Study of Eclipsing Binary and Multiple Systems in OB Associations IV: Cas OB6 Member DN Cas

An early-type, massive, short-period ($P_{\mathrm{o}\mathrm{r}\mathrm{b}}=2^{\mathrm{d}}.310951$) eclipsing spectroscopic binary DN Cas has been re-visited with new spectral and photometric data. The masses and radii of the components have been obtained as $M_1=19.04\pm 0.07M_{\odot }$, $M_2=13.73\pm 0.05M_{\odot }$ and $R_1=7.22\pm0.06 R_\odot$,$R_2=5.79\pm0.06R_\odot$, respectively. Both components present synchronous rotation ($V_{\mathrm{r}\mathrm{o}\mathrm{t}1}=160$km s${}^{-1}$, $V_{\mathrm{r}\mathrm{o}\mathrm{t}2}=130$km s${}^{-1}$) with their orbit. Orbital period analysis yielded a physically bound additional component in the system with a minimum mass of $M_3=0.88M_{\odot }$ orbiting in an eccentric orbit ($e=0.37\pm 0.2$) with an orbital period of $P_{12}=42\pm 9$ yrs. High precision absolute parameters of the system allowed us to derive a distance to DN Cas as 1.7$\pm$0.2 kpc which locates the system within the borders of the Cas OB6 association (d=1.8 kpc; Mel’nik & Dambis, 2009). The space velocities and the age of DN Cas are in agreement with those of Cas OB6. The age of DN Cas ($\tau =$3-5 Myr) is found to be 1-2 Myr older than the embedded clusters (IC 1795, IC 1805 and IC 1848) in the Cas OB6 association, which implies a sequential star formation in the association.