AC27
Starspots, rotation and stellar ages
Follow a patch around a star, learn how its light constrains a clock, and test what a fixed cluster calibration can tell us about age.
L1
A starspot tells the time at its own latitude
A dark patch can reveal a stellar surface clock. Its latitude, lifetime and viewing angle decide how that clock relates to rotation and age.
L1
Turn changing starlight into competing periods
Derive a surface light signal, fit a repeating clock to saved observations, and keep harmonic and daily aliases in a proper probability calculation.
L2
How a stellar wind slows rotation
Follow angular momentum into a magnetized wind, integrate saturated and unsaturated braking, and separate wind loss from contraction.
L3
A rotation age is a distribution on a chosen scale
Combine a saved-data period likelihood with temperature-dependent cluster sequences, then test priors, stalling and calibration boundaries.
L4
Hold out a whole cluster and test a rotation clock
Download fixed author sources, recover all benchmark rows, retain sample-version differences, and independently reproduce conditional cluster-age checks.
L4
Read the evidence for changing magnetic braking
Follow fixed seismic, magnetic-torque and photometric-activity papers, with their samples, Rossby definitions and inference steps kept distinct.
Follow the starspot and compare its clock
Sources and calculation scope
- Curtis et al. (2019), A Temporary Epoch of Stalled Spin-Down for Low-Mass Stars: Insights from NGC6811 with Gaia and Kepler arXiv1905.06869v3
Sections2–4 and source Table1: NGC6811 periods, quarter handling, membership, extinction and cool-star stalling. The TeX table has172rows; source-version differences are retained.
- Curtis et al. (2020), When Do Stalled Stars Resume Spinning Down? Advancing Gyrochronology with Ruprecht147, arXiv2010.02272v1
Sections2–6, AppendixA, Table4, Figures2and8–12; named Benchmark_Clusters.txt and Table_1-Ruprecht147_Catalog.txt. The independent temperature-selected fit uses the actual machine table, not the135YY selection described for another fit.
- Matt et al. (2015), The Mass-Dependence of Angular Momentum Evolution in Sun-like Stars, arXiv1412.4786v1
Sections2.1–2.3, equations1–11 and Table1. Saturated/unsaturated torque structure and constant-inertia limits inform the teaching example; the full mass-dependent synthetic cluster is a separate model.
- Bouma, Palumbo & Hillenbrand (2023), The Empirical Limits of Gyrochronology, arXiv2303.08830v1
Sections2–5, Table1 and equations1–3: nonseparable calibration, dispersion, selection, errors and posterior validation. This course supplies its own narrower fixed-scale prescription, not a reproduction of gyro-interp.
- Hall et al. (2021), Weakened magnetic braking supported by asteroseismic rotation rates of Kepler dwarfs, arXiv2104.10919v1
Figures2–4 and Methods1–2. Read sample cuts, seismic/spot clocks and mixture inference together. The98.4%concerns posterior mass above a mixture weight, not a universal star fraction.
- Metcalfe et al. (2024), Weakened Magnetic Braking in the Exoplanet Host Star51Peg, arXiv2401.01944v1
Sections2–4, Table1 and Figures1–4. Trace the large-scale magnetic map, X-ray-based mass loss, period and seismic properties into the torque prescription. Preserve the paper’s Rossby normalization.
- Santos et al. (2025), Signature of spin-down stalling in stellar magnetic activity: The case of the open cluster NGC6811, arXiv2504.05413v1
Sections2–6 and Figures1–5, with bias appendices as reading targets. Follow the141-star cluster and33,731-star field selections and the photometric activity definition before interpreting the transition.
- Sandquist et al. (2016), eclipsing-binary constraints on NGC6811, arXiv1608.03917v1
The abstract and published discussion identify component-dependent age and model-systematic issues. They motivate a separate external-scale layer; this first conditional model does not propagate a full binary-age likelihood.
- AAS Journals, article charges and copyright policy
Access and copyright policy reviewed2026-11-03. Free access to pre-2021articles does not automatically grant a CC-BY table redistribution license; named origin downloads keep original material local.