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By using XSHOOTER spectra acquired at the ESO Very Large Telescope, we havestudied the surface chemical composition of the companion star to the binarymillisecond pulsar PSR J1740-5340 in the globular cluster NGC 6397. Themeasured abundances of Fe, Mg, Al and Na confirm that the star belongs to thecluster. On the other hand, the measured surface abundance of nitrogen([N/Fe]=+0.53 +- 0.15 dex) combined with the carbon upper limit ([C/Fe] <-2dex) previously obtained from UVES spectra allow us to put severe constraintson its nature, strongly suggesting that the pulsar companion is a deeply peeledstar. In fact, the comparison with theoretical stellar models indicates thatthe matter currently observed at the surface of this star has been processed bythe hydrogen-burning CN-cycle at equilibrium. In turn, this evidence suggeststhat the pulsar companion is a low mass (~0.2 Msun) remnant star, descendingfrom a ~0.8 Msun progenitor which lost ~70-80 % of its original materialbecause of mass transfer activity onto the pulsar.

New clues on the nature of the companion to PSR~J1740-5340 in NGC6397 from XSHOOTER spectroscopy