2008/10/20 by Juna A. Kollmeier, Andrew Gould, G. R. Knapp +2 · 31 citations
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Galactic Center #Galactic halo #Galaxies: Formation, Evolution, Phenomena #Galaxy #Halo #Hypervelocity #Physics #Population #Proper motion #Radial velocity #Sky #Stars #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1088/0004-637x/697/2/1543
published in The Astrophysical Journal 697(2), 1543-1548 (IOP Publishing) · Submitted to ApJ; 14 pages including 2 figures
arxiv created 2008/10/20 · openalex publication_date 2009/05/14 · arxiv updated 2015/05/12 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
We present limits on the ejection of solar-metallicity ("metal-rich") old-population hypervelocity stars (HVS) from a sample of over 290,000 stars selected from the Sloan Digital Sky Survey. We derive the speed at the solar circle from the measured positions and radial velocities (RVs) by assuming a radial orbit and adopting a simple isothermal model of the Galactic halo, which enables us to identify candidate bound and unbound ejectees. We examine the kinematics and metallicity distribution of this sample and find no metal-rich ejectees, from which our limits are derived. However, while tuned for metal-rich stars, our experiment is also sensitive to metal-poor ejectees. We find four candidate bound metal-poor F-stars from this sample, all with negative Galactocentric RV (i.e., returning toward the Galactic center (GC)). We additionally find two candidate metal-poor unbound stars (one F and one G). However, existing proper-motion measurements of these two stars make them unlikely to be emerging from the GC. The metal-rich nondetection places a limit on the rate of ejection of old-population stars from the GC of <35 Myr −1 . Comparing to the rate for more massive B-star ejectees of ∼0.6 Myr −1 , our limit on the rate of ejection of old-population HVS shows that the mass function at the GC is not bottom-heavy and is consistent with being normal to top-heavy. Future targeted surveys of old-population HVS could determine if it is indeed top-heavy.