Infrared light curves and absolute stellar parameters of the Algol system δ librae: Is δ librae really an overmassive Algol binary?

We present the first infrared (IR) light curves in the J, H and K bands of δ Lib obtained at different observing runs from 1994 to 1998. These IR light curves, showing a secondary minimum much deeper than in visual bands, have been analysed in order to determine a new set of physical parameters. A new program using the Roche geometry, and stellar surface brightness from ATLAS model atmospheres, has been used in the analysis and allows us to determine the physical parameters and the distance of the binary. We compare these results with the Hipparcos parallax, with the spectroscopic masses of the components derived from the radial velocity curves, and with evolutionary stellar model predictions. The adoption of a mass M1≃2.85 M⊙ for the primary star would remove the discrepancies between our results and the Hipparcos distance, and the unusual location of the δ Lib components in the Teff - log g diagram. Our photometric analysis suggests that the stellar masses in δ Lib could be overestimated, casting doubt on the claim that the primary component of the system is overmassive and oversized compared with single main-sequence stars of similar masses.