94 research outputs found
Some evolutionary aspects of the binary stellar systems containing neutron star
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
difficult 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 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.Comment: Accepted to published in the Odessa Astronomical Publications, 2012,
vol. 25/1, p.35-3
Some Statistical Picture of Magnetic CP Stars Evolution
We discuss some statistical results on the evolution of magnetic CP stars in
the framework of the supposition about their binary nature.Comment: 3 pages, 3 figure
Analysis of the spectral energy distribution of the coolest RCrB type carbon star DY Per
We analyse the spectral energy distribution of the evolved carbon giant DY
Per with a spectral synthesis technique. The red giant shows the photometric
features of R CrB type stars. We derive the atmospheric parameters of DY Per
using three variants of molecular line lists. We estimate Teff to be in the
range 2900 < Teff < 3300 K. We adopted log g = 0. The star may be metal
deficient and hydrogen deficient. The maximum possible carbon abundance in the
star, [C]=0.94, provides the following atmospheric parameters: Tef=3100 K,
[Fe/H] = 0, log(C/O)=0.6, [N/Fe] = 0, [H/He] = 0, with Jorgensen's line lists
for the molecules C2 and CN.Comment: 4 pages, 2 tables, 3 figs, accepted by Odessa asronomical observatory
Publ., 200
A Search for Nitrogen-Enhanced Metal-Poor Stars
Theoretical models of very metal-poor intermediate-mass Asymptotic Giant
Branch (AGB) stars predict a large overabundance of primary nitrogen. The very
metal-poor, carbon-enhanced, s-process-rich stars, which are thought to be the
polluted companions of now-extinct AGB stars, provide direct tests of the
predictions of these models. Recent studies of the carbon and nitrogen
abundances in metal-poor stars have focused on the most carbon-rich stars,
leading to a potential selection bias against stars that have been polluted by
AGB stars that produced large amounts of nitrogen, and hence have small [C/N]
ratios. We call these stars Nitrogen-Enhanced Metal-Poor (NEMP) stars, and
define them as having [N/Fe] > +0.5 and [C/N] < -0.5. In this paper, we report
on the [C/N] abundances of a sample of 21 carbon-enhanced stars, all but three
of which have [C/Fe] < +2.0. If NEMP stars were made as easily as
Carbon-Enhanced Metal-Poor (CEMP) stars, then we expected to find between two
and seven NEMP stars. Instead, we found no NEMP stars in our sample. Therefore,
this observational bias is not an important contributor to the apparent dearth
of N-rich stars. Our [C/N] values are in the same range as values reported
previously in the literature (-0.5 to +2.0), and all stars are in disagreement
with the predicted [C/N] ratios for both low-mass and high-mass AGB stars. We
suggest that the decrease in [C/N] from the low-mass AGB models is due to
enhanced extra-mixing, while the lack of NEMP stars may be caused by
unfavorable mass ratios in binaries or the difficulty of mass transfer in
binary systems with large mass ratios.Comment: 14 pages, 7 figures, to be published in Ap
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