AN ALUMINUM/CALCIUM-RICH, IRON-POOR, WHITE DWARF STAR: EVIDENCE FOR AN EXTRASOLAR PLANETARY LITHOSPHERE?

The presence of elements heavier than helium in white dwarf atmospheres is often a signpost for the existence of rocky objects that currently or previously orbited these stars. We have measured the abundances of various elements in the hydrogen-atmosphere white dwarfs G149-28 and NLTT 43806. In comparison with other white dwarfs with atmospheres polluted by heavy elements, NLTT 43806 is substantially enriched in aluminum but relatively poor in iron. We compare the relative abundances of Al and eight other heavy elements seen in NLTT 43806 with the elemental composition of bulk Earth, with simulated extrasolar rocky planets, with solar system meteorites, with the atmospheric compositions of other polluted white dwarfs, and with the outer layers of the Moon and Earth. The best agreement is found with a model that involves accretion of a mixture of terrestrial crust and upper mantle material onto NLTT 43806. The implication is that NLTT 43806 is orbited by a differentiated rocky planet, perhaps quite similar to Earth, that has suffered a collision that stripped away some of its outer layers.

[1]  K. Lodders,et al.  Survey and evaluation of eucrite bulk compositions , 1998 .

[2]  D. L. Anderson.  Theory of Earth , 2014 .

[3]  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.

[4]  R. Napiwotzki,et al.  The magnetic and metallic degenerate G77-50 , 2011, 1101.2203.

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

[6]  Pierre Bergeron,et al.  PHOTOMETRIC CALIBRATION OF HYDROGEN- AND HELIUM-RICH WHITE DWARF MODELS , 1995 .

[7]  S. Vennes,et al.  The cool magnetic DAZ white dwarf NLTT 10480 , 2011, 1106.0993.

[8]  P. Bergeron,et al.  PRECISE ESTIMATES OF THE SYNTHETIC SPECTRAL DISTANCES TO DA WHITE DWARFS , 2008 .

[9]  A. Davis,et al.  A petrologic and ion microprobe study of a Vigarano Type B refractory inclusion: Evolution by multiple stages of alteration and melting , 1993 .

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

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

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

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

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

[15]  S. Xu,et al.  EXTRASOLAR REFRACTORY-DOMINATED PLANETESIMALS: AN ASSESSMENT , 2012, 1211.2453.

[16]  P. Bergeron,et al.  A SPECTROSCOPIC ANALYSIS OF WHITE DWARFS IN THE KISO SURVEY , 2010, 1003.4313.

[17]  V. K. Rai,et al.  Primordial compositions of refractory inclusions , 2008 .

[18]  E. Jarosewich,et al.  Chemical analyses of meteorites: A compilation of stony and iron meteorite analyses , 1990 .

[19]  C. Hawkesworth,et al.  Evolution of the continental crust , 2006, Nature.

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

[21]  T. R. Marsh,et al.  POSSIBLE SIGNS OF WATER AND DIFFERENTIATION IN A ROCKY EXOPLANETARY BODY , 2010, 1101.0158.

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

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

[24]  Don L. Anderson,et al.  New Theory of the Earth: Elasticity and solid-state geophysics , 2007 .

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

[26]  M. Kilic,et al.  A NEAR-INFRARED SPECTROSCOPIC SURVEY OF COOL WHITE DWARFS IN THE SLOAN DIGITAL SKY SURVEY , 2009 .

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

[28]  J. Farihi,et al.  X-RAY AND INFRARED OBSERVATIONS OF TWO EXTERNALLY POLLUTED WHITE DWARFS , 2009 .

[29]  S. Vennes,et al.  The heavily polluted atmosphere of the DAZ white dwarf GALEX J193156.8+011745 , 2010, 1002.2069.

[30]  Spectroscopic Identification of Cool White Dwarfs in the Solar Neighborhood , 2006, astro-ph/0601477.

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