Alex Gianninas April 16 th , 2014 UT Arlington Physics Colloquium

1. Alex Gianninas April16th, 2014 UT Arlington PhysicsColloquium The Shortest Period Binary White Dwarfs: Sources of Gravitational Waves and Underluminous Supernovae Explosions

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

3. White dwarfs are the dense stellar remnants of 97% of all stars in the Galaxy • 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

4. He Gravitationalsettlingquicklycreates a stratifiedinternal structure C/O H He Non-DA (DO, DB, DQ, DZ) (20%) C/O C/O DA (80%) Hot DQ

5. WDswith M < 0.45 M must beformed in binarysystems BinaryEvolution Gianninaset al. (2011)

6. Binary companions strip 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!

7. ELM WDs should have He cores H H He He C/O DA ELM DA

8. ELM WDs are the potentialprogenitors of many types of astrophysicalobjects • Progenitors of Type Iasupernovae (Iben & Tutukov 1984) • Progenitors of underluminous .Iasupernovae (Bildstenet al. 2007) • Progenitors of AM CVn systems (Kilic et al., 2014) • Progenitors of R CrB stars (Clayton 2013) • Pulsar companions (Kaplan et al. 2013, Ransom et al. 2014) • Shortest period systemsare important sources of gravitational waves • The ELM Survey is a targeted search for Extremely Low Mass WDs (M < 0.30 M)

9. Candidates are selected mostly via SDSS colors • 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)

10. ELM WDsstraddle the color-colorspacebetween normal WDs and A stars Brown et al. (2012)

11. We have an ongoing multi-site campaign to confirm the nature of our ELM WD candidates • Observatories • Mount Hopkins, AZ: • MMT (6.5m) • FLWO (1.5m) • Kitt Peak, AZ: KPNO 4m • Once confirmed, we seek to improve our orbital solution by better sampling all phases of the orbit

12. The ELM Survey has been extremely successful thus far • 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

13. Orbital solutions yield the period (P) and velocity semi-amplitude (K) Brown et al. (2013)

14. The orbital parameters put limits on M2 and the merger time • Mass Function  Lower limit on M2 • Merger time  Upper limit on 

15. Some ELM WDsmaybe Type Iaprogenitors • 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)

16. We have identified the first unambiguous progenitors of AM CVn (cataclysmic variables, novae) • Have massive Companions • Pulsars? No detections with Chandra • Will undergo stable mass transfer Kilic et al. (2013)

17. The orbital parameters put limits on M2 and the merger time • Mass Function  Lower limit on M2 • Merger time  Upper limit on 

18. There are model dependent and model independent methods to determine M • Model dependent: two ingredients • Precise measurements of the atmospheric parameters (Teff and log g) • Evolutionary models • Model independent: • Eclipses • Ellipsoidal variations (tidal distortion)

19. The Hydrogen Balmer lines are very sensitive to Teff and log g

20. Model fits allow us to measure the atmospheric parameters

21. New grids of models were required for ELM WDs • New regime in surface gravity (log g < 7.0) • New grid of models (down to log g = 4.5) computed • Need to include higher Balmer lines (up to H12) in the models and the fits since lines are still present in WDs with log g < 7.0

23. ELM WDs undergo a series of H-shell flashes as they evolve Althaus et al. (2013)

24. A statistical approach is used 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)

25. ELM WDs with log g < 6.0 all have metals

28. J0745has more than just Ca

29. J0745 is the most metal rich WD from the ELM Survey Gianninas et al. (2014)

30. J0745is unique for its Teff • 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. (2014)

31. For more massive WDs, metals originate from circumstellar 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

32. HST (COS) Yes! 10 orbits Keck (HIRES) TBD…

34. J0651is the 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

35. The midpoint of the eclipses reveals that the orbit is decaying ! Hermes et al. (2013)

36. The rate of decayagreeswith the prediction of General Relativity! Hermes et al. (2013)

37. The Hulse-Taylor binary pulsar take 30 years to display the same period shift! Weisberg & Taylor (2005)

38. eLISA • Replaces LISA • Two beams instead of three • Reduced sensitivity • Frequency range spans four decades (~0.1 mHz – ~1 Hz) • “The Gravitational Universe” approved as science theme for ESA L3 project ( launch in ~2034)

39. J0651 will be a verification source for eLISA Galactic foreground eLISA, after 2 yrs Gianninaset al. (2014, submitted)

40. J0651 presents a unique opportunity to measurerotation 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)

41. The Rossiter-McLaughlin Effectproduces an anomaly in the RV curve Winn et al. (2005)

42. We can predict the magnitude of the R-M effect using models • 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

43. The R-M effect in J0651 would produce a ~40 km/s shift in RV

44. We were awarded ½ night on Keck I with LRIS • Only telescope where we could obtain necessary S/N • 5 - 7 spectra (t ~ 25s) per exposure to reduce number of times we read the CCD and ensure the best possible temporal sampling • Needed to synchronize blue and red sides of instruments (different read times) • 6 hours of observing = 313 spectra

45. The folded RV curve does not show any obvious signature of the R-M effect

46. Conclusions • ELM Survey: targeted search for extremely low-mass WDs • Success: >60 systems avec P < 1 day • Observed Phenomena: • Pulsations • Metals • Eclipses • Orbital Decay • Ellipsoidal Variations

47. There isstillplenty of work to bedone! • ELM Survey • Upcoming observing runs: MMT, KPNO 4m • LAMOST? • Southern Hemisphere? • Spitzer • J0745 • HSTdata to be analyzed • Keck: TBD • J0651 • Finish data reduction and analysis

48. Is this the fateof J0651?