This is a corrigendum for Gaia Collaboration (2021). It corrects errors in Sects. 6.3.2 and 7.2 and Appendix A, which erroneously state that the correction to theG-band fluxes and magnitudes ...presented in Riello et al. (2021) (their Table 5) should be applied to sources in Gaia EDR3 with six-parameter astrometric solutions. In fact, the corrections should be applied to sources with twoparameter or six-parameter astrometric solutions. The corrected Astronomical Data Query Language (ADQL) query and Python source code from Appendix A are presented in the new version of Appendix A below. Following the discovery of the above error, a more detailed investigation was done for the sources with two-parameter (2-p) astrometric solutions. Out of the 344 million 2-p sources present in Gaia EDR3, about 20 million have an astrometric solution in which the actual source colour was used instead of a default colour. This means that for these 20 million 2-p sources the Gband correction should actually not be applied. These sources are mostly faint, with 96% at magnitudes G > 20, and for 75% of these 20 million sources the correction that is (wrongly) applied amounts to less than 4 milli-magnitudes. It was thus decided not to make a special effort to exclude these sources from the correction. Should a user of the Gaia EDR3 data wish to undo the wrong correction for one or more of these 20 million sources, the list of source IDs and applied corrections can be provided on request. Appendix A: G-band corrections for sources with two-parameter or six-parameter astrometric solutions Figure A.1 shows how to formulate an ADQL query, to be executed in the Gaia EDR3 archive, that contains an on-the-fly calculation of the corrected G-band fluxes or magnitudes. These queries are somewhat complex and create a performance overhead. Hence downloading the requisite Gaia EDR3 fields and calculating the corrections a posteriori may be more efficient. Example Python code to do this is included in Fig. A.2. The Python code is also available as a Jupyter notebook1. Appendix A: G-band corrections for sources with two-parameter or six-parameter astrometric solutions Figure A.1 shows how to formulate an ADQL query, to be executed in the Gaia EDR3 archive, that contains an on-the-fly calculation of the corrected G-band fluxes or magnitudes. These queries are somewhat complex and create a performance overhead. Hence downloading the requisite Gaia EDR3 fields and calculating the corrections a posteriori may be more efficient. Example Python code to do this is included in Fig. A.2. The Python code is also available as a Jupyter notebook.
The ESA space astrometry mission Gaia will measure the positions, parallaxes and proper motions of the 1 billion brightest stars on the sky. Expected accuracies are in the 7–25 μas range down to 15 ...mag and sub-mas accuracies at the faint limit (20 mag). The astrometric data are complemented by low-resolution spectrophotometric data in the 330–1000 nm wavelength range and, for the brighter stars, radial velocity measurements. The scientific case covers an extremely wide range of topics in galactic and stellar astrophysics, solar system and exoplanet science, as well as the establishment of a very accurate, dense and faint optical reference frame. With a planned launch around 2012 and an (extended) operational lifetime of 6 years, final results are expected around 2021. We give a brief overview of the science goals of Gaia, the overall project organisation, expected performance, and some key technical features and challenges.
Gaia Data Release 3 Arenou, F.; Faigler, S.; Kervella, P. ...
Astronomy and astrophysics (Berlin),
06/2023, Letnik:
674
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
The
Gaia
DR3 catalogue contains, for the first time, about 800 000 solutions with either orbital elements or trend parameters for astrometric, spectroscopic, and eclipsing binaries, and ...combinations of these three.
Aims.
With this paper, we aim to illustrate the huge potential of this large non-single-star catalogue.
Methods.
Using the orbital solutions and models of the binaries, we have built a catalogue of tens of thousands of stellar masses or lower limits thereof, some with consistent flux ratios. Properties concerning the completeness of the binary catalogues are discussed, statistical features of the orbital elements are explained, and a comparison with other catalogues is performed.
Results.
Illustrative applications are proposed for binaries across the Hertzsprung-Russell Diagram (HRD). Binarity is studied in the giant branch and a search for genuine spectroscopic binaries among long-period variables is performed. The discovery of new EL CVn systems illustrates the potential of combining variability and binarity catalogues. Potential compact object companions are presented, mainly white dwarf companions or double degenerates, but one candidate neutron star is also found. Towards the bottom of the main sequence, the orbits of previously suspected binary ultracool dwarfs are determined and new candidate binaries are discovered. The long awaited contribution of
Gaia
to the analysis of the substellar regime shows the brown dwarf desert around solar-type stars using true rather than minimum masses, and provides new important constraints on the occurrence rates of substellar companions to M dwarfs. Several dozen new exoplanets are proposed, including two with validated orbital solutions and one super-Jupiter orbiting a white dwarf, all being candidates requiring confirmation. Besides binarity, higher order multiple systems are also found.
Conclusions.
By increasing the number of known binary orbits by more than one order of magnitude,
Gaia
DR3 will provide a rich reservoir of dynamical masses and an important contribution to the analysis of stellar multiplicity.
Gaia Data Release 2 Hobbs, D.; Michalik, D.; Geyer, R. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616, Številka:
A14
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context. The second release of Gaia data ( Gaia DR2) contains the astrometric parameters for more than half a million quasars. This set defines a kinematically non-rotating reference frame in the ...optical domain. A subset of these quasars have accurate VLBI positions that allow the axes of the reference frame to be aligned with the International Celestial Reference System (ICRF) radio frame. Aims. We describe the astrometric and photometric properties of the quasars that were selected to represent the celestial reference frame of Gaia DR2 ( Gaia -CRF2), and to compare the optical and radio positions for sources with accurate VLBI positions. Methods. Descriptive statistics are used to characterise the overall properties of the quasar sample. Residual rotation and orientation errors and large-scale systematics are quantified by means of expansions in vector spherical harmonics. Positional differences are calculated relative to a prototype version of the forthcoming ICRF3. Results. Gaia -CRF2 consists of the positions of a sample of 556 869 sources in Gaia DR2, obtained from a positional cross-match with the ICRF3-prototype and AllWISE AGN catalogues. The sample constitutes a clean, dense, and homogeneous set of extragalactic point sources in the magnitude range G ≃ 16 to 21 mag with accurately known optical positions. The median positional uncertainty is 0.12 mas for G < 18 mag and 0.5 mas at G = mag. Large-scale systematics are estimated to be in the range 20 to 30 μ as. The accuracy claims are supported by the parallaxes and proper motions of the quasars in Gaia DR2. The optical positions for a subset of 2820 sources in common with the ICRF3-prototype show very good overall agreement with the radio positions, but several tens of sources have significantly discrepant positions. Conclusions. Based on less than 40% of the data expected from the nominal Gaia mission, Gaia -CRF2 is the first realisation of a non-rotating global optical reference frame that meets the ICRS prescriptions, meaning that it is built only on extragalactic sources. Its accuracy matches the current radio frame of the ICRF, but the density of sources in all parts of the sky is much higher, except along the Galactic equator.
Gaia Data Release 2 Holl, B.; Audard, M.; Nienartowicz, K. ...
Astronomy and astrophysics (Berlin),
10/2018, Letnik:
618
Journal Article
Recenzirano
Odprti dostop
Context.
The
Gaia
Data Release 2 (DR2) contains more than half a million sources that are identified as variable stars.
Aims.
We summarise the processing and results of the identification of variable ...source candidates of RR Lyrae stars, Cepheids, long-period variables (LPVs), rotation modulation (BY Dra-type) stars,
δ
Scuti and SX Phoenicis stars, and short-timescale variables. In this release we aim to provide useful but not necessarily complete samples of candidates.
Methods.
The processed
Gaia
data consist of the
G
,
G
BP
, and
G
RP
photometry during the first 22 months of operations as well as positions and parallaxes. Various methods from classical statistics, data mining, and time-series analysis were applied and tailored to the specific properties of
Gaia
data, as were various visualisation tools to interpret the data.
Results.
The DR2 variability release contains 228 904 RR Lyrae stars, 11 438 Cepheids, 151 761 LPVs, 147 535 stars with rotation modulation, 8882
δ
Scuti and SX Phoenicis stars, and 3018 short-timescale variables. These results are distributed over a classification and various Specific Object Studies tables in the
Gaia
archive, along with the three-band time series and associated statistics for the underlying 550 737 unique sources. We estimate that about half of them are newly identified variables. The variability type completeness varies strongly as a function of sky position as a result of the non-uniform sky coverage and intermediate calibration level of these data. The probabilistic and automated nature of this work implies certain completeness and contamination rates that are quantified so that users can anticipate their effects. Thismeans that even well-known variable sources can be missed or misidentified in the published data.
Conclusions.
The DR2 variability release only represents a small subset of the processed data. Future releases will include more variable sources and data products; however, DR2 shows the (already) very high quality of the data and great promise for variability studies.
Gaia Early Data Release 3 Hodgkin, S. T.; Harrison, D. L.; Breedt, E. ...
Astronomy and astrophysics (Berlin),
08/2021, Letnik:
652
Journal Article
Recenzirano
Odprti dostop
Context.
Since July 2014, the
Gaia
mission has been engaged in a high-spatial-resolution, time-resolved, precise, accurate astrometric, and photometric survey of the entire sky.
Aims.
We present the
...Gaia
Science Alerts project, which has been in operation since 1 June 2016. We describe the system which has been developed to enable the discovery and publication of transient photometric events as seen by
Gaia
.
Methods.
We outline the data handling, timings, and performances, and we describe the transient detection algorithms and filtering procedures needed to manage the high false alarm rate. We identify two classes of events: (1) sources which are new to
Gaia
and (2)
Gaia
sources which have undergone a significant brightening or fading. Validation of the
Gaia
transit astrometry and photometry was performed, followed by testing of the source environment to minimise contamination from Solar System objects, bright stars, and fainter near-neighbours.
Results.
We show that the
Gaia
Science Alerts project suffers from very low contamination, that is there are very few false-positives. We find that the external completeness for supernovae,
C
E
= 0.46, is dominated by the
Gaia
scanning law and the requirement of detections from both fields-of-view. Where we have two or more scans the internal completeness is
C
I
= 0.79 at 3 arcsec or larger from the centres of galaxies, but it drops closer in, especially within 1 arcsec.
Conclusions.
The per-transit photometry for
Gaia
transients is precise to 1% at
G
= 13, and 3% at
G
= 19. The per-transit astrometry is accurate to 55 mas when compared to
Gaia
DR2. The
Gaia
Science Alerts project is one of the most homogeneous and productive transient surveys in operation, and it is the only survey which covers the whole sky at high spatial resolution (subarcsecond), including the Galactic plane and bulge.
Gaia GraL: Gaia DR2 Gravitational Lens Systems Delchambre, L.; Krone-Martins, A.; Wertz, O. ...
Astronomy and astrophysics (Berlin),
02/2019, Letnik:
622, Številka:
622
Journal Article, Web Resource
Recenzirano
Odprti dostop
Aims
. In this work, we aim to provide a reliable list of gravitational lens candidates based on a search performed over the entire
Gaia
Data Release 2 (
Gaia
DR2). We also aim to show that the ...astrometric and photometric information coming from the
Gaia
satellite yield sufficient insights for supervised learning methods to automatically identify strong gravitational lens candidates with an efficiency that is comparable to methods based on image processing.
Methods
. We simulated 106 623 188 lens systems composed of more than two images, based on a regular grid of parameters characterizing a non-singular isothermal ellipsoid lens model in the presence of an external shear. These simulations are used as an input for training and testing our supervised learning models consisting of extremely randomized trees (ERTs). These trees are finally used to assign to each of the 2 129 659 clusters of celestial objects extracted from the
Gaia
DR2 a discriminant value that reflects the ability of our simulations to match the observed relative positions and fluxes from each cluster. Once complemented with additional constraints, these discriminant values allow us to identify strong gravitational lens candidates out of the list of clusters.
Results
. We report the discovery of 15 new quadruply-imaged lens candidates with angular separations of less than 6″ and assess the performance of our approach by recovering 12 of the 13 known quadruply-imaged systems with all their components detected in
Gaia
DR2 with a misclassification rate of fortuitous clusters of stars as lens systems that is below 1%. Similarly, the identification capability of our method regarding quadruply-imaged systems where three images are detected in
Gaia
DR2 is assessed by recovering 10 of the 13 known quadruply-imaged systems having one of their constituting images discarded. The associated misclassification rate varies between 5.83% and 20%, depending on the image we decided to remove.
The authors compare stellar catalogues with position and proper motion components using a decomposition on a set of orthogonal vector spherical harmonics. They aim to show the theoretical and ...practical advantages of this technique as a result of invariance properties and the independence of the decomposition from a prior model. They describe the mathematical principles used to perform the spectral decomposition, evaluate the level of significance of the multipolar components, and examine the transformation properties under space rotation. The principles are illustrated with a characterisation of systematic effects in the FK5 catalogue compared to Hipparcos and with an application to extraction of the rotation and dipole acceleration in the astrometric solution of QSOs expected from Gaia.
Gaia Data Release 2 Glass, F.; Brown, A. G. A.; de Bruijne, J. H. J. ...
Astronomy and astrophysics (Berlin),
03/2019, Letnik:
623
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
The ESA
Gaia
mission provides a unique time-domain survey for more than 1.6 billion sources with
G
≲ 21 mag.
Aims.
We showcase stellar variability in the Galactic colour-absolute magnitude ...diagram (CaMD). We focus on pulsating, eruptive, and cataclysmic variables, as well as on stars that exhibit variability that is due to rotation and eclipses.
Methods.
We describe the locations of variable star classes, variable object fractions, and typical variability amplitudes throughout the CaMD and show how variability-related changes in colour and brightness induce “motions”. To do this, we use 22 months of calibrated photometric, spectro-photometric, and astrometric
Gaia
data of stars with a significant parallax. To ensure that a large variety of variable star classes populate the CaMD, we crossmatched
Gaia
sources with known variable stars. We also used the statistics and variability detection modules of the
Gaia
variability pipeline. Corrections for interstellar extinction are not implemented in this article.
Results. Gaia
enables the first investigation of Galactic variable star populations in the CaMD on a similar, if not larger, scale as was previously done in the Magellanic Clouds. Although the observed colours are not corrected for reddening, distinct regions are visible in which variable stars occur. We determine variable star fractions to within the current detection thresholds of
Gaia
. Finally, we report the most complete description of variability-induced motion within the CaMD to date.
Conclusions. Gaia
enables novel insights into variability phenomena for an unprecedented number of stars, which will benefit the understanding of stellar astrophysics. The CaMD of Galactic variable stars provides crucial information on physical origins of variability in a way that has previously only been accessible for Galactic star clusters or external galaxies. Future
Gaia
data releases will enable significant improvements over this preview by providing longer time series, more accurate astrometry, and additional data types (time series BP and RP spectra, RVS spectra, and radial velocities), all for much larger samples of stars.
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