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V. F. Gopka

Publications and source records attributed to V. F. Gopka.

7 recordsLinked to original sources
arXiv2013

Abnormal lithium abundance in several Ap-Bp stars

Using observations of rapidly rotating roAp star HD 12098, obtained with 6m telescope of SAO RAS in 2005-2008 in nine rotational phases (0.001-0.817), and code V. Tsymbal ROTATE we identified 3 lithium spots on the surface of star, one of them coincided with the position of one magnetic pole and two others are located near the other pole, symmetrically with respect to it. Perhaps magnetic field of the star has a more complex structure than the dipole (Shavrina 2008). Lithium abundance in the spots is greater than cosmic one. It can be explained by diffusion of lithium in the presence of a magnetic field or by production of lithium in the reactions of "spallation" on the surface of star near the magnetic poles (see, for example, Goriely 2007). Enhanced lithium abundances was also determined for other two slowly rotating Ap stars HR 465 and HD 965. The analysis is performed using a synthetic spectrum method taking into account magnetic splitting of lines by the SYNTHM code of Khan (2004).

astro-ph.SR↗
arXiv2012

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.

astro-ph.SR↗
arXiv2007

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).

astro-ph↗
arXiv2003

The chemical composition of a mild barium star HD202109

We present the result of chemical abundances of a mild barium star HD202109 (zeta Cyg) determined from the analysis of spectrum obtained by using a 2-m telescope at the Peak Terskol Observatory and a high-resolution spectrometer with R=80,000, signal to noise ratio >100. We also present the atmospheric parameters of the star determined by using various methods including iron-line abundance analysis. For line identifications, we use whole-range synthetic spectra computed by using the Kurucz database and the latest lists of spectral lines. Among the determined abundances of 51 elements, those of P, S, K, Cu, Zn, Ge, Rb, Sr, Nb, Mo, Ru, Rh, Pd, In, Sm, Gd, Tb, Dy, Er, Tm, Hf, Os, Ir, Pt, Tl, and Pb have not been previously known. Under the assumption that the overabundance pattern of Ba stars is due to wind-accretion process, adding information of more element abundances enables one to show that the heavy element overabundances of HD202109 can be explained with the wind accretion scenario model.

astro-ph↗
arXiv2003

The spectrum of the roAp star HD 101065(Przybylski's star) in the Li I 6708 A spectral region

We carried out a detailed analysis of spectra of the unique roAp star HD 101065 (Przybylski's star) near the resonance doublet Li I 6708 A, using a most complete line list including all possible transitions between REE levels of NIST database. Our model calculations were performed under two assumptions: blend of Li and REE lines, and blend of REE lines only. They prove that Li lines are present in the range 6707.72-6708.02 AA, and that the resulting Li abundance is 3.1 dex (in the scale log N(H) = 12.0, while the isotopic ratio 6Li/7Li is near to 0.3.

astro-ph↗
arXiv1998

Atmospheric abundances of CP SB2 star components of equal masses. II. 66 Eridani

We report the results of abundance determination for the components of the SB2 star 66 Eri (M_A/M_B=0.97) from high resolution CCD echelle spectra with S/N>=100 taken with the 1-m telescope of Special Astrophysical Observatory (Zelenchuck, Russia). The atmospheric parameters of the components were determined using all available photometric, spectrophotometric and spectral data. The abundances of 27 elements were found. The abundances of components are different. The B component, previously classified as an Hg-Mn star, does not show anomalies typical of this group such as deficit of He, Al and excess of P, Ga, but shows overabundances of heavy elements which amount up to 4-5 dex. The A component also shows moderate Mn and Ba excess. Lines of other heavy elements were not detected. Estimates of upper limits to their abundances do not permit to exclude completely the presence of fainter anomalies in the A component either.

astro-ph↗