AAS 195th Meeting, January 2000
Session 50. Stellar Atmospheres
Display, Thursday, January 13, 2000, 9:20am-6:30pm, Grand Hall

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[50.13] Origins, Structure, and Evolution of Magnetic Activity in the Cool Half of the H--R Diagram: an HST~STIS Survey

T.R. Ayres, A. Brown (CASA), S.A. Drake (GSFC), A.K. Dupree (SAO), M. Guedel (Paul Scherrer Institut), E. Guinan (Villanova), G.M. Harper (CASA), C. Jordan (Oxford), J.L. Linsky (JILA), D. Reimers, J.H.M.M. Schmitt (Hamburg), T. Simon (IfA)

\noindent In HST's cycle~8, we are carrying out a major ultraviolet spectral survey of late-type stars using the powerful capabilities of the Space Telescope Imaging Spectrograph (STIS). The origin of the hot UV emissions of otherwise cool stars is a fundamental puzzle in astrophysics. Magnetic phenomena---at the heart of chromospheric and coronal activity, and perhaps wind driving as well---play a central role in many cosmic settings.

Our objective is to obtain high-quality ultraviolet spectra of a diverse collection of F--K stars, of all luminosity classes. Such a major project was unthinkable before STIS, but now is practical given the high resolution, broad spectral coverage, and sensitivity of the second generation spectrograph. Here, we discuss our choice of the thirteen targets; the observing strategy (which captures the entire UV spectrum between 1150--3000~Å\ at resolutions \lambda/\delta\lambda~,30--100\times103 with good S/N); and preliminary results for the several targets observed to date (\zeta~Dor, F7~V, 1~May 1999, 2 CVZ orbits; V711~Tau, K1~IV+G5~IV, 15~September 1999, 5 orbits; \beta~Cam, G0~I, 19~September 1999, 4 CVZ orbits). The observation of V711~Tau (HR~1099) was carried out during a long transmission grating pointing by the Chandra\/ X-ray Observatory, in support of its ``Emission Line Project.'' \\ \noindent This work was supported by grant GO-08280.01-97A from STScI. Observations were from the NASA/ESA HST,\/ collected at the STScI, operated by AURA, under contract NAS5-26555.

The author(s) of this abstract have provided an email address for comments about the abstract: ayres@casa.colorado.edu

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