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 Hambly, N. C.; Cropper, M.; Boudreault, S. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
Recenzirano
Odprti dostop
Context. The European Space Agency’s Gaia satellite was launched into orbit around L2 in December 2013. This ambitious mission has strict requirements on residual systematic errors resulting from ...instrumental corrections in order to meet a design goal of sub-10 microarcsecond astrometry. During the design and build phase of the science instruments, various critical calibrations were studied in detail to ensure that this goal could be met in orbit. In particular, it was determined that the video-chain offsets on the analogue side of the analogue-to-digital conversion electronics exhibited instabilities that could not be mitigated fully by modifications to the flight hardware. Aims. We provide a detailed description of the behaviour of the electronic offset levels on short (<1 ms) timescales, identifying various systematic effects that are known collectively as “offset non-uniformities”. The effects manifest themselves as transient perturbations on the gross zero-point electronic offset level that is routinely monitored as part of the overall calibration process. Methods. Using in-orbit special calibration sequences along with simple parametric models, we show how the effects can be calibrated, and how these calibrations are applied to the science data. While the calibration part of the process is relatively straightforward, the application of the calibrations during science data processing requires a detailed on-ground reconstruction of the readout timing of each charge-coupled device (CCD) sample on each device in order to predict correctly the highly time-dependent nature of the corrections. Results. We demonstrate the effectiveness of our offset non-uniformity models in mitigating the effects in Gaia data. Conclusions. We demonstrate for all CCDs and operating instrument/modes on board Gaia that the video-chain noise-limited performance is recovered in the vast majority of science samples.
Gaia Data Release 2 Sartoretti, P.; Katz, D.; Cropper, M. ...
Astronomy and astrophysics (Berlin),
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 Soubiran, C.; Jasniewicz, G.; Chemin, L. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
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 Cropper, M.; Katz, D.; Sartoretti, P. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
Recenzirano
This paper presents the specification, design, and development of the Radial Velocity Spectrometer (RVS) on the European Space Agency’s Gaia mission. Starting with the rationale for the full six ...dimensions of phase space in the dynamical modelling of the Galaxy, the scientific goals and derived top-level instrument requirements are discussed, leading to a brief description of the initial concepts for the instrument. The main part of the paper is a description of the flight RVS, considering the optical design, the focal plane, the detection and acquisition chain, and the as-built performance drivers and critical technical areas. After presenting the pre-launch performance predictions, the paper concludes with the post-launch developments and mitigation strategies, together with a summary of the in-flight performance at the end of commissioning.
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 Cropper, M.; Katz, D.; Sartoretti, P. ...
Astronomy and astrophysics (Berlin),
8/2018, Letnik:
616
Journal Article, Web Resource
Recenzirano
Odprti dostop
This paper presents the specification, design, and development of the Radial Velocity Spectrometer (RVS) on the European Space Agency’s
Gaia
mission. Starting with the rationale for the full six ...dimensions of phase space in the dynamical modelling of the Galaxy, the scientific goals and derived top-level instrument requirements are discussed, leading to a brief description of the initial concepts for the instrument. The main part of the paper is a description of the flight RVS, considering the optical design, the focal plane, the detection and acquisition chain, and the as-built performance drivers and critical technical areas. After presenting the pre-launch performance predictions, the paper concludes with the post-launch developments and mitigation strategies, together with a summary of the in-flight performance at the end of commissioning.
Gaia Data Release 3 Katz, D.; Sartoretti, P.; Guerrier, A. ...
Astronomy and astrophysics (Berlin),
06/2023, Letnik:
674
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
Gaia
Data Release 3 (
Gaia
DR3) contains the second release of the combined radial velocities. It is based on the spectra collected during the first 34 months of the nominal mission. The ...longer time baseline and the improvements of the pipeline made it possible to push the processing limit from
G
RVS
= 12 in
Gaia
DR2 to
G
RVS
= 14 mag.
Aims.
We describe the new functionalities implemented for
Gaia
DR3, the quality filters applied during processing and post-processing, and the properties and performance of the published velocities.
Methods.
For
Gaia
DR3, several functionalities were upgraded or added to the spectroscopic pipeline. The calibrations were improved in order to better model the temporal evolution of the straylight and of the instrumental point spread function (PSF). The overlapped spectra, which were mostly discarded in
Gaia
DR2, are now handled by a dedicated module. The hot star template mismatch, which prevented publication of hot stars in
Gaia
DR2, is largely mitigated now, down to
G
RVS
= 12 mag. The combined radial velocity of stars brighter than or equal to
G
RVS
= 12 mag is calculated in the same way as in
Gaia
DR2, that is, as the median of the epoch radial velocity time series. The combined radial velocity of the fainter stars is measured from the average of the cross-correlation functions.
Results.
Gaia
DR3 contains the combined radial velocities of 33 812 183 stars. With respect to
Gaia
DR2, the temperature interval has been expanded from
T
eff
∈ 3600, 6750 K to
T
eff
∈ 3100, 14 500 K for the bright stars (
G
RVS
≤ 12 mag) and 3100, 6750 K for the fainter stars. The radial velocities sample a significant part of the Milky Way: they reach a few kiloparsecs beyond the Galactic centre in the disc and up to about 10−15 kpc vertically into the inner halo. The median formal precision of the velocities is 1.3 km s
−1
at
G
RVS
= 12 and 6.4 km s
−1
at
G
RVS
= 14 mag. The velocity zeropoint exhibits a small systematic trend with magnitude that starts around
G
RVS
= 11 mag and reaches about 400 m s
−1
at
G
RVS
= 14 mag. A correction formula is provided that can be applied to the published data. The
Gaia
DR3 velocity scale agrees satisfactorily with APOGEE, GALAH, GES, and RAVE; the systematic differences mostly remain below a few hundred m s
−1
. The properties of the radial velocities are also illustrated with specific objects: open clusters, globular clusters, and the Large Magellanic Cloud. For example, the precision of the data allows mapping the line-of-sight rotational velocities of the globular cluster 47 Tuc and of the Large Magellanic Cloud.
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.
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