University of Cambridge > > Exoplanet Seminars > White Dwarf Planetary Systems: a window onto exoplanetary composition

White Dwarf Planetary Systems: a window onto exoplanetary composition

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If you have a question about this talk, please contact Dr Emily Sandford.

Planetary systems around white dwarf stars are diverse and intriguing. Nearly 50% of single white dwarfs are polluted with exoplanetary material, and it is from this that the bulk composition of exoplanets can be inferred. It is hypothesised that this material originates from the outer planetary system, gets perturbed onto highly eccentric orbits, tidally disrupts forming a disc of dust and gas, and then accretes. The key to understanding these enigmatic systems is through the accretion of the dust and gas, however, only 4% show evidence for an observable circumstellar dust disc, and more rarely, 0.067% show evidence for an observable circumstellar gas disc. This talk will present the abundances of the planetary material accreting onto a sample of white dwarfs with gas discs, are there compositional differences? What can this tell us about how accretion proceeds?

We will also present recent observations of these gaseous debris discs, which are mostly focused on line-emission from atomic transitions (most notably the 860nm Ca II triplet). We will show how these observations can be used to monitor the evolution of the gaseous components of these discs, and how velocity images can be generated using the method of Doppler Tomography to better understand their structure. In particular we will show velocity images for the gaseous discs around SDSSJ1228 +1040 and HE1349 –2305, and observations of more gas discs from a recent X-Shooter monitoring program.

White dwarfs whose atmospheres are polluted by heavy metals provide a means to effectively dissect planetary material and measure the relative abundances of key rock-forming elements. These abundances can be understood in terms of the evolutionary history of planetary bodies which have been recently accreted onto the white dwarf. We will describe how these abundances can be modelled, using HE1349 –2305 and SDSS1228 +1040 as case studies. We will then place these results into the broader context of white dwarf pollution, discussing in particular the ubiquity of core-mantle differentiation in the galaxy.

This talk is part of the Exoplanet Seminars series.

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