1. Alex Gianninas April 16 th, 2014 UT Arlington Physics Colloquium

2. Collaborators  University of Oklahoma Mukremin Kilic, Sara Barber, Paul Canton Mukremin Kilic, Sara Barber, Paul Canton  Smithsonian Astrophysical Observatory Warren Brown, Scott Kenyon Warren Brown, Scott Kenyon  University of Warwick JJ Hermes JJ Hermes  Université de Montréal Patrick Dufour, Pierre Bergeron Patrick Dufour, Pierre Bergeron 2

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    ~ 10 6    log g ~ 8.0 (log g  = 4.4) (log g  = 4.4)  T eff ~ 150,000  3000 K 3000 K  No H burning  WDs cool over several Gyrs 3

4. Gravitational settling quickly creates a stratified internal structure 4 C/O He H DA (80%) C/O He Non-DA (DO, DB, DQ, DZ) (20%) C/O Hot DQ

5. WDs with M < 0.45 M  must be formed in binary systems 5 Binary Evolution Gianninas et 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! 6

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

8. ELM WDs are the potential progenitors of many types of astrophysical objects  Progenitors of Type Ia supernovae (Iben & Tutukov 1984) (Iben & Tutukov 1984)  Progenitors of underluminous.Ia supernovae (Bildsten et 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 systems are important sources of gravitational waves  The ELM Survey is a targeted search for Extremely Low Mass WDs (M < 0.30 M  ) 8

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) 9

10. ELM WDs straddle the color-color space between normal WDs and A stars 10 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: Mount Hopkins, AZ: ○ MMT (6.5m) ○ FLWO (1.5m) Kitt Peak, AZ: KPNO 4m Kitt Peak, AZ: KPNO 4m  Once confirmed, we seek to improve our orbital solution by better sampling all phases of the orbit 11

12. The ELM Survey has been extremely successful thus far 12 PaperELM WDMerger Systems Brown et al. (2010) I126 Kilic et al. (2011)II42 Brown et al. (2012) III76 Kilic et al. (2012)IV75 Brown et al. (2013) V176 Before ELM Survey: Before ELM Survey: Only 6 known merger systems Only 6 known merger systems Shortest known period is P = 1.5 hr 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 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) 13 Brown et al. (2013)

14. The orbital parameters put limits on M 2 and the merger time  Mass Function  Lower limit on M 2 14  Merger time  Upper limit on 

15. Some ELM WDs may be Type Ia progenitors  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 15 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 16 Kilic et al. (2013)

17. The orbital parameters put limits on M 2 and the merger time  Mass Function  Lower limit on M 2 17  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 (T eff and log g) Precise measurements of the atmospheric parameters (T eff and log g) Evolutionary models Evolutionary models  Model independent: Eclipses Eclipses Ellipsoidal variations (tidal distortion) Ellipsoidal variations (tidal distortion) 18

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

20. Model fits allow us to measure the atmospheric parameters 20

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 21

22. 22

23. ELM WDs undergo a series of H- shell flashes as they evolve 23 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 T eff - log g plane  Still much uncertainty 24 Althaus et al. (2013)

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

26. 26

27. 27

28. J0745 has more than just Ca 28

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

30. J0745 is unique for its T eff  T eff = 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! 30 Gianninas et al. (2014)

31. Circumbinary disks for ELM WDs? Circumbinary disks for ELM WDs?  Radiative levitation?  Recent H-shell flash? For more massive WDs, metals originate from circumstellar disks 31 Optically thick Dotted i = 30° Dashed-dotted i = 60° R in = 1.3 R  R out = 1.4 – 5.0 R 

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

33. 33

34. J0651 is 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 34

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

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

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

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

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

40. J0651 presents a unique opportunity to measure 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 40 Berger et al. (2005)

41. The Rossiter-McLaughlin Effect produces an anomaly in the RV curve 41 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  ) 1. Rotationally broaden line profile of primary to simulate integrated spectrum (S  ) 2. Unbroadened line profile, Doppler shifted to the red/blue (S p ) 2. Unbroadened line profile, Doppler shifted to the red/blue (S p ) 3. S tr = S  - S p 3. S tr = S  - S p 42

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

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 44

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

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

47. There is still plenty of work to be done!  ELM Survey Upcoming observing runs: MMT, KPNO 4m Upcoming observing runs: MMT, KPNO 4m LAMOST? LAMOST? Southern Hemisphere? Southern Hemisphere?  Spitzer  J0745 HST data to be analyzed HST data to be analyzed Keck: TBD Keck: TBD  J0651 Finish data reduction and analysis Finish data reduction and analysis 47

48. Is this the fate of J0651? 48