HI and optical spectroscopy towards the M15 intermediate-velocity cloud

We present single-dish Arecibo 21-cm H i observations, covering a 0 degrees 675x0 degrees 625 RA-Dec. grid, of the intermediate-velocity cloud (IVC) c entred upon the M15 globular cluster. The velocity and positional structure of the IVC gas at V-LSR=70 km s(-1) are investigated; it is found to be cl umpy and has a peak surface density N(H i)similar to 8x10(19) cm(-2). Addit ionally, we have performed a long H i integration towards HD 203664, a Gala ctic halo star some 3 degrees1 from M15, in which optical IVC absorption ha s previously been detected. No H i with a velocity exceeding 60 km s(-1) wa s found to a brightness temperature limit of 0.05 K. However, additional po intings did detect IVC gas approximately mid-way between HD 203664 and M15. Finally, we present both Arecibo H i pointings and low-resolution spectra in the Ca ii H and K lines towards 15 field stars in the general field towa rds M15, in an attempt to obtain the distance to the IVC. Intermediate-velo city H i is detected towards seven sightlines. Stellar spectral types are d erived for 12 of the sample. Assuming that these stars lie on the main sequ ence, their distances are estimated to lie in the range 150 less than or eq ual tod less than or equal to 1350 pc. No Ca ii absorption is observed, eit her because the IVC is further away than similar to 1350 pc or more likely because the gas along these sightlines is of too low a density to be detect ed by the current observations.