Upper limits on the power in solar oscillations at 1.2 mm, 9 mm, 3.7 cm, and 11.1 CM wavelengths

Details Upper limits on the power in solar oscillations at 1.2 mm, 9 mm, 3.7 cm, and 11.1 CM wavelengths Upper limits on the power in solar oscillations at 1.2 mm, 9 mm, 3.7 cm, and 11.1 CM wavelengths

Oct 1980

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980a%26a....90..192k&link_type=abstract

Astronomy and Astrophysics, vol. 90, no. 1-2, Oct. 1980, p. 192-197.

Astronomy and Astrophysics

Astronomy

5

Chromosphere, Radio Astronomy, Solar Atmosphere, Solar Oscillations, Bremsstrahlung, Brightness Temperature, Power Spectra

Scientific paper

A search for solar oscillations has been made using the NRAO 36-ft telescope at 1.2 mm, the NRL 85-ft telescope at 9 mm, and the NRAO four-element interferometer at 3.7 and 11.1 cm wavelengths. After corrections for the small coherence length of the optically observed oscillations, for their known spectral bandwidth, and for the visibility function of the interferometer, upper limits have been placed on the fluctuating power at oscillation frequencies near 3 mHz. The interferometric observations at 3.7 cm and the single-dish observations at 1.2 and 9 mm imply that less than 0.3, 0.04, and 0.1%, respectively, of the bremsstrahlung photons emitted from the chromosphere show periodic fluctuations. This is 1 to 3 orders of magnitude less than the fraction (approximately 1 to 2%) reported at ultraviolet wavelengths. Simple arguments in terms of weak shock theory suggest that the observable oscillations at centimeter and millimeter wavelengths should be intrinsically weaker in the thermal bremmstrahlung radiation than the optical, but the 3.7 cm wavelength results are explained only by the absence of periodic fluctuations at the level of formation.

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