Astrogeology

Seven White Dwarfs With Circumstellar Gas Discs II: Tracing The Composition Of Exoplanetary Building Blocks

By Keith Cowing
Status Report
astro-ph.EP
June 18, 2024
Filed under , , , , , ,
Seven White Dwarfs With Circumstellar Gas Discs II: Tracing The Composition Of Exoplanetary Building Blocks
Logarithmic number abundance ratio of polluted white dwarfs comparing those with detectable circumstellar gas in emission (orange) compared to without (blue), normalised to solar (black dashed line) using solar abundances from Lodders et al. (2009). The grey ellipses show a 1 ๐œŽ, 2 ๐œŽ and 3 ๐œŽ error ellipse based on solar abundances with individual element errors of 0.1 dex, typical abundance errors for polluted white dwarfs. Larger figure below — astro-ph.EP

This second paper presents an in-depth analysis of the composition of the planetary material that has been accreted onto seven white dwarfs with circumstellar dust and gas emission discs with abundances reported in Paper I.

The white dwarfs are accreting planetary bodies with a wide range of oxygen, carbon, and sulfur volatile contents, including one white dwarf that shows the most enhanced sulfur abundance seen to date. Three white dwarfs show tentative evidence (2-3ฯƒ) of accreting oxygen-rich material, potentially from water-rich bodies, whilst two others are accreting dry, rocky material.

One white dwarf is accreting a mantle-rich fragment of a larger differentiated body, whilst two white dwarfs show an enhancement in their iron abundance and could be accreting core-rich fragments. Whilst most planetary material accreted by white dwarfs display chondritic or bulk Earth-like compositions, these observations demonstrate that core-mantle differentiation, disruptive collisions, and the accretion of core-mantle differentiated material are important.

Less than one percent of polluted white dwarfs host both observable circumstellar gas and dust. It is unknown whether these systems are experiencing an early phase in the disruption and accretion of planetary bodies, or alternatively if they are accreting larger planetary bodies.

From this work there is no substantial evidence for significant differences in the accreted refractory abundance ratios for those white dwarfs with or without circumstellar gas, but there is tentative evidence for those with circumstellar gas discs to be accreting more water rich material which may suggest that volatiles accrete earlier in a gas-rich phase.

Figures showing the logarithmic number abundance ratio of polluted white dwarfs comparing those with detectable circumstellar gas in emission (orange) compared to without (blue), normalised to solar (black dashed line) using solar abundances from Lodders et al. (2009). The grey ellipses show a 1 ๐œŽ, 2 ๐œŽ and 3 ๐œŽ error ellipse based on solar abundances with individual element errors of 0.1 dex, typical abundance errors for polluted white dwarfs. The arrows show how the abundances are affected by: heating of the pollutant body during formation (see Sections 2.1 and 4) and sinking in the white dwarfsโ€™ atmosphere (solid line shows steady state, and dotted line shows 3๐œSi into the declining phase). The histograms show the 1D distribution for those with detectable circumstellar gas in emission (orange solid line) compared to without (blue dashed line). FG main sequence star data are from Hinkel et al. (2014), chondrite data from Alexander (2019b,a), and other meteorite (achondrites, stoney-iron meteorites, and iron meteorites) data from Nittler et al. (2004). Abundances of the polluted material for the white dwarfs with detectable gas discs are from: Dufour et al. (2012); Melis et al. (2012); Wilson et al. (2015); Melis & Dufour (2017a); Xu et al. (2019); Rogers et al. (2023), and abundances for white dwarfs without detectable gas discs are from: Zuckerman et al. (2007); Klein et al. (2011); Melis et al. (2011); Zuckerman et al. (2011); Gรคnsicke et al. (2012); Jura et al. (2012); Kawka & Vennes (2012); Farihi et al. (2013); Xu et al. (2013); Vennes & Kawka (2013); Xu et al. (2014); Raddi et al. (2015); Farihi et al. (2016); Kawka & Vennes (2016); Gentile Fusillo et al. (2017); Hollands et al. (2017); Xu et al. (2017); Blouin et al. (2018); Swan et al. (2019); Xu et al. (2019); Fortin-Archambault et al. (2020); Hoskin et al. (2020); Kaiser et al. (2021); Gonzรกlez Egea et al. (2021); Klein et al. (2021); Izquierdo et al. (2021); Elms et al. (2022); Hollands et al. (2021); Johnson et al. (2022); Doyle et al. (2023); Izquierdo et al. (2023); Swan et al. (2023); Vennes et al. (2024). — astro-ph.EP

L. K. Rogers, A. Bonsor, S. Xu, A. M. Buchan, P. Dufour, B. L. Klein, S. Hodgkin, M. Kissler-Patig, C. Melis, C. Walton, A. Weinberger

Comments: Accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2406.11470 [astro-ph.EP] (or arXiv:2406.11470v1 [astro-ph.EP] for this version)
Submission history
From: Laura Rogers
[v1] Mon, 17 Jun 2024 12:31:37 UTC (751 KB)
https://arxiv.org/abs/2406.11470
Astrobiology

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Naโ€™Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) ๐Ÿ––๐Ÿป