The Coronal Structure of II Pegasi from Chandra/HETGS and EUVE Spectra.

II Pegasi (HD 224085) is a single-lined, highly active RS CVn binary star. It has been frequently observed in the visible, UV, and X-ray regions; it is known to flare frequently. We observed it for 40 ks with the Chandra High Resolution Transmission Grating Spectrometer (HETGS) on 17-18 October, 1999, and for 419 ks with EUVE from 21 October to November 6, 1999. The X-ray spectrum showed a strong continuum and a number of emission lines, such as Fe XXV, Si XIII-XIV, Mg XI-XII, Ne X, O VII-VIII, and N VII, spanning a decade in temperature of maximum emissivity. About half-way through the observation, the X-ray flux doubled during 10 ks, after which it peaked and began a slow decline at the observation's end. We will present line fluxes and temperature estimates from line ratios as well as continuum fits, for both flare and non-flare states. We will also examine density sensitive lines, look for line shifts and broadening, and estimate coronal abundances. We will also examine flare and line light-curves to characterize changes as a function of time. EUVE data will provide further temperature and density diagnostics, though at a different time. Work at MIT was supported by NASA through the HETG contract NAS8-38249 and through Smithsonian Astrophysical Observatory (SAO) contract SVI--61010 for the Chandra X-ray Center (CXC).