Trumpler 20-an old and rich open cluster

We show that the open cluster Trumpler 20, contrary to the earlier findings, is actually an old Galactic open cluster. New CCD photometry and high-resolution spectroscopy are used to derive the main parameters of this cluster. At [Fe/H] = -0.11 for a single red giant star, the metallicity is slightly subsolar. The best fit to the colour-magnitude diagrams is achieved using a 1.3-Gyr isochrone with convective overshoot. The cluster appears to have a significant reddening at E(B-V) = 0.46 (for B0 spectral type), although for red giants this high reddening yields the colour temperature exceeding the spectroscopic T-eff by about 200 K. Trumpler 20 is a very rich open cluster, containing at least 700 members brighter than M-V = +4. It may extend over the field of view available in our study at 20 x 20 arcmin(2).