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Published online by Cambridge University Press: 22 February 2018
Comet Kohoutek (1973f) has been observed with the 50 cm (f/15) reflecting telescope of the European Southern Observatory, La Silla, Chile, on fourteen nights between January 16 and 30, when the heliocentric and geocentric distances of the comet were r=0 66 - 1 00 A. U and Δ =0 81 - 0.96 A. U. , respectively The 40″ and 80″ diaphragms were used for the photometry of the cometary head (EMI 6256 A photomultiplier) in the UBV system and with six interference filters: CN 3884 Å, CO+ 4267 Å, C2 4737 Å, C2 5172 Å, cont. 5300 Å and Na 5893 Å.
The atmospheric conditions were good but the accuracy of our observations was lower than usual due to large extinction (air mass 25 to 43) and twilight. The mean error of one measurement of log F in all but Na 5893 Å filters can be estimated at ±0.02, whereas the accuracy through the Na filter was substantially lower