New Photometric Models of Four Near-Contact Binaries: EP Cassiopeiae, AK Canis Minoris, FG Geminorum, and DF Puppis

We present new photometric observations of EP Cas, AK CMi, and PG Gem, which were obtained during the period from 2008 October to 2011 March using the 60 cm telescope at the Xinglong station. Several light-minimum times were determined, and orbital periods were revised. By using the 2003-version Wilson-Devinney code, photometric solutions of EP Cas, AK CMi, PG Gem, and DP Pup were deduced from multicolor light curves. The results imply that the four systems are Algol-type near-contact binaries (NCBs), whose less-massive components are filling their Roche lobes. With mass and angular-momentum loss, the separation between both components will decrease, and the primary will finally fill its Roche lobe. Algol-type NCBs of this kind, such as EP Cas, AK CMi, PG Gem, and DF Pup, may evolve into the contact configuration as a progenitor of a W UMa-type binary.