NEW OBSERVATIONS WITH THE HST GODDARD HIGH RESOLUTION SPECTROGRAPH OF THE LOW-REDSHIFT LYMAN-ALPHA CLOUDS IN THE 3C 273 LINE OF SIGHT

摘要

We present spectra of 3C 273 between 1216 and 1250 A obtained in the (pre-COSTAR [Corrective Optics Space Telescope Axial Replacement instrument]) configuration of the GHRS, taken with the G160M grating, with a resolution of ≈ 20 km s~(-1). The two strong Lyα lines at velocities of ～1000 and ～1600 km s~(-1) are well fitted with Voigt profiles and yield column densities, Doppler parameters and redshifts of log N(H i) = 14.19 ± 0.04, V_(Dop) = 40.7 ± 3.0 km s~(-1), V = 1012.4 ± 2.0 km s~(-1), and log N (H i) = 14.22 ± 0.07, V_(Dop) = 34.2 ± 3.3 km s~(-1) and V = 1582.0 ± 2.0 km s~(-1), respectively. Motivated by the initial announcement by Williams and Schommer of detectable Hα emission associated with the ～1600 km s~(-1) cloud, we discuss the difficulty of finding models which can account for emission of that magnitude given the observed neutral hydrogen column density, though a recent reobservation by these authors has shown the initial detection to be spurious. The C/H abundance ratio is probably less than about one-fourth of the solar abundance in these clouds, although this result is very uncertain and model dependent.