2003AJ....125.1546K

We present photometric and spectroscopic observations of the optical companion to the millisecond radio pulsar PSR J1740-5340 in the globular cluster NGC 6397. An analysis of the photometric variability in the B, V, and I bands indicates an inclination of the system of 43°.9±2°.1 if the optical companion fills its Roche lobe (a semidetached configuration). The spectroscopic data show a radial velocity variation with a semiamplitude of K=137.2±2.4 km/s, and a system velocity γ=17.6±1.5 km/s, consistent with cluster membership. We use these results to derive a mass of the optical companion of M₁=0.296±0.034 M_☉and M₂=1.53±0.19 M_☉for the pulsar. There is evidence for secular change of the amplitude of the optical light curve of the variable measured over 7 years. The change does not have interpretation and its presence complicates reliable determination of the absolute parameters of the binary.