Probing the Przybylski star for Deuterium

The Przybylski star spectrum has been studied in order to search for deuterium lines. Since this star is extremely enriched in the s-process elements, which are the product of interaction between free neutrons and seed nuclei, we might as well expect to detect deuterium in this star. However, no visible spectroscopic manifestation of deuterium has been detected. Perhaps, the reason of this result is the convective "destruction" of this isotope.Comment: 4 pages, 2 figures, accepted to Astronomische Nachrichte

An enigma of Przybylski's star: is there promethium on its surface?

We carried out a new attempt to check for the presence promethium lines in the spectrum of HD101065 (Przybylski's star). The neutron capture element promethium does not have stable isotopes and the maximum half-life time is about 18 years. Thus its presence in this peculiar star would indicate an ongoing process of irradiation of its surface layers with free neutrons. Unfortunately, almost all promethium lines are heavily blended with lines of other neutron capture elements and other species. We selected and analysed three lines of promethium (Pm I and Pm II) and came to the conclusion that at present it is impossible to definitely claim the presence of this element in Przybylski's star atmosphere.Comment: Accepted for publication in Astronomische Nachrichte

Li abundances and chromospheric activity of BY Dra type stars

Atmospheric parameters and Li abundances have been determined for 162 stars observed at high resolution, high signal to noise ratio with the ELODIE echelle spectrograph (OHP, France). Among them, about 70 stars are active stars with a large fraction of BY Dra type stars. For all stars, rotational velocities were obtained with a calibration of the cross-correlation function, effective temperatures by the line depth ratio method, surface gravities by the parallaxe method and by the ionization balance of iron. The frequency of stars with observed lithium is significantly higher in active stars than in non active stars. Among active stars, no clear correlation has been found between different indicators of activity for our sample stars, but some correlation of an index R′H K and vsini is observed

Magellanic Clouds Cepheids: Thorium Abundances

The analysis of the high-resolution spectra of 31 Magellanic Clouds Cepheid variables enabled the identification of thorium lines. The abundances of thorium were found with spectrum synthesis method. The calculated thorium abundances exhibit correlations with the abundances of other chemical elements and atmospheric parameters of the program stars. These correlations are similar for both Clouds. The correlations of iron abundances of thorium, europium, neodymium, and yttrium relative to the pulsational periods are different in the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC), namely the correlations are negative for LMC and positive or close to zero for SMC. One of the possible explanations can be the higher activity of nucleosynthesis in SMC with respect to LMC in the recent several hundred million years

Anchors for the cosmic distance scale : the Cepheids U Sagittarii, CF Cassiopeiae, and CEab Cassiopeiae

New and existing X-ray, UBVJHKsW(1−4), and spectroscopic observations were analyzed to constrain fundamental parameters for M25, NGC 7790, and dust along their sight-lines. The star clusters are of particular importance because they host the classical Cepheids USgr, CF Cas, and the visual binary Cepheids CEa and CEb Cas. Precise results from the multiband analysis, in tandem with a comprehensive determination of the Cepheids’ period evolution (dP/dt) from ∼140 years of observations, helped to resolve concerns raised regarding the clusters and their key Cepheid constituents. Specifically, the distances derived for members of M25 and NGC7790 are 630 ± 25 pc and 3.40 ± 0.15 kpc, respectively

Anchors for the cosmic distance scale : the Cepheids U Sagittarii, CF Cassiopeiae, and CEab Cassiopeiae

New and existing X-ray, UBVJHKsW(1−4), and spectroscopic observations were analyzed to constrain fundamental parameters for M25, NGC 7790, and dust along their sight-lines. The star clusters are of particular importance because they host the classical Cepheids USgr, CF Cas, and the visual binary Cepheids CEa and CEb Cas. Precise results from the multiband analysis, in tandem with a comprehensive determination of the Cepheids’ period evolution (dP/dt) from ∼140 years of observations, helped to resolve concerns raised regarding the clusters and their key Cepheid constituents. Specifically, the distances derived for members of M25 and NGC7790 are 630 ± 25 pc and 3.40 ± 0.15 kpc, respectively