Peeking beneath the precision floor I: metallicity spreads and multiple elemental dispersions in the globular clusters NGC 288 and NGC 362

Abstract

The view of globular clusters (GCs) as simple systems continues to unravel, revealing complex objects hosting multiple chemical peculiarities. Using differential abundance analysis, we probe the chemistry of the Type I GC, NGC 288 and the Type II GC, NGC 362 at the 2\% level for the first time. We measure 20 elements and find differential measurement uncertainties on the order 0.01-0.02 dex in both clusters. The smallest uncertainties are measured for Fe I in both clusters, with an average uncertainty of $\sim$0.013 dex. Dispersion in the abundances of Na, Al, Ti I, Ni, Fe I, Y, Zr, Ba and Nd are recovered in NGC 288, none of which can be explained by a spread in He. This is the first time, to our knowledge, a statistically significant spread in $s$-process elements and a potential spread in metallicity has been detected in NGC 288. In NGC 362, we find significant dispersion in the same elements as NGC 288, with the addition of Co, Cu, Zn, Sr, La, Ce, and Eu. Two distinct groups are recovered in NGC 362, separated by 0.3 dex in average differential $s$-process abundances. Given strong correlations between Al and several $s$-process elements, and a significant correlation between Mg and Si, we propose that the $s$-process rich group is younger. This agrees with asymptotic giant branch star (AGB) enrichment between generations, if there is overlap between low- and intermediate-mass AGBs. In our scenario, the older population is dominated by the $r$-process with a ${\Delta }^{\mathrm{La}}-{\Delta }^{\mathrm{Eu}}$ ratio of $-0.16\pm 0.06$. We propose that the $r$-process dominance and dispersion found in NGC 362 are primordial.

First paper in a series. Accepted for publication in MNRAS

References in corpus (35)

• Array Programming with NumPy
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Galactic chemical evolution: Carbon through Zinc
• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. IX. The Atlas of Multiple Stellar Populations
• Spectroscopic and Photometric evidence of two stellar populations in the Galactic Globular Cluster NGC6121 (M4)
• The kinematic status and mass content of the Sculptor dwarf spheroidal galaxy
• What is a globular cluster? An observational perspective
• DAOSPEC: an automatic code for measuring equivalent widths in high-resolution stellar spectra
• The Solar Twin Planet Search. I. Fundamental parameters of the stellar sample
• Evolution and nucleosynthesis of asymptotic giant branch stellar models of low metallicity
• Iron and s-elements abundance variations in NGC5286: comparison with anomalous globular clusters and Milky Way satellites
• Iron and neutron-capture element abundance variations in the globular cluster M2 (NGC 7089)
• Homogeneous photometry VII. Globular clusters in the Gaia era
• A large C+N+O abundance spread in giant stars of the globular cluster NGC 1851
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XIX. A Chemical Tagging of the Multiple Stellar Populations Over the Chromosome Maps
• Nucleosynthesis Predictions for Intermediate-Mass AGB Stars: Comparison to Observations of Type I Planetary Nebulae
• Multiple populations in globular clusters and their parent galaxies
• linemake: An Atomic and Molecular Line List Generator
• The Southern Stellar Stream Spectroscopic Survey (S5): Chemical Abundances of Seven Stellar Streams
• CNO abundances in the globular clusters NGC 1851 and NGC 6752
• The Accreted Nuclear Clusters of the Milky Way
• R-Process elements from magnetorotational hypernovae
• Primordial r-process Dispersion in Metal-Poor Globular Clusters
• The halo+cluster system of the Galactic globular cluster NGC1851
• Chemical abundances along the 1G sequence of the chromosome maps: The Globular Cluster NGC 3201
• Low-resolution Spectroscopy for the Globular Clusters with Signs of Supernova Enrichment: M22, NGC 1851 and NGC 288
• Reversed radial distribution trend of subpopulations in the globular clusters NGC 362 and NGC 6723
• The s-Process Enrichment of the Globular Clusters M4 and M22
• What is the Milky Way outer halo made of? High resolution spectroscopy of distant red giants
• Simulations of globular clusters within their parent galaxies: Metallicity spreads and anomalous precursor populations
• Light Element Chemistry and the Double Red Giant Branch in the Galactic Globular Cluster NGC 288
• Investigating a predicted metallicity [Fe/H] variation in the Type II Globular Cluster NGC 362

Cited by in corpus (3)

• Peeking beneath the precision floor -- II. Probing the chemo-dynamical histories of the potential globular cluster siblings, NGC 288 and NGC 362
• A stellar census in globular clusters with MUSE. Metallicity spread and dispersion among first-population stars
• Abundance of strontium in the Galactic globular cluster 47 Tuc