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

GSFC, May Solar limb astrometry from the Reuven Ramaty High-Energy Solar Spectroscopic Imager RHESSI

GSFC, May

Historical background The properties L O, M O, and   (and X, Y, and Z) more or less characterize a star, but none of them are really constant The observed variations of L O, the “solar constant,” include ~ half a dozen known components The solar shape and the total irradiance are strongly linked: d(ln L O )/d(ln R O ) = w

GSFC, May Historical background The properties L O, M O, and   (and X, Y, and Z) more or less characterize a star, but none of them are really constant The observed variations of L O, the “solar constant,” include ~ half a dozen known terms The solar shape and the total irradiance are strongly linked: d(ln L O )/d(ln R O ) = w … but we are not sure about the magnitude, or sign, of w!

GSFC, May Total solar irradiance variations - highlights

GSFC, May ARAA 26, 473 (1988) Frohlich, 2005 * *

GSFC, May ARAA 26, 473 (1988) Frohlich, 2005 Flares Minutes 200 ppm at most Woods et al. 2004

GSFC, May Two recent-suggested possible additional components R.C. Willson & A. Mordvinov, “Secular total irradiance trend during solar cycles 21-23,” GRL (2003) G. Withbroe, “Quiet Sun contributions to the total solar irradiance,” Solar Phys. 235, 369 (2006)

GSFC, May Two recent-suggested possible additional components R.C. Willson & A. Mordvinov, “Secular total irradiance trend during solar cycles 21-23,” GRL 2003 (controversial) G. Withbroe, “Quiet Sun contributions to the total solar irradiance,” Solar Phys. 235, 369 (2006)

GSFC, May Two recent-suggested possible additional components R.C. Willson & A. Mordvinov, “Secular total irradiance trend during solar cycles 21-23,” GRL 2003 (controversial) G. Withbroe, “Quiet Sun contributions to the total solar irradiance,” Solar Phys. 235, 369 (2006) (identifiable with the “active network”?)

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

GSFC, May Solar limb astrometry from the Reuven Ramaty High-Energy Solar Spectroscopic Imager RHESSI

GSFC, May 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 SAS reduced data Four limb pixels * 6 Normalization to R 0 Deviations from mean profile

GSFC, May FWHM ≈ 4.5 arcsec ≈ 2.6 pixels

GSFC, May Data

GSFC, May The p-modes explain some “random” noise August 2004: 57-orbit incoherent sum spectrum

GSFC, May August 2004: 57-orbit incoherent sum spectrum

GSFC, May SOHO/MDI view of limb p-modes: “Rossby hills”? Kuhn et al. 2000

GSFC, May The oblateness signal Oblateness / mas (random error ~10 -4 pixels)

GSFC, May Very early oblateness measurements Auwers, 1891

GSFC, May Very early oblateness measurements Auwers, 1891 P - A > 0 => prolate!

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

GSFC, May SOHO/MDI Emilio et al., 2000

GSFC, May Oblateness results SDS mas MDI mas RHESSI mas

GSFC, May Oblateness results SDS mas MDI mas RHESSI mas

GSFC, May The oblateness signal II mas

GSFC, May Synoptic-chart representation of RHESSI (early reductions)

GSFC, May 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 Wilson effect: historical background Alexander Wilson, local Glasgow font designer, physician, meteorologist and astronomer de La Lande, Maskelyne… ADS Sunspot umbrae appear as depressions of the photosphere (but are they really, or is it just a trick of opacity? Or is it the same thing?) Limb darkening ~ height variation (limb at  5000 =.005?)

GSFC, May On three fine days in 18th-century Glasgow…

GSFC, May Tbe Wilson effect: observation and modeling 1,000 x

GSFC, May Timewise modeling

GSFC, May The problem of faculae Granulation, solfläckar och facklor nära solranden (from the Swedish Solar Telescope homepage)

GSFC, May The problem of faculae Faculae are now recognized in white light to be ordinary facular granules see behind magnetic flux tubes The structures are on small scales and have time-variable 3-dimensional structure It seems hopeless to understand their structure in simple terms, and the modeling needs validation Faculae may therefore be noise from RHESSI’s point of view

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

GSFC, May 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 expect to measure higher-order shape terms Sunspots, faculae, and p-modes show clear signals We dare to think about g-modes, but the analysis will be very challenging

GSFC, May 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?