Chemo-kinematics of the Milky Way from the SDSS-III MARVELS survey (original) (raw)
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Kinematics and chemical properties of the Galactic stellar populations
Astronomy & Astrophysics, 2013
Aims. We analyze chemical and kinematical properties of about 850 FGK solar neighborhood long-lived dwarfs observed with the HARPS high-resolution spectrograph. The stars in the sample have log g ≥ 4 dex, 5000 ≤ T eff ≤ 6500 K, and -1.39 ≤ [Fe/H] ≤ 0.55 dex. The aim of this study is to characterize and explore the kinematics and chemical properties of stellar populations of the Galaxy in order to understand their origins and evolution. Methods. We apply a purely chemical analysis approach based on the [α/Fe] vs. [Fe/H] plot to separate Galactic stellar populations into the thin disk, thick disk and high-α metal-rich (hαmr). Then, we explore the population's stellar orbital eccentricity distributions, their correlation with metallicity, and rotational velocity gradients with metallicity in the Galactic disks to provide constraints on the various formation models. Results. We identified a gap in the [α/Fe] -[Fe/H] plane for the α-enhanced stars, and by performing a bootstrapped Monte Carlo test we obtained a probability higher than 99.99% that this gap is not due to small-number statistics. Our analysis shows a negative gradient of the rotational velocity of the thin disk stars with [Fe/H] (-17 km s −1 dex −1 ), and a steep positive gradient for both the thick disk and hαmr stars with the same magnitude of about +42 km s −1 dex −1 . For the thin disk stars we observed no correlation between orbital eccentricities and metallicity, but observed a steep negative gradient for the thick disk and hαmr stars with practically the same magnitude (≈ -0.18 dex −1 ). The correlations observed for the nearby stars (on average 45 pc) using high-precision data in general agree well with the results obtained for the SDSS sample of stars located further from the Galactic plane. Conclusions. Our results suggest that radial migration played an important role in the formation and evolution of the thin disk. For the thick disk stars it is not possible to reach a firm conclusion about their origin. Based on the eccentricity distribution of the thick disk stars only their accretion origin can be ruled out, and the heating and migration scenario could explain the positive steep gradient of V φ with [Fe/H]. Analyzing the hαmr stellar population we found that they share properties of both the thin and thick disk population. A comparison of the properties of the hαmr stars with that of the subsample of stars from the N-body/SPH simulation using radial migration suggest that they may have originated from the inner Galaxy. Further detailed investigations would help to clarify their exact nature and origin.
Kinematics of stellar populations with RAVE data
New Astronomy, 2012
We study the kinematics of the Galactic thin and thick disk populations using stars from the RAVE survey's second data release together with distance estimates from Breddels et al. (2009). The velocity distribution exhibits the expected moving groups present in the solar neighborhood. We separate thick and thin disk stars by applying the X (stellar-population) criterion of Schuster et al. (1993), which takes into account both kinematic and metallicity information. For 1906 thin disk and 110 thick disk stars classified in this way, we find a vertical velocity dispersion, mean rotational velocity and mean orbital eccentricity of (σ W , V Φ , e) thin = (18±0.3 km s −1 , 223±0.4 km s −1 , 0.07±0.07) and (σ W , V Φ , e) thick = (35±2 km s −1 , 163±2 km s −1 , 0.31±0.16), respectively. From the radial Jeans equation, we derive a thick disk scale length in the range 1.5 − 2.2 kpc, whose greatest uncertainty lies in the adopted form of the underlying potential. The shape of the orbital eccentricity distribution indicates that the thick disk stars in our sample most likely formed in situ with minor gas-rich mergers and/or radial migration being the most likely cause for their orbits. We further obtain mean metal abundances of [M/H] thin = +0.03 ± 0.17, and [M/H] thick = −0.51 ± 0.23, in good agreement with previous estimates. We estimate a radial metallicity gradient in the thin disk of-0.07 dex kpc −1 , which is larger than predicted by chemical evolution models where the disk grows insideout from infalling gas. It is, however, consistent with models where significant migration of stars shapes the chemical signature of the disk, implying that radial migration might play at least part of a role in the thick disk's formation.
Galactic kinematics and dynamics from Radial Velocity Experiment stars
Monthly Notices of the Royal Astronomical Society, 2014
We analyse the kinematics of ∼400 000 stars that lie within ∼2 kpc of the Sun and have spectra measured in the Radial Velocity Experiment. We decompose the sample into hot and cold dwarfs, red-clump and non-clump giants. The kinematics of the clump giants are consistent with being identical with those of the giants as a whole. Without binning the data we fit Gaussian velocity ellipsoids to the meridional-plane components of velocity of each star class and give formulae from which the shape and orientation of the velocity ellipsoid can be determined at any location. The data are consistent with the giants and the cool dwarfs sharing the same velocity ellipsoids, which have vertical velocity dispersion rising from 21 km s −1 in the plane to ∼55 km s −1 at |z| = 2 kpc and radial velocity dispersion rising from 37 km s −1 to 82 km s −1 in the same interval. At (R, z), the longest axis of one of these velocity ellipsoids is inclined to the Galactic plane by an angle ∼0.8 arctan(z/R). We use a novel formula to obtain precise fits to the highly non-Gaussian distributions of v φ components in eight bins in the (R, z) plane. We compare the observed velocity distributions with the predictions of a published dynamical model fitted to the velocities of stars that lie within ∼150 pc of the Sun and star counts towards the Galactic pole. The predictions for the v z distributions are exceptionally successful. The model's predictions for v φ are successful except for the hot dwarfs, and its predictions for v r fail significantly only for giants that lie far from the plane. If distances to the model's stars are overestimated by 20 per cent, the predicted distributions of v r and v z components become skew, and far from the plane broader. The broadening significantly improves the fits to the data. The ability of the dynamical model to give such a good account of a large body of data to which it was not fitted inspires confidence in the fundamental correctness of the assumed, disc-dominated, gravitational potential.
Local Stellar Kinematics from RAVE Data: IV. Solar Neighbourhood Age–Metallicity Relation
Publications of the Astronomical Society of Australia, 2013
We investigated the age–metallicity relation using a sample of 5691 F- and G-type dwarfs from RAdial Velocity Experiment Data Release 3 (RAVE DR3) by applying several constraints. (i) We selected stars with surface gravities log g(cm s−2) ≥ 3.8 and effective temperatures in the 5310leTtextefftext(K)le73005310\le T_{\text{eff}}\text{(K)}\le 73005310leTtextefftext(K)le7300 range and obtained a dwarf sample. (ii) We plotted the dwarfs in metallicity sub-samples in the Ttextefftext−−(J−Ks)0T_{\text{eff}}\text{--}(J-K_s)_0Ttextefftext−−(J−K_s)_0 plane to compare with the corresponding data of González Hernández & Bonifacio (2009) and identified the ones in agreement. (iii) We fitted the reduced dwarf sample obtained from constraints (i) and (ii) to the Padova isochrones and re-identified those which occupy the plane defined by isochrones with ages t ≤ 13 Gyr. (iv) Finally, we omitted dwarfs with total velocity errors larger than 10.63 km s−1. We estimated the ages using the Bayesian procedure of Jørgensen & Lindegren (2005). The largest age–metallicity slope was found for early F...
Local stellar kinematics from RAVE data - II. Radial metallicity gradient
Monthly Notices of the Royal Astronomical Society, 2012
We investigate radial metallicity gradients for a sample of dwarf stars from the RAdial Velocity Experiment (RAVE) Data Release 3 (DR3). We select a total of approximately 17 000 F-type and G-type dwarfs, using a selection of colour, log g and uncertainty in the derived space motion, and calculate for each star a probabilistic (kinematic) population assignment to a thick or thin disc using space motion and additionally another (dynamical) assignment using stellar vertical orbital eccentricity. We additionally subsample by colour, to provide samples biased toward young thin-disc and older thin-disc stars. We derive a metallicity gradient as a function of Galactocentric radial distance, i.e. d[M/H]/dR m = −0.051 ± 0.005 dex kpc −1 , for the youngest sample, F-type stars with vertical orbital eccentricities e v ≤ 0.04. Samples biased toward older thin-disc stars show systematically shallower abundance gradients.
Galactic kinematics and dynamics from RAVE stars
We analyse the kinematics of ~400000 RAVE stars. We split the sample into hot and cold dwarfs, red-clump and non-clump giants. The kinematics of the clump giants are consistent with being identical with those of non-clump giants. We fit Gaussian velocity ellipsoids to the meridional-plane components of velocity of each star class and give formulae from which the shape and orientation of the velocity ellipsoid can be determined at any location. The data are consistent with the giants and the cool dwarfs sharing the same velocity ellipsoids; sigma_z rises from 21 kms in the plane to sim 55 kms at |z|=2 kpc, while sigma_r rises from 37 kms to 82 kms. At (R,z) the longest axis of one of these velocity ellipsoids is inclined to the Galactic plane by an angle ~0.8 arctan(z/R). We use a novel formula to obtain precise fits to the highly non-Gaussian distributions of v_phi components. We compare the observed velocity distributions with the predictions of a dynamical model fitted to the velo...
The Astronomical Journal, 2000
We present a revised catalog of 2106 Galactic stars, selected without kinematic bias and with available radial velocities, distance estimates, and metal abundances in the range [4.0 ¹ [Fe/H] ¹ 0.0. This update of the 1995 Beers & Sommer-Larsen catalog includes newly derived homogeneous photometric distance estimates, revised radial velocities for a number of stars with recently obtained high-resolution spectra, and reÐned metallicities for stars originally identiÐed in the HK objective-prism survey (which account for nearly half of the catalog) based on a recent recalibration. A subset of 1258 stars in this catalog have available proper motions based on measurements obtained with the Hipparcos astrometry satellite or taken from the updated Astrographic Catalogue (second epoch positions from either the Hubble Space T elescope Guide Star Catalog or the T ycho Catalogue), the Yale/San Juan Southern Proper Motion Catalog 2.0, and the Lick Northern Proper Motion Catalog. Our present catalog includes 388 RR Lyrae variables (182 of which are newly added), 38 variables of other types, and 1680 nonvariables, with distances in the range 0.1 to 40 kpc.
The relation between chemical abundances and kinematics of the Galactic disc with RAVE
Astronomy & Astrophysics, 2013
Aims. We study the relations between stellar kinematics and chemical abundances of a large sample of RAVE giants in search of the selection criteria needed for disentangling different Galactic stellar populations, such as thin disc, thick disc and halo. A direct comparison between the chemo-kinematic relations obtained with our medium spectroscopic resolution data and those obtained from a high-resolution sample is carried out with the aim of testing the robustness of the RAVE data. Methods. We selected a sample of 2167 giant stars with signal-to-noise per spectral measurements above 75 from the RAVE chemical catalogue and followed the analysis performed by Gratton and colleagues on 150 subdwarf stars spectroscopically observed at high resolution. We then used 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. We successfully identified three stellar populations that could be associated with the Galactic thin disc, a dissipative component composed mostly of thick-disc stars, as well as a component comprised of halo stars (presence of debris stars cannot be excluded). 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) that 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.
Kinematic parameters of young subsystems and the galactic rotation curve
Astronomy Letters, 2002
We analyze the space velocities of blue supergiants, long-period Cepheids, and young open star clusters (OSCs), as well as the H I and H II radial-velocity fields by the maximum-likelihood method. The distance scales of the objects are matched both by comparing the first derivatives of the angular velocity Ω determined separately from radial velocities and proper motions and by the statistical-parallax method. The former method yields a short distance scale (for R 0 = 7.5 kpc, the assumed distances should be increased by 4%), whereas the latter method yields a long distance scale (for R 0 = 8.5 kpc, the assumed distances should be increased by 16%). We cannot choose between these two methods. Similarly, the distance scale of blue supergiants should be shortened by 9% and lengthened by 3%, respectively. The H II distance scale is matched with the distance scale of Cepheids and OSCs by comparing the derivatives Ω determined for H II from radial velocities and for Cepheids and OSCs from space velocities. As a result, the distances to H II regions should be increased by 5% in the short distance scale. We constructed the Galactic rotation curve in the Galactocentric distance range 2-14 kpc from the radial velocities of all objects with allowance for the difference between the residual-velocity distributions. The axial ratio of the Cepheid+OSC velocity ellipsoid is well described by the Lindblad relation, while σ u ≈ σ ν for gas. The following rotation-curve parameters were obtained: Ω 0 = (27.5 ± 1.4) km s −1 kpc −1 and A = (17.1 ± 0.5) km s −1 kpc −1 for the short distance scale (R 0 = 7.5 kpc); and Ω 0 = (26.6 ± 1.4) km s −1 kpc −1 and A = (15.4 ± 0.5) km s −1 kpc −1 for the long distance scale (R 0 = 8.5 kpc). We propose a new method for determining the angular velocity Ω 0 from stellar radial velocities alone by using the Lindblad relation. Good agreement between the inferred Ω 0 and our calculations based on space velocities suggests that the Lindblad relation holds throughout the entire sample volume. Our analysis of the heliocentric velocities for samples of young objects reveals noticeable streaming motions (with a velocity lag of ∼7 km s −1 relative to the LSR), whereas a direct computation of the perturbation amplitudes in terms of the linear density-wave theory yields a small amplitude for the tangential perturbations.
Basic physical parameters of a selected sample of evolved stars
Astronomy & Astrophysics, 2006
We present the detailed spectroscopic analysis of 72 evolved stars, which were previously studied for accurate radial velocity variations. Using one Hyades giant and another well studied star as the reference abundance, we determine the [Fe/H] for the whole sample. These metallicities, together with the T eff values and the absolute V-band magnitude derived from Hipparcos parallaxes, are used to estimate basic stellar parameters (ages, masses, radii, (B−V) 0 and log g) using theoretical isochrones and a Bayesian estimation method. The (B−V) 0 values so estimated turn out to be in excellent agreement (to within ∼ 0.05 mag) with the observed (B−V), confirming the reliability of the T eff -(B−V) 0 relation used in the isochrones. On the other hand, the estimated log g values are typically 0.2 dex lower than those derived from spectroscopy; this effect has a negligible impact on [Fe/H] determinations. The estimated diameters θ have been compared with limb darkening-corrected ones measured with independent methods, finding an agreement better than 0.3 mas within the 1 < θ < 10 mas interval (or, alternatively, finding mean differences of just 6 %). We derive the age-metallicity relation for the solar neighborhood; for the first time to our knowledge, such a relation has been derived from observations of field giants rather than from open clusters and field dwarfs and subdwarfs. The age-metallicity relation is characterized by close-to-solar metallicities for stars younger than ∼ 4 Gyr, and by a large [Fe/H] spread with a trend towards lower metallicities for higher ages. In disagreement with other studies, we find that the [Fe/H] dispersion of young stars (less than 1 Gyr) is comparable to the observational errors, indicating that stars in the solar neighbourhood are formed from interstellar matter of quite homogeneous chemical composition. The three giants of our sample which have been proposed to host planets are not metal rich; this result is at odds with those for main sequence stars. However, two of these stars have masses much larger than a solar mass so we may be sampling a different stellar population from most radial velocity searches for extrasolar planets. We also confirm the previous indication that the radial velocity variability tends to increase along the RGB, and in particular with the stellar radius. 2 L. da Silva et al.: Basic physical parameters of Giant stars