Sun‐as‐a‐Star Spectrum Variations 1974–2006

We have observed selected Fraunhofer lines, both integrated over the FullDisk and for a small circular region near the center of the solar disk, on1,215 days for the past 30 years. Full Disk results: Ca II K 393 nm nicelytracks the 11 year magnetic cycle based on sunspot number with a peak amplitudein central intensity of ~37%. The wavelength of the mid-line core absorptionfeature, called K3, referenced to nearby photospheric Fe, displays an activitycycle variation with an amplitude of 3 milli-Angstroms. Other chromosphericlines track Ca II K intensity with lower relative amplitudes. Low photosphere:Temperature sensitive CI 5380 nm appears constant in intensity to 0.2%. Highphotosphere: The cores of strong Fe I lines, Na D1 and D2, and the Mg I blines, present a puzzling signal perhaps indicating a role for the 22 y Halecycle. Solar minimum around 1985 was clearly seen, but the following minimum in1996 was missing. This anomalous behavior is not seen in comparison atmosphericO2. Center Disk results: Both Ca II K and C I 538 nm intensities are constant,indicating that the basal quiet atmosphere is unaffected by cycle magnetismwithin our observational error. A lower limit to the Ca II K central intensityatmosphere is 0.040. The wavelength of Ca II K3 varies with the cycle by 6milli-Angstroms, a factor of 2X over the full disk value. This may indicate thepredominance of radial motions at Center Disk. This is not an effect of motionsin plages since they are absent at Center Disk. This 11 y variation in thecenter of chromospheric lines could complicate the radial velocity detection ofplanets around solar-type stars. An appendix provides instructions for URLaccess to both the raw and reduced data.Comment: 38 pages with 20 figures. Accepted for publication in The Astrophysical Journa