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

An early-type, massive, short-period (P_orb=2^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 M₁=19.04± 0.07 M_⊙, M₂=13.73± 0.05 M_⊙ and R₁=7.22± 0.06 R_⊙, R₂=5.79± 0.06 R_⊙, respectively. Both components present synchronous rotation (V_rot1=160 km s^-1, V_rot2=130 km s^-1) with their orbit. Orbital period analysis yielded a physically bound additional component in the system with a minimum mass of M₃=0.88 M_⊙ orbiting in an eccentric orbit (e = 0.37 ± 0.2) with an orbital period of P ₁₂ = 42 ± 9 yr. High precision absolute parameters of the system allowed us to derive a distance to DN Cas as 1.7 ± 0.2 kpc which locates the system within the borders of the Cas OB6 association (d = 1.8 kpc). The space velocities and the age of DN Cas are in agreement with those of Cas OB6. The age of DN Cas (τ = 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.