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ABSTRACT: We determine lithium abundances in atmospheres of three carbon stars from synthetic spectrum fitting in the λλ 668–674 nm
range using the Li I λ 670.8 nm resonance doublet. To produce synthetic spectra, we use a modified list of atomic lines from
the VALD database and three alternative line lists of CN and C2 molecules which are modifications of line lists from the Jorgensen’s website (http://stella.nbi.dk) and from the Kurucz database (1993, CD-ROM nos. 1–23). The spectral lines from these lists were tested by matching synthetic
spectra to observed spectra of the sun, Arcturus, and early R star HD 100764. We perform analysis of the blends involving
the Li I λ 670.8 nm doublet in spectra of N stars AW Cyg and UX Dra. The lithium abundances in HD 100764, AW Cyg, and UX Dra
are estimated to be lgN(Li) ≈ 2, −1.4, and −0.9, respectively. Discrepancies of lithium abundances lgN(Li) obtained with the help of molecular line lists do not seem to exceed 0.2 dex.
Kinematics and Physics of Celestial Bodies 04/2012; 27(5):233-248. · 0.36 Impact Factor
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ABSTRACT: We have derived the atmospheric parameters of the R CrB carbon star DY Per. The spectrum of DY Per near its maximum brightness
was obtained using the 2.6-m ZTSh telescope of the Crimean Astrophysical Observatory, and has a resolution of about 1.74 Å
per pixel. We compare the absolute observed and theoretical spectral energy distributions (SEDs) of DY Per for λλ 430–730
nm for the first time. The model atmospheres were computed using a code written by Ya.V. Pavlenko in the classical approximation,
taking into account the main opacity sources in carbon-star atmospheres. The theoretical SEDs were computed using the list
of atomic lines from the VALD database and the molecular line lists from CD-ROM No. 18 of Kurucz’s database. The estimated
by spectral synthesis effective temperature of DY Per is in the range of 2900–3100 K, if we assume log g = 0. We find a metal deficiency in the atmosphere of DY Per. Quantitative estimates of the overall metallicity, carbon and
nitrogen abundances, and the H/He ratio are somewhat uncertain: −2 ≤ [Fe/H] ≤ −0.5, 0.65 ≤ [C/Fe] ≤ 1.35, 0.0 ≤ [N/Fe] ≤ 0.8,
1/9 ≤ H/He ≤ 9/1. These high H/He values do not quite agree with qualitative observational estimates made by other authors.
Our results confirm that DY Per is a unique stellar object. This is the coolest and possibly the most metal-poor of all known
R CrB stars. We conclude that the large deficiencies of metals and hydrogen lead to [C/Fe] values in the atmosphere of DY
Per characteristic of R CrB stars.
Astronomy Reports 04/2012; 53(3):187-202. · 0.73 Impact Factor
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ABSTRACT: We calculated 240 model atmospheres of carbon giants with high carbon abundance (2800 K ≤ T
eff ≤ 3400 K, 0.06 ≤ log(C/O) ≤ 2.7). This set of models was used for modelling of the energy distribution in the spectrum of
an evolved carbon star DY Per demonstrating photometric features of the R CrB type stars. Most of the models are metal-poor
(−3.5 ≤ [Fe/H] < 0) and a portion of them was calculated with the hydrogen deficiency (1/9 ≤ H/He < 9/1). The calculations
of the models were carried out taking into account specific for carbon stars sources of opacity in the frame of the classic
approaches. The opacity sampling method was used to calculate the opacity due to the atomic and molecular line absorption.
Kinematics and Physics of Celestial Bodies 04/2012; 25(6):302-308. · 0.36 Impact Factor
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ABSTRACT: We analyse the spectral energy distribution of the evolved carbon giant DY Per with a spectral synthesis technique. The red giant shows the photometric features of R CrB type stars. We derive the atmospheric parameters of DY Per using three variants of molecular line lists. We estimate Teff to be in the range 2900 < Teff < 3300 K. We adopted log g = 0. The star may be metal deficient and hydrogen deficient. The maximum possible carbon abundance in the star, [C]=0.94, provides the following atmospheric parameters: Tef=3100 K, [Fe/H] = 0, log(C/O)=0.6, [N/Fe] = 0, [H/He] = 0, with Jorgensen's line lists for the molecules C2 and CN. Comment: 4 pages, 2 tables, 3 figs, accepted by Odessa asronomical observatory Publ., 2009
05/2009;
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ABSTRACT: We present the results of modelling the 0.45--1 micron spectral energy distribution of V838 Mon for 2002 November. Synthetic spectra were calculated using the NextGen model atmospheres of Hauschildt et al. (1999), which incorporate line lists for H2O, TiO, CrH, FeH, CO, and MgH, as well as the VALD atomic line list. Fits to the observed spectra show that, in 2002 November, the effective temperature of V838 Mon was approximately 2000 +/-100 K. Our theoretical spectra show a comparatively weak dependence on log g. Preliminary analysis of the hot star observed together with V838 Mon shows it to be a normal B3V dwarf. Comment: 7 pages, 4 figs, accepted by A&A
09/2006;
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ABSTRACT: We present the results of our analysis of a high resolution (R ~ 30000) infrared spectrum of V4334 Sgr (Sakurai's Object) around the first overtone CO bands, obtained in 1998 July. The 12CO and 13CO bands are well-resolved, and we compute synthetic hydrogen-deficient model atmosphere spectra to determine the 12C/13C ratio. We find 12C/13C ~ 4 +/-1, consistent with the interpretation of V4334 Sgr as an object that has undergone a very late thermal pulse. Comment: 5 pages, 7 figs, accepted by AAL
02/2004;
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ABSTRACT: Theoretical spectral energy distributions for Sakurai's object at 300–1000 nm are derived. A model-atmosphere grid with T
eff=5000–6250 K and logg=0.0–1.0 is computed for the chemical composition of Sakurai's object using opacity sampling including molecular and atomic
absorption. Opacity due to absorption in 20 band systems of diatomic molecules is computed using the JOLA technique. The theoretical
fluxes are compared with the observed energy distribution in a spectrum of Sakurai's object taken in April 1997. It is shown
that (a) the theoretical energy distributions agree well qualitatively with the observed spectrum and depend strongly on the
effective temperature; (b) C2 and CN molecular bands are dominant in the visible and near-infrared spectrum, while atomic absorption is important at UV
and blue wavelengths; and (c) comparison of the observed and computed spectra yields an effective temperature for Sakurai's
object in April 1997 T
eff≈5250–5500 K. The dependence of the computed spectra at 300–1000 nm on the input parameters and adopted approximations is
also discussed.
Astronomy Reports 01/2000; 44(4):209-218. · 0.73 Impact Factor
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ABSTRACT: Theoretical spectral energy distributions were computed for a grid of hydrogen-deficient and carbon-rich model atmospheres of T(eff) in the range of 5000-6250 K and log g = 1.0 - 0.0 by the technique of opacity sampling, taking into account continuous, molecular band and atomic line absorption. These energy distributions were compared with the spectrum of V4334 Sgr (Sakurai's object) of April, 1997 in the wavelength interval 300-1000 nm. We show that (1) the shape of the theoretical spectra depends strongly on T(eff) but only very weakly on the hydrogen abundance; (2) the comparison of the observed and computed spectra permits to estimate T(eff) approximately 5500 K for V4334 Sgr in April, 1997, and its interstellar reddening (plus a possible circumstellar contribution) E(B-V) approximately 0.70. Comment: 7 pages, 8 figures, LaTeX, accepted by Astronomy and Astrophysics
12/1999;
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Astrophysics 01/1983; 19. · 0.47 Impact Factor
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ABSTRACT: We compute opacities for the electronic molecular band systems A{^6}\sum{^+}-\times{^6}\sum{^+} of CrH and CrD, and A{^2}\prod-\times{^2}\sum{^+} of MgH and MgD. The opacities are computed by making use of existing spectroscopic constants for MgH and CrH. These constants are adjusted for the different reduced masses of MgD and CrD. Frank-Condon factors are used to provide intensities for the individual vibronic bands. These results are used in the computation of synthetic spectra between T{_e_f_f}= 1800 and 1200 K with an emphasis on the realization of `deuterium test', first proposed by Bejar et al. to distinguish brown dwarfs from planetary mass objects. We discuss the possible use of CrD and MgD electronic bands for the `deuterium test'. We find CrD to be the more promising of the two deuterides, potentially, the most useful bands of CrH/CrD are the \bigtriangleup v=+1 and \bigtriangleup v=-1 at 0.795 and 0.968 μm.
Pavlenko, Y.V. and Harris, G.J. and Tennyson, J. and Jones, H.R.A. and Brown, J.M. and Hill, C. and Yakovina, L.A. (2008) The electronic bands of CrD, CrH, MgD and MgH: application to the ‘deuterium test’. Monthly Notices of the Royal Astronomical Society, 386 (3). pp. 1338-1346. ISSN 00358711.
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81:564.
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ABSTRACT: We present the results of our analysis of a high resolution ($R\simeq30\,000$) infrared spectrum of V4334 Sgr (Sakurai's Object) around the first overtone CO bands, obtained in 1998 July. The $^{12}$CO and $^{13}$CO bands are well-resolved, and we compute synthetic hydrogen-deficient model atmosphere spectra to determine the $^{12}$C/$^{13}$C ratio. We find $^{12}$C/$^{13}$C $\simeq$ $4$ $\pm$ $1$, consistent with the interpretation of V4334 Sgr as an object that has undergone a very late thermal pulse.
http://dx.doi.org/10.1051/0004-6361:20040078.
