Les Naines Blanches de Trs Faibles Masses: Sources d'Ondes Gravitationnelles et d'Explosions de Supernovae Sous-Lumineuses

The Shortest Period Binary White Dwarfs: Sources ofGravitational Waves and Underluminous Supernovae ExplosionsAlex GianninasApril 16th, 2014UT Arlington Physics Colloquium

1CollaboratorsUniversity of OklahomaMukremin Kilic, Sara Barber, Paul CantonSmithsonian Astrophysical ObservatoryWarren Brown, Scott KenyonUniversity of WarwickJJ HermesUniversit de MontralPatrick Dufour, Pierre Bergeron

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White dwarfs are the dense stellar remnants of 97% of all stars in the GalaxyM ~ 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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Gravitational settling quickly creates a stratified internal structure4C/OHeHDA (80%)C/OHeNon-DA (DO, DB, DQ, DZ)(20%)C/OHot DQWDs with M < 0.45 M must be formed in binary systems5

Binary EvolutionGianninas et al. (2011)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) WDELM WDs are found almost exclusively in short-period binaries (P < 1 day)Many will merge in less than a Hubble time!6

ELM WDs should have He cores7C/OHeHDAHeHELM DAELM WDs are the potential progenitors of many types of astrophysical objectsProgenitors of Type Ia supernovae (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 wavesThe ELM Survey is a targeted search for Extremely Low Mass WDs (M < 0.30 M)

8Candidates are selected mostly via SDSS colorsHypervelocity Survey (Warren Brown, SAO): search for B type stars leaving the Galaxy, colors similar to ELM WDs 15% of targets are in fact ELM WDsSpectroscopy from the Sloan Digital Sky Survey (SDSS)SDSS colors (u-g, g-r)

9ELM WDs straddle the color-color space between normal WDs and A stars10Brown et al. (2012)

We have an ongoing multi-site campaign to confirm the nature of our ELM WD candidatesObservatoriesMount Hopkins, AZ: MMT (6.5m) FLWO (1.5m) Kitt Peak, AZ: KPNO 4mOnce confirmed, we seek to improve our orbital solution by better sampling all phases of the orbit11

The ELM Survey has been extremely successful thus far12PaperELM WDMerger SystemsBrown et al. (2010)I126Kilic et al. (2011)II42Brown et al. (2012)III76Kilic et al. (2012)IV75Brown et al. (2013)V

176Before ELM Survey: Only 6 known merger systems Shortest known period is P = 1.5 hrELM Survey has found 8 systems with P < 1.5 hr and 3 with P < 1 hr Orbital solutions yield the period (P) and velocity semi-amplitude (K)13

Brown et al. (2013)The orbital parameters put limits on M2 and the merger timeMass Function Lower limit on M214

Merger time Upper limit on

Some ELM WDs may be Type Ia progenitorsSuper-Chandrasekhar mass systems not necessarily Type Ia progenitors Mass ratio is important0.2 + 1.2 M systems Stable mass transfer system (AM CVn, .Ia SN)Can be WD+NS binaries

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Brown et al. (2013)We have identified the first unambiguous progenitors of AM CVn (cataclysmic variables, novae)Have massive CompanionsPulsars? No detections with ChandraWill undergo stable mass transfer16

Kilic et al. (2013)The orbital parameters put limits on M2 and the merger timeMass Function Lower limit on M217

Merger time Upper limit on

There are model dependent and model independent methods to determine MModel dependent: two ingredientsPrecise measurements of the atmospheric parameters (Teff and log g)Evolutionary models Model independent:EclipsesEllipsoidal variations (tidal distortion)

18The Hydrogen Balmer lines are very sensitive to Teff and log g19

Model fits allow us to measure the atmospheric parameters20

New grids of models were required for ELM WDsNew 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 < 7.02122

ELM WDs undergo a series of H-shell flashes as they evolve23

Althaus et al. (2013)A statistical approach is used to calculate masses and agesMean weighted by the time spent at each point in Teff - log g planeStill much uncertainty24

Althaus et al. (2013)ELM WDs with log g < 6.0 all have metals25

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J0745 has more than just Ca28

J0745 is the most metal rich WD from the ELM Survey 29

Gianninas et al. (2014)J0745 is unique for its TeffTeff = 8380 Klog g = 6.21Abundanceslog Ca/H = -5.8log Mg/H = -3.9log Cr/H = -6.1log Ti/H = -5.6log Fe/H = -4.5All nearly solar!30

Gianninas et al. (2014) Circumbinary disks for ELM WDs?

Radiative levitation?Recent H-shell flash?

For more massive WDs, metals originate from circumstellar disks31Optically thick

Dottedi = 30

Dashed-dottedi = 60

Rin = 1.3 RRout = 1.4 5.0 R

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HST (COS)Yes!10 orbits

Keck(HIRES)TBD

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J0651 is the poster child for ELM WDsShortest period ELM WD binary P = 12.75 min!Eclipsing!After initial discovery, photometric follow-up at McDonald, APO, Gemini North and GTC34

The midpoint of the eclipses reveals that the orbit is decaying !35

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

Hermes et al. (2013)

The Hulse-Taylor binary pulsar take 30 years to display the same period shift! 37Weisberg & Taylor (2005)eLISA Replaces LISA Two beams instead of threeReduced sensitivityFrequency range spans four decades (~0.1 mHz ~1 Hz)The Gravitational Universe approved as science theme for ESA L3 project ( launch in ~2034)38

J0651 will be a verification source for eLISA39Galactic foregroundeLISA, after 2 yrsGianninas et al. (2014, submitted)J0651 presents a unique opportunity to measure rotation rateIsolated WDs : slow rotators ( < 10s of km/s), measured with Ca line profileEvolution in compact binaries and interactions with companions could ELM WDs be fast rotators?Tidal forces synchronized orbitsFor J0651 = 200 km/s40Berger et al. (2005)

The Rossiter-McLaughlin Effect produces an anomaly in the RV curve41

Winn et al. (2005)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 - Sp42

The R-M effect in J0651 would produce a ~40 km/s shift in RV43We were awarded night on Keck I with LRISOnly 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 spectra44

The folded RV curve does not show any obvious signature of the R-M effect45

ConclusionsELM Survey: targeted search for extremely low-mass WDs Success: >60 systems avec P < 1 dayObserved Phenomena:PulsationsMetalsEclipsesOrbital DecayEllipsoidal Variations46There is still plenty of work to be done! ELM SurveyUpcoming observing runs: MMT, KPNO 4mLAMOST?Southern Hemisphere?SpitzerJ0745HST data to be analyzedKeck: TBDJ0651Finish data reduction and analysis

47Is this the fate of J0651?48