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T.R. Ayres, A. Brown, G.M. Harper, P.D. Bennett (CASA), J.L. Linsky (JILA), K.G. Carpenter (GSFC), R.D. Robinson (CSC)
The Space Telescope Imaging Spectrograph (STIS) conducted a series of observations of the archetype ``noncoronal'' red giant Arcturus (HD~124897; \alpha~Boo; K1~III) on 24~August~1998, 17--23~UT. The STIS program was the result of a failed cycle~5 pointing, which could not be rescheduled during the abbreviated cycle~6, and was carried over to cycle~7. Three grating settings---E230H (t\rm exp= 1340~s), E230M (2493~s), and E140M (5208~s)---covered the ultraviolet spectrum from 1150--2850~Å, at resolutions between R~4\times104 - 1\times105, with essentially no gaps.
The resulting spectrograms are stunning. The resolution is very high, as is the S/N; the spectral coverage is broad and comprehensive. The far-UV interval (1150--1700~Å) is a rich emission line spectrum, dominated by the broad resonance transitions of atomic hydrogen (\lambda1215) and oxygen (\lambda1305 triplet). There are numerous narrow emissions, mostly from low-excitation species such as Si~I, Fe~II, and fluoresced bands of carbon monoxide. Surprisingly, high-excitation species---Si~IV (\lambda1393: 6\times104~K) and C~IV (\lambda1548: 1\times105~K)---are present as well (as seen in the earlier ``failed'' GHRS spectra). The mid-UV (1700--2600~Å) shows additional emission lines, particularly [C~II] and [Si~II] in the 2325~Å\ region; the photospheric continuum rises strongly toward the longer wavelengths. The 2600--2850~Å\ interval is mostly a photospheric absorption spectrum, although the bright chromospheric emission doublet of Mg~II lords over the 2800~Å\ region.
We present a comprehensive spectral atlas based on our reductions of the STIS echellograms. We discuss the processing strategies, line identifications, and some of the preliminary results from our analysis of this windy, noncoronal giant. \noindent 1This work was supported by grants GO-06066.01-94A from STScI, and NAG5-3226 from NASA. Observations were from the NASA/ESA HST,\/ collected at the STScI, operated by AURA, under contract NAS5-26555.
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