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

2. Collaborators University of Oklahoma
Mukremin Kilic, Sara Barber, Paul Canton
Smithsonian Astrophysical Observatory
Warren Brown, Scott Kenyon
University of Warwick
JJ Hermes
Université de Montréal
Patrick Dufour, Pierre Bergeron
2/17/2019
UNT Colloquium

3. White Dwarf Properties
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
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4. Internal Structure of WDsHe
C/O H He
Non-DA (DO, DB, DQ, DZ)
C/O
C/O DA
Hot DQ
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5. Gianninas et al. (2011)
Binary Evolution
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6. Many will merge in less than a Hubble time!
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!
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7. Internal Structure of WDsH H He He
C/O DA
ELM DA
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8. ELM Survey Targeted search for Extremely Low Mass WDs M < 0.25 M
Motivation:
Progenitors of Type Ia supernovae
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
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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)
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10. ELM Survey: Target Selection
Brown et al. (2010)
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11. ELM Survey: Target Selection
Brown et al. (2012)
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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
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13. ELM Survey: Success Rate
Paper
ELM WD
Merger Systems
Brown et al. (2010) I 12 6
Kilic et al. (2011) II 4 2
Brown et al. (2012)
III 7
Kilic et al. (2012) IV 5
Brown et al. (2013) V 17
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
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14. Orbital solutions provide period (P) and velocity semi-amplitude (K)
Brown et al. (2013)
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15. Orbital Parameters Mass Function  Lower limit on M2
Merger time  Upper limit on 
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16. ELM Survey: Results
Super-Chandrasekhar mass systems not necessarily Type Ia progenitors
Mass ratio is important
M systems → Stable mass transfer system (AM CVn, .Ia SN)
Can be WD+NS binaries
Brown et al. (2013)
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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)
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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)
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19. Hydrogen Balmer lines (model spectra)
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20. Spectroscopic Fits
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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
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22. 2/17/2019
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23. Latest Evolutionary Models
H-shell flash
Althaus et al. (2013)
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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
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Althaus et al. (2013)

25. Results for ELM sample ∆ Pulsating □ Non-pulsating 2/17/2019
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26. ZZ Ceti Instability Strip
Non-Pulsating
Pulsating
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27. Results for ELM sample ∆ Pulsating □ Non-pulsating 2/17/2019
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28. 1st Pulsating ELM WD: J1840 Hermes et al. (2012) 2/17/2019
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29. J1112 et J1518
Hermes et al. (2012)
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30. J1614 et J2228
Hermes et al. (2013)
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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
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32. Extended Instability Strip
Van Grootel et al. (2013)
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33. Results for ELM sample ∆ Pulsating □ Non-pulsating Ca lines He lines
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34. 2/17/2019
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35. ALL ELM WDs with log g < 6.0 have Ca lines!
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36. Ca abundances
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37. He abundances
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38. J (J0745)
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39. J0745 : A whole lot of metals! Gianninas et al. (2013, submitted)
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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)
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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
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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
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43. HST
(COS)
Yes!
10 orbits
Keck
(HIRES)
TBD…
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44. 2/17/2019
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45. J065133.34+284423.4 (J0651) ‘‘Poster child” for ELM WDs
Shortest period ELM WD binary  P = min!
Eclipsing!
After initial discovery, photometric follow-up at McDonald, APO, Gemini North and GTC
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46. Direct detection of orbital decay!
Light Curves
Direct detection of orbital decay!
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Hermes et al. (2013)

47. O-C Diagram
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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)
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49. Rossiter-McLaughlin Effect
Winn et al. (2005)
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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
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51. Magnitude of R-M Effect ~ 40 km/s
Prediction
Magnitude of R-M Effect ~ 40 km/s
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52. Keck Observations 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
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53. Observations Keck : J0651
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54. Observations Keck : J0651
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55. 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
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56. More to come… ELM Survey Spectroscopic Analysis Spitzer J0745 J0651
Upcoming observing runs: MMT, KPNO 4m
LAMOST?
Southern Hemisphere?
Spectroscopic Analysis
Abundances
Spitzer
J0745
HST: December 6 and 7
Keck: TBD
J0651
Finish data reduction and analysis
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57. Fate of J0651?
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