Doppler imaging of stellar surface structure - XIX. The solar-type components of the close binary (sigma)^2 Coronae Borealis

We perform evolutionary calculations for a binary system to produce observed binary parameters for the PSR J1740-5340. Our calculations support the model proposed by DʹAmico et al. (2001) in which this binary may be the progenitor of a millisecond pulsar + helium white dwarf system. We propose an observational test to verify this hypothesis. We propose that observations of abundances of C, N, O elements in the spectra of the optical companion of PSR J 1740-5340 may give additional information about the nature of the secondary being either i) a perturbed low-mass main-sequence star or ii) an evolved star with helium core and thin hydrogen envelope which has lost its main envelope during semi-detached evolution.