DETAILED COMPOSITIONAL ANALYSIS OF THE HEAVILY POLLUTED DBZ WHITE DWARF SDSS J073842.56+183509.06: A WINDOW ON PLANET FORMATION?

We present a new model atmosphere analysis of the most metal-contaminated white dwarf known, the DBZ SDSS J073842.56+183509.06. Using new high-resolution spectroscopic observations taken with Keck and Magellan, we determine precise atmospheric parameters and measure abundances of 14 elements heavier than helium. We also report new Spitzer mid-infrared photometric data that are used to better constrain the properties of the debris disk orbiting this star. Our detailed analysis, which combines data taken from seven different observational facilities (Galaxy Evolution Explorer, Gemini, Keck, Magellan, MMT, Sloan Digital Sky Survey, and Spitzer), clearly demonstrates that J0738+1835 is accreting large amounts of rocky terrestrial-like material that has been tidally disrupted into a debris disk. We estimate that the body responsible for the photospheric metal contamination was at least as large as Ceres, but was much drier, with less than 1% of the mass contained in the form of water ice, indicating that it formed interior to the snow line around its parent star. We also find a correlation between the abundances (relative to Mg and bulk Earth) and the condensation temperature; refractory species are clearly depleted, while the more volatile elements are possibly enhanced. This could be the signature of a body that formed in a lower temperature environment than where Earth formed. Alternatively, we could be witnessing the remains of a differentiated body that lost a large part of its outer layers.

[1]  John H. Debes,et al.  Are There Unstable Planetary Systems around White Dwarfs , 2002 .

[2]  M. Couture,et al.  HIRES: the high-resolution echelle spectrometer on the Keck 10-m Telescope , 1994, Astronomical Telescopes and Instrumentation.

[3]  Ralf S. Klessen,et al.  American Institute of Physics Conference Series , 2010 .

[4]  M. Jura,et al.  WATER FRACTIONS IN EXTRASOLAR PLANETESIMALS , 2011, 1110.1774.

[5]  B. Zuckerman,et al.  ANCIENT PLANETARY SYSTEMS ARE ORBITING A LARGE FRACTION OF WHITE DWARF STARS , 2010, 1007.2252.

[6]  D. Lauretta,et al.  Erratum to “Making the Earth: Combining dynamics and chemistry in the Solar System” [Icarus 205 (2010) 321–337] , 2010 .

[7]  F. Kupka,et al.  The Vienna Atomic Line Database: Present State and Future Development , 1997 .

[8]  Stephen A. Shectman,et al.  The MagE spectrograph , 2008, Astronomical Telescopes + Instrumentation.

[9]  M. Jura,et al.  THE SURVIVAL OF WATER WITHIN EXTRASOLAR MINOR PLANETS , 2010, 1001.2595.

[10]  G. Fontaine,et al.  Diffusion coefficients for stellar plasmas , 1986 .

[11]  Marc J. Kuchner,et al.  The Dust Cloud around the White Dwarf G29-38 , 2005, astro-ph/0511358.

[12]  Ben Zuckerman,et al.  Metal Lines in DA White Dwarfs , 2003 .

[13]  T. Marsh,et al.  A Gaseous Metal Disk Around a White Dwarf , 2006, Science.

[14]  K. Lodders.  Solar System Abundances and Condensation Temperatures of the Elements , 2003 .

[15]  H. C. Stempels,et al.  VALD{2: Progress of the Vienna Atomic Line Data Base ? , 1999 .

[16]  James Liebert,et al.  On the Spectral Evolution of Cool, Helium-Atmosphere White Dwarfs: Detailed Spectroscopic and Photometric Analysis of DZ Stars , 2007, astro-ph/0703758.

[17]  M. Jura.  A Tidally Disrupted Asteroid around the White Dwarf G29-38 , 2003 .

[18]  Gilles Fontaine,et al.  A study of metal abundance patterns in cool white dwarfs. II - Simulations of accretion episodes , 1993 .

[19]  G. Manhès,et al.  Chemical composition of the Earth and the volatility control on planetary genetics , 2001 .

[20]  M. Jura,et al.  POLLUTION OF SINGLE WHITE DWARFS BY ACCRETION OF MANY SMALL ASTEROIDS , 2008, 0802.4075.

[21]  Pierre Brassard,et al.  The Potential of White Dwarf Cosmochronology , 2001 .

[22]  G. Fontaine,et al.  THE DISCOVERY OF THE MOST METAL-RICH WHITE DWARF: COMPOSITION OF A TIDALLY DISRUPTED EXTRASOLAR DWARF PLANET , 2010, 1006.3710.

[23]  J. Southworth,et al.  SDSS J104341.53+085558.2: a second white dwarf with a gaseous debris disc , 2007, 0705.0447.

[24]  J. Farihi,et al.  STRENGTHENING THE CASE FOR ASTEROIDAL ACCRETION: EVIDENCE FOR SUBTLE AND DIVERSE DISKS AT WHITE DWARFS , 2010, 1003.2627.

[25]  B. Zuckerman,et al.  INFRARED SIGNATURES OF DISRUPTED MINOR PLANETS AT WHITE DWARFS , 2009, 0901.0973.

[26]  Ted von Hippel,et al.  THE DUST CLOUD AROUND THE WHITE DWARF G 29-38. II. SPECTRUM FROM 5 TO 40 μm AND MID-INFRARED PHOTOMETRIC VARIABILITY , 2008, 0810.3276.

[27]  B. Zuckerman,et al.  CHEMICAL ABUNDANCES IN THE EXTERNALLY POLLUTED WHITE DWARF GD 40: EVIDENCE OF A ROCKY EXTRASOLAR MINOR PLANET , 2009, 0912.1422.

[28]  B. Zuckerman,et al.  The Chemical Composition of an Extrasolar Minor Planet , 2007, 0708.0198.

[29]  Albrecht W. Hofmann,et al.  The chemical composition of the Earth , 1995 .

[30]  D. Koester,et al.  Accretion and diffusion in white dwarfs - New diffusion timescales and applications to GD 362 and G 29-38 , 2009, 0903.1499.

[31]  B. Gaensicke,et al.  SDSS J084539.17+225728.0: the first DBZ white dwarf with a metal‐rich gaseous debris disc , 2008, 0809.2600.

[32]  P. Dufour,et al.  The discovery of a debris disc around the DAV white dwarf PG 1541+651 , 2011, 1110.3799.

[33]  Kurtis A. Williams,et al.  Accepted for publication in the Astrophysical Journal Preprint typeset using L ATEX style emulateapj v. 10/09/06 PROBING THE LOWER MASS LIMIT FOR SUPERNOVA PROGENITORS AND THE HIGH-MASS END OF THE INITIAL-FINAL MASS RELATION FROM WHITE DWARFS IN THE OPEN , 2022 .

[34]  M. A. Barstow,et al.  Rocky planetesimals as the origin of metals in DZ stars , 2010, 1001.5025.

[35]  David P. O'Brien,et al.  THE COMPOSITIONAL DIVERSITY OF EXTRASOLAR TERRESTRIAL PLANETS. I. IN SITU SIMULATIONS , 2010, 1004.0971.

[36]  A. Gianninas,et al.  Discovery of a Cool, Massive, and Metal-rich DAZ White Dwarf , 2004, astro-ph/0410706.

[37]  Gilles Fontaine,et al.  Diffusion in white dwarfs - New results and comparative study , 1986 .

[38]  J. Farihi,et al.  Externally Polluted White Dwarfs with Dust Disks , 2007, 0704.1170.

[39]  Rebecca A. Bernstein,et al.  MASE: A New Data-Reduction Pipeline for the Magellan Echellette Spectrograph , 2009, 0910.1834.

[40]  B. Zuckerman,et al.  ROCKY EXTRASOLAR PLANETARY COMPOSITIONS DERIVED FROM EXTERNALLY POLLUTED WHITE DWARFS , 2011, 1108.1565.

[41]  M. Jura,et al.  Carbon Deficiency in Externally Polluted White Dwarfs: Evidence for Accretion of Asteroids , 2006, astro-ph/0609045.

[42]  UCSD,et al.  ECHOES OF A DECAYING PLANETARY SYSTEM: THE GASEOUS AND DUSTY DISKS SURROUNDING THREE WHITE DWARFS , 2010, 1007.2023.

[43]  Carl Melis,et al.  AN ALUMINUM/CALCIUM-RICH, IRON-POOR, WHITE DWARF STAR: EVIDENCE FOR AN EXTRASOLAR PLANETARY LITHOSPHERE? , 2011, 1107.2167.

[44]  R. Rafikov.  Runaway accretion of metals from compact discs of debris on to white dwarfs , 2011, 1102.4343.

[45]  B. Gaensicke.  Gaseous Debris Disks around White Dwarfs , 2011, 1101.3946.

[46]  University of Leicester,et al.  ACCRETION OF A TERRESTRIAL-LIKE MINOR PLANET BY A WHITE DWARF , 2011, 1102.0311.

[47]  G. Fazio,et al.  The Infrared Array Camera (IRAC) for the Spitzer Space Telescope , 2004, astro-ph/0405616.