Enhanced Noble Gases in the Coronae of Active Stars

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Abstract

We have analyzed Chandra High-Energy Transmission Grating spectra of the active RS CVn-type binary V711 Tauri (HR 1099; HD 22468) in order to examine the chemical composition of its coronae. Observed fluxes and flux upper limits for spectral lines from a range of charge states of iron, covering species Fe XVI-Fe XXV, have been used to determine the emission measure distribution as a function of temperature, while the observed Fe line-to-continuum ratio has been used to examine the absolute iron abundance, Fe/H. Abundances of elements O, Ne, Mg, Si, S, and Ar relative to both Fe and H have been estimated by comparison of observed line fluxes with predictions based on the emission measure distribution. We confirm results of earlier studies finding the coronae of V711 Tau to be metal-poor and derive an iron abundance of Fe/H = 7.0 ± 0.1. We find the noble gas elements Ne and Ar to be enhanced relative to the local cosmic value and enhanced by an order of magnitude relative to Fe. Very mild enhancements of O and Mg relative to Fe are also discerned. By examination of coronal abundances of Ne relative to Fe culled from the literature, in addition to Ne lines seen in hitherto unpublished Chandra spectra, we conclude that large Ne abundance enhancements are a common feature of active stellar coronae.

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