High-resolution optical observations of two early-type stars towards the high-velocity cloud Complex M
High-resolution optical spectra of the early-type stars HD 93521 and BD +38 deg2182, which lie only 27 arcmin apart on the sky in the direction of the high-velocity cloud (HVC) Complex M, reveal the presence of weak HVC absorption in the Ca K line towards BD +38 deg2182, with a velocity of V_LSR=-96.0+/-1.5 km s^-1 and an equivalent width W_lambda=11+/-2 mA. However, the HVC is not detected either in the Na D line for BD +38 deg2182 or in the Ca K and Na D lines towards HD 93521. These observations, combined with revised stellar distance estimates, imply that the HVC is at a distance from the Galactic plane of 1.8<=z<=4.6 kpc. The Ca/H abundance in the HVC is found to be at least ~=2 per cent of the solar value, consistent with the material being returning condensations from a Galactic fountain flow.