Solar Granules in the Ultraviolet and Yellow.

Abstract

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Solar Granules in the Ultraviolet and Yellow. Evans, John W. Abstract Studies of rms vertical velocities in the solar atmosphere, evidenced by local Doppler shifts in Fraunhofer lines, show a marked dependence on both line strength and the wavelength region. The rms velocities increase towards the ultraviolet, and with increasing line strength (i.e., with height in the solar atmosphere). This is a report of an investigation to determine whether the detail of photospheric granular structure also varies between widely separated wavelength regions. The observational material consists of four pairs of spectrograms showing good spatial resolution along the slit. Each pair consists of a short length of the spectrum centered at N3954 (UV) and another at N5888 (Y) exposed simultaneously. The spectrograph slit was carefully oriented perpendicular to the horizon, parallel to the small displacements caused by differential atmospheric refraction. Each UV frame was traced perpendicular to dispersion by a digital microdensitometer at five continuum wavelengths, and each Y frame at three wavelengths. The cross correlations between the four pairs are 0.85+0.02, and we conclude that the granular structure at N3954 is very nearly identical with that at N5888. This result directly contradicts that found by Vassiljeva (Solar Phys. 1,16,1966) from photoelectric scanning across the solar disk with a sensitive spot 0 "2 in diameter. She found that the correlation rapidly decreased with wavelength difference, and had a value of only about 0.1 for a span of 1900 A. The Sacramento Peak spectrograms showed a relative displacement along the slit of 2 "1 between the UV and y images due to atmospheric refractive dispersion. I suggest that the low correlations between the structures Vassilj eva recorded at widely different wavelengths are the result of the atmospheric dispersion. This would cause her 0 "2 sensitive spot to scan along parallel lines in different colors, the separation of which would increase with wavelength difference, and inclination to the vertical circle. Publication: The Astronomical Journal Pub Date: September 1967 DOI: 10.1086/110537 Bibcode: 1967AJ.....72S.795E full text sources ADS |