A cool, magnetic white dwarf accreting planetary debris

Author:

Vennes Stéphane1,Kawka Adela2ORCID,Klein Beth L3,Zuckerman B3,Weinberger Alycia J4,Melis Carl5

Affiliation:

1. Mathematical Sciences Institute, The Australian National University , Canberra, ACT 0200 , Australia

2. International Centre for Radio Astronomy Research – Curtin University , GPO Box U1987, Perth, WA 6845 , Australia

3. Department of Physics and Astronomy, University of California , Los Angeles, CA 90095-1562 , USA

4. Earth and Planets Laboratory, Carnegie Institution for Science , 5241 Broad Branch Rd NW, Washington, DC 20015 , USA

5. Center for Astrophysics and Space Sciences, University of California , San Diego, CA 92093-0424 , USA

Abstract

ABSTRACT We present an analysis of spectroscopic data of the cool, highly magnetic, and polluted white dwarf 2MASS J0916−4215. The atmosphere of the white dwarf is dominated by hydrogen, but numerous spectral lines of magnesium, calcium, titanium, chromium, iron, and strontium, along with Li i, Na i, Al i, and K i lines, are found in the incomplete Paschen–Back regime, most visibly, in the case of Ca ii lines. Extensive new calculations of the Paschen–Back effect in several spectral lines are presented and results of the calculations are tabulated for the Ca ii H&K doublet. The abundance pattern shows a large lithium and strontium excess, which may be viewed as a signature of planetary debris akin to Earth’s continental crust accreted on to the star, although the scarcity of silicon indicates possible dilution in bulk Earth material. Accurate abundance measurements proved sensitive to the value of the broadening parameter due to collisions with neutral hydrogen ($\Gamma$H i), particularly in saturated lines such as the resonance lines of Ca i and Ca ii. We found that $\Gamma$H i if formulated with values from the literature could be overestimated by a factor of 10 in most resonance lines.

Funder

National Science Foundation

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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