HST/STIS observations of the high-velocity interstellar cloud HVC 291.2-41.2+80: a warm, mainly ionized high-velocity cloud

Abstract

We present intermediate-resolution HST/STIS spectra of a high-velocity interstellar cloud (v_LSR=+80kms^-1) towards DI1388, a young star in the Magellanic Bridge located between the Small and Large Magellanic Clouds. The STIS data have a signal-to-noise ratio (S/N) of 20-45 and a spectral resolution of about 6.5kms^-1 (FWHM). The high-velocity cloud absorption is observed in the lines of Cii, Oi, Siii, Siiii, Siiv and Siii. Limits can be placed on the amount of Sii and Feii absorption that is present. An analysis of the relative abundances derived from the observed species, particularly Cii and Oi, suggests that this high-velocity gas is warm (T_k~10³-10⁴K) and predominantly ionized. This hypothesis is supported by the presence of absorption produced by highly ionized species, such as Siiv. This sightline also intercepts two other high-velocity clouds that produce weak absorption features at v_LSR=+113 and +130kms^-1 in the STIS spectra.