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We present photometric and spectroscopic observations of the opticalcompanion to the millisecond radio pulsar PSR J1740-5340 in the globularcluster NGC 6397. An analysis of the photometric variability in the B, V, andI-bands indicates an inclination of the system of 43.9+-2.1 degrees if theoptical companion fills its Roche lobe (a semi-detached configuration). Thespectroscopic data show a radial velocity variation with a semi-amplitude ofK=137.2 +- 2.4 km/sec, and a system velocity gamma=17.6 +- 1.5 km/sec,consistent with cluster membership. We use these results to derive a mass ofthe optical companion of M1=0.296 +- 0.034 Msol and M2=1.53 +- 0.19 Msol forthe pulsar. There is evidence for secular change of the amplitude of theoptical light curve of the variable measured over seven years. The change doesnot have interpretation and its presence complicates reliable determination ofthe absolute parameters of the binary.Comment: 24 pages, 9 figures, submitted to A

Photometry and Spectroscopy of the Optical Companion to the Pulsar PSR J1740−5340 in the Globular Cluster NGC 6397