NOAO >   Observing Info >   Approved Programs >   2011B-0554

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Proposal Information for 2011B-0554


PI: Jay Farihi, University of Leicester, jf123@star.le.ac.uk
Address: Physics Department, University Road, Leicester LE1 7RH, UK

CoI: Donald Hoard, California Institute of Technology
CoI: Boris Gansicke, University of Warwick
CoI: Carolyn Brinkworth, California Institute of Technology

Title: Identifying Water and Differentiation in a Rocky Exoplanetary Body Orbiting GD 61

Abstract: Our team has recently published \em Spitzer observations that reveal the presence of warm dust from a tidally destroyed rocky and possibly icy planetary body orbiting the white dwarf GD 61. \em FUSE far-ultraviolet and HIRESb optical spectra of the debris-contaminated star reveal traces of H, O, Mg, Si, Fe, and Ca in the He-dominated atmosphere. The nominal ratios of these elements indicate an excess of O relative to that expected from rock-forming metal oxides, and thus it is possible that water was accreted together with the terrestrial-like debris. Thus the parent body of the debris may be analogous to water- rich Solar System asteroids, which are perhaps the best candidates for water delivery to the primordial, dry Earth. Additionally, Fe is found to be deficient relative to Mg and Si, suggesting the material may have originated as the outer layers of a differentiated parent body, as is widely accepted for the Moon. \em However, each existing spectroscopic dataset contains only one or two transitions for some, but not all, these critical elements, resulting in uncertainties that preclude firm statistical confidence in O excess due to water. Here, we request Keck ESI spectroscopy to detect multiple transitions of O, Si, Mg, Ca, Fe, and thus precisely determine the O fraction of the parent body relative to that bound in metal oxides. The requested data will provide the first robust measure of the water fraction and bulk chemical composition of a terrestrial body orbiting another star.


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