Gaia Data Release 2 Arenou, F.; Luri, X.; Babusiaux, C. ...
Astronomy & astrophysics,
08/2018, Letnik:
616
Journal Article
Recenzirano
Odprti dostop
Context. The second Gaia data release (DR2) contains very precise astrometric and photometric properties for more than one billion sources, astrophysical parameters for dozens of millions, radial ...velocities for millions, variability information for half a million stars from selected variability classes, and orbits for thousands of solar system objects. Aims. Before the catalogue was published, these data have undergone dedicated validation processes. The goal of this paper is to describe the validation results in terms of completeness, accuracy, and precision of the various Gaia DR2 data. Methods. The validation processes include a systematic analysis of the catalogue content to detect anomalies, either individual errors or statistical properties, using statistical analysis and comparisons to external data or to models. Results. Although the astrometric, photometric, and spectroscopic data are of unprecedented quality and quantity, it is shown that the data cannot be used without dedicated attention to the limitations described here, in the catalogue documentation and in accompanying papers. We place special emphasis on the caveats for the statistical use of the data in scientific exploitation. In particular, we discuss the quality filters and the consideration of the properties, systematics, and uncertainties from astrometry to astrophysical parameters, together with the various selection functions.
Gaia Data Release 2 Soubiran, C.; Jasniewicz, G.; Chemin, L. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
Recenzirano
Aims. The Radial Velocity Spectrometer (RVS) on board the ESA satellite mission Gaia has no calibration device. Therefore, the radial velocity zero point needs to be calibrated with stars that are ...proved to be stable at a level of 300 m s−1 during the Gaia observations. Methods. We compiled a dataset of ~71 000 radial velocity measurements from five high-resolution spectrographs. A catalogue of 4813 stars was built by combining these individual measurements. The zero point was established using asteroids. Results. The resulting catalogue has seven observations per star on average on a typical time baseline of 6 yr, with a median standard deviation of 15 m s−1. A subset of the most stable stars fulfilling the RVS requirements was used to establish the radial velocity zero point provided in Gaia Data Release 2. The stars that were not used for calibration are used to validate the RVS data.
Gaia Data Release 2 Katz, D.; Sartoretti, P.; Cropper, M. ...
Astronomy and astrophysics (Berlin),
02/2019, Letnik:
622
Journal Article
Recenzirano
Odprti dostop
Context. For Gaia DR2, 280 million spectra collected by the Radial Velocity Spectrometer instrument on board Gaia were processed, and median radial velocities were derived for 9.8 million sources ...brighter than GRVS = 12 mag. Aims. This paper describes the validation and properties of the median radial velocities published in Gaia DR2. Methods. Quality tests and filters were applied to select those of the 9.8 million radial velocities that have the quality to be published in Gaia DR2. The accuracy of the selected sample was assessed with respect to ground-based catalogues. Its precision was estimated using both ground-based catalogues and the distribution of the Gaia radial velocity uncertainties. Results. Gaia DR2 contains median radial velocities for 7 224 631 stars, with Teff in the range 3550, 6900 K, which successfully passed the quality tests. The published median radial velocities provide a full-sky coverage and are complete with respect to the astrometric data to within 77.2% (for G ≤ 12.5 mag). The median radial velocity residuals with respect to the ground-based surveys vary from one catalogue to another, but do not exceed a few 100 m s−1. In addition, the Gaia radial velocities show a positive trend as a function of magnitude, which starts around GRVS ~ 9 mag and reaches about + 500 m s−1 at GRVS = 11.75 mag. The origin of the trend is under investigation, with the aim to correct for it in Gaia DR3. The overall precision, estimated from the median of the Gaia radial velocity uncertainties, is 1.05 km s−1. The radial velocity precision is a function of many parameters, in particular, the magnitude and effective temperature. For bright stars, GRVS ∈ 4, 8 mag, the precision, estimated using the full dataset, is in the range 220–350 m s−1, which is about three to five times more precise than the pre-launch specification of 1 km s−1. At the faint end, GRVS = 11.75 mag, the precisions for Teff = 5000 and 6500 K are 1.4 and 3.7 km s−1, respectively.
Gaia Data Release 2 Sartoretti, P.; Katz, D.; Cropper, M. ...
Astronomy & astrophysics,
08/2018, Letnik:
616
Journal Article
Recenzirano
Odprti dostop
Context. The Gaia Data Release 2 (DR2) contains the first release of radial velocities complementing the kinematic data of a sample of about 7 million relatively bright, late-type stars. Aims. This ...paper provides a detailed description of the Gaia spectroscopic data processing pipeline, and of the approach adopted to derive the radial velocities presented in DR2. Methods. The pipeline must perform four main tasks: (i) clean and reduce the spectra observed with the Radial Velocity Spectrometer (RVS); (ii) calibrate the RVS instrument, including wavelength, straylight, line-spread function, bias non-uniformity, and photometric zeropoint; (iii) extract the radial velocities; and (iv) verify the accuracy and precision of the results. The radial velocity of a star is obtained through a fit of the RVS spectrum relative to an appropriate synthetic template spectrum. An additional task of the spectroscopic pipeline was to provide first-order estimates of the stellar atmospheric parameters required to select such template spectra. We describe the pipeline features and present the detailed calibration algorithms and software solutions we used to produce the radial velocities published in DR2. Results. The spectroscopic processing pipeline produced median radial velocities for Gaia stars with narrow-band near-IR magnitude GRVS ≤ 12 (i.e. brighter than V ~ 13). Stars identified as double-lined spectroscopic binaries were removed from the pipeline, while variable stars, single-lined, and non-detected double-lined spectroscopic binaries were treated as single stars. The scatter in radial velocity among different observations of a same star, also published in Gaia DR2, provides information about radial velocity variability. For the hottest (Teff ≥ 7000 K) and coolest (Teff ≤ 3500 K) stars, the accuracy and precision of the stellar parameter estimates are not sufficient to allow selection of appropriate templates. The radial velocities obtained for these stars were removed from DR2. The pipeline also provides a first-order estimate of the performance obtained. The overall accuracy of radial velocity measurements is around ~200–300 m s−1, and the overall precision is ~1 km s−1; it reaches ~200 m s−1 for the brightest stars.
Gaia Data Release 2 Arenou, F.; Luri, X.; Babusiaux, C. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
Recenzirano
Odprti dostop
Context.
The second
Gaia
data release (DR2) contains very precise astrometric and photometric properties for more than one billion sources, astrophysical parameters for dozens of millions, radial ...velocities for millions, variability information for half a million stars from selected variability classes, and orbits for thousands of solar system objects.
Aims.
Before the catalogue was published, these data have undergone dedicated validation processes. The goal of this paper is to describe the validation results in terms of completeness, accuracy, and precision of the various
Gaia
DR2 data.
Methods.
The validation processes include a systematic analysis of the catalogue content to detect anomalies, either individual errors or statistical properties, using statistical analysis and comparisons to external data or to models.
Results.
Although the astrometric, photometric, and spectroscopic data are of unprecedented quality and quantity, it is shown that the data cannot be used without dedicated attention to the limitations described here, in the catalogue documentation and in accompanying papers. We place special emphasis on the caveats for the statistical use of the data in scientific exploitation. In particular, we discuss the quality filters and the consideration of the properties, systematics, and uncertainties from astrometry to astrophysical parameters, together with the various selection functions.
Gaia Data Release 2 Katz, D.; Sartoretti, P.; Cropper, M. ...
Astronomy and astrophysics (Berlin),
02/2019, Letnik:
622
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
For
Gaia
DR2, 280 million spectra collected by the Radial Velocity Spectrometer instrument on board
Gaia
were processed, and median radial velocities were derived for 9.8 million sources ...brighter than
G
RVS
= 12 mag.
Aims.
This paper describes the validation and properties of the median radial velocities published in
Gaia
DR2.
Methods.
Quality tests and filters were applied to select those of the 9.8 million radial velocities that have the quality to be published in
Gaia
DR2. The accuracy of the selected sample was assessed with respect to ground-based catalogues. Its precision was estimated using both ground-based catalogues and the distribution of the
Gaia
radial velocity uncertainties.
Results. Gaia
DR2 contains median radial velocities for 7 224 631 stars, with
T
eff
in the range 3550, 6900 K, which successfully passed the quality tests. The published median radial velocities provide a full-sky coverage and are complete with respect to the astrometric data to within 77.2% (for
G
≤ 12.5 mag). The median radial velocity residuals with respect to the ground-based surveys vary from one catalogue to another, but do not exceed a few 100 m s
−1
. In addition, the
Gaia
radial velocities show a positive trend as a function of magnitude, which starts around
G
RVS
~ 9 mag and reaches about + 500 m s
−1
at
G
RVS
= 11.75 mag. The origin of the trend is under investigation, with the aim to correct for it in
Gaia
DR3. The overall precision, estimated from the median of the
Gaia
radial velocity uncertainties, is 1.05 km s
−1
. The radial velocity precision is a function of many parameters, in particular, the magnitude and effective temperature. For bright stars,
G
RVS
∈ 4, 8 mag, the precision, estimated using the full dataset, is in the range 220–350 m s
−1
, which is about three to five times more precise than the pre-launch specification of 1 km s
−1
. At the faint end,
G
RVS
= 11.75 mag, the precisions for
T
eff
= 5000 and 6500 K are 1.4 and 3.7 km s
−1
, respectively.
Gaia Data Release 2 Soubiran, C.; Jasniewicz, G.; Chemin, L. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article, Web Resource
Recenzirano
Odprti dostop
Aims. The Radial Velocity Spectrometer (RVS) on board the ESA satellite mission Gaia has no calibration device. Therefore, the radial velocity zero point needs to be calibrated with stars that are ...proved to be stable at a level of 300 m s −1 during the Gaia observations. Methods. We compiled a dataset of ~71 000 radial velocity measurements from five high-resolution spectrographs. A catalogue of 4813 stars was built by combining these individual measurements. The zero point was established using asteroids. Results. The resulting catalogue has seven observations per star on average on a typical time baseline of 6 yr, with a median standard deviation of 15 m s −1 . A subset of the most stable stars fulfilling the RVS requirements was used to establish the radial velocity zero point provided in Gaia Data Release 2. The stars that were not used for calibration are used to validate the RVS data.
Gaia Data Release 2 Sartoretti, P.; Katz, D.; Cropper, M. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
The
Gaia
Data Release 2 (DR2) contains the first release of radial velocities complementing the kinematic data of a sample of about 7 million relatively bright, late-type stars.
Aims.
This ...paper provides a detailed description of the
Gaia
spectroscopic data processing pipeline, and of the approach adopted to derive the radial velocities presented in DR2.
Methods.
The pipeline must perform four main tasks: (i) clean and reduce the spectra observed with the Radial Velocity Spectrometer (RVS); (ii) calibrate the RVS instrument, including wavelength, straylight, line-spread function, bias non-uniformity, and photometric zeropoint; (iii) extract the radial velocities; and (iv) verify the accuracy and precision of the results. The radial velocity of a star is obtained through a fit of the RVS spectrum relative to an appropriate synthetic template spectrum. An additional task of the spectroscopic pipeline was to provide first-order estimates of the stellar atmospheric parameters required to select such template spectra. We describe the pipeline features and present the detailed calibration algorithms and software solutions we used to produce the radial velocities published in DR2.
Results.
The spectroscopic processing pipeline produced median radial velocities for
Gaia
stars with narrow-band near-IR magnitude
G
RVS
≤ 12 (i.e. brighter than
V
~ 13). Stars identified as double-lined spectroscopic binaries were removed from the pipeline, while variable stars, single-lined, and non-detected double-lined spectroscopic binaries were treated as single stars. The scatter in radial velocity among different observations of a same star, also published in
Gaia
DR2, provides information about radial velocity variability. For the hottest (
T
eff
≥ 7000 K) and coolest (
T
eff
≤ 3500 K) stars, the accuracy and precision of the stellar parameter estimates are not sufficient to allow selection of appropriate templates. The radial velocities obtained for these stars were removed from DR2. The pipeline also provides a first-order estimate of the performance obtained. The overall accuracy of radial velocity measurements is around ~200–300 m s
−1
, and the overall precision is ~1 km s
−1
; it reaches ~200 m s
−1
for the brightest stars.
Gaia Data Release 2 Forveille, Thierry; Kotak, Rubina; Shore, Steve ...
Astronomy & astrophysics,
08/2018, Letnik:
616
Journal Article
Recenzirano
Odprti dostop
Astronomy & Astrophysics has the great pleasure of publishing a special issue on the second data release (DR2) of the Gaia space mission which has been obtaining exquisite astrometric and photometric ...measurements since July 2014. Gaia DR2 is based on the analysis on the first 22 months of the mission, and is the first data release that allows a peek at the full potential of the Gaia mission. It represents a game-changing leap for stellar and Galactic astronomy. The release provides parallaxes, proper motions and two-colour photometry for over a billion sources, and radial velocities for 7 million stars. The articles in this special issue describe the complex data processing of the Gaia observations, provide extensive validation checks, and quantify important caveats on the remaining shortcomings of the DR2 data. They also provide spectacular illustrations of the scientific potential of the new data, and will no doubt form the basis for excellent science over the coming years.
The Alpha Magnetic Spectrometer is a large acceptance cosmic-ray detector
(
0.5
m
2
sr
)
designed to operate at an altitude of 400
km on the International Space Station. The AMS-02 silicon tracker ...contains 2264 silicon microstrip sensors (total active area
6.75
m
2
). The internal alignment parameters of the assembled tracker have been determined on the ground with cosmic-ray muons. The alignment procedure is described and results for the alignment precision and position resolution are reported.
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