Search for Metal Pollution in 81 DA White Dwarfs

TL;DR

This study uses UV spectroscopy of 81 DA white dwarfs to detect metal pollution, revealing ongoing accretion in a majority of these stars and providing insights into their atmospheric composition and accretion sources.

Contribution

It presents the first UV spectroscopic survey of 81 DA white dwarfs in a specific temperature range, detecting metal pollution and analyzing potential accretion mechanisms.

Findings

Approximately 60% of stars show metal pollution.

Silicon is the most commonly detected metal.

Ongoing accretion is confirmed in these white dwarfs.

Abstract

A total of 81 DA white dwarfs have been observed with the Cosmic Origins Spectrograph on the Hubble Space Telescope in a snapshot program. The targets were selected to be in the $T_{\rm eff}$ range from 17000 - 25000 K, where optical metal lines become weak and difficult to detect. Because of the strong Si, C, and O resonance lines in the UV, this survey has a sensitivity that is comparable to that of the Keck/VLT searches for CaII K in cooler white dwarfs. These objects also have no convection zone and thus very short diffusion timescales, assuring that accretion is currently ongoing. The spectra have high resolution and in most cases fairly good S/N. About 60% of them show photospheric metal pollution, predominantly of Si, but in some cases additional metals are present. We report the results of a preliminary analysis and discuss the sources of the accreted matter and the possible r\^ole of radiative levitation.