1. RHESSI and the solar radius H.S. Hudson, M.D. Fivian & H.J. Zahid Space Sciences Lab, UC Berkeley First report of our semi-intentional optical limb astrometry

2. GSFC, May 18 2006 Far into the past… Auwers, 1891

3. GSFC, May 18 2006 Solar Disk Sextant (1992, 1994, 1995, 1996 flights) Egidi et al., Solar Phys. 236, 407 (2006)

4. GSFC, May 18 2006 Michelson Doppler Interferometer Emilio et al., 2000

5. GSFC, May 18 2006 Operating principle of the RHESSI Solar Aspect Sensor (SAS) Sensor: 1024-pixel linear CCD, 1.73 arc sec/pixel Spectral band: 670 nm x 12 nm FWHM Readout: limbs ~100 sec -1, chords ~1 min -1

6. GSFC, May 18 2006 Data

7. GSFC, May 18 2006 The p-modes explain excess “random” noise August 2004: 57-orbit incoherent sum spectrum

8. GSFC, May 18 2006 The oblateness signal Current fit 9.72 +/- 0.19 mas (random error ~10 -4 pixels)

9. GSFC, May 18 2006 Oblateness results SDS8.21 +- 0.84 mas MDI10.76 +- 0.78 mas RHESSI9.72 +- 0.19 mas

10. GSFC, May 18 2006 Synoptic-chart representation of RHESSI (early reductions)

11. GSFC, May 18 2006 New data reduction: July-September, 2004

12. GSFC, May 18 2006 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 function Planetary tides

13. GSFC, May 18 2006 What about g-modes? Rogers & Glatzmaier 2005 Toner et al. 1999

14. GSFC, May 18 2006 Conclusions The RHESSI/SAS data provide (by far) the best measures of solar limb-shape variations, an independent window on the solar interior We can see oblateness and higher-order stationary terms; we can see sunspots, faculae, and p-modes We dare to think about g-modes, but it will be a hugely difficult data analysis: ten years’ integration to measure mm/sec motions

15. GSFC, May 18 2006 Radius quiz questions What is the scale of the solar radius at 30 kHz? At what wavelength is the minimum opacity of the solar atmosphere? How large are the planetary tides on the Sun?