The old, metal-poor, anticentre open cluster Trumpler 5

TL;DR

This study characterizes the old, metal-poor open cluster Trumpler 5 in the Galactic anticentre, determining its age, metallicity, reddening, and distance through photometric and spectroscopic analyses, contributing to understanding Galactic structure.

Contribution

It provides a detailed analysis of Trumpler 5's properties using synthetic CMDs and spectroscopic data, offering new constraints on its age, metallicity, and reddening.

Findings

Tr 5 has subsolar metallicity, [Fe/H] ≈ -0.4 dex.

Age of Tr 5 is between 2.9 and 4 Gyr.

Reddening E(B-V) is between 0.60 and 0.66 mag.

Abstract

As part of a long term programme, we analyse the evolutionary status and properties of the old and populous open cluster Trumpler 5 (Tr 5), located in the Galactic anticentre direction, almost on the Galactic plane. Tr 5 was observed with WFI@MPG/ESO Telescope using the Bessel $U$, $B$, and $V$ filters. The cluster parameters have been obtained using the synthetic colour-magnitude diagram (CMD) method, i.e. the direct comparison of the observational CMD with a library of synthetic CMDs generated with different stellar evolution sets (Padova, FRANEC, and FST). Age, reddening, and distance are derived through the synthetic CMD method using stellar evolutionary models with subsolar metallicity ($Z=0.004$ or $Z=0.006$). Additional spectroscopic observations with UVES@VLT of three red clump stars of the cluster were used to determine more robustly the chemical properties of the cluster. Our analysis shows that Tr 5 has subsolar metallicity, with [Fe/H]$=-0.403\pm0.006$ dex (derived from spectroscopy), age between 2.9 and 4 Gyr (the lower age is found using stellar models without core overshooting), reddening $E(B-V)$ in the range 0.60 to 0.66 mag complicated by a differential pattern (of the order of $\sim\pm0.1$ mag), and distance modulus $(m-M)_0=12.4\pm0.1$ mag.