Trumpler 20 - an old and rich open cluster

TL;DR

This study reclassifies Trumpler 20 as an old, rich Galactic open cluster with detailed photometric and spectroscopic analysis revealing its age, metallicity, and significant reddening, and highlights its large stellar population.

Contribution

The paper provides the first comprehensive photometric and spectroscopic characterization of Trumpler 20, establishing it as an old, metal-poor, and populous open cluster.

Findings

Age estimated at 1.3 Gyr using isochrone fitting

Metallicity determined as [Fe/H]=-0.11

Contains at least 700 members brighter than M_V=+4

Abstract

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 color-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 color 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'x20'.