Oscillations of the upper chromosphere |
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Authors: | Gouttebroze P Vial J-C Bocchialini K Lemaire P Leibacher JW |
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Institution: | (1) Institut d'Astrophysique Spatiale, Univ. Paris XI/CNRS, Bat. 121, F-91405 Orsay cedex, France;(2) National Solar Observatory, P.O. Box 26732, Tucson, Arizona, 85726, U.S.A |
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Abstract: | Variations of intensity and wavelength in several UV lines have been observed with the SUMER spectroheliometer onboard SOHO, and they have been analysed to obtain oscillation spectra and phase differences between lines of different ions. Lines intensities of neutral or singly ionized atoms (with temperature of formation 30 000 K) exhibit an increase of oscillatory power between 2.5 and 7 mHz, which may be considered as the signature of p modes. Lines of highly ionized elements (with a temperature of formation 50 000 K) yield power spectra which are continuously decreasing with frequency. Brightness variations of the continuum at different wavelengths between 1000 and 1400 Å present oscillations in the same frequency range. Thus, p modes seem to be efficiently stopped by the transition region. No clear evidence is found for the existence of a chromospheric oscillation mode. Phase comparisons between lines formed at different altitudes (in particular Si i and Si ii) indicate that these lines oscillate in phase, within the precision of the measurements. |
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