CNO abundances of some field horizontal-branch and Population I A stars

From observations of infrared lines, oxygen and nitrogen abundances of the prototype field horizontal-branch stars HD 109995 and HD 161817, the somewhat similar star HD 64488, and the sharp-lined Population I A stars Theta Leo and HR 6559 have been obtained, as well as carbon abundances of HD 161817 and Theta Leo. The results for HD 161817 may be in accord with the predictions of Sweigart and Mengel (1979) for dredge-up during the previous red-giant stage if the non-LTE effects for the O I lines have been properly accounted for, and those for the C I and N I lines are small. This star and HD 109995 are apparently both oxygen and nitrogen poor to the same degree although their iron abundances differ by 0.3 dex.