M92 (NGC~6341) Is a Metal-Complex Globular Cluster with an Atypical Primordial Population

Abstract

We present a multiple stellar population study of the metal-poor globular cluster (GC) M92 (NGC 6341), which is long known for the substantial metallicity dispersion, using our own photometric system. We find two groups with slightly different mean metallicities, the metal-poor (MP) stars with [Fe/H] = $-$2.412$\pm$0.03, while the metal-rich (MR) ones with $-$2.282$\pm$0.002. The MP constitutes about 23\% of the total mass with a more central concentration. Our populational tagging based on the [C/Fe] and [N/Fe] provides the mean n(P):n(I):n(E) = 32.2:31.6:36.2 ($\pm$2.4), where P, I, and E denote the primordial, intermediate, and extreme populations, respectively. Our populational number ratio is consistent with those of others. However, the MP has a significantly different populational number ratio than the mean value, and the domination of the primordial population in the MP is consistent with observations of Galactic GCs that less massive GCs contain larger fractions of the primordial population. Structural and constituent differences between the MP and MR may indicate that M92 is a merger remnant in a dwarf galaxy environment, consistent with recent suggestions that M92 is a GC in a dwarf galaxy or a remnant nucleus of the progenitor galaxy. Discrepancy between our method and those widely used for the HST photometry exists in the primordial population. Significant magnesium and oxygen depletions of $-$0.8 and $-$0.3 dex, respectively, and helium enhancement of $\Delta Y$ $\gtrsim$ 0.03 are required to explain the presence of this abnormal primordial group. No clear explanation is available with limited information of detailed elemental abundances.

arXiv commentAccepted for publication to the Astrophysical Journal Letters

References in corpus (26)

• Theoretical isochrones in several photometric systems I. Johnson-Cousins-Glass, HST/WFPC2, HST/NICMOS, Washington, and ESO Imaging Survey filter sets
• Multiple Stellar Populations in Globular Clusters
• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• A catalogue of masses, structural parameters and velocity dispersion profiles of 112 Milky Way globular clusters
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. IX. The Atlas of Multiple Stellar Populations
• The Abundances of Neutron Capture Species in the Very Metal-Poor Globular Cluster M15: An Uniform Analysis of RGB and RHB Stars
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XVI. The helium abundance of multiple populations
• The updated BaSTI stellar evolution models and isochrones: II. alpha-enhanced calculations
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters - XVII. Public Catalogue Release
• Enrichment by supernovae in globular clusters with multiple populations
• Multiple populations in globular clusters and their parent galaxies
• Heavy Element Dispersion in the Metal-Poor Globular Cluster M92
• The eye of Gaia on globular clusters structure: tidal tails
• Formation of Second Generation Stars in Globular Clusters
• A Survey of CN and CH Variations in Galactic Globular Clusters from SDSS Spectroscopy
• Multiple Stellar Populations of Globular Clusters from Homogenous Ca by Photometry I. M22 (NGC 6656)
• Multiple stellar populations of globular clusters from homogeneous Ca-Cn photometry. II. M5 (NGC 5904) and a new filter system
• The Pristine survey -- XVI. The metallicity of 26 stellar streams around the Milky Way detected with the STREAMFINDER in Gaia EDR3
• The hidden past of M92: Detection and characterization of a newly formed 17° long stellar stream using the Canada-France Imaging Survey
• Confirmation of a metallicity spread amongst first population stars in globular clusters
• Multiple stellar populations of globular clusters from homogeneous Ca--CN photometry. III. NGC 6752
• Formation of globular clusters with multiple stellar populations from massive gas clumps in high-z gas-rich dwarf galaxies
• Multiple stellar populations of globular clusters from homogeneous Ca--CN photometry. IV. Toward precision populational tagging
• Multiple Stellar Populations of Globular Clusters From Homogeneous Ca-CN-CH-NH Photometry. VII. Metal-Poor Populations in 47 Tucanae (NGC 104)
• Multiple Stellar Populations of Globular Clusters from Homogeneous Ca-CN-CH-NH Photometry. VI. M3 (NGC 5272) is not a Prototypical Normal Globular Cluster
• Formation of Multiple Populations of M5 (NGC 5904)

Cited by in corpus (6)

• MgAl burning chain in Omega Centauri
• r-process Abundance Patterns in the Globular Cluster M92
• MOCCA: Effects of pristine gas accretion and cluster migration on globular cluster evolution, global parameters, and multiple stellar populations
• A Comparative Study Between M30 and M92 : M92 Is A Merger Remnant With A Large Helium Enhancement
• Benchmarking the effective temperature scale of red giant branch stellar models: the case of the metal-poor halo giant HD 122563
• Carbon Abundance of Globular Cluster M22 (NGC 6656) and the Surface Carbon Depletion Rates of the Milky Way Globular Clusters