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We present an analysis of X-Shooter spectra of the polluted, hydrogen-richwhite 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 alongwith magnesium and aluminum lines from which we draw the abundance pattern.Moreover, the photospheric Ca H&K lines are possibly blended with acircumstellar component shifted by -20 km/s relative to the photosphere. Acomparison with a sample of four white dwarfs with similar parameters showconsiderable variations in their abundance patterns, particularly in thecalcium to magnesium abundance ratio that varies by a factor of five withinthis sample. The observed variations, even after accounting for diffusioneffects, imply similar variations in the putative accretion source. Also, wefind that silicon and sodium are significantly underabundant in the atmosphereof NLTT 25792, a fact that may offer some clues on the nature of the accretionsource.

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