A long-period orbit for the binary Wolf-Rayet star HD 193793, WC7 + O4-5

HD 193793 is shown to be a WC7 + O4-5 binary with an orbital period of 1085 days (2.97 yr) and a mass ratio of M(W-R)/M(0) - 0.22 + or - 0.09. The orbital parameters yield a mass of approximately 13 solar masses for the WC7 component assuming a mass of approximately 60 solar masses for the O star. HD 193793 has the second longest period of any known W-R binary. No correlation of the orbit (e.g., periastron passage) with the two recently observed IR outbursts is apparent.