FOURIER-TRANSFORM SPECTROMETER OBSERVATIONS OF SOLAR CARBON-MONOXIDE .3. TIME-RESOLVED SPECTROSCOPY OF THE DELTA-UPSILON =1BANDS

We have recorded time series of the 2100 cm-1 (4.8 μM) Δυ = 1 absorption bands of carbon monoxide at the center of the solar disk and at the extreme limb using the Fourier transform spectrometer of the McMath telescope. The photospheric 5 minute oscillation appears prominently - strongly in line shift, less strongly in line intensity - at Sun center through a 5″ aperture comparable in spatial extent to the p-mode "wavepackets." The peak-to-peak brightness-temperature amplitude of ≈ 300 K agrees with the earlier work of Noyes and Hall, and the peak-to-peak Doppler shift of ≈ 1100 m s-1 is similar to their predictions for the near-adiabatic response of the high-altitude gas to the evanescent waves. However, the 70° phase lag of maximum core intensity with respect to maximum redshift for the strongest Δυ = 1 absorptions is less than the 90° expected in the adiabatic limit. Phase lags of 40° for weak Δυ = 1 lines are similar to those seen in far-infrared (50-100 μm) continuum intensities and indicate a radiative relaxation time of about 40 s in the middle photosphere. We do not find in our short (≈40 minute) time series a dominant 4 minute signal in the line intensity like that reported by Deming and collaborators in a long-duration (19 hr) sampling of a 904 cm-1 rotational line of OH; nor do we see any evidence for extreme fluctuations (ΔT ≈ 1000 K) on short time scales like those proposed by Kalkofen, Ulmschneider, and Schmilz to explain the apparent nonlinear thermal averaging of different spectral diagnostics of the photosphere-chromosphere Tmin. The strong Δυ = 1 lines exhibit systematic Doppler shifts \υL\ ≲ 1 km s-1, contrary to the predictions of transonic redshifts if the CO "clouds" are associated with a dynamic cooling phase of the Ca II "cell flashes." CO Δυ = 1 spectra at the extreme limb (μ = 0.15) show a continued drop in temperature with increasing altitude, contrary to the expectations of the best available chromospheric reference models. The anomalous behavior of the strong CO fundamental lines presents a series dilemma that must be resolved before the energy balance and heating of the low chromosphere can be ascertained with any confidence.