2005A&A...443..525S

We describe medium-resolution spectroscopic observations taken with the ESO Multi-Mode Instrument (⁴⁴Sc emmi) in the Ca⁴⁴Sc II K line (λ_air=3933.661Å) towards 7 QSOs located in the line-of-sight to the Magellanic Bridge. At a spectral resolution R=λ/Δλ=6000, five of the sightlines have a signal-to-noise (S/N) ratio of ∼20 or higher. Definite Ca absorption due to Bridge material is detected towards 3 objects, with probable detection towards two other sightlines. Gas-phase Ca⁴⁴Sc II K Bridge and Milky Way abundances or lower limits for the all sightlines are estimated by the use of Parkes 21-cm H⁴⁴Sc I emission line data. These data only have a spatial resolution of 14-arcmin compared with the optical observations which have milli-arcsecond resolution. With this caveat, for the three objects with sound Ca⁴⁴Sc II K detections, we find that the ionic abundance of Ca⁴⁴Sc II K relative to H⁴⁴Sc I, A=log(N(CaK)/N(H⁴⁴Sc I)) for low-velocity Galactic gas ranges from -8.3 to -8.8dex, with H⁴⁴Sc I column densities varying from 3-6x10²⁰cm^–2. For Magellanic Bridge gas, the values of A are ∼0.5dex higher, ranging from ~-7.8 to -8.2dex, with N(H⁴⁴Sc I)=1-5x10²⁰cm^–2. Higher values of A correspond to lower values of N(H⁴⁴Sc I), although numbers are small. For the sightline towards B0251-675, the Bridge gas has two different velocities, and in only one of these is Ca⁴⁴Sc II tentatively detected, perhaps indicating gas of a different origin or present-day characteristics (such as dust content), although this conclusion is uncertain and there is the possibility that one of the components could be related to the Magellanic Stream. Higher signal-to-noise Ca⁴⁴Sc II K data and higher resolution H⁴⁴Sc I data are required to determine whether A changes with N(H⁴⁴Sc I) over the Bridge and if the implied difference in the metalicity of the two Bridge components towards B0251-675 is real.