8 research outputs found
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
Sulphur in the Sculptor dwarf spheroidal galaxy - Including NLTE corrections
In Galactic halo stars, sulphur has been shown to behave like other
-elements, but until now, no comprehensive studies have been done on
this element in stars of other galaxies. Here, we use high-resolution ESO
VLT/FLAMES/GIRAFFE spectra to determine sulphur abundances for 85 stars in the
Sculptor dwarf spheroidal galaxy, covering the metallicity range . The abundances are derived from the S~I triplet at
9213, 9228, and 9238~\AA. These lines have been shown to be sensitive to
departure from local thermodynamic equilibrium, i.e. NLTE effects. Therefore,
we present new NLTE corrections for a grid of stellar parameters covering those
of the target stars. The NLTE-corrected sulphur abundances in Sculptor show the
same behaviour as other -elements in that galaxy (such as Mg, Si, and
Ca). At lower metallicities () the abundances are
consistent with a plateau at , similar to what is
observed in the Galactic halo, . With increasing
[Fe/H], the [S/Fe] ratio declines, reaching negative values at
. The sample also shows an increase in [S/Mg] with
[Fe/H], most probably because of enrichment from Type Ia supernovae.Comment: 9 pages, 11 figures, 2 tables + 3 online tables, accepted in A&
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
SOME EVOLUTIONARY ASPECTS OF THE BINARY STELLAR SYSTEMS CONTAINING NEUTRON STAR
ABSTRACT. The obvious lack of the binary stellar systems that contain neutron stars (NS) is observed at present. Partly it is caused by the fact that it is very dicult to detect neutron star in a binary system if this relativistic component does not manifest itself as a radio pulsar. Among 1879 pulsars that are listed in the ATNF pulsar catalogue, only 141 pulsars are known to be the companions in binary systems. Only 81 objects having median mass estimation of more than 0.2 M ⊙ constitute the binary systems with pulsars. Nevertheless, such systems should be much more numerous and their investigation is of the great interest because thier structure and evolution can certainly help in our understanding of many unique properties that are seen in some stars