Discovery spectroscopy determines the binary and atmospheric parameters
blue-shifted
red-shifted
Brown et al. 2012, ApJ, 744, 142
T eff = 10,540 ± 170 K
log(g) = 6.01 ± 0.06
P orb = 87.996 ± 0.006 min
K 1 = 508 ± 4 km s-‐‑1
M 2 > 1.10 M¤ if M 1 = 0.17 M¤
t merge < 170 Myr
J1741+6526: An 88-min WD+WD binary
ELM WDs and Predicted CNO Flashes Althaus et al. 2013, A&A, 557, A19
• Two low-mass WDs of different masses often cross the same points in a T eff —log(g) diagram
• There is a non-uniqueness to using T eff ,log(g) for ELM WD mass
Discovery of Pulsations in Low-Mass WDs Hermes et al. 2012, ApJ, 750, L28
Hermes et al. 2013, ApJ, 765, 102
Hermes et al. 2013, MNRAS, 436, 3573
Kilic et al. 2015, MNRAS, 446, 26
• CNO flashes erode the hydrogen layer mass of ELM WDs
• An observational test would come from pulsating WDs: asteroseismology
• Since October 2011 we discovered the first five pulsating low-mass,
Hermes et al. 2012, ApJ, 757, L21
P orb = 765.20644(95) s
K 1 = 616.9 ± 5.0 km s-‐‑1
i = 86.3 ± 1.0 deg
T eff,1 = 16,340 ± 260 K
M 1 = 0.252 ± 0.04 M¤
T eff,2 = 10,370 ± 360 K
M 2 = 0.50 ± 0.04 M¤
J0651+2844: A 12.75-min WD+WD Binary
• This 12.75-min WD+WD binary is decaying > 3.5 times faster than the 7.75-hr Hulse-Taylor binary pulsar, which was the first indirect detection of gravitational radiation (1993 Nobel prize in physics)
Weisberg et al. 2010, ApJ, 722, 1030
J0651+2844
PSR B1913+16
• Tidal torques should increase the rate of orbital decay in J0651+2844
– Additional angular momentum is lost from the orbit to spin-up the WDs to remain synchronized, leading to >5% faster rate of orbital decay (e.g., Piro 2011, ApJ, 740, L53; Fuller & Lai 2012, MNRAS, 421, 426)
The Fate of the WDs in J0651+2844