The enigmatic globular cluster UKS~1 obscured by the bulge: \textit{H}-band discovery of nitrogen-enhanced stars

Abstract

The presence of nitrogen-enriched stars in globular clusters provides key evidence for multiple stellar populations (MPs), as has been demonstrated with globular cluster spectroscopic data towards the bulge, disk, and halo. In this work, we employ the VVV Infrared Astrometric Catalogue (VIRAC) and the DR16 SDSS-IV release of the APOGEE survey to provide the first detailed spectroscopic study of the bulge globular cluster UKS~1. Based on these data, a sample of six selected cluster members was studied. We find the mean metallicity of UKS~1 to be [Fe/H]$=-0.98\pm 0.11$, considerably more metal-poor than previously reported, and a negligible metallicity scatter, typical of that observed by APOGEE in other Galactic globular clusters. In addition, we find a mean radial velocity of $66.1\pm 12.9$ km s${}^{-1}$, which is in good agreement with literature values, within 1$\sigma$. By selecting stars in the VIRAC catalogue towards UKS~1, we also measure a mean proper motion of (${\mu }_{\alpha }\cos (\delta )$, ${\mu }_{\delta }$) $=$ ($-2.77\pm 0.23$,$-2.43\pm 0.16$) mas yr${}^{-1}$. We find strong evidence for the presence of MPs in UKS~1, since four out of the six giants analysed in this work have strong enrichment in nitrogen ([N/Fe]$\gtrsim +0.95$) accompanied by lower carbon abundances ([C/Fe]$\lesssim -0.2$). Overall, the light- (C, N), $\alpha$- (O, Mg, Si, Ca, Ti), Fe-peak (Fe, Ni), Odd-Z (Al, K), and the \textit{s}-process (Ce, Nd, Yb) elemental abundances of our member candidates are consistent with those observed in globular clusters at similar metallicity. Furthermore, the overall star-to-star abundance scatter of elements exhibiting the multiple-population phenomenon in UKS~1 is typical of that found in other global clusters (GCs), and larger than the typical errors of some [X/Fe] abundances. Results from statistical isochrone fits in the VVV colour-magnitude diagrams indicate an age ...

16 pages, 9 figures, 3 tables, A&A (in press)

References in corpus (28)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• The Dartmouth Stellar Evolution Database
• The Sixteenth Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE) Spectrographs
• Target Selection for the SDSS-IV APOGEE-2 Survey
• Origin of the abundance patterns in Galactic globular clusters: constraints on dynamical and chemical properties of globular clusters
• The elemental composition of the Sun III. The heavy elements Cu to Th
• Constraining the thick disc formation scenario of the Milky Way
• Homogeneous Analysis of Globular Clusters from the APOGEE Survey with the BACCHUS Code. II. The Southern Clusters and Overview
• VIRAC: The VVV Infrared Astrometric Catalogue
• Exploring Anticorrelations and Light Element Variations in Northern Globular Clusters Observed by the APOGEE Survey
• Light, Alpha, and Fe-Peak Element Abundances in the Galactic Bulge
• APOGEE Chemical Abundances of Globular Cluster Giants in the Inner Galaxy
• A homogeneous analysis of globular clusters from the APOGEE survey with the BACCHUS code. I. The Northern clusters
• Extinction ratios in the inner Galaxy as revealed by the VVV survey
• Atypical Mg-poor Milky Way field stars with globular cluster second-generation like chemical patterns
• How Many Components? Quantifying the Complexity of the Metallicity Distribution in the Milky Way Bulge with APOGEE
• Distances of the bulge globular clusters Terzan 5, Liller 1, UKS 1 and Terzan 4 based on HST NICMOS photometry
• Kinematics of the local disk from the RAVE survey and the Gaia first data release
• New galactic star clusters discovered in the VVV survey. Candidates projected on the inner disk and bulge
• Chemodynamics of newly identified giants with globular cluster like abundance patterns in the bulge, disk, and halo of the Milky Way
• The Relationship Between Globular Cluster Mass, Metallicity, and Light Element Abundance Variations
• Two Groups of Red Giants with Distinct Chemical Abundances in the Bulge Globular Cluster NGC 6553 Through the Eyes of APOGEE
• Evidence of AGB pollution in Galactic globular clusters from the Mg-Al anticorrelations observed by the APOGEE survey
• Self-consistent analysis of stellar clusters: An application to HST data of the halo globular cluster NGC 6752
• Purveyors of fine halos. II. Chemodynamical association of halo stars with Milky Way globular clusters
• Galactic globular clusters: a new catalog of masses, structural parameters, velocity dispersion profiles, proper motions and space orbits
• Chemical abundances in the metal-intermediate GC NGC 6723

Cited by in corpus (26)

• The Chemo-Dynamical Groups of Galactic Globular Clusters
• Aluminum Enhanced Metal-Poor Stars buried in the Inner Galaxy
• Dynamically Tagged Groups of Metal-Poor Stars from the Best \& Brightest Survey
• VVV CL001: Likely the Most Metal-Poor Surviving Globular Cluster in the Inner Galaxy
• Galactic ArchaeoLogIcaL ExcavatiOns (GALILEO) I. An updated census of APOGEE N-rich giants across the Milky Way
• APOGEE discovery of a chemically atypical star disrupted from NGC 6723 and captured by the Milky Way bulge
• APOGEE spectroscopic evidence for chemical anomalies in dwarf galaxies: The case of M~54 and Sagittarius
• A census of new globular clusters in the Galactic bulge
• Jurassic: A Chemically Anomalous Structure in the Galactic Halo
• Discovery of a new nearby globular cluster with extreme kinematics located in the extension of a halo stream
• CAPOS: the bulge Cluster APOgee Survey II. The Intriguing "Sequoia" Globular Cluster FSR 1758
• Abundance analysis of APOGEE spectra for 58 metal-poor stars from the bulge spheroid
• Unveiling the nature of 12 new low-luminosity Galactic Globular Cluster Candidates
• CAPOS: The bulge Cluster APOgee Survey III. Spectroscopic Tomography of Tonantzintla 2
• APOGEE-2S Discovery of Light- and Heavy-Element Abundance Correlations in the Bulge Globular Cluster NGC 6380
• Inspection of 19 globular cluster candidates in the Galactic bulge with the VVV survey
• APOGEE-2S view of the globular cluster Patchick 125 (Gran 3). New metallicity and elemental abundances from high-resolution spectroscopy
• Galactic ArchaeoLogIcaL ExcavatiOns (GALILEO) II. t-SNE Portrait of Local Fossil Relics and Structures
• Chrono-chemodynamical analysis of the globular cluster NGC 6355: Looking for the fundamental bricks of the Bulge
• CAPOS: The bulge Cluster APOgee Survey V. Elemental abundances of the bulge globular cluster HP 1
• Spectroscopic Observations of Obscured Populations in the Inner Galaxy: 2MASS-GC02, Terzan 4, and the 200 km/s stellar peak
• Investigating Phosphorus Abundances in a Sample of APOGEE-2 Bulge Globular Clusters
• Variable stars in the VVV globular clusters. II. NGC6441, NGC6569, NGC6626 (M28), NGC6656 (M22), 2MASS-GC02, and Terzan10
• A possible GeV-TeV connection in the direction of the Globular Cluster UKS 1
• Photo-chemo-dynamical analysis and the origin of the bulge globular cluster Palomar 6
• UVES analysis of red giants in the bulge globular cluster NGC 6522