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Why We Need SONG

This article explores the critical need for the Stellar Observation Network Group (SONG) in modeling the near-surface layers of stars. We currently face challenges such as convection, turbulence, and low-temperature opacities that introduce discrepancies between observed and modeled frequencies. Low-frequency modes, especially l=3, are essential for accurate inversions and diagnostics. By integrating these modes, SONG aims to enhance our understanding of stellar physics, improve modeling accuracy, and provide clearer insights into the behavior of stars.

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Why We Need SONG

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  1. Why We Need SONG Sarbani Basu Yale University

  2. Image courtesy J. Christensen-Dalsgaard

  3. Observing in Velocity: Lower Noise

  4. Observing in Velocity: non-zero l=3 response

  5. We do not know how to model the near surface layers of stars. Problems • convection/turbulence • Atmospheres • Low temperature opacities • Treatment of radiation in optically thin layers • ….. The PESKY SURFACE TERM These problems introduce a frequency dependent offset between observed and modelled frequencies.

  6. Surface term in Standard Solar Models

  7. Same interior physics could still give rise to different surface terms

  8. What happens with deficient physics?

  9. Low Frequencies will help in modelling by defining the surface term

  10. Surface Term and Echelle Diagrams

  11. What we observe

  12. What we observe

  13. What happens if we do not have low-frequency modes

  14. What happens if we do not have low-frequency modes

  15. Add Lower frequencies

  16. What else? Define other diagnostics

  17. l=3 modes will allow inversions A HermitianEigenvalue problem, therefore use the variational principle:

  18. How we invert frequecies

  19. The mode-sets

  20. The solutions

  21. The Averaging Kernels

  22. Cross-term kernels

  23. Lower Turning Points of modes

  24. Add Low-Frequency modes to l=0,1,2 sets

  25. The Best Kepler Modeset (so far) Low frequency modes will made a huge difference

  26. Conclusions • Low-frequency modes will help us to model stars better. • l=3 modes will help us invert frequency differences between a star and its model to determine how good a model is. • SONG will be able to provide both low-frequency modes, as well as l=3 modes ERGO WE NEED SONG

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