RHESSI and the solar radius

H.S. Hudson, M.D. Fivian & H.J. Zahid

Space Sciences Lab, UC Berkeley

First report of our semi-intentionaloptical limb astrometry

GSFC, May 18 2006

Far into the past…

Auwers, 1891

GSFC, May 18 2006

Solar Disk Sextant (1992, 1994, 1995, 1996 flights)

Egidi et al., Solar Phys. 236, 407 (2006)

GSFC, May 18 2006

Michelson Doppler Interferometer

Emilio et al., 2000

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

GSFC, May 18 2006

Data

GSFC, May 18 2006

The p-modes explain excess “random” noise

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

August 2004: 57-orbit incoherent sum spectrum

GSFC, May 18 2006

The oblateness signal

Current fit 9.72 +/- 0.19 mas(random error ~10-4 pixels)

GSFC, May 18 2006

Oblateness results

SDS 8.21 +- 0.84 mas

MDI 10.76 +- 0.78 mas

RHESSI 9.72 +- 0.19 mas

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

GSFC, May 18 2006

Synoptic-chart representation of RHESSI(early reductions)

GSFC, May 18 2006

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

New data reduction: July-September, 2004

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

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

GSFC, May 18 2006

What about g-modes?

Rogers & Glatzmaier 2005

Toner et al. 1999

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

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?