¹Ted M Johnson,¹Beth L. Klein,²D. Koester,³Carl Melis,¹B. Zuckerman,¹M. Jura
The Astrophysical Journal 941, 113 Open Access Link to Article [DOI 10.3847/1538-4357/aca089]
¹Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1562, USA; tedjohnson12@g.ucla.edu
²Institut fur Theoretische Physik und Astrophysik, University of Kiel, D-24098 Kiel, Germany
³Center for Astrophysics and Space Sciences, University of California, San Diego, CA 92093-0424, USA

Ultraviolet and optical spectra of the hydrogen-dominated atmosphere white dwarf star G238-44 obtained with FUSE, Keck/HIRES, HST/COS, and HST/STIS reveal 10 elements heavier than helium: C, N, O, Mg, Al, Si, P, S, Ca, and Fe. G238-44 is only the third white dwarf with nitrogen detected in its atmosphere from polluting planetary system material. Keck/HIRES data taken on 11 nights over 24 yr show no evidence for variation in the equivalent width of measured absorption lines, suggesting stable and continuous accretion from a circumstellar reservoir. From measured abundances and limits on other elements, we find an anomalous abundance pattern and evidence for the presence of metallic iron. If the pollution is from a single parent body, then it would have no known counterpart within the solar system. If we allow for two distinct parent bodies, then we can reproduce the observed abundances with a mix of iron-rich Mercury-like material and an analog of an icy Kuiper Belt object with a respective mass ratio of 1.7:1. Such compositionally disparate objects would provide chemical evidence for both rocky and icy bodies in an exoplanetary system and would be indicative of a planetary system so strongly perturbed that G238-44 is able to capture both asteroid and Kuiper Belt–analog bodies near-simultaneously within its <100 Myr cooling age.