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تسجيل مستخدم جديدCalibration of the Gaia Radial Velocity Spectrometer from ground-based observations of candidate standard stars
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The Radial Velocity Spectrometer (RVS) on board of Gaia will perform a large spectroscopic survey to determine the radial velocities of some 1.5x10^8 stars. We present the status of ground-based observations of a sample of 1420 candidate standard stars designed to calibrate the RVS. Each candidate star has to be observed several times before Gaia launch (and at least once during the mission) to ensure that its radial velocity remains stable during the whole mission. Observations are performed with the high-resolution spectrographs SOPHIE, NARVAL and CORALIE, completed with archival data of the ELODIE and HARPS instruments. The analysis shows that about 7% of the current catalogue exhibits variations larger than the adopted threshold of 300 m/s. Consequently, those stars should be rejected as reference targets, due to the expected accuracy of the Gaia RVS. Emphasis is also put here on our observations of bright asteroids to calibrate the ground-based velocities by a direct comparison with celestial mechanics. It is shown that the radial velocity zero points of SOPHIE, NARVAL and CORALIE are consistent with each other, within the uncertainties. Despite some scatter, their temporal variations remain small with respect to our adopted stability criterion.
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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 during the
Gaia observations. Methods. We compiled a dataset of ~71000 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 six years, with a median standard deviation of 15 m/s. 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.
A new full-sky catalog of Radial Velocity standard stars is being built for the determination of the Radial Velocity Zero Point of the RVS on board of Gaia. After a careful selection of 1420 candidates matching well defined criteria, we are now obser
ving all of them to verify that they are stable enough over several years to be qualified as reference stars. We present the status of this long-term observing programme on three spectrographs : SOPHIE, NARVAL and CORALIE, complemented by the ELODIE and HARPS archives. Because each instrument has its own zero-point, we observe intensively IAU RV standards and asteroids to homogenize the radial velocity measurements. We can already estimate that ~8% of the candidates have to be rejected because of variations larger than the requested level of 300 m/s.
This paper presents the specification, design, and development of the Radial Velocity Spectrometer (RVS) on the European Space Agencys 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.
The calibration of the Radial Velocity Spectrometer (RVS) onboard the ESA Gaia satellite (to be launched in 2012) requires a list of standard stars with a radial velocity (RV) known with an accuracy of at least 300 m/s. The IAU Commission 30 lists of
RV standard stars are too bright and not dense enough. We describe the selection criteria due to the RVS constraints for building an adequate full-sky list of at least 1000 RV standards from catalogues already published in the literature. A preliminary list of 1420 candidate standard stars is built and its properties are shown. An important re-observation programme has been set up in order to ensure within it the selection of objects with a good stability until the end of the Gaia mission (around 2018). The present list of candidate standards is available at CDS and usable for many other projects.
We present a new catalogue of 18 080 radial velocity standard stars selected from the APOGEE data. These RV standard stars are observed at least three times and have a median stability ($3sigma_{rm RV}$) around 240 m s$^{-1}$ over a time baseline lon
ger than 200 days. They are largely distributed in the northern sky and could be extended to the southern sky by the future APOGEE-2 survey. Most of the stars are red giants ($J - K_{rm s} ge 0.5$) owing to the APOGEE target selection criteria. Only about ten per cent of them are main-sequence stars. The $H$ band magnitude range of the stars is 7-12.5 mag with the faint limit much fainter than the magnitudes of previous RV standard stars. As an application, we show the new set of standard stars to determine the radial velocity zero points of the RAVE, the LAMOST {and the Gaia-RVS} Galactic spectroscopic surveys.
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