THE METALLICITY AND DUST CONTENT OF HVC-287.5- EVIDENCE FOR A MAGELLANIC CLOUDS ORIGIN(22.5+240 )

We estimate the abundances of S and Fe in the high-velocity cloud HVC 287.5 + 22.5 + 240, which has a velocity of 240 km s(-1) with respect to the local standard of rest and Galactic direction I similar to 287 degrees and b similar to 23 degrees. The measurements are based on UV absorption lines of these elements in the Hubble Space Telescope spect rum of NGC 3783, a background Seyfert galaxy, as well as new H I 21 cm interferometric data taken with the Australia Telescope Compact Array . We find S/H = 0.25 +/- 0.07 times solar, Fe/H = 0.033 +/- 0.006 time s solar, and S/Fe = 7.6 +/- 2.2 times solar. The S/H value provides an accurate measure of the chemical enrichment level in the HVC, while t he supersolar S/Fe ratio clearly indicates the presence of dust, which depletes the gas-phase abundance of Fe. The metallicity and depletion information obtained here, coupled with the velocity and position of the HVC, strongly suggest that it originated from the Magellanic Cloud s. It is likely, though not necessary, that the same processes that ge nerated the Magellanic Stream are responsible for HVC 287.5 + 22.5 + 2 40.