152 research outputs found

    Analysis of first overtone bands of isotopologues of CO and SiO in stellar spectra

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    The first overtone (Δv\Delta v = 2) bands of the monosubstituted isotopologues of CO at 2.3 μ\mum in the spectrum of Arcturus (K2 III), and of the monosubstituted isotopologues of SiO at 4 μ\mum in the spectrum of the red giant HD196610 (M6 III) are modelled. To investigate problems involving the computation of the first overtone bands of isotopologues of CO and SiO in spectra of late-type stars and to determine isotopic abundances. We use fits of theoretical synthetic spectra to the observed stellar molecular bands of CO and SiO to determine abundances of isotopes of C, O and Si. Fits of synthetic spectra of the \CO first overtone bands at 2.3 μ\mum computed with three available line lists (Goorvitch, HITEMP2010 and Li et al.) to the observed spectrum of Arcturus provide the same carbon abundance [C]=0.6-0.6 and isotopic ratio of carbon 12^{12}C/13^{13}C=10 ±\pm 2. However, the quality of fits to the observed spectrum differ for three line lists used. Furthermore, the derived oxygen isotopic ratio 16^{16}O/18^{18}O = 2000 ±\pm 500 is larger than that known in the solar system where 16^{16}O/18^{18}O = 500. The silicon isotopic ratio in the atmosphere of the red giant HD196610 is revised. Using the ExoMol SiO line list with appropriate statistical weights for the SiO isotopologues the `non-solar' ratio 28^{28}Si:29^{29}Si:30^{30}Si = 0.86±\pm0.03:0.12±\pm0.02:0.02±\pm0.01 is obtained. We found that a) the computed isotopic carbon and silicon ratios determined by the fits to the observed spectrum depend on the adopted abundance of C and Si, respectively; b) Correct treatment of the nuclear spin degeneracies parameter is of crucial importance for the use of nowadays HITRAN/ExoMol line lists in the astrophysical computations.Comment: 9 pages, 6 figures, accepted by A&

    Astronomy in Ukraine

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    The current and prospective status of astronomical research in Ukraine is discussed. A brief history of astronomical research in Ukraine is presented and the system organizing scientific activity is described, including astronomy education, institutions and staff, awarding higher degrees/titles, government involvement, budgetary investments and international cooperation. Individuals contributing significantly to the field of astronomy and their accomplishments are mentioned. Major astronomical facilities, their capabilities, and their instrumentation are described. In terms of the number of institutions and personnel engaged in astronomy, and of past accomplishments, Ukraine ranks among major nations of Europe. Current difficulties associated with political, economic and technological changes are addressed and goals for future research activities presented.Comment: Paper to be published in ``Organizations and Strategies in Astronomy'' -- Vol. 7, Ed. A. Heck, 2006, Springer, Dordrecht; 25 pages, 2 figs, 2 table

    Vsini-s for late-type stars from spectral synthesis in K-band region

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    We analyse medium-resolution spectra (R\sim 18000) of 19 late type dwarfs in order to determine vsini-s using synthetic rather than observational template spectra. For this purpose observational data around 2.2 μ\mum of stars with spectral classes from G8V to M9.5V were modelled. We find that the Na I (2.2062 and 2.2090 μ\mum) and 12^{12}CO 2-0 band features are modelled well enough to use for vsini determination without the need for a suitable observational template spectra. Within the limit of the resolution of our spectra, we use synthetic spectra templates to derive vsini values consistent with those derived in the optical regime using observed templates. We quantify the errors in our vsini determination due to incorrect choice of model parameters \Teff, log gg, vmicrov_{\rm micro}, [Fe/H] or FWHM and show that they are typically less than 10 per cent. We note that the spectral resolution of our data(\sim 16 km/s) limited this study to relatively fast rotators and that resolutions of 60000 will required to access most late-type dwarfs.Comment: 8 pages, 4 figures, 3 tables, accepted to the MNRA