---
title: "Star cluster colours and populations"
description: "Follow birth masses into unresolved light, a finite aperture and source-native age comparisons."
canonical_url: "https://sandboxphysics.com/stories/cluster-populations/"
language: "en"
page_type: "story"
alternate_languages:
  zh-CN: "https://sandboxphysics.com/zh/stories/cluster-populations/"
last_modified: "2026-11-04"
---

AC32

# Star cluster colours and populations

Sandbox Physics · 2026-11-03

Trace one population from component masses to light. Add companions, change the physical field and inspect native-model support before interpreting a broad colour diagram.

1. L1

   ## [Same birthday, different stars](https://sandboxphysics.com/stories/cluster-populations/same-birthday-different-stars/)

   Unequal masses, unresolved pairs and a finite field can broaden a coeval colour diagram. Follow the light before assigning an age spread.

2. L1

   ## [Draw masses before counting stars](https://sandboxphysics.com/stories/cluster-populations/draw-masses-before-counting-stars/)

   Turn a component IMF into finite draws and native-node weights, then distinguish components from unresolved systems.

3. L2

   ## [Two stars, one point](https://sandboxphysics.com/stories/cluster-populations/two-stars-one-point/)

   Add component light within each band, then carry the same system through its actual distance and observing cone.

4. L3

   ## [An age comparison needs a model](https://sandboxphysics.com/stories/cluster-populations/an-age-comparison-needs-a-model/)

   Check native ages, phases, passbands, interpolation failures and boundary minima before treating a diagram comparison as an age statement.

5. L3

   ## [A fixed patch of M67](https://sandboxphysics.com/stories/cluster-populations/a-fixed-patch-of-m67/)

   Fetch a named Gaia cone and native models locally, rerun selections and comparisons, and build verified twelve-age import files.

6. L4

   ## [A concentrated core is not a clock](https://sandboxphysics.com/stories/cluster-populations/a-concentrated-core-is-not-a-clock/)

   Read fixed simulation and abundance papers to distinguish mass segregation, formation history, finite samples and chemical populations.

[Drag the aperture and follow the same light](https://sandboxphysics.com/labs/star-cluster/?analysis=populations)

## Sources and calculation scope

1. [Reyes et al. (2024), a precise M67 isochrone; native ISOA data](https://zenodo.org/records/12616441)

   The original ISOA file supplies one 3.95 Gyr age. Our CC BY 4.0slice uses98 monotonic rows with central hydrogen fraction above0.001; its native absolute magnitudes areGaia DR2, notEDR3.

2. [Kroupa (2001), On the variation of the initial mass function](https://arxiv.org/abs/astro-ph/0009005v1)

   Read the distinction between a component mass distribution and unresolved systems. The finite0.1–8 solar-mass family in our local model is a stated teaching truncation, not a fittedM67IMF.

3. [PARSEC/CMD3.8 official input help and phase labels](https://stev.oapd.inaf.it/cmd_3.8/help.html)

   PinnedPARSEC 1.2S, solar-scaled composition, OBC andGaia EDR3Vega, native returned ages andAvnodes. Source labels are approximate; our equal-phase rule prevents bridging labelled boundaries but does not certify continuous evolutionary branches.

4. [MIST official isochrone interface and user documentation](https://mist.science/isochrones.html)

   The local comparison usesMIST 1.2, MESA 7503, nonrotating, solar iron abundance, Av 0, and the originalGaia EDR3columns. Full original numerical hashes identify the twelve-node file; code licensing does not establish table redistribution permission.

5. [Gaia DR3 documentation and archive](https://www.cosmos.esa.int/web/gaia/dr3)

   Astrometric reference epoch2016.0 is not a universal epoch for mean photometry. The tutorial uses a fixed cone and explicit astrometric cuts; source rows and real point plots are made only on the reader computer.

6. [Official Gaia data license](https://www.cosmos.esa.int/web/gaia-users/license)

   The dedicated data-license page specifiesCC BY-NC 3.0 IGO. This package supplies a named upstream recipe, not a rehostedGaia catalogue, individual-source derivative table or real-source scatter plot.

7. [Polak et al., arXiv2408.14592v2 (16 September2025)](https://arxiv.org/html/2408.14592v2)

   Sections2–4, Figures2–4 and AppendixA. Separate ongoing formation, dynamical rearrangement, ejections and wind-driven mass-rank changes; inspect which stars define each mass-segregation statistic.

8. [Huang et al. (2024), arXiv2401.17584v1](https://arxiv.org/html/2401.17584v1)

   SectionIII/Figure3/Table2 and SectionIV/Figure4/Table3. Eight giant-star abundances and the conditional population-selection argument concern chemical multiple populations, not an unresolved-binary ridge.