Finding Extreme Subdwarfs

Abstract

I develop a new technique to identify M-type extreme subdwarfs (esdMs) and demonstrate that it is substantially more efficient than previous methods. I begin by obtaining spectroscopy and improved photometry of a sample of 54 late-type halo candidates using the rNLTT reduced proper motion (RPM) diagram. From spectroscopy, I find that four of these are esdMs, three of which were previously unknown. From the improved photometry, I show that all four lie in a narrow RPM corridor that contains only 4 non-esdMs. Hence, with good photometry (i.e., without spectroscopy), it appears possible to select esdM candidates with a 50% esdM yield. This is more than an order of magnitude more efficient than previous methods.

23 pages, 10 figures. Submitted to AJ

References in corpus (8)

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• M-Subdwarfs: Spectroscopic Classification and the Metallicity Scale
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• A Volume-Limited Sample of Ultracool Dwarfs. I. Construction, Space Density, and a Gap in the L/T Transition
• An Infrared High Proper Motion Survey Using 2MASS and SDSS: Discovery of M, L and T Dwarfs
• Trigonometric Parallaxes and Proper Motions of 134 Southern Late M, L, and T Dwarfs from the Carnegie Astrometric Planet Search Program
• A spectroscopic and proper motion search of Sloan digital Sky Survey: red subdwarfs in binary systems
• Multiplicity of the Galactic Senior Citizens: A high-resolution search for cool subdwarf companions
• Optical BVRI Photometry of Common Proper Motion F/G/K+M Wide Separation Binaries