HR Diagram Inference Lab

Observer CMD

Use arrow keys to move selection on the plot. Press Home/End to jump to boundary stars.

Selected Star

Inference

Click a star or use the keyboard on the plot to inspect a specific point.

Stage
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Effective temperature K
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Luminosity L/L_sun
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Radius R/R_sun
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Mass
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Plain-language interpretation

Click a star to begin the inference workflow.

Ask whether this star is unusually bright or faint for its temperature.

Step Guide 3 prompts

Measurement-built map: observer CMD versus theorist HR coordinates.

  1. Identify the main sequence, giant branch, and white dwarf region from the synthetic population map.
  2. Pick one hot-faint star and infer its radius using Stefan-Boltzmann scaling.
  3. Reveal mass colors and infer the mass-gradient direction along the main sequence.
Model Notes Tout + CMD calibration
  • Main sequence properties use Tout et al. (1996) ZAMS fits for L(M,Z) and R(M,Z), with Teff from Stefan-Boltzmann closure.
  • Observer CMD mapping uses empirical bolometric correction and Teff-color calibration, plus deterministic Gaussian photometric scatter.
  • Radius guides follow L/L_sun = (R/R_sun)^2 (T/T_sun)^4.
Start here a route through the diagram

Start Here

Start Here

Use the workflow below to move from pattern recognition to physical inference.

  1. Find the main sequence
  2. Click a star
  3. Compare temperature and luminosity
  4. Turn on radius lines
  5. Reveal mass colors
Inference log write and export your claims

Inference Log

Classroom notes
Sentence starters