Optical photometry and spectroscopy of the suspected "cool Algol" AV Delphini: Determination of the physical properties

We present new spectroscopic and BVRI photometric observations of the double-lined eclipsing binary AV Del ( period = 3.85 days) conducted over six observing seasons. A detailed radial velocity and light-curve analysis of the optical data shows the system to be most likely semidetached, with the less massive and cooler star filling its Roche lobe. The system is probably a member of the rare class of "cool Algol'' systems, which are distinguished from the "classical'' Algol systems in that the mass-gaining component is also a late-type star rather than a B- or A-type star. By combining the spectroscopic and photometric analyses, we derive accurate absolute masses for the components of M-1 = 1.453 +/- 0.028 M-. and M-2 = 0.705 +/- 0.014 M-. and radii of R-1 = 2.632 +/- 0.030 R-. and R-2 = 4.233 +/- 0.060 R-., as well as effective temperatures of 6000 +/- 200 and 4275 +/- 150 K for the primary and secondary, respectively. There are no obvious signs of activity (spottedness) in the optical light curve of the binary.