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Gran 5 Cluster Hosts Dual Stellar Populations: A Recent Research

The seven spectroscopic target stars are marked by green circles.

Introduction: Unveiling Dual Stellar Populations in Gran 5

Astronomers utilizing the Gemini-South telescope have carried out high-resolution near-infrared spectroscopy on the stars of the Gran 5 Galactic Globular Cluster. Their research uncovered two separate stellar populations with differing metallicities. The findings were published on October 28 in a paper on arXiv.

Understanding Globular Clusters and Their Significance

What Are Globular Clusters?

Globular Clusters (GCs) are groupsof tightly bound stars that orbit galaxies, providing astronomers with valuable insights into stellar and galactic evolution. These clusters serve as natural laboratories, particularly aiding in the study of the formation and evolution of early-type galaxies, as their origins appear to be closely tied to phases of intense star formation.

Gran 5: A Low-Mass Globular Cluster

Gran 5 is a recently identified low-mass globular cluster, located approximately 14,600 light years from the Galactic center. With a mass of around 22,900 solar masses, it is believed to be an accreted object linked to the Gaia–Enceladus–Sausage kinematic structure in the Milky Way's halo.

Research Methodology: High-Resolution Spectroscopy

Studying Gran 5 with the IGRINS Spectrometer

To further understand the stellar populations of Gran 5 and uncover their detailed chemical properties, a team of astronomers, headed by Dongwook Lim from Yonsei University in Seoul, South Korea, studied seven stars within the cluster using the Immersion Grating Infrared Spectrometer (IGRINS).

The researchers reported in their paper, "High-resolution near-infrared spectroscopy was performed on seven stars in the Gran 5 field using IGRINS on the Gemini-South telescope."

Spectroscopy Results: Stellar Membership and Metallicity

From the spectroscopy of the seven stars, Lim's team determined that six were members of the cluster, while one star was excluded due to its markedly different radial velocity. The six cluster members exhibited heliocentric radial velocities of approximately -60 km/s and low metallicities around -0.65 dex, confirming Gran 5 as a genuine globular cluster.

Key Findings: Two Stellar Population in Gran 5

Distinct Metallicity Groups

The study, however, revealed that the stars examined can be separated into two groups based on metallicity, with mean values of -0.76 dex and -0.55 dex for each group. Since no correlation was observed between these groups and heliocentric radial velocities or atmospheric parameters, the astronomers suggest that Gran 5 contains two distinct stellar populations with different metallicities.

Gran 5's Chemo-Dynamical Properties

The authors of the paper highlight that their study represents the first detection of two stellar populations with distinct metallicities in a low-mass globular cluster. They also note that the chemo-dynamical properties of Gran 5 indicate it is not associated with the Gaia-Enceladus-Sausage structure, but rather belongs to the Galactic bulge or disk.

Conclusion: Implications for, Stellar Evolution and Cluster Formation

Metallicity Variation: A Sign of Different Formation Processes?

The researchers conclude that the metallicity variation observed in Gran 5 might be due to different formation processes or the cluster's loss of a substantial amount of mass throughout its evolution.

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