HR Diagram Inference Lab

draft readiness: experimental Stars ASTR201 14 min

Active development: draft / experimental

Tout-1996 ZAMS model and instrument workflow are implemented; classroom parity and launch-gate QA remain in progress.

Launch demo Open fullscreen Station card Instructor notes

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Predict

Before revealing mass colors, predict where high-mass and low-mass stars should lie along the main sequence.

Play

Start in Observer CMD mode and identify main sequence, giant-branch, and white-dwarf structures.
Switch to Theorist HR mode and enable radius lines to infer stellar size from L and T_eff.
Use the evolve-a-star tool to compare track shape and timescale for 0.8 and 20 M_sun stars.
Reveal mass colors and infer the hidden mass gradient direction along the main sequence.
Add one-sentence claims to the inference log and export JSON.

Explain

Explain how the same population can be interpreted as an observer CMD and a theorist HR map, then justify one radius and one mass inference.

Learning goals

Use observer-space and theorist-space views to interpret stellar populations as measurement-built maps.
Infer stellar radius from luminosity and effective temperature with explicit Stefan-Boltzmann reasoning.
Infer hidden mass ordering along the main sequence after staged reveal controls are enabled.
Connect mass-dependent lifetimes to conceptual stellar-evolution tracks.

Misconceptions targeted

Temperature alone determines total stellar luminosity.
Main-sequence fits apply equally to giant and compact remnant stars.
Metallicity only changes spectral lines and not bulk stellar structure.
Logarithmic axes distort physics rather than reveal dynamic range.

Model notes

Main-sequence luminosity and radius use Tout et al. (1996) analytic ZAMS fits over 0.1 <= M/Msun <= 100 and 1e-4 <= Z <= 0.03.
Theorist HR mode uses base-10 logarithmic axes: log(L/L_sun) versus log(T_eff) with hot-left orientation.
Observer CMD mode uses M_V versus (B-V), with deterministic photometric scatter and brighter-up magnitude inversion.
Radius guides follow Stefan-Boltzmann scaling: $$\frac{L}{L_{\odot}}=\left(\frac{R}{R_{\odot}}\right)^2\left(\frac{T_{\rm eff}}{T_{\odot}}\right)^4$$.

About this demo

This ASTR 201 instrument treats the HR diagram as both a measurement-built map and a hidden-variable inference engine, with staged reveals and explicit model assumptions.