We present spherically symmetric and plane-parallel photoionization models of NGC 346, an H II region in the Small Magellanic Cloud. The models are based on...

We have compared direct estimates of the ionizing photon flux from the stars observed within the H II region NGC 346 in the Small Magellanic Cloud with its...

The existence of an extended component of diffuse ionized gas (DIG) is a well-known property of spiral galaxies. The integrated ensuremath {{H}alpha }...

We analyze the physical conditions, chemical composition, and other properties of the photoionized Herbig-Haro (HH) object HH 204 through Very Large Telescope...

We report the first reliable measurement of the nebular [O i] lambda 5577 emission line in the Orion nebula. Diagnostic diagrams based on the [O i] lambda...

Line profiles in ensuremath {{H}alpha } emission from H II region populations in spiral galaxies show emission features at +/-50 km/s from the main emission...

We present evidence that the H II regions of high luminosity in disk galaxies may be density bounded, so that a significant fraction of the ionizing photons...

Based on the best observations of extragalactic H II regions of low metallicity available in the literature we redetermine the primordial helium abundance, Y[p]...

The abundance of O in planetary nebulae (PNe) has been historically used as a metallicity indicator of the interstellar medium (ISM), where they originated; e.g...