Observations of High Frequency Waves in the Solar Atmosphere

摘要

An agile (tiltable) mirror was used in conjunction with the echelle spectrograph of the Vacuum Tower Telescope at Sacramento Peak to measure propagating acoustic waves in the solar atmosphere. The agile mirror permits the removal of image motion caused by the earth's atmosphere before feeding the image into the spectrograph. A CCD array was used to record 132 spectral points across the photospheric line Fe I 5434 every 1.5 seconds at 100 spatial points along the spectrograph slit. Spatial resolution along the slit was 0.33 and the spectral resolution is 9.2 mA. The images were stabilized using the signal from a quad-cell locked onto small sunspots or pores. Several, approximately one-hour-long observing runs were made with the slit either crossing the spot or displaced several arc-seconds from the spot. Observations were made at disk center and at a heliocentric angle of 37 deg. (cos(theta)=0.8). We have computed phase differences between velocities in the line core and at various bisector levels in the line as a function of frequency. The image stabilization permits us to see wave propagation out to about 24-28 mHz without any further correction for seeing. After correction for radiative transfer effects, we find a flux of energy in the propagating waves that is sufficient to heat the chromosphere. Reprints. RH