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Title: A DARK SPOT ON A MASSIVE WHITE DWARF

We present the serendipitous discovery of eclipse-like events around the massive white dwarf SDSS J152934.98+292801.9 (hereafter J1529+2928). We selected J1529+2928 for time-series photometry based on its spectroscopic temperature and surface gravity, which place it near the ZZ Ceti instability strip. Instead of pulsations, we detect photometric dips from this white dwarf every 38 minutes. Follow-up optical spectroscopy observations with Gemini reveal no significant radial velocity variations, ruling out stellar and brown dwarf companions. A disintegrating planet around this white dwarf cannot explain the observed light curves in different filters. Given the short period, the source of the photometric dips must be a dark spot that comes into view every 38 minutes due to the rotation of the white dwarf. Our optical spectroscopy does not show any evidence of Zeeman splitting of the Balmer lines, limiting the magnetic field strength to B < 70 kG. Since up to 15% of white dwarfs display kG magnetic fields, such eclipse-like events should be common around white dwarfs. We discuss the potential implications of this discovery on transient surveys targeting white dwarfs, like the K2 mission and the Large Synoptic Survey Telescope.
Authors:
; ; ;  [1] ; ; ;  [2] ;  [3] ;  [4] ;  [5]
  1. Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks St., Norman, OK 73019 (United States)
  2. Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States)
  3. Smithsonian Astrophysical Observatory, 60 Garden St., Cambridge, MA 02138 (United States)
  4. Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)
  5. Institut de recherche sur les exoplanétes (iREx), Département de Physique, Université de Montréal, C.P. 6128, Succ. Centre-Ville, Montréal, QC H3C 3J7 (Canada)
Publication Date:
OSTI Identifier:
22518668
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 814; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTROSCOPY; BALMER LINES; DIAGRAMS; ECLIPSE; GRAVITATION; MAGNETIC FIELDS; PHOTOMETRY; PLANETS; PULSATIONS; RADIAL VELOCITY; ROTATION; STARSPOTS; TELESCOPES; TRANSIENTS; VISIBLE RADIATION; WHITE DWARF STARS; ZEEMAN EFFECT