Related papers: Revised element abundances for WC-type central sta…

We recall the basic physical principles governing the evolution of stars with some emphasis on the role played by the nuclear reactions. We argue that in general it is not possible from observations of stars to deduce constraints on the…

We use ultraviolet space-based (FUSE, HST) and optical/IR ground-based (2.3m MSSSO, NTT) spectroscopy to determine the physical parameters of six WC4-type Wolf-Rayet stars in the Large Magellanic Cloud. Stellar parameters are revised…

A growing number of Galactic Wolf-Rayet (WR) stars, in particular WC and transitional WN/C (WNC) objects, have been reported at comparatively low luminosities. If confirmed, these low-luminosity WR stars provide stringent tests of…

Stellar model atmospheres form the basis for any element abundance determination and hence are crucial ingredients for studies of stellar, galactic and cosmic evolution. With recent observational progress with the advent of 8m-class…

We interpret the peculiar super-solar nitrogen abundance recently reported by the James Webb Space Telescope observations for GN-z11 ($z=10.6$) using our state-of-the-art chemical evolution models. The observed CNO ratios can be…

Abundance patterns of the elements C, N, and O are sensitive probes of stellar nucleosynthesis processes and, in addition, O abundances are an important input for stellar age determinations. Understanding the nature of the observed…

As part of a multi-year survey for Wolf-Rayet stars in the Magellanic Clouds, we have discovered a new type of Wolf-Rayet star with both strong emission and absorption. While one might initially classify these stars as WN3+O3V binaries…

We present a detailed chemical abundance study of evolved stars in 10 open clusters based on Hydra multi-object echelle spectra obtained with the WIYN 3.5m telescope. From an analysis of both equivalent widths and spectrum synthesis,…

We report the abundances of 30 elements in 23 metal-poor ([Fe/H] <-1.7) giants. These are based on 7774 equivalent widths and spectral synthesis of 229 additional lines. Hyperfine splitting is taken into account when appropriate. Our choice…

We investigate the non-Local Thermodynamic Equilibrium (non-LTE) line formation of neutral carbon in late-type stars in order to remove some of the potential systematic errors in stellar abundance analyses employing C I features. The…

We investigate anew the distribution of absolute carbon abundance, $A$(C) $= \log\,\epsilon $(C), for carbon-enhanced metal-poor (CEMP) stars in the halo of the Milky Way, based on high-resolution spectroscopic data for a total sample of…

Wolf-Rayet ([WR]) and weak emission-line ($wels$) central stars of planetary nebulae (PNe) have hydrogen-deficient atmospheres, whose origins are not well understood. In the present study, we have conducted plasma diagnostics and abundance…

Context. Oxygen sequence Wolf-Rayet (WO) stars are thought to represent the final evolutionary stage of the most massive stars. The characteristic strong O vi emission possibly originates from an enhanced oxygen abundance in the stellar…

Based on a simple, but fairly successful, model of the chemical evolution of the Milky Way disk, we study the evolution of the abundances of the elements He, C, N, O, Ne, Mg, Al, Si, S, Ar and Fe. We use metallicity dependent yields for…

Over the last half-century quantitative stellar spectroscopy has made great progress. However, most stellar abundance analyses today still employ rather simplified models, which can introduce severe systematic errors swamping the…

Towards the end of their evolution hot massive stars develop strong stellar winds and appear as emission line stars, such as WR stars or LBVs. The quantitative description of the mass loss in these important pre-SN phases is hampered by…

We present a simple analytical method to describe the structure of a spherically expanding envelope with strong mass outflow. The structure is consistently connected to the hydrostatic stellar interior and provides an adequate description…

The correlation between host star iron abundance and the exoplanet occurrence rate is well-established and arrived at in several studies. Similar correlations may be present for the most abundant elements, such as carbon and oxygen, which…

Elemental abundances are key to our understanding of star formation and evolution in the Galactic center. Previous work on this topic has been based on infrared (IR) observations, but X-ray observations have the potential of constraining…

We present an analysis of eight star-forming galaxies with $\langle z \rangle = 4.0$ from the JWST EXCELS survey for which we obtain robust chemical abundance estimates for the $\alpha$-elements O, Ne and Ar. The $\alpha$-elements are…