WAVELENGTH VARIATION OF P-MODE INTENSITY FLUCTUATIONS

We measure the oscillatory signal in the solar p-mode band as a function of optical wavelength using a grating spectrometer and Fourier transform spectrometer. Two separate regions of the spectrum are studied, 23,600-26,085 cm-1 and 14,700-15,060 cm-1. In the blue region we find that the magnitude of relative intensity fluctuations in the p-mode band is found to increase rapidly with decreasing mean spectral intensity and increasing height in the solar photosphere. The absolute magnitude of p-mode intensity oscillations is observed to decrease with decreasing spectral intensity. We find that two absorption lines in the Balmer series of hydrogen (H-gamma and H-delta) have diminished amplitudes of relative intensity oscillations in the p-mode band compared to other solar absorption lines of similar strength. We also discover that these two lines as well as Ca II H and K lines have absolute intensity fluctuations in the p-mode band which are 50% less than the absolute intensity fluctuations of the nearby continuum spectral regions. We comment on the applicability of this finding to spectrophotometric asteroseismological observations. Throughout the red spectral region, recorded at high spectral resolution, we detect an asymmetry in the intensity oscillations of the p-mode band across the line profiles of all the spectral lines in the region. The p-mode intensity oscillations are strongest in the blue wings of these lines. This is consistent with the stronger gradient dI/d-lambda in the blue wings of solar photospheric spectrum lines. We find no significant phase differences between the p-mode Doppler shifts of the various photospheric and chromospheric lines in the blue spectral region. The p-mode intensity oscillations in the lines of both the blue and red spectral regions generally lead p-mode blueward Doppler shifts by one-fourth cycle. This is consistent with the description of p-modes in the photosphere and up to the chromosphere as adiabatic, evanescent acoustic waves.