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Stars on the ZAMS: Mass, Metallicity, and H-R Position

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

Predict

Before using controls, predict what happens to Teff and L when mass increases along the ZAMS at fixed metallicity.

Play

Play

  1. Use ZAMS mode with the mass slider at Z=0.02 and follow the marker along the ZAMS track.
  2. Hold mass fixed and vary metallicity to see how L, R, and Teff shift.
  3. Switch to Stefan mode, keep Teff fixed, and increase R to see the vertical shift in L.
  4. Turn on constant-R guides and identify the nearest guide for each state.
  5. Select an override preset (for example a red supergiant) and compare it against nearby ZAMS states.
Explain

Explain

Use one ZAMS case and one override case to explain how assumptions change what the model is allowed to infer.

Learning goals
  • Relate stellar mass and metallicity to ZAMS luminosity, radius, and effective temperature.
  • Interpret H-R diagram position on base-10 log-log axes using explicit model assumptions and units.
  • Distinguish surface emitted flux (F) from total luminosity (L) using Stefan-Boltzmann scaling.
  • Distinguish ZAMS-inferred stars from intentional non-ZAMS override presets.

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
  • ZAMS luminosity and radius use analytic fits from Tout et al. (1996) over 0.1 <= M/Msun <= 100 and 1e-4 <= Z <= 0.03.
  • Explore view uses base-10 log-log axes: $\log_{10}(T_{\rm eff}\,[\mathrm{kK}])$ and $\log_{10}(L/L_{\odot})$.
  • Stefan mode exposes the explicit closure equations: $$F=\sigma T^4$$ and $$\frac{L}{L_{\odot}}=\left(\frac{R}{R_{\odot}}\right)^2\left(\frac{T_{\rm eff}}{T_{\odot}}\right)^4$$.
  • Override presets intentionally bypass ZAMS constraints so evolved/compact stars can be compared with explicit warning text, and metallicity is shown as not-applied while override mode is active.

About this demo

This ASTR 201 instrument turns the H-R diagram into a model-driven lab by tying each plotted point to explicit ZAMS assumptions and units.