| 121. |
- 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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| 122. |
- 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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| 123. |
- 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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| 124. |
- 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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| 125. |
- 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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| 126. |
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| 127. |
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| 128. |
- Piskunov, Nikolai, professor, 1957-, et al.
(författare)
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A unique infrared spectropolarimetric unit for CRIRES
- 2018
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Ingår i: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VII. - : SPIE-INT SOC OPTICAL ENGINEERING. - 9781510619586
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Konferensbidrag (refereegranskat)abstract
- High-resolution infrared spectropolarimetry has many science applications in astrophysics. One of them is measuring weak magnetic fields using the Zeeman effect. Infrared domain is particularly advantageous as Zeeman splitting of spectral lines is proportional to the square of the wavelength while the intrinsic width of the line cores increases only linearly. Important science cases include detection and monitoring of global magnetic fields on solar-type stars, study of the magnetic field evolution from stellar formation to the final stages of the stellar life with massive stellar winds, and the dynamo mechanism operation across the boundary between fully-and partially-convective stars. CRIRES+ (the CRIRES upgrade project) includes a novel spectropolarimetric unit (SPU) based on polarization gratings. The novel design allows to perform beam-splitting very early in the optical path, directly after the tertiary mirror of the telescope (the ESO Very Large Telescope, VLT), minimizing instrumental polarization. The new SPU performs polarization beam-splitting in the near-infrared while keeping the telescope beam mostly unchanged in the optical domain, making it compatible with the adaptive optics system of the CRIRES+ instrument. The SPU consists of four beam-splitters optimized for measuring circular and linear polarization of spectral lines in YJ and HK bands. The SPU can perform beam switching allowing to correct for throughput in each beam and for variations in detector pixel sensitivity. Other new features of CRIRES+, such as substantially increased wavelength coverage, stability and advanced data reduction pipeline will further enhance the sensitivity of the polarimetric mode. The combination of the SPU, CRIRES+ and the VLT is a unique facility for making major progress in understanding stellar activity. In this article we present the design of the SPU, laboratory measurements of individual components and of the whole unit as well as the performance prediction for the operation at the VLT.
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| 129. |
- Prusti, T., et al.
(författare)
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The Gaia mission
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 595
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Tidskriftsartikel (refereegranskat)abstract
- Gaia is a cornerstone mission in the science programme of the European Space Agency (ESA). The spacecraft construction was approved in 2006, following a study in which the original interferometric concept was changed to a direct-imaging approach. Both the spacecraft and the payload were built by European industry. The involvement of the scientific community focusses on data processing for which the international Gaia Data Processing and Analysis Consortium (DPAC) was selected in 2007. Gaia was launched on 19 December 2013 and arrived at its operating point, the second Lagrange point of the Sun-Earth-Moon system, a few weeks later. The commissioning of the spacecraft and payload was completed on 19 July 2014. The nominal five-year mission started with four weeks of special, ecliptic-pole scanning and subsequently transferred into full-sky scanning mode. We recall the scientific goals of Gaia and give a description of the as-built spacecraft that is currently (mid-2016) being operated to achieve these goals. We pay special attention to the payload module, the performance of which is closely related to the scientific performance of the mission. We provide a summary of the commissioning activities and findings, followed by a description of the routine operational mode. We summarise scientific performance estimates on the basis of in-orbit operations. Several intermediate Gaia data releases are planned and the data can be retrieved from the Gaia Archive, which is available through the Gaia home page.
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| 130. |
- Randich, S., et al.
(författare)
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The Gaia-ESO Public Spectroscopic Survey : Implementation, data products, open cluster survey, science, and legacy
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 666
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Tidskriftsartikel (refereegranskat)abstract
- Context. In the last 15 years different ground-based spectroscopic surveys have been started (and completed) with the general aim of delivering stellar parameters and elemental abundances for large samples of Galactic stars, complementing Gaia astrometry. Among those surveys, the Gaia-ESO Public Spectroscopic Survey, the only one performed on a 8m class telescope, was designed to target 100 000 stars using FLAMES on the ESO VLT (both Giraffe and UVES spectrographs), covering all the Milky Way populations, with a special focus on open star clusters. Aims. This article provides an overview of the survey implementation (observations, data quality, analysis and its success, data products, and releases), of the open cluster survey, of the science results and potential, and of the survey legacy. A companion article reviews the overall survey motivation, strategy, Giraffe pipeline data reduction, organisation, and workflow. Methods. We made use of the information recorded and archived in the observing blocks; during the observing runs; in a number of relevant documents; in the spectra and master catalogue of spectra; in the parameters delivered by the analysis nodes and the working groups; in the final catalogue; and in the science papers. Based on these sources, we critically analyse and discuss the output and products of the Survey, including science highlights. We also determined the average metallicities of the open clusters observed as science targets and of a sample of clusters whose spectra were retrieved from the ESO archive. Results. The Gaia-ESO Survey has determined homogeneous good-quality radial velocities and stellar parameters for a large fraction of its more than 110 000 unique target stars. Elemental abundances were derived for up to 31 elements for targets observed with UVES. Lithium abundances are delivered for about 1/3 of the sample. The analysis and homogenisation strategies have proven to be successful; several science topics have been addressed by the Gaia-ESO consortium and the community, with many highlight results achieved. Conclusions. The final catalogue will be released through the ESO archive in the first half of 2022, including the complete set of advanced data products. In addition to these results, the Gaia-ESO Survey will leave a very important legacy, for several aspects and for many years to come.
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