The puzzling properties of the helium white dwarf orbiting the millisecond pulsar PSR J1911-5958A in NGC 6752

We have used phase-resolved high-resolution images and low-resolution spectra taken at the ESO Very Large Telescope to study the properties of the low-mass helium white dwarf companion to the millisecond pulsar PSR J1911-5958A (COM J1911-5958A), in the halo of the Galactic globular cluster NGC 6752. The radial velocity curve confirms that COM J1911-5958A is orbiting the pulsar and allows us to derive a systemic velocity of the binary system nicely in agreement with that of NGC 6752. This strongly indicates that the system is a member of the cluster, despite its very offset position (similar to 74 core radii) with respect to the core. Constraints on the orbital inclination (greater than or similar to 70 degrees) and pulsar mass (1.2-1.5 M-circle dot) are derived from the mass ratio M-PSR/M-COM = 7.49 +/- 0.64 and photometric properties of COM J1911-5958A. The light curve in the B band shows two phases of unequal brightening (Delta mag similar to 0.3 and 0.2, respectively) located close to quadratures and superimposed on an almost steady baseline emission: this feature is quite surprising and needs to be further investigated.