Kuhn - HMI Science Interests: Limb 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 HMI Team 4/30/03

Focus areas Limb Astrometry Limb brightness rotational constraints through limb harmonics secular radius variations limb seismology (low frequency modes) Limb brightness thermal magnetic diagnostics limb seismology HMI Team 4/30/03

Limb astrometry dr Angle of arrival fluctuations define dr dI Photometric gain uncertainty (flatfielding) defines dr In practice limb isn’t knife edge, spacecraft pointing jitter is about 0.01 pixel, long term stability limitations are due to optics and thermal drifts [1px=2”] HMI Team 4/30/03

Shape, rotation, and gravitational figure (-1) (10) (50) HMI Team 4/30/03

Shape and gravitational potential HMI Team 4/30/03

Emilio et al.: No W measured -- limits only Bush et al. 2002 sees different “temperature” trend after SoHO vacation. HMI Team 4/30/03

Interpreting solar radius change < 0.02 HMI Team 4/30/03

Oscillations: astrometry vs. Doppler measurements, random telegraph f=16 HMI Team 4/30/03

Astrometric advantages HMI Team 4/30/03

P-mode limb oscillations P-mode 5min limb shape oscillations 15cm/s 10 microarcsec HMI Team 4/30/03

G-modes in velocity and displacement 1600 days of MDI astrometry (l=6) Appourchaux et al. (2000) HMI Team 4/30/03

Low frequency oscillations HMI Team 4/30/03

Another branch of the solar dispersion relation: r-modes 100m x 90,000km HMI Team 4/30/03

Antishadows HMI Team 4/30/03

Focus areas Limb Astrometry Limb brightness rotational constraints through limb harmonics secular radius variations limb seismology (low frequency modes) Limb brightness thermal magnetic diagnostics limb seismology HMI Team 4/30/03