Supergiant GCIRS 22 in the Milky Way Nuclear Star Cluster: Revised alpha abundances

Abstract

Context: The chemical abundances of alpha-elements in Galactic Centre (GC) supergiants provide key insights into the chemical enrichment and star formation history of the Milky Way's Nuclear Star Cluster. Previous studies have reported enhanced alpha-element abundances, raising questions about the chemical evolution of this unique region. Aims: We aim to reassess the alpha-element abundances in the GC supergiant GCIRS 22 using updated spectral modelling and non-local thermodynamic equilibrium (NLTE) corrections to resolve discrepancies from earlier abundance analyses. Methods: High-resolution near-infrared spectra of GCIRS 22 were analysed using contemporary line lists and precise stellar parameters derived from scandium line diagnostics. We applied comprehensive NLTE corrections to accurately determine the abundances of silicon and calcium. Results: Our analysis reveals solar-scale alpha abundances ([Ca/Fe] = 0.06 $\pm$ 0.07; [Si/Fe] = $-$0.08 $\pm$ 0.20) for GCIRS 22, significantly lower than previous LTE-based findings. NLTE corrections reduce the calcium abundance by approximately 0.3,dex compared to LTE estimates, aligning our results with recent studies and highlighting the importance of accurate NLTE modelling. Conclusions: The solar-scale alpha-element abundances observed in GCIRS 22 suggest that recent star formation in the region has not been dominated by Type II supernovae, such as those expected from a recent starburst. Our findings support a scenario of episodic star formation, characterized by intermittent bursts separated by extended quiescent phases, or potentially driven by gas inflows from the inner disk, funnelled by the Galactic bar. Future comprehensive NLTE studies of additional GC stars will be essential for refining our understanding of the region's chemical evolution and star formation history.

References in corpus (56)

• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Grids of stellar models with rotation - I. Models from 0.8 to 120 Msun at solar metallicity (Z = 0.014)
• Multimodal nested sampling: an efficient and robust alternative to MCMC methods for astronomical data analysis
• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• ExoMol molecular line lists XXX: a complete high-accuracy line list for water
• The Nuclear Bulge of the Galaxy. III. Large-Scale Physical Characteristics of Stars and Interstellar Matter
• Spectroscopy Made Easy: Evolution
• Nuclear Star Clusters
• Interstellar Extinction Law toward the Galactic Center III: J, H, Ks bands in the 2MASS and the MKO systems, and 3.6, 4.5, 5.8, 8.0 micron in the Spitzer/IRAC system
• The Payne: self-consistent ab initio fitting of stellar spectra
• The Effective Temperatures and Physical Properties of Magellanic Cloud Red Supergiants: The Effects of Metallicity
• Dissipationless Formation and Evolution of the Milky Way Nuclear Star Cluster
• Masses and Scaling Relations for Nuclear Star Clusters, and their Coexistence with Central Black Holes
• Improved GRAVITY astrometric accuracy from modeling of optical aberrations
• Line lists for the A2PI-X2Sigma+ (red) and {B2Sigma+-X2Sigma} (violet) Systems of CN, 13C14N, and 12C15N, and Application to Astronomical Spectra
• Chemical Abundances of Luminous Cool Stars in the Galactic Center from High-Resolution Infrared Spectroscopy
• Really Cool Stars and the Star Formation History at the Galactic Center
• Self-gravitating accretion disk in Sgr A* few million years ago: was Sgr A* a failed quasar?
• Early formation and recent starburst activity in the nuclear disc of the Milky Way
• Constraining the role of star cluster mergers in nuclear cluster formation: Simulations confront integral-field data
• The GALAH Survey: Non-LTE departure coefficients for large spectroscopic surveys
• Three classical Cepheid variable stars in the nuclear bulge of the Milky Way
• The Milky Way's nuclear star cluster: Old, metal-rich, and cuspy
• The nuclear cluster of the Milky Way: Our primary testbed for the interaction of a dense star cluster with a massive black hole
• Simulations of the Milky Way's central molecular zone -- II. Star formation
• Discovery of low-metallicity stars in the central parsec of the Milky Way
• The solar silicon abundance based on 3D non-LTE calculations
• The NIRSPEC Brown Dwarf Spectroscopic Survey II: High-Resolution J-Band Spectra of M, L and T Dwarfs
• The chemical abundances in the Galactic Centre from the atmospheres of Red Supergiants
• Metallicity of Red Giants in the Galactic Bulge from Near-Infrared Spectroscopy
• Really Cool Stars at the Galactic Center
• On the rotation of nuclear star clusters formed by cluster-inspirals
• New constraints on the structure of the nuclear stellar cluster of the Milky Way from star counts and MIR imaging
• Mg line formation in late-type stellar atmospheres: II. Calculations in a grid of 1D models
• Stellar ages, masses, extinctions and orbital parameters based on spectroscopic parameters of Gaia DR3
• Age Dating the Galactic Bar with the Nuclear Stellar Disc
• Detailed Abundances for the Old Population near the Galactic Center: I. Metallicity distribution of the Nuclear Star Cluster
• 3D non-LTE iron abundances in FG-type dwarfs
• Detailed abundances in the Galactic center: Evidence of a metal-rich alpha-enhanced stellar population
• The Star Formation History of the Milky Way's Nuclear Star Cluster
• On the origin of a rotating metal-poor stellar population in the Milky Way Nuclear Cluster
• Ca line formation in late-type stellar atmospheres: I. The model atom
• Evidence against anomalous compositions for giants in the Galactic Nuclear Star Cluster
• The nuclear star cluster and nuclear stellar disc of the Milky Way: Different stellar population and star formation history
• Stellar Populations in the Central 0.5 pc of Our Galaxy III: The Dynamical Sub-structures
• Fluorine Abundances in the Galactic Nuclear Star Cluster
• The Inner 2 pc of Sagittarius A*: Simulations of the Circumnuclear Disk and Multiphase Gas Accretion in the Galactic Center
• Spectroscopically Identified Intermediate Age Stars at 0.5 - 3 pc Distance from Sgr A*
• Evidence of Deep Mixing in IRS 7, a Cool Massive Supergiant Member of the Galactic Nuclear Star Cluster
• Smooth kinematic and metallicity gradients reveal that the Milky Way's nuclear star cluster and disc might be part of the same structure
• A spectroscopic map of the Galactic centre -- Observations and resolved stars
• MAGIS (Measuring Abundances of red super Giants with Infrared Spectroscopy) project I. Establishment of an abundance analysis procedure for red supergiants and its evaluation with nearby stars
• Measuring the alpha-abundance of subsolar-metallicity stars in the Milky Way's central half-parsec: testing globular cluster and dwarf galaxy infall scenarios
• A Wide Metallicity Range for Gyr-old Stars in the Nuclear Star Cluster