNT Colloquium

  50. Prediction • Follow recipe from Winn et al. (2005) • 1. Rotationally broaden line profile of primary to simulate integrated spectrum (S) • 2. Unbroadened line profile, Doppler shifted to the red/blue (Sp) • 3. Str = S - Sp UNT Colloquium

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