85 research outputs found
Binary stars in the RAVE survey
We searched the sample of RAVE survey spectra for both types of spectroscopic binary stars in order to estimate their number in the sample and perform a study on newly discovered binaries
A RAVE investigation on Galactic open clusters I. Radial velocities and metallicities
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) over bar and ([M/H]) over bar 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) over bar for 110 Galactic open clusters. For 37 OCs we publish (RV) over bar for the first time. Moreover, we determined ([M/H]) over bar for 81 open clusters, extending the number of OCs with ([M/H]) over bar by 69
Chromospherically Active Stars in the RAVE Survey. I. The Catalogue
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 figure
Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18
Combining the precise parallaxes and optical photometry delivered by Gaia's
second data release (Gaia DR2) with the photometric catalogues of PanSTARRS-1,
2MASS, and AllWISE, we derive Bayesian stellar parameters, distances, and
extinctions for 265 million stars brighter than G=18. Because of the wide
wavelength range used, our results substantially improve the accuracy and
precision of previous extinction and effective temperature estimates. After
cleaning our results for both unreliable input and output data, we retain 137
million stars, for which we achieve a median precision of 5% in distance, 0.20
mag in V-band extinction, and 245 K in effective temperature for G<14,
degrading towards fainter magnitudes (12%, 0.20 mag, and 245 K at G=16; 16%,
0.23 mag, and 260 K at G=17, respectively). We find a very good agreement with
the asteroseismic surface gravities and distances of 7000 stars in the Kepler,
the K2-C3, and the K2-C6 fields, with stellar parameters from the APOGEE
survey, as well as with distances to star clusters. Our results are available
through the ADQL query interface of the Gaia mirror at the Leibniz-Institut
f\"{u}r Astrophysik Potsdam (gaia.aip.de) and as binary tables at data.aip.de.
As a first application, in this paper we provide distance- and
extinction-corrected colour-magnitude diagrams, extinction maps as a function
of distance, and extensive density maps, demonstrating the potential of our
value-added dataset for mapping the three-dimensional structure of our Galaxy.
In particular, we see a clear manifestation of the Galactic bar in the stellar
density distributions, an observation that can almost be considered a direct
imaging of the Galactic bar.Comment: 25 pages, 23 figures + appendix, accepted for publication in A&A.
Data (doi:10.17876/gaia/dr.2/51) are available through ADQL queries at
gaia.aip.d
The RAVE survey: the Galactic escape speed and the mass of the Milky Way
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 , is km/s (90%
confidence) with an additional 5% systematic uncertainty, where 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 , the
mass interior to (dark matter and baryons), is M (corresponding to M). 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 &
Astrophysic
CHROMOSPHERICALLY ACTIVE STARS in the RAVE SURVEY. II. YOUNG DWARFS in the SOLAR NEIGHBORHOOD
© 2017. The American Astronomical Society. All rights reserved. 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 main-sequence dwarfs in a range from a few 10 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 Gyr and ∼2000 younger than 100 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. Of the RAVE objects from DR5, 50% 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
Chromospherically Active Stars in the RAVE Survey. II. Young dwarfs in the Solar neighborhood
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 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 and 2000 younger than . The young age of the most active stars is confirmed by their position off the main sequence in the versus diagram showing strong ultraviolet excess, mid-infrared excess in the versus diagram and very cool temperatures (). 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
Chemical gradients in the Milky Way from the RAVE data
Aims. 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. Thanks to the large number of stars of our RAVE sample we can study how the gradients vary as function of the distance from the Galactic plane.
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. The three samples were analysed by using the very same method for comparison purposes. We integrated the Galactic orbits and obtained the guiding radii (R-g) and the maximum distances from the Galactic plane reached by the stars along their orbits (Z(max)). We measured the chemical gradients as functions of R-g at different Z(max).
Results. We found that the chemical gradients of the RAVE and GCS samples are negative and show consistent trends, although they are not equal: at Z(max) < 0.4 kpc and 4.5 < R-g(kpc) < 9.5, the iron gradient for the RAVE sample is d[Fe/H]/dR(g) = -0.065 dex kpc(-1), whereas for the GCS sample it is d[Fe/H]/dR(g) = -0.043 dex kpc(-1) with internal errors of +/-0.002 and +/-0.004 dex kpc(-1), respectively. The gradients of the RAVE and GCS samples become flatter at larger Z(max). Conversely, the mock sample has a positive iron gradient of d[Fe/H]/dR(g) = +0.053 +/- 0.003 dex kpc(-1) at Z(max) < 0.4 kpc and remains positive at any Z(max). These positive and unrealistic values originate from the lack of correlation between metallicity and tangential velocity in the Besancon model. In addition, the low metallicity and asymmetric drift of the thick disc causes a shift of the stars towards lower R-g and metallicity which, together with the thin-disc stars with a higher metallicity and R-g, generates a fictitious positive gradient of the full sample. The flatter gradient at larger Z(max) found in the RAVE and the GCS samples may therefore be due to the superposition of thin-and thick-disc stars, which mimicks a flatter or positive gradient. This does not exclude the possibility that the thick disc has no chemical gradient. The discrepancies between the observational samples and the mock sample can be reduced by i) decreasing the density; ii) decreasing the vertical velocity; and iii) increasing the metallicity of the thick disc in the Besancon model
The RAVE-on Catalog of Stellar Atmospheric Parameters and Chemical Abundances for Chemo-dynamic Studies in the Gaia Era
The orbits, atmospheric parameters, chemical abundances, and ages of
individual stars in the Milky Way provide the most comprehensive illustration
of galaxy formation available. The Tycho-Gaia Astrometric Solution (TGAS) will
deliver astrometric parameters for the largest ever sample of Milky Way stars,
though its full potential cannot be realized without the addition of
complementary spectroscopy. Among existing spectroscopic surveys, the RAdial
Velocity Experiment (RAVE) has the largest overlap with TGAS (200,000
stars). We present a data-driven re-analysis of 520,781 RAVE spectra using The
Cannon. For red giants, we build our model using high-fidelity APOGEE stellar
parameters and abundances for stars that overlap with RAVE. For main-sequence
and sub-giant stars, our model uses stellar parameters from the K2/EPIC. We
derive and validate effective temperature , surface gravity
, and chemical abundances of up to seven elements (O, Mg, Al, Si, Ca,
Fe, Ni). We report a total of 1,685,851 elemental abundances with a typical
precision of 0.07 dex, a substantial improvement over previous RAVE data
releases. The synthesis of RAVE-on and TGAS is the most powerful data set for
chemo-dynamic analyses of the Milky Way ever produced
Kepler eclipsing binary stars. VII. the catalogue of eclipsing binaries found in the entire Kepler data set
The primary Kepler Mission provided nearly continuous monitoring of ~200,000 objects with unprecedented photometric precision. We present the final catalog of eclipsing binary systems within the 105 deg2 Kepler field of view. This release incorporates the full extent of the data from the primary mission (Q0-Q17 Data Release). As a result, new systems have been added, additional false positives have been removed, ephemerides and principal parameters have been recomputed, classifications have been revised to rely on analytical models, and eclipse timing variations have been computed for each system. We identify several classes of systems including those that exhibit tertiary eclipse events, systems that show clear evidence of additional bodies, heartbeat systems, systems with changing eclipse depths, and systems exhibiting only one eclipse event over the duration of the mission. We have updated the period and galactic latitude distribution diagrams and included a catalog completeness evaluation. The total number of identified eclipsing and ellipsoidal binary systems in the Kepler field of view has increased to 2878, 1.3% of all observed Kepler targets
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