Kuhn - HMI Science Interests: Limb photometry and astrometry

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Kuhn - HMI Science InterestsLimb photometry and
astrometry

• HMI, with 4Kx4K (or even 2Kx2K) pixel resolution
  will improve limb astrometry and photometry in
  some respects by over an order of magnitude
• HMI roll calibration and lessons learned from MDI
  thermal environment may do better than an order
  of magnitude improvement in some astrometric goals

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Focus areas

• Limb Astrometry
• rotational constraints through limb harmonics
• secular radius variations
• limb seismology (low frequency modes)
• Limb brightness
• thermal magnetic diagnostics
• limb seismology

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Limb astrometry
dr
Angle of arrival fluctuations define dr
dI
Photometric gain uncertainty (flatfielding)
defines dr
In practice limb isnt knife edge, spacecraft
pointing jitter is about 0.01 pixel, long term
stability limitations are due to optics and
thermal drifts 1px2
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Shape, rotation, and gravitational figure
(-1)
(10)
(50)
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Shape and gravitational potential
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Emilio et al. No W measured -- limits only
Bush et al. 2002 sees different
temperature trend after SoHO vacation.
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Interpreting solar radius change
lt 0.02
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Oscillations astrometry vs. Doppler
measurements, random telegraph
t20
f16
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Astrometric advantages
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P-mode limb oscillations
P-mode 5min limb shape oscillations
15cm/s 10 microarcsec
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G-modes in velocity and displacement
1600 days of MDI astrometry (l6)
Appourchaux et al. (2000)
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Low frequency oscillations
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Another branch of the solar dispersion relation
r-modes
100m x 90,000km
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Antishadows
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Focus areas

• Limb Astrometry
• rotational constraints through limb harmonics
• secular radius variations
• limb seismology (low frequency modes)
• Limb brightness
• thermal magnetic diagnostics
• limb seismology