The Galactic evolution of phosphorus Caffau, E.; Bonifacio, P.; Faraggiana, R. ...
Astronomy and astrophysics (Berlin),
08/2011, Letnik:
532
Journal Article
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Context. As a galaxy evolves, its chemical composition changes and the abundance ratios of different elements are powerful probes of the underlying evolutionary processes. Phosphorous is an element ...whose evolution has remained quite elusive until now, because it is difficult to detect in cool stars. The infrared weak P i lines of the multiplet 1, at 1050−1082 nm, are the most reliable indicators of the presence of phosphorus. The availability of CRIRES at VLT has permitted access to this wavelength range in stellar spectra. Aims. We attempt to measure the phosphorus abundance of twenty cool stars in the Galactic disk. Methods. The spectra are analysed with one-dimensional model-atmospheres computed in local thermodynamic equilibrium (LTE). The line formation computations are performed assuming LTE. Results. The ratio of phosphorus to iron behaves similarly to sulphur, increasing towards lower metallicity stars. Its ratio with respect to sulphur is roughly constant and slightly larger than solar, P/S = 0.10 ± 0.10. Conclusions. We succeed in taking an important step towards the understanding of the chemical evolution of phosphorus in the Galaxy. However, the observed rise in the P/Fe abundance ratio is steeper than predicted by Galactic chemical evolution model developed by Kobayashi and collaborators. Phosphorus appears to evolve differently from the light odd-Z elements sodium and aluminium. The constant value of P/S with metallicity implies that P production is insensitive to the neutron excess, thus processes other than neutron captures operate. We suggest that proton captures on 30Si and α captures on 27Al are possibilities to investigate. We see no clear distinction between our results for stars with planets and stars without any detected planet.
Context. The analysis of the solar spectra using hydrodynamical simulations, with a specific selection of lines, atomic data, and method for computing deviations from local thermodynamical ...equilibrium, has led to a downward revision of the solar metallicity, Z. We are using the latest simulations computed with the CO5BOLD code to reassess the solar chemical composition. Our previous analyses of the key elements, oxygen and nitrogen, have not confirmed any extreme downward revision of Z, as derived in other works based on hydrodynamical models. Aims: We determine the solar photospheric carbon abundance with a radiation-hydrodynamical CO5BOLD model and compute the departures from local thermodynamical equilibrium by using the Kiel code. Methods: We measured equivalent widths of atomic C I lines on high-resolution, high signal-to-noise ratio solar atlases of disc-centre intensity and integrated disc flux. These equivalent widths were analysed with our latest solar 3D hydrodynamical simulation computed with CO5BOLD. Deviations from local thermodynamic equilibrium we computed in 1D with the Kiel code, using the average temperature structure of the hydrodynamical simulation as a background model. Results: Our recommended value for the solar carbon abundance relies on 98 independent measurements of observed lines and is A(C)=8.50 ± 0.06. The quoted error is the sum of statistical and systematic errors. Combined with our recent results for the solar oxygen and nitrogen abundances, this implies a solar metallicity of Z = 0.0154 and Z/X = 0.0211. Conclusions: Our analysis implies a solar carbon abundance that is about 0.1 dex higher than what was found in previous analyses based on different 3D hydrodynamical computations. The difference is partly driven by our equivalent width measurements (we measure, on average, larger equivalent widths than the other work based on a 3D model), in part because of the different properties of the hydrodynamical simulations and the spectrum synthesis code. The solar metallicity we obtain from the CO5BOLD analyses is in slightly better agreement with the constraints of helioseismology than the previous 3D abundance results.
Sulphur abundance in Galactic stars Caffau, E.; Bonifacio, P.; Faraggiana, R. ...
Astronomy and astrophysics (Berlin),
10/2005, Letnik:
441, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We investigate sulphur abundance in 74 Galactic stars by using high resolution spectra obtained at ESO VLT and NTT telescopes. For the first time the abundances are derived, where possible, from ...three optical multiplets: Mult. 1, 6, and 8. By combining our own measurements with data in the literature we assemble a sample of 253 stars in the metallicity range $\rm -3.2 \la Fe/H \la +0.5$. Two important features, which could hardly be detected in smaller samples, are obvious from this large sample: 1) a sizeable scatter in S/Fe ratios around Fe/H$\sim -1; 2$) at low metallicities we observe stars with S/Fe$\sim 0.4$, as well as stars with higher S/Fe ratios. The latter do not seem to be kinematically different from the former ones. Whether the latter finding stems from a distinct population of metal-poor stars or simply from an increased scatter in sulphur abundances remains an open question.
Rotational velocities of A-type stars Royer, F.; Gerbaldi, M.; Faraggiana, R. ...
Astronomy and astrophysics (Berlin),
01/2002, Letnik:
381, Številka:
1
Journal Article
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Within the scope of a Key Programme determining fundamental parameters of stars observed by HIPPARCOS, spectra of 525 B8 to F2-type stars brighter than V=8 have been collected at ESO. Fourier ...transforms of several line profiles in the range 4200-4500 Å are used to derive v sin i from the frequency of the first zero. Statistical analysis of the sample indicates that measurement error is a function of v sin i and this relative error of the rotational velocity is found to be about 6% on average. The results obtained are compared with data from the literature. There is a systematic shift from standard values from \citet{Slk_75}, which are 10 to 12% lower than our findings. Comparisons with other independent v sin i values tend to prove that those from Slettebak et al. are underestimated. This effect is attributed to the presence of binaries in the standard sample of Slettebak et al., and to the model atmosphere they used. Based on observations made at the European Southern Observatory (ESO), La Silla, Chile, in the framework of the Key Programme 5-004-43K. Table 4 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or via cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/105
UV flux distributions of γ Doradus stars Gerbaldi, M.; Faraggiana, R.; Caffau, E.
Astronomy and astrophysics (Berlin),
09/2007, Letnik:
472, Številka:
1
Journal Article
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Context.It seems that the recently identified class of pulsating stars, the γ Dor type-variables, includes objects with different metal abundances and a large percentage of binaries. Aims.We looked ...for indicators of metal abundance peculiarities and stellar binarity in a sample of 40 confirmed γ Dor stars. Methods.Absolute magnitudes from Hipparcos parallaxes and UV magnitudes, from the S2/S68 experiment on board the TD1 satellite, are retrieved from databases and compared with predicted values. A set of non variable normal stars is used to check the consistency of this analysis and also serve as reference stars. Results.Twenty-nine stars of the γ Dor star sample, which is 73% of it, are discovered having abnormal UV fluxes constantly showing UV flux excesses compared to those computed with the atmospheric parameters (Teff , log g, and metallicity) determined from calibration of the $uvby{\beta}$ indices. The reason for this UV excess of flux at 196.5 nm and at 236.5 nm, which was previously known only for HD 209295, cannot be ascribed to binarity alone. An extra source of UV flux or less UV absorption – yet unknown – must be present.
The heterogeneous class of λ Bootis stars Gerbaldi, M.; Faraggiana, R.; Lai, O.
Astronomy and astrophysics (Berlin),
12/2003, Letnik:
412, Številka:
2
Journal Article
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We demonstrate that it is arduous to define the λ Boo stars as a class of objects exhibiting uniform abundance peculiarities which would be generated by a mechanism altering the structure of their ...atmospheric layers. We collected the stars classified as λ Boo up to now and discuss their properties, in particular the important percentage of confirmed binaries producing composite spectra (including our adaptive optics observations) and of misclassified objects. The unexplained RV variables (and thus suspected binaries), the known SB for which we lack information on the companion, the stars with an UV flux inconsistent with their classification, and the fast rotating stars for which no accurate abundance analysis can be performed, are also reviewed.
The selective abundance of C, N, O (almost solar) with respect to that of other elements (underabundant) in lambda Boo stars has been interpreted as a characteristic peculiarity of these objects, ...when considered as single stars. We show here that a similar selective abundance is predicted from the composite spectra resulting from two unresolved stars in the same temperature range as the lambda Boo stars.
Sulphur abundances in Terzan 7 Caffau, E.; Bonifacio, P.; Faraggiana, R. ...
Astronomy and astrophysics (Berlin),
06/2005, Letnik:
436, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present here the first measurements of sulphur abundances in extragalactic stars. We make use of high resolution spectra, obtained with UVES at the ESO 8.2 m Kueyen telescope, of three giants of ...the Globular Cluster Terzan 7, which belongs to the Sagittarius dwarf galaxy. We measure the sulphur abundances using the lines of $\ion{S}{i}$ multiplet 1. The S/Fe ratios for all three stars are nearly solar, thus considerably lower than what is found in Galactic stars of comparable iron content $({\rm Fe/H} \sim -0.50$). This finding is in keeping with the abundances of other α-chain elements in this cluster and in Sagittarius and other dSphs in general. These low α-chain elements to iron ratios suggest that Sagittarius and its Globular Clusters have experienced a low or bursting star-formation rate. Our sulphur abundances imply $\langle \log ({\rm S/O})\rangle = -1.61$ which is comparable to what is found in many $\ion{H}{ii}$ regions of similar oxygen content, and is slightly lower than the solar value ($\log ({\rm S/O})_{\odot} = -1.51$). These are also the first measurements of sulphur abundances in a Globular Cluster, thus a direct comparison of Terzan 7 and Galactic Globular Clusters is not possible yet. However our analysis suggests that the lines of $\ion{S}{i}$ multiplet 1 should be measurable for other Globular Clusters at least down to a metallicity ~–1.5.
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