The ELM Survey: A Targeted Search for the Most Extreme White Dwarf Binary Systems Alex Gianninas Astronomy Colloquium Wesleyan University February 25th, 2015

Outline Intro: Stellar Evolution & White Dwarfs 101 Extremely Low Mass White Dwarfs The ELM Survey Highlights from 2014 Takeaways

Stellar Evolution and White Dwarfs 101 No H burning, WDs cool over several billion years (Gyrs) Teff ~ 150,000 K  3000 K M ~ 0.6 M R ~ 0.01 R ~ 1 R log g ~ 8.0 (log g = 4.4, log g  = 3.0)

Stellar Evolution and White Dwarfs 101 No H burning, WDs cool over several billion years (Gyrs) Teff ~ 150,000 K  3000 K M ~ 0.6 M R ~ 0.01 R ~ 1 R log g ~ 8.0 (log g = 4.4, log g  = 3.0) 𝒈= 𝑮𝑴 𝑹 𝟐

Gravitational settling quickly creates a stratified internal structure He Gravitational settling quickly creates a stratified internal structure C/O H He Non-DA (He-rich) C/O C/O DA (H-rich) Hot DQ

Extremely Low Mass (ELM) WDs have M < 0 Extremely Low Mass (ELM) WDs have M < 0.3 M and form in compact binaries Gianninas et al. (2011, ApJ, 743, 138) Binary Evolution

Extremely Low-Mass (ELM) WDs have He cores and are formed in compact binaries Iben & Tutukov (1984, ApJ, 54, 335)

ELM WDs have He cores and considerably larger radii 𝑹~ 𝟏 𝑴 𝟑 ELM WDs have He cores and considerably larger radii H H He He C/O ELM

The ELM Survey The ELM Survey is an ongoing, targeted search for ELM WDs M < 0.30 M (5 < log g < 7) Found in short-period (P < 1 day) binary systems Motivation Progenitors of SN Ia, .Ia, AM CVn, R CrB Neutron star companions Gravitational wave verification sources Laboratories to test GR, tidal effects Papers I – V + VI : 62 + 12 new ELM WDs

SDSS colors work well for choosing ELM WD candidates Brown et al. (2012, ApJ, 744, 142) Gianninas et al. (2015, in prep)

Radial Velocity Follow-Up FLWO 1.5m MMT 6.5m KPNO 4m

More Balmer lines are visible in ELM WDs due to the lower log g The optical spectra of ELM WDs are dominated by the Hydrogen Balmer lines DA ELM H H H H J1600+2721: systemic velocity ~ -300 km/s, possible Halo WD J1250+2621: first ELM WD from LAMOST candidates More Balmer lines are visible in ELM WDs due to the lower log g

ELM VI: 12 new ELM WDs 𝑷 𝑲 𝟑 𝟐𝝅𝑮 = 𝑴 𝒇 = (𝒎 𝟐 𝐬𝐢𝐧 𝒊 ) 𝟑 (𝒎 𝟏 +𝒎 𝟐 ) 𝟐 J1600+2721: systemic velocity ~ -300 km/s, possible Halo WD J1250+2621: first ELM WD from LAMOST candidates 𝑷 𝑲 𝟑 𝟐𝝅𝑮 = 𝑴 𝒇 = (𝒎 𝟐 𝐬𝐢𝐧 𝒊 ) 𝟑 (𝒎 𝟏 +𝒎 𝟐 ) 𝟐 Gianninas et al. (2015, in prep)

Hydrogen Balmer lines are very sensitive to both Teff and log g

Standard Spectroscopic Technique Gianninas et al. (2015, in prep)

There is still a lot of uncertainty in the evolutionary models Althaus et al. (2013, A&A, 557, A19) Istrate et al. (2014, A&A, 571, L3) Discuss lower limit for (ELM) WD masses Gianninas et al. (2015 ApJ, in prep)

Some ELM WDs may be Type Ia progenitors Brown et al. (2013, ApJ, 769, 66) Super-Chandrasekhar mass systems not necessarily Type Ia progenitors WD+NS binaries? No radio or X-ray detections

Some ELM WDs are likely progenitors of AM CVn systems Gianninas et al. (2015, in prep)

Cooler ELM WD binaries have longer periods or else they would have already merged K-S statistic = 0.5622 Gianninas et al. (2015, in prep)

INDIVIDUAL HIGHLIGHTS

J0651: the poster child for ELM WDs Shortest period ELM WD binary  P = 12.75 min! Eclipsing! Hermes et al. (2012, ApJ, 757, 21)

The shift in the midpoint of the eclipses reveals that the orbit is decaying ! Hermes et al. (2012, ApJ, 757, 21)

The rate of decay agrees with the prediction of General Relativity! Hermes et al. (2015, in prep)

PSR B1913+16: The Hulse-Taylor pulsar Orbital decay of a binary pulsar system (PSR +NS) Test of GR 1993 Nobel Prize in Physics It took 30 years to display the same period shift as J0651! Weisberg & Taylor (2005, ASPC, 328, 25)

WD 0931+444: a new 20-min ELM WD! Preliminary SDSS DR10 selection Kilic et al. (2014, MNRAS, 441, L1 )

WD 0931+444 looks like a DA+dM… DA+dM1 : Silvestri et al. (2006) Rebassa-Mansergas et al. (2007,2010) Heller et al. (2009) MMT 6.5m SDSS Kilic et al. (2014, MNRAS, 441, L1 )

Gemini data shows that M dwarf is indeed a background object GMOS-North time resolved spectroscopy Na I doublet H Kilic et al. (2014, MNRAS, 441, L1 )

ELM WDs are among the best gravitational wave verification sources for eLISA eLISA after 2 years Amaro-Seoane et al. (2013) Average Galactic Foreground Nelemans et al. (2001) Kilic et al. (2015, ASSP, 40, 167)

Several PSR have ELM WD companions Recent example: triple system PSR J0337+1715 (Ransom et al., 2014, Nature) Several of the ELM WD companions are in the correct range of Teff and log g (i.e. instability strip) to pulsate

ELM WD instability strip is an extension of ZZ Ceti Instability Strip Gianninas et al. (2014, ApJ, 794,35)

Several PSR have ELM WD companions Recent example: triple system PSR J0337+1715 (Ransom et al., 2014, Nature) Several of the ELM WD companions are in the correct range of Teff and log g (i.e. instability strip) to pulsate No pulsations detected for ELM companions of PSR J1012+5307+ and PSR J1911-5958 (Steinfadt et al. 2010)

PSR J1909-3744 No strong evidence for pulsations Kilic et al. (2015, MNRAS, 446,L26)

PSR J1738+0333 First pulsating ELM WD companion to a PSR! Kilic et al. (2015, MNRAS, 446, L26)

Updated ELM WD instability strip Kilic et al. (2015, MNRAS, 446, L26)

TAKEAWAYS ELM Survey has discovered 74 ELM WDs and many more are in the pipeline Starting to be able to do some statistics 2014 Highlights: J0651 : detection of orbital decay Discovery of a new 20-min system : 2nd gravitational wave verification source Discovery of first PSR + pulsating ELM WD

Collaborators University of Oklahoma: Mukremin Kilic, Paul Canton Smithsonian Astrophysical Observatory: Warren Brown, Scott Kenyon University of Warwick: JJ Hermes Université de Montréal: Patrick Dufour, Pierre Bergeron University of Texas: Keaton Bell, Samuel Harrold Instituto de Astrofisica de Canarias: Carlos Allende Prieto