We present new photometric observations in the BV RI bands of the double-lined eclipsing binary BD +05 \arcdeg 706 conducted over three observing seasons , as well as new X-ray observations obtained with the ROSAT satellite covering a full orbital cycle ( P = 18.9 days ) .
A detailed light-curve analysis of the optical data shows the system to be semidetached , confirming indications from an earlier analysis by ( ) , with the less massive and cooler star filling its Roche lobe .
The system is a member of the rare class of cool Algol systems , which are different 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 new photometry with a reanalysis of the spectroscopic observations reported by ( ) we derive accurate absolute masses for the components of M _ { 1 } = 2.633 \pm 0.028 M _ { \sun } and M _ { 2 } = 0.5412 \pm 0.0093 M _ { \sun } , radii of R _ { 1 } = 7.55 \pm 0.20 R _ { \sun } and R _ { 2 } = 11.02 \pm 0.21 R _ { \sun } , as well as effective temperatures of 5000 \pm 100 K and 4640 \pm 150 K for the primary and secondary , respectively .
There are obvious signs of activity ( spottedness ) in the optical light curve of the binary .
Our X-ray light curve clearly shows the primary eclipse but not the secondary eclipse , suggesting that the primary star is the dominant source of the activity in the system .
The depth and duration of the eclipse allow us to infer some of the properties of the X-ray emitting region around that star .