The Search for the Shortest Period Binary WDs: The Latest Results from the ELM

Survey

Alexandros GianninasEUROWD14

Université de MontréalAugust 15th, 2014

The ELM Survey

• Extremely Low-Mass WDs – M < 0.30 M (5 < log g < 7)

– He-core WDs– Found in P < 1 d binary systems

• The ELM Survey is an ongoing, targeted search for ELM WDs

• Papers I – V + VI : 61 + 12 ELM WDs Brown et al. (2010, 2012, 2013), Kilic et al. (2011, 2012) + Gianninas et al. (2014, in prep)

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SDSS colors work well for choosing ELM WD candidates

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Brown et al. (2012, ApJ, 744, 142) Gianninas et al. (2014, in prep)

Radial Velocity Follow-Up

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FLWO 1.5m MMT 6.5m KPNO 4m

ELM VI: 12 new ELM WDs

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Gianninas et al. (2014, in prep)

Standard Spectroscopic Technique

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Gianninas et al. (2014, in prep)

Many ELM WDs have Ca lines…

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Gianninas et al. (2014, arXiv:1408.3118)

… some have Mg lines…

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Gianninas et al. (2014, arXiv:1408.3118)

… others have a lot more!

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Gianninas et al. (2014, ApJ, 781, 104)

J0745+1949

See also

GALEX J1717+6757Hermes et al. (2014) + posterVennes et al. (2011)

PSR J1816+4510Kaplan et al. (2013)

Some even have Helium

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Gianninas et al. (2014, arXiv:1408.3118)

a lot of it!

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Gianninas et al. (2014, arXiv:1408.3118)

Althaus et al. (2013)

Dorman et al. (1998)

with Ca with Ca & He

Where do the metals come from?• Accretion from

circumbinary disk?– Typical Roche radius for

WDs ≈ 1 - 1.5 R

– Stable orbits around a binary ~2x the orbital separation (a) (Holman et al. 1999)

– All metal-rich ELMs (except J0745) have a > 1 R

• H-shell flash?– Kaplan et al. (2013)– Diffusion times too short

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Gianninas et al. (2014, arXiv:1408.3118)

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with Ca with Ca & He Gianninas et al. (2014, arXiv:1408.3118)

WD 0931+444: a new 20 minute ELM WD

• C. A. Prieto: SDSS DR10 selection

• W. Brown: end of the night “shot in the dark”

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Kilic et al. (2014, MNRAS, 441, L1 )

WD 0931+444: a new 20 minute ELM WD

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Kilic et al. (2014, MNRAS, 441, L1 )

MMT 6.5m SDSS

DA+dM1 : Silvestri et al. (2006) Rebassa-Mansergas et al. (2007,2010) Heller et al. (2009)

WD 0931+444: a new 20 minute ELM WD

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Kilic et al. (2014, MNRAS, 441, L1 )

GMOS-North time resolved spectroscopy

Na I H

Gravitational Wave Verification Sources

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Kilic et al. (2014, ASSP, in press)

Average Galactic ForegroundNelemans et al. (2001)

eLISA after 2 yearsAmaro-Seoane et al.

(2013)

Two populations are emerging

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Gianninas et al. (2014, in prep)

Updated Instability Strip: ML2/=0.8

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Gianninas et al. (2014, arXiv:1408.3118)

Magenta: New ELM Pulsator (see Keaton Bell’s poster C1)

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Blue: ELM VI sample

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Red: …stay tuned!

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CONCLUSIONS

• ELM Survey: 74 new ELM WDs and more to come– Starting to be able to do some statistics

• Helium might be the ‘smoking gun’ for a recent H-shell flash, not metals

• ELMs are important sources of gravitational waves (two verification sources)

• Mapping out the instability strip from within (7 known pulsators) and without

• Wish list:– Expand survey to the southern hemisphere– Constrain parameters of the secondaries

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Collaborators

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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

University of Texas: Keaton Bell, Samuel Harrold

Instituto de Astrofisica de Canarias: Carlos Allende Prieto

The ‘high log g problem’ at low log g

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Gianninas et al. (2014, arXiv:1408.3118)

How precise is ‘precise’?

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Gianninas et al. (2014, arXiv:1408.3118)