1. June 29, 2006, SPD - AAS, New Hampshire1 The Optical Solar Limb as Observed by RHESSI ‘New Oblateness Measurement’ M. D. Fivian, H. S. Hudson, H. J. Zahid Space Sciences Laboratory, UC Berkeley

2. M. D. Fivian et al.: The Optical Solar Limb As Observed by RHESSI2 RHESSI/SAS Instrument

3. M. D. Fivian et al.: The Optical Solar Limb As Observed by RHESSI3 RHESSI: Solar Aspect System Sensor Calibration  Limb position Geometrical Calibration  Sun center and Radii

4. M. D. Fivian et al.: The Optical Solar Limb As Observed by RHESSI4 Potentially Observable Limb Features p-modes ! g-modes r-modes ? Granulation Other convective motions Sunspots ! Faculae ! Active network Flares Prominences Coronal holes ? Oblateness ! Higher-order shape terms Gravitational moments J2, J4… Global temperature variation Limb-darkening functions Planetary tides Dynamo signatures ? Local Features Global Features

5. M. D. Fivian et al.: The Optical Solar Limb As Observed by RHESSI5 Historical Results First Oblateness Measurement (Auwers, 1891) Absolute Radius Measurements (Kuhn, ApJ 613)

6. M. D. Fivian et al.: The Optical Solar Limb As Observed by RHESSI6 RHESSI/SAS Radius Measurements

7. M. D. Fivian et al.: The Optical Solar Limb As Observed by RHESSI7 Confusion/Signal of Magnetic Activity N W S E N

8. M. D. Fivian et al.: The Optical Solar Limb As Observed by RHESSI8 Sensitivity of Oblateness Measurement

9. M. D. Fivian et al.: The Optical Solar Limb As Observed by RHESSI9 Oblateness Results SDS8.21 ± 0.84 mas MDI10.76 ± 0.78 mas RHESSI10.84 ± 0.11 mas SDS MDI RHESSI

10. M. D. Fivian et al.: The Optical Solar Limb As Observed by RHESSI10 Conclusions The RHESSI aspect sensors provide radius determinations of unprecedented precision At this new level of precision, we find strong signatures of solar magnetism The data will allow us to constrain solar interior models, supplementing helioseismology in a fundamentally new manner