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ASTRONOMY and ASTROPHYSICS Chemical Analysis of 8 Recently View metadata,A&A citation manuscript and similar no.papers at core.ac.uk ASTRONOMYbrought to you by CORE (will be inserted by hand later) ANDprovided by CERN Document Server Your thesaurus codes are: ASTROPHYSICS 06(08.01.1; 08.03.02; 08.16.2) September 14, 2000 Chemical analysis of 8 recently discovered extra-solar planet host stars? N.C. Santos1, G. Israelian2, and M. Mayor1 1 Observatoire de Gen`eve, 51 ch. des Maillettes, CH{1290 Sauverny, Switzerland 2 Instituto de Astrofisica de Canarias, E{38200 La Laguna, Tenerife, Spain Received / Accepted Abstract. We present the chemical analysis of a new set planets is increasing, this fact is becoming more and more of stars known to harbor low mass companions, namely sharp. HD 1237, HD 52265, HD 82943, HD 83443, HD 169830, and Recent work showed that the high metallicity of the HD 202206. In addition, we have also analyzed HD 13445 stars with giant planets cannot be the result of stellar and HD 75289, already studied elsewhere. The abundances population effects (Gonzalez 1999). Furthermore, Gonza- of C and α-elements O, S, Si, Ca and Ti are presented and lez & Laws (2000) add more evidence for chemical anoma- discussed in the context of the metallicity distribution of lies in stars with planetary companions. Their study sug- the stars with extra-solar planets. We compare the metal- gests that the anomalies not only involve the [Fe/H] in- licity distribution of stars with planets with the same dis- dex, but possibly also the ratios [Li/H], [C/H] and [N/H]. tribution of field dwarfs. The results further confirm that The observed correlations between the presence of planets stars with planets are over-abundant in [Fe/H]. and the existence of chemical anomalies represent the only known physical connection between their presence and a Key words: stars: abundances – stars: chemically pecu- stellar photospheric parameter, and their study is thus of liar – planetary systems major importance. In addition to the discovery of a planet around HD 1237 (Naef et al. 2000), the Geneva extra-solar planet search group recently announced the discovery of 8 new low- 1. Introduction mass companions to solar type stars (all with masses below 15 M 1). These new planets and brown-dwarfs are in- Before the discovery of the first extra-solar planet (Mayor ∼ Jup & Queloz 1995), the constraints on the planetary forma- cluded in a volume-limited sample of dwarfs (Udry et al. tion models were confined to the Solar System example. 2000). In this paper we present and discuss the abundance Today more than 40 extra-solar planetary systems are analysisoftheelementsC,O,S,Ca,Ti,Fe,andSiinthe known. These discoveries immediately opened new hori- new candidates, HD 1237, HD 52265, HD 82943, HD 83443, zons to this field, but also brought a bunch of new ques- HD 169830, and HD 202206. Planets have also been dis- tions and problems. In fact, the extra-solar planets found covered during the CORALIE survey around HD 13445 to date don’t have much in common with our own so- (Queloz et al. 2000) and HD 75289 (Udry et al. 2000). We lar system. Their physical characteristics were completely also present a spectroscopic analysis of these two stars, unexpected. Some of them, like the extreme proximity of already studied by Flynn & Morell (1997), and Gon- some of the new planets to their “mother” stars are sur- zalez & Laws (2000), respectively. The other three re- prising and still defy current formation models. A review cently announced candidates (HD 108147, HD 162020 and of the subject can be found in Marcy, Cochran & Mayor HD 168746) will be the subject of a future publication. (1999). One particular fact became evident soon after the first 2. Observations and data reduction extra-solar planets were discovered. The metallicity of the stars with planets proved to be distinctively different from The spectra were obtained during three separate runs, be- the one found in field single dwarfs, being very metal- tween January and April 2000, using the new 1.2-m Eu- rich (Gonzalez 1997, 1998). As the number of extra-solar ler Swiss telescope at La Silla (ESO), Chile, equipped with the CORALIE echelle spectrograph. The resolving Send offprint requests to: [email protected] power (λ/∆λ) of the spectrograph is about 50 000, and ? Based on observations collected at the La Silla Observatory, the spectra cover the visible spectrum between 3800 and ESO (Chile), with the echelle spectrograph CORALIE at the 1.2-m Euler Swiss telescope 1 www.eso.org/outreach/press{rel/pr{2000/pr{13{00.html 2 N.C. Santos et al.: Chemical analysis of 8 planetary host stars revised version of the line abundance code MOOG (Sne- den 1973), and a grid of Kurucz et al. (1993) ATLAS9 atmospheres. Atomic data for iron lines was taken from the list of Gonzalez & Laws (2000). This choice was done so that our results would be in the same scale with theirs. Since we could not obtain a Solar spectrum, we also used the gf-values listed by these authors. The line-lists for other elements were compiled from different authors, and semi-empirical gf-values were com- puted using equivalent widths obtained in the High Reso- lution Solar Atlas (Kurucz et al. 1984), and a solar model 1 with Teff = 5777 K, log g = 4.438 and ξt =1kms− .We decided to adopt a value of log (Fe) = 7.47 (the same used by Gonzalez & Laws 2000). For other elements, the values were taken from Anders & Grevesse (1989). Measured equivalent widths for the lines in the ob- served stars were determined by Gaussian fitting using the SPLOT task in IRAF. In Tables 1 and 2 we present the results, as well as the line parameters used (log gf and χl). Fig. 1. Two sample CORALIE spectra of the K0 dwarf HD 13445 (upper panel), and of the F8 dwarf HD 169830 (lower panel). 3.2. Stellar parameters and Abundances Stellar atmospheric parameters were computed using the ˚ 6800 A without gaps. The spectra have S/N ratios between standard technique based on the Fe ionization balance. about 150 and 350 (for the faintest objects we doubled We first adopted initial atmospheric parameters computed the exposures). In Fig. 1 we present two sample spectra from ubvy-photometry of Hauck & Mermilliod (1997) us- of HD 13445 and HD 169830. ing the calibrations of Olsen (1984) for Teff and log g, The reduction of the spectra was carried out using Schuster & Nissen (1989) for [Fe/H] and Edvardsson et standard tasks in the echelle package of IRAF2.The al. (1993) for ξt. Then, using the set of Fe i and Fe ii lines wavelength calibration was done using the spectrum of a presented in Table 1, we iterated until the correlation coef- Thorium-Argon lamp that was taken in the beginning of ficients between log (Fe i)andχl, and between log (Fe i) the night. and log (Wλ/λ) were zero (Fig. 2). The abundances de- After wavelength calibrated, the spectra were cor- rived from the Fe ii lines were forced to be equal to those rected for the radial-velocity Doppler shift using the ve- obtained from Fe i. The final atmospheric parameters, as locity computed in the context of the planet search pro- well as the resulting iron abundances, are summarized in gramme, and normalized using the CONTINUUM task in Table 3. IRAF. In this step we divided the spectra into 350 A˚ wide intervals, that were normalized separately using 3rd order Errors in the parameters were estimated in the same spline functions, and added together at the end. A visual way as in Gonzalez & Vanture (1998). The values were 1 inspection of the resulting spectra showed that the results rounded to 25 K in Teff, 0.05 dex in log g, and 0.05 km s− were quite satisfactory. in ξt. Uncertainties in the abundances of all elements were 3. Analysis then determined adding the errors due to the sensitivities of the resulting abundances to changes of the atmospheric 3.1. Spectrum Synthesis: Method parameters (see Table 4 for two examples), and the dis- persion of the abundances for the individual lines of each Abundance determination was done using a standard Lo- element. For elements with only one line measured, the cal Thermodynamic Equilibrium (LTE) analysis with a errors only take into account the sensitivities to the atmo- 2 IRAF is distributed by National Optical Astronomy Ob- spheric parameters. The dependence on ξt is always very servatories, operated by the Association of Universities for Re- small, and has no important implications in the final er- search in Astronomy, Inc., under contract with the National rors. The final abundance determinations and errors for Science Foundation, U.S.A. C, O, S, Ca, Ti i,Tiii, and Si are presented in Table 5. N.C. Santos et al.: Chemical analysis of 8 planetary host stars 3 Table 1. Fe i and Fe ii line parameters and measured equivalent widths. λ0 χl log gf HD 1237 HD 13445 HD 52265 HD 75289 HD 82943 HD 83443 HD 169830 HD 202206 Equivalent Widths (mA)˚ Fe i log =7:47 5044.21 2.85 2.04 101.7 95.4 74.7 78.1 83.1 102.9 66.9 91.6 5247.05 0.09 −4.93 104.2 86.4 71.3 73.2 69.8 104.3 53.1 82.5 5322.05 2.28 −2.86 80.1 69.0 62.1 65.0 65.2 94.0 51.5 75.1 5806.73 4.61 −0.90 70.7 55.0 59.9 61.9 64.2 84.7 50.1 75.2 5852.22 4.55 −1.18 58.4 44.4 44.6 49.1 52.0 66.2 35.9 57.5 5855.09 4.61 −1.52 33.0 22.3 25.2 28.5 29.4 42.8 20.2 35.1 5856.09 4.29 −1.56 48.2 34.5 36.9 41.3 41.7 59.1 29.6 47.5 6027.06 4.08 −1.09 79.3 65.7 69.3 73.9 76.8 89.0 64.5 82.7 6056.01 4.73 −0.40 94.6 77.7 78.8 83.0 83.9 102.5 71.7 94.8 6079.01 4.65 −1.02 67.4 45.9 50.3 55.2 55.9 73.0 42.9 67.0 6089.57 5.02 −0.86 48.7 36.8 34.9 41.2 41.8 61.0 31.5 51.3 6151.62 2.18 −3.29 70.2 59.7 46.4 50.0 55.0 74.1 37.0 64.1 6157.74
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