  We describe a moderate-resolution (20-25 km/s) FUSE study of the low-redshift
intergalactic medium. We report on studies of 7 extragalactic sightlines and 12
Ly-beta absorbers that correspond to Ly-alpha lines detected by HST/GHRS and
STIS. These absorbers appear to contain a significant fraction of the low-z
baryons and were a major discovery of the HST spectrographs. Using FUSE data,
with 40 mA (4-sigma) Lyb detection limits, we have employed the equivalent
width ratio of Lyb/Lya and occasionally higher Lyman lines, to determine the
doppler parameter, b, and accurate column densities, N(HI), for moderately
saturated lines. We detect Lyb absorption corresponding to all Lya lines with
EW > 200 mA. The Lyb/Lya ratios yield a preliminary distribution function of
doppler parameters, with mean <b> = 31.4 +/- 7.4 km/s and median b = 28 km/s,
comparable to values at redshifts z = 2.0-2.5. If thermal, these b-values
correspond to T(HI) ~ 50,000 K, although the inferred doppler parameters are
considerably less than the widths derived from Lya profile fitting,
<b(dopp)/b(width)> = 0.52. The typical increase in column density over that
derived from profile fitting is Delta[log N(HI)] = 0.3, but ranges up to 1.0
dex. Our data suggest that the low-z Lya absorbers contain sizable non-thermal
motions or velocity components in the line profile, perhaps arising from
cosmological expansion and infall.
