| 1. |
- Hobbs, David, et al.
(författare)
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Gaia and the Astrometric Global Iterative Solution
- 2008
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Ingår i: Proceedings of IInternational Astronomical Union, IAU Symposium. ; 248, s. 119-120
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Konferensbidrag (refereegranskat)abstract
- Gaia is an ESA space astrometry mission due for launch in 2011-12. We describe part of the work carried out in the Gaia Data Processing and Analysis Consortium, namely the Astrometric Global Iterative Solution (AGIS) currently being implemented at the European Space Astronomy Center (ESAC) in Spain and largely based on algorithms developed at Lund Observatory. Some provisional results based on simulated observations of one million stars are presented, demonstrating convergence at microarcsec level independent of starting conditions.
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| 2. |
- Michalik, Daniel, et al.
(författare)
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Combining and Comparing Astrometric Data from Different Epochs: A Case Study with Hipparcos and Nano-JASMINE
- 2012
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Ingår i: Astronomical Data Analysis Software and Systems XXI (ASP Conference Series). ; 461, s. 549-552
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Konferensbidrag (refereegranskat)abstract
- The Hipparcos mission (1989-1993) resulted in the first space-based stellar catalogue including measurements of positions, parallaxes and annual proper motions accurate to about one milli-arcsecond. More space astrometry missions will follow in the near future. The ultra-small Japanese mission Nano-JASMINE (launch in late 2013) will determine positions and annual proper motions with some milli-arcsecond accuracy. In mid 2013 the next-generation ESA mission Gala will deliver some tens of micro-arcsecond accurate astrometric parameters. Until the final Gala catalogue is published in early 2020 the best way of improving proper motion values is the combination of positions from different missions separated by long time intervals. Rather than comparing positions from separately reduced catalogues, we propose an optimal method to combine the information from the different data sets by making a joint astrometric solution. This allows to obtain good results even when each data set alone is insufficient for an accurate reduction. We demonstrate our method by combining Hipparcos and simulated Nano-JASMINE data in a joint solution. We show a significant improvement over the conventional catalogue combination.
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| 3. |
- Michalik, Daniel, et al.
(författare)
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Improving distance estimates to nearby bright stars: Combining astrometric data from Hipparcos, Nano-JASMINE and Gaia
- 2013
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Ingår i: Advancing the Physics of Cosmic Distances, Proceedings of the International Astronomical Union, IAU Symposium, Volume 289, pp. 414-417. ; 289, s. 414-417
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Starting in 2013, Gaia will deliver highly accurate astrometric data, which eventually will supersede most other stellar catalogues in accuracy and completeness. It is, however, limited to observations from magnitude 6 to 20 and will therefore not include the brightest stars. Nano-JASMINE, an ultrasmall Japanese astrometry satellite, will observe these bright stars, but with much lower accuracy. Hence, the Hipparcos catalogue from 1997 will likely remain the main source of accurate distances to bright nearby stars. We are investigating how this might be improved by optimally combining data from all three missions through a joint astrometric solution. This would take advantage of the unique features of each mission: the historic bright-star measurements of Hipparcos, the updated bright-star observations of Nano-JASMINE, and the very accurate reference frame of Gaia. The long temporal baseline between the missions provides additional benefits for the determination of proper motions and binary detection, which indirectly improve the parallax determination further. We present a quantitative analysis of the expected gains based on simulated data for all three missions.
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| 4. |
- Michalik, Daniel, et al.
(författare)
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Joint astrometric solution of HIPPARCOS and Gaia. A recipe for the Hundred Thousand Proper Motions project
- 2014
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 571
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Tidskriftsartikel (refereegranskat)abstract
- Context. The first release of astrometric data from Gaia is expected in 2016. It will contain the mean stellar positions and magnitudes from the first year of observations. For more than 100 000 stars in common with the HIPPARCOS Catalogue it will be possible to compute very accurate proper motions due to the time difference of about 24 years between the two missions. This Hundred Thousand Proper Motions (HTPM) project is planned to be part of the first release. Aims. Our aim is to investigate how early Gaia data can be optimally combined with information from the HIPPARCOS Catalogue in order to provide the most accurate and reliable results for HTPM. Methods. The Astrometric Global Iterative Solution (AGIS) was developed to compute the astrometric core solution based on the Gala observations and will be used for all releases of astrometric data from Gaia. We adapt AGIS to process HIPPARCOS data in addition to Gaia observations, and use simulations to verify and study the joint solution method. Results. For the HTPM stars we predict proper motion accuracies between 14 and 134 pas yr-1, depending on stellar magnitude and amount of Gaia data available. Perspective effects will be important for a significant number of HTPM stars, and in order to treat these effects accurately we introduce a formalism called scaled model of kinematics (SMOK). We define a goodness-of-fit statistic which is sensitive to deviations from uniform space motion, caused for example by binaries with periods of 10-50 years. Conclusions. HTPM will significantly improve the proper motions of the HIPPARCOS Catalogue well before highly accurate Gaiaonly results become available. Also, HTPM will allow us to detect long period binary and exoplanetary candidates which would be impossible to detect from Gaia data alone. The full sensitivity will not be reached with the first Gaia release but with subsequent data releases. Therefore HTPM should be repeated when more Gaia data become available.
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| 5. |
- O'Mullane, William, et al.
(författare)
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Implementing the Gaia Astrometric Global Iterative Solution (AGIS) in Java
- 2011
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Ingår i: Experimental Astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 31:2-3, s. 215-241
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides a description of the Java software framework which has been constructed to run the Astrometric Global Iterative Solution for the Gaia mission. This is the mathematical framework to provide the rigid reference frame for Gaia observations from the Gaia data itself. This process makes Gaia a self calibrated, and input catalogue independent, mission. The framework is highly distributed typically running on a cluster of machines with a database back end. All code is written in the Java language. We describe the overall architecture and some of the details of the implementation.
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