THE BEAT OF THE SOLAR CHROMOSPHERES COLD HEART

The cold heart of the solar chromosphere is best investigated using fu ndamental band lines of carbon monoxide, CO, at 4.7 mu m. We have obta ined time series of CO spectra in the quiet sun and in active-region p lage at the solar limb and at disk centre. In addition, we have record ed time series in sunspot umbrae located near disk centre. The power s pectra and RMS amplitudes of the quiet-sun oscillations at disk centre and at the limb are not compatible with a generally hot chromosphere which is periodically cooled, but support recent suggestions that the low chromosphere is pervasively cool, interspersed with hot, possibly shocked material. In the plage the CO oscillations provide indirect ev idence for the expansion of hot material (probably inside magnetic ele ments) with height. In umbrae the CO lines exhibit well-separated 3 mi n and 5 min peaks.We also present spectra of the phase shift between v elocity and intensity oscillations of CO lines. At disk centre in the quiet sun the phase shift is on the whole similar to that seen in atom ic lines formed near the classical temperature minimum, although with some properties peculiar to CO. In plages the quality of the phase shi ft is marginal, but suggests either large radiative damping or propaga ting waves in the 4 mHz frequency range. Finally, in sunspots the phas e shift resembles that of atomic chromospheric lines in some umbrae.