Fundamental parameters of the eclipsing binary DD CMa and evidence for mass exchange

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 $P_{\mathrm{o}}=2.0084530\pm 0.0000006\mathrm{d}$. Our spectra reveal H$\beta$ and H$\alpha$ absorptions with weak emission shoulders and we also find color excess in the WISE 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 B 2.5 dwarf and a B 9 giant of radii 3.2 and 3.7 ${\mathrm{R}}_{\odot }$, respectively, orbiting in a circular orbit of radius 6.75 ${\mathrm{R}}_{\odot }$. We also found $M_{\mathrm{c}}=1.7\pm 0.1{\mathrm{M}}_{\odot }$, $T_{\mathrm{c}}=11350\pm 100\mathrm{K}$ and $M_{\mathrm{h}}=6.4\pm 0.1{\mathrm{M}}_{\odot }$, $T_{\mathrm{h}}=20000\pm 500\mathrm{K}$, 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.

14 pages with 13 figures

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