Paper: astro-ph/0606279
Date: Mon, 12 Jun 2006 20:17:59 GMT (238kb)

Title: The First DIRECT Distance Determination to a Detached Eclipsing Binary
in M33

Authors: A. Z. Bonanos, K. Z. Stanek, R. P. Kudritzki, L.M. Macri, D. D.
Sasselov, J. Kaluzny, P. B. Stetson, D. Bersier, F. Bresolin, T. Matheson,
B.J. Mochejska, N. Przybilla, A.H. Szentgyorgyi, J. Tonry, G. Torres

Comments: 36 pages, 12 figures, submitted to ApJ
\\
We present the first direct, i.e. not involving intermediate steps, distance
determination to a detached eclipsing binary in M33, which was found by the
DIRECT Project. Located in the OB 66 association at coordinates (alpha,
delta)=(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 Mo and 30.0+/-3.3 Mo and radii of 12.3+/-0.4 Ro and
8.8+/-0.3 Ro, respectively. We derive temperatures of 37000+/-1500 K and
35600+/-1500 K. Using BVRJHKs photometry for the flux calibration, we obtain a
distance modulus of 24.92+/-0.12 mag (964+/-54 kpc), which is ~0.3 mag longer
than the Key Project distance to M33. We discuss the implications of our result
and the importance of establishing M33 as an independent rung on the
cosmological distance ladder.

\\ ( http://arXiv.org/abs/astro-ph/0606279 , 238kb)