The chemical composition of NGC 2363.

Abstract

Photoelectric spectrophotometry in the 3400 - 7400 Å is presented for the metal-poor extragalactic H II region NGC 2363. Based on these data, on IUE observations and on ionization structure models the authors have obtained the chemical abundances. The C/O ratio is a factor of two smaller than in the solar vicinity and under reasonable assumptions implies that most of the C in the solar vicinity is produced by intermediate mass stars. The N/C ratio is the same in NGC 2363 and in the Orion nebula, but the N/H ratio is 17 times smaller than in the Orion nebula. From line ratios involving five He emission lines it is found that N(He)/N(H) = 0.077±0.006(3σ), which corresponds to Y = 0.235±0.013(3σ).