Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
| The European Large-Area ISO Survey (ELAIS): the final band-merged catalogue
We present the final band-merged European Large-Area ISO Survey (ELAIS)Catalogue at 6.7, 15, 90 and 175 μm, and the associated data at U,g', r', i', Z, J, H, K and 20 cm. The origin of the survey, infrared andradio observations, data-reduction and optical identifications arebriefly reviewed, and a summary of the area covered and the completenesslimit for each infrared band is given. A detailed discussion of theband-merging and optical association strategy is given. The totalCatalogue consists of 3762 sources. 23 per cent of the 15-μm sourcesand 75 per cent of the 6.7-μm sources are stars. For extragalacticsources observed in three or more infrared bands, colour-colour diagramsare presented and discussed in terms of the contributing infraredpopulations. Spectral energy distributions (SEDs) are shown for selectedsources and compared with cirrus, M82 and Arp220 starburst, and activegalactic nuclei (AGN) dust torus models.Spectroscopic redshifts are tabulated, where available. For the N1 andN2 areas, the Isaac Newton Telescope ugriz Wide Field Survey permitsphotometric redshifts to be estimated for galaxies and quasars. Theseagree well with the spectroscopic redshifts, within the uncertainty ofthe photometric method [~10 per cent in (1 +z) for galaxies]. Theredshift distribution is given for selected ELAIS bands andcolour-redshift diagrams are discussed.There is a high proportion of ultraluminous infrared galaxies(log10 of 1-1000 μm luminosity Lir > 12.22)in the ELAIS Catalogue (14 per cent of 15-μm galaxies with known z),many with Arp220-like SEDs. 10 per cent of the 15-μm sources aregenuine optically blank fields to r'= 24: these must have very highinfrared-to-optical ratios and probably have z > 0.6, so arehigh-luminosity dusty starbursts or Type 2 AGN. Nine hyperluminousinfrared galaxies (Lir > 13.22) and nine extremely redobjects (EROs) (r-K > 6) are found in the survey. The latter areinterpreted as ultraluminous dusty infrared galaxies at z~ 1. The largenumbers of ultraluminous galaxies imply very strong evolution in thestar formation rate between z= 0 and 1. There is also a surprisinglylarge population of luminous (Lir > 11.5), cool(cirrus-type SEDs) galaxies, with Lir-Lopt > 0,implying AV > 1.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Wide field search for nearby faint stars
A project to search for nearby stars in a wide field using Schmidtplates is presented. A field intensively observed allowed us to select alist of nearby stars candidates. CCD astrometry of 20 of these, acquiredat the 1.23m telescope of Calar Alto is presented. Trigonometricparallaxes and proper motions have been determined. We confirm for sixof our targets that they are nearby stars with distances smaller than 40parsecs from the Sun (smaller than 20 parsecs for three of them) andwith relative errors smaller than 20 percent. One of these appears to bea bright (V = 15.8) large proper motions star (mu >0farcs4 ) notmentioned in the NLTT catalog and absent from CDS data base. Based onobservations made at Cerga Schmidt telescope, Tautenburg Schmidttelescope, Calar-Alto Schmidt telescope, Calar-Alto $1.23m$ telescopeand Telescope Bernard Lyot at Pic du Midi. Based on measurements made atMAMA automatic measuring machine
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Ercole |
| Ascensione retta: | 16h35m49.94s |
| Declinazione: | +40°53'17.2" |
| Magnitudine apparente: | 7.954 |
| Distanza: | 89.767 parsec |
| Moto proprio RA: | -23.6 |
| Moto proprio Dec: | -224.4 |
| B-T magnitude: | 9.212 |
| V-T magnitude: | 8.058 |
Cataloghi e designazioni:
|
INHABITED SKY
