Gaia Early Data Release 3 Lindegren, L.; Klioner, S. A.; Hernández, J. ...
Astronomy and astrophysics (Berlin),
05/2021, Letnik:
649
Journal Article
Recenzirano
Odprti dostop
Context. Gaia
Early Data Release 3 (
Gaia
EDR3) contains results for 1.812 billion sources in the magnitude range
G
= 3–21 based on observations collected by the European Space Agency
Gaia
satellite ...during the first 34 months of its operational phase.
Aims.
We describe the input data, the models, and the processing used for the astrometric content of
Gaia
EDR3, as well as the validation of these results performed within the astrometry task.
Methods.
The processing broadly followed the same procedures as for
Gaia
DR2, but with significant improvements to the modelling of observations. For the first time in the
Gaia
data processing, colour-dependent calibrations of the line- and point-spread functions have been used for sources with well-determined colours from DR2. In the astrometric processing these sources obtained five-parameter solutions, whereas other sources were processed using a special calibration that allowed a pseudocolour to be estimated as the sixth astrometric parameter. Compared with DR2, the astrometric calibration models have been extended, and the spin-related distortion model includes a self-consistent determination of basic-angle variations, improving the global parallax zero point.
Results. Gaia
EDR3 gives full astrometric data (positions at epoch J2016.0, parallaxes, and proper motions) for 1.468 billion sources (585 millionwith five-parameter solutions, 882 million with six parameters), and mean positions at J2016.0 for an additional 344 million.Solutions with five parameters are generally more accurate than six-parameter solutions, and are available for 93% of the sources brighter than the 17th magnitude. The median uncertainty in parallax and annual proper motion is 0.02–0.03 mas at magnitude
G
= 9–14, and around 0.5 mas at
G
= 20. Extensive characterisation of the statistical properties of the solutions is provided, including the estimated angular power spectrum of parallax bias from the quasars.
Multiply imaged quasars in the Gaia DR1 Ducourant, C.; Delchambre, L.; Finet, F. ...
Proceedings of the International Astronomical Union,
04/2017, Letnik:
12, Številka:
S330
Journal Article
Recenzirano
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Because of to its exceptional resolving power, Gaia should detect a few thousands gravitational lensed systems. These consist in multiple images of background quasars. The estimated number of lens ...phenomena in the sky, however, depends on the cosmological model considered. By taking into account the observational bias that will restrict the detection of lensed quasars, identification of these up to a given limiting magnitude will constrain the cosmological parameters. We have investigated the known gravitationally lensed quasars present in the Gaia DR1, and found that a significant number of components of these systems have been measured and are present in the Gaia DR1 catalogue although quasi none of them have all their components detected. We additionally examined the immediate surroundings of QSOs from the large Quasar catalogue, LQAC3, and detected several configurations compatible with gravitational lensing phenomena. A more global strategy to systematically detect the potential candidates in the various releases of the Gaia catalogue is presented.
Context. Gaia Data Release 2 provides high-precision astrometry and three-band photometry for about 1.3 billion sources over the full sky. The precision, accuracy, and homogeneity of both astrometry ...and photometry are unprecedented. Aims. We highlight the power of the Gaia DR2 in studying many fine structures of the Hertzsprung-Russell diagram (HRD). Gaia allows us to present many different HRDs, depending in particular on stellar population selections. We do not aim here for completeness in terms of types of stars or stellar evolutionary aspects. Instead, we have chosen several illustrative examples. Methods. We describe some of the selections that can be made in Gaia DR2 to highlight the main structures of the Gaia HRDs. We select both field and cluster (open and globular) stars, compare the observations with previous classifications and with stellar evolutionary tracks, and we present variations of the Gaia HRD with age, metallicity, and kinematics. Late stages of stellar evolution such as hot subdwarfs, post-AGB stars, planetary nebulae, and white dwarfs are also analysed, as well as low-mass brown dwarf objects. Results. The Gaia HRDs are unprecedented in both precision and coverage of the various Milky Way stellar populations and stellar evolutionary phases. Many fine structures of the HRDs are presented. The clear split of the white dwarf sequence into hydrogen and helium white dwarfs is presented for the first time in an HRD. The relation between kinematics and the HRD is nicely illustrated. Two different populations in a classical kinematic selection of the halo are unambiguously identified in the HRD. Membership and mean parameters for a selected list of open clusters are provided. They allow drawing very detailed cluster sequences, highlighting fine structures, and providing extremely precise empirical isochrones that will lead to more insight in stellar physics. Conclusions. Gaia DR2 demonstrates the potential of combining precise astrometry and photometry for large samples for studies in stellar evolution and stellar population and opens an entire new area for HRD-based studies.
Gaia Early Data Release 3 Carrasco, J. M.; Cooper, W. J.; Brown, A. G. A. ...
Astronomy and astrophysics (Berlin),
05/2021, Letnik:
649
Journal Article, Web Resource
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Aims.
We produce a clean and well-characterised catalogue of objects within 100 pc of the Sun from the
Gaia
Early Data Release 3. We characterise the catalogue through comparisons to the full data ...release, external catalogues, and simulations. We carry out a first analysis of the science that is possible with this sample to demonstrate its potential and best practices for its use.
Methods.
Theselection of objects within 100 pc from the full catalogue used selected training sets, machine-learning procedures, astrometric quantities, and solution quality indicators to determine a probability that the astrometric solution is reliable. The training set construction exploited the astrometric data, quality flags, and external photometry. For all candidates we calculated distance posterior probability densities using Bayesian procedures and mock catalogues to define priors. Any object with reliable astrometry and a non-zero probability of being within 100 pc is included in the catalogue.
Results.
We have produced a catalogue of 331 312 objects that we estimate contains at least 92% of stars of stellar type M9 within 100 pc of the Sun. We estimate that 9% of the stars in this catalogue probably lie outside 100 pc, but when the distance probability function is used, a correct treatment of this contamination is possible. We produced luminosity functions with a high signal-to-noise ratio for the main-sequence stars, giants, and white dwarfs. We examined in detail the Hyades cluster, the white dwarf population, and wide-binary systems and produced candidate lists for all three samples. We detected local manifestations of several streams, superclusters, and halo objects, in which we identified 12 members of
Gaia
Enceladus. We present the first direct parallaxes of five objects in multiple systems within 10 pc of the Sun.
Conclusions.
We provide the community with a large, well-characterised catalogue of objects in the solar neighbourhood. This is a primary benchmark for measuring and understanding fundamental parameters and descriptive functions in astronomy.
Echelle spectra of 10 bright asteroids are presented and compared against an observed twilight spectrum and a computed Solar spectrum. Spectra covering a 2130 Å spectral range centered on $\lambda = ...5785$ Å are of high resolving power and high signal to noise ratio. We compare detailed properties of spectral lines and not albedo variations. It is shown that the normalized Solar and asteroid spectra are identical except for radial velocity (RV) shifts which can be predicted at accuracy level of 1 m s-1. So asteroids are proposed as new and extremely accurate radial velocity standards. Predicted and measured RVs of observed asteroids match within the limits of accuracy of the instrument. There are numerous absorption lines in the reflected Solar spectrum. This allows a direct mapping of the resolving power of a spectrograph between and along echelle spectral orders. Thus asteroid spectra can be used to test the wavelength calibration and resolving power of spectrographs on the ground as well as in space, including the Gaia mission of ESA. All spectra are given in electronic form.
Gaia Data Release 2 Lindegren, L.; Hernández, J.; Bombrun, A. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
Recenzirano
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Context. Gaia
Data Release 2 (
Gaia
DR2) contains results for 1693 million sources in the magnitude range 3 to 21 based on observations collected by the European Space Agency
Gaia
satellite during ...the first 22 months of its operational phase.
Aims.
We describe the input data, models, and processing used for the astrometric content of
Gaia
DR2, and the validation of these resultsperformed within the astrometry task.
Methods.
Some 320 billion centroid positions from the pre-processed astrometric CCD observations were used to estimate the five astrometric parameters (positions, parallaxes, and proper motions) for 1332 million sources, and approximate positions at the reference epoch J2015.5 for an additional 361 million mostly faint sources. These data were calculated in two steps. First, the satellite attitude and the astrometric calibration parameters of the CCDs were obtained in an astrometric global iterative solution for 16 million selected sources, using about 1% of the input data. This primary solution was tied to the extragalactic International Celestial Reference System (ICRS) by means of quasars. The resulting attitude and calibration were then used to calculate the astrometric parameters of all the sources. Special validation solutions were used to characterise the random and systematic errors in parallax and proper motion.
Results.
For the sources with five-parameter astrometric solutions, the median uncertainty in parallax and position at the reference epoch J2015.5 is about 0.04 mas for bright (
G
< 14 mag) sources, 0.1 mas at
G
= 17 mag, and 0.7 masat
G
= 20 mag. In the proper motion components the corresponding uncertainties are 0.05, 0.2, and 1.2 mas yr
−1
, respectively.The optical reference frame defined by
Gaia
DR2 is aligned with ICRS and is non-rotating with respect to the quasars to within 0.15 mas yr
−1
. From the quasars and validation solutions we estimate that systematics in the parallaxes depending on position, magnitude, and colour are generally below 0.1 mas, but the parallaxes are on the whole too small by about 0.03 mas. Significant spatial correlations of up to 0.04 mas in parallax and 0.07 mas yr
−1
in proper motion are seen on small (< 1 deg) and intermediate (20 deg) angular scales. Important statistics and information for the users of the
Gaia
DR2 astrometry are given in the appendices.
Gaia Data Release 2 Bastian, U.; Babusiaux, C.; Breddels, M. A. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616, Številka:
A12
Journal Article, Web Resource
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Context.
Aims.
The goal of this paper is to demonstrate the outstanding quality of the second data release of the
Gaia
mission and its power for constraining many different aspects of the dynamics of ...the satellites of the Milky Way. We focus here on determining the proper motions of 75 Galactic globular clusters, nine dwarf spheroidal galaxies, one ultra-faint system, and the Large and Small Magellanic Clouds.
Methods.
Using data extracted from the
Gaia
archive, we derived the proper motions and parallaxes for these systems, as well as their uncertainties. We demonstrate that the errors, statistical and systematic, are relatively well understood. We integrated the orbits of these objects in three different Galactic potentials, and characterised their properties. We present the derived proper motions, space velocities, and characteristic orbital parameters in various tables to facilitate their use by the astronomical community.
Results.
Our limited and straightforward analyses have allowed us for example to (
i
) determine absolute and very precise proper motions for globular clusters; (
ii
) detect clear rotation signatures in the proper motions of at least five globular clusters; (
iii
) show that the satellites of the Milky Way are all on high-inclination orbits, but that they do not share a single plane of motion; (
iv
) derive a lower limit for the mass of the Milky Way of 9.1
-2.6
+6.2
× 10
11
M
⊙
based on the assumption that the Leo I dwarf spheroidal is bound; (
v
) derive a rotation curve for the Large Magellanic Cloud based solely on proper motions that is competitive with line-of-sight velocity curves, now using many orders of magnitude more sources; and (
vi
) unveil the dynamical effect of the bar on the motions of stars in the Large Magellanic Cloud.
Conclusions.
All these results highlight the incredible power of the
Gaia
astrometric mission, and in particular of its second data release.
Gaia Data Release 1 Brown, A G A; Vallenari, A; Prusti, T ...
Astronomy and astrophysics (Berlin),
11/2016, Letnik:
595
Journal Article, Web Resource
Recenzirano
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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 super(-1) for the proper motions. A systematic component of ~0.3 mas should be added to the parallax uncertainties. For the subset of ~94000 Hipparcos stars in the primary data set, the proper motions are much more precise at about 0.06 mas yr super(-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 to ~0.03 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.
The Yarkovsky effect, which causes a slow drifting of the orbital elements (mainly the semimajor axis) of km-sized asteroids and meteors, is the weak non-gravitational force experienced by these ...bodies due to the emission of thermal photons. This effect is believed to play a role in the delivery of near-Earth asteroids (NEAs) from the main belt, in the spreading of the orbital elements of asteroid families, and in the orbital evolution of potentially hazardous asteroids.
Here we present preliminary results of simulationing indicating that the perturbations induced by the Yarkovsky effect on the positions of some tens of NEAs can be observed by means of the high-precision astrometric observations that will be provided by the ESA mission Gaia.
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