Variations of Solar Radius Observed with RHESSI
Abstract
The Solar Aspect System (SAS) of the rotating (at 15 rpm) RHESSI spacecraft has three subsystems. Each of these measures the position of the limb by sampling the full solar chord profile with a linear CCD using a narrow bandwidth filter at 670 nm. With a resolution of each CCD of 1.7 arcsec/pixel, the accuracy of each of the 6 limb positions is theoretically better than 50 mas using 4 pixels at each limb. Since the launch of RHESSI early 2002, solar limbs are sampled with at least 100 Hz. That provides a database of currently 4 x 109 single radius measurements. The main function of SAS is to determine the RHESSI pointing relative to Sun center. The observed precision of this determination has a typical instantaneous (16 Hz) value of about 200 mas (rms). We show and discuss first results of variations of solar radius observed with RHESSI.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2003
- Bibcode:
- 2003AGUFMSH32A1103F
- Keywords:
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- 7522 Helioseismology;
- 7529 Photosphere;
- 7537 Solar and stellar variability;
- 7538 Solar irradiance;
- 7544 Stellar interiors and dynamo theory