By using XSHOOTER spectra acquired at the ESO Very Large Telescope , we have studied the surface chemical composition of the companion star to the binary millisecond pulsar PSRÂ J1740-5340Â in the globular cluster NGC 6397 .
The measured abundances of Fe , Mg , Al and Na confirm that the star belongs to the cluster .
On the other hand , the measured surface abundance of nitrogen ( [ N/Fe ] = +0.53 \pm 0.15 dex ) combined with the carbon upper limit ( [ C/Fe ] < -2 dex ) previously obtained from UVES spectra allow us to put severe constraints on its nature , strongly suggesting that the pulsar companion is a deeply peeled star .
In fact , the comparison with theoretical stellar models indicates that the matter currently observed at the surface of this star has been processed by the hydrogen-burning CN-cycle at equilibrium .
In turn , this evidence suggests that the pulsar companion is a low mass ( \sim 0.2 { M } _ { \odot } ) remnant star , descending from a \sim 0.8 { M } _ { \odot } Â progenitor which lost \sim 70 - 80 % of its original material because of mass transfer activity onto the pulsar .