Gaia Data Release 2 Lindegren, L.; Hernández, J.; Bombrun, A. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
Recenzirano
Odprti dostop
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.
The Hipparcos Catalogue Perryman, M a C; Lindegren, L; Kovalevsky, J. ...
Astronomy and astrophysics (Berlin),
07/1997, Letnik:
323, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The principal observational characteristics of the Hipparcos Catalogue, and a summary of its main astrometric and photometric properties, are presented. Median astrometric standard errors (in ...position, parallax, and annual proper motion) are in the range 0.7-0.9 milliarcsec (mas) for stars brighter than 9 mag at the catalogue epoch (J1991.25). The catalogue is a ma-terialisation of the ICRS reference system, coinciding with its principal axes at the level of ±0.6 mas, and with proper motions consistent with an inertial system at the level of ±0.25 mas/yr. The 118 218 constituent stars provide a mean sky density of ∼ 3 stars deg −2. The catalogue is available in printed and machine-readable forms.
The Gaia satellite was selected as a cornerstone mission of the European Space Agency (ESA) in 2000 October and confirmed in 2002 with a current target launch date of 2011. The Gaia mission will ...gather on the same observational principles as Hipparcos detailed astrometric, photometric and spectroscopic properties of about one billion sources brighter than V= 20 mag. The nature of the measured objects ranges from near-Earth objects (NEOs) to gamma-ray burst afterglows, and encompasses virtually any kind of stars in our Galaxy. Gaia will provide multicolour (in about 20 passbands extending over the visible range) photometry with typically 250 observations distributed over 40 well-separated epochs during the 5-yr mission. The multi-epoch nature of the project will permit the detection and analysis of variable sources whose number is currently estimated in the range of several tens of millions, among the detectable sources. In this paper, we assess the performances of Gaia in analysing photometric periodic phenomena. We first quickly present the overall observational principle before discussing the implication of the scanning law in the time-sampling. Then from extensive simulations one assesses the performances in the recovery of periodic signals as a function of the period, signal-to-noise ratio and position on the sky for simple sinusoidal variability.
The third data release of in June 2022, included the first large sample of sparse photometric data for more than 150\,000 Solar System objects (SSOs), mainly asteroids. The SSO photometric data can ...be processed to derive information on the physical properties for a large number of objects, including spin properties, surface photometric behaviour in a variety of illumination conditions, and overall shape. After selecting a set of 22\,815 objects for which an adequate number of accurate photometric measurements had been obtained by we applied the 'genetic' algorithm of photometric inversion developed by the Data Processing and Analysis Consortium to process SSO photometric data. Given the need to minimise the required data processing time, the algorithm was set to adopt a simple triaxial ellipsoid shape model. Our results show that in spite of the limited variety of observing circumstances and the limited numbers of measurements per object at present (in the majority of cases no greater than $40$ and still far from the number expected at the end of the mission of about $60$ - $70$), the proportion of correct determinations for the spin period among the observed targets is about $85$<!PCT!>. This percentage is based on a comparison with reliable literature data following a moderate filtering procedure developed to remove dubious solutions. The analysis performed in this paper is important in the context of developing further improvements to the adopted data reduction procedure. This includes the possible development of better solution filtering procedures that take into account, for each object, the possible presence of multiple, equivalent spin period solutions that have not been systematically investigated in this preliminary application.
Gaia promises for the reference frame Mignard, F.
Proceedings of the International Astronomical Union,
08/2012, Letnik:
10, Številka:
H16
Journal Article
Recenzirano
Odprti dostop
Expectations of the Gaia astrometry mission regarding the realisation of an optical kinematical reference frame based on extragalactic sources are summarized.
Context. Over the last decade, the positional observations of Mars have reached such an accuracy that the uncertainty of the asteroid masses has become the main cause of uncertainty in its ephemeris. ...Currently, only about 36 masses are estimated by direct measurements with a formal accuracy better than 10%. However, the true errors are probably larger due to unaccounted systematic effects. Thus, asteroid masses are still a limitation in the accurate modeling of the perturbations on Mars. Nevertheless, two future space missions, Gaia and Dawn, could improve the situation by combining their results. Aims. The main objective of this paper is to identify and provide a list of major perturbers of Mars which could bring significant disturbances over the next 50 years, having in perspective the expected contribution of Gaia to asteroid mass determination. It will also point out the asteroids whose mass only could be improved from ground-based observations – by direct measurements or size and shape derivation. Methods. The selection procedure of Mars' perturbers includes analytical and numerical treatments. The analytical analysis is based on harmonic decomposition of the perturbations on the longitude and semi-major axis of Mars as a function of the mean longitude of the planet and the perturbing asteroid to the first order in asteroid mass. Regarding the numerical treatments, the first consists in selecting the potential perturbers, filtering them out with the cumulative deviations of Mars' path over the next 50 years. The second one uses the accumulation of the perturbations on the semi-major axis, eccentricity, and inclination of Mars due to each asteroid over the same period of time. Thus, a list of perturbers of Mars is derived from the number of selections by each method. Results. 62 asteroids have been selected as the most perturbing – or potentially so – for the orbit of Mars, among which 32 were already listed by Williams in 1984, and all are in the list of 300 perturbing asteroids derived by the same author in about 1995. More interestingly, 53 belong to the list of asteroids for which Gaia could give their mass with a relative precision better than 50% and 27 less than 10%, a further indication of the importance of Gaia to contribute to improving Mars' ephemeris. Nevertheless, 7 of them will have a mass poorly estimated – with a relative error greater than 30% – and 9 without estimates at all. Therefore, ground-based observations may be useful to overcome these limitations.
Gaia Early Data Release 3 Brown, A. G. A.; Prusti, T.; Eyer, L. ...
Astronomy and astrophysics (Berlin),
05/2021, Letnik:
649
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
We present the early installment of the third
Gaia
data release,
Gaia
EDR3, consisting of astrometry and photometry for 1.8 billion sources brighter than magnitude 21, complemented with the ...list of radial velocities from
Gaia
DR2.
Aims.
A summary of the contents of
Gaia
EDR3 is presented, accompanied by a discussion on the differences with respect to
Gaia
DR2 and an overview of the main limitations which are present in the survey. Recommendations are made on the responsible use of
Gaia
EDR3 results.
Methods.
The raw data collected with the
Gaia
instruments during the first 34 months of the mission have been processed by the
Gaia
Data Processing and Analysis Consortium and turned into this early third data release, which represents a major advance with respect to
Gaia
DR2 in terms of astrometric and photometric precision, accuracy, and homogeneity.
Results. Gaia
EDR3 contains celestial positions and the apparent brightness in
G
for approximately 1.8 billion sources. For 1.5 billion of those sources, parallaxes, proper motions, and the (
G
BP
−
G
RP
) colour are also available. The passbands for
G
,
G
BP
, and
G
RP
are provided as part of the release. For ease of use, the 7 million radial velocities from
Gaia
DR2 are included in this release, after the removal of a small number of spurious values. New radial velocities will appear as part of
Gaia
DR3. Finally,
Gaia
EDR3 represents an updated materialisation of the celestial reference frame (CRF) in the optical, the
Gaia
-CRF3, which is based solely on extragalactic sources. The creation of the source list for
Gaia
EDR3 includes enhancements that make it more robust with respect to high proper motion stars, and the disturbing effects of spurious and partially resolved sources. The source list is largely the same as that for
Gaia
DR2, but it does feature new sources and there are some notable changes. The source list will not change for
Gaia
DR3.
Conclusions. Gaia
EDR3 represents a significant advance over
Gaia
DR2, with parallax precisions increased by 30 per cent, proper motion precisions increased by a factor of 2, and the systematic errors in the astrometry suppressed by 30–40% for the parallaxes and by a factor ~2.5 for the proper motions. The photometry also features increased precision, but above all much better homogeneity across colour, magnitude, and celestial position. A single passband for
G
,
G
BP
, and
G
RP
is valid over the entire magnitude and colour range, with no systematics above the 1% level
Summary of the contents and survey properties Brown, A.G.A.; Granvik, Mikael; Zwitter, T.
Astronomy and astrophysics (Berlin),
2018, 2018-01-01, Letnik:
16, Številka:
A1
Journal Article
Recenzirano
Odprti dostop
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 G(BP) (330-680 nm) and G(RP) (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.
Gaia Data Release 2 Prusti, T.; Evans, D. W.; Eyer, L. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article, Web Resource
Recenzirano
Odprti dostop
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
G
BP
(330–680 nm) and
G
RP
(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.
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