We present echelle spectrograph observations in the Na D lines , at resolutions of 6.2 - 8.5 km s ^ { -1 } , for 11 stars located in the line-of-sight to the M 15 intermediate velocity cloud ( IVC ) , which has a radial velocity of \sim +70 km s ^ { -1 } in the Local Standard of Rest .
This cloud is a part of IVC Complex gp .
The targets range in magnitude from m _ { V } =13.3 - 14.8 .
Seven of the observed stars are in the M 15 globular cluster , the remaining four being field stars .
Three of the observed cluster stars are located near a peak in intensity of the IVC H i column density as observed at a resolution of \sim 1 arcmin .
Intermediate velocity gas is detected in absorption towards 7 stars , with equivalent widths in Na D _ { 2 } ranging from \sim 0.09 - 0.20Å , corresponding to log _ { 10 } ( N _ { Na } cm ^ { -2 } ) \sim 11.8 - 12.5 , and Na i /H i column density ratios ( neglecting the H ii component ) ranging from \sim ( 1 - 3 ) \times 10 ^ { -8 } .
Over scales ranging from 30 arcsec to 1 arcmin , the Na i column density and the Na i /H i ratio varies by upto 70 per cent and a factor of \sim 2 , respectively .
Combining the current sightlines with previously obtained Na i data from Kennedy et al .
( 1998b ) , the Na i /H i column density ratio over cluster sightlines varies by upto a factor of \sim 25 , when using H i data of resolution \sim 2 \times 1 arcmin .
One cluster star , M 15 ZNG-1 , was also observed in the Ca i ( \lambda _ { air } =4226.728Å ) and Ca ii ( \lambda _ { air } =3933.663Å ) lines .
A column density ratio N ( Ca i ) / N ( Ca ii ) < 0.03 was found , typical of values seen in the warm ionised interstellar medium .
Towards this sightline , the IVC has a Na i /Ca ii column density ratio of \sim 0.25 , similar to that observed in the local interstellar medium .
Finally , we detect tentative evidence for IV absorption in K i ( \lambda _ { air } =7698.974Å ) towards 3 cluster stars , which have N ( K i ) / N ( H i ) ratios of \sim 0.5 - 3 \times 10 ^ { -9 } .