Abstract
Umbral line profiles of Hα, Na D2 and Hei 10830 have been observed photoelectrically with a pressure scanning spectrometer, URSIES (Ultravariable Resolution Single Interferometer Echelle Scanner). Intermittent pulse counting techniques are applied with integration times as short as 0.8 s which permits selection of moments of good seeing and guiding even in poor climates.
The Hα line profile shows in a medium-sized spot (A u = 100 × 10–6 SH) a pronounced weakening in the wings but a persistence of the line core in agreement with the results of Fricke and Elsässer (1965).
The profile of the Hei 10830 line shows an unexpected strengthening over the umbra of the two spots which have been observed. The strengthening of the line in the umbral spectrum of a third spot has been confirmed by Dr. Mallia at the Oxford Solar Station (Gornergrat, Switzerland).
Na D2 line profile together with continuum observations at λ4260, λ5890, and λ6530 have been accounted for with an empirical (T, τ) relation by one of us (Yun, 1971). The wavelength dependence and the absolute values from 4000 Å to 14000 Å of the intensity curve generated by this relation shows very good agreement with the intensities observed by Wöhl et al. (1970) in a spot of similar diameter.
Precision observations of the continuum at λ5890 indicate umbra-to-disk continuum ratios that are higher (0.104) than the Mercury calibrated value by Mattig (0.086) even when a maximal correction for scattered light is applied. Only Zwaan's (1965) cool umbral model atmosphere approaches Mattig's continuum value, but this model renders the absorption wings in Na D2 much too deep. It is suggested that future definitive observations should be carried out with coronagraphs under coronal skies or in satellites.
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Work supported by NASA Grant NGR-39-005-066.
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Fay, T.D., Wyller, A.A. & Yun, H.S. Photoelectric line profiles in umbral spectra. Sol Phys 23, 58–77 (1972). https://doi.org/10.1007/BF00153892
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DOI: https://doi.org/10.1007/BF00153892