A Compact High Velocity Cloud near the Magellanic Stream: Metallicity
  and Small-Scale Structure
  The Magellanic Stream (MS) is a well-resolved gaseous tail originating from
the Magellanic Clouds. Studies of its physical properties and chemical
composition are needed to understand its role in Galactic evolution. We
investigate the properties of a compact HVC (CHVC 224.0-83.4-197) lying close
on the sky to the MS to determine whether it is physically connected to the
Stream and to examine its internal structure. Our study is based on analysis of
HST/COS spectra of three QSOs (Ton S210, B0120-28, and B0117-2837) all of which
pass through this single cloud at small angular separation (\lessim
0.72{\deg}), allowing us to compare physical conditions on small spatial
scales. No significant variation is detected in the ionization structure from
one part of the cloud to the other. Using Cloudy photoionization models, toward
Ton S210 we derive elemental abundances of [C/H] = -1.21 +/- 0.11, [Si/H] =
-1.16 +/- 0.11, [Al/H] = -1.19 +/- 0.17 and [O/H] = -1.12 +/- 0.22, which agree
within 0.09 dex. The CHVC abundances match the 0.1 solar abundances measured
along the main body of the Stream. This suggests that the CHVC (and by
extension the extended network of filaments to which it belongs) has an origin
in the MS. It may represent a fragment that has been removed from the Stream as
it interacts with the gaseous Galactic halo.
