Photo-chemo-dynamical analysis and the origin of the bulge globular cluster Palomar 6

TL;DR

This study combines spectroscopic, photometric, and dynamical analyses to investigate Palomar 6, revealing its chemical composition, age, distance, and probable Galactic origin, providing insights into the early chemical enrichment of the Galaxy.

Contribution

It presents a comprehensive multi-method analysis of Palomar 6, including high-resolution spectroscopy, HST photometry, and orbital modeling, to determine its properties and origin.

Findings

Mean metallicity [Fe/H] = -1.10

Alpha-element enhancement 0.29-0.38

High abundances of heavy elements and Eu

Abstract

Palomar 6 (Pal~6) is a moderately metal-poor globular cluster projected towards the Galactic bulge. A full analysis of the cluster can give hints on the early chemical enrichment of the Galaxy and a plausible origin of the cluster. The aim of this study is threefold: a detailed analysis of high-resolution spectroscopic data obtained with the UVES spectrograph at the Very Large Telescope (VLT) at ESO, the derivation of the age and distance of Pal~6 from Hubble Space Telescope (HST) photometric data, and an orbital analysis to determine the probable origin of the cluster. High-resolution spectra of six red giant stars in the direction of Palomar 6 were obtained at the $8$m VLT UT2-Kueyen telescope equipped with the UVES spectrograph in FLAMES$+$UVES configuration. Spectroscopic parameters were derived through excitation and ionisation equilibrium of \ion{Fe}{I} and \ion{Fe}{II} lines, and the abundances were obtained from spectrum synthesis. From HST photometric data, the age and distance were derived through a statistical isochrone fitting. Finally, a dynamical analysis was carried out for the cluster assuming two different Galactic potentials. Four stars that are members of Pal~6 were identified in the sample, which gives a mean radial velocity of $174.3\pm1.6$ km\,s$^{-1}$ and a mean metallicity of [Fe/H]$\,=-1.10\pm0.09$ for the cluster. We found an enhancement of $\alpha$-elements (O, Mg, Si, and Ca) $0.29<\,$[X/Fe]$\,<0.38$ and the iron-peak element Ti of [Ti/Fe]$\,\sim+0.3$. The odd-Z elements (Na and Al) show a mild enhancement of [X/Fe]$\,\sim +0.25$. The abundances of both first- (Y and Zr) and second-peak (Ba and La) heavy elements are relatively high, with $+0.4<\,$[X/Fe]$\,<+0.60$ and $+0.4<\,$[X/Fe]$\,<+0.5$, respectively. The r-element Eu is also relatively high with [Eu/Fe]$\,\sim +0.6$. $\mathbf{\left[Truncated\right]}$