BV phot. of a detached eclipsing binary in M 33

Located in the OB 66 association at coordinates (RA,DE)=(01:33:46.17,+30:44:39.9) for J2000.0, it was one of the most suitable detached eclipsing binaries found by DIRECT for distance determination, given its apparent magnitude and orbital period. We obtained follow-up BV time-series photometry, JHKs photometry, and optical spectroscopy from which we determined the parameters of the system.

It contains two O7 main-sequence stars, with masses of 33.4+/-3.5 and 30.0+/-3.3M_{sun}_ and radii of 12.3+/-0.4 and 8.8+/-0.3R_{sun}_, respectively. We derive temperatures of 37000+/-1500 and 35600+/-1500K. Using BVRJHKs photometry for the flux calibration, we obtain a distance modulus of 24.92+/-0.12mag (964+/-54kpc), which is 0.3mag longer than the Key Project distance to M33.