Fading Memories of Magnetic Youths – WE-Heraeus-Seminar (2023)

Invited talk at the 779 WE-Heraeus-Seminar: "From the Heliosphere to Astrospheres - Lessons for Exoplanets and their Habitability"

Abstract: Telescopic observations of sunspots have been collected since Galileo, tracking their motions on the rotating solar surface and evolution in time. Despite the ever improving precision of space-based photometry, starspot distributions on distant stars are notoriously hard to infer from rotational modulation of disk-integrated stellar photometry. While we expect that young F, G, and K stars have larger spot coverage than older stars based on spectroscopic activity indicators, the relationship between age and spot coverage is challenging to constrain because the inversion problem suffers from many degeneracies. We take an approximate Bayesian approach to the photometric inversion problem. We extract a simple observational light curve statistic for cluster stars observed with Kepler, K2, and TESS photometry, and infer which spot coverages are consistent with the observations via a simple starspot forward model. The clusters range in age from 10 Myr to 4 Gyr, and decrease in typical spot coverage with age, from about 10% to 1%, respectively. Such constraints are in demand as exoplanet characterization pushes to smaller and younger planets, and spectroscopic contamination by stellar magnetic activity interferes with transmission spectroscopy, for example.

Transcript

1. Fading Memories 
 of Magnetic Youths Brett Morris Space Telescope Science Institute
 Baltimore, MD, USA NASA SDO
2. Fading Memories 
 of Magnetic Youths Brett Morris Space Telescope Science Institute
 Baltimore, MD, USA NASA SDO
3. 2 NASA SDO Stars spin, driving magnetic activity (spots) As stars age: spin slower, less activity = fewer spots
4. 2 NASA SDO Stars spin, driving magnetic activity (spots) As stars age: spin slower, less activity = fewer spots
5. Skumanich (1972) Rotation period Calcium II H & K emission Lithium Abundance
6. 4 NASA Goddard Space Flight Center Surface magnetic activity traces dynamics deep inside
7. 4 NASA Goddard Space Flight Center Surface magnetic activity traces dynamics deep inside
8. 5 SDO/Goddard/NASA Surface magnetic activity generates eruptions which blast planets (including Earth!)
9. 5 SDO/Goddard/NASA Surface magnetic activity generates eruptions which blast planets (including Earth!)
10. Big Question How does the area covered by dark, magnetic spots on stellar surfaces vary with stellar age?
11. The Data Brightness Brightness
12. Classic Bayesian Inference
13. Classic Bayesian Inference 1. Make a physical model for stellar brightness 2. De fi ne a likelihood 3. Use e.g. MCMC to infer spot properties
14. Luger et al. (2021)
15. Luger et al. (2021) Brightness measurements are terribly degenerate
16. Skumanich (1972) Rotation period Calcium II H & K emission Lithium Abundance
17. Pole-on Equator-on Amp = 0 Amp = max Morris (2020)
18. Pole-on Equator-on Amp = 0 Amp = max Morris (2020)
19. Gagné+ 2018 The Neighborhood
20. Brightness–Rotation space Morris (2020) Brightness change (%)
21. Amplitude and Age Morris (2020) n ⇡ 1 2 <latexit sha1_base64="aweLuGKF1jPO5zpkJY+zmd3N6CU=">AAAB/nicbVDLSgMxFM3UV62vUXHlJlgEV2WmCrosunFZwT6gM5RMmmlDM0lIMmIZBvwVNy4Ucet3uPNvTNtZaOuBC4dz7uXeeyLJqDae9+2UVlbX1jfKm5Wt7Z3dPXf/oK1FqjBpYcGE6kZIE0Y5aRlqGOlKRVASMdKJxjdTv/NAlKaC35uJJGGChpzGFCNjpb57xGGApFTiEQaxQjjz86ye992qV/NmgMvEL0gVFGj23a9gIHCaEG4wQ1r3fE+aMEPKUMxIXglSTSTCYzQkPUs5SogOs9n5OTy1ygDGQtniBs7U3xMZSrSeJJHtTJAZ6UVvKv7n9VITX4UZ5TI1hOP5ojhl0Ag4zQIOqCLYsIklCCtqb4V4hGwKxiZWsSH4iy8vk3a95p/X6ncX1cZ1EUcZHIMTcAZ8cAka4BY0QQtgkIFn8ArenCfnxXl3PuatJaeYOQR/4Hz+AOJQlXA=</latexit> Amp = atn <latexit sha1_base64="OEpcPY+lc2LpVWl3VSxeexCrErU=">AAAB/3icbVDLSgMxFL3js9ZXVXDjJlgEV2WmCroRqm5cVrAPaMeSSTNtaJIZkoxQxln4K25cKOLW33Dn35g+Ftp6IHA4517uyQlizrRx3W9nYXFpeWU1t5Zf39jc2i7s7NZ1lChCayTikWoGWFPOJK0ZZjhtxopiEXDaCAbXI7/xQJVmkbwzw5j6AvckCxnBxkqdwn5bYNNXIr0UcYYuEEbmPpVZp1B0S+4YaJ54U1KEKaqdwle7G5FEUGkIx1q3PDc2foqVYYTTLN9ONI0xGeAebVkqsaDaT8f5M3RklS4KI2WfNGis/t5IsdB6KAI7OUqrZ72R+J/XSkx47qdMxomhkkwOhQlHJkKjMlCXKUoMH1qCiWI2KyJ9rDAxtrK8LcGb/fI8qZdL3kmpfHtarFxN68jBARzCMXhwBhW4gSrUgMAjPMMrvDlPzovz7nxMRhec6c4e/IHz+QN1iJW8</latexit> Brightness change (%)
22. Morris (2020) Equator-on Pole-on Inferring Spot Coverage fS Spot Radii Spot latitudes Spot Longitudes Stellar inclination Smoothed Amplitude }
23. Morris (2020) Equator-on Pole-on Inferring Spot Coverage fS Spot Radii Spot latitudes Spot Longitudes Stellar inclination Smoothed Amplitude } Likelihood?
24. Psc-Eri Model Vary: • Spot latitude • Spot contrast • Spot radius Approximate Bayesian Computation Morris (2020) Measure: • Di ff erence 
 between 
 observations
 and simulations Brightness change (%)
25. Psc-Eri Model Vary: • Spot latitude • Spot contrast • Spot radius Approximate Bayesian Computation Morris (2020) Measure: • Di ff erence 
 between 
 observations
 and simulations Brightness change (%)
26. Inferring Spot Coverage fS Morris (2020) Brightness change (%)
27. Inferring Spot Coverage fS Morris (2020) Brightness change (%) Spot covering fraction
28. Inferring Spot Coverage fS Morris (2020) fS = atn <latexit sha1_base64="x6TupPj8KCXcPUx6EyKeG50jGfk=">AAAB9HicbVBNS8NAEJ34WetX1aOXxSJ4KkkV9CIUvXisaD+gjWWz3djFzSbuTgol9Hd48aCIV3+MN/+N2zYHrT4YeLw3w8y8IJHCoOt+OQuLS8srq4W14vrG5tZ2aWe3aeJUM95gsYx1O6CGS6F4AwVK3k40p1EgeSt4uJz4rSHXRsTqFkcJ9yN6r0QoGEUr+WHvhpwTSvAuU+NeqexW3CnIX+LlpAw56r3SZ7cfszTiCpmkxnQ8N0E/oxoFk3xc7KaGJ5Q90HvesVTRiBs/mx49JodW6ZMw1rYUkqn6cyKjkTGjKLCdEcWBmfcm4n9eJ8XwzM+ESlLkis0WhakkGJNJAqQvNGcoR5ZQpoW9lbAB1ZShzaloQ/DmX/5LmtWKd1ypXp+Uaxd5HAXYhwM4Ag9OoQZXUIcGMHiEJ3iBV2foPDtvzvusdcHJZ/bgF5yPb4rCkU4=</latexit> n ⇡ 1 2 <latexit sha1_base64="5eVMWJ7488Ho14TzrgZP4jChGJU=">AAACAHicbVDLSgMxFM34rPU16sKFm2AR3FhmqqDLohuXFewDOkPJpJk2NJOEJCOWYTb+ihsXirj1M9z5N6btLLT1wIXDOfdy7z2RZFQbz/t2lpZXVtfWSxvlza3tnV13b7+lRaowaWLBhOpESBNGOWkaahjpSEVQEjHSjkY3E7/9QJSmgt+bsSRhggacxhQjY6Wee8hhgKRU4hGewSBWCGd+ntXynlvxqt4UcJH4BamAAo2e+xX0BU4Twg1mSOuu70kTZkgZihnJy0GqiUR4hAakaylHCdFhNn0ghydW6cNYKFvcwKn6eyJDidbjJLKdCTJDPe9NxP+8bmriqzCjXKaGcDxbFKcMGgEnacA+VQQbNrYEYUXtrRAPkU3B2MzKNgR//uVF0qpV/fNq7e6iUr8u4iiBI3AMToEPLkEd3IIGaAIMcvAMXsGb8+S8OO/Ox6x1ySlmDsAfOJ8/rC+V0Q==</latexit> Spot covering fraction
29. MCMC for individual examples Morris (2020)
30. Maximum Sun Morris (2020) MCMC for individual examples Spot covering fraction
32. The features in the transmission spectrum likely originate in both
 the starspots and the planetary atmosphere.
33. • Spot coverage declines with age, following Skumanich • Approximate Bayesian Computation allows likelihood-free inference
 • Spot coverage at 10 Myr exceeds 10%, declines below 1% at 4 Gyr
 • Spots a ff ect characterization of young exoplanet atmospheres Spot covering fraction Summary