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