X-ray Evidence of the Common Envelope Phase of V471 Tauri

Abstract

Chandra Low Energy Transmission Grating Spectrograph observations of the pre-cataclysmic binary V471 Tau have been used to estimate the C/N abundance ratio of the K dwarf component for the first time. While the white dwarf component dominates the spectrum longward of 50 AA, at shorter wavelengths the observed X-ray emission is entirely due to coronal emission from the K dwarf. The H-like resonance lines of C and N yield an estimate of their logarithmic abundance ratio relative to the Sun of [C/N]=-0.38+/-0.15 - half of the currently accepted solar value. We interpret this result as the first clear observational evidence for the presumed common envelope phase of this system, during which the surface of the K dwarf was contaminated by CN-cycle processed material dredged up into the red giant envelope. We use the measured C/N ratio to deduce that 0.015-0.04 Msun was accreted by the K dwarf while engulfed, and show that this is consistent with a recent tentative detection of 13C in the K dwarf photosphere, and with the measured Li abundance in the scenario where the red giant companion was Li-rich during the common envelope phase.

6 pages, 2 figures, ApJL accepted

References in corpus (6)

• A Reappraisal of the Solar Photospheric C/O Ratio
• Hubble Space Telescope Spectroscopy of V471 Tauri: Oversized K Star, Paradoxical White Dwarf
• Photospheric Abundances of Volatile and Refractory Elements in Planet-Harboring Stars
• Chemical Abundances from Inversions of Stellar Spectra: Analysis of Solar-Type Stars with Homogeneous and Static Model Atmospheres
• From the Heart of The Ghoul: C and N Abundances in the Corona of Algol B
• On the use of 12CO/13CO as a test of common-envelope evolution

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• On the Formation of Galactic Black Hole Low-Mass X-ray Binaries
• The Coronae of AB Dor and V471 Tau: Primordial angular momentum vs tidal spin-up
• Mid-Infrared Observations of the White Dwarf Brown Dwarf Binary GD 1400
• Some Like it Hot: The X-Ray Emission of The Giant Star YY Mensae
• A confined dynamo: magnetic activity of the K-dwarf component in the pre-cataclysmic binary system V471 Tauri
• Close to the Dredge: Precise X-ray C and N Abundances in lambda Andromeda and its Precocious RGB Mixing Problem
• Variability of eclipse timing:the case of V471 Tauri
• Chandra X-ray Observatory High-resolution X-ray Spectroscopy of Stars: Modeling and Interpretation