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

Abstract

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 M-1 = 19.04 +/- 0.07M circle dot, M-2 = 13.73 +/- 0.05M circle dot and R-1 = 7.22 +/- 0.06R circle dot, R-2 = 5.79 +/- 0.06 R circle dot, 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 M-3 = 0.88M circle dot 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 (t = 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.