Bibcode
Foing, B. H.; Beckman, J.; Crivellari, L.; Galleguillos, D.
Bibliographical reference
ESO Messenger (ISSN 0722-6691), no. 41, Sept. 1985, p. 18-22.
Advertised on:
9
1985
Citations
2
Refereed citations
2
Description
The characteristics of the chromospheres of late-type dwarf stars were
studied using the CoudeEchelle Spectrograph (CES) at ESO and the IUE.
The study focused on the h and k Mg II lines of F and G dwarfs. The
stability of the IUE spectra permitted calculations of averaged
absorption features and the subtraction of the Mg II lines to leave
intrinsic chromospheric and photospheric line characteristics. Stras
with Mg emission cores are very similar in their chromospheres, while
stars with Ca II cores vary greatly and exhibit more intense emissions.
The higher activity has been linked to magnetic forces which produce
spicules with diameters in the range of 1000 km. CES spectra on the Ca
II core H lines in Epsilon Eri and Alpha Cen B, active and passive
stars, respectively, show a 40 percent lower intensity in the quiescnet
star than in the active star, which has an asymmetric core emission and
a sharp central absorption with Ca IR triplet lines. The emission
features in the active stars are similar to those of the active regions,
photospheric spots, chromospheric plages and coronal structures observed
in the sun.