Context. The derivation of radial velocities from large numbers of spectra that typically result from survey work, requires automation. However, except for the classical cases of slowly rotating ...late-type spectra, existing methods of measuring Doppler shifts require fine-tuning to avoid a loss of accuracy due to the idiosyncrasies of individual spectra. The radial velocity spectrometer (RVS) on the Gaia mission, which will start operating very soon, prompted a new attempt at creating a measurement pipeline to handle a wide variety of spectral types. Aims. The present paper describes the theoretical background on which this software is based. However, apart from the assumption that only synthetic templates are used, we do not rely on any of the characteristics of this instrument, so our results should be relevant for most telescope-detector combinations. Methods. We propose an approach based on the simultaneous use of several alternative measurement methods, each having its own merits and drawbacks, and conveying the spectral information in a different way, leading to different values for the measurement. A comparison or a combination of the various results either leads to a “best estimate” or indicates to the user that the observed spectrum is problematic and should be analysed manually. Results. We selected three methods and analysed the relationships and differences between them from a unified point of view; with each method an appropriate estimator for the individual random error is chosen. We also develop a procedure for tackling the problem of template mismatch in a systematic way. Furthermore, we propose several tests for studying and comparing the performance of the various methods as a function of the atmospheric parameters of the observed objects. Finally, we describe a procedure for obtaining a knowledge-based combination of the various Doppler-shift measurements.
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 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 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.
The recognition of familiar words was evaluated in 20-month-old children raised in a rhotic accent environment to parents that had either rhotic or non-rhotic accents. Using an Intermodal ...Preferential Looking task children were presented with familiar objects (e.g. ‘bird’) named in their rhotic or non-rhotic form. Children were only able to identify familiar words pronounced in a rhotic accent, irrespective of their parents’ accent. This suggests that it is the local community rather than parental input that determines accent preference in the early stages of acquisition. Consequences for the architecture of the early lexicon and for models of word learning are discussed.
A method, based on the Karhunen-Loève (KL) transformation, to improve the signal-to-noise ratio of a multispectral data cube is presented. As an illustration we have re-analyzed near-infrared ...multi-spectral images of the young planetary nebula NGC 7027 previously observed by Cox et al. (CITE). Our KL analysis clearly shows an enhancement of both spectral and spatial information, particularly in the case of low signal-to-noise ratio images.
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.
The Gaia Data Release 2 contains the 1st 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 1st-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 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. Abridged
For Gaia DR2 (GDR2), 280 million spectra, collected by the RVS instrument on-board Gaia, were processed and median radial velocities were derived for 9.8 million sources brighter than Grvs = 12 mag. ...This paper describes the validation and properties of the median radial velocities published in GDR2. Quality tests and filters are applied to select, from the 9.8 million radial velocities, those with the quality to be published in GDR2. The accuracy of the selected sample is assessed with respect to ground-based catalogues. Its precision is estimated using both ground-based catalogues and the distribution of the Gaia radial velocity uncertainties. GDR2 contains median radial velocities for 7 224 631 stars, with Teff in the range 3550, 6900 K, which passed succesfully the quality tests. The published median radial velocities provide a full sky-coverage and have a completness with respect to the astrometric data of 77.2\% (for \(G \leq 12.5\) 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 100s m/s. In addition, the Gaia radial velocities show a positive trend as a function of magnitude, which starts around Grvs \(\sim 9\) mag and reaches about \(+500\) m/s at Grvs \(= 11.75\) mag. The overall precision, estimated from the median of the Gaia radial velocity uncertainties, is 1.05 km/s. The radial velocity precision is function of many parameters, in particular the magnitude and effective temperature. For bright stars, Grvs in 4, 8 mag, the precision is in the range 200-350 m/s, which is about 3 to 5 times more precise than the pre-launch specification of 1 km/s. At the faint end, Grvs = 11.75 mag, the precisions for Teff = 5000 K and 6500 K are respectively 1.4 km/s and 3.7 km/s.
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