Hubble Space Telescope FUV Spectra of the Post-Common-Envelope Hyades Binary V471 Tauri

TL;DR

This study analyzes HST spectra of the magnetic white dwarf in V471 Tauri, revealing emission features, accretion signatures, and magnetic activity, providing insights into the star's atmosphere, accretion processes, and magnetic field structure.

Contribution

First detailed spectroscopic analysis of V471 Tauri's white dwarf, identifying accretion features, magnetic activity, and emission characteristics in the FUV spectrum.

Findings

Detected emission lines from N V, Si IV, C IV, He II.

Identified metal absorption features modulated with white dwarf rotation.

Evidence of a secondary accretion pole and metal accretion signatures.

Abstract

We have carried out an analysis of the HST STIS archival spectra of the magnetic white dwarf in the Hyades eclipsing-spectroscopic, post-common envelope binary V471 Tauri, time resolved on the orbit and on the X-ray rotational phase of the magnetic white dwarf. An HST STIS spectrum obtained during primary eclipse reveals a host of transition region/chromospheric emission features including N V (1238, 1242), Si IV (1393, 1402), C IV (1548, 1550) and He II (1640). The spectroscopic characteristics and emission line fluxes of the transition region/chromosphere of the very active, rapidly rotating, K2V component of V471 Tauri, are compared with the emission characteristics of fast rotating K dwarfs in young open clusters. We have detected a number of absorption features associated with metals accreted onto the photosphere of the magnetic white dwarf from which we derive radial velocities. All of the absorption features are modulated on the 555s rotation period of the white dwarf with maximum line strength at rotational phase 0.0 when the primary magnetic accretion region is facing the observer. The photospheric absorption features show no clear evidence of Zeeman splitting and no evidence of a correlation between their variations in strength and orbital phase. We report clear evidence of a secondary accretion pole. We derive C and Si abundances from the Si IV and C III features. All other absorption lines are either interstellar or associated with a region above the white dwarf and/or with coronal mass ejection events illuminated as they pass in front of the white dwarf.