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...
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PublicationThe Calibration of the O/H Abundance Indicators for Extragalactic H II Regions based on O II Recombination Lines
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PublicationThe chemical composition gradient across M 33
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...
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PublicationThe chemical composition of Galactic ring nebulae around massive stars
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...
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PublicationThe CO structure of NGC 7027 - A bipolar nebula in the making
Intermediate resolution mapping and limited off-center spectroscopy of the post-main-sequence molecular outflow source NGC 7027 are presented. The CO envelope...
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PublicationThe core-halo structure of IC 418
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...
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PublicationThe dependence of the gradients of oxygen and nitrogen-to-oxygen on stellar age in MaNGA galaxies
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...
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PublicationThe diffuse ionized gas in galaxies
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...
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PublicationThe Effect of Collisional Enhancement of Balmer Lines on the Determination of the Primordial Helium Abundance
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...
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PublicationThe embedded cluster IRAS17136 - 3617 associated with the nebulosity GM24
Radio, infrared, and optical observations of the embedded infrared cluster IRAS17136 - 3617 are reviewed. The cluster consists of more than 25 stars with a...