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- ItemGaia Data Release 2 : Properties and validation of the radial velocities(Les Ulis : EDP Sciences, 2019) Katz, D.; Sartoretti, P.; Cropper, M.; Panuzzo, P.; Seabroke, G.M.; Viala, Y.; Benson, K.; Blomme, R.; Jasniewicz, G.; Jean-Antoine, A.; Huckle, H.; Smith, M.; Baker, S.; Crifo, F.; Damerdji, Y.; David, M.; Dolding, C.; Frémat, Y.; Gosset, E.; Guerrier, A.; Guy, L. P.; Haigron, R.; Janßen, K.; Marchal, O.; Plum, G.; Soubiran, C.; Thévenin, F.; Ajaj, M.; Allende Prieto, C.; Babusiaux, C.; Boudreault, S.; Chemin, L.; Delle Luche, C.; Fabre, C.; Gueguen, A.; Hambly, N. C.; Lasne, Y.; Meynadier, F.; Pailler, F.; Panem, C.; Royer, F.; Tauran, G.; Zurbach, C.; Zwitter, T.; Arenou, F.; Bossini, D.; Gerssen, J.; Gómez, A.; Lemaitre, V.; Leclerc, N.; Morel, T.; Munari, U.; Turon, C.; Vallenari, A.; Žerjal, M.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 2 [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.
- ItemAbsolute dimensions and apsidal motion of the eclipsing binaries V889 Aquilae and V402 Lacertae(Les Ulis : EDP Sciences, 2022) Baroch, D.; Giménez, A.; Morales, J. C.; Ribas, I.; Herrero, E.; Perdelwitz, V.; Jordi, C.; Granzer, T.; Allende Prieto, C.Context. Double-lined eclipsing binaries allow the direct determination of masses and radii, which are key for testing stellar models. With the launch of the TESS mission, many well-known eclipsing binaries have been observed at higher photometric precision, permitting the improvement of the absolute dimension determinations. Aims. Using TESS data and newly obtained spectroscopic observations, we aim to determine the masses and radii of the eccentric eclipsing binary systems V889 Aql and V402 Lac, together with their apsidal motion parameters. Methods. We simultaneously modelled radial velocity curves and times of eclipse for each target to precisely determine the orbital parameters of the systems, which we used to analyse the light curves and then obtain their absolute dimensions. We compared the obtained values with those predicted by theoretical models. Results. We determined masses and radii of the components of both systems with relative uncertainties lower than 2%. V889 Aql is composed of two stars with masses 2:17±0:02 M⊙ and 2:13±0:01 M⊙ and radii 1:87±0:04 R⊙ and 1:85±0:04 R⊙.We find conclusive evidence of the presence of a third body orbiting V889 Aql with a period of 67 yr. Based on the detected third light and the absence of signal in the spectra, we suggest that this third body could in turn be a binary composed of two ±1.4 M⊙ stars. V402 Lac is composed of two stars with masses 2:80 ± 0:05 M⊙ and 2:78 ± 0:05 M⊙ and radii 2:38 ± 0:03 R⊙ and 2:36 ± 0:03 R⊙. The times of minimum light are compatible with the presence of a third body for this system too, although its period is not yet fully sampled. In both cases we have found a good agreement between the observed apsidal motion rates and the model predictions.
- ItemGaia Data Release 2 : Processing the spectroscopic data(Les Ulis : EDP Sciences, 2018) Sartoretti, P.; Katz, D.; Cropper, M.; Panuzzo, P.; Seabroke, G. M.; Viala, Y.; Benson, K.; Blomme, R.; Jasniewicz, G.; Jean-Antoine, A.; Huckle, H.; Smith, M.; Baker, S.; Crifo, F.; Damerdji, Y.; David, M.; Dolding, C.; Frémat, Y.; Gosset, E.; Guerrier, A.; Guy, L. P.; Haigron, R.; Janßen, K.; Marchal, O.; Plum, G.; Soubiran, C.; Thévenin, F.; Ajaj, M.; Allende Prieto, C.; Babusiaux, C.; Boudreault, S.; Chemin, L.; Delle Luche, C.; Fabre, C.; Gueguen, A.; Hambly, N. C.; Lasne, Y.; Meynadier, F.; Pailler, F.; Panem, C.; Riclet, F.; Royer, F.; Tauran, G.; Zurbach, C.; Zwitter, T.; Arenou, F.; Gomez, A.; Lemaitre, V.; Leclerc, N.; Morel, T.; Munari, U.; Turon, C.; Žerjal, M.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 (Te≥ 7000 K) and coolest (Te≤ 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.