A comparison of oxygen and nitrogen abundances in young clusters and associations and in the interstellar gas

Abstract

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 |$6 \lt R_\text g \lt 13$| kpc. An oxygen abundance gradient of |$-0.03 \pm 0.02$| 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 |$6 \lt R_\text g \lt 10$| kpc the mean abundances are |$12 + \text{log}[\text{O/H}]=8.84 \pm 0.11$| and |$12 + \text{log}[\text{N/H}]=7.91 \pm 0.13$|⁠. When compared with the gas-phase abundances as found from ultraviolet absorption-line studies, the data suggest depletions into grains of |$0.28 \pm 0.13$| dex for oxygen and |$0.07 \pm 0.14$| dex for nitrogen.