The Metallicity and Dust Content of HVC 287.5+22.5+240: Evidence for a Magellanic Clouds Origin^*

     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 l ∼ 287° and b ∼ 23°. The measurements are based on UV absorption lines of these elements in the Hubble Space Telescope spectrum 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 times 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 the 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 Clouds. It is likely, though not necessary, that the same processes that generated the Magellanic Stream are responsible for HVC 287.5+22.5+240.