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| 2. |
- Creevey, O. L., et al.
(författare)
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Gaia Data Release 3 : Astrophysical parameters inference system (Apsis). I. Methods and content overview
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 674
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Tidskriftsartikel (refereegranskat)abstract
- Gaia Data Release 3 contains a wealth of new data products for the community. Astrophysical parameters are a major component of this release, and were produced by the Astrophysical parameters inference system (Apsis) within the Gaia Data Processing and Analysis Consortium (DPAC). The aim of this paper is to describe the overall content of the astrophysical parameters in Gaia DR3 and how they were produced. In Apsis, we use the mean BP /RP and mean RVS spectra along with astrometry and photometry, and we derive the following parameters: source classification and probabilities for 1.6 billion objects; interstellar medium characterisation and distances for up to 470 million sources, including a 2D total Galactic extinction map; 6 million redshifts of quasar candidates; 1.4 million redshifts of galaxy candidates; and an analysis of 50 million outlier sources through an unsupervised classification. The astrophysical parameters also include many stellar spectroscopic and evolutionary parameters for up to 470 million sources. These comprise T-eff, log g, and [M /H] (470 million using BP /RP, 6 million using RVS), radius (470 million), mass (140 million), age (120 million), chemical abundances (up to 5 million), diffuse interstellar band analysis (0.5 million), activity indices (2 million), H ff equivalent widths (200 million), and further classification of spectral types (220 million) and emission-line stars (50 000). This paper is the first in a series of three papers, and focusses on describing the global content of the parameters in Gaia DR3. The accompanying Papers II and III focus on the validation and use of the stellar and non-stellar products, respectively. This catalogue is the most extensive homogeneous database of astrophysical parameters to date, and is based uniquely on Gaia data. It will only be superseded by Gaia Data Release 4, and will therefore remain a key reference over the next four years, providing astrophysical parameters independent of other ground- and space-based data.
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| 3. |
- Fouesneau, M., et al.
(författare)
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Gaia Data Release 3 Apsis. II. Stellar parameters
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 674
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Tidskriftsartikel (refereegranskat)abstract
- Context. The third Gaia data release (Gaia DR3) contains, beyond the astrometry and photometry, dispersed light for hundreds of millions of sources from the Gaia prism spectra (BP and RP) and the spectrograph (RVS). This data release opens a new window on the chemo-dynamical properties of stars in our Galaxy, essential knowledge for understanding the structure, formation, and evolution of the Milky Way. Aims. To provide insight into the physical properties of Milky Way stars, we used these data to produce a uniformly derived all-sky catalogue of stellar astrophysical parameters: atmospheric properties (T-e ff, log g, [M /H], [alpha/Fe], activity index, emission lines, and rotation), 13 chemical abundance estimates, evolution characteristics (radius, age, mass, and bolometric luminosity), distance, and dust extinction. Methods. We developed the astrophysical parameter inference system (Apsis) pipeline to infer astrophysical parameters of Gaia objects by analysing their astrometry, photometry, BP /RP, and RVS spectra. We validate our results against those from other works in the literature, including benchmark stars, interferometry, and asteroseismology. Here we assess the stellar analysis performance from Apsis statistically. Results. We describe the quantities we obtained, including the underlying assumptions and the limitations of our results. We provide guidance and identify regimes in which our parameters should and should not be used. Conclusions. Despite some limitations, this is the most extensive catalogue of uniformly inferred stellar parameters to date. They comprise T-eff, log g, and [M/H] (470 million using BP/RP, 6 million using RVS), radius (470 million), mass (140 million), age (120 million), chemical abundances (5 million), di ffuse interstellar band analysis (half a million), activity indices (2 million), H ff equivalent widths (200 million), and further classifications of spectral types (220 million) and emission-line stars (50 thousand). More precise and detailed astrophysical parameters based on epoch BP, RP, and RVS spectrophotometry are planned for the next Gaia data release.
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| 4. |
- Wade, G. A., et al.
(författare)
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The MiMeS survey of magnetism in massive stars : introduction and overview
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 456:1, s. 2-22
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The MiMeS (Magnetism in Massive Stars) project is a large-scale, high-resolution, sensitive spectropolarimetric investigation of the magnetic properties of O- and early B-type stars. Initiated in 2008 and completed in 2013, the project was supported by three Large Program allocations, as well as various programmes initiated by independent principal investigators, and archival resources. Ultimately, over 4800 circularly polarized spectra of 560 O and B stars were collected with the instruments ESPaDOnS (Echelle SpectroPolarimetric Device for the Observation of Stars) at the Canada-France-Hawaii Telescope, Narval at the Telescope Bernard Lyot and HARPSpol at the European Southern Observatory La Silla 3.6 m telescope, making MiMeS by far the largest systematic investigation of massive star magnetism ever undertaken. In this paper, the first in a series reporting the general results of the survey, we introduce the scientific motivation and goals, describe the sample of targets, review the instrumentation and observational techniques used, explain the exposure time calculation designed to provide sensitivity to surface dipole fields above approximately 100 G, discuss the polarimetric performance, stability and uncertainty of the instrumentation, and summarize the previous and forthcoming publications.
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| 5. |
- Folsom, C. P., et al.
(författare)
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Magnetic fields and chemical peculiarities of the very young intermediate-mass binary system HD 72106
- 2008
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 391:2, s. 901-914
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Tidskriftsartikel (refereegranskat)abstract
- The recently discovered magnetic Herbig Ae and Be stars may provide qualitatively new information about the formation and evolution of magnetic Ap and Bp stars. We have performed a detailed investigation of one particularly interesting binary system with a Herbig Ae secondary and a late B-type primary possessing a strong, globally ordered magnetic field. 20 high-resolution Stokes V spectra of the system were obtained with the ESPaDOnS instrument mounted on the Canada-France-Hawaii Telescope. In these observations we see clear evidence for a magnetic field in the primary, but no evidence for a magnetic field in the secondary. A detailed abundance analysis was performed for both stars, revealing strong chemical peculiarities in the primary and normal chemical abundances in the secondary. The primary is strongly overabundant in Si, Cr and other iron-peak elements, as well as Nd, and underabundant in He. The primary therefore appears to be a very young Bp star. In this context, line profile variations of the primary suggest non-uniform lateral distributions of surface abundances. Interpreting the 0.639 95 +/- 0.000 09 d variation period of the Stokes I and V profiles as the rotational period of the star, we have modelled the magnetic field geometry and the surface abundance distributions of Si, Ti, Cr and Fe using magnetic Doppler imaging. We derive a dipolar geometry of the surface magnetic field, with a polar strength B-d = 1230 G and an obliquity beta = 57 degrees. The distributions Ti, Cr and Fe are all qualitatively similar, with an elongated patch of enhanced abundance situated near the positive magnetic pole. The Si distribution is somewhat different, and its relationship to the magnetic field geometry less clear.
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| 6. |
- Grunhut, J. H., et al.
(författare)
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The MiMeS survey of Magnetism in Massive Stars : magnetic analysis of the O-type stars
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 465:2, s. 2432-2470
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Tidskriftsartikel (refereegranskat)abstract
- We present the analysis performed on spectropolarimetric data of 97 O-type targets included in the framework of the Magnetism in Massive Stars (MiMeS) Survey. Mean least-squares deconvolved Stokes I and V line profiles were extracted for each observation, from which we measured the radial velocity, rotational and non-rotational broadening velocities, and longitudinal magnetic field B-l. The investigation of the Stokes I profiles led to the discovery of two new multiline spectroscopic systems (HD 46106, HD 204827) and confirmed the presence of a suspected companion in HD 37041. We present a modified strategy of the leastsquares deconvolution technique aimed at optimizing the detection of magnetic signatures while minimizing the detection of spurious signatures in Stokes V. Using this analysis, we confirm the detection of a magnetic field in six targets previously reported as magnetic by the MiMeS collaboration (HD 108, HD 47129A2, HD 57682, HD 148937, CPD-28 2561, and NGC 1624-2), as well as report the presence of signal in Stokes V in three new magnetic candidates (HD 36486, HD 162978, and HD 199579). Overall, we find a magnetic incidence rate of 7 +/- 3 per cent, for 108 individual O stars (including all O-type components part of multiline systems), with a median uncertainty of the B-l measurements of about 50 G. An inspection of the data reveals no obvious biases affecting the incidence rate or the preference for detecting magnetic signatures in the magnetic stars. Similar to A- and B-type stars, we find no link between the stars' physical properties (e.g. T-eff, mass, and age) and the presence of a magnetic field. However, the Of?p stars represent a distinct class of magnetic O-type stars.
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| 7. |
- Sordo, Rosanna, et al.
(författare)
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Stellar libraries for Gaia
- 2011
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 328:Conference 1, s. 012006-
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Tidskriftsartikel (refereegranskat)abstract
- Gaia will observe up to a billion stellar sources. Automated algorithms are under development to derive the atmospheric parameters of all observed spectra, from low resolution optical spectra alone or in synergy with high resolution spectra in the near-IR Ca II triplet region. To do so, a large database of state-of-the-art stellar libraries has been produced for the Gaia community, computed using different codes optimized for specific purposes. The choice to use different spectral codes in different regions of the H-R diagram raises the problem of the coherence of the different spectra, specifically in the transition zones. We present a comparison between the libraries from the point of view of spectra simulations for training the Gaia algorithms. We also present the implementation of these libraries into a Simple Stellar Population code.
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| 8. |
- Alecian, E., et al.
(författare)
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First HARPSpol discoveries of magnetic fields in massive stars
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 536, s. L6-
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Tidskriftsartikel (refereegranskat)abstract
- In the framework of the Magnetism in Massive Stars (MiMeS) project, a HARPSpol Large Program at the 3.6m-ESO telescope has recently started to collect high-resolution spectropolarimetric data of a large number of Southern massive OB stars in the field of the Galaxy and in many young clusters and associations. We report on the first discoveries of magnetic fields in two massive stars with HARPSpol - HD 130807 and HD 122451, and confirm the presence of a magnetic field at the surface of HD 105382 that was previously observed with a low spectral resolution device. The longitudinal magnetic field measurements strongly vary for HD 130807 from similar to-100 G to similar to 700 G. Those of HD 122451 and HD 105382 are less variable with values ranging from similar to-40 to -80 G, and from similar to-300 to -600 G, respectively. The discovery and confirmation of three new magnetic massive stars, including at least two He-weak stars, is an important contribution to one of MiMeS objectives: the understanding of the origin of magnetic fields in massive stars and their impact on stellar structure and evolution.
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| 9. |
- Vallenari, A., et al.
(författare)
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Synthetic stellar libraries and SSP simulations in the Gaia Era
- 2009
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Ingår i: Proceedings of the International Astronomical Union. ; , s. 444-445
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Konferensbidrag (refereegranskat)abstract
- The Gaia mission will obtain accurate positions, parallaxes and proper motions for 109 object all over the sky. In addition, it will collect low resolution spectroscopy in the optical range for ∼ 109 objects, stars, galaxies, and QSOs. Parameters of those objects are expected to be part of the final Catalog. Complete and up-to-date libraries of synthetic stellar spectra are needed to train the algorithms to classify this huge amount of data. Here we focus on the use of the synthetic libraries of spectra calculated by the Gaia community to derive grids of Single Stellar Populations as building blocks of population synthesis models. © International Astronomical Union 2010.
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| 10. |
- Grunhut, H, et al.
(författare)
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Discovery of a magnetic field in the O9 sub-giant star HD 57682 by the MiMeS Collaboration
- 2009
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 400:1, s. L94-L98
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Tidskriftsartikel (refereegranskat)abstract
- We report the detection of a strong, organized magnetic field in the O9IV star HD 57682, using spectropolarimetric observations obtained with ESPaDOnS at the 3.6-m Canada-France-Hawaii Telescope within the context of the Magnetism in Massive Stars (MiMeS) Large Programme. From the fitting of our spectra using non-local thermodynamic equilibrium model atmospheres, we determined that HD 57682 is a 17(-9)(+19)M(circle dot) star with a radius of 7.0(-1.8)(+2.4)R(circle dot) and a relatively low mass-loss rate of 1.4(-0.95)(+3.1) x 10(-9) M-circle dot yr(-1). The photospheric absorption lines are narrow, and we use the Fourier transform technique to infer v sin i = 15 +/- 3 km s(-1). This v sin i implies a maximum rotational period of 31.5 d, a value qualitatively consistent with the observed variability of the optical absorption and emission lines, as well as the Stokes V profiles and longitudinal field. Using a Bayesian analysis of the velocity-resolved Stokes V profiles to infer the magnetic field characteristics, we tentatively derive a dipole field strength of 1680(-356)(+134)G. The derived field strength and wind characteristics imply a wind that is strongly confined by the magnetic field.
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