We determine the metallicity distribution function (MDF) of the Galactic halo by means of a sample of 1638 metal-poor stars selected from the Hamburg/ESO objective-prism survey (HES). The sample was ...corrected for minor biases introduced by the strategy for spectroscopic follow-up observations of the metal-poor candidates, namely "best and brightest stars first". Comparison of the metallicities Fe/H of the stars determined from moderate-resolution (i.e., R similar to 2000) follow-up spectra with results derived from abundance analyses based on high-resolution spectra (i.e., R > 20 000) shows that the Fe/H estimates used for the determination of the halo MDF are accurate to within 0.3 dex, once highly C-rich stars are eliminated. We determined the selection function of the HES, which must be taken into account for a proper comparison between the HES MDF with MDFs of other stellar populations or those predicted by models of Galactic chemical evolution. The latter show a reasonable agreement with the overall shape of the HES MDF for Fe/H > -3.6, but only a model of Salvadori et al. (2007) with a critical metallicity for low-mass star formation of Z(cr) = 10(-3.4) Z(circle dot) reproduces the sharp drop at Fe/H similar to -3.6 present in the HES MDF. Although currently about ten stars at Fe/H < -3.6 are known, the evidence for the existence of a tail of the halo MDF extending to Fe/H similar to -5.5 is weak from the sample considered in this paper, because it only includes two stars Fe/H < -3.6. Therefore, a comparison with theoretical models has to await larger statistically complete and unbiased samples. A comparison of the MDF of Galactic globular clusters and of dSph satellites to the Galaxy shows qualitative agreement with the halo MDF, derived from the HES, once the selection function of the latter is included. However, statistical tests show that the differences between these are still highly significant.
High-resolution spectra of six giants and three core-helium-burning “clump” stars in the open cluster NGC 7789 have been obtained with the SOFIN spectrograph on the Nordic Optical Telescope to ...investigate abundances of up to 20 chemical elements. Abundances of carbon were studied using the ${\rm C}_2$ Swan (0, 1) band head at 5635.5 Å. The wavelength interval 7980–8130 Å with strong CN features was analysed in order to determine nitrogen abundances and $^{12}{\rm C}/^{13}{\rm C}$ isotope ratios. The oxygen abundances were determined from the O I line at 6300 Å. The overall metallicity of evolved stars in the cluster was found to be close to solar ($\rm Fe/H=-0.04\pm0.05$). Compared with the Sun and other dwarf stars of the Galactic disk, mean abundances in the investigated giant stars suggest that carbon is depleted by about 0.2 dex, and nitrogen and oxygen are close to solar. In the clump stars investigated, carbon is depleted by about 0.2 dex, the mean abundance of nitrogen is enhanced by 0.26 dex and oxygen is lower by 0.14 dex. This has the effect of lowering the mean C/N ratios to the value of $1.9\pm0.5$ in the giant stars and to the value of $1.3\pm0.2$ in the clump stars. The mean $^{12}{\rm C}/^{13}{\rm C}$ ratios are lowered to about the same value of $9\pm1$ in the giants and clump stars investigated. Concerning other chemical elements an overabundance of sodium is noticeable and of silicon and calcium one is suspected. Abundances of iron-group and heavier chemical elements in all nine stars were found to be close to solar.
Chemical abundances in 43 metal-poor stars Jonsell, K.; Edvardsson, B.; Gustafsson, B. ...
Astronomy and astrophysics (Berlin),
09/2005, Letnik:
440, Številka:
1
Journal Article, Web Resource
Recenzirano
Odprti dostop
We have derived abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe, Ni, and Ba for 43 metal-poor field stars in the solar neighbourhood, most of them subgiants or turn-off-point stars with iron ...abundances Fe/H ranging from -0.4 to -3.0. About half of this sample has not been spectroscopically analysed in detail before. Effective temperatures were estimated from uvby photometry, and surface gravities primarily from Hipparcos parallaxes. The analysis is differential relative to the Sun, and was carried out with plane-parallel MARCS models. Various sources of error are discussed and found to contribute a total error of about 0.1–0.2 dex for most elements, while relative abundances, such as Ca/Fe, are most probably more accurate. For the oxygen abundances, determined in an NLTE analysis of the 7774 Å triplet lines, the errors may be somewhat larger. We made a detailed comparison with similar studies and traced the reasons for the, in most cases, relatively small differences. Among the results we find that O/Fe possibly increases beyond Fe/H = –1.0, though considerably less so than in results obtained by others from abundances based on OH lines. We did not trace any tendency toward strong overionization of iron, and find the excesses, relative to Fe and the Sun, of the α elements Mg, Si, and Ca to be smaller than those of O. We discuss some indications that also the abundances of different α elements relative to Fe vary and the possibility that some of the scatter around the trends in abundances relative to iron may be real. This may support the idea that the formation of Halo stars occurred in smaller systems with different star formation rates. We verify the finding by Gratton et al. (2003b, A&A, 406, 131) that stars that do not participate in the rotation of the galactic disk show a lower mean and larger spread in α/Fe than stars participating in the general rotation. The latter stars also seem to show some correlation between α/Fe and rotation speed. We trace some stars with peculiar abundances, among these two Ba stars, HD 17072 and HD 196944, the second already known to be rich in s elements. Finally we advocate that a spectroscopic study of a larger sample of halo stars with well-defined selection criteria is very important, in order to add to the very considerable efforts that various groups have already made.
Context. The formation and evolution of the Milky Way bulge is not yet well understood and its classification is ambiguous. Constraints can, however, be obtained by studying the abundances of key ...elements in bulge stars. Aims. The aim of this study is to determine the chemical evolution of C, N, O, and a few other elements in stars in the Galactic bulge, and to discuss the sensitivities of the derived abundances from molecular lines. Methods. High-resolution, near-infrared spectra in the H band were recorded using the CRIRES spectrometer on the Very Large Telescope. Due to the high and variable visual extinction in the line-of-sight towards the bulge, an analysis in the near-IR is preferred. The C, N, and O abundances can all be determined simultaneously from the numerous molecular lines in the wavelength range observed. Results. The three giant stars in Baade's window presented here are the first bulge stars observed with CRIRES during its science verification observations. We have especially determined the C, N, and O abundances, with uncertainties of less than 0.20 dex, from CO, CN, and OH lines. Since the systematic uncertainties in the derived C, N, and O abundances due to uncertainties in the stellar fundamental parameters, notably T-eff, are significant, a detailed discussion of the sensitivities of the derived abundances is included. We find good agreement between near-IR and optically determined O, Ti, Fe, and Si abundances. Two of our stars show a solar C+N/Fe, suggesting that these giants have experienced the first dredge-up and that the oxygen abundance should reflect the original abundance of the giants. The two giants fit into the picture, in which there is no significant difference between the oxygen abundance in bulge and thick-disk stars. Our determination of the sulphur abundances is the first for bulge stars. The high S/Fe values for all the stars indicate a high star-formation rate in an early phase of the bulge evolution.
Context. In analyses of stellar spectra and colours, and for the analysis of integrated light from galaxies, a homogeneous grid of model atmospheres of late-type stars and corresponding flux spectra ...is needed. Aims. We construct an extensive grid of spherically-symmetric models (supplemented with plane-parallel ones for the highest surface gravities), built on up-to-date atomic and molecular data, and make it available for public use. Methods. The most recent version of the MARCS program is used. Results. We present a grid of about 104 model atmospheres for stars with 2500 K ≤ Teff ≤ 8000 K, -1 ≤ log g = log $(GM/R^2)$ ≤ 5 (cgs) with various masses and radii, -5 ≤ Me/H ≤ +1, with α/Fe = 0.0 and 0.4 and different choices of C and N abundances. This includes “CN-cycled” models with C/N = 4.07 (solar), 1.5 and 0.5, C/O ranging from 0.09 to (normally) 5.0 to also represent stars of spectral types R, S and N, and with 1.0 ≤ $\xi_{\rm t}$ ≤ 5 km s-1. We also list thermodynamic quantities (T, Pg, Pe, ρ , partial pressures of molecules, etc.) and provide them on the World Wide Web, as well as calculated fluxes in approximately 108 000 wavelength points. Underlying assumptions in addition to 1D stratification (spherical or plane-parallel) include hydrostatic equilibrium, mixing-length convection and local thermodynamic equilibrium. We discuss a number of general properties of the models, in particular in relation to the effects of changing abundances, of blanketing, and of sphericity. We illustrate positive and negative feedbacks between sphericity and molecular blanketing. We compare the models with those of other available grids and find excellent agreement with plane-parallel models of Castelli & Kurucz (if convection is treated consistently) within the overlapping parameter range. Although there are considerable departures from the spherically-symmetric NextGen models, the agreement with more recent PHOENIX models is gratifying. Conclusions. The models of the grid show considerable regularities, but some interesting departures from general patterns occur for the coolest models due to the molecular opacities. We have tested a number of approximate “rules of thumb” concerning effects of blanketing and sphericity and often found them to be astonishingly accurate. Some interesting new phenomena have been discovered and explored, such as the intricate coupling between blanketing and sphericity, and the strong effects of carbon enhancement on metal-poor models. We give further details of line absorption data for molecules, as well as details of models and comparisons with observations in subsequent papers.
This study investigated self-image and coping ability in a group of patients with symptoms from indoor environment. A follow-up questionnaire was sent to 239 patients previously referred with ...nonspecific building-related symptoms at University Hospital in Umeå, Sweden. One hundred seventy-four women and 14 men answered and the patient group rated their self-image as more spontaneous, more positive, and less negative than a control group. The patient group rated higher on the cognitive scale in the Coping Resources Inventory (CRI) than the control group. The female patients had an increased risk of not being able to work associated with a low score on negative self-image. The authors conclude that certain personality traits may be potential risk factors that increase the probability of encountering and experiencing stressful work situations. The resulting stress may increase workers' susceptibility to indoor environment exposure.
Objectives
The aim of this study was to describe and analyse the medical and social prognoses of patients with non-specific building-related symptoms.
Methods
A follow-up questionnaire focusing on ...current medical and social status, care, treatment, other actions taken and personality traits was sent to 239 patients with non-specific building-related symptoms assessed during the period between1986 and 1998 at University Hospital in Umeå, Sweden. The response rate was 79%.
Results
Fatigue, irritation of the eyes, and facial erythema were the most common weekly symptoms reported at follow-up. As females constituted 92% of the respondents, statistical analyses were restricted to women. The level and severity of symptoms decreased over time, although nearly half of the patients claimed that symptoms were more or less unchanged after 7 years or more, despite actions taken. Twenty-five percent of the patients were on the sick-list, and 20% drew disability pension due to persistent symptoms at follow-up. The risk of having no work capabilities at follow-up was significantly increased if the time from onset to first visit at the hospital clinic was more than 1 year. This risk was also significantly higher if the patient at the first visit had five or more symptoms. All risk assessments were adjusted for length of follow-up. Symptoms were often aggravated by different situations in everyday life.
Conclusions
Long-lasting symptoms aggravated by environmental factors exist within this group of patients. The results support that early and comprehensive measures for rehabilitation are essential for the patients.
This article aims to contribute to a better understanding of how to integrate customers within service development by assessing different methods of obtaining use information. The article reviews and ...classifies methods for customer integration and it also presents a new framework that suggests four modes of customer integration in which data is classified either as insitu (data captured in a customer's use situation) or exsitu (data captured outside the use situation) and as either incontext or excontext. Context is defined as a resource constellation that is available for customers to enable value co-creation. Accordingly, incontext refers to methods in which the customer is in the actual use context and has access to various resources, while excontext refers to a situation in which the customer is outside the use context and, therefore, has no direct access to the resources.
► We review methods for customer integration from a service perspective. ► develop a model framing methods based on the dimensions situation and context. ► Situation (insitu–exsitu) and context (incontext–excontext) capture service logic. ► Provides a tool for deciding and selecting methods for customer integration.
High-resolution spectra of 13 core helium-burning stars in the thick disk of the Galaxy have been obtained with the SOFIN
spectrograph on the Nordic Optical Telescope to investigate abundances of up ...to 22 chemical elements. Abundances of carbon were
studi
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