Tara Final Presentation :�Star Cluster Disintegration

Presenter : Jing-Yuan Lai / Professor Wing-Ping Chen

Outline

• Introduction
• Cluster
• H-R Diagram
• Data Source
• Objectives
• NGC2158
• Data Analysis
• Result
• Picture Reference
• Impression

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Cluster Image

A star cluster is a large group of stars held together by their own gravity.

New Hubble image of star cluster Messier 15

The Pleiades from DSS (NASA/ESA/AURA/Caltech)

Cluster Evolution

Star clusters form through the gravitational collapse and fragmentation of giant molecular clouds (GMCs)

• Molecular cloud collapse
• Star formation
• Gas expulsion
• Dynamical relaxation
• Mass loss
• Star cluster dissolution.

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Open Clusters (OCs) v.s. Globular Clusters (GCs)

OCs form from the same molecular cloud, and their member stars share nearly identical ages, distances, and chemical compositions.

NGC 2547 (OCs) v.s. 47 Tucanae (GCs)

H-R Diagram

The main sequence turn off age tells us how old the cluster is

H-R diagram of M3

�Star Cluster Evolution and Changes in the H-R Diagram

Isochrones

An isochrone is a curve on the H-R diagram connecting stars of the same age and metallicity but different masses

Isochrone examples

Gaia DR3

Data Source

NGC2158

DSS2 image of NGC 2158 in the Red band

Near clusters of NGC 2158

NGC 2158 from stellarium

NGC 2158 is located within the constellation Gemini, appearing close to another well-known open cluster, M35

NGC2158

surface density of Gaia DR3 (Ahmed & Tadross (2025))

CMD of the member stars (Ahmed & Tadross (2025) )

These plots from Ahmed & Tadross (2025) characterize the structure and stellar population of NGC 2158

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Data Anlysis

Strange stars

pm shows two dense center

Data Anlysis

Strange stars are concentrated in certain locations.

�Is it part of the Galactic disk?

Strange stars

Strange stars

strange stars may be NGC2168

Member selection

Member selection

member stars of NGC2168 are 2094

Theoretical Isochrone

Isochrone fitting

Ages of NGC2168 are 1.5 Gyrs to 4 Gyrs

Results

Picture Reference

• https://phys.org/news/2025-05-unveiling-birth-star-cluster-groups.html
• https://pages.uoregon.edu/jschombe/ast122/lectures/lec15.html
• https://www.researchgate.net/figure/A-schematic-visualising-the-evolution-of-the-molecular-cloud-filament-shown-by-the-black_fig1_322275331
• https://esahubble.org/wordbank/globular-cluster/
• https://blogs.iu.edu/sciu/2016/09/20/star-clusters/

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Picture Reference

• https://www.astronomy.com/science/what-is-the-difference-between-a-globular-star-cluster-and-an-open-star-cluster/
• https://faculty.washington.edu/ivezic/REU08/GDP/distance/background3.html
• https://www.researchgate.net/figure/sochrones-for-a-cluster-of-stars-with-masses-between-07-M-and-35-M-that-evolved-in-a_fig2_51891502
• https://exoplanetes.umontreal.ca/en/gaia-a-new-era-for-astronomy/
• https://theskylive.com/sky/deepsky/ngc2158-object

Impressrion

Thank you for listening !