scispace - formally typeset
Search or ask a question
Author

Anthony G. A. Brown

Bio: Anthony G. A. Brown is an academic researcher from Leiden University. The author has contributed to research in topics: Stars & Astrometry. The author has an hindex of 50, co-authored 234 publications receiving 25984 citations. Previous affiliations of Anthony G. A. Brown include University of Manchester & Australia Telescope National Facility.
Topics: Stars, Astrometry, Population, Galaxy, Milky Way


Papers
More filters
Journal ArticleDOI
TL;DR: The second Gaia data release, Gaia DR2 as mentioned in this paper, is a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products.
Abstract: Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system. Aims: A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results. Methods: The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Results: Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0.5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the GBP (330-680 nm) and GRP (630-1050 nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14 000 minor planets in the solar system epoch astrometry and photometry are presented. Finally, Gaia DR2 also represents a new materialisation of the celestial reference frame in the optical, the Gaia-CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to Gaia DR1, and we stress the need to consider the two data releases as independent. Conclusions: Gaia DR2 represents a major achievement for the Gaia mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the Gaia survey which covers a very substantial fraction of the volume of our galaxy.

8,308 citations

Journal ArticleDOI
TL;DR: Gaia as discussed by the authors 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.
Abstract: Gaia is a cornerstone mission in the science programme of the EuropeanSpace 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.

5,164 citations

Journal ArticleDOI
TL;DR: The first Gaia data release, Gaia DR1 as discussed by the authors, consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the Hipparcos and Tycho-2 catalogues.
Abstract: Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7. Aims: A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release. Methods: The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue. Results: Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the Hipparcos and Tycho-2 catalogues - a realisation of the Tycho-Gaia Astrometric Solution (TGAS) - and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of 3000 Cepheid and RR Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yr-1 for the proper motions. A systematic component of 0.3 mas should be added to the parallax uncertainties. For the subset of 94 000 Hipparcos stars in the primary data set, the proper motions are much more precise at about 0.06 mas yr-1. For the secondary astrometric data set, the typical uncertainty of the positions is 10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to0.03 mag over the magnitude range 5 to 20.7. Conclusions: Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature five-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data.

2,174 citations

Journal ArticleDOI
TL;DR: In this article, a comprehensive survey of the stellar content of the OB associations within 1 kpc from the Sun is presented, based on Hipparcos positions, proper motions, and parallaxes.
Abstract: A comprehensive census of the stellar content of the OB associations within 1 kpc from the Sun is presented, based on Hipparcos positions, proper motions, and parallaxes. It is a key part of a long-term project to study the formation, structure, and evolution of nearby young stellar groups and related star-forming regions. OB associations are unbound moving groups, which can be detected kinematically because of their small internal velocity dispersion. The nearby associations have a large extent on the sky, which traditionally has limited astrometric membership determination to bright stars (V 6 mag), with spectral types earlier than ~B5. The Hipparcos measurements allow a major improvement in this situation. Moving groups are identified in the Hipparcos Catalog by combining de Bruijne's refurbished convergent point method with the Spaghetti method of Hoogerwerf & Aguilar. Astrometric members are listed for 12 young stellar groups, out to a distance of ~650 pc. These are the three subgroups Upper Scorpius, Upper Centaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as Vel OB2, Tr 10, Col 121, Per OB2, α Persei (Per OB3), Cas–Tau, Lac OB1, Cep OB2, and a new group in Cepheus, designated as Cep OB6. The selection procedure corrects the list of previously known astrometric and photometric B- and A-type members in these groups and identifies many new members, including a significant number of F stars, as well as evolved stars, e.g., the Wolf-Rayet stars γ2 Vel (WR 11) in Vel OB2 and EZ CMa (WR 6) in Col 121, and the classical Cepheid δ Cep in Cep OB6. Membership probabilities are given for all selected stars. Monte Carlo simulations are used to estimate the expected number of interloper field stars. In the nearest associations, notably in Sco OB2, the later-type members include T Tauri objects and other stars in the final pre–main-sequence phase. This provides a firm link between the classical high-mass stellar content and ongoing low-mass star formation. Detailed studies of these 12 groups, and their relation to the surrounding interstellar medium, will be presented elsewhere. Astrometric evidence for moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, Cam OB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive. OB associations do exist in many of these regions, but they are either at distances beyond ~500 pc where the Hipparcos parallaxes are of limited use, or they have unfavorable kinematics, so that the group proper motion does not distinguish it from the field stars in the Galactic disk. The mean distances of the well-established groups are systematically smaller than the pre-Hipparcos photometric estimates. While part of this may be caused by the improved membership lists, a recalibration of the upper main sequence in the Hertzsprung-Russell diagram may be called for. The mean motions display a systematic pattern, which is discussed in relation to the Gould Belt. Six of the 12 detected moving groups do not appear in the classical list of nearby OB associations. This is sometimes caused by the absence of O stars, but in other cases a previously known open cluster turns out to be (part of) an extended OB association. The number of unbound young stellar groups in the solar neighborhood may be significantly larger than thought previously.

1,354 citations

Journal ArticleDOI
Stephen G. Oliver1, Q. J. M. van der Aart2, M. L. Agostoni-Carbone3, Michel Aigle, Lilia Alberghina3, Despina Alexandraki, G. Antoine4, Rashida Anwar1, Juan P. G. Ballesta, Paule Bénit4, Gilbert Berben, Elisabetta Bergantino, N. Biteau, P. A. Bolle, Monique Bolotin-Fukuhara5, Anthony G. A. Brown1, Alistair J. P. Brown6, J. M. Buhler, C. Carcano3, Giovanna Carignani, Håkan Cederberg, R. Chanet4, Roland Contreras, Marc Crouzet, B. Daignan-Fornier5, E. Defoor7, M. Delgado, Jan Demolder, C. Doira5, Evelyne Dubois, Bernard Dujon8, A. Düsterhöft, D. Erdmann, M. Esteban, F. Fabre4, Cécile Fairhead8, Gérard Faye4, Horst Feldmann9, Walter Fiers, M. C. Francingues-Gaillard5, L. Franco, Laura Frontali10, H. Fukuhara4, L. J. Fuller11, P. Galland, Manda E. Gent1, D. Gigot, Véronique Gilliquet, Glansdorff Nn, André Goffeau12, M. Grenson13, P. Grisanti10, Leslie A. Grivell14, M. de Haan14, M. Haasemann, D. Hatat15, Janet Hoenicka, Johannes H. Hegemann, C. J. Herbert16, François Hilger, Stefan Hohmann, Cornelis P. Hollenberg, K. Huse, F. Iborra5, K. J. Indje1, K. Isono17, C. Jacq15, M. Jacquet5, C. M. James1, J. C. Jauniaux13, Y. Jia16, Alberto Jiménez, A. Kelly18, U. Kleinhans, P Kreisl, G. Lanfranchi, C Lewis11, C. G. vanderLinden19, G Lucchini3, K Lutzenkirchen, M.J. Maat14, L. Mallet5, G. Mannhaupet9, Enzo Martegani3, A. Mathieu4, C. T. C. Maurer19, David J. McConnell18, R. A. McKee11, F. Messenguy, Hans-Werner Mewes, Francis Molemans, M. A. Montague18, M. Muzi Falconi3, L. Navas, Carol S. Newlon20, D. Noone18, C. Pallier5, L. Panzeri3, Bruce M. Pearson11, J. Perea15, Peter Philippsen, A. Pierard, Rudi J. Planta19, Paolo Plevani3, B. Poetsch, Fritz M. Pohl21, B. Purnelle12, M. Ramezani Rad, S. W. Rasmussen, A. Raynal5, Miguel Remacha, P. Richterich21, Aki Roberts6, F. Rodriguez3, E. Sanz, I. Schaaff-Gerstenschlager, Bart Scherens, Bertold Schweitzer, Y. Shu15, J. Skala12, Piotr P. Slonimski16, F. Sor4, C. Soustelle5, R. Spiegelberg, Lubomira Stateva1, H. Y. Steensma2, S. Steiner, Agnès Thierry8, George Thireos, Maria Tzermia, L. A. Urrestarazu13, Giorgio Valle, I. Vetter9, J. C. van Vliet-Reedijk19, Marleen Voet7, Guido Volckaert7, P. Vreken19, H. Wang18, John R. Warmington1, D. von Wettstein, Barton Luke Wicksteed6, C. Wilson10, H. Wurst21, G. Xu, A. Yoshikawa17, Friedrich K. Zimmermann, J. G. Sgouros 
07 May 1992-Nature
TL;DR: The entire DNA sequence of chromosome III of the yeast Saccharomyces cerevisiae has been determined, which is the first complete sequence analysis of an entire chromosome from any organism.
Abstract: The entire DNA sequence of chromosome III of the yeast Saccharomyces cerevisiae has been determined. This is the first complete sequence analysis of an entire chromosome from any organism. The 315-kilobase sequence reveals 182 open reading frames for proteins longer than 100 amino acids, of which 37 correspond to known genes and 29 more show some similarity to sequences in databases. Of 55 new open reading frames analysed by gene disruption, three are essential genes; of 42 non-essential genes that were tested, 14 show some discernible effect on phenotype and the remaining 28 have no overt function.

811 citations


Cited by
More filters
Journal ArticleDOI
Eric S. Lander1, Lauren Linton1, Bruce W. Birren1, Chad Nusbaum1  +245 moreInstitutions (29)
15 Feb 2001-Nature
TL;DR: The results of an international collaboration to produce and make freely available a draft sequence of the human genome are reported and an initial analysis is presented, describing some of the insights that can be gleaned from the sequence.
Abstract: The human genome holds an extraordinary trove of information about human development, physiology, medicine and evolution. Here we report the results of an international collaboration to produce and make freely available a draft sequence of the human genome. We also present an initial analysis of the data, describing some of the insights that can be gleaned from the sequence.

22,269 citations

Journal ArticleDOI
TL;DR: The second Gaia data release, Gaia DR2 as mentioned in this paper, is a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products.
Abstract: Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system. Aims: A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results. Methods: The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Results: Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0.5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the GBP (330-680 nm) and GRP (630-1050 nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14 000 minor planets in the solar system epoch astrometry and photometry are presented. Finally, Gaia DR2 also represents a new materialisation of the celestial reference frame in the optical, the Gaia-CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to Gaia DR1, and we stress the need to consider the two data releases as independent. Conclusions: Gaia DR2 represents a major achievement for the Gaia mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the Gaia survey which covers a very substantial fraction of the volume of our galaxy.

8,308 citations

Journal ArticleDOI
TL;DR: Gaia as discussed by the authors 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.
Abstract: Gaia is a cornerstone mission in the science programme of the EuropeanSpace 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.

5,164 citations

Journal Article
TL;DR: The first direct detection of gravitational waves and the first observation of a binary black hole merger were reported in this paper, with a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ.
Abstract: On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160) Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

4,375 citations

Journal ArticleDOI
25 Oct 1996-Science
TL;DR: The genome of the yeast Saccharomyces cerevisiae has been completely sequenced through a worldwide collaboration and provides information about the higher order organization of yeast's 16 chromosomes and allows some insight into their evolutionary history.
Abstract: The genome of the yeast Saccharomyces cerevisiae has been completely sequenced through a worldwide collaboration. The sequence of 12,068 kilobases defines 5885 potential protein-encoding genes, approximately 140 genes specifying ribosomal RNA, 40 genes for small nuclear RNA molecules, and 275 transfer RNA genes. In addition, the complete sequence provides information about the higher order organization of yeast's 16 chromosomes and allows some insight into their evolutionary history. The genome shows a considerable amount of apparent genetic redundancy, and one of the major problems to be tackled during the next stage of the yeast genome project is to elucidate the biological functions of all of these genes.

4,254 citations