On VI emission lines in Hyades F stars
Abstract
We propose to obtain additional empirical constraints on the atmospheric heating mechanisms operating in stellar transition regions (TR) and coronae. In particular, we will address the question of whether different heating mechanisms may be working in different layers of a given star and whether the relative importance of the mechanisms changes from star to star. The heating mechanisms may depend on Teff, gravity, rotation, magnetic fields, age, chemical composition, and, possibly, binarity. In order to identify the heating mechanisms, we need to disentangle the dependences on all these parameters. We propose to do this by observing the 1032 & 1038 Å O VI emission lines in a large sample of main sequence Hyades F stars. These stars are chosen since they are the brightest cluster stars with strong TR-emission and because marked changes in the heating mechanisms apparently occur around spectral type F5, leading to easily-observable effects on our spectral diagnostics. In addition, the age, chemical composition, and surface gravity of these stars are essentially the same, removing dependences on 3 of the stellar parameters. Relations between the lower-TR and upper-TR emissions, together with their relationships to the coronal X-ray emission will tell us the relationship between heating mechanisms in the different layers. We already have reliable lower-TR emission line (e.g. C IV) measurements for 15 Hyades F stars observed by IUE and will be obtaining such for 17 additional Hyades F stars in an approved Cycle 7 HST program. FUSE will provide the critically needed flux measurements of upper-TR lines (O VI), as well as of an additional lower-TR line, C III.
- Publication:
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FUSE Proposal
- Pub Date:
- 2000
- Bibcode:
- 2000fuse.prop.A106B
- Keywords:
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- FUSE Proposal ID #A106