rhessi and the solar radius h.s. hudson, m.d. fivian & h.j. zahid space sciences lab, uc...
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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
Solar Disk Sextant (1992, 1994, 1995, 1996 flights)
Egidi et al., Solar Phys. 236, 407 (2006)
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
The p-modes explain excess “random” noise
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August 2004: 57-orbit incoherent sum spectrum
GSFC, May 18 2006
Oblateness results
SDS 8.21 +- 0.84 mas
MDI 10.76 +- 0.78 mas
RHESSI 9.72 +- 0.19 mas
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GSFC, May 18 2006
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New data reduction: July-September, 2004
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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
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