The authors discuss the nature of S 201 in the light of new optical and infrared observations, in terms of the interaction between an evolved H II region and a...

Based on O II recombination lines we present a new calibration (called O II_{RL}) of Pagel's O_{23} indicator to determine the O/H abundance ratio in...

The abundance gradient in M 33 is studied on the basis of IPCS and CCD data on emission lines in selected H II regions, using O II, O III, S II, and S III in...

We present deep spectra of ring nebulae associated with Wolf-Rayet (WR) and O-type stars: NGC 6888, G2.4+1.4, RCW 58, S 308, NGC 7635 and RCW 52. The data have...

Intermediate resolution mapping and limited off-center spectroscopy of the post-main-sequence molecular outflow source NGC 7027 are presented. The CO envelope...

Deep spectra of the planetary nebula IC 418 were obtained in the wavelength range 4190-5850 A. The data made it possible to map an extended halo about the...

We derived the oxygen abundance (O/H), the nitrogen-to-oxygen (N/O) abundance ratio, and their corresponding radial gradients for a sample of 1431 galaxies from...

An investigation of the diffuse ionized gas (DIG) and its underlying physical processes is the focal point of this study. We aim to survey the prevalence...

This paper describes a new determination of the primordial helium abundance (YP), based on the abundance analysis of five metal-poor extragalactic H II regions...