New Observations with the HST Goddard High Resolution Spectrograph of the Low-Redshift Lyman-Alpha Clouds in the 3C 273 Line of Sight

Abstract

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_ = 407+/-30 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.