The polluted atmosphere of the white dwarf NLTT 25792 and the diversity of circumstellar environments

Abstract

We present an analysis of X-Shooter spectra of the polluted, hydrogen-rich white dwarf NLTT 25792. The spectra show strong lines of calcium (Ca H&K, near-infrared calcium triplet, and Ca I 4226 and numerous lines of iron along with magnesium and aluminum lines from which we draw the abundance pattern. Moreover, the photospheric Ca H&K lines are possibly blended with a circumstellar component shifted by -20 km/s relative to the photosphere. A comparison with a sample of four white dwarfs with similar parameters show considerable variations in their abundance patterns, particularly in the calcium to magnesium abundance ratio that varies by a factor of five within this sample. The observed variations, even after accounting for diffusion effects, imply similar variations in the putative accretion source. Also, we find that silicon and sodium are significantly underabundant in the atmosphere of NLTT 25792, a fact that may offer some clues on the nature of the accretion source.

Accepted for publication in ApJ

References in corpus (8)

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• Another one grinds the dust: Variability of the planetary debris disc at the white dwarf SDSS J104341.53+085558.2
• Evidence of enhanced magnetism in cool, polluted white dwarfs
• PEWDD: A database of white dwarfs enriched by exo-planetary material
• Asynchronous accretion can mimic diverse white dwarf pollutants I: core and mantle fragments