| 1. |
- Gilmore, G., et al.
(författare)
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The Gaia-ESO Public Spectroscopic Survey
- 2012
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Ingår i: The Messenger. - 0254-4423. ; 147, s. 25-31
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Tidskriftsartikel (refereegranskat)abstract
- The Gaia-ESO Public Spectroscopic Survey has begun and will obtain high quality spectroscopy of some 100000 Milky Way stars, in the field and in open clusters, down to magnitude 19, systematically covering all the major components of the Milky Way. This survey will provide the first homogeneous overview of the distributions of kinematics and chemical element abundances in the Galaxy. The motivation, organisation and implementation of the Gaia-ESO Survey are described, emphasising the complementarity with the ESA Gaia mission. Spectra from the very first observing run of the survey are presented.
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| 2. |
- Heiter, Ulrike, et al.
(författare)
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On the metallicity of open clusters. II. Spectroscopy
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 561, s. A93-
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Tidskriftsartikel (refereegranskat)abstract
- Context. Open clusters are an important tool for studying the chemical evolution of the Galactic disk. Metallicity estimates are available for about ten percent of the currently known open clusters. These metallicities are based on widely differing methods, however, which introduces unknown systematic effects. Aims. In a series of three papers, we investigate the current status of published metallicities for open clusters that were derived from a variety of photometric and spectroscopic methods. The current article focuses on spectroscopic methods. The aim is to compile a comprehensive set of clusters with the most reliable metallicities from high-resolution spectroscopic studies. This set of metallicities will be the basis for a calibration of metallicities from different methods. Methods. The literature was searched for [Fe/H] estimates of individual member stars of open clusters based on the analysis of high-resolution spectra. For comparison, we also compiled [Fe/H] estimates based on spectra with low and intermediate resolution. At medium and high resolution, we found that differences in the analysis methods have a stronger effect on the metallicity than that of quality differences in the observations. We retained only highly probable cluster members and introduced a restriction on atmospheric parameters. Results. We combined 641 individual metallicity values for 458 stars in 78 open clusters from 86 publications to form our final set of high-quality cluster metallicities. The photometric metallicities discussed in the first paper of this series are systematically lower than the spectroscopic ones by about 0.1 dex, and the differences show a scatter of about 0.2 dex. In a preliminary comparison of our spectroscopic sample with models of Galactic chemical evolution, none of the models predicts the observed radial metallicity gradient. Conclusions. Photometric metallicities show a large intrinsic dispersion, while the more accurate spectroscopic sample presented in this paper comprises fewer than half the number of clusters. Only a sophisticated combination of all available photometric and spectroscopic data will allow us to trace the metallicity distribution in the Galactic disk on a local and global scale.
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| 3. |
- Paunzen, E., et al.
(författare)
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A photometric long-term study of chemically peculiar stars in open clusters
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 525, s. A16-
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Tidskriftsartikel (refereegranskat)abstract
- Context. Photometric variability of chemically peculiar (CP) stars of the upper main sequence is closely connected to their local stellar magnetic field and their rotational period. Long term investigations, as presented here, help us to identify possible stellar cycles (as in the Sun). Furthermore, these data provide a basis for detailed surface mapping techniques. Aims. Photoelectric Stromgren uvby time series for 27 CP stars within the boundaries of open clusters are presented. In addition, Hipparcos photometric data (from 1989 to 1993) are used for our analysis. Our observations cover a time period of about six years (1986 to 1992) with typically fifteen measurements for each objects. These observations help us to determine the rotational periods of these objects. Methods. A standard reduction procedure was applied to the data. When possible, we merged our data sets with already published ones to obtain a more significant result. A detailed time series analysis was performed, involving five different methods to minimize spurious detections. Results. We established, for the first time, variability for fourteen CP stars. For additional two stars, a merging of already published data sets, resulted in more precise periods, whereas for six objects, the published periods could be confirmed. Last, but not least, no significant variations were found for five stars. Apart from six stars, all targets seem to be members of their host open clusters. Conclusions. The present observations fill an important gap in previous photometric long-time studies of CP stars. The presented open cluster members are excellent targets for follow-up observations, employing for example polarimetric, high-resolution spectroscopic, and surface mapping techniques.
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| 4. |
- Paunzen, E., et al.
(författare)
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A SPECTRAL ATLAS OF lambda BOOTIS STARS
- 2014
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Ingår i: Serbian Astronomical Journal. - 1450-698X. ; 188, s. 75-84
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Tidskriftsartikel (refereegranskat)abstract
- Since the discovery of lambda Bootis stars, a permanent confusion about their classification can be found in literature. This group of non-magnetic, Population I, metal-poor A to F-type stars, has often been used as some sort of trash can for "exotic" and spectroscopically dubious objects. Some attempts have been made to establish a homogeneous group of stars which share the same common properties. Unfortunately, the flood of "new" information (e.g. UV and IR data) led again to a whole zoo of objects classified as lambda Bootis stars, which, however, are apparent non-members. To overcome this unsatisfying situation, a spectral atlas of well established lambda Bootis stars for the classical optical domain was compiled. It includes intermediate dispersion (40 and 120 angstrom mm(-1)) spectra of three lambda Bootis, as well as appropriate MK standard stars. Furthermore, "suspicious" objects, such as shell and Field Horizontal Branch stars, have been considered in order to provide to classifiers a homogeneous reference. As a further step, a high resolution (8 angstrom mm(-1)) spectrum of one "classical" lambda Bootis star in the same wavelength region (3800 - 4600 angstrom) is presented. In total, 55 lines can be used for this particular star to derive detailed abundances for nine heavy elements (Mg, Ca, Sc, Ti, Cr, Mn, Fe, Sr and Ba).
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| 5. |
- Paunzen, E., et al.
(författare)
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HD 210111 : a new lambda Bootis-type spectroscopic binary system
- 2012
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 419:4, s. 3604-3607
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Tidskriftsartikel (refereegranskat)abstract
- The small group of ? Bootis stars comprises late B- to early F-type stars, with moderate to extreme (up to a factor of 100) surface underabundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O and S). The main mechanisms responsible for this phenomenon are atmospheric diffusion, meridional mixing and accretion of material from their surroundings. In particular, spectroscopic binary (SB) systems with ? Bootis-type components are very important to investigate the evolutionary status and accretion process in more detail. For HD 210111, d Scuti-type pulsation was also found, which gives the opportunity to use the tools of asteroseismology for further investigations. The latter could result in strict constraints for the amount of diffusion for this star. Together with models for the accretion and its source, this provides a unique opportunity to shed more light on these important processes. We present classification and high-resolution spectra for HD 210111. A detailed investigation of the most likely combinations of single star components was performed. For this, composite spectra with different stellar astrophysical parameters were calculated and compared to the observations to find the best-fitting combination. HD 210111 comprises two equal (within the estimated errors) stars with Teff= 7400 K, log g= 3.8 dex, [M/H] =-1.0 dex and v sin i= 30 km s-1. This result is in line with other strict observational facts published so far for this object. This is only the third detailed investigation of the ? Bootis-type SB system, but the first one with a known infrared excess.
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| 6. |
- Paunzen, E., et al.
(författare)
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Investigating the possible connection between lambda Bootis stars and intermediate Population II type stars
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 567, s. A67-
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Tidskriftsartikel (refereegranskat)abstract
- Context The it Bootis stars are located at the upper maid sequence of the Hertzsprung-Russell diagram and exhibit a peculiar abundance pattern. The light elements (C, N, O, and S) present solar abundances whereas all other elements are moderately to strongly underabundant It has not yet been determined whether that abundance pattern is intrinsic, or is restricted to the stellar surface. Aims. If we follow the hypothesis that the A Bootis stars are intrinsically metal-weak, then there should be a connection with the intermediate Population II and F-weak objects. Such a possible affinity has not been previously investigated. Methods. We present detailed elemental abundances, including those of the light elements carbon and oxygen, for 38 bright intermediate Population If and F-weak objects. In addition, we investigate the kinematic characteristics of the groups, Results. From photometric. spectroscopic, and kinematic data, there is no distinction between the intermediate Population II and F-weak type stars. We therefore conclude that the two groups are identical. However, it is possible to distinguish the lambda Bootis stars from the intermediate Population II stars on the basis of elemental abundances though not in terms of their kinematics. Conclusions. The lambda Bootis stars seem to be distinct from the intermediate Population II group. Further asteroseisrnologic investigations and analyses of spectroscopic binary systems are needed to strengthen this conclusion.
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| 7. |
- Paunzen, E., et al.
(författare)
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On the metallicity of open clusters : I. Photometry
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 517, s. A32-
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Tidskriftsartikel (refereegranskat)abstract
- Context. Metallicity is one of four free parameters typically considered when fitting isochrones to the cluster sequence. Unfortunately, this parameter is often ignored or assumed to be solar in most papers. Hence an unknown bias is introduced in the estimation of the other three cluster parameters (age, reddening and distance). Furthermore, studying the metallicity of open clusters allows us not only to derive the Galactic abundance gradient on a global scale, but also to trace the local solar environment in more detail. Aims. In a series of three papers, we investigate the current status of published metallicities for open clusters from widely different photometric and spectroscopic methods. A detailed comparison of the results allows us to establish more reliable photometric calibrations and corrections for isochrone fitting techniques. Well established databases such as WEBDA help us to perform a homogeneous analysis of available measurements for a significant number of open clusters. Methods. The literature was searched for [Fe/H] estimates on the basis of photometric calibrations in any available filter system. On the basis of results published by Tadross, we demonstrate the caveats of the calibration choice and its possible impact. In total, we find 406 individual metallicity values for 188 open clusters within 64 publications. The values were, finally, unweightedly averaged. Results. Our final sample includes [Fe/H] values for 188 open clusters. Tracing the solar environment within 4000 x 4000 pc(2) we identify a patchy metallicity distribution as an extension to the Local Bubble that significantly influences the estimation of the Galactic metallicity gradient, even on a global scale. In addition, further investigations of more distant open clusters are clearly needed to obtain a more profound picture at Galactocentric distances beyond 10 000 pc. Conclusions. Only a combination of all available photometric and spectroscopic data will shed more light on how the local and global Galactic properties are correlated with metallicity.
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| 8. |
- Paunzen, E., et al.
(författare)
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The first Delta a observations of three globular clusters
- 2014
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 443:3, s. 2492-2498
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Tidskriftsartikel (refereegranskat)abstract
- Globular clusters are main astrophysical laboratories to test and modify evolutionary models. Thought to be rather homogeneous in their local elemental distribution of members, results suggest a wide variety of chemical peculiarities. Besides different main sequences, believed to be caused by different helium abundances, peculiarities of blue horizontal-branch stars and on the red giant branch were found. This whole zoo of peculiar objects has to be explained in the context of stellar formation and evolution. The tool of Delta a photometry is employed in order to detect peculiar stars in the whole spectral range. This three filter narrow-band system measures the flux distribution in the region from 4900 to 5600 angstrom in order to find any peculiarities around 5200 angstrom. It is highly efficient to detect classical chemically peculiar stars of the upper main sequence, Be/Ae, shell and metal-weak objects in the Milky Way and Magellanic Clouds. We present Delta a photometry of 2266 stars from 109 individual frames for three globular clusters (NGC 104, NGC 6205, and NGC 7099). A comparison with published abundances, for three horizontal-branch stars, only, yields an excellent agreement. According to the 3 sigma detection limit of each globular cluster, about 3 per cent of the stars lie in abnormal regions in the diagnostic diagrams. The first observations of three widely different aggregates give very promising results, which will serve as a solid basis for follow-up observations including photometric as well as spectroscopic studies.
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