NOAO > Observing Info > Approved Programs > 2009B-0537
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NOAO > Observing Info > Approved Programs > 2009B-0537 |
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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: Calibrating the metallicity scale of low-mass halo stars using wide binaries
Abstract:
We propose to obtain spectra of stars in common proper motion
doubles, kinematically identified as local low-mass subdwarfs from the
Galactic halo population (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 under
the assumption that physical doubles have near identical metal
abundances. Subdwarf pairs will effectively trace 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
critical to determine the metallicity of over 3,500 (single star) halo M
subdwarfs recently 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.
National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360
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NOAO > Observing Info > Approved Programs > 2009B-0537 |
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