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Jean Kovalevsky - One of the best experts on this subject based on the ideXlab platform.
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Encyclopedia of Space Science and Technology - Optical Astrometry from Space
Encyclopedia of Space Science and Technology, 2003Co-Authors: Jean KovalevskyAbstract:Astrometry plays a very particular part in the realm of astronomy. One can define Astrometry as the part of astronomy that measures the apparent positions of celestial bodies on the sky. And, because these positions vary with time, the objective is to describe and study these motions that, for stars, provide two essential parameters: the proper motion and the parallax from which the distance is derived. As an extension, one ascribes also to Astrometry the measurement of apparent dimensions and shapes of celestial bodies. However, in this article, the determination of star positions, the primary goal of space Astrometry is considered. The physical quantities that are measured by Astrometry are angles that are often very small. Radians are not used in Astrometry; the basic units are degrees and seconds of arc (denoted″). Smaller units are necessary, and astrometrists are currently using milliseconds of arc and now are starting to use one millionth part of a second of arc. Some basics that have to be known for further understanding are given. Before describing what space has brought to Astrometry and what it is expected to bring in the future, it is necessary, for comparison, to present the achievements of ground-based astrometric observations. One must distinguish two classes of instruments that differ by the area of the sky measured. Descriptions of the instrument are mentioned in space missions have been launched: Hipparcos and facilities on the Hubble Space Telescope. These are described. The successful entry of Astrometry among space astronomical techniques is a powerful incentive to devise and propose to space agencies new more powerful, more effective space astrometric missions with a better science return to cost ratio. Many projects have been presented during the last decade. Some have already been thoroughly studied, and engineered descriptions of a possible realization exist. The two most ambitious projects are described. However, they have not yet been built, so the information given here is provisional. Other projects will only be mentioned, even if some might be launched before those more sophisticated. Keywords: Astrometry; ground-based Astrometry; hipparcos mission; data reduction; hubble space telescope; space interometry mission; FAME; GAIA; DIVA; LIGHT
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Future of Astrometry
Astronomy and Astrophysics Library, 2002Co-Authors: Jean KovalevskyAbstract:In Sect. 1.2, various objectives of Astrometry were presented. Then, in subsequent chapters, the most effective Earth-based and space astrometric instruments in use were described. The question which now arises is: to what extent do they fulfil the above goals and what are the astronomical and astrophysical problems that require further advances in Astrometry? In short, the answer is that demands are increasing: the recent successes of Astrometry, and particularly of Hipparcos, led astrophysicists to acknowledge the major impact of Astrometry on their science and to imagine how much more profit they would get if Astrometry were to provide significantly more accurate results for many more stars. In the following sections, we describe these needs and how they could be met in the future.
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Presentation of Astrometry
Astronomy and Astrophysics Library, 2002Co-Authors: Jean KovalevskyAbstract:What is Astrometry? What are its objectives and its place in astronomy? By what means are these goals achieved? These are the questions that we answer in this chapter before entering into the detailed description of the basic techniques of Astrometry.
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THE NEW Astrometry
Reports on Progress in Physics, 1998Co-Authors: Jean KovalevskyAbstract:First, the main objectives of Astrometry are presented and the most important features or phenomena that intervene in the measurement of positions of celestial objects are shortly described. Then, the two classical astrometric techniques that are still very much used, especially since the invention of CCDs, transit instrument and astrophotography, are described. The third section is devoted to the application of interferometric techniques to Astrometry, in optical and in radio wavelengths. In the fourth section, it is shown how much precise time measurements are important in modern Astrometry, in particular for ranging to the Moon or planets, and in studying pulsars. Then, Astrometry from satellites is presented describing the Hipparcos satellite and its results, and the applications of the Hubble Space Telescope. Finally, after presenting the new needs of astrophysics for more accurate Astrometry, a description of two major projects, GAIA and SIM, and of a few other smaller satellites that may be launched during the next decade is given.
Erik Høg - One of the best experts on this subject based on the ideXlab platform.
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Solar system and small-field Astrometry
arXiv: Instrumentation and Methods for Astrophysics, 2014Co-Authors: Erik Høg, George KaplanAbstract:Astrometric issues for solar system studies are discussed. An overview gives references and cover all aspects of the solar system where Astrometry is important: orbits of planets, moons, asteroids and NEOs, masses of asteroids, occultations of asteroids and KBOs, and families of asteroids and KBOs. The roles of Astrometry from the ground, from Gaia and from a Gaia successor are discussed, but not small-field Astrometry from space. It appears from work with CCD cameras at the 1.55 m astrometric reflector in Flagstaff that an accuracy of 1 mas is the best possible from the ground during one night observing when using ordinary telescopes, i.e. without wave-front correctors, and for field sizes larger than 2 arcmin. It has been seen that the same accuracies can be reached with the much larger 4-m class telescope on Hawaii although it is not specifically designed for Astrometry. The accuracy of 1 mas from the ground refers mainly to non-moving point sources, but it is expected that 1 mas can be reached from the ground for solar system bodies from many nights of observations when phase effects are taken into account.
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Astrometry 1960-80: from Hamburg to Hipparcos
arXiv: Instrumentation and Methods for Astrophysics, 2014Co-Authors: Erik HøgAbstract:Astrometry, the most ancient branch of astronomy, was facing extinction during much of the 20th century in the competition with astrophysics. The revival of Astrometry came with the European Astrometry satellite Hipparcos, approved by ESA in 1980 and launched 1989. Photon-counting Astrometry was the basic measuring technique in Hipparcos, a technique invented by the author in 1960 in Hamburg. The technique was implemented on the Repsold meridian circle for the Hamburg expedition to Perth in Western Australia where it worked well during 1967-72. This success paved the way for space Astrometry, pioneered in France and implemented on Hipparcos. This report gives a detailed personal account of my life and work in Hamburg Bergedorf where I lived with my family half a century ago.
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Astrometry during the past 100 years
arXiv: Instrumentation and Methods for Astrophysics, 2011Co-Authors: Erik HøgAbstract:The satellite missions Hipparcos and Gaia by the European Space Agency will together bring a decrease of astrometric errors by a factor 10000, four orders of magnitude, more than was achieved during the preceding 500 years. This modern development of Astrometry was at first obtained by photoelectric Astrometry. An experiment with this technique in 1925 led to the Hipparcos satellite mission in the years 1989-93 as described in the following reports Nos. 1 and 10. The report No. 11 is about the subsequent period of space Astrometry with CCDs in a scanning satellite. This period began in 1992 with my proposal of a mission called Roemer, which led to the Gaia mission due for launch in 2013. My contributions to the history of Astrometry and optics are based on 50 years of work in the field of Astrometry but the reports cover spans of time within the past 2000 years, e.g., 400 years of Astrometry, 650 years of optics, and the "miraculous" approval of the Hipparcos satellite mission during a few months of 1980.
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Astrometry Lost and Regained
Open Astronomy, 2011Co-Authors: Erik HøgAbstract:AbstractTechnological and scientific developments during the past century made a new branch of astronomy flourish, i.e. astrophysics, and resulted in our present deep understanding of the whole Universe. But this brought Astrometry almost to extinction because it was considered to be dull and old-fashioned, especially by young astronomers. Astrometry is the much older branch of astronomy, in fact 2000 years of age, which performs accurate measurements of positions, motions and distances of stars and other celestial bodies. Astrometric data are of great scientific and practical importance for investigation of celestial phenomena and also for control of telescopes and satellites and for monitoring of Earth rotation. Our main subject is the development during the 20th century which finally made Astrometry flourish as an integral part of astronomy through the success of the Hipparcos astrometric satellite, soon to be followed by the even more powerful Gaia mission.
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400 years of Astrometry: from Tycho Brahe to Hipparcos
Experimental Astronomy, 2009Co-Authors: Erik HøgAbstract:Galileo Galilei’s use of the newly invented telescope for astronomical observation resulted immediately in epochal discoveries about the physical nature of celestial bodies, but the advantage for Astrometry came much later. The quadrant and sextant were pre-telescopic instruments for measurement of large angles between stars, improved by Tycho Brahe in the years 1570–1590. Fitted with telescopic sights after 1660, such instruments were quite successful, especially in the hands of John Flamsteed. The meridian circle was a new type of astrometric instrument, already invented and used by Ole Romer in about 1705, but it took a hundred years before it could fully take over. The centuries-long evolution of techniques is reviewed, including the use of photoelectric Astrometry and space technology in the first Astrometry satellite, Hipparcos, launched by ESA in 1989. Hipparcos made accurate measurement of large angles a million times more efficiently than could be done in about 1950 from the ground, and it will soon be followed by Gaia which is expected to be another one million times more efficient for optical Astrometry.
Richard Dodson - One of the best experts on this subject based on the ideXlab platform.
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Precise radio Astrometry and new developments for the next generation of instruments
The Astronomy and Astrophysics Review, 2020Co-Authors: María J. Rioja, Richard DodsonAbstract:We present a technique-led review of the progression of precise radio Astrometry, from the first demonstrations, half a century ago, until to date and into the future. We cover the developments that have been fundamental to allow high accuracy and precision Astrometry to be regularly achieved. We review the opportunities provided by the next generation of instruments coming online, which are primarily: SKA, ngVLA, and pathfinders, along with EHT and other (sub)mm-wavelength arrays, Space-VLBI, Geodetic arrays, and optical Astrometry from GAIA. From the historical development, we predict the future potential astrometric performance, and, therefore, the instrumental requirements that must be provided to deliver these. The next generation of methods will allow ultra-precise Astrometry to be performed at a much wider range of frequencies (hundreds of MHz to hundreds of GHz). One of the key potentials is that Astrometry will become generally applicable, and, therefore, unbiased large surveys can be performed. The next-generation methods are fundamental in allowing this. We review the small but growing number of major astrometric surveys in the radio, to highlight the scientific impact that such projects can provide. Based on these perspectives, the future of radio Astrometry is bright. We foresee a revolution coming from: ultra-high-precision radio Astrometry, large surveys of many objects, improved sky coverage, and at new frequency bands other than those available today. These will enable the addressing of a host of innovative open scientific questions in astrophysics.
Mareki Honma - One of the best experts on this subject based on the ideXlab platform.
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The First VERA Astrometry Catalog
Publications of the Astronomical Society of Japan, 2020Co-Authors: Tomoya Hirota, Ross A. Burns, Takumi Nagayama, Mareki Honma, Yuuki Adachi, James O. Chibueze, Yoon Kyung Choi, Kazuya Hachisuka, Kazuhiro Hada, Yoshiaki HagiwaraAbstract:We present the first Astrometry catalog from the Japanese VLBI (very long baseline interferometer) project VERA (VLBI Exploration of Radio Astrometry). We have compiled all the Astrometry results from VERA, providing accurate trigonometric annual parallax and proper motion measurements. In total, 99 maser sources are listed in the VERA catalog. Among them, 21 maser sources are newly reported while the rest of 78 sources are referred to previously published results or those in preparation for forthcoming papers. The accuracy in the VERA Astrometry are revisited and compared with those from the other VLBI Astrometry projects such as BeSSeL (The Bar and Spiral Structure Legacy) Survey and GOBELINS (the Gould's Belt Distances Survey) with the VLBA (Very Long Baseline Array). We have confirmed that most of the Astrometry results are consistent with each other, and the largest error sources are due to source structure of the maser features and their rapid variation, along with the systematic calibration errors and different analysis methods. Combined with the BeSSeL results, we estimate the up-to-date fundamental Galactic parameter of $R_{0}=7.92\pm0.16_{\rm{stat.}}\pm0.3_{\rm{sys.}}$~kpc and $\Omega_{\odot}=30.17\pm0.27_{\rm{stat.}}\pm0.3_{\rm{sys.}}$~km~s$^{-1}$~kpc$^{-1}$, where $R_{0}$ and $\Omega_{\odot}$ are the distance from the Sun to the Galactic center and the Sun's angular velocity of the Galactic circular rotation, respectively.
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microarcsecond radio Astrometry
Annual Review of Astronomy and Astrophysics, 2014Co-Authors: M. J. Reid, Mareki HonmaAbstract:Astrometry provides the foundation for astrophysics. Accurate positions are required for the association of sources detected at different times or wavelengths, and distances are essential to estimate the size, luminosity, mass, and ages of most objects. Very long baseline interferometry at radio wavelengths, with diffraction-limited imaging at submilliarcsecond resolution, has long held the promise of microarcsecond Astrometry. However, only in the past decade has this been routinely achieved. Currently, parallaxes for sources across the Milky Way are being measured with ∼10 μas accuracy, and proper motions of galaxies are being determined with accuracies of ∼1 μas year−1. The astrophysical applications of these measurements cover many fields, including star formation, evolved stars, stellar and supermassive black holes, Galactic structure, the history and fate of the Local Group, the Hubble constant, and tests of general relativity. This review summarizes the methods used and the astrophysical applicatio...
M. J. Reid - One of the best experts on this subject based on the ideXlab platform.
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microarcsecond radio Astrometry
Annual Review of Astronomy and Astrophysics, 2014Co-Authors: M. J. Reid, Mareki HonmaAbstract:Astrometry provides the foundation for astrophysics. Accurate positions are required for the association of sources detected at different times or wavelengths, and distances are essential to estimate the size, luminosity, mass, and ages of most objects. Very long baseline interferometry at radio wavelengths, with diffraction-limited imaging at submilliarcsecond resolution, has long held the promise of microarcsecond Astrometry. However, only in the past decade has this been routinely achieved. Currently, parallaxes for sources across the Milky Way are being measured with ∼10 μas accuracy, and proper motions of galaxies are being determined with accuracies of ∼1 μas year−1. The astrophysical applications of these measurements cover many fields, including star formation, evolved stars, stellar and supermassive black holes, Galactic structure, the history and fate of the Local Group, the Hubble constant, and tests of general relativity. This review summarizes the methods used and the astrophysical applicatio...
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Micro-Arcsecond Radio Astrometry
Annual Review of Astronomy and Astrophysics, 2014Co-Authors: M. J. Reid, M. HonmaAbstract:Astrometry provides the foundation for astrophysics. Accurate positions are required for the association of sources detected at different times or wavelengths, and distances are essential to estimate the size, luminosity, mass, and ages of most objects. Very Long Baseline Interferometry at radio wavelengths, with diffraction-limited imaging at sub-milliarcsec resolution, has long held the promise of micro-arcsecond Astrometry. However, only in the past decade has this been routinely achieved. Currently, parallaxes for sources across the Milky Way are being measured with ~10 uas accuracy and proper motions of galaxies are being determined with accuracies of ~1 uas/y. The astrophysical applications of these measurements cover many fields, including star formation, evolved stars, stellar and super-massive black holes, Galactic structure, the history and fate of the Local Group, the Hubble constant, and tests of general relativity. This review summarizes the methods used and the astrophysical applications of micro-arcsecond radio Astrometry.