17th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun

Type: Oral

Topic: Evolved Stars and Hot-Cool Star Connection

Abstract
The Advanced Spectral Library (ASTRAL) is a {\em Hubble Space Telescope}\/ (HST) Large Treasury Project. During 2010--2011, ASTRAL collected high-quality ultraviolet (1150--3100~\AA) echelle spectra of eight iconic bright late-type stars -- all well-known cosmic denizens with vaguely unpronounceable names like Procyon and Betelgeuse -- utilizing the powerful Space Telescope Imaging Spectrograph (STIS). ASTRAL was allocated 146 HST orbits for the purpose, about twenty per star for the targets outside of {\em HST}'s Continuous Viewing Zone. The objective was to record each of the objects with broad uninterrupted UV coverage at the highest signal-to-noise and highest spectral resolution attainable within the available spacecraft time, and given a variety of observing constraints. This was achieved by splicing together echellegrams taken in multiple FUV and NUV prime echelle settings of STIS, with a specialized observing strategy to mitigate detector fixed pattern noise, ensure accurate wavelength scales, and preserve the absolute radiometric level of the UV spectral energy distributions. Public access to the processed spectra is through the ASTRAL website: http://casa.colorado.edu/$\sim$ayres/ASTRAL/. The present paper describes this revolutionary project and preliminary results, especially for the cool giants and supergiants of the sample. These display spectacularly diverse UV spectra owing to a co-mingling of processes that produce on the one hand high-temperature "subcoronal" material, and on the other highly extended cooler chromospheric zones and winds.\\ Supported by grants from the Space Telescope Science Institute, operated by AURA for NASA.