Related papers: C, N, O, and Na Abundances of Cepheid Variables: I…
Evolved low-mass stars of a wide range of metallicity bear signatures of a non-standard mixing event in their surface abundances of Li, C, and N, and in their 12C/13C ratio. A Na overabundance has also been reported in some giants of open…
Standard spectroscopic analyses of Cepheid variables are based on hydrostatic one-dimensional model atmospheres, with convection treated using various formulations of mixing-length theory. This paper aims to carry out an investigation of…
We predict how the C, N, and O abundances within the interstellar medium of galaxies evolve as functions of the galaxy star formation history (SFH). We adopt a hydrodynamical cosmological simulation, focusing on three star-forming disc…
Nitrogen abundances and carbon isotope ratios (12C/13C) in the atmospheres of red giants are known to be influenced by dredge-up of H-burning products and serve as useful probes to study the nature of evolution-induced envelope mixing. We…
Massive stars burn hydrogen through the CNO cycle during most of their evolution. When mixing is efficient, or when mass transfer in binary systems happens, chemically processed material is observed at the surface of O and B stars. ON stars…
We report the result of our near-infrared survey of short-period variable stars (P<60d) in a field-of-view of 20'x30' towards the Galactic Centre. Forty-five variables are discovered and we classify the variables based on their light curve…
The GES survey using FLAMES at the VLT has obtained high-resolution UVES spectra for a large number of giant stars, allowing a determination of the abundances of the key chemical elements C and N at their surface. The surface abundances of…
Classical Cepheids are not only excellent standard candles, but also invaluable tools to test stellar evolution and pulsation theories. Rates of their pulsation period change, quantified usually through $O-C$ diagrams, can be confronted…
We present a millimetre molecular line survey of seven high mass loss rate carbon stars in both the northern and southern skies. A total of 196 emission lines (47 transitions) from 24 molecular species were detected. The observed CO…
Recent work has shown that most globular clusters have at least two chemically distinct components, as well as cluster-to-cluster differences in the mean [O/Fe], [Mg/Fe], and [Si/Fe] ratios at similar [Fe/H] values. In order to investigate…
A prerequisite for probing theortical evolutionary models for high-mass stars is the determination of stellar physical properties with a high accuracy. We do this for three binary systems containing components with masses above 10 Msun:…
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…
Based on our prior accurate determination of fundamental parameters for 36 Galactic A-, F- and G-type supergiants and bright giants (luminosity classes I and II), we undertook a non-LTE analysis of the carbon abundance in their atmospheres.…
Anomalous Cepheids (ACEPs) are intermediate mass metal-poor pulsators mostly discovered in dwarf galaxies of the Local Group. However, recent Galactic surveys, including the Gaia DR3, found a few hundreds of ACEPs in the Milky Way. Their…
It has been shown recently that the infrared emission of Cepheids, which is constant over the pulsation cycle, might be due to a pulsating shell of ionized gas of about 15\% of the stellar radius, which could be attributed to the…
Pulsation period of Cepheids should change as stars evolve through the instability strip. Rates of these changes found by other authors based on the decades-long O-C diagrams show rather good agreement with theoretical predictions. We have…
Recent studies of spectral lines of the CNO elements in the Sun and unevolved disk and halo stars show that most published abundance data may be affected by systematic errors due to inadequate 1D modelling of stellar atmospheres. This…
One of the most interesting results from the OGLE-III study of the LMC Cepheids is the large number of objects that pulsate simultaneously in the first and second overtone (denoted 1O/2O). Double-mode Cepheids yield important constraint on…
To broaden the understanding of classical Cepheid structure, evolution and atmospheres, we have extended our continuing secret lives of Cepheids program by obtaining XMM/Chandra X-ray observations, and Hubble space telescope (HST) / cosmic…
We present metallicities, [Fe/H], and elemental abundance ratios, [X/Fe], for a sample of 24 Cepheids in the outer Galactic disk. The sample have Galactocentric distances covering 12 < R_GC (kpc) < 17.2 making them the most distant Galactic…