R. Campbell

The radial velocity experiment (RAVE): First data release

We present the first data release of the Radial Velocity Experiment (RAVE), an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, and surface gravity) of up to one million stars using the Six Degree Field multiobject spectrograph on the 1.2 m UK Schmidt Telescope of the Anglo-Australian Observatory. The RAVE program started in 2003, obtaining medium-resolution spectra (median R 1⁄4 7500) in the Ca-triplet region (8410–8795 8) for southern hemisphere stars drawn from the Tycho-2 and SuperCOSMOS catalogs, in the magnitude range 9 < I < 12. The first data release is described in this paper and contains radial velocities for 24,748 individual stars (25,274 measurements when including reobservations). Those data were obtained on 67 nights between 2003 April 11 and 2004 April 3. The total sky coverage within this data release is 4760 deg. The average signal-to-noise ratio of the observed spectra is 29.5, and 80% of the radial velocities have uncertainties better than 3.4 km s . Combining internal errors and zero-point errors, the mode is found to be 2 km s . Repeat observations are used to assess the stability of our radial velocity solution, resulting in a variance of 2.8 km s . We demonstrate that the radial velocities derived for the first data set do not show any systematic trend with color or signal-to-noise ratio. The RAVE radial velocities are complemented in the data release with proper motions from Starnet 2.0, Tycho-2, and SuperCOSMOS, in addition to photometric data from the major optical and infrared catalogs (Tycho-2, USNO-B, DENIS, and the TwoMicron All Sky Survey). The data release can be accessed via the RAVE Web site.

THE RADIAL VELOCITY EXPERIMENT (RAVE): FOURTH DATA RELEASE

We present the stellar atmospheric parameters (effective temperature, surface gravity, overall metallicity), radial velocities, individual abundances, and distances determined for 425,561 stars, which constitute the fourth public data release of the RAdial Velocity Experiment (RAVE). The stellar atmospheric parameters are computed using a new pipeline, based on the algorithms of MATISSE and DEGAS. The spectral degeneracies and the Two Micron All Sky Survey photometric information are now better taken into consideration, improving the parameter determination compared to the previous RAVE data releases. The individual abundances for six elements (magnesium, aluminum, silicon, titanium, iron, and nickel) are also given, based on a special-purpose pipeline that is also improved compared to that available for the RAVE DR3 and Chemical DR1 data releases. Together with photometric information and proper motions, these data can be retrieved from the RAVE collaboration Web site and the Vizier database.

The Radial Velocity Experiment (RAVE)

We present the second data release of the Radial Velocity Experiment (RAVE), an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity, and rotational velocity) of up to one million stars using the 6dF multi-object spectrograph on the 1.2-m UK Schmidt Telescope of the Anglo-Australian Observatory (AAO). The RAVE program started in 2003, obtaining medium resolution specUniversity of Ljubljana, Faculty of Mathematics and Physics, Ljubljana, Slovenia Astrophysikalisches Institut Potsdam, Potsdam, Germany Observatoire de Strasbourg, Strasbourg, France INAF, Osservatorio Astronomico di Padova, Sede di Asiago, Italy RSAA, Australian national University, Canberra, Australia Anglo Australian Observatory, Sydney, Australia Johns Hopkins University, Baltimore MD, USA Macquarie University, Sydney, Australia Institute of Astronomy, University of Cambridge, UK e2v Centre for Electronic Imaging, School of Engineering and Design, Brunel University, Uxbridge, UK Astronomisches Rechen-Institut, Center for Astronomy of the University of Heidelberg, Heidelberg, Germany Kapteyn Astronomical Institute, University of Groningen, Groningen, the Netherlands University of Victoria, Victoria, Canada Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Australia Rudolf Pierls Center for Theoretical Physics, University of Oxford, UK Institute of Astronomy, School of Physics, University of Sydney, NSW 2006, Australia Sterrewacht Leiden, University of Leiden, Leiden, the Netherlands University of Leicester, Leicester, UK MPI fuer extraterrestrische Physik, Garching, Germany University of Central Lancashire, Preston, UK University of Rochester, Rochester NY, USA University of Edinburgh, Edinburgh, UK

Local stellar kinematics from RAVE data – I. Local standard of rest

We analyze a sample of 82850 stars from the RAVE survey, with well-determined velocities and stellar parameters, to isolate a sample of 18026 high-probability thin-disc dwarfs within 600 pc of the Sun. We derive space motions for these stars, and deduce the solar space velocity with respect to the Local Standard of Rest. The peculiar solar

Distance determination for RAVE stars using stellar models . II. Most likely values assuming a standard stellar evolution scenario

The RAdial Velocity Experiment (RAVE) is a spectroscopic survey of the Milky Way which already collected over 400000 spectra of ∼330000 different stars. We use the subsample of spectra with spectroscopically determined values of stellar parameters to determine the distances to these stars. The list currently contains 235064 high quality spectra which show no peculiarities and belong to 210872 different stars. The numbers will grow as the RAVE survey progresses. The public version of the catalog will be made available through the CDS services along with the ongoing RAVE public data releases. The distances are determined with a method based on the work by Breddels et al. (2010, A&A, 511, A16). Here we assume that the star undergoes a standard stellar evolution and that its spectrum shows no peculiarities. The refinements include: the use of either of the three isochrone sets, a better account of the stellar ages and masses, use of more realistic errors of stellar parameter values, and application to a larger dataset. The derived distances of both dwarfs and giants match within ∼21% to the astrometric distances of Hipparcos stars and to the distances of observed members of open and globular clusters. Multiple observations of a fraction of RAVE stars show that repeatability of the derived distances is even better, with half of the objects showing a distance scatter of <11%. RAVE dwarfs are ∼300 pc from the Sun, and giants are at distances of 1 to 2 kpc, and up to 10 kpc. This places the RAVE dataset between the more local Geneva-Copenhagen survey and the more distant and fainter SDSS sample. As such it is ideal to address some of the fundamental questions of Galactic structure and evolution in the pre-Gaia era. Individual applications are left to separate papers, here we show that the full 6-dimensional information on position and velocity is accurate enough to discuss the vertical structure and kinematic properties of the thin and thick disks.

Estimation of the tilt of the stellar velocity ellipsoid from RAVE and implications for mass models

We present a measure of the inclination of the velocity ellipsoid at 1 kpc below the Galactic plane using a sample of red clump giants from the RAdial Velocity Experiment (RAVE) Data Release 2. We find that the velocity ellipsoid is tilted towards the Galactic plane with an inclination of 7 degrees.3 +/- 1 degrees.8. We compare this value to computed inclinations for two mass models of the Milky Way. We find that our measurement is consistent with a short scalelength of the stellar disc (Rd similar or equal to 2 kpc) if the dark halo is oblate or with a long scalelength (Rd similar or equal to 3 kpc) if the dark halo is prolate. Once combined with independent constraints on the flattening of the halo, our measurement suggests that the scalelength is approximately halfway between these two extreme values, with a preferred range 2.5-2.7 kpc for a nearly spherical halo. Nevertheless, no model can be clearly ruled out. With the continuation of the RAVE survey, it will be possible to provide a strong constraint on the mass distribution of the Milky Way using refined measurements of the orientation of the velocity ellipsoid.

Detection of a radial velocity gradient in the extended local disc with RAVE

Using a sample of 213 713 stars from the Radial Velocity Experiment (RAVE) survey, limited to a distance of 2 kpc from the Sun and to |z| rsim 3 km s-1 kpc-1, where K and C are the Oort constants measuring the local divergence and radial shear of the velocity field, respectively. In order to illustrate the effect, assuming a zero radial velocity of the local standard of rest we then reconstruct the two-dimensional Galactocentric velocity maps using two different sets of proper motions and photometric distances based either on isochrone fitting or on K-band magnitudes, and considering two sets of values for the Galactocentric radius of the Sun and local circular speed. Further observational confirmation of our finding with line-of-sight velocities of stars at low latitudes, together with further modelling, should help constrain the non-axisymmetric components of the Galactic potential, including the bar, the spiral arms and possibly the ellipticity of the dark halo.

Distance determination for RAVE stars using stellar models

Aims. We develop a method for deriving distances from spectroscopic data and obtaining full 6D phase-space coordinates for the RAVE survey’s second data release. Methods. We used stellar models combined with atmospheric properties from RAVE (effective temperature, surface gravity and metallicity) and (J − Ks) photometry from archival sources to derive absolute magnitudes. In combination with apparent magnitudes, sky coordinates, proper motions from a variety of sources and radial velocities from RAVE, we are able to derive the full 6D phasespace coordinates for a large sample of RAVE stars. This method is tested with artificial data, Hipparcos trigonometric parallaxes and observations of the open cluster M 67. Results. When we applied our method to a set of 16 146 stars, we found that 25% (4037) of the stars have relative (statistical) distance errors of 4), 25% (1744) have relative distance errors <31%, while 50% (3488) and 75% (5231) have relative errors smaller than 36% and 42%, respectively. Our full dataset shows the expected decrease in the metallicity of stars as a function of distance from the Galactic plane. The known kinematic substructures in the U and V velocity components of nearby dwarf stars are apparent in our dataset, confirming the accuracy of our data and the reliability of our technique. We provide independent measurements of the orientation of the UV velocity ellipsoid and of the solar motion, and they are in very good agreement with previous work. Conclusions. The distance catalogue for the RAVE second data release is available at http://www.astro.rug.nl/~rave, and will be updated in the future to include new data releases.

THE RAVE CATALOG OF STELLAR ELEMENTAL ABUNDANCES: FIRST DATA RELEASE

We present chemical elemental abundances for 36,561 stars observed by the RAdial Velocity Experiment (RAVE), an ambitious spectroscopic survey of our Galaxy at Galactic latitudes vertical bar b vertical bar > 25 degrees and with magnitudes in the range 9 <I(DENIS) <13. RAVE spectra cover the Ca-triplet region at 8410-8795 angstrom with resolving power R similar to 7500. This first data release of the RAVE chemical catalog is complementary to the third RAVE data release of radial velocities and stellar parameters, and it contains chemical abundances for the elements Mg, Al, Si, Ca, Ti, Fe, and Ni, with a mean error of similar to 0.2 dex, as judged from accuracy tests performed on synthetic and real spectra. Abundances are estimated through a dedicated processing pipeline in which the curve of growth of individual lines is obtained from a library of absorption line equivalent widths to construct a model spectrum that is then matched to the observed spectrum via a chi(2) minimization technique. We plan to extend this pipeline to include estimates for other elements, such as oxygen and sulfur, in future data releases.

ORIGINS OF THE THICK DISK AS TRACED BY THE ALPHA ELEMENTS OF METAL-POOR GIANT STARS SELECTED FROM RAVE

Theories of thick-disk formation can be differentiated by measurements of stellar elemental abundances. We have undertaken a study of metal-poor stars selected from the RAVE spectroscopic survey of bright stars to establish whether or not there is a significant population of metal-poor thick-disk stars ([Fe/H] less than or similar to -1.0) and to measure their elemental abundances. In this Letter, we present abundances of four alpha-elements (Mg, Si, Ca, and Ti) and iron for a subsample of 212 red giant branch and 31 red clump/horizontal branch stars from this study. We find that the [alpha/Fe] ratios are enhanced, implying that enrichment proceeded by purely core-collapse supernovae. This requires that star formation in each star-forming region had a short duration. The relative lack of scatter in the [alpha/Fe] ratios implies good mixing in the interstellar medium prior to star formation. In addition, the ratios resemble that of the halo, indicating that the halo and thick disk share a similar massive star initial mass function. We conclude that the alpha-enhancement of the metal-poor thick disk implies that direct accretion of stars from dwarf galaxies similar to surviving dwarf galaxies today did not play a major role in the formation of the thick disk.