NOAO >   Observing Info >   Approved Programs >   2011B-0127

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Proposal Information for 2011B-0127


PI: John Subasavage, Cerro Tololo Interamerican Observatory, jsubasavage@ctio.noao.edu
Address: Casilla 603, La Serena, Chile

CoI: Jay Farihi, University of Leicester
CoI: Steve Margheim, Gemini Observatory - South
CoI: Boris Gaensicke, University of Warwick

Title: The Hidden Radial Velocity Companion to the Nearby Halo Star and Prototype Carbon Dwarf G77-61

Abstract: Discovered in 1977, the nearby main-sequence star G77-61 is an extremely metal-poor visitor from the Galactic halo and prototype of the dwarf carbon class of stars. Over 30 years later, both its physical parameters and evolutionary status remain poorly understood, epitomizing the shortcoming that exists for the entire class of dwarf carbon stars; a notable component of Galactic chemical and evolutionary history that has been overlooked. As a low-mass star, G77-61 must be externally polluted by carbon-rich material, presumably from a giant companion that has since evolved into a white dwarf. Indeed, radial velocity measurements made 25 years ago seemed to indicate an unseen companion with a period near 245 days. But this tentative result is difficult to reconcile with theoretical expectations, as a wide orbit inhibits significant mass transfer, and periods on 1 yr timescales are absent among white dwarf - red dwarf binaries in the Galactic disk. We propose to robustly determine the orbital period of the G77-61, enabling an accurate reconstruction of its chemical history and orbital evolution, thus constraining models for Galactic stellar and chemical evolution via the larger class of dwarf carbon stars.


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