NOAO >   Observing Info >   Approved Programs >   2008B-0449

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Proposal Information for 2008B-0449


PI: Sebastien Lepine, American Museum of Natural History, lepine@amnh.org
Address: Astrophysics, Central Park West at 79th street, New York, NY 10024, USA

Title: M subdwarf halo binaries and a calibration of the metallicity scale for low-mass stars.

Abstract: We propose to obtain spectra of common proper motion doubles, kinematically identified as local low-mass subdwarfs from the Galactic halo (sdM+sdM). Based on their spectral subtypes and on accurate measurements of the TiO and CaH molecular bandstrengths, we will (1) obtain confirmation that the pairs are physical binaries, and (2) use them to refine and calibrate the metallicity scale in low-mass, metal- poor stars. The metal-poor, M subdwarfs show significant variations in the absolute and relative strengths of their TiO and CaH molecular bands, which are believed to be a function of both effective temperature and metallicity. Spectral analysis of the sdM+sdM pairs will isolate the effects of a variation in effective temperature, effectively tracing iso-metallicity contours in the CaH/TiO bandstrength diagram. These results will provide a test to the current classification scheme of M subdwarfs. Absolute metallicity measurements of earlier-type subdwarfs, now determined in separate programs, will be combined to the results of this proposed program to obtain the first reliable metallicity calibration in M subdwarfs over the full subtype range. The new calibration will be used to determine the metallicity of over 3,500 (single star) halo M subdwarfs identified in the Sloan Digital Sky Survey spectroscopic database, clearing the the way to a comprehensive study of the chemical evolution of the Galaxy from the point of view of low-mass stars.


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