A COMPARISON OF OXYGEN AND NITROGEN ABUNDANCES IN YOUNG CLUSTERS AND ASSOCIATIONS AND IN THE INTERSTELLAR GAS

We have used previously published observations of main-sequence B-type stars lying in 11 young stellar clusters and associations to estimate non-LTE abundances of oxygen and nitrogen over galactocentric distances 6 < R(g) < 13 kpc. An oxygen abundance gradient of -0.03 +/- 0.02 dex kpc-1 is found, agreeing with earlier preliminary findings from early-type stars. The smaller number of nitrogen abundance estimates precludes any similar conclusion. For 6 < R(g) < 10 kpc the mean abundances are 12 + log [O/H] = 8.84 +/- 0.11 and 12 + log [N/H] = 7.91 +/- 0.13. When compared with the gas-phase abundances as found from ultraviolet absorption-line studies, the data suggest depletions into grains of 0.28 +/- 0.13 dex for oxygen and 0.07 +/- 0.14 dex for nitrogen.