Solar luminosity variation. I - C I 5380 as a temperature indicator and a search for global oscillations

Abstract

The high-excitation, weak Fraunhofer line C 1 5380.3 A is shown to originate within the same photospheric layers as the Sun's continuous radiation. By monitoring the central depth of the C I line relative to the local continuum, in unfocused sunlight, we may follow temperature, and hence luminosity changes of the whole Sun as a function of time. The technique is practically insensitive to telluric absorption effects and instrumental spectral response. A power spectrum analysis of 100 hours of observations reveals no dominant oscillation of period P rising above the 3 a uncertainty limit of 0.4 K for m < p < 60 . For power at 2h40m the limit is 1.0 K; for 5h20m, 2.0 K. The day-to-day fluctuation for a 3 month period is 0.85 K rms (which corresponds to 0.06% in the solar constant, or 0.0006 mag in luminosity). Subject headings: Sun: atmospheric motions - Sun: general