Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...18111907f&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #119.07; Bulletin of the American Astronomical Society, Vol. 25, p.742
Astronomy and Astrophysics
Astronomy
1
Scientific paper
The Ultraviolet Imaging Telescope (UIT) obtained objective grating spectra in 8 fields during the ASTRO-1 mission in December 1990. In this mode spectra are recorded (on film) in the range lambda lambda 1400--3400 Angstroms with a resolution of ~ 19 Angstroms over a 38(') field-of-view. Each image has been digitized and linearized as described by Stecher et al. (ApJ 395, L1, 1992). 6 of 8 frames were of sufficient exposure time to record ~ 20-30 spectra per frame. The limiting magnitude for which a low S/N spectrum can be detected in the longest exposures is ~ 16.5 in the A1 filter (lambda_ {eff} = 2490 Angstroms,\ Delta lambda = 1150 Angstroms, corresponding to a star of spectral type B0 V with V ~ 19.5, or G0 V with V ~ 14.5 mag. From the spectrum of QSO 1821+643, we estimate a limiting detectable flux in a 1000 second exposure of ~ 1 times 10(-15) ergs sec(-1) cm(-2) Angstroms (-1) at 2000 Angstroms. We use the spectrum of G191B2B, a white dwarf standard, to obtain an absolute flux calibration. Initial inspection of extracted spectra indicate that most objects are field stars with 11 <= m2490 <= 16. These spectra show a variety of morphologies, most are red. No faint `UV-excess' objects have been found. Spectral features due to FeII lambda 2600, and MgII lambda 2800 are present in the data. Classification is performed using the UV Stellar Group library (Fanelli et al. ApJS 82, 197, 1992). In fields observed at low galactic latitude spectra with strong, well-defined lambda lambda 2200 interstellar absorption are observed. The UIT appears well-suited for studies of the variation of the 2200 Angstroms feature within half-degree fields. Due to operational constraints during the flight, target fields for grating observations were not optimized for moderate-dispersion spectroscopy. The UIT will be flown again during the ASTRO-2 mission, currently manifested for late 1994.
Bohlin Ralph
Fanelli Michael N.
Neff Susan G.
O'Connell Robert West
Roberts Morton S.
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