Drake, N

Gopka, V F

Lambert, D L

Rostopchin, S

Yushchenko, A

CERN Document Server

PoS(NIC-IX)105Heaviest s-process elements in the atmospheres ofbarium stars HD204075 and HD101013Vera Gopka∗Astronomical observatory, Odessa National University, 65014, Odessa, UkraineE-mail: gopkavera@mail.ruAlexander YushchenkoAstrophysical Research Center for the Structure and Evolution of the Cosmos, Sejong University,143-747, Seoul, KoreaE-mail: yua@sejong.ac.krDavid LambertThe W.J. McDonald Observatory, University of Texas, Austin, TX 78712, USAE-mail: dll@gandhi.as.utexas.eduNatalia Drake†Observatorio Nacional, Rio de Janeiro, BrazilE-mail: drake@on.brSergey Rostopchin‡The W.J. McDonald Observatory, University of Texas, Austin, TX 78712, USAE-mail: sir@astro.as.utexas.eduThe detailed chemical abundance patterns of barium stars HD204075 and HD101013 are usedfor investigations of heaviest s-process elements. Special attention is devoted to elements withZ>70, up to Pb. Spectrum synthesis method is used for abundance calculations. High resolu-tion spectra were obtained at 2.7 meter telescope of McDonald observatory (spectral resolutionR=60,000, signal to noise ratio S/N>400) and VLT (R=80,000, S/N>400). CNO and Fe abun-dances are found for HD204075 and HD101013. Heavy (Z≥64) elements abundances are foundfor HD204075. The results of previous investigations of HD204075 and our data is in good aggre-ment with s-process enriched pattern. Our estimates show that the abundances of Z≥64 elementsin HD101013 are significantly higher than in HD204075.International Symposium on Nuclear Astrophysics — Nuclei in the Cosmos — IXJune 25-30 2006CERN, Geneva, Switzerland∗Speaker.†Sobolev Astronomical Institute, St. Petersburg State University, St. Petersburg, Russia‡Crimean Astrophysical Observatoty, Nauchny, Crimea, 98409, Ukrainec© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/PoS(NIC-IX)105Heaviest s-process elements in the atmospheres of barium stars HD204075 and HD101013 Vera Gopka1. IntroductionThe majority of Ba-stars have luminosities of normal giants, it is possible to point the stars ofthis type in a large range in luminosity from class IV-V to class Ib.The most widely-accepted hypothesis is that the overabundances of heavy elements in theatmospheres of barium stars were produced by the accretion of matter ejected from their formerAGB companions. These AGB companions have quickly evolved to be white dwarfs and can notbe easily detected now.This paper is devoted to investigation of two barium stars, and HD204075 (ζ Cap, G9Ib)and HD101013 (G9III). The stars were investigated in many papers, [8, 13] can be pointed as anexamples. The most recent investigations of chemical composition of these objects were made byAntipova et al. [3, 4]. The abundances of 29 elements from Na to Dy and of 25 elements from Cto Eu were found for HD101013 and HD204075 respectively.We used abundance patterns, found in [3, 4] as the first approximation and tried to investigateLi, CNO, Fe and elements with Z≥64 in the atmospheres of these stars. We found the abundancesof 16 elements with Z≥64 in the atmospheres of HD204075 and estimated that these elements aremore abundant in HD101013 in comparison with HD204075. In the following sections we willdescribe the determination of atmosphere parameters, abundances of Li, CNO, Fe, Tc, and heavy(Z≥64) elements. Comparison of abundance pattern of HD204075 with theoretical predictionsis made in the final section. Detailed abundance pattern for barium stars in this range of atomicnumbers is known only for prototype of mild barium stars HD202109 [12].2. Observations and atmosphere modelsSpectrum of HD101013 was obtained at 2.7 meter telescope of McDonald observatory. Spec-tral resolving power was R=60,000, signal to noise ratio is near S/N=400 in red region and nearS/N=150 at wavelength λ=4000 . Wavelength coverage is from 3520 to 10211 Å. For HD204075we used the spectrum observed at VLT [5] in the wavelength range from 3040 to 10400 Å, S/N≥300in red part of the spectrum and S/N near 100 at λ=3050 Å. Resolving power was pointed by [5] tobe equal R=80,000.To find atmosphere parameters we used the method of calculating the iron abundance for dif-ferent atmosphere models. Details can be found in [12]. The grid of atmosphere models wereinterpolated from Kurucz ATLAS9 grid. We tried to find models where correlations of iron abun-dances vs equivalent widths and energies of low levels of iron lines were forced to zero. Additionalrequirements were the minimal error of iron abundance, zero difference of neutral and ionizediron abundances, and zero correlation of iron abundances with wavelength. Several iterations weremade for each star.For HD101013 we found effective temperature Teff=4930 K, surface gravity log g=2.74, mi-croturbulent velocity vmicro=1.56 km s−1, and iron abundance logN(Fe)=7.33 in the scale logN(H)=12.This abundance scale will be used here after. 119 lines of neutral iron and 19 lines of ionized ironwere used for calculation.The result for HD204075 is Teff=5260 K, log g=1.72, vmicro=2.55 km s−1, logN(Fe)=7.31. 106lines of Fe I and 31 lines of Fe II were used.2PoS(NIC-IX)105Heaviest s-process elements in the atmospheres of barium stars HD204075 and HD101013 Vera GopkaFigure 1: Spectra of HD204075 and HD101013 in the vicinity of Pb I line 4057.806 Å. Axes are wavelengthin angstroms and relative fluxes. Open squares – observed spectrum of HD204075 (VLT spectrum). Filledsquares – observed spectrum of HD101013 (McDonald observatory 2.7 m telescope). Curve – syntheticspectrum of HD101013. The strongest lines in synthetic spectrum are marked in the bottom part of the plot.Position of Pb line is pointed by vertical dotted line.3. Abundance determinationsSpectrum synthesis was used to find the abundances of all elements except iron. See [12] forfull description of used programs and line lists.3.1 Li and CNOCNO elements strongly influence the appearance of the spectrum. To find the abundances ofthese elements atomic and molecular lines, mainly in red spectral region, were used. After severaliterations we found the following abundances:HD101013 – logN(Li)<0.4, logN(C)=8.54, C12/C13=16, logN(N)=8.20, logN(O)=8.75;HD204075 – logN(C)=8.7, C12/C13>20, logN(N)=8.1, logN(O)=8.43.These values were used for calculations of abundances of heavier elements. Our results are ingood agreement with previous determinations of Li abundance in barium stars [9].3.2 TechnetiumWe used the list of oscillator strengths of lines of neutral and ionized technetium published in3PoS(NIC-IX)105Heaviest s-process elements in the atmospheres of barium stars HD204075 and HD101013 Vera GopkaTable 1: Abundances of heavy elements in HD204075HD204075n ∆logN logN64 Gd I 8 0.74(21) 1.8666 Dy II 10 0.09(27) 1.2367 Ho I 2 −0.10(19) 0.1668 Er II 20 0.11(24) 1.0469 Tm II 4 −0.01(25) −0.0170 Yb I 2 −0.03(16) 1.05Yb II 1 −0.43 0.6571 Lu II 2 0.72(21) 0.7872 Hf II 9 0.28(23) 1.1674 W I 2 0.83(17) 1.9476 Os I 4 0.53(21) 1.9877 Ir I 3 −0.10(29) 1.2578 Pt I 1 0.00 1.8081 Tl I 1 0.80 1.7082 Pb I 3 −0.47(28) 1.48[6, 2, 11] and other papers. There were no signs of Tc in HD101013, but we detected the possible Tclines in the spectrum of HD204075. Four lines of neutral technetium, namely 3726.345, 4124.217,4262.270, and 5924.468 Å, and one line of Tc II (3195.21 Å) permit to calculate the upper limitsof abundances 1.7, 2.2, 1.5, 2.0, 1.5 respectively. Similar limit (1.6) was found by [7]. [10] alsoreported the absence of Tc lines using IUE spectra.3.3 Heavy elementsFor all lines of heavy elements we tried to find the counterparts in the solar spectrum. Theseprocedure is usually accepted to avoid the uncertainties in oscillator strengths. But it was impossi-ble to find the corresponding features in the solar spectrum for majority of the lines. That is whyour analysis is based mainly on absolute values of oscillator strengths. The values of abundancesfor HD204075 can be found in Table 1. The columns are the atomic number and identificationof the element (ion), the number of used lines and mean abundance with final figures of error inbrackets. There are relative (with respect to solar values [1]) and absolute abundances. Errors arepointed only for relative abundances. It should be mentioned that the majority of lines of theseelements are located in the blue and near ultraviolet part of the spectrum and derived abundancesare strongly affected by continuum placement.Our preliminary results for HD101013 show that the abundances of heavy elements in this starcan be higher than in HD204075. As an example we compare the spectra of both stars in Fig. 1. Itis evident, that the lead line λ 4057.806 Å in the spectrum of HD101013 is significantly strongerthan in the spectrum of HD204075.These results can be treated as preliminary values for detailed analysis of chemical composi-tion of the stars.4PoS(NIC-IX)105Heaviest s-process elements in the atmospheres of barium stars HD204075 and HD101013 Vera GopkaFigure 2: Abundance pattern of HD204075. Axes are atomic numbers and abundances with respect to iron.Antipova et al. [4] data are marked by circles, our values – by crosses. Line – s-process enriched matter.The curve is taken from [12] and scaled by factor 3.0.4. ConclusionFigure 2 shows the abundance patterns of HD204075. The extremums of abundance curvescan be fitted by scaled s-process enriched pattern taken from [12]. This pattern was calculatedfor wind accretion scenario. The abundances of the heaviest s-process elements in HD101013 arehigher than that in HD204075, this result is preliminary and needs additional investigation. Specialattention was devoted to technetium, the lines of this element in HD204075 can exist.The results of this paper will be used as the first approximation to find the homogeneousabundance patterns, to compare it with previous investigations and with theoretical predictions.References[1] N. Grevesse, A.J. Sauval Standard solar composition Space Science reviews 85 (1998) 161[2] S.M. Andrievsky, L.V. Chernysheva, D.N. Doikov, A.V. Yushchenko, Oscillator strengths andphotoionization cross sections for Tc I and Tc II, in Molecular Opacities in the Stellar Environment.IAU Colloq. 146, ed. P. Thejll, & U.G. Jorgensen, 1994, (Poster session, p. 9)[3] L.I. Antipova, A.A. Boyarchuk, Yu.V. Pakhomov, & V.E. Panchuk Studies of classical barium stars,Astronomy Reports 47 (2003) 648[4] L.I. Antipova, A.A. Boyarchuk, Yu.V. Pakhomov, & V.E. Panchuk Analysis of atmosphericabundances in classical barium stars , Astronomy Reports 48 (2004) 6585PoS(NIC-IX)105Heaviest s-process elements in the atmospheres of barium stars HD204075 and HD101013 Vera Gopka[5] S. Bagnulo, E. Jehin, C. Ledoux, R. Cabanac, C. Melo, R. Gilmozzi, and the ESO Paranal ScienceOperations Team, A Library of High-Resolution Spectra of Stars across the Hertzsprung-RussellDiagram, htt p : //www.sc.eso.org/santiago/uvespop/index.html, 2002[6] A.S. Bakhtiyarov, The theoretical calculations of the energy spectrum and the oscillator strengths ofTc II, Astrofizica 29 (1988) 625[7] A.M. Boesgaard, & R.A. Fesen A search for technetium in the Ba II star ζ Capricorni, Publ. Astron.Soc. Pacific 86 (1974) 76[8] M.J. Harris, D.L. Lambert, V.V. Smith Oxygen isotopic abundances in evolved stars. I. Six bariumstars Astrophys. J. 292 (1985) 620[9] D.L. Lambert, V.V. Smith, J. Heath Lithium in barium stars Publ. Astron. Soc. Pacific 105 (1993) 568[10] I.R. Little-Marenin, S.J. Little, A search for technetium (Tc II) in barium stars, Astronomical J. 93(1987) 1539[11] P. Palmeri, C.F. Fisher, J.F. Wyart J.F., M.R. Godefroid, Oscillator strength calculations in neutraltechnetium, Mon. Not. Royal Astron. Soc.363 (2005) 452[12] A.V. Yushchenko, V.F. Gopka, C. Kim, Y.C. Liang, F.A. Musaev, & G.A. Galazutdinov, The chemicalcomposition of the mild barium star HD202109, Astron. Astrophys.413 (2004) 1105[13] L. 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Heaviest s-process elements in the atmospheres of barium stars

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