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Lennart Lindegren
Lennart Lindegren is a member of the staff at Lund Observatory, Sweden, where he obtained his PhD in 1980, and became a full professor of astronomy in 2000. Space astrometry and its various applications has been his main focus in astronomy since 1976. He has been involved in ESA's Hipparcos and Gaia missions throughout their duration.
During the early studies of ESA's Hipparcos space astrometry mission, and while still a graduate student in 1976, he was "recruited" to the project by Erik Høg and thereafter was involved in various aspects of the mission definition and data analysis. He set out the overall principles of the astrometric data reduction aiming to combine and solve together the attitude, the system and the astrometric parameters of the stars. This crucial '3-step procedure' was used successfully by the two consortia (NDAC and FAST) later entrusted by ESA with the Hipparcos data processing.
The principle of reconstructing space astrometric positions from one-dimensional observations carried out in the innovative Hipparcos sky scanning mode was new to the field and challenging to implement given the available computational power in 1997. The numerical principles had to be demonstrated, together with the solution’s statistical properties. Already by the end of 1976, Lindegren had produced a set of definitive technical notes and simulations showing how to obtain a 'rigid sphere' with all astrometric parameters from a scanning satellite. Since that time he has contributed to several aspects of space astrometry.
From 1990 Lennart Lindegren led the Consortium NDAC (Northern Data Analysis Consortium) sharing with FAST (led by Jean Kovalevsky) the data processing of Hipparcos. In addition to the overall scientific coordinating responsibilities, he developed many of the approaches and algorithms related to the mission: his innovation, insight, and mathematical rigour impacted the optical and focal plane design, the instrument calibration, the scanning law, the attitude determination (and the associated 'dynamical smoothing'), the double star analysis (as observed via a signal modulated by a grid), the effects of chromaticity and thermal load fluctuations, the optimum combination of the NDAC and FAST catalogue solutions, and the link to an extragalactic reference frame.
He was member of ESA's Hipparcos Science Team for the entire duration of the project (1976–1997).
Erik Høg has written: "A new era of my life began on 1 September 1973 when I returned to Denmark with my family of five, after 15 years in Hamburg. I had obtained a tenure at the Copenhagen University where I was going to work on the construction of automatic control of the meridian circle in Brorfelde. Very soon, however, I heard of a young student at Lund Observatory who worked alone on modernizing the old meridian circle there. I went to Lund and 'found' Lennart. A few years later, Andrew Murray, my old colleague and member of the Hipparcos science team, would say: 'Erik, the best you have ever done for astronomy was to find Lennart!' and I agreed". Later Høg writes: "Of his numerous papers I will only mention two. He wrote a paper on 'Photoelectric astrometry', a subject I had proposed, where he systematically discussed the performance of methods for precise image location from observations. It remains a classical paper. The second paper to mention is about the rigidity of the celestial coordinate system obtained by the one-dimensional observations in a scanning satellite as TYCHO/Option A/Hipparcos. The question was asked in 1976 as mentioned above, but it took years before we had the answer which was affirmative. The study was led by Lennart and contains his brilliant mathematical analysis of the simulations, but he modestly left the position as first author to another person."
Before the Hipparcos Catalogue was published, he was the first (with Michael Perryman), to set forth a new proposal for a more ambitious mission in terms of accuracy and sensitivity, resting on the same fundamental principles as Hipparcos. This was initially Roemer, and finally Gaia, eventually selected by ESA in 2000 (for a projected launch in 2012), and actually launched in December 2013. Lindegren contributed to the initial design of what was in the early phase an interferometer and in the assessment of the astrometric accuracy achievable. He also led the detailed design of the overall scheme of the astrometric solution, being a block iterative adjustment determining the attitude, the calibration and the system directly from the CCD images. This Astrometric Global Iterative Solution (AGIS) is now fully operational within the Gaia Data Processing and Analysis Consortium (DPAC).
Lindegren was a member of the ESA Gaia Science Advisory Group before mission selection, and the Gaia Science Team since selection in 2000.
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Lennart Lindegren
Lennart Lindegren is a member of the staff at Lund Observatory, Sweden, where he obtained his PhD in 1980, and became a full professor of astronomy in 2000. Space astrometry and its various applications has been his main focus in astronomy since 1976. He has been involved in ESA's Hipparcos and Gaia missions throughout their duration.
During the early studies of ESA's Hipparcos space astrometry mission, and while still a graduate student in 1976, he was "recruited" to the project by Erik Høg and thereafter was involved in various aspects of the mission definition and data analysis. He set out the overall principles of the astrometric data reduction aiming to combine and solve together the attitude, the system and the astrometric parameters of the stars. This crucial '3-step procedure' was used successfully by the two consortia (NDAC and FAST) later entrusted by ESA with the Hipparcos data processing.
The principle of reconstructing space astrometric positions from one-dimensional observations carried out in the innovative Hipparcos sky scanning mode was new to the field and challenging to implement given the available computational power in 1997. The numerical principles had to be demonstrated, together with the solution’s statistical properties. Already by the end of 1976, Lindegren had produced a set of definitive technical notes and simulations showing how to obtain a 'rigid sphere' with all astrometric parameters from a scanning satellite. Since that time he has contributed to several aspects of space astrometry.
From 1990 Lennart Lindegren led the Consortium NDAC (Northern Data Analysis Consortium) sharing with FAST (led by Jean Kovalevsky) the data processing of Hipparcos. In addition to the overall scientific coordinating responsibilities, he developed many of the approaches and algorithms related to the mission: his innovation, insight, and mathematical rigour impacted the optical and focal plane design, the instrument calibration, the scanning law, the attitude determination (and the associated 'dynamical smoothing'), the double star analysis (as observed via a signal modulated by a grid), the effects of chromaticity and thermal load fluctuations, the optimum combination of the NDAC and FAST catalogue solutions, and the link to an extragalactic reference frame.
He was member of ESA's Hipparcos Science Team for the entire duration of the project (1976–1997).
Erik Høg has written: "A new era of my life began on 1 September 1973 when I returned to Denmark with my family of five, after 15 years in Hamburg. I had obtained a tenure at the Copenhagen University where I was going to work on the construction of automatic control of the meridian circle in Brorfelde. Very soon, however, I heard of a young student at Lund Observatory who worked alone on modernizing the old meridian circle there. I went to Lund and 'found' Lennart. A few years later, Andrew Murray, my old colleague and member of the Hipparcos science team, would say: 'Erik, the best you have ever done for astronomy was to find Lennart!' and I agreed". Later Høg writes: "Of his numerous papers I will only mention two. He wrote a paper on 'Photoelectric astrometry', a subject I had proposed, where he systematically discussed the performance of methods for precise image location from observations. It remains a classical paper. The second paper to mention is about the rigidity of the celestial coordinate system obtained by the one-dimensional observations in a scanning satellite as TYCHO/Option A/Hipparcos. The question was asked in 1976 as mentioned above, but it took years before we had the answer which was affirmative. The study was led by Lennart and contains his brilliant mathematical analysis of the simulations, but he modestly left the position as first author to another person."
Before the Hipparcos Catalogue was published, he was the first (with Michael Perryman), to set forth a new proposal for a more ambitious mission in terms of accuracy and sensitivity, resting on the same fundamental principles as Hipparcos. This was initially Roemer, and finally Gaia, eventually selected by ESA in 2000 (for a projected launch in 2012), and actually launched in December 2013. Lindegren contributed to the initial design of what was in the early phase an interferometer and in the assessment of the astrometric accuracy achievable. He also led the detailed design of the overall scheme of the astrometric solution, being a block iterative adjustment determining the attitude, the calibration and the system directly from the CCD images. This Astrometric Global Iterative Solution (AGIS) is now fully operational within the Gaia Data Processing and Analysis Consortium (DPAC).
Lindegren was a member of the ESA Gaia Science Advisory Group before mission selection, and the Gaia Science Team since selection in 2000.
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