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We probe the gravitational force perpendicular to the Galactic plane at the position of the Sun based on a sample of red giants, with measurements taken from the DR3 Gaia catalogue. Measurements far out of the Galactic plane up to 3.5 kpc allow us to determine directly the total mass density, where dark matter is dominant and the stellar and gas densities are very low. In a complementary way, we have also used a new determination of the local baryonic mass density to help determine the density of dark matter in the Galactic plane at the solar position. For the local mass density of dark matter, we obtained $\rho_\mathrm{dm}$=0.0128$\pm $0.0008= 0.486 $\pm$0.030 Gev cm$^{-3}$. For the flattening of the gravitational potential of the dark halo, it is $q_\mathrm{\phi,h}$=0.843$\pm0.035$. For its density, $q_\mathrm{\rho,h}$=0.781$\pm$0.055., Comment: accepted for publication in Astronomy & Astrophysics

This paper shows how a self-consistent dynamical model can be obtained by fitting the gravitational potential of the Milky Way to the stellar kinematics and densities from Gaia data. Using the Besancon Galaxy Model we derive a potential and the disc stellar distribution functions are computed based on three integrals of motion to model stationary stellar discs. The gravitational potential and the stellar distribution functions are built self-consistently, and then adjusted to be in agreement with the kinematics and the density distributions obtained from Gaia observations. A Markov chain Monte Carlo (MCMC) is used to fit the free parameters of the dynamical model to Gaia parallax and proper motion distributions. The fit is done on several sets of Gaia eDR3 data, widely spread in longitudes and latitudes. We are able to determine the velocity dispersion ellipsoid and its tilt for sub-components of different ages, both varying with R and z. The density laws and their radial scale lengths, for the thin and thick disc populations are also obtained self-consistently. This new model has some interesting characteristics, such as a flaring thin disc. The thick disc is found to present very distinctive characteristics from the old thin disc, both in density and kinematics. This well supports the idea that thin and thick discs were formed in distinct scenarios as the density and kinematics transition between them is found to be abrupt. The dark matter halo is shown to be nearly spherical. We also derive the Solar motion to be (10.79 $\pm$ 0.56, 11.06 $\pm$ 0.94, 7.66 $\pm$ 0.43) km/s, in good agreement with recent studies. The resulting fully self-consistent gravitational potential, still axisymmetric, is a good approximation of a smooth mass distribution in the Milky Way and can be used for further studies, including to compute orbits for real stars in our Galaxy (abridged)., Comment: Final version, 26 pages, 14 figures. A&A in press

We investigate the properties of the double sequences of the Milky Way discs visible in the [$\alpha$/Fe] vs [Fe/H] diagram. In the framework of Galactic formation and evolution, we discuss the complex relationships between age, metallicity, [$\alpha$/Fe], and the velocity components. We study stars with measured chemical, seismic and astrometric properties from the APOGEE survey, the Kepler and Gaia satellites, respectively. We separate the [$\alpha$/Fe]-[Fe/H] diagram into 3 stellar populations: the thin disc, the high-$\alpha$ metal-poor thick disc and the high-$\alpha$ metal-rich thick disc and characterise each of these in the age-chemo-kinematics parameter space. We compare results obtained from different APOGEE data releases and using two recent age determinations. We use the Besan\c{c}on Galaxy model (BGM) to highlight selection biases and mechanisms not included in the model. The thin disc exhibits a flat age-metallicity relation while [$\alpha$/Fe] increases with stellar age. We confirm no correlation between radial and vertical velocities with [Fe/H], [$\alpha$/Fe] and age for each stellar population. Considering both samples, V$_\varphi$ decreases with age for the thin disc, while it increases with age for the h$\alpha$mp thick disc. Although the age distribution of the h$\alpha$mr thick disc is very close to that of the h$\alpha$mp thick disc between 7 and 14 Gyr, its kinematics seems to follow that of the thin disc. This feature, not predicted by the hypotheses included in the BGM, suggests a different origin and history for this population. Finally, we show that there is a maximum dispersion of the vertical velocity, $\sigma_Z$, with age for the h$\alpha$mp thick disc around 8 Gyr. The comparisons with the BGM simulations suggest a more complex chemo-dynamical scheme to explain this feature, most likely including mergers and radial migration effects, Comment: Accepted for publication in Aastronomy & Astrophysics on 28/06/2021, 19 pages, 16 figures

In the context of large spectroscopic surveys of stars, data-driven methods are key in deducing physical parameters for millions of spectra in a short time. Convolutional neural networks (CNNs) enable us to connect observables (e.g. spectra, stellar magnitudes) to physical properties (atmospheric parameters, chemical abundances, or labels in general). We trained a CNN, adopting stellar atmospheric parameters and chemical abundances from APOGEE DR16 (resolution R=22500) data as training set labels. As input, we used parts of the intermediate-resolution RAVE DR6 spectra (R~7500) overlapping with the APOGEE DR16 data as well as broad-band ALL_WISE and 2MASS photometry, together with Gaia DR2 photometry and parallaxes. We derived precise atmospheric parameters Teff, log(g), and [M/H] along with the chemical abundances of [Fe/H], [alpha/M], [Mg/Fe], [Si/Fe], [Al/Fe], and [Ni/Fe] for 420165 RAVE spectra. The precision typically amounts to 60K in Teff, 0.06 in log(g) and 0.02-0.04 dex for individual chemical abundances. Incorporating photometry and astrometry as additional constraints substantially improves the results in terms of the accuracy and precision of the derived labels. We provide a catalogue of CNN-trained atmospheric parameters and abundances along with their uncertainties for 420165 stars in the RAVE survey. CNN-based methods provide a powerful way to combine spectroscopic, photometric, and astrometric data without the need to apply any priors in the form of stellar evolutionary models. The developed procedure can extend the scientific output of RAVE spectra beyond DR6 to ongoing and planned surveys such as Gaia RVS, 4MOST, and WEAVE. We call on the community to place a particular collective emphasis and on efforts to create unbiased training samples for such future spectroscopic surveys., Comment: 31 pages, 30 figures, accepted for publication in A&A, in Press

The second data release of the Gaia mission has revealed, in stellar velocity and action space, multiple ridges, the exact origin of which is still debated. Recently, we demonstrated that a large Galactic bar with pattern speed 39 km/s/kpc does create most of the observed ridges. Among those ridges, the Hercules moving group would then be associated to orbits trapped at the co-rotation resonance of the bar. Here we show that a distinctive prediction of such a model is that the angular momentum of Hercules at the Sun's radius must significantly decrease with increasing Galactocentric azimuth, i.e. when getting closer to the major axis of the bar. We show that such a dependence of the angular momentum of trapped orbits on the azimuth would on the other hand not happen close to the outer Lindblad resonance of a faster bar, unless the orbital distribution is still far from phase-mixed, namely for a bar perturbation younger than ~ 2 Gyr. Using Gaia DR2 and Bayesian distances from the StarHorse code, and tracing the average Galactocentric radial velocity as a function of angular momentum and azimuth, we show that the Hercules angular momentum changes significantly with azimuth as expected for the co-rotation resonance of a dynamically old large bar., Comment: 4 pages, 2 figures, A&A in press

We test the performance of the semi-analytic self-consistent Just-Jahrei{\ss} disc model (JJ model) with the astrometric data from the Tycho-Gaia Astrometric Solution (TGAS) sub-catalogue of the first Gaia data release (Gaia DR1), as well as the radial velocities from the fifth data release of the Radial Velocity Experiment survey (RAVE DR5). We use a sample of 19,746 thin disc stars from the TGAS$\times$RAVE cross-match selected in the local solar cylinder of 300 pc radius and 1 kpc height below the Galactic plane and simulate this sample via the forward modelling technique. First, we convert the predicted vertical density laws of the thin disc populations into a mock sample. Then the obtained mock populations are reddened with a 3D dust map and are subjected to the selection criteria corresponding to the RAVE and TGAS observational limitations as well as to additional cuts applied to the data sample. We calculate the quantities of interest separately at different heights above the Galactic plane taking into account the distance error effects separately in horizontal and vertical directions. We investigate the simulated sample in terms of the vertical number density profiles, Hess diagrams and velocity distribution functions. Basing on a good agreement of our simulations with the data, we conclude that our fiducial disc model confidently reproduces the vertical trends in the thin disc stellar population properties. Thus, it can serve as a starting point for the future extension of the JJ model to other Galactocentric distances., Comment: 16 pages, 13 figures. Accepted for publication in Astronomy&Astrophysics

We highlight the power of the Gaia DR2 in studying many fine structures of the Hertzsprung-Russell diagram (HRD). Gaia allows us to present many different HRDs, depending in particular on stellar population selections. We do not aim here for completeness in terms of types of stars or stellar evolutionary aspects. Instead, we have chosen several illustrative examples. We describe some of the selections that can be made in Gaia DR2 to highlight the main structures of the Gaia HRDs. We select both field and cluster (open and globular) stars, compare the observations with previous classifications and with stellar evolutionary tracks, and we present variations of the Gaia HRD with age, metallicity, and kinematics. Late stages of stellar evolution such as hot subdwarfs, post-AGB stars, planetary nebulae, and white dwarfs are also analysed, as well as low-mass brown dwarf objects. The Gaia HRDs are unprecedented in both precision and coverage of the various Milky Way stellar populations and stellar evolutionary phases. Many fine structures of the HRDs are presented. The clear split of the white dwarf sequence into hydrogen and helium white dwarfs is presented for the first time in an HRD. The relation between kinematics and the HRD is nicely illustrated. Two different populations in a classical kinematic selection of the halo are unambiguously identified in the HRD. Membership and mean parameters for a selected list of open clusters are provided. They allow drawing very detailed cluster sequences, highlighting fine structures, and providing extremely precise empirical isochrones that will lead to more insight in stellar physics. Gaia DR2 demonstrates the potential of combining precise astrometry and photometry for large samples for studies in stellar evolution and stellar population and opens an entire new area for HRD-based studies., Comment: Published in the A&A Gaia Data Release 2 special issue. Tables 2 and A.4 corrected. Tables available at http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/616/A10

Before the publication of the Gaia DR2 we confirmed with RAVE and TGAS an observation recently made with the GALAH survey by Quillen ey al. concerning the Coma Berenices moving group in the Solar neighbourhood, namely that it is only present at negative Galactic latitudes. This allowed us to show that it is coherent in vertical velocity, providing a first evidence for incomplete vertical phase-mixing. We estimated for the first time from dynamical arguments that the moving group must have formed at most ~ 1.5 Gyr ago, and related this to a pericentric passage of the Sagittarius dwarf satellite galaxy. The present note is a rewritten version of the original arXiv post on this result now also including a confirmation of our finding with Gaia DR2., Comment: AAS Research Notes

We use data from the Radial Velocity Experiment (RAVE) and the Tycho-Gaia astrometric solution catalogue (TGAS) to compute the velocity fields yielded by the radial (VR), azimuthal (Vphi) and vertical (Vz) components of associated Galactocentric velocity. We search in particular for variation in all three velocity components with distance above and below the disc midplane, as well as how each component of Vz (line-of-sight and tangential velocity projections) modifies the obtained vertical structure. To study the dependence of velocity on proper motion and distance we use two main samples: a RAVE sample including proper motions from the Tycho-2, PPMXL and UCAC4 catalogues, and a RAVE-TGAS sample with inferred distances and proper motions from the TGAS and UCAC5 catalogues. In both samples, we identify asymmetries in VR and Vz. Below the plane we find the largest radial gradient to be dVR / dR = -7.01+- 0.61 km\s kpc, in agreement with recent studies. Above the plane we find a similar gradient with dVR / dR= -9.42+- 1.77 km\s kpc. By comparing our results with previous studies, we find that the structure in Vz is strongly dependent on the adopted proper motions. Using the Galaxia Milky Way model, we demonstrate that distance uncertainties can create artificial wave-like patterns. In contrast to previous suggestions of a breathing mode seen in RAVE data, our results support a combination of bending and breathing modes, likely generated by a combination of external or internal and external mechanisms., Comment: 19 p., 17 fig., accepted MNRAS

Deciphering the assembly history of the Milky Way is a formidable task, which becomes possible only if one can produce high-resolution chrono-chemo-kinematical maps of the Galaxy. Data from large-scale astrometric and spectroscopic surveys will soon provide us with a well-defined view of the current chemo-kinematical structure of the Milky Way, but will only enable a blurred view on the temporal sequence that led to the present-day Galaxy. As demonstrated by the (ongoing) exploitation of data from the pioneering photometric missions CoRoT, Kepler, and K2, asteroseismology provides the way forward: solar-like oscillating giants are excellent evolutionary clocks thanks to the availability of seismic constraints on their mass and to the tight age-initial-mass relation they adhere to. In this paper we identify five key outstanding questions relating to the formation and evolution of the Milky Way that will need precise and accurate ages for large samples of stars to be addressed, and we identify the requirements in terms of number of targets and the precision on the stellar properties that are needed to tackle such questions. By quantifying the asteroseismic yields expected from PLATO for red-giant stars, we demonstrate that these requirements are within the capabilities of the current instrument design, provided that observations are sufficiently long to identify the evolutionary state and allow robust and precise determination of acoustic-mode frequencies. This will allow us to harvest data of sufficient quality to reach a 10% precision in age. This is a fundamental pre-requisite to then reach the more ambitious goal of a similar level of accuracy, which will only be possible if we have to hand a careful appraisal of systematic uncertainties on age deriving from our limited understanding of stellar physics, a goal which conveniently falls within the main aims of PLATO's core science., Comment: 17 pages, 9 figures, accepted for publication in Astronomical Notes

Parallaxes for 331 classical Cepheids, 31 Type II Cepheids and 364 RR Lyrae stars in common between Gaia and the Hipparcos and Tycho-2 catalogues are published in Gaia Data Release 1 (DR1) as part of the Tycho-Gaia Astrometric Solution (TGAS). In order to test these first parallax measurements of the primary standard candles of the cosmological distance ladder, that involve astrometry collected by Gaia during the initial 14 months of science operation, we compared them with literature estimates and derived new period-luminosity ($PL$), period-Wesenheit ($PW$) relations for classical and Type II Cepheids and infrared $PL$, $PL$-metallicity ($PLZ$) and optical luminosity-metallicity ($M_V$-[Fe/H]) relations for the RR Lyrae stars, with zero points based on TGAS. The new relations were computed using multi-band ($V,I,J,K_{\mathrm{s}},W_{1}$) photometry and spectroscopic metal abundances available in the literature, and applying three alternative approaches: (i) by linear least squares fitting the absolute magnitudes inferred from direct transformation of the TGAS parallaxes, (ii) by adopting astrometric-based luminosities, and (iii) using a Bayesian fitting approach. TGAS parallaxes bring a significant added value to the previous Hipparcos estimates. The relations presented in this paper represent first Gaia-calibrated relations and form a "work-in-progress" milestone report in the wait for Gaia-only parallaxes of which a first solution will become available with Gaia's Data Release 2 (DR2) in 2018., Comment: 29 pages, 25 figures. Accepted for publication by A&A

We present a novel analysis of the metal-poor star sample in the complete Radial Velocity Experiment (RAVE) Data Release 5 catalog with the goal of identifying and characterizing all very metal-poor stars observed by the survey. Using a three-stage method, we first identified the candidate stars using only their spectra as input information. We employed an algorithm called t-SNE to construct a low-dimensional projection of the spectrum space and isolate the region containing metal-poor stars. Following this step, we measured the equivalent widths of the near-infrared CaII triplet lines with a method based on flexible Gaussian processes to model the correlated noise present in the spectra. In the last step, we constructed a calibration relation that converts the measured equivalent widths and the color information coming from the 2MASS and WISE surveys into metallicity and temperature estimates. We identified 877 stars with at least a 50% probability of being very metal-poor $(\rm [Fe/H] < -2\,\rm dex)$, out of which 43 are likely extremely metal-poor $(\rm [Fe/H] < -3\,\rm dex )$. The comparison of the derived values to a small subsample of stars with literature metallicity values shows that our method works reliably and correctly estimates the uncertainties, which typically have values $\sigma_{\rm [Fe/H]} \approx 0.2\,\mathrm{dex}$. In addition, when compared to the metallicity results derived using the RAVE DR5 pipeline, it is evident that we achieve better accuracy than the pipeline and therefore more reliably evaluate the very metal-poor subsample. Based on the repeated observations of the same stars, our method gives very consistent results. The method used in this work can also easily be extended to other large-scale data sets, including to the data from the Gaia mission and the upcoming 4MOST survey., Comment: Accepted by A&A

Context. The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution (TGAS). This is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and parallax are calculated using Hipparcos and Tycho-2 positions in 1991.25 as prior information. Aims. We investigate the scientific potential and limitations of the TGAS component by means of the astrometric data for open clusters. Methods. Mean cluster parallax and proper motion values are derived taking into account the error correlations within the astrometric solutions for individual stars, an estimate of the internal velocity dispersion in the cluster, and, where relevant, the effects of the depth of the cluster along the line of sight. Internal consistency of the TGAS data is assessed. Results. Values given for standard uncertainties are still inaccurate and may lead to unrealistic unit-weight standard deviations of least squares solutions for cluster parameters. Reconstructed mean cluster parallax and proper motion values are generally in very good agreement with earlier Hipparcos-based determination, although the Gaia mean parallax for the Pleiades is a significant exception. We have no current explanation for that discrepancy. Most clusters are observed to extend to nearly 15 pc from the cluster centre, and it will be up to future Gaia releases to establish whether those potential cluster-member stars are still dynamically bound to the clusters. Conclusions. The Gaia DR1 provides the means to examine open clusters far beyond their more easily visible cores, and can provide membership assessments based on proper motions and parallaxes. A combined HR diagram shows the same features as observed before using the Hipparcos data, with clearly increased luminosities for older A and F dwarfs., Comment: Accepted for publication by A&A. 21 pages main text plus 46 pages appendices. 34 figures main text, 38 figures appendices. 8 table in main text, 19 tables in appendices

We explore the correlations between velocity and metallicity and the possible distinct chemical signatures of the velocity over-densities of the local Galactic neighbourhood. We use the large spectroscopic survey RAVE and the Geneva Copenhagen Survey. We compare the metallicity distribution of regions in the velocity plane ($v_R,v_\phi$) with that of their symmetric counterparts ($-v_R,v_\phi$). We expect similar metallicity distributions if there are no tracers of a sub-population (e.g., a dispersed cluster, accreted stars), if the disk of the Galaxy is axisymmetric, and if the orbital effects of the spiral arms and the bar are weak. We find that the metallicity-velocity space of the solar neighbourhood is highly patterned. A large fraction of the velocity plane shows differences in the metallicity distribution when comparing symmetric $v_R$ regions. The typical differences in the median metallicity are of $0.05$ dex with a statistical significance of at least $95\%$, and with values up to $0.6$ dex. For low azimuthal velocity $v_\phi$, stars moving outwards in the Galaxy have on average higher metallicity than those moving inwards. These include stars in the Hercules and Hyades moving groups and other velocity branch-like structures. For higher $v_\phi$, the stars moving inwards have higher metallicity than those moving outwards. The most likely interpretation of the metallicity asymmetry is that it is due to the orbital effects of the bar and the radial metallicity gradient of the disk. We present a simulation that supports this idea. We have also discovered a positive gradient in $v_\phi$ with respect to metallicity at high metallicities, apart from the two known positive and negative gradients for the thick and thin disks, respectively., Comment: Accepted for publication in A&A, minor corrections to resemble the published version

A large sample of over 38,000 chromospherically active candidate solar-like stars and cooler dwarfs from the RAVE survey is addressed in this paper. An improved activity identification with respect to the previous study was introduced to build a catalog of field stars in the Solar neighborhood with an excess emission flux in the calcium infrared triplet wavelength region. The central result of this work is the calibration of the age--activity relation for the main sequence dwarfs in a range from a few $10 \; \mathrm{Myr}$ up to a few Gyr. It enabled an order of magnitude age estimation of the entire active sample. Almost 15,000 stars are shown to be younger than $1\;\mathrm{Gyr}$ and $\sim$2000 younger than $100\;\mathrm{Myr}$. The young age of the most active stars is confirmed by their position off the main sequence in the $J-K$ versus $N_{UV}-V$ diagram showing strong ultraviolet excess, mid-infrared excess in the $J-K$ versus $W_1-W_2$ diagram and very cool temperatures ($J-K>0.7$). They overlap with the reference pre-main sequence RAVE stars often displaying X-ray emission. The activity level increasing with the color reveals their different nature from the solar-like stars and probably represents an underlying dynamo generating magnetic fields in cool stars. 50\% of the RAVE objects from DR5 are found in the TGAS catalog and supplemented with accurate parallaxes and proper motions by Gaia. This makes the database of a large number of young stars in a combination with RAVE's radial velocities directly useful as a tracer of the very recent large-scale star formation history in the Solar neighborhood. The data are available online in the Vizier database., Comment: 21 pages, 14 figures, accepted to ApJ

We present a set of 87 RAVE stars with detected solar like oscillations, observed during Campaign 1 of the K2 mission (RAVE K2-C1 sample). This dataset provides a useful benchmark for testing the gravities provided in RAVE Data Release 4 (DR4), and is key for the calibration of the RAVE Data Release 5 (DR5). In the present work, we use two different pipelines, GAUFRE (Valentini et al. 2013) and Sp_Ace (Boeche & Grebel 2016), to determine atmospheric parameters and abundances by fixing log(g) to the seismic one. Our strategy ensures highly consistent values among all stellar parameters, leading to more accurate chemical abundances. A comparison of the chemical abundances obtained here with and without the use of seismic log(g) information has shown that an underestimated (overestimated) gravity leads to an underestimated (overestimated) elemental abundance (e.g. [Mg/H] is underestimated by ~0.25 dex when the gravity is underestimated by 0.5 dex). We then perform a comparison between the seismic gravities and the spectroscopic gravities presented in the RAVE DR4 catalogue, extracting a calibration for log(g) of RAVE giants in the colour interval 0.50<(J - Ks)<0.85. Finally, we show a comparison of the distances, temperatures, extinctions (and ages) derived here for our RAVE K2-C1 sample with those derived in RAVE DR4 and DR5.DR5 performs better than DR4 thanks to the seismic calibration, although discrepancies can still be important for objects for which the difference between DR4/DR5 and seismic gravities differ by more than ~0.5 dex. The method illustrated in this work will be used for analysing RAVE targets present in the other K2 campaigns, in the framework of Galactic Archaeology investigations., Comment: 20 pages, 27 figures, accepted

We report the identification of extended tidal debris potentially associated with the globular cluster NGC 3201, using the RAVE catalogue. We find the debris stars are located at a distance range of 1-7 kpc based on the forthcoming RAVE distance estimates. The derived space velocities and integrals of motion show interesting connections to NGC 3201, modulo uncertainties in the proper motions. Three stars, which are among the 4 most likely candidates for NGC 3201 tidal debris, are separated by 80 degrees on the sky yet are well matched by the 12 Gyr, [Fe/H] = -1.5 isochrone appropriate for the cluster. This is the first time tidal debris around this cluster has been reported over such a large spatial extent, with implications for the cluster$'$s origin and dynamical evolution., Comment: Accepted 2016 January 8. Received 2015 December 10; in original form 2015 November 13 MNRAS

Using six-dimesional phase-space information from the Fourth Data release of the Radial Velocity Experiment (RAVE) over the range of Galactic longitude 240$^{\circ}< l <$ 360$^{\circ}$ and $V_{LSR} < -239$ kms$^{-1}$, we have computed orbits for 329 RAVE stars that were originally selected as chemically and kinematically related to $\omega$ Centauri. The orbits were integrated in a Milky-Way-like axisymmetric Galactic potential, ignoring the effects of the dynamical evolution of $\omega$ Centauri due to the tidal effects of the Galaxy disk on the cluster along time. We also ignored secular changes in the Milky Way potential over time. In a Monte Carlo scheme, and under the assumption that the stars may have been ejected with velocities greater than the escape velocity ($V_{rel}>V_{esc,0}$) from the cluster, we identified 15 stars as having close encounters with $\omega$ Centauri: (\textit{i}) 8 stars with relative velocities $V_{rel}< 200 $ kms$^{-1}$ may have been ejected $\sim$ 200 Myr ago from $\omega$ Centauri; (\textit{ii}) other group of 7 stars were identified with high relative velocity $V_{rel}> 200 $ kms$^{-1}$ during close encounters, and seems unlikely that they have been ejected from $\omega$ Centauri. We also confirm the link between J131340.4-484714 as potential member of $\omega$ Centauri, and probably ejected $\sim$ 2.0 Myr ago, with a relative velocity $V_{rel}\sim80$ kms$^{-1}$., Comment: 10 pages, 8 figures, accepted for publication in Astron. and Astrophys

We present an estimate of the third integral of motion for axisymmetric three-dimensional potentials. This estimate is based on a Staeckel approximation and is explicitly written as a function of the potential. We tested this scheme for the Besancon Galactic model and two other disc-halo models and find that orbits of disc stars have an accurately conserved third quasi integral. The accuracy ranges from of 0.1% to 1% for heights varying from z = 0~kpc to z= 6 kpc and Galactocentric radii R from 5 to 15kpc. We also tested the usefulness of this quasi integral in analytic distribution functions of disc stellar populations: we show that the distribution function remains approximately stationary and that it allows to recover the potential and forces by applying Jeans equations to its moments., Comment: 9 pages, 9 figures, accepted for publication in Astron. and Astrophys

We present the identification of potential members of nearby Galactic globular clusters using radial velocities from the RAdial Velocity Experiment Data Release 4 (RAVE-DR4) survey database. Our identifications are based on three globular clusters -- NGC 3201, NGC 5139 ($\omega$ Cen) and NGC 362 -- all of which are shown to have |RV|>100 km/s. The identification of globular cluster stars in RAVE DR4 data offers a unique opportunity to test the precision and accuracy of the stellar parameters determined with the currently available Stellar Parameter Pipelines (SPPs) used in the survey, as globular clusters are ideal testbeds for the validation of stellar atmospheric parameters, abundances, distances and ages. For both NGC 3201 and $\omega$ Cen, there is compelling evidence for numerous members (> 10) in the RAVE database; in the case of NGC 362 the evidence is more ambiguous, and there may be significant foreground and/or background contamination in our kinematically-selected sample. A comparison of the RAVE-derived stellar parameters and abundances with published values for each cluster and with BASTI isochrones for ages and metallicities from the literature reveals overall good agreement, with the exception of the apparent underestimation of surface gravities for giants, in particular for the most metal-poor stars. Moreover, if the selected members are part of the main body of each cluster our results would also suggest that the distances from Binney et al. 2013, where only isochrones more metal-rich than -0.9 dex were used, are typically underestimated by ~ 40% with respect to the published distances for the clusters, while the distances from Zwitter et al. 2010 show stars ranging from 1 to ~ 6.5 kpc -- with indications of a trend toward higher distances at lower metallicities -- for the three clusters analysed in this study., Comment: Accepted for publication MNRAS, 3 April 2015

We study the kinematics of a local sample of stars, located within a cylinder of 500 pc radius centered on the Sun, in the RAVE dataset. We find clear asymmetries in the $v_R$-$v_\phi$ velocity distributions of thin and thick disk stars: here are more stars moving radially outwards for low azimuthal velocities and more radially inwards for high azimuthal velocities. Such asymmetries have been previously reported for the thin disk as being due to the Galactic bar, but this is the first time that the same type of structures are seen in the thick disk. Our findings imply that the velocities of thick disk stars should no longer be described by Schwarzschild's, multivariate Gaussian or purely axisymmetric distributions. Furthermore, the nature of previously reported substructures in the thick disk needs to be revisited as these could be associated with dynamical resonances rather than to accretion events. It is clear that dynamical models of the Galaxy must fit the 3D velocity distributions of the disks, rather than the projected 1D, if we are to understand the Galaxy fully., Comment: Accepted for publication in ApJL; 7 pages, 3 figures, 1 table

Using the RAdial Velocity Experiment fourth data release (RAVE DR4), and a new metallicity calibration that will be also taken into account in the future RAVE DR5, we investigate the existence and the properties of super-solar metallicity stars ([M/H] > +0.1 dex) in the sample, and in particular in the Solar neighbourhood. We find that RAVE is rich in super-solar metallicity stars, and that the local metallicity distribution function declines remarkably slowly up to +0.4 dex. Our results show that the kinematics and height distributions of the super-solar metallicity stars are identical to those of the [M/H] < 0 thin-disc giants that we presume were locally manufactured. The eccentricities of the super-solar metallicity stars indicate that half of them are on a roughly circular orbit (e < 0.15), so under the assumption that the metallicity of the interstellar medium at a given radius never decreases with time, they must have increased their angular momenta by scattering at corotation resonances of spiral arms from regions far inside the Solar annulus. The likelihood that a star will migrate radially does not seem to decrease significantly with increasing amplitude of vertical oscillations within range of oscillation amplitudes encountered in the disc., Comment: accepted to MNRAS, 11 pages, 11 figures

We aim to characterize high-velocity (HiVel) stars in the solar vicinity both chemically and kinematically using the fourth data release of the RAdial Velocity Experiment (RAVE). We used a sample of 57 HiVel stars with Galactic rest-frame velocities larger than 275 km s$^{-1}$. With 6D position and velocity information, we integrated the orbits of the HiVel stars and found that, on average, they reach out to 13 kpc from the Galactic plane and have relatively eccentric orbits consistent with the Galactic halo. Using the stellar parameters and [$\alpha$/Fe] estimates from RAVE, we found the metallicity distribution of the HiVel stars peak at [M/H] = -1.2 dex and is chemically consistent with the inner halo. There are a few notable exceptions that include a hypervelocity star (HVS) candidate, an extremely high-velocity bound halo star, and one star that is kinematically consistent with the halo but chemically consistent with the disk. High-resolution spectra were obtained for the metal-rich HiVel star candidate and the second highest velocity star in the sample. Using these high-resolution data, we report the discovery of a metal-rich halo star that has likely been dynamically ejected into the halo from the Galactic thick disk. This discovery could aid in explaining the assembly of the most metal-rich component of the Galactic halo., Comment: 14 pages, 13 figures, 4 tables. Accepted for publication in MNRAS

Stellar population studies of globular clusters have suggested that the brightest clusters in the Galaxy might actually be the remnant nuclei of dwarf spheroidal galaxies. If the present Galactic globular clusters formed within larger stellar systems, they are likely surrounded by extra-tidal halos and/or tails made up of stars that were tidally stripped from their parent systems. The stellar surroundings around globular clusters are therefore one of the best places to look for the remnants of an ancient dwarf galaxy. Here an attempt is made to search for tidal debris around the supernovae enriched globular clusters M22 and NGC 1851 as well as the kinematically unique cluster NGC 3201. The stellar parameters from the Radial Velocity Experiment (RAVE) are used to identify stars with RAVE metallicities, radial velocities and elemental-abundances consistent with the abundance patterns and properties of the stars in M22, NGC 1851 and NGC 3201. The discovery of RAVE stars that may be associated with M22 and NGC 1851 are reported, some of which are at projected distances of ~10 degrees away from the core of these clusters. Numerous RAVE stars associated with NGC 3201 suggest that either the tidal radius of this cluster is underestimated, or that there are some unbound stars extending a few arc minutes from the edge of the cluster's radius. No further extra-tidal stars associated with NGC 3201 could be identified. The bright magnitudes of the RAVE stars make them easy targets for high resolution follow-up observations, allowing an eventual further chemical tagging to solidify (or exclude) stars outside the tidal radius of the cluster as tidal debris. In both our radial velocity histograms of the regions surrounding NGC 1851 and NGC 3201, a peak of stars at 230 km/s is seen, consistent with extended tidal debris from omega Centauri., Comment: accepted to A&A

We provide APASS photometry in the Landolt BV and Sloan g'r'i' bands for all the 425,743 stars included in the latest 4th RAVE Data Release. The internal accuracy of the APASS photometry of RAVE stars, expressed as error of the mean of data obtained and separately calibrated over a median of 4 distinct observing epochs and distributed between 2009 and 2013, is 0.013, 0.012, 0.012, 0.014 and 0.021 mag for B, V, g', r' and i' band, respectively. The equally high external accuracy of APASS photometry has been verified on secondary Landolt and Sloan photometric standard stars not involved in the APASS calibration process, and on a large body of literature data on field and cluster stars, confirming the absence of offsets and trends. Compared with the Carlsberg Meridian Catalog (CMC-15), APASS astrometry of RAVE stars is accurate to a median value of 0.098 arcsec. Brightness distribution functions for the RAVE stars have been derived in all bands. APASS photometry of RAVE stars, augmented by 2MASS JHK infrared data, has been chi2 fitted to a densely populated synthetic photometric library designed to widely explore in temperature, surface gravity, metallicity and reddening. Resulting Teff and E(B-V), computed over a range of options, are provided and discussed, and will be kept updated in response to future APASS and RAVE data releases. In the process it is found that the reddening caused by an homogeneous slab of dust, extending for 140 pc on either side of the Galactic plane and responsible for E(B-V,poles)=0.036 +/- 0.002 at the galactic poles, is a suitable approximation of the actual reddening encountered at Galactic latitudes |b|>=25 deg., Comment: Astronomical Journal, in press. Resolution of Figures degrated to match arXiv file size limits

We provide new constraints on the chemo-dynamical models of the Milky Way by measuring the radial and vertical chemical gradients for the elements Mg, Al, Si, Ti, and Fe in the Galactic disc and the gradient variations as a function of the distance from the Galactic plane ($Z$). We selected a sample of giant stars from the RAVE database using the gravity criterium 1.7$<$log g$<$2.8. We created a RAVE mock sample with the Galaxia code based on the Besan\c con model and selected a corresponding mock sample to compare the model with the observed data. We measured the radial gradients and the vertical gradients as a function of the distance from the Galactic plane $Z$ to study their variation across the Galactic disc. The RAVE sample exhibits a negative radial gradient of $d[Fe/H]/dR=-0.054$ dex kpc$^{-1}$ close to the Galactic plane ($|Z|<0.4$ kpc) that becomes flatter for larger $|Z|$. Other elements follow the same trend although with some variations from element to element. The mock sample has radial gradients in fair agreement with the observed data. The variation of the gradients with $Z$ shows that the Fe radial gradient of the RAVE sample has little change in the range $|Z|\lesssim0.6$ kpc and then flattens. The iron vertical gradient of the RAVE sample is slightly negative close to the Galactic plane and steepens with $|Z|$. The mock sample exhibits an iron vertical gradient that is always steeper than the RAVE sample. The mock sample also shows an excess of metal-poor stars in the [Fe/H] distributions with respect to the observed data. These discrepancies can be reduced by decreasing the number of thick disc stars and increasing their average metallicity in the Besan\c con model., Comment: 13 pages, 9 figures, 5 tables, A&A accepted

We determine the Galactic potential in the solar neigbourhood from RAVE observations. We select red clump stars for which accurate distances, radial velocities, and metallicities have been measured. Combined with data from the 2MASS and UCAC catalogues, we build a sample of 4600 red clump stars within a cylinder of 500 pc radius oriented in the direction of the South Galactic Pole, in the range of 200 pc to 2000 pc distances. We deduce the vertical force and the total mass density distribution up to 2 kpc away from the Galactic plane by fitting a distribution function depending explicitly on three isolating integrals of the motion in a separable potential locally representing the Galactic one with four free parameters. Because of the deep extension of our sample, we can determine nearly independently the dark matter mass density and the baryonic disc surface mass density. We find (i) at 1kpc Kz/(2piG) = 68.5 pm 1.0 Msun/pc2, and (ii) at 2 kpc Kz/(2piG) = 96.9 pm 2.2 Msun/pc2. Assuming the solar Galactic radius at R0 = 8.5 kpc, we deduce the local dark matter density rhoDM (z=0) = 0.0143 pm 0.0011Msun pc3 = 0.542 pm 0.042 Gev/cm3 and the baryonic surface mass density Sigma = 44.4 pm 4.1 Msun/pc2 . Our results are in agreement with previously published Kz determinations up to 1 kpc, while the extension to 2 kpc shows some evidence for an unexpectedly large amount of dark matter. A flattening of the dark halo of order 0.8 can produce such a high local density in combination with a circular velocity of 240 km/s . Another explanation, allowing for a lower circular velocity, could be the presence of a secondary dark component, a very thick disc resulting either from the deposit of dark matter from the accretion of multiple small dwarf galaxies, or from the presence of an effective phantom thick disc in the context of effective galactic-scale modifications of gravity., Comment: 14 pages, 13 figures, accepted to Astronomy and Astrophysics

We use the kinematics of $\sim200\,000$ giant stars that lie within $\sim 1.5$ kpc of the plane to measure the vertical profile of mass density near the Sun. We find that the dark mass contained within the isodensity surface of the dark halo that passes through the Sun ($(6\pm0.9)\times10^{10}\,\mathrm{M_\odot}$), and the surface density within $0.9$ kpc of the plane ($(69\pm10)\,\mathrm{M_\odot\,pc^{-2}}$) are almost independent of the (oblate) halo's axis ratio $q$. If the halo is spherical, 46 per cent of the radial force on the Sun is provided by baryons, and only 4.3 per cent of the Galaxy's mass is baryonic. If the halo is flattened, the baryons contribute even less strongly to the local radial force and to the Galaxy's mass. The dark-matter density at the location of the Sun is $0.0126\,q^{-0.89}\,\mathrm{M_\odot\,pc^{-3}}=0.48\,q^{-0.89}\,\mathrm{GeV\,cm^{-3}}$. When combined with other literature results we find hints for a mildly oblate dark halo with $q \simeq 0.8$. Our value for the dark mass within the solar radius is larger than that predicted by cosmological dark-matter-only simulations but in good agreement with simulations once the effects of baryonic infall are taken into account. Our mass models consist of three double-exponential discs, an oblate bulge and a Navarro-Frenk-White dark-matter halo, and we model the dynamics of the RAVE stars in the corresponding gravitational fields by finding distribution functions $f(\mathbf{J})$ that depend on three action integrals. Statistical errors are completely swamped by systematic uncertainties, the most important of which are the distance to the stars in the photometric and spectroscopic samples and the solar distance to the Galactic centre. Systematics other than the flattening of the dark halo yield overall uncertainties $\sim 15$ per cent., Comment: 20 pages, 17 figures, accepted for publication in MNRAS

We investigate the kinematic parameters of the Milky Way disc using the RAVE and GCS stellar surveys. We do this by fitting a kinematic model to the data taking the selection function of the data into account. For stars in the GCS we use all phase-space coordinates, but for RAVE stars we use only $(l,b,v_{\rm los})$. Using MCMC technique, we investigate the full posterior distributions of the parameters given the data. We investigate the `age-velocity dispersion' relation for the three kinematic components ($\sigma_R,\sigma_{\phi},\sigma_z$), the radial dependence of the velocity dispersions, the Solar peculiar motion ($U_{\odot},V_{\odot}, W_{\odot} $), the circular speed $\Theta_0$ at the Sun and the fall of mean azimuthal motion with height above the mid-plane. We confirm that the Besan\c{c}on-style Gaussian model accurately fits the GCS data, but fails to match the details of the more spatially extended RAVE survey. In particular, the Shu distribution function (DF) handles non-circular orbits more accurately and provides a better fit to the kinematic data. The Gaussian distribution function not only fits the data poorly but systematically underestimates the fall of velocity dispersion with radius. We find that correlations exist between a number of parameters, which highlights the importance of doing joint fits. The large size of the RAVE survey, allows us to get precise values for most parameters. However, large systematic uncertainties remain, especially in $V_{\odot}$ and $\Theta_0$. We find that, for an extended sample of stars, $\Theta_0$ is underestimated by as much as $10\%$ if the vertical dependence of the mean azimuthal motion is neglected. Using a simple model for vertical dependence of kinematics, we find that it is possible to match the Sgr A* proper motion without any need for $V_{\odot}$ being larger than that estimated locally by surveys like GCS., Comment: 27 pages, 13 figures, accepted for publication in ApJ

The velocity dispersions of stars near the Sun are known to increase with stellar age, but age can be difficult to determine so a proxy like the abundance of alpha elements (e.g., Mg) with respect to iron, [alpha/Fe], is used. Here we report an unexpected behavior found in the velocity dispersion of a sample of giant stars from the RAdial Velocity Experiment (RAVE) survey with high quality chemical and kinematical information, in that it decreases strongly for stars with [Mg/Fe] > 0.4 dex (i.e., those that formed in the first Gyr of the Galaxy's life). These findings can be explained by perturbations from massive mergers in the early Universe, which have affected more strongly the outer parts of the disc, and the subsequent radial migration of stars with cooler kinematics from the inner disc. Similar reversed trends in velocity dispersion are also found for different metallicity subpopulations. Our results suggest that the Milky Way disc merger history can be recovered by relating the observed chemo-kinematic relations to the properties of past merger events., Comment: 9 pages, 5 figures, Accepted to ApJL. Interpretation section expanded, different Fig.5, typos corrected, references added. Conclusions unchanged

By selecting in the RAVE-DR4 survey the stars located between 1 and 2 kpc above the Galactic plane, we question the consistency of the simplest three-component model (thin disc, thick disc, halo) for the Milky Way. We confirm that the metallicity and azimuthal velocity distribution functions of the thick disc are not Gaussian. In particular, we find that the thick disc has an extended metallicity tail going at least down to [M/H]=-2 dex, contributing roughly at 3% of the entire thick disc population and having a shorter scale-length compared to the canonical thick disc. The mean azimuthal velocity of these metal-poor stars allows us to estimate the correlation between the metallicity and the orbital velocity, which is an important constraint on the formation mechanisms of the Galactic thick disc. Given our simple approach, we find dVphi/d[M/H] ~ 50 km/s/dex, which is in a very good agreement with previous literature values. We complete the study with a brief discussion on the implications of the formation scenarios for the thick disc, and suggest that given the above mentioned characteristics, a thick disc mainly formed by radial migration mechanisms seems unlikely., Comment: 17 pages, 18 figures, accepted for publication in MNRAS

Context. Galactic open clusters (OCs) mainly belong to the young stellar population in the Milky Way disk, but are there groups and complexes of OCs that possibly define an additional level in hierarchical star formation? Current compilations are too incomplete to address this question, especially regarding radial velocities (RVs) and metallicities ($[M/H]$). Aims. Here we provide and discuss newly obtained RV and $[M/H]$ data, which will enable us to reinvestigate potential groupings of open clusters and associations. Methods.We extracted additional RVs and $[M/H]$ from the RAdial Velocity Experiment (RAVE) via a cross-match with the Catalogue of Stars in Open Cluster Areas (CSOCA). For the identified OCs in RAVE we derived RV and $[M/H]$ from a cleaned working sample and compared the results with previous findings. Results. Although our RAVE sample does not show the same accuracy as the entire survey, we were able to derive reliable RV for 110 Galactic open clusters. For 37 OCs we publish RV for the first time. Moreover, we determined $[M/H]$ for 81 open clusters, extending the number of OCs with $[M/H]$ by 69., Comment: 21 pages, 9 Tables, 21 Figures

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 2MASS 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 which 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 website and the Vizier database., Comment: 40 pages, 36 figures, accepted in AJ

RAVE, the unbiased magnitude limited survey of the southern sky stars, contained 456,676 medium-resolution spectra at the time of our analysis. Spectra cover the CaII IRT range which is a known indicator of chromospheric activity. Our previous work (Matijevi\v{c} et al. 2012) classified all spectra using locally linear embedding. It identified 53,347 cases with a suggested emission component in calcium lines. Here we use a spectral subtraction technique to measure the properties of this emission. Synthetic templates are replaced by the observed spectra of non-active stars to bypass the difficult computations of non-LTE profiles of the line cores and stellar parameter dependence. We derive both the equivalent width of the excess emission for each calcium line on a 5\AA\ wide interval and their sum EW_IRT for ~44,000 candidate active dwarf stars with S/N>20 and with no respect to the source of their emission flux. From these ~14,000 show a detectable chromospheric flux with at least 2\sigma\ confidence level. Our set of active stars vastly enlarges previously known samples. Atmospheric parameters and in some cases radial velocities of active stars derived from automatic pipeline suffer from systematic shifts due to their shallower calcium lines. We re-estimate the effective temperature, metallicity and radial velocities for candidate active stars. The overall distribution of activity levels shows a bimodal shape, with the first peak coinciding with non-active stars and the second with the pre main-sequence cases. The catalogue will be publicly available with the next RAVE public data releases., Comment: 13 pages, 9 figures

Aim: We aim at measuring the chemical gradients of the elements Mg, Al, Si, and Fe along the Galactic radius to provide new constraints on the chemical evolution models of the Galaxy and Galaxy models such as the Besancon model. Methods: We analysed three different samples selected from three independent datasets: a sample of 19,962 dwarf stars selected from the RAVE database, a sample of 10,616 dwarf stars selected from the Geneva-Copenhagen Survey (GCS) dataset, and a mock sample (equivalent to the RAVE sample) created by using the GALAXIA code, which is based on the Besancon model. We measured the chemical gradients as functions of the guiding radius (Rg) at different distances from the Galactic plane reached by the stars along their orbit (Zmax). Results: The chemical gradients of the RAVE and GCS samples are negative and show consistent trends, although they are not equal: at Zmax<0.4 kpc and 4.5

Diffuse interstellar bands are usually observed in spectra of hot stars, where interstellar lines are rarely blended with stellar ones. The need for hot stars is a strong limitation in the number of sightlines we can observe and the distribution of sightlines in the Galaxy, as hot stars are rare and concentrated in the Galactic plane. We are introducing a new method, where interstellar lines can be observed in spectra of cool stars in large spectroscopic surveys. The method is completely automated and does not require prior knowledge of the stellar parameters. If known, the stellar parameters only reduce the computational time and are not involved in the extraction of the interstellar spectrum. The main step in extracting interstellar lines is a construction of the stellar spectrum, which is in our method done by finding other observed spectra that lack interstellar features and are otherwise very similar to the spectrum in question. Such spectra are then combined into a single stellar spectrum template, which matches the stellar component in an observed spectrum. We demonstrate the performance of this new method on a sample of 482,430 spectra observed in RAVE survey. However, many spectra have to be combined (48 on average) in order to achieve a S/N ratio high enough to measure the DIB's profile, hence limiting the spatial information about the ISM. Only one strong interstellar line is included in the RAVE spectral range, a diffuse interstellar band at 8620 \AA. We compare its equivalent width with extinction maps and with Bayesian reddening, calculated for individual stars, and provide a linear relation between the equivalent width and reddening. Separately from the introduced method, we calculate equivalent widths of the diffuse interstellar band in spectra of hot stars with known extinction and compare all three linear relations with each other and with relations from the literature., Comment: 12 pages, 10 figures, submitted to ApJ

We construct new estimates on the Galactic escape speed at various Galactocentric radii using the latest data release of the Radial Velocity Experiment (RAVE DR4). Compared to previous studies we have a database larger by a factor of 10 as well as reliable distance estimates for almost all stars. Our analysis is based on the statistical analysis of a rigorously selected sample of 90 high-velocity halo stars from RAVE and a previously published data set. We calibrate and extensively test our method using a suite of cosmological simulations of the formation of Milky Way-sized galaxies. Our best estimate of the local Galactic escape speed, which we define as the minimum speed required to reach three virial radii $R_{340}$, is $533^{+54}_{-41}$ km/s (90% confidence) with an additional 5% systematic uncertainty, where $R_{340}$ is the Galactocentric radius encompassing a mean over-density of 340 times the critical density for closure in the Universe. From the escape speed we further derive estimates of the mass of the Galaxy using a simple mass model with two options for the mass profile of the dark matter halo: an unaltered and an adiabatically contracted Navarro, Frenk & White (NFW) sphere. If we fix the local circular velocity the latter profile yields a significantly higher mass than the un-contracted halo, but if we instead use the statistics on halo concentration parameters in large cosmological simulations as a constraint we find very similar masses for both models. Our best estimate for $M_{340}$, the mass interior to $R_{340}$ (dark matter and baryons), is $1.3^{+0.4}_{-0.3} \times 10^{12}$ M$_\odot$ (corresponding to $M_{200} = 1.6^{+0.5}_{-0.4} \times 10^{12}$ M$_\odot$). This estimate is in good agreement with recently published independent mass estimates based on the kinematics of more distant halo stars and the satellite galaxy Leo I., Comment: 16 pages, 15 figures; accepted for publication in Astronomy & Astrophysics

Non-axisymmetries in the Galactic potential (spiral arms and bar) induce kinematic groups such as the Hercules stream. Assuming that Hercules is caused by the effects of the Outer Lindblad Resonance of the Galactic bar, we model analytically its properties as a function of position in the Galaxy and its dependence on the bar's pattern speed and orientation. Using data from the RAVE survey we find that the azimuthal velocity of the Hercules structure decreases as a function of Galactocentric radius, in a manner consistent with our analytical model. This allows us to obtain new estimates of the parameters of the Milky Way's bar. The combined likelihood function of the bar's pattern speed and angle has its maximum for a pattern speed of $\Omega_b=(1.89 \pm 0.08) \times \Omega_0$ where $\Omega_0$ is the local circular frequency. Assuming a Solar radius of 8.05 kpc and a local circular velocity of 238 km/s, this corresponds to $\Omega_b=56\pm 2$ km/s/kpc. On the other hand, the bar's orientation $\phi_b$ cannot be constrained with the available data. In fact, the likelihood function shows that a tight correlation exists between the pattern speed and the orientation, implying that a better description of our best fit results is given by the linear relation $\Omega_b/\Omega_0=1.91 + 0.0044[\phi_b(\deg)-48]$, with standard deviation of 0.02. For example, for an angle of $\phi_b=30\deg$ the pattern speed is $54.0\pm0.5$ km/s/kpc. These results are not very sensitive to the other Galactic parameters such as the circular velocity curve or the peculiar motion of the Sun, and are robust to biases in distance., Comment: 16 pages, 16 figures, 3 tables, 2 appendix (2 tables, 2 figures), accepted for publication in A&A

The determination of the LSR is still a matter of debate. The classical value of the tangential peculiar motion of the Sun with respect to the LSR was challenged in recent years, claiming a significantly larger value. We show that the RAdial Velocity Experiment (RAVE) sample of dwarf stars is an excellent data set to derive tighter boundary conditions to chemodynamical evolution models of the extended solar neighbourhood. We present an improved Jeans analysis, which allows a better interpretation of the measured kinematics of stellar populations in the Milky Way disc. We propose an improved version of the Str\"omberg relation with the radial scalelengths as the only unknown. Binning RAVE stars in metallicity reveals a bigger asymmetric drift (corresponding to a smaller radial scalelength) for more metal-rich populations. With the standard assumption of velocity-dispersion independent radial scalelengths in each metallicity bin, we redetermine the LSR. The new Str\"omberg equation yields a joint LSR value of V_\sun=3.06 \pm 0.68 km/s, which is even smaller than the classical value based on Hipparcos data. The corresponding radial scalelength increases from 1.6 kpc for the metal-rich bin to 2.9 kpc for the metal-poor bin, with a trend of an even larger scalelength for young metal-poor stars. When adopting the recent Sch\"onrich value of V_\sun=12.24 km/s for the LSR, the new Str\"omberg equation yields much larger individual radial scalelengths of the RAVE subpopulations, which seem unphysical in part. The new Str\"omberg equation allows a cleaner interpretation of the kinematic data of disc stars in terms of radial scalelengths. Lifting the LSR value by a few km/s compared to the classical value results in strongly increased radial scalelengths with a trend of smaller values for larger velocity dispersions., Comment: Accepted for publication in A&A; 13 pages, 9 figures

Aims: We study the relations between stellar kinematics and chemical abundances of a large sample of RAVE giants in search for selection criteria needed for disentangling different Galactic stellar populations. Methods: We select a sample of 2167 giant stars with signal-to-noise per spectral measurements above 75 from the RAVE chemical catalogue and follow the analysis performed by Gratton and colleagues on 150 subdwarf stars spectroscopically observed at high-resolution. We then use a larger sample of 9131 giants (with signal-to-noise above 60) to investigate the chemo-kinematical characteristics of our stars by grouping them into nine subsamples with common eccentricity ($e$) and maximum distance achieved above the Galactic plane ($Z_max$). Results: The RAVE kinematical and chemical data proved to be reliable by reproducing the results by Gratton et al. obtained with high-resolution spectroscopic data. Our analysis, based on the $e$-$Z_max$ plane combined with additional orbital parameters and chemical information, provides an alternative way of identifying different populations of stars. In addition to extracting canonical thick- and thin-disc samples, we find a group of stars in the Galactic plane ($Z_max<1$ kpc and 0.4 $< e < $0.6), which show homogeneous kinematics but differ in their chemical properties. We interpret this as a clear sign that some of these stars have experienced the effects of heating and/or radial migration, which have modified their original orbits. The accretion origin of such stars cannot be excluded., Comment: accepted for publication in A&A

The RAVE survey, combined with proper motions and distance estimates, can be used to study in detail stellar kinematics in the extended solar neighbourhood (solar suburb). Using the red clump, we examine the mean velocity components in 3D between an R of 6 and 10 kpc and a Z of -2 to 2 kpc, concentrating on North-South differences. Simple parametric fits to the R, Z trends for VPHI and the velocity dispersions are presented. We confirm the recently discovered gradient in mean Galactocentric radial velocity, VR, finding that the gradient is more marked below the plane, with a Z gradient also present. The vertical velocity, VZ, also shows clear structure, with indications of a rarefaction-compression pattern, suggestive of wave-like behaviour. We perform a rigorous error analysis, tracing sources of both systematic and random errors. We confirm the North-South differences in VR and VZ along the line-of-sight, with the VR estimated independent of the proper motions. The complex three-dimensional structure of velocity space presents challenges for future modelling of the Galactic disk, with the Galactic bar, spiral arms and excitation of wave-like structures all probably playing a role., Comment: MNRAS, accepted (22 pages, 19 figures)

Aims. We study the Milky Way thin disk with the Radial Velocity Experiment (RAVE) survey. We consider the thin and thick disks as different Galactic components and present a technique to statistically disentangle the two populations. Then we focus our attention on the thin disk component. Methods. We disentangle the thin disk component from amixture of the thin and thick disks using a data set providing radial velocities, proper motions, and photometrically determined distances. Results. We present the trend of the velocity dispersions in the thin disk component of the Milky Way (MW) in the radial direction above and below the Galactic plane using data from the RAdial Velocity Experiment (RAVE). The selected sample is a limited subsample from the entire RAVE catalogue, roughly mapping up to 500 pc above and below the Galactic plane, a few degrees in azimuthal direction and covering a radial extension of 2.0 kpc around the solar position. The solar motion relative to the local standard of rest is also re-determined with the isolated thin disk component. Major results are the trend of the velocity mean and dispersion in the radial and vertical direction. In addition the azimuthal components of the solar motion relative to the local standard of rest and the velocity dispersion are discussed., Comment: accepted on A&A, please see companion paper "THICK disk kinem..."

Using the RAVE survey, we recently brought to light a gradient in the mean galactocentric radial velocity of stars in the extended solar neighbourhood. This gradient likely originates from non-axisymmetric perturbations of the potential, among which a perturbation by spiral arms is a possible explanation. Here, we apply the traditional density wave theory and analytically model the radial component of the two-dimensional velocity field. Provided that the radial velocity gradient is caused by relatively long-lived spiral arms that can affect stars substantially above the plane, this analytic model provides new independent estimates for the parameters of the Milky Way spiral structure. Our analysis favours a two-armed perturbation with the Sun close to the inner ultra-harmonic 4:1 resonance, with a pattern speed \Omega_p=18.6^{+0.3}_{-0.2} km/s/kpc and a small amplitude A=0.55 \pm 0.02% of the background potential (14% of the background density). This model can serve as a basis for numerical simulations in three dimensions, additionally including a possible influence of the galactic bar and/or other non-axisymmetric modes., Comment: 9 pages, 4 figures, accepted for publication in MNRAS

We analyse the kinematics of disc stars observed by the RAVE survey in and beyond the Solar neighbourhood.We detect significant overdensities in the velocity distributions using a technique based on the wavelet transform.We find that the main local kinematic groups are large scale features, surviving at least up to ~1 kpc from the Sun in the direction of anti-rotation, and also at ~700 pc below the Galactic plane.We also find that for regions located at different radii than the Sun, the known groups appear shifted in the velocity plane. For example, the Hercules group has a larger azimuthal velocity for regions inside the Solar circle and a lower value outside. We have also discovered a new group at (U, V) = (92,-22) km/s in the Solar neighbourhood and confirmed the significance of other previously found groups. Some of these trends detected for the first time are consistent with dynamical models of the effects of the bar and the spiral arms. More modelling is required to definitively characterise the non-axisymmetric components of our Galaxy using these groups., Comment: Minor changes to match the accepted version in MNRAS Letters

The RAdial Velocity Experiment (RAVE) is a medium resolution R~7500 spectroscopic survey of the Milky Way which already obtained over half a million stellar spectra. They present a randomly selected magnitude-limited sample, so it is important to use a reliable and automated classification scheme which identifies normal single stars and discovers different types of peculiar stars. To this end we present a morphological classification of 350,000 RAVE survey stellar spectra using locally linear embedding, a dimensionality reduction method which enables representing the complex spectral morphology in a low dimensional projected space while still preserving the properties of the local neighborhoods of spectra. We find that the majority of all spectra in the database ~90-95% belong to normal single stars, but there is also a significant population of several types of peculiars. Among them the most populated groups are those of various types of spectroscopic binary and chromospherically active stars. Both of them include several thousands of spectra. Particularly the latter group offers significant further investigation opportunities since activity of stars is a known proxy of stellar ages. Applying the same classification procedure to the sample of normal single stars alone shows that the shape of the projected manifold in two dimensional space correlates with stellar temperature, surface gravity and metallicity., Comment: 28 pages, 11 figures, accepted for publication in ApJS

We performed a spectroscopic survey of nearly 700 stars probing the galactic thick disc far from the solar neighbourhood towards the galactic coordinates (l~277, b~47). The derived effective temperatures, surface gravities and overall metallicities were then combined with stellar evolution isochrones, radial velocities and proper motions to derive the distances, kinematics and orbital parameters of the sample stars. The targets belonging to each galactic component (thin disc, thick disc, halo) were selected either on their kinematics or according to their position above the galactic plane, and the vertical gradients were also estimated. We present here atmospheric parameters, distances and kinematics for this sample, and a comparison of our kinematic and metallicity distributions with the Besancon model of the Milky Way. The thick disc far from the solar neighbourhood is found to differ only slightly from the thick disc properties as derived in the solar vicinity. For regions where the thick disc dominates, we measured vertical velocity and metallicity trends of d(V_phi)/dZ = 19 +/- 8 km/s/kpc and d[M/H]/dZ = -0.14 +/- 0.05 dex/kpc, respectively. These trends can be explained as a smooth transition between the different galactic components, although intrinsic gradients could not be excluded. In addition, a correlation d(V_phi)/d[M/H] = -45 +/- 12 km/s/dex between the orbital velocity and the metallicity of the thick disc is detected. This gradient is inconsistent with the SDSS photometric survey analysis, which did not detect any such trend, and challenges radial migration models of thick disc formation. Estimations of the scale heights and scale lengths for different metallicity bins of the thick disc result in consistent values, with hR~3.4 \pm 0.7 kpc, and hZ~694 \pm 45 pc, showing no evidence of relics of destroyed massive satellites., Comment: 19 pages, 15 figures, accepted for publication in A&A

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 $|$b$|>25^{\circ}$ and with magnitudes in the range 9$

We apply the method of Burnett & Binney (2010) for the determination of stellar distances and parameters to the internal catalogue of the Radial Velocity Experiment (Steinmetz et al. 2006). Subsamples of stars that either have Hipparcos parallaxes or belong to well-studied clusters, inspire confidence in the formal errors. Distances to dwarfs cooler than ~6000 K appear to be unbiased, but those to hotter dwarfs tend to be too small by ~10% of the formal errors. Distances to giants tend to be too large by about the same amount. The median distance error in the whole sample of 216,000 stars is 28% and the error distribution is similar for both giants and dwarfs. Roughly half the stars in the RAVE survey are giants. The giant fraction is largest at low latitudes and in directions towards the Galactic Centre. Near the plane the metallicity distribution is remarkably narrow and centred on [M/H]-0.04 dex; with increasing |z| it broadens out and its median moves to [M/H] ~ -0.5. Mean age as a function of distance from the Galactic centre and distance |z| from the Galactic plane shows the anticipated increase in mean age with |z|., Comment: 14 pages accepted for publication in Astronomy & Astrophysics

Repeated spectroscopic observations of stars in the Radial Velocity Experiment (RAVE) database are used to identify and examine single-lined binary (SB1) candidates. The RAVE latest internal database (VDR3) includes radial velocities, atmospheric and other parameters for approximately quarter million of different stars with little less than 300,000 observations. In the sample of ~20,000 stars observed more than once, 1333 stars with variable radial velocities were identified. Most of them are believed to be SB1 candidates. The fraction of SB1 candidates among stars with several observations is between 10% and 15% which is the lower limit for binarity among RAVE stars. Due to the distribution of time spans between the re-observation that is biased towards relatively short timescales (days to weeks), the periods of the identified SB1 candidates are most likely in the same range. Because of the RAVE's narrow magnitude range most of the dwarf candidates belong to the thin Galactic disk while the giants are part of the thick disk with distances extending to up to a few kpc. The comparison of the list of SB1 candidates to the VSX catalog of variable stars yielded several pulsating variables among the giant population with the radial velocity variations of up to few tens of km/s. There are 26 matches between the catalog of spectroscopic binary orbits (SB9) and the whole RAVE sample for which the given periastron time and the time of RAVE observation were close enough to yield a reliable comparison. RAVE measurements of radial velocities of known spectroscopic binaries are consistent with their published radial velocity curves., Comment: 10 pages, 7 figures, accepted for publication in AJ