Abundance gradients in the Milky Way for alpha elements, Iron peak elements, Barium, Lanthanum and Europium

We model the abundance gradients in the disk of the Milky Way for several chemical elements (O, Mg, Si, S, Ca, Sc, Ti, Co, V, Fe, Ni, Zn, Cu, Mn, Cr, Ba, La and Eu), and compare our results with the most recent and homogeneous observational data. We adopt a chemical evolution model able to well reproduce the main properties of the solar vicinity. We compute, for the first time, the abundance gradients for all the above mentioned elements in the galactocentric distance range 4 - 22 kpc. The comparison with the observed data on Cepheids in the galactocentric distance range 5-17 kpc gives a very good agreement for many of the studied elements. In addition, we fit very well the data for the evolution of Lanthanum in the solar vicinity for which we present results here for the first time. We explore, also for the first time, the behaviour of the abundance gradients at large galactocentric distances by comparing our results with data relative to distant open clusters and red giants and select the best chemical evolution model model on the basis of that. We find a very good fit to the observed abundance gradients, as traced by Cepheids, for most of the elements, thus confirming the validity of the inside-out scenario for the formation of the Milky Way disk as well as the adopted nucleosynthesis prescriptions.Comment: 11 pages, 9 figures, accepted for publication in A&

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 $M_{\odot}$ 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

A New Method of the Corotation Radius Evaluation in our Galaxy

We propose a new method for determination of the rotation velocity of the galactic spiral density waves, correspondingly, the corotation radius, $r_C$, in our Galaxy by means of statistical analysis of radial oxygen distribution in the galactic disc derived over Cepheids. The corotation resonance happens to be located at $r_C \sim 7.0 - 7.6$ kpc, depending on the rate of gas infall on to the galactic disc, the statistical error being $\sim 0.3 - 0.4$ kpc. Simultaneously, the constant for the rate of oxygen synthesis in the galactic disc was determined. We also argue in favour of a very short time-scale formation of the galactic disc, namely: $t_f \sim 2$ Gyr. This scenario enables to solve the problem of the lack of intergalactic gas infall.Comment: 5 pages, 5 figure, 1 tabl

On the possible nature of Bp-Ap Stars: an application to HD101065 and HR465

We have proposed the new explanation of some magnetic chemically peculiar (MCP) stars anomalies, which is based on assumption that such stars can be the close binary systems with a secondary component being neutron star. Within this hypothesis one can naturally explain the main anomalous features of MCP stars: first of all, an existence of the short-lived radioactive isotopes detected in some stars (like Przybylski's star and HR465), and some others peculiarities (e.g. the behavior of CU Vir in radio range, the phenomenon of the roAp stars).Comment: 5 pages, 5 figure

NLTE determination of the sodium abundance in a homogeneous sample of extremely metal-poor stars

Abundance ratios in extremely metal-poor (EMP) stars are a good indication of the chemical composition of the gas in the earliest phases of the Galaxy evolution. It had been found from an LTE analysis that at low metallicity, and in contrast with most of the other elements, the scatter of [Na/Fe] versus [Fe/H] was surprisingly large and that, in giants, [Na/Fe] decreased with metallicity. Since it is well known that the formation of sodium lines is very sensitive to non-LTE effects, to firmly establish the behaviour of the sodium abundance in the early Galaxy, we have used high quality observations of a sample of EMP stars obtained with UVES at the VLT, and we have taken into account the non-LTE line formation of sodium. The profiles of the two resonant sodium D lines (only these sodium lines are detectable in the spectra of EMP stars) have been computed in a sample of 54 EMP giants and turn-off stars (33 of them with [Fe/H]< -3.0) with a modified version of the code MULTI, and compared to the observed spectra. With these new determinations in the range -4 <[Fe/H]< -2.5, both [Na/Fe] and [Na/Mg] are almost constant with a low scatter. In the turn-off stars and "unmixed" giants (located in the low RGB): [Na/Fe] = -0.21 +/- 0.13 or [Na/Mg] = -0.45 +/- 0.16. These values are in good agreement with the recent determinations of [Na/Fe] and [Na/Mg] in nearby metal-poor stars. Moreover we confirm that all the sodium-rich stars are "mixed" stars (i.e., giants located after the bump, which have undergone an extra mixing). None of the turn-off stars is sodium-rich. As a consequence it is probable that the sodium enhancement observed in some mixed giants is the result of a deep mixing.Comment: 8 pages, 9 figures; accepted for publication in A&

Spectroscopic Observations of the Comet 29P/Schwassmann-Wachmann 1 at the SOAR Telescope

We carried out photometric and spectroscopic observations of comet 29P/ Schwassmann-Wachmann 1 at the SOAR 4.1-meter telescope (Chile) on August 12, 2016. This paper presents the results of only spectroscopic analysis. The spectra revealed presence of CO$^+$ and N$_2^+$ emissions in the cometary coma at a distance of 5.9 AU from the Sun. The ratio [N$_2^+$]/[CO$^+$] within the projected slit seems to be 0.01. We have also estimated spectral gradient value for the comet