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

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 $174.3\pm 1.6$ km\,s${}^{-1}$ and a mean metallicity of [Fe/H]$=-1.10\pm 0.09$ for the cluster. We found an enhancement of $\hat{I}\pm$-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]$\sim +0.6$. $\left[\mathbf{Truncated}\right]$

23 pages, 26 figures, and 12 tables. References added, typos corrected, published version