The coronal metallicity of the intermediate activity dwarf ξ Bootis A.
DRAKE J.J. and KASHYAP V.
Abstract (from CDS):
Extreme Ultraviolet Explorer (EUVE) spectra from a 270 ks observation of the intermediate activity star ξ Boo A (G8 V) have been analyzed in order to determine the metallicity of its coronal plasma. This analysis was based on a new method that used both the EUVE spectroscopic and photometric (Deep Survey) data, together with theoretical model spectra. By comparison of observed and synthetic spectra computed using the CHIANTI database, we estimated that about 20% of the observed line flux is not accounted for in the theoretical model. Allowing for the ``missing lines'' in our analysis, we obtain a coronal metallicity for ξ Boo A of [M/H]=0.1+0.2–0.15 relative to the solar photosphere. This is slightly higher than the photospheric metallicity of [M/H]=-0.15±0.05 and lends support to the results of our earlier analysis of the same spectral data that indicated that coronal abundances of elements with low first ionization potentials (FIPs) are systematically higher than those of elements with high FIPs. These results, coupled with other evidence, imply that stars of intermediate activity level–stars more active than the Sun but significantly less active than the most active single and binary stars–do not suffer from any depletion of metals in their coronae as some coronal metallicities estimated for more active stars have appeared to suggest. The observation of a solar-like FIP effect on ξ Boo A adds support to the notion that stars of intermediate activity level have coronae characterized by a high surface coverage of bright solar-like active regions.