CAPOS: The bulge Cluster APOgee Survey VIII. Final ASPCAP results for all clusters

TL;DR

This paper presents comprehensive ASPCAP-based chemical and kinematic analysis of all bulge globular clusters in the CAPOS survey, revealing their metallicity distribution, elemental abundances, and chemodynamical classifications.

Contribution

It provides the final homogeneous ASPCAP parameters for 18 bulge globular clusters, introduces a new chemodynamical classification scheme, and updates the metallicity distribution distinguishing in and ex situ clusters.

Findings

Bimodal metallicity distribution with peaks at -0.45 and -1.1.

No significant internal metallicity variation within clusters.

Small difference in [Si/Fe] between in and ex situ clusters.

Abstract

Bulge globular clusters(BGCs) are exceptional tracers of the formation and chemodynamical evolution of this oldest Galactic component. However, until now, observational difficulties have prevented us from taking full advantage of these powerful Galactic archeological tools. CAPOS, the bulge Cluster APOgee Survey, addresses this key topic by observing a large number of BGCs, most of which have been poorly studied. We aim to obtain accurate mean values for metallicity,[alpha/Fe],and radial velocity, as well as abundances for 11 other elements. We present final parameters based on ASPCAP for all 18 CAPOS BGCs. We carry out a stringent membership selection, finding 303 with SNR>70 and 125 with lower SNR. We reinforced the finding that stars with high [N/Fe] abundances show higher [Fe/H] than their lower [N/Fe] counterparts. Mg,Ca and global alpha abundances show similar trends, while Si is well-behaved. The [Fe/H] value of these 2nd population stars is corrected to derive the mean metallicity. Mean metallicities are determined to a precision of 0.05 dex,[alpha/Fe] to 0.06 dex, and radial velocity to 3.4 km/s. No clusters show strong evidence for internal metallicity variation, including M22. Abundances for 11 other elements using only 1st population stars are calculated and are generally in good agreement with the literature. We develope a new chemodynamical GC classification scheme, synthesizing several recent studies. We also compile up-to-date metallicities. The BGC metallicity distribution is bimodal, with peaks at [Fe/H]=-0.45 and -1.1, with the metal-poor peak strongly dominant, while exsitu GCs are unimodal, with a peak at -1.6. Surprisingly, we find only a small, statistically insignificant difference in the mean [Si/Fe] of in and exsitu GCs. The 4 GCs with the lowest [Si/Fe] values are all exsitu, relatively young, and 3 belong to Sagittarius, but no other correlations are evident.