A Characterization of the Circumstellar Gas around WD 1124-293 using Cloudy

TL;DR

This study uses Cloudy modeling to analyze circumstellar gas around WD 1124-293, revealing composition, location, and stability over time, and introduces a new method for studying exo-planetary material.

Contribution

It presents a self-consistent Cloudy model of circumstellar gas around a polluted white dwarf, linking photospheric and circumstellar compositions and demonstrating a novel analysis approach.

Findings

Circumstellar gas is located about a hundred WD radii away.

Photospheric and circumstellar compositions are consistent.

The amount of Ca in circumstellar gas has remained stable over two decades.

Abstract

Between 30 - 50% of white dwarfs (WDs) show heavy elements in their atmospheres. This "pollution" is thought to arise from the accretion of planetesimals perturbed by outer planet(s) to within the WD's tidal disruption radius. A small fraction of these WDs show either emission or absorption from circumstellar (C-S) gas. The abundances of metals in the photospheres of WDs with C-S gas are mostly similar to the bulk composition of the Earth. The C-S component arises from gas produced through collisions and/or the sublimation of disintegrating planetesimals. High resolution spectroscopic observations of WD 1124-293 reveal photospheric and C-S absorption of Ca in multiple transitions. Here, we present high signal-to-noise ratio spectra, an updated WD atmosphere analysis, and a self-consistent model of its C-S gas. We constrain the abundances of Ca, Mg, and Fe in the photosphere of WD 1124-293, and find agreement with the abundances of these 3 species in the C-S gas. We find the location of the C-S gas is about a hundred white dwarf radii, the C-S and photospheric compositions are thus far consistent, the gas is not isothermal, and the amount of C-S Ca has not changed in two decades. We also demonstrate how to use Cloudy to model C-S gas viewed in absorption around polluted WDs. Modeling the abundances of C-S gas around polluted WDs with Cloudy provides a new method to measure the composition of exo-planetesimals and will allow a direct comparison to the composition of rocky bodies in the Solar System.