High dispersion spectroscopic observations of Venus: VIII. The carbon dioxide band at 10 627 Å

Abstract

Observations of the 10 627 Å band of carbon dioxide in the spectrum of Venus were made from January, 1965 through December, 1967. The spectra were obtained at the coudé focus of the Struve reflector at dispersions of 2.8, 3.8, and 5.4 Å/mm. The 17 best plates from this period were used to derive rotational temperatures by two methods. In the first method we made linear least-squares fits to a square root absorption law and derived temperatures ranging from 217° to 279°K, with an average temperature of 240 ± 3°K. The second method also required a linear least-squares fit, this time to the curve of growth. This fit gave slopes from 0.40 to 0.57, corresponding to rotational temperatures of from 220° to 288°K, with an average temperature of 241 ± 3°K. Finally, averaging the measurements of 29 plates obtained from the 10 362, 10 488, and 10 627 Å bands of CO 2, using the curve of growth method of data reduction, gives T rot = 237° ± 2°K (formal standard deviation). This last value of the temperature should be the most accurate. Our values of T rot show no large variations with phase or band considered. We searched for spatial and temporal variations in the apparent amount of carbon dioxide in the absorption path. The amount appeared to vary significantly with the phase of Venus, and also with the time of observation. Some spatial variation in the abundance may occur.