Abstract

We present a detailed photometric and spectroscopic analysis of DD CMa, based on published survey photometry and new spectroscopic data. We find an improved orbital period of P-o = 2.0084530(6) days. Our spectra reveal H beta and H alpha absorptions with weak emission shoulders, and we also find a color excess in the Wide-field Infrared Survey Explorer multiband photometry, interpreted as signatures of circumstellar matter. We model the V-band orbital light curve derived from the ASAS and ASAS-SN surveys, assuming a semidetached configuration and using the mass ratio and temperature of the hotter star derived from our spectroscopic analysis. Our model indicates that the system consists of a B2.5 dwarf and a B9 giant of radii 3.2 and 3.7 R, respectively, orbiting in a circular orbit of radius 6.75 R. We also found M-c = 1.7 0.1 M, T-c = 11,350 100 K, and M-h = 6.4 0.1 M, T-h = 20,000 500 K, for the cooler and hotter star, respectively. We find broad single emission peaks in H alpha and H beta after subtracting the synthetic stellar spectra. Our results are consistent with mass exchange between the stars and suggest the existence of a stream of gas being accreted onto the early B-type star.