the search for the shortest period binary wds: the latest results from the elm survey alexandros...
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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)