  We examined the sizes of the absorption clouds in a z=1.3911 damped Ly-alpha
absorber (DLA) in the double image lensed quasar Q0957+561 A,B (separation 135
pc at the absorber redshift). Using HIRES/Keck spectra, we studied the MgII
2796,2803 doublet, FeII multiplet, and MgI 2853 transition in absorption. We
defined six "clouds" in the system of sightline A and seven clouds in the
system of sightline B. An examination of the N(v) profiles, using the apparent
optical depth method, reveals no clear physical connection between the clouds
in A and those in B. The observed column density ratios of all clouds is
log[N(MgI)/N(FeII)] ~ -2 across the full velocity range in both systems and
also spatially (in both sightlines). This is a remarkable uniformity not seen
in Lyman limit systems. The uniformity of the cloud properties suggests that
the multiple clouds are not part of a "halo". Based upon photoionization
modeling, we constrain the ionization parameters in the range -6.2 < log(U) <
-5.1, where the range brackets known abundance ratio and dust depletion
patterns. The inferred cloud properties are densities of 2 < n_H < 20 cm^-3,
and line of sight sizes of 1 < D < 25 pc. The masses of the clouds in system A
are 10 < M/M_sun < 1000 and in system B are 1 < M/M_sun < 60 for spherical
clouds. For planar clouds, the upper limits are 400 M_sun and 160 M_sun for A
and B, respectively. We favor a model of the absorber in which the DLA region
itself is a single cloud in thiscomplex, which could be a parcel of gas in a
galactic ISM. A spherical cloud of ~10 pc would be limited to one of the
sightlines (A) and imply a covering factor less than 0.1 for the DLA complex.
We infer that the DLA cloud properties are consistent with those of lower
density, cold clouds in the Galactic interstellar medium.

Astrophysics