Astronomy and Astrophysics – Astronomy
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.2221c&link_type=abstract
American Astronomical Society Meeting 210, #22.21; Bulletin of the American Astronomical Society, Vol. 39, p.127
Astronomy and Astrophysics
Astronomy
Scientific paper
We have examined approximately 18 years of full-disk photometric images of the Sun (1986 through 2004) obtained at the San Fernando Observatory (SFO) looking for variations in the solar radius. The data are from the Cartesian Full Disk Telescope number 1 (CFDT1). This telescope produces images having 512 x 512 pixels with a pixel size of 5.12 arc-sec. We have only used red images obtained at a wavelength of 672.3 nm. Except for infrequent repairs or upgrades, the telescope is seldom modified. Operating at F/40, the focus of the telescope is not routinely adjusted. We have corrected for focal changes due to telescope modifications, differential atmospheric refraction, and temperature changes. We have compared observed image radii with those calculated from the ephemeris. The residuals are then fit by least squares to sinusoids of 10 and 11 year periods to look for a solar cycle signal. For the 11 year period we find that the apparent solar radius is greatest at cycle maximum for solar cycles 22 and 23. The peak-to-peak amplitude is 0.136 +/- 0.010 arc-sec with a multiple regression coefficient, squared, of 0.0404 which is significant at better than p = 0.02 level. The cause of the apparent radius change is under investigation. This work was partially supported by grants from NASA ( NAG5-12905) and NSF (ATM-0533511). Many CSUN students have contributed to this work.
Chapman Gary A.
Dobias Jan J.
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