Volume 394, Number 3, November II 2002
|Page(s)||911 - 926|
|Section||Interstellar and circumstellar matter|
|Published online||21 October 2002|
Coronal density diagnostics with Helium-like triplets: CHANDRA–LETGS observations of Algol, Capella, Procyon, ϵ Eri, α Cen A&B, UX Ari, AD Leo, YY Gem, and HR 1099
Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
2 Max-Planck-Institut für Extraterrestrische Physik (MPE), Postfach 1603, 85740 Garching, Germany
3 Space Research Organization Netherlands (SRON), Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
4 Astronomical Institute “Anton Pannekoek”, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
Corresponding author: J.-U. Ness, firstname.lastname@example.org
Accepted: 1 August 2002
We present an analysis of ten cool stars (Algol, Capella, Procyon, ϵ Eri, α Cen A&B, UX Ari, AD Leo, YY Gem, and HR 1099) observed with the Low Energy Transmission Grating Spectrometer (LETGS) on board the Chandra X-ray Observatory. This sample contains all cools stars observed with the LETGS presently available to us with integration times sufficiently long to warrant a meaningful spectral analysis. Our sample comprises inactive, moderately active, and hyperactive stars and samples the bulk part of activity levels encountered in coronal X-ray sources. We use the LETGS spectra to carry out density and temperature diagnostics with an emphasis on the H-like and the He-like ions. We find a correlation between line flux ratios of the Lyα and He-like resonance lines with the mean X-ray surface flux. We determine densities using the He-like triplets. For all stars we find no significant deviations from the low-density limit for the ions of Ne, Mg, and Si, while the measured line ratios for the ions of C, N, and O do show evidence for departures from the low-density limit in the active stars, but not in the inactive stars. Best measurements can be made for the O vii triplet where we find significant deviations from the low-density limit for the stars Algol, Procyon, YY Gem, ϵ Eri, and HR 1099. We discuss the influence of radiation fields on the interpretation of the He-like triplet line ratios in the low-Z ions, which is relevant for Algol, and the influence of dielectronic satellite lines, which is relevant for Procyon. For the active stars YY Gem, ϵ Eri, and HR 1099 the low ratios can unambiguously be attributed to high densties in the range 1– cm-3 at O vii temperatures. We find our LETGS spectra to be an extremely useful tool for plasma diagnostics of stellar coronae.
Key words: atomic data / techniques: spectroscopic / stars: coronae / stars: late-type / stars: activity / X-rays: stars
© ESO, 2002
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.