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Register a new userA new catalogue of radial velocity standard stars from the APOGEE data
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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 longer 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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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.
The Radial Velocity Experiment (RAVE) is a magnitude-limited (9<I<12) spectroscopic survey of Galactic stars randomly selected in the southern hemisphere. The RAVE medium-resolution spectra (R~7500) cover the Ca-triplet region (8410-8795A). The 6th and final data release (DR6 or FDR) is based on 518387 observations of 451783 unique stars. RAVE observations were taken between 12 April 2003 and 4 April 2013. Here we present the genesis, setup and data reduction of RAVE as well as wavelength-calibrated and flux-normalized spectra and error spectra for all observations in RAVE DR6. Furthermore, we present derived spectral classification and radial velocities for the RAVE targets, complemented by cross matches with Gaia DR2 and other relevant catalogs. A comparison between internal error estimates, variances derived from stars with more than one observing epoch and a comparison with radial velocities of Gaia DR2 reveals consistently that 68% of the objects have a velocity accuracy better than 1.4 km/s, while 95% of the objects have radial velocities better than 4.0 km/s. Stellar atmospheric parameters, abundances and distances are presented in subsequent publication. The data can be accessed via the RAVE Web (http://rave-survey.org) or the Vizier database.
The gravitational redshift induced by stellar surface gravity is notoriously difficult to measure for non-degenerate stars, since its amplitude is small in comparison with the typical Doppler shift induced by stellar radial velocity. In this study, we make use of the large observational data set of the Gaia mission to achieve a significant reduction of noise caused by these random stellar motions. By measuring the differences in velocities between the components of pairs of co-moving stars and wide binaries, we are able to statistically measure gravitational redshift and nullify the effect of the peculiar motions of the stars. For the subset of stars considered in this study, we find a positive correlation between the observed differences in Gaia radial velocities and the differences in surface gravity inferred from effective temperature and luminosity measurements. This corresponds to the first ever measurement of extra-Solar surface gravity induced gravitational redshift in non-degenerate stars. Additionally, we study the sub-dominant effects of convective blueshifting of emission lines, effects of binary motion, and possible systematic errors in radial velocity measurements within Gaia. Results from the technique presented in this study are expected to improve significantly with data from the next Gaia data release. Such improvements could be used to constrain the mass-luminosity relation and stellar models which predict the magnitude of convective blueshift.
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.
The intermediate-mass pre-main sequence Herbig Ae/Be stars are key to understanding the differences in formation mechanisms between low- and high-mass stars. The study of the general properties of these objects is hampered by the fact that few and mostly serendipitously discovered sources are known. Our goal is to identify new Herbig Ae/Be candidates to create a homogeneous and well defined catalogue of these objects. We have applied machine learning techniques to 4,150,983 sources with data from Gaia DR2, 2MASS, WISE, and IPHAS or VPHAS+. Several observables were chosen to identify new Herbig Ae/Be candidates based on our current knowledge of this class, which is characterised by infrared excesses, photometric variabilities, and H$alpha$ emission lines. Classical techniques are not efficient for identifying new Herbig Ae/Be stars mainly because of their similarity with classical Be stars, with which they share many characteristics. By focusing on disentangling these two types of objects, our algorithm has also identified new classical Be stars. We have obtained a large catalogue of 8470 new pre-main sequence candidates and another catalogue of 693 new classical Be candidates with a completeness of $78.8pm1.4%$ and $85.5pm1.2%$, respectively. Of the catalogue of pre-main sequence candidates, at least 1361 sources are potentially new Herbig Ae/Be candidates according to their position in the Hertzsprung-Russell diagram. In this study we present the methodology used, evaluate the quality of the catalogues, and perform an analysis of their flaws and biases. For this assessment, we make use of observables that have not been accounted for by the algorithm and hence are selection-independent, such as coordinates and parallax based distances. The catalogue of new Herbig Ae/Be stars that we present here increases the number of known objects of the class by an order of magnitude.
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