The Lowest Mass White Dwarf
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Publisher:American Astronomical Society
Citation:Mukremin Kilic et al, "The Lowest Mass White Dwarf," The Astrophysical Journal 660, no. 2 (2007), doi:10.1086/514327
Extremely low mass white dwarfs are very rare objects likely formed in compact binary systems. We present MMT optical spectroscopy of 42 low-mass white dwarf candidates serendipitously discovered in a survey for hypervelocity B-type stars. One of these objects, SDSS J0917+46, has T_eff = 11,288 ± 72 K and log g = 5.48 ± 0.03; with an estimated mass of 0.17 Msun, it is the lowest gravity/mass white dwarf currently known. However, 40 of the low-mass candidates are normal DA white dwarfs with apparently inaccurate SDSS g magnitudes. We revisit the identification of low-mass white dwarf candidates previously found in the SDSS and conclude that four objects have M < 0.2 Msun. None of these white dwarfs show excess emission from a binary companion, and radial velocity searches will be necessary to constrain the nature of the unseen companions.