Перегляд за Автор "Kniazev, A. Yu."
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Документ CHEMICAL COMPOSITION AND ATMOSPHERE PARAMETERS OF THE DOUBLE-MODE CEPHEID U TRA(Astroprint, 2013) Usenko, I. A.; Kniazev, A. Yu.; Berdnikov, L. N.; Kravtsov, V. V.Four high-resolution spectra of the doble-mode Cepheid U TrA have been obtained during its pulsational period. For the first time, we obtained accurate atmosphere parameters and the chemical abundance of a number of elements, in particular of sodium, magnesium, and aluminium. We estimated the mean Teff = 6085 29 K, log g = 2.00 0.15, and Vt = 3.90 0.25 kms -1 . A deficit of carbon ([C=H] = –0.35 0.23 dex), overabundance of both sodium ([Na=H] = +0.15 0.25 dex) and aluminium ([Al=H] = +0.30 0.32 dex) are typical for Cepheids passing through the first dredge-up phase. The abundance of iron ([Fe=H] = +0.01 0.15 dex) is very close to the solar one. Moreover, we find that -elements, those of Fe-group, as well as ”light”- and ”heavy”-, s- and rprocess elements, all of them have abundances close to solar values, too, excepting maybe several elements with slight enhance or deficit.Документ FUNDAMENTAL PARAMETERS AND CHEMICAL COMPOSITION OF CEPHEID X SGR.(Astroprint, 2012) Usenko, I. A.; Kniazev, A. Yu.; Berdnikov, L. N.; Kravtsov, V. V.Five high-resolutioned spectra of unusual Cepheid X Sgr have been obtained during its pulsational period. For the first time we obtain accurate fundamental parameters and abundances of chemical elements, in particular of sodium, magnesium and aluminium. We estimate the mean Teff = 6143 30 K; log g = 2.00; Vt = 4.35 kms -1 . The estimated effective temperature and surface gravity are relatively high compared to the typical values characteristic of Cepheids with pulsational period around 7 days. A deficit of carbon ([C/H] = -0.26 0.04 dex), overabundances of sodium ([Na/H] =+0.31 0.04 dex) and aluminium ([Al/H] = +0.21 0.08 dex) are typical for Cepheids passing through the first dredge-up phase. However, an obvious overabundance of magnesium([Mg/H] = +0.19 0.04 dex) is unusual. The abundance of iron ([Fe/H] = -0.02 0.01 dex) is very close to the solar one. Abundances of α - elements, (those of Fe-group, as well as ”light ” and ”heavy”, s- and r-process elements) are comparable to the solar values, except for several elements showing slight over- or underabundances.Документ HD 121135: features of its chemical composition(Одеський національний університет імені І. І. Мечникова, 2020) Mishenina, T. V.; Usenko, I. A.; Kniazev, A. Yu.; Kovtyukh, Valery V.; Ковтюх, Валерій В.Low metallicity star HD121135 ([Fe/H] = -1.5) have been investigated spectroscopically. Its atmospheric parameters and elemental abundances have been determined, including elements of neutron (n-) capture processes, which are the keys in the study of early Galaxy enrichment. Na, Mg, Ni, Co, Sr, Y, Zr, Mo, Ba, La, Ce, Pr, Sm, Eu, Gd, Dy, Ho, Os, Th abundances were calculated using the synthetic spectrum method, factoring in the hyperfine structure (HFS) for the Eu II lines. Si, Ca, Sc abundances were determined using the equivalent widths of their lines. The carbon content was computed by the molecular synthesis fitting for the region of CH (4300-4330 ÅÅ). For the abundances determinations of C, Na, Mg, Ba, and Th the NLTE corrections have been applied. We have determined for the first time the abundances of several n-capture elements and found that the behaviors of these elements do not show a significant trend with increasing atomic number. The elements ratios of [Eu/Fe] = 0.06, [Ba/Eu] = 0.13, [Sr/Ba] = - 0.05 do not support the HD121135 status as a r-process enrichment star. We have obtained the thorium abundance [Th/Fe] = 0.26. The carbon content confirms the effect of canonical additional mixing in this star.Документ Manifestation of stellar evolution in metal-deficient stars(Одеський національний університет імені І. І. Мечникова, 2023) Mishenina, Tamara V.; Usenko, I. A.; Kniazev, A. Yu.; Gorbaneva, T. N.; Мішеніна, Тамара ВасилівнаMetal-poor stars allow us to establish the early history of the Milky Way, furthermore the stars on advanced evolution stage (e.g. giants, AGB stars etc.) give the opportunity to research the peculiarities of stellar evolution at low metallicity. On the base of the 11m Southern African Large Telescope (SALT) spectra obtained using HRS fibre-fed echelle-spectrograph during 2018 -2020, the atmospheric parameters and elemental abundances of four metal-poor stars HE 1523-0901, HD 6268, HD 121135, and HD 195636 ( [Fe/H] ~ -1.5 – -3.0) have been obtained. The iron abundance was determined based on the equivalent widths of absorption lines. The carbon abundance was obtained using the molecular synthesis fitting for the CH (4300-4330 ÅÅ) region, nitrogen from CN at 3883 Å, oxygen from [O] line at 6300 Å and IR triplet at 7770 Å The relationship between the chemical enrichment of stars and their stellar evolution is considered. It may be associated with the processes of mixing inside the stars, and the mechanisms of matter transfer during stellar evolution.Документ MULTIPHASE SPECTROSCOPIC OBSERVATIONS OF THE LONG-PERIOD CEPHEIDS l CARINAE(Astroprint, 2013) Usenko, I. A.; Kravtsov, V. V.; Kovtyukh, Valery V.; Berdnikov, L. N.; Kniazev, A. Yu.; Chini, R.; Fokin, A. B.Thirty three spectra (one spectrum for the each of 33 observational nights) have been performed to cover all pulsational period of the 35.5-days Cepheid l Car. Due to these data we have obtained for the first time the detailed curves of effective temperature, gravity and turbulent velocity. Curves of gravity and turbulent velocity show complicated changes, connceted probably with dynamics of extensive Cepheid’s atmosphere. The mean atmosphere parameters of l Car are: Teff = 4984 15 K; log g = 1.13; Vt = 6.67 km s−1. Having a solar metallicity [Fe/H] = +0.02 dex, this Cepheid demonstrate sudden results for the ”key” elements abundances of yellow supergiants evolution, – all they are close to the solar ones. In this case l Car resembles to SV Vul, – Cepheid with 45-days pulsational period and nearly like spectral type. It is possible that l Car is an object crossing the Cepheids instability strip for the first time. The content of other elements is close to solar one too.Документ SPECTROSCOPIC INVESTIGATIONS OF CEPHEIDS IN CARINA(Astroprint, 2010-07) Usenko, I. A.; Berdnikov, L. N.; Kravtsov, V. V.; Kniazev, A. Yu.; Chini, R.; Hoffmeister, V. H.; Stahl, O.; Drass, H.Spectroscopic investigations of seven southern CepheidsWWCar, SX Car, UZ Car, UY Car, GX Car, HW Car and YZ Car have been performed. It was founded out six objects have metallicities, close to solar one and their CNO-, odd elements and Mg content indicate that these objects are on the stage after the first dredge-up. CepheidWWCar is an unusual objects because it has noticeable overabundance of [C/H] = +0.3 dex, [N/H] = +0.95 dex, whereas sodium in deficient ([Na/H] = -0.46 dex), and magnesium content is the largest ([Mg/H] = -0.12 dex) in comparison with other objects from this list having close pulsation periods.Документ Spectroscopic investigations of Galactic clusters with associated cepheid variables II NGC 5662 and V CEN(Одеський національний університет імені І. І. Мечникова, 2018) Usenko, I. A.; Kniazev, A. Yu.; Kovtyukh, Valery V.; Mishenina, T. V.; Miroshnichenko, A. S.; Turner, D. G.; Protsyuk, Yu. I.We present the results of a spectroscopic and photometric investigation of 15 objects from the open cluster NGC 5662, which contains the Cepheid V Cen. Besides the Cepheid, we studied one G-supergiant, two K-giants, four B-giants, and seven main sequence stars. Radial velocities (RV), vsini, TeS, logg, and [Fe/Hj were determined using model fitting. We have derived the color-excesses, reddenings, and intrinsic colors for these stars to determine their true Tff and log g from comparison to the atmosphere models, especially for hot stars, and to determine their absolute magnitudes. RV and GAIA DR2 2018 parallax/distanee values for these stars allowed us to determine their membership in the cluster and to construct it 3D kinematic models. These parallaxes and reddenings led to the distances in a range of 700875 pc, while photometric My gave the distances of 550-660 pc. Two objects from our list were found to be non-members of the cluster, and two other objects to be background stars. All members have [Fe/Hj = —0.1 ±0.04 dex. The main sequence stars and B-giants have abundances of C, N, and Na close to the solar one, while the cool supergiants and giants show a deficit of carbon, an overabundance of nitrogen, and a small overabundance or close to the solar sodium content. Two Li-rich K-giants, HD 127733 and HD 127753, were discovered in the cluster.Документ Spectroscopic investigations of galactic clusters with associated Cepheid variables. III. Collinder 394 and BB SGR(Одеський національний університет імені І. І. Мечникова, 2019) Usenko, I. A.; Kniazev, A. Yu.; Katkov, I. Yu.; Kovtyukh, Valery V.; Mishenina, T. V.; Miroshnichenko, A. S.; Turner, D. G.We present the results of a spectroscopic and photometric investigation of 20 objects from the open cluster Collinder 394, which contains the Cepheid BB Sgr. Besides the Cepheid, we studied tree K-giants, four B-giants, and twelve B-A-F main sequence stars. Radial velocities (RV), v sin i, Teff, log g, were determined using spectroscopic model fitting and atmosphere models. We have derived the color-excesses, reddenings, and intrinsic colors for these stars using their Teff and log g from comparison to the atmosphere models, especially for hot stars. Proper motions, RV and GAIA DR2 2018 parallax/distance values for these stars allowed us to determine their membership in the cluster and absolute magnitudes. We found that seven stars do not belong to the cluster. The parallaxes and reddenings of 13 confidently cluster members led to the distances in a range of 630–800 pc, although the majority of them (8 objects) are located at a mean distance of 657.7±66.7 pc, and 5 objects with the Cepheid could probably belong to the cluster’s corona. All the members have [Fe/H] near 0.1 dex. The main sequence B-star No. 76 (HD 174307) has a low rotational velocity projection, and this fact allows us to determine its chemical composition to compare with that of the Cepheid BB Sgr. Its CNO and Na abundances are close to the solar one, while the Cepheid show a deficit of carbon, an overabundance of nitrogen, nearly solar oxygen, and an overabundance of sodium. Three foreground K-giants have different C abundances (from a deficit to the solar), and Na (from the solar to an overabundance) as well as a solar-like O content. The foreground F7-8 V star No. 75 (CPD −20◦7218) was revealed to be a Li-rich star, while the A7 V star No. 69 (BD −20◦5290) has an anomalous deficit of CNO with overabundances of some α, r- and s-process elements.Документ Spectroscopic investigations of galactic clusters with associated cepheid variables. IV. Collinder 220 and UW CAR(Одеський національний університет імені І. І. Мечникова, 2020) Usenko, I. A.; Kniazev, A. Yu.; Katkov, I. Yu.; Kovtyukh, Valery V.; Mishenina, T. V.; Miroshnichenko, A. S.; Turner, D. G.We present the results of a spectroscopic and photometric investigation of 18 probable members of the open cluster Collinder 220, which contains the Cepheid UW Car. Besides the Cepheid, we studied tree K-giants, two B-giants, and twelve B-A-F main sequence stars. Radial velocities (RV), v sin i, Te , and log g were determined using spectroscopic model fitting and atmosphere models. We have derived color-excesses, reddenings, and intrinsic colors for these stars using their Te and log g from comparison to the atmosphere models, especially for hot stars. Proper motions, RV, and the GAIA DR2 2018 parallaxes allowed us to determine their membership in the cluster and absolute magnitudes. We found that seven stars along with the Cepheid can be the cluster members with a high confidence. The parallaxes and reddenings of the 7 confident cluster members led to the distances in a range of 1900–2800 pc, while the other stars are probably foreground objects. All the members have [Fe/H] near 0.1 dex. The B-giant HD90435 located near the cluster’s “turn-off” point has a low projected rotational velocity, and this fact allows us to determine its chemical composition to compare with that of the Cepheid UW Car. The CNO abundances of HD90435 are nearly solar, while the Cepheid shows a deficit of carbon, an overabundance of nitrogen, a nearly solar oxygen, and an overabundance of sodium. The confident cluster member, K-supergiant CPD 57 3199, has CNO- and Na abundances close to those of UW Car.Документ Spectroscopic investigations of galactic open cluster Collinder 394 – new results(Одеський національний університет імені І. І. Мечникова, 2021) Usenko, I. A.; Kniazev, A. Yu.; Miroshnichenko, A. S.; Danford, S.; Kovtyukh, Valery V.; Mishenina, Tamara V.; Мішеніна, Тамара Василівна; Мишенина, Тамара ВасильевнаConfident main-sequence (MS) members of the Collinder 394 open cluster are perfect objects to check the correctness of their distances, obtained from the GAIA GR2 (2018) catalogue. The differences in the distances to the open cluster Collinder 394, determined by photometry and from the GAIA parallaxes have raised doubts about the correctness of the latter. Therefore we used spectroscopically determined Teff and log gvalues for these stars from Usenko et al. (2019) and tried to solve the inverse problem: determine radii of these stars using the derived distances and calibrations “Teff-radius” for MS stars and compare with similar ones. For this purpose we used the calibrations from Torres et al. (2010), based on the nearest MS eclipsing binaries and compilations for MS stars from Mamajek (2018). As a result, we obtained relationships that connect Teff, log g, radii, masses, and distances for the confident Collinder 394 MS stars. We have confirmed the correctness of the GAIA DR2 (2018) distances for these stars and determined their radii and masses. The latter estimates turned out to be close to those of the evolutionary masses calculated by the PARSEC models.Документ Spectroscopical study of faint Southern Cepheids with Southern African Large Telescope (SALT). First results.(Одеський національний університет імені І. І. Мечникова, 2017) Usenko, I. A.; Kniazev, A. Yu.; Kovtyukh, Valery V.; Belik, S. I.; Berdnikov, L. N.First Cepheids observations using echelle-spectrograph HRS fed by Southern African Large Telescope (SALT) were realized during 2016. All spectra have been obtained in the medium resoltion mode (R 31000–41000) wth high S/N ratio near 50–220. All data were processed using package developed by authors based on the standard system of astronomical data reduction MIDAS. Using new echelle data we found the atmosphere parameters and chemical composition for 30 faint Cepheids of southern hemisphere, where for the most of theses stars these results we obtained for the first time. 28 stars are Cepheids after the first-dredge up stage, while ASAS 075842-25336.1 and ASAS 1131714-6605.0 having remarkable Li I 6707.8 ˚A absorption line and anomalous CNO and Na content could be consider as first crossing of the Cepheids instability strip.Документ Status refinement of metal-poor star HD 6268(Одеський національний університет імені І. І. Мечникова, 2018) Mishenina, T. V.; Usenko, I. A.; Kniazev, A. Yu.; Kovtyukh, Valery V.; Мишенина, Т. В.; Усенко, І. А.; Князев, А. Ю.; Ковтюх, Валерій В.Metal-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.Документ TYC5594-576-1: R-process enrichment metal-poor star(Одеський національний університет імені І. І. Мечникова, 2021) Mishenina, Tamara V.; Usenko, I. A.; Kniazev, A. Yu.; Kovtyukh, Valery V.; Мішеніна, Тамара Василівна; Мишенина, Тамара ВасильевнаAtmospheric parameters and elemental abundances of metal-poor Population II star TYC5594- 576-1 ([Fe/H] = –2.8) have been studied, including the elements of neutron (n-) capture processes, as an im portant part of the enrichment sources of early Galaxy. Na, Mg, Al, Co, Sr, Y, Zr, Mo, Ba, La, Ce, Pr, Sm, Eu, Gd, Dy, Os, and Th abundances were determined using the synthetic spectrum method, taken into account the hyperfine structure (HFS) for the Ba II, La II and Eu II lines. The abundances of Si, Ca, Sc, N were determined based on the equivalent widths of their lines. The carbon abundance was obtained by the molecular synthesis fitting for the CH region of 4300-4330 ÅÅ. For the abundances determinations of C, Na, Mg, Al, Ba, and Th the NLTE corrections have been applied. We have determined the abundances of several n capture elements for the first time and found that the be haviour of these elements abundances shows a significant trend with increasing atomic number. The elements ratios of [Eu/Fe] = 1.85, [Ba/Eu] = –1.24, [Sr/Ba] = –1.04 con firm the status of TYC5594-576-1 as a r-process enrich ment star, with lower strontium [Sr/Fe] = –0.33 and higher thorium [Th/Fe] = 1.28 abundances. The obtained europium and thorium excesses testifies to the early en richment of the Galaxy by the r-process elements as a result of the merger of neutron stars or black holes. The car bon abundance confirms the effect of canonical additional mixing in this star.