Репозитарій ОНУ імені І.І.Мечникова

Перегляд за Автор "Mishenina, Tamara V."

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From spectroscopy to the chemical evolution of the galaxy. Part 1.
(Одеський національний університет імені І. І. Мечникова, 2022) Mishenina, Tamara V.; Мішеніна, Тамара Василівна
A brief review of the results obtained at Odesa Astronomical Observatory based on the stellar spectra analyses from 1892 to 2000 is presented. The review begins with the first observations of emission lines in solar prominences carried out in 1892 under the direction of Alexander Kononowitsch and includes an overview of spectrophotometric studies performed at the observatory using instruments and telescopes designed inhouse; theoretical consideration of the issues of modelling physical conditions in stars and spectra simulation. It also describes the main results of the research of stars of various types, including cool giants K-, M spectral types, stars with various peculiarities of chemical composition, having enhanced lines of metals and CN bands, eclipsing binaries and binaries of different types, semi-regular and long-period variable stars, RR Lyraes, 5 Scuti and I Bootes stars, the diversity of Cepheids, blue stragglers in field and cluster populations, hot B Main-Sequence stars, etc., and finally, the enrichment with neutron-capture elements in the galactic stars.
Hafnium abundances in fgk dwarf of galactic disk
(Одеський національний університет імені І. І. Мечникова, 2018) Gorbanova, Tetiana I.; Mishenina, Tamara V.; Горбаньова, Тетяна Іванівна; Мішеніна, Тамара Василівна
In this work we present new observational data for hafnium (72). Hf is an important element that is between the lightest rare-earth elements (e.g., La, Z = 57) with elements of the third r-process peak (Os, Ir, Pt, Z =76-78). Hafnium is the heaviest (Z = 72) stable element represented by low-excitation (<1:5 eV) ionized lines in the spectra of the cool stars (Lawler et al., 2007). This element is important as a stable reference element for nucleocosmochronometry, and also to study of the sources of its production and enrichment with n (neutron)-capture elements of Galactic disc. We provide the analysis of the spectra of 126 FGK dwarfs in metallicity range from −1.0 < [Fe/H] < +0.3 that were taken from our starting sample of 276 stars (Mishenina et al. 2013). The observed stars belong to the substructures of the Galaxy disc. The observations were conducted using the 1.93 m telescope at Observatoire de Haute-Provence (OHP, France) equipped with the echelle type spectrographs ELODIE and SOPHIE. The results are based on analyses of spectra that have a typical S/N ~ 100-300 and a resolution of 42 000 (ELODIE) and 75 000(SOPHIE). The hafnium abundance was derived by comparing the observed and synthetic spectra in the region of two Hf II line (λ4080.437 Å and λ4093.155 Å), making use of the LTE approximation. The obtained hafnium abundance decrease with increasing metallicity in both discs, and have a big scatter at all metallicities. The dependence of our Hf abundance on metallicity and their comparison with those of other authors is presented. It corresponds to typical behavior of the elements behind the iron peak, the elements formed in the processes of neutron capture. The sources of the Hf enrichment of Galactic disc are considered.
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 Василівна
Metal-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.
Molybdenum abundance in some open clusters
(Одеський національний університет імені І. І. Мечникова, 2018) Shereta, E. P.; Carraro, G.; Gorbanova, Tetiana I.; Mishenina, Tamara V.; Шерета, Е. П.; Карраро, Ж.; Горбаньова, Тетяна Іванівна; Мішеніна, Тамара Василівна
This paper presents the results of determination of the molybdenum abundances in 13 G, K type stars in the open clusters NGC 2477 and NGC 2506. The abundances of molybdenum were determined using stellar atmosphere models by Castelli & Kurucz (2004), as well as a modified STARSP LTE spectral synthesis code (Tsymbal, 1996). For the used Mo I lines 5506 and 5533 Å the oscillator strengths log gf were adopted from the latest version of the VALD database dated 2016 (Kupka et al., 1999). The high resolution spectra were obtained with a VLT telescope at the European Southern observatory (ESO, Chile). We used atmospheric parameters of the investigated stars which we had obtained earlier. We have found out that the molybdenum abundances depend on metallicity [Fe/H] in giants of NGC 2506 and NGC 2477. For the stars in NGC 2506, molybdenum is slightly overabundant as compared to the solar abundance; such an overabundance is slightly higher in the stars of the second investigated cluster NGC 2477. Further investigation of the Mo abundance in larger number of open clusters is required to draw reliable conclusions.
Molybdenum and ruthenium in the Galaxy
(Одеський національний університет імені І. І. Мечникова, 2018) Mishenina, Tamara V.; Gorbanova, Tetiana I.; Мішеніна, Тамара Василівна; Горбаньова, Тетяна Іванівна
We present a brief overview of the molybdenum and ruthenium present-day nucleosynthesis calculations and abundance determinations in stars belonging to different substructures (populations) in the Galaxy. The following sources of Mo, Ru production were considered: the Asymptotic Giant Branch (AGB) stars of different masses (main s-process), massive stars (weak s-process), neutrino-induced winds from the core-collapse supernova CCSNe (weak r-process), merging of neutron stars (main rprocess). Many production sites of the p-nuclei have been proposed: the Type II and Ia supernovae (at the presupernova phase, during and after the supernova explosion), the rp-process in neutrino-driven winds, the high-entropy wind (HEW), the νp-process; inside in a supercritical accretion disk (SSAD), in the He-accreting CO white dwarfs of sub-Chandrasekhar mass, and in the carbon deflagration model for Type Ia. We also emphasize on some additional processes such as the i- process in rapidly accreting white dwarfs (RAWDs), the lighter element primary process LEPP as well as another formation channel, namely the charged-particle process (r- process). The contribution to the solar abundance of neutron capture elements and the Galactic Chemical Evolution (GCE) models for n-capture elements were considered. The Mo and Ru observations in metal-poor stars, Ba stars, globular clusters, meteoritic matter (presolar grains) as well as our new Mo and Ru determinations in Galactic disc are presented. Having analysed our date in the near solar metallicities we found out that there are different sources contributing to the Mo and Ru abundances, and that the main s-process contribution to the Mo and Ru abundances is lower than to the predominant s-element (Y, Zr and Ba) solar abundances. By comparing the behavior of Mo and Ru in the wide range of [Fe/H] with GCE models one can see that the theoretical description of the galactic behavior of Mo not depicts sufficient and we are faced with the underproduction of molybdenum in the sources and in processes that used at the GCE creation. Additional sources may be the p-process (SN Ia and/or SN II), νp-process (massive stars) or several more exotic processes.
Paramètres stellaires fondamentaux et l’investigation de la Galaxie
(2019) Mishenina, Tamara V.; Мішеніна, Тамара Василівна; Мишенина, Тамара Васильевна
Il s'agit de la coopération Ukraine (Odessa) - France (Bordeaux) dans le domaine de l'astrophysique, ses origines et résultats. L'abondance de tout élément chimique, de l'hydrogène à l'uranium, etc., nous permet de tester et d'améliorer les théories cosmologiques, la théorie de la nucléosynthèse et l'évolution des étoiles, ainsi que la théorie de la formation et de l'enrichissement en éléments chimiques des galaxies. C'est ainsi qu'en 2000, mon équipe et moi avions prévu d'étudier les problèmes liés à l'enrichissement de notre Galaxie en éléments, issus de la capture de neutrons. Pour ce faire, il nous fallait des spectres d'étoiles dans une large gamme de métallicité et de bonne qualité. Nous avons trouvé de spectres requis d'étoiles dans les archives spectrales du télescope de 1,93 m et du spectrographe ELODIE de l'Observatoire de Haute Provence (France). Les spectres étaient librement disponibles, nous en avons profité et ensuite nous avons publié l'article dans la revue européenne «Astronomy and Astrophysics». Mais avan, j'ai écrit une lettre à Caroline Soubiran. Caroline Soubiran est l'une des observateurs et compilateurs des programmes d'archivage et de traitement du spectre de l’ELODIE, un expert dans la domain de la cinématique et de la dynamique de la Galaxie. En 2002, elle m’a invité à l’Observatoire de Bordeaux ( l'OASU -Observatoire Aquitain des Sciences de l‘Univers). Cela etait le debut. Puis, en 2003, il y a eu mon voyage d'affaires à l’Université de Strasbourg et mon collègue Valery Kovtyukh a visité Bordeaux. En 2005-2006, nous avons obtenu une subvention destinée à la recherche dans le cadre du programme " Dnipro" de la coopération franco-ukrainienne qui s’appele «Paramètres stellaires fondamentaux et l’investigation de la Galaxie». Caroline Soubiran a visité l’Université d’Odessa et notre observatoire en 2005-2006. Notre coopération se poursuit à l'heure actuelle.
Solar Twins: Lithium Abundance Scatter (that is the question)
(2019) Mishenina, Tamara V.; Soubiran, C.; Charbonnel, C.; Katsova, M. M.; Nizamov, B. A.; Мішеніна, Тамара Василівна; Мишенина, Тамара Васильевна
In order to shed new light on the dispersion of Li in the atmosphere of solar type stars, a set of 56 solar analogs including 22 solar twins is analysed. Lithium abundances are derived by comparing observed and synthetic spectra in the region of Li I line 6707 Å in LTE approximation. The behavior of Li abundances as a function of the effective temperature Teff, age, rotational velocities vsini and chromospheric activity log R’HK is discussed in the context of stellar and galactic evolution.
Specific features of the enrichment of metal-poor stars with neutron-capture (r-process) elements
(Odesa I. I. Mechnikov National University, 2024) Mishenina, Tamara V.; Gorbanova, Tetiana I.; Dmytrenko, A.; Pignatari, M.; Thielemann, F.-K.; Мішеніна, Тамара Василівна; Горбаньова, Тетяна Іванівна; Дмитренко, А.; Піньятарі, М.; Тілеманн, Ф.-К.
In contrast to stars with near-solar metallicity (Galactic disk stars), metal-deficient stars show an abundance scatter of up to 3 dex in the enrichment with neutron-capture elements, in particular the r-process elements. The reasons of such a large variation in the in the r-process nucleosynthesis is currently matter of debate. Possible scenarios could be the presence of various r-process stellar and mechanisms in the early unevenly mixed Galaxy, as well as different stellar origin, either galactic or extragalactic, that reflect entering the Galaxy after the capture or coalescence of both individual stars and more complex stellar associations and star formations. In order to study differences in the enrichment with the r-process elements, we selected 20 metal-deficient stars, the spectra of which were collected in the UVES/VLT archive. We employed earlier determined atmospheric parameters to calculate the abundances of about 20 neutron-capture elements via the synthetic spectrum method, taking into account the hyperfine structure for a number of elements. We performed an analysis of the enrichment with the r-process elements grounded on multiple levels of enrichment intensity – namely, limited r-process, r-I and r-II – and the arrangement of stars by their belonging to different populations of the Galaxy, based on the stars’ spatial velocity components.
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 Васильевна
Confident 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.
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 Володимирович
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.
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 Васильевна
Atmospheric 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.
Галактика, ее строение и обогащение химическими элементами
(2017) Мишенина, Тамара Васильевна; Мішеніна, Тамара Василівна; Mishenina, Tamara V.
В монографии представлено общее описание Галактики, ее структуры и современное понимание ее химической эволюции. Рассмотрены проблемы, связанные с изучением структуры и развитием Галактики, производством химических элементов и обогащением межзвездной среды. Подчеркнута роль, которую играет теоретическое моделирование, опирающееся на расчеты нуклеосинтеза и на связь наблюдаемых кинематических свойств и химического состава различных галактических структур. Монография может быть использована при чтении курсов общей и теоретической астрофизики, звездной астрономии, будет полезной для студентов, аспирантов, молодых ученых, а также для всех, кто интересуется современным состоянием изучения нашей Галактики.
Млечный Путь – наша галактика
(Одесский национальный университет имени И. И. Мечникова, 2021) Мішеніна, Тамара Василівна; Мишенина, Тамара Васильевна; Mishenina, Tamara V.
Светящаяся полоса, которую мы наблюдаем в вечернем летне-осеннем небе, опоясывающая небосвод широким кольцом, называется Млечный Путь (рис.1). Название Млечный Путь является калькой с лат. via lactea "молочная дорога", которое, в свою очередь, калька с др.-греч. "молочный круг". Восходит оно к древнегреческой легенде о молоке богини Геры, кормившей им Геракла. Млечный Путь – это не только обозначение видимых звёзд, которые для наблюдателя составляют Млечный Путь, такое название носит и наша галактика Млечный Путь, или Галактика.

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