Context. Open clusters are ideal test particles for studying the chemical evolution of the Galactic disc. However, the number and accuracy of existing high-resolution abundance determinations, not ...only of Fe/H, but also of other key elements, remains largely insufficient. Aims. We attempt to increase the number of Galactic open clusters that have high quality abundance determinations, and to gather all the literature determinations published so far. Methods. Using high-resolution (R ~ 30 000), high-quality (S/N ≥ 60 per pixel), we obtained spectra for twelve stars in four open clusters with the fibre spectrograph FOCES, at the 2.2 Calar Alto Telescope in Spain. We employ a classical equivalent-width analysis to obtain accurate abundances of sixteen elements: Al, Ba, Ca, Co, Cr, Fe, La, Mg, Na, Nd, Ni, Sc, Si, Ti, V, and Y. We derived oxygen abundances by means of spectral synthesis of the 6300 Å forbidden line. Results. We provide the first determination of abundance ratios other than Fe for NGC 752 giants, and ratios in agreement with the literature for the Hyades, Praesepe, and Be 32. We use a compilation of literature data to study Galactic trends of Fe/H and α/Fe with Galactocentric radius, age, and height above the Galactic plane. We find no significant trends, but some indication for a flattening of Fe/H at large Rgc, and for younger ages in the inner disc. We also detect a possible decrease in Fe/H with |z| in the outer disc, and a weak increase in α/Fe with Rgc.
Context. Open clusters are convenient probes of the structure and history of the Galactic disk. They are also fundamental to stellar evolution studies. The second Gaia data release contains precise ...astrometry at the submilliarcsecond level and homogeneous photometry at the mmag level, that can be used to characterise a large number of clusters over the entire sky. Aims. In this study we aim to establish a list of members and derive mean parameters, in particular distances, for as many clusters as possible, making use of Gaia data alone. Methods. We compiled a list of thousands of known or putative clusters from the literature. We then applied an unsupervised membership assignment code, UPMASK, to the Gaia DR2 data contained within the fields of those clusters. Results. We obtained a list of members and cluster parameters for 1229 clusters. As expected, the youngest clusters are seen to be tightly distributed near the Galactic plane and to trace the spiral arms of the Milky Way, while older objects are more uniformly distributed, deviate further from the plane, and tend to be located at larger Galactocentric distances. Thanks to the quality of Gaia DR2 astrometry, the fully homogeneous parameters derived in this study are the most precise to date. Furthermore, we report on the serendipitous discovery of 60 new open clusters in the fields analysed during this study.
Context. The Gaia Second Data Release provides precise astrometry and photometry for more than 1.3 billion sources. This catalog opens a new era concerning the characterization of open clusters and ...test stellar models, paving the way for better understanding of the disk properties. Aims. The aim of the paper is to improve the knowledge of cluster parameters, using only the unprecedented quality of the Gaia photometry and astrometry. Methods. We have made use of the membership determination based on the precise Gaia astrometry and photometry. We applied an automated Bayesian tool, BASE-9, to fit stellar isochrones on the observed G, GBP, GRP magnitudes of the high probability member stars. Results. We derive parameters such as age, distance modulus, and extinction for a sample of 269 open clusters, selecting only low reddening objects and discarding very young clusters, for which techniques other than isochrone-fitting are more suitable for estimating ages.
A wealth of tiny galactic systems populates the surroundings of the Milky Way. However, some of these objects might have originated as former satellites of the Magellanic Clouds, in particular of the ...Large Magellanic Cloud (LMC). Examples of the importance of understanding how many systems are genuine satellites of the Milky Way or the LMC are the implications that the number and luminosity-mass function of satellites around hosts of different mass have for dark matter theories and the treatment of baryonic physics in simulations of structure formation. Here we aim at deriving the bulk motions and estimates of the internal velocity dispersion and metallicity properties in four recently discovered distant southern dwarf galaxy candidates, Columba I, Reticulum III, Phoenix II, and Horologium II. We combined Gaia DR2 astrometric measurements, photometry, and new FLAMES/GIRAFFE intermediate-resolution spectroscopic data in the region of the near-IR Ca II triplet lines; this combination is essential for finding potential member stars in these low-luminosity systems. We find very likely member stars in all four satellites and are able to determine (or place limits on) the bulk motions and average internal properties of the systems. The systems are found to be very metal poor, in agreement with dwarf galaxies and dwarf galaxy candidates of similar luminosity. Of these four objects, we can only firmly place Phoenix II in the category of dwarf galaxies because of its resolved high velocity dispersion ( 9.5 −4.4+6.8 km s−1 9.5 −4.4 +6.8 km s −1 $ 9.5_{-4.4}^{+6.8}\, {\rm {km\,s}}^{-1} $ ) and intrinsic metallicity spread (0.33 dex). For Columba I we also measure a clear metallicity spread. The orbital pole of Phoenix II is well constrained and close to that of the LMC, suggesting a prior association. The uncertainty on the orbital poles of the other systems is currently very large, so that an association cannot be excluded, except for Columba I. Using the numbers of potential former satellites of the LMC identified here and in the literature, we obtain for the LMC a dark matter mass of M200 = 1.9 −0.9+1.3 × 1011 M⊙ M 200 = 1.9 −0.9 +1.3 × 10 11 M ⊙ $ M_{200}=1.9_{-0.9}^{+1.3}\times10^{11}\, M_{\odot} $ .
•We proposed an approach for determination of effective properties of porous materials.•The approach is based on the generalized differential effective medium method.•The pores are modeled as ...inclusions of two types: spheroidal and cylindrical.•The relative concentrations of inclusions depend on the total porosity of the material.•Our model describes well the experimental data for different physical properties.
In this paper we propose an approach for calculating the effective physical properties of porous materials (for example, sedimentary rocks) which is based on the unified structure of the pore space. This approach is based on the Generalized Differential Effective Medium (GDEM) method. This method generalizes the classical differential scheme (DEM) for the case of many types of inclusions. The physical properties of a composite calculated using the GDEM depend on how the solution is constructed.
A porous medium is represented by the elastic weakly conductive matrix with embedded inclusions of two types (spheroidal and cylindrical), saturated with a conductive liquid. The cylindrical inclusions appear in the system when the porosity value exceeds the void percolation. Parameters, that characterize the inclusions (the aspect ratio of spheroidal inclusions and the relative part of cylindrical inclusions), are determined in the inverse problem solving process for the experimental data approximation of the effective conductivity as a porosity function. These parameters, obtained by solving the inverse problem, were used to calculate the effective elastic moduli, electrical conductivity, and dielectric permittivity of porous media. The results obtained describe well the available experimental data for different effective physical properties.
Context. The present number of Galactic open clusters that have high resolution abundance determinations, not only of Fe/H, but also of other key elements, is largely insufficient to enable a clear ...modeling of the Galactic disk chemical evolution. Aims. To increase the number of Galactic open clusters with high quality measurements. Methods. We obtained high resolution (R ~ 30 000), high quality (S/N ~ 50–100 per pixel), echelle spectra with the fiber spectrograph FOCES, at Calar Alto, Spain, for three red clump stars in each of five Open Clusters. We used the classical equivalent width analysis method to obtain accurate abundances of sixteen elements: Al, Ba, Ca, Co, Cr, Fe, La, Mg, Na, Nd, Ni, Sc, Si, Ti, V, and Y. We also derived the oxygen abundance using spectral synthesis of the 6300 Å forbidden line. Results. Three of the clusters were never studied previously with high resolution spectroscopy: we found Fe/H = +0.03±0.02 (±0.10) dex for Cr 110; Fe/H = +0.01±0.05 (±0.10) dex for NGC 2099 (M 37), and Fe/H = -0.05±0.03 (±0.10) dex for NGC 2420. This last finding is higher than typical literature estimates by 0.2–0.3 dex approximately and in closer agreement with Galactic trends. For the remaining clusters, we find that Fe/H = +0.05±0.02 (±0.10) dex for M 67 and Fe/H = +0.04±0.07 (±0.10) dex for NGC 7789. Accurate (to ~0.5 km s-1) radial velocities were measured for all targets, and we provide the first velocity estimate derived from high resolution data for Cr 110, $\langle V_{\rm r}\rangle$ = 41.0±3.8 km s-1. Conclusions. With our analysis of the new clusters Cr 110, NGC 2099, and NGC 2420, we increase the sample of clusters with high-resolution-based abundances by 5%. All our program stars show abundance patterns which are typical of open clusters, very close to solar with few exceptions. This is true for all the iron-peak and s-process elements considered, and no significant α-enhancement is found. No significant (anti-)correlations for Na, Al, Mg, and O abundances are found. If anticorrelations are present, the involved spreads must be <0.2 dex. We then compile high resolution data of 57 OC from the literature and find a gradient of Fe/H with Galactocentric radius of –0.06±0.02 dex kpc-1, in agreement with past work and with results for Cepheids and B stars in the same range. A change of slope is seen outside RGC = 12 kpc and α/Fe shows a tendency to increase with RGC. We also confirm the absence of a significant age-metallicity relation, finding slopes of –2.6±1.1 $\times$ 10-11 dex Gyr-1 and 1.1±5.0 $\times$ 10-11 dex Gyr-1 for Fe/H and α/Fe respectively.
Propagation of elastic waves in porous fluid-saturated formations is often accompanied by electromagnetic radiation (seismoelectric effect), which has an electrokinetic nature. The magnitude of the ...generated electric current depends on the velocity of the relative flow between solid grains and a liquid in the primary pores. When the elastic wave is scattered by an inclusion, an additional liquid flow is generated. This flow induces a supplemental electromagnetic field.
In this work, we have calculated an additional electric field generated by the scattering of an elastic wave on the vug (spherical cavity) located in an electrolyte-saturated poroelastic rock. The solution of the corresponding electrokinetic equations was obtained in the quasi-static approach. We have considered the problem for “open” and “closed” interfaces between the porous matrix and the vug. The solution was obtained for conducting and non-conducting fluids in the vug. The dependences of the magnitude of the generated electric field on the frequency and the rock parameters are presented.
The results obtained demonstrate that the magnitude of the generated electric field depends considerably on the parameters of the rock (porosity and hydrodynamic permeability), as well as on the parameters of the fluid inside the inclusion (electric conductivity and bulk modulus). The calculations show that for an open interface the amplitude of the generated electric field is larger by more than an order of magnitude than for a closed interface. This is because the amplitude of the filtration flow near the vug surface is larger.
•We considered the problem of scattering of an acoustic wave by a spherical cavity (vug).•We studied the problem of generation of electromagnetic wave by an acoustic wave.•The solution of this problem was obtained by a quasi-static approach.•The electromagnetic field amplitude depends on the porosity of the matrix
Open cluster kinematics with Gaia DR2 Soubiran, C.; Cantat-Gaudin, T.; Romero-Gómez, M. ...
Astronomy & astrophysics,
11/2018, Letnik:
619
Journal Article
Recenzirano
Odprti dostop
Context. Open clusters are very good tracers of the evolution of the Galactic disc. Thanks to Gaia, their kinematics can be investigated with an unprecedented precision and accuracy. Aims. The ...distribution of open clusters in the 6D phase space is revisited with Gaia DR2. Methods. The weighted mean radial velocity of open clusters was determined, using the most probable members available from a previous astrometric investigation that also provided mean parallaxes and proper motions. Those parameters, all derived from Gaia DR2 only, were combined to provide the 6D phase-space information of 861 clusters. The velocity distribution of nearby clusters was investigated, as well as the spatial and velocity distributions of the whole sample as a function of age. A high-quality subsample was used to investigate some possible pairs and groups of clusters sharing the same Galactic position and velocity. Results. For the high-quality sample of 406 clusters, the median uncertainty of the weighted mean radial velocity is 0.5 km s−1. The accuracy, assessed by comparison to ground-based high-resolution spectroscopy, is better than 1 km s−1. Open clusters nicely follow the velocity distribution of field stars in the close solar neighbourhood as previously revealed by Gaia DR2. As expected, the vertical distribution of young clusters is very flat, but the novelty is the high precision to which this can be seen. The dispersion of vertical velocities of young clusters is at the level of 5 km s−1. Clusters older than 1 Gyr span distances to the Galactic plane of up to 1 kpc with a vertical velocity dispersion of 14 km s−1, typical of the thin disc. Five pairs of clusters and one group with five members might be physically related. Other binary candidates that have been identified previously are found to be chance alignments.
Context.
Open clusters (OCs) trace the evolution of the Galactic disc with great accuracy.
Gaia
and large ground-based spectroscopic surveys make it possible to determine their properties and study ...their kinematics with unprecedented precision.
Aims.
We study the kinematical behaviour of the OC population over time. We take advantage of the latest age determinations of OCs to investigate the correlations of the 6D phase-space coordinates and orbital properties with age. The phase-space distribution, age-velocity relation, and action distribution are compared to those of field stars. We also investigate the rotation curve of the Milky Way traced by OCs, and we compare it to that of other observational or theoretical studies.
Methods.
We gathered nearly 30 000 radial velocity (RV) measurements of OC members from both
Gaia
-RVS data and ground-based surveys and catalogues. We computed the weighted mean RV, Galactic velocities, and orbital parameters of 1382 OCs. We investigated their distributions as a function of age and by comparison to field stars.
Results.
We provide the largest RV catalogue available for OCs, half of it based on at least three members. Compared to field stars, we note that OCs are not on exactly the same arches in the radial-azimuthal velocity plane, while they seem to follow the same diagonal ridges in the Galactic radial distribution of azimuthal velocities. Velocity ellipsoids in different age bins all show a clear anisotropy. The heating rate of the OC population is similar to that of field stars for the radial and azimuthal components, but it is significantly lower for the vertical component. The rotation curve drawn by our sample of clusters shows several dips that match the wiggles derived from nonaxisymmetric models of the Galaxy. From the computation of orbits, we obtain a clear dependence of the maximum height and eccentricity on age. Finally, the orbital characteristics of the sample of clusters as shown by the action variables follow the distribution of field stars. The additional age information of the clusters indicates some (weak) age dependence of the known moving groups.
We extend our previous calibration of the infrared Ca ii triplet (CaT) as a metallicity indicator to the metal-poor regime by including observations of 55 field stars with Fe/H down to −4.0 dex. ...While we previously solved the saturation at high metallicity using a combination of a Lorentzian and a Gaussian to reproduce the line profiles, in this paper we address the non-linearity at low metallicity following the suggestion of Starkenburg et al. of adding two non-linear terms to the relation among the Fe/H, luminosity and strength of the calcium triplet lines. Our calibration thus extends from −4.0 to +0.5 in metallicity and is presented using four different luminosity indicators: V − V
HB, M
V
, M
I
and M
K
. The calibration obtained in this paper results in a tight correlation between Fe/H abundances measured from high-resolution spectra and Fe/H values derived from the CaT, over the whole metallicity range covered.
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