The Sun as a Star 1974-2009

Bill Livingston, Lloyd Wallace, Dick White, & Anna Kwa

Observing the full disk is Sun is difficult and there seems to be no ideal way. In general, the better the integration, the poorer the S/N. We form a pinhole image on the grating of the 13.5 m spectrometer, or on the beam-splitter in the Fourier Transform Spectrometer (FTS), good S/N. Others use fiber optics to scramble the image. Beckers (1976) projected a tiny image on the slit. Osipov (1997) scans a small image. These “others” have a poor S/N. The McMath-Pierce full disk archives have several irrecoverable faults: the 1992 grating change meant observing a different star, an FTS A-D non-linearity introduced zero level shifts. Never-the-less, we have a good 35 year record of chromospheric Ca K index (20% p-p) and He 10830 intensity (60%). Center disk, the quiet Ca K atmosphere does not show the activity cycle. The photosphere appears to be constant within our errors (<1%).

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