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 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 Early Data Release 3 Seabroke, G. M.; Fabricius, C.; Teyssier, D. ...
Astronomy and astrophysics (Berlin),
09/2021, Letnik:
653
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context. Gaia
’s Early Third Data Release (EDR3) does not contain new radial velocities because these will be published in
Gaia
’s full third data release (DR3), expected in the first half of 2022. ...To maximise the usefulness of EDR3,
Gaia
’s second data release (DR2) sources (with radial velocities) are matched to EDR3 sources to allow their DR2 radial velocities to also be included in EDR3. This presents two considerations: (i) a list of 70 365 sources with potentially contaminated DR2 radial velocities has been published; and (ii) EDR3 is based on a new astrometric solution and a new source list, which means sources in DR2 may not be in EDR3.
Aims.
The two aims of this work are: (i) investigate the list in order to improve the DR2 radial velocities being included in EDR3 and to avoid false-positive hypervelocity candidates; and (ii) match the DR2 sources (with radial velocities) to EDR3 sources.
Methods.
Thetwo methods of this work are: (i) unpublished, preliminary DR3 radial velocities of sources on the list, and high-velocity stars not on the list, are compared with their DR2 radial velocities to identify and remove contaminated DR2 radial velocities from EDR3; and (ii) proper motions and epoch position propagation is used to attempt to match all sources with radial velocities in DR2 to EDR3 sources. The comparison of DR2 and DR3 radial velocities is used to resolve match ambiguities.
Results.
EDR3 contains 7 209 831 sources with a DR2 radial velocity, which is 99.8% of sources with a radial velocity in DR2 (7 224 631). 14 800 radial velocities from DR2 are not propagated to any EDR3 sources because (i) 3871 from the list are found to either not have a DR3 radial velocity or it differs significantly from its DR2 value, and five high-velocity stars not on the list are confirmed to have contaminated radial velocities, in one case because of contamination from the non-overlapping Radial Velocity Spectrometer windows of a nearby, bright star; and (
ii
) 10 924 DR2 sources could not be satisfactorily matched to any EDR3 sources, so their DR2 radial velocities are also missing from EDR3.
Conclusions.
The reliability of radial velocities in EDR3 has improved compared to DR2 because the update removes a small fraction of erroneous radial velocities (0.05% of DR2 radial velocities and 5.5% of the list). Lessons learnt from EDR3 (e.g. bright star contamination) will improve the radial velocities in future
Gaia
data releases. The main reason for radial velocities from DR2 not propagating to EDR3 is not related to DR2 radial velocity quality. It is because the DR2 astrometry is based on one component of close binary pairs, while EDR3 astrometry is based on the other component, which prevents these sources from being unambiguously matched.
Gaia Data Release 3 Blomme, R.; Frémat, Y.; Sartoretti, P. ...
Astronomy and astrophysics (Berlin),
06/2023, Letnik:
674
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
The second
Gaia
data release, DR2, contained radial velocities of stars with effective temperatures up to
T
eff
= 6900 K. The third data release,
Gaia
DR3, extends this up to
T
eff
= 14 ...500 K.
Aims.
We derive the radial velocities for hot stars (i.e., in the
T
eff
= 6900 − 14 500 K range) from data obtained with the Radial Velocity Spectrometer (RVS) on board
Gaia
.
Methods.
The radial velocities were determined by the standard technique of measuring the Doppler shift of a template spectrum that was compared to the observed spectrum. The RVS wavelength range is very limited. The proximity to and systematic blueward offset of the calcium infrared triplet to the hydrogen Paschen lines in hot stars can result in a systematic offset in radial velocity. For the hot stars, we developed a specific code to improve the selection of the template spectrum, thereby avoiding this systematic offset.
Results.
With the improved code, and with the correction we propose to the DR3 archive radial velocities, we obtain values that agree with reference values to within 3 km s
−1
(in median). Because of the required S/N for applying the improved code, the hot star radial velocities in DR3 are mostly limited to stars with a magnitude in the RVS wavelength band ≤12 mag.
Context.Gaia Data Release 3 (DR3) contains the first release of magnitudes estimated from the integration of Radial Velocity Spectrometer (RVS) spectra for a sample of about 32.2 million stars ...brighter than GRVS∼ 14 mag (or G ∼ 15 mag). Aims. In this paper, we describe the data used and the approach adopted to derive and validate the GRVS magnitudes published in DR3. We also provide estimates of the GRVS passband and associated GRVS zero-point. Methods. We derived GRVS photometry from the integration of RVS spectra over the wavelength range from 846 to 870 nm. We processed these spectra following a procedure similar to that used for DR2, but incorporating several improvements that allow a better estimation of GRVS. These improvements pertain to the stray-light background estimation, the line spread function calibration, and the detection of spectra contaminated by nearby relatively bright sources. We calibrated the GRVS zero-point every 30 h based on the reference magnitudes of constant stars from the HIPPARCOS catalogue, and used them to transform the integrated flux of the cleaned and calibrated spectra into epoch magnitudes. The GRVS magnitude of a star published in DR3 is the median of the epoch magnitudes for that star. We estimated the GRVS passband by comparing the RVS spectra of 108 bright stars with their flux-calibrated spectra from external spectrophotometric libraries. Results. The GRVS magnitude provides information that is complementary to that obtained from the G, GBP, and GRP magnitudes, which is useful for constraining stellar metallicity and interstellar extinction. The median precision of GRVS measurements ranges from about 0.006 mag for the brighter stars (i.e. with 3.5 ∼ GRVS ∼ 6.5 mag) to 0.125 mag at the faint end. The derived GRVS passband shows that the effective transmittance of the RVS is approximately 1.23 times better than the pre-launch estimate.
Gaia Data Release 3 Frémat, Y.; Royer, F.; Marchal, O. ...
Astronomy and astrophysics (Berlin),
06/2023, Letnik:
674
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
The third release of the
Gaia
catalogue contains radial velocities for 33 812 183 stars with effective temperatures ranging from 3100 K to 14 500 K. The measurements are based on the ...comparison of the spectra observed with the Radial Velocity Spectrometer (RVS; wavelength coverage: 846–870 nm, median resolving power: 11 500) to synthetic data broadened to the adequate along-scan line spread function. The additional line-broadening, fitted as it would only be due to axial rotation, is also produced by the pipeline and is available in the catalogue (field name
vbroad
).
Aims.
We describe the properties of the line-broadening information extracted from the RVS and published in the catalogue, and analyse the limitations imposed by the adopted method, wavelength range, and instrument.
Methods.
We used simulations to express the link between the line-broadening measurement provided in
Gaia
Data Release 3 and
V
sin
i
. We then compared the observed values to the measurements published by various catalogues and surveys (GALAH, APOGEE, LAMOST, etc.).
Results.
While we recommend caution in the interpretation of the
vbroad
measurement, we also find a reasonable general agreement of the
Gaia
Data Release 3 line-broadening values and values in other catalogues. We discuss and establish the validity domain of the published
vbroad
values. The estimate tends to be overestimated at the lower
V
sin
i
end, and at
T
eff
> 7500 K its quality and significance degrade rapidly when
G
RVS
> 10. Despite all the known and reported limitations, the
Gaia
Data Release 3 line-broadening catalogue contains measurements obtained for 3 524 677 stars with
T
eff
ranging from 3500 to 14 500 K, and
G
RVS
< 12. It gathers the largest stellar sample ever considered for the purpose, and allows a first mapping of the
Gaia
line-broadening parameter across the Hertzsprung-Russel diagram.
Context.Gaia Data Release 3 (DR3) contains the first release of magnitudes estimated from the integration of Radial Velocity Spectrometer (RVS) spectra for a sample of about 32.2 million stars ...brighter than GRVS ∼ 14 mag (or G ∼ 15 mag). Aims: In this paper, we describe the data used and the approach adopted to derive and validate the GRVS magnitudes published in DR3. We also provide estimates of the GRVS passband and associated GRVS zero-point. Methods: We derived GRVS photometry from the integration of RVS spectra over the wavelength range from 846 to 870 nm. We processed these spectra following a procedure similar to that used for DR2, but incorporating several improvements that allow a better estimation of GRVS. These improvements pertain to the stray-light background estimation, the line spread function calibration, and the detection of spectra contaminated by nearby relatively bright sources. We calibrated the GRVS zero-point every 30 h based on the reference magnitudes of constant stars from the HIPPARCOS catalogue, and used them to transform the integrated flux of the cleaned and calibrated spectra into epoch magnitudes. The GRVS magnitude of a star published in DR3 is the median of the epoch magnitudes for that star. We estimated the GRVS passband by comparing the RVS spectra of 108 bright stars with their flux-calibrated spectra from external spectrophotometric libraries. Results: The GRVS magnitude provides information that is complementary to that obtained from the G, GBP, and GRP magnitudes, which is useful for constraining stellar metallicity and interstellar extinction. The median precision of GRVS measurements ranges from about 0.006 mag for the brighter stars (i.e. with 3.5≲ GRVS ≲6.5 mag) to 0.125 mag at the faint end. The derived GRVS passband shows that the effective transmittance of the RVS is approximately 1.23 times better than the pre-launch estimate.
Context.
Studies of the correlation between different diffuse interstellar bands (DIBs) are important for exploring their origins. However, the
Gaia
–RVS spectral window between 846 and 870 nm ...contains few DIBs, the strong DIB at 862 nm being the only convincingly confirmed one.
Aims.
Here we attempt to confirm the existence of a broad DIB around 864.8 nm and estimate its characteristics using the stacked
Gaia
–RVS spectra of a large number of stars. We study the correlations between the two DIBs at 862 nm (
λ
862) and 864.8 nm (
λ
864.8), as well as the interstellar extinction.
Methods.
We obtained spectra of the interstellar medium (ISM) absorption by subtracting the stellar components using templates constructed from real spectra at high Galactic latitudes with low extinctions. We then stacked the ISM spectra in Galactic coordinates (ℓ,
b
) – pixelized by the HEALPix scheme – to measure the DIBs. The stacked spectrum is modeled by the profiles of the two DIBs, Gaussian for
λ
862 and Lorentzian for
λ
864.8, and a linear continuum. We report the fitted central depth (CD), central wavelength, equivalent width (EW), and their uncertainties for the two DIBs.
Results.
We obtain 8458 stacked spectra in total, of which 1103 (13%) have reliable fitting results after applying numerous conservative filters. This work is the first of its kind to fit and measure
λ
862 and
λ
864.8 simultaneously in cool-star spectra. Based on these measurements, we find that the EWs and CDs of
λ
862 and
λ
864.8 are well correlated with each other, with Pearson coefficients (
r
p
) of 0.78 and 0.87, respectively. The full width at half maximum (FWHM) of
λ
864.8 is estimated as 1.62 ± 0.33 nm which compares to 0.55 ± 0.06 nm for
λ
862. We also measure the vacuum rest-frame wavelength of
λ
864.8 to be
λ
0
= 864.53 ± 0.14 nm, smaller than previous estimates.
Conclusions.
We find solid confirmation of the existence of the DIB around 864.8 nm based on an exploration of its correlation with
λ
862 and estimation of its FWHM. The DIB
λ
864.8 is very broad and shallow. That at
λ
862 correlates better with
E
(
BP
−
RP
) than
λ
864.8. The profiles of the two DIBs could strongly overlap with each other, which contributes to the skew of the
λ
862 profile.
Gaia Data Release 3 Sartoretti, P.; Marchal, O.; Babusiaux, C. ...
Astronomy and astrophysics (Berlin),
06/2023, Letnik:
674
Journal Article
Recenzirano
Context.Gaia
Data Release 3 (DR3) contains the first release of magnitudes estimated from the integration of Radial Velocity Spectrometer (RVS) spectra for a sample of about 32.2 million stars ...brighter than
G
RVS
∼ 14 mag (or
G
∼ 15 mag).
Aims.
In this paper, we describe the data used and the approach adopted to derive and validate the
G
RVS
magnitudes published in DR3. We also provide estimates of the
G
RVS
passband and associated
G
RVS
zero-point.
Methods.
We derived
G
RVS
photometry from the integration of RVS spectra over the wavelength range from 846 to 870 nm. We processed these spectra following a procedure similar to that used for DR2, but incorporating several improvements that allow a better estimation of
G
RVS
. These improvements pertain to the stray-light background estimation, the line spread function calibration, and the detection of spectra contaminated by nearby relatively bright sources. We calibrated the
G
RVS
zero-point every 30 h based on the reference magnitudes of constant stars from the H
IPPARCOS
catalogue, and used them to transform the integrated flux of the cleaned and calibrated spectra into epoch magnitudes. The
G
RVS
magnitude of a star published in DR3 is the median of the epoch magnitudes for that star. We estimated the
G
RVS
passband by comparing the RVS spectra of 108 bright stars with their flux-calibrated spectra from external spectrophotometric libraries.
Results.
The
G
RVS
magnitude provides information that is complementary to that obtained from the
G
,
G
BP
, and
G
RP
magnitudes, which is useful for constraining stellar metallicity and interstellar extinction. The median precision of
G
RVS
measurements ranges from about 0.006 mag for the brighter stars (i.e. with 3.5≲
G
RVS
≲6.5 mag) to 0.125 mag at the faint end. The derived
G
RVS
passband shows that the effective transmittance of the RVS is approximately 1.23 times better than the pre-launch estimate.
Gaia Early Data Release 3 Seabroke, G M; Fabricius, C; Teyssier, D ...
Astronomy & astrophysics,
09/2021, Letnik:
653
Journal Article
Recenzirano
Odprti dostop
Context. Gaia’s Early Third Data Release (EDR3) does not contain new radial velocities because these will be published in Gaia’s full third data release (DR3), expected in the first half of 2022. To ...maximise the usefulness of EDR3, Gaia’s second data release (DR2) sources (with radial velocities) are matched to EDR3 sources to allow their DR2 radial velocities to also be included in EDR3. This presents two considerations: (i) a list of 70 365 sources with potentially contaminated DR2 radial velocities has been published; and (ii) EDR3 is based on a new astrometric solution and a new source list, which means sources in DR2 may not be in EDR3. Aims. The two aims of this work are: (i) investigate the list in order to improve the DR2 radial velocities being included in EDR3 and to avoid false-positive hypervelocity candidates; and (ii) match the DR2 sources (with radial velocities) to EDR3 sources. Methods. Thetwo methods of this work are: (i) unpublished, preliminary DR3 radial velocities of sources on the list, and high-velocity stars not on the list, are compared with their DR2 radial velocities to identify and remove contaminated DR2 radial velocities from EDR3; and (ii) proper motions and epoch position propagation is used to attempt to match all sources with radial velocities in DR2 to EDR3 sources. The comparison of DR2 and DR3 radial velocities is used to resolve match ambiguities. Results. EDR3 contains 7 209 831 sources with a DR2 radial velocity, which is 99.8% of sources with a radial velocity in DR2 (7 224 631). 14 800 radial velocities from DR2 are not propagated to any EDR3 sources because (i) 3871 from the list are found to either not have a DR3 radial velocity or it differs significantly from its DR2 value, and five high-velocity stars not on the list are confirmed to have contaminated radial velocities, in one case because of contamination from the non-overlapping Radial Velocity Spectrometer windows of a nearby, bright star; and (ii) 10 924 DR2 sources could not be satisfactorily matched to any EDR3 sources, so their DR2 radial velocities are also missing from EDR3. Conclusions. The reliability of radial velocities in EDR3 has improved compared to DR2 because the update removes a small fraction of erroneous radial velocities (0.05% of DR2 radial velocities and 5.5% of the list). Lessons learnt from EDR3 (e.g. bright star contamination) will improve the radial velocities in future Gaia data releases. The main reason for radial velocities from DR2 not propagating to EDR3 is not related to DR2 radial velocity quality. It is because the DR2 astrometry is based on one component of close binary pairs, while EDR3 astrometry is based on the other component, which prevents these sources from being unambiguously matched.
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