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Why We Need SONG. Sarbani Basu Yale University. Image courtesy J. Christensen-Dalsgaard. Observing in Velocity: Lower Noise. Observing in Velocity: non-zero l =3 response. We do not know how to model the near surface layers of stars. Problems convection/turbulence Atmospheres - PowerPoint PPT Presentation
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Why We Need SONG
Sarbani BasuYale University
Image courtesyJ. Christensen-Dalsgaard
Observing in Velocity: Lower Noise
Observing in Velocity: non-zero l=3 response
THE PESKY SURFACE TERM
We do not know how to model the near surface layers of stars. Problems
(1)convection/turbulence(2)Atmospheres (3)Low temperature opacities(4)Treatment of radiation in optically thin layers(5)…..
These problems introduce a frequency dependent offset between observed and modelled frequencies.
Surface term in Standard Solar Models
Same interior physics could still give rise to different surface terms
What happens with deficient physics?
Low Frequencies will help in modelling by defining the surface term
Surface Term and Echelle Diagrams
What we observe
What we observe
What happens if we do not have low-frequency modes
aν
obsν0
⎛
⎝
⎜⎜⎜
⎞
⎠
⎟⎟⎟
b
What happens if we do not have low-frequency modes
aν
obsν0
⎛
⎝
⎜⎜⎜
⎞
⎠
⎟⎟⎟
b
Add Lower frequencies
What else? Define other diagnostics
Separation Ratio: r
02=
ν(0,n+1) −ν(2,n)ν(1,n+1) −ν(1,n)
Separation Ratio: r
13=
ν(1,n+1) −ν(3,n)ν(2,n+1) −ν(2,n)
2nd differences: δ 2ν =ν(n−1, l) −2ν(n, l) +ν(n+1, l)
l=3 modes will allow inversions
A Hermitian Eigenvalue problem, therefore use the variational principle:
How we invert frequecies
The mode-sets
The solutions
The Averaging Kernels
Cross-term kernels
Lower Turning Points of modes
Add Low-Frequency modes to l=0,1,2 sets
The Best Kepler Modeset (so far)
Low frequency modes will made a huge difference
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