Constraints on the outer atmospheric structure of late-type giant stars with IUE: application to α Tau (K5III) and β Gru (M5III)⋆

Open Access
Publisher Website
Google Scholar
Abstract
Empirical constaints on the outer atmospheric structures of α Tau and β Gru are derived using high resolution spectra from the International Ultraviolet Explorer (IUE) satellite, with methods which have been described and applied to α Boo (K2III) in an earlier paper. These stars have IUE spectra which are typical of giant stars later than ∼K0 which lie on the ‘wind’ side of the ‘corona/wind division’ in the H–R diagram. The methods are based on the interpretation of emission-line fluxes and profiles, combining emission measures, column density measurements from opacity-sensitive line ratios and electron-density measurements from CII] line ratios. Many of the conclusions derived earlier for α Boo are confirmed for the later type stars considered here: radiative processes are vitally important in determining the observed spectra because of the low particle densities in red giants. A consistent set of constraints is derived only when such processes are taken into account. There is no evidence from IUE that the emission regions are significantly extended in the sense suggested by previous workers. For α Tau the constraints are used to examine the reliability of an earlier chromospheric model of Kelch et al. Finally the general implications of this work on the outer atmospheres of late-type giant stars are discussed.

This publication has 0 references indexed in Scilit: