SPM-11, September 12, 2005 VARIATIONS OF SOLAR RADIUS: OBSERVATIONS WITH RHESSI M.D. Fivian, H.S. Hudson and R.P. Lin Space Sciences Lab, UC Berkeley.

SPM-11, September 12, 2005

VARIATIONS OF SOLAR RADIUS: OBSERVATIONS

WITH RHESSI

M.D. Fivian, H.S. Hudson and R.P. Lin

Space Sciences Lab, UC Berkeley


RHESSI radius observations

• Solar aspect sensor (SAS) determines precise limb location for X-ray telescope rotating at 0.25 rps

• Spin stabilization requires rapid cadence of precise limb measures - some 6 x 109 obtained thus far

• Experiment resembles that of Dicke & Goldenberg (1974), but in space rather than in New Jersey



The SAS data are precise

• RMS error < 30 mas per point

• Data are abundant: current rate of collection is ~ 100 sec-1

• “Solar constant” provides a (statistically) standard candle for reference

• Rotation helps to control systematic errors



Oblateness


Recent solar oblateness results(Sofia et al., 1995)



Effects of solar activity




Dealing with systematic errors

yes


Potential applications of data

• Faculae• Facular drift• Sunspot Wilson

depression• Limb flares (“white

light prominences”)

• Oblateness• Higher-order figure• Long-period g-modes?• Variability


Conclusions

• RHESSI limb sensors have adequate precision and coverage for many applications

• Solar activity (faculae and spots) can easily be seen at the limb

• The oblateness signal is detectable in a relatively short integration


End

SPM-11, September 12, 2005 VARIATIONS OF SOLAR RADIUS: OBSERVATIONS WITH RHESSI M.D. Fivian, H.S. Hudson and R.P. Lin Space Sciences Lab, UC Berkeley.

Documents

oblateness slide

variability slide

uc berkeley slide

short integration slide

new jersey slide

solar constant

precise limb location

variations of solar