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We present recent observations of lines of the fundamental vibration--rotation transitions of carbon monoxide (CO) in the solar atmosphere obtained with the 256$^2$ infrared array detector at the McMath telescope on Kitt Peak. Standard, plane parallel, solar models have these lines form in LTE around the temperature minimum region; they should be indicative of electron temperatures there. However, matching observed line profiles in a standard solar model requires temperatures as low as 3700~K which are not confirmed by any other spectral diagnostic. We investigate whether this discrepancy can be solved by invoking spatial inhomogeneities or temporal variations or a combination of both. To this end we obtained series of spectra-spectroheliograms at different positions on the disk as well as time series of slit-spectra at a single position. The former type of observations allow us to study spatial inhomogeneities in stronger and weaker lines and the IR continuum at 4.6$\mu$m and to distinguish between variations due to the 5-minute oscillations and the more steady patterns due to magnetic fields by comparing heliograms taken several minutes apart.
We also obtained spectra with the slit crossing the limb giving us a more rigid registration of the intensity variations above the limb as compared to previous single-detector measurements. Early analysis shows that high and low excitation lines behave differently at the limb which may bear information on the temperature structure of the atmosphere just above the minimum.
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