AAS 197, January 2001
Session 44. Observations and Analysis of Stellar Atmospheres
Display, Tuesday, January 9, 2001, 9:30am-7:00pm, Exhibit Hall

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[44.07] Origins, Structure, and Evolution of Magnetic Activity in the Cool Half of the H--R Diagram: Progress Report on a Major HST~STIS Stellar 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 early October 2000, HST\/ completed a year and a half long ultraviolet spectral survey of late-type stars with its Space Telescope Imaging Spectrograph (STIS). Thirteen stars were observed, ranging over spectral types F7--K0 on the main sequence, F8--G8 in the giant branch, and G0--G8 in the supergiants. A total of 72 observation sequences were executed, some consisting of several independent exposures (up to 13: in the case of HR~1099, recorded during a long grating observation by Chandra\,). Spectra were taken in the medium resolution echelle modes (E140M, E230M: R~~30--40,000) below about 2500~Å, and in the high-resolution echelle mode (E230H: R~~105) between 2500--3000~Å. For each target, about 70% of the exposure time was devoted to the key E140M interval (1150--1700~Å).

Although the observations were collected primarily to study the magnetically disturbed outer atmospheres of late-type stars, they also are valuable for investigating the local interstellar medium through UV absorptions in \ion{H}{1}, \ion{O}{1}, \ion{Fe}{2}, and \ion{Mg}{2}, and for measuring the cosmologically significant D/H ratio. We present examples of the superb spectra resulting from the program, and discuss some of the new insights we have gained concerning plasma dynamics in the 105~K layers of the stellar ``transition zone;'' the super-rotational broadening of the \ion{Si}{4}, \ion{C}{4}, and \ion{N}{5} emissions in Hertzsprung gap giants; and the spectral peculiarities of the ``hybrid chromosphere'' supergiants.\\ \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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