[12.06] Late-type Stars with Coronae but No Chromospheres?

AAS 201st Meeting, January, 2003
Session 12. Activity in Cool Stars
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[12.06] Late-type Stars with Coronae but No Chromospheres?

D. J. Christian (Johns Hopkins University), M. Mathioudakis, D. Jevremovic (Queen's University Belfast), D. J. Mullan (Univ. of Delaware, Bartol Research Inst.), N. Lehner (Johns Hopkins University)

We present high resolution optical observations of several late-type stars selected from ROSAT and EUVE surveys. These particular stars show no Balmer or Ca II emission typical of late-type stars with X-ray evidence for coronae. Since our sample shows no evidence for binarity in their optical spectra, these stars may have no chromospheres. We present preliminary results from simulated spectra using the MULTI code of Carlsson for solving multi-level non-LTE radiative transfer problems in plane parallel atmospheres. These simulations can reproduce the observed Ca II line profiles. Stars without chromospheres are expected to have high density coronae and transition regions, which we will investigate with future FUV and X-ray observations.

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