Bibcode
Kilic, M.; Brown, Warren R.; Gianninas, A.; Hermes, J. J.; Allende Prieto, C.; Kenyon, S. J.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society: Letters, Volume 444, Issue 1, p.L1-L5
Fecha de publicación:
10
2014
Número de citas
45
Número de citas referidas
40
Descripción
We report the discovery of a detached 20-min orbital period binary white
dwarf (WD). WD 0931+444 (SDSS J093506.93+441106.9) was previously
classified as a WD + M dwarf system based on its optical spectrum. Our
time-resolved optical spectroscopy observations obtained at the 8 m
Gemini and 6.5 m MMT reveal peak-to-peak radial velocity variations of
≈400 km s-1 every 20 min for the WD, but no velocity
variations for the M dwarf. In addition, high-speed photometry from the
McDonald 2.1 m telescope shows no evidence of variability nor evidence
of a reflection effect. An M dwarf companion is physically too large to
fit into a 20 min orbit. Thus, the orbital motion of the WD is almost
certainly due to an invisible WD companion. The M dwarf must be either
an unrelated background object or the tertiary component of a
hierarchical triple system. WD 0931+444 contains a pair of WDs, a 0.32
M⊙ primary and a ≥0.14 M⊙ secondary, at
a separation of ≥0.19 R⊙. After J0651+2844, WD
0931+444 becomes the second shortest period detached binary WD currently
known. The two WDs will lose angular momentum through gravitational wave
radiation and merge in ≤9 Myr. The log h ≃ -22 gravitational
wave strain from WD 0931+444 is strong enough to make it a verification
source for gravitational wave missions in the milli-Hertz frequency
range, e.g. the evolved Laser Interferometer Space Antenna (eLISA),
bringing the total number of known eLISA verification sources to nine.
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