We present the spectroscopic observations for 11 confirmed globular clusters of M31 with the OMR spectrograph on 2.16m telescope at Xinglong site of National Astronomical Observatories , Chinese Academy of Sciences .
Nine of our sample clusters are located in the halo of M31 and the most remote one is out to a projected radius of 78.75 kpc from the galactic center .
For all our sample clusters , we measured the Lick absorption-line indices and the radial velocities .
It is noted that most GCs of our sample are distinct from the HI rotation curve of M31 galaxy , especially for B514 , MCGC5 , H12 and B517 , suggesting that most of our sample clusters do not have kinematic association with the star forming young disk of the galaxy .
We fitted the absorption line indices with the updated stellar population model Thomas et al . ( 47 ) with two different tracks of Cassisi and Padova , separately , by applying the \chi ^ { 2 } - minimization method .
The fitting results show that all our sample clusters are older than 10 Gyr , and metal-poor ( -0.91 \leq [ Fe/H ] \leq - 2.38 dex ) .
After merging the spectroscopic metallicity of our work with the previously published ones , we extended the cluster sample out to a projected radius of 117 kpc from the galaxy ’ s center .
We found the metallicity gradient for all the confirmed clusters exists with a slope of -0.028 \pm 0.001 dex kpc ^ { -1 } .
However , the slope turns to be -0.018 \pm 0.001 dex kpc ^ { -1 } for all the halo clusters , which is much shallower .
If we only consider the outer halo clusters with r _ { p } > 25 kpc , the slope becomes -0.010 \pm 0.002 dex kpc ^ { -1 } and if one cluster G001 is excluded from the outer halo sample , the slope is -0.004 \pm 0.002 dex kpc ^ { -1 } .
Thus we conclude that metallicity gradient for M31 outer halo clusters is not significant , which agrees well with the previous findings .