Перегляд за Автор "Usenko, Igor O."
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Документ Refined physical properties of the HD 327083 binary system(Одеський національний університет імені І. І. Мечникова, 2022) Nodyarov, A. S.; Miroshnichenko, A. S.; Khokhlov, S. A.; Zharikov, S. V.; Manset, N.; Usenko, Igor O.; Усенко, Ігор ОлександровичHD 327083 is a member of a small group of supergiants exhibiting the B[e] phenomenon. It was found to be a binary system with an early-B and an early-F supergiant components. However the fundamental and orbital parameters of the system were not accurately known. We determined a new set of the system parameters that include the orbital period and the components’ masses using a combination of photometric and spectroscopic data. A new orbital period of 107.7 days was found from both the spectral line positional variations and the visual light curve. Absorption lines of the cool component show a radial velocity semi-amplitude of 48.3 kms-1 , similar to that of emission lines that originate around the hot component. The system shows partial eclipses. We estimated the components’ masses to be nearly equal and close to 6-8 Mq . The masses turned out to be smaller then the evolutionary masses that may be a consequence of a recent mass-transfer.Документ Spectroscopic studies of Polaris: getting back to normal life of a Cepheid?(Odesa I. I. Mechnikov National University, 2024) Usenko, Igor O.; Miroshnichenko, A. S.; Danford, S.; Vaidman, N. L.; Turner, D. G.; Majaess, D. J.; Protsyuk, S. V.; Усенко, Ігор Олександрович; Мірошніченко, А. С.; Данфорд, С.; Вайдман, Н. Л.; Тьорнер, Д.; Маджаєсс, Д. Дж.; Процюк, С. В.Based on 583 radial velocity (RV) measurements we obtained at the Three College Observatory (TCO, North Carolina, USA) in 2015–2024, (including 396 not previously analyzed from 2020–2024) as well as on 236 RV data from the German amateur R. Bücke (2011–2022), we calculated the pulsation period and amplitude of the Cepheid Polaris Aa system (α UMi). The analysis showed that the pulsation period was stable within a few minutes in 2020–2024. During this time, the pulsation amplitude was increasing and reached the 1960s level (4–6 km s−1), when its sharp decline began. Since its new growth began after Polaris Ab, the system secondary component, passed a periastron, we concluded that the observed amplitude changes were due to its orbital motion. It is clear that Polaris Aa is returning to normal pulsating activity.Документ Status refinement of metal-poor star HD 6268(Одеський національний університет імені І. І. Мечникова, 2018) Mishenina, Tamara V.; Usenko, Igor O.; Kniazev, A. Yu.; Kovtyukh, Valery V.; Мішеніна, Тамара Василівна; Усенко, Ігор Олександрович; Князев, А. Ю.; Ковтюх, Валерій ВолодимировичMetal-poor stars in the Galaxy enable observations of the light and neutron-capture (n-capture) elements produced by their progenitors and deduction of the characteristics of the early Galaxy from the elemental abundances in these stars. Stars with deficiency of metals ([Fe/H] < –2) vary significantly in their chemical composition, in particular, in their content of CNO elements, as well as the iron-peak and n-capture elements. A detailed study of the elemental abundances in these stars makes it possible to test experimental models of stellar evolution, nucleosynthesis, homogeneity (the degree of mixing) of interstellar matter, etc., at low metallicity in the Galaxy. The metal-poor star HD 6268 with [Fe/H] close to – 2.5 and low carbon abundance was selected as a target one for this study. The spectral material was collected using the Southern African Large Telescope (SALT) fibre-fed echelle-spectrograph HRS in the medium resolution mode (R~31000-41000) with a high S/N ratio near 100-200 within the range from 3900 to 8700 ÅÅ. The atmospheric stellar parameters and abundances of 30 chemical elements in the metal-poor star HD 6268 were determined under the LTE approximation using the atmosphere models by Kurucz & Castelli (2003), as well as the equivalent widths EWs and WIDH9 code developed by Kurucz. The abundances of C, Na, Mg, K, Ba, La, Ce, Pr, Sm and Eu were obtained by the synthetic spectrum method factoring in the hyperfine structure (HFS) for the Eu II line 4129 A. The carbon abundance was determined by the molecular synthesis fitting in the region of CH (4300-4330 ÅÅ). For the abundances of Na, Mg, K and Ba, we applied the NLTE corrections. As a result, we found out that the abundances of C and N confirm their changes associated with canonical extra mixing proposed by Denissenkov & Pinsonneault (2008). The Na-O correlation is open to question unlike the Na-Si correlation which is likely to exist. The Al-Mg and Al-Na correlations are consistent with the data obtained for the field giants with [C/Fe] < –0.5 (Roederer et al., 2014). According to the distribution of elements depending on their atomic numbers in the atmosphere of HD 6268, it is a metal-poor main r-process enriched star.