Fundamental Parameters of the Eclipsing Binary DD CMa and Evidence for Mass Exchange

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 β and H α 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 α and H β 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.