K-grains as a three-dimensional phenomenon. II. Phase analysis of the spatio-temporal pattern.
Abstract
We have observed spatially one- and two-dimensional time series of CaiiK spectra to study the spatio-temporal excitation pattern of the Ca K_2V_ grains. We compare the phases of chromospheric velocity fluctuations (V) measured in K_3_ with those of spectral brightness measured at fixed wavelength intervals in K_2V_ and K_2R_ (I). Temporal crosscorrelation functions of prominent chromospheric (3min) wavetrains reproduce the commonly observed coincidence of brightness maxima in K_2V_ and extreme redshift of K_3_, whereas the corresponding V-I phases in the k-ν diagrams reveal a distinct dichotomy: Only in the gaps between the p-mode ridges do the spectra exhibit homogeneous areas with a stable phase of approximately 180deg in agreement with the crosscorrelation result. On the ridges the V-I phase switches to distinctly lower values near -90deg, with K_3_ redshift preceding K_2V_ brightening. The latter value is similar to the characteristic V-I phase measured in the core of other chromospheric lines. Our findings support the contention that a) K-grains are excited by superposition of resonant p-modes, and b) that p-modes exhibit a uniform signature of their dynamic behaviour throughout the full height range of the chromosphere.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- April 1996
- Bibcode:
- 1996A&A...308..192H
- Keywords:
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- SUN: CHROMOSPHERE;
- OSCILLATIONS