In a search for new white dwarfs in DR12 of the Sloan Digital Sky Survey, Kepler et al. (2016) found atmospheric parameters for thousands of objects with effective temperatures below 20,000 K and surface gravities between 5.5 < log(g) < 6.5. They classified these objects as cool subdwarfs — sdA — and speculated that many may be extremely low-mass (ELM) white dwarfs (helium-core white dwarfs with masses below 0.3 Msun). We present evidence — using radial velocities, photometric colors, and reduced proper motions — that the vast majority (>99%) of these objects are unlikely to be ELM white dwarfs. Their true identity remains an interesting question.
J. Hermes, B. Gaensicke and E. Breedt
Mon, 27 Feb 17
Comments: 7 pages, 3 figures, 2 tables. As appears in the ASP Conference Series proceedings of “20th European Workshop Workshop on White Dwarfs” held at the University of Warwick, UK on July 25-29th, 2016