PI: Jay Farihi, University of Leicester, email@example.com
Address: Physics Department, University Road, Leicester LE1 7RH, UK
CoI: Seth Redfield, Wesleyan University
CoI: Detlev Koester, University of Kiel
CoI: Martin Barstow, University of Leicester
CoI: Nigel Hambly, Royal Observatory Edinburgh
CoI: Ralf Napiwotzski, University of Hertfordshire
Title: The Origin of Metals in Cool White Dwarfs: Disrupted Minor Planets or Interstellar Gas?
Abstract: We propose to investigate the origin and abundances of metals in a sample of externally polluted, cool, helium atmosphere white dwarfs discovered in the SDSS. It is challenging to explain their photospheric metals via interstellar accretion because the majority of these stars lie above the Galactic gas and dust layer at |z|>100 pc, and have no detected hydrogen. A distinct alternative for some fraction of these stars is the accretion of tidally disrupted minor planets; a scenario strongly supported by \em Spitzer observations of warm dust disks at more than one dozen similarly metal-polluted white dwarfs. The proposed observations will enable: 1) radial velocity measurements for a full 3D spatial and kinematical picture of this sample and its relationship, if any, to the interstellar medium; 2) improved metal abundance analyses, including the likely detection of additional heavy elements; and 3) determination of hydrogen abundances or upper limits, which will help distinguish between interstellar (H-rich) or circumstellar (H-poor) accreted material. For those white dwarfs found to be externally polluted by rocky, circumstellar material, the proposed spectroscopy will indirectly determine the bulk composition of their extrasolar asteroids.
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