Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
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}
| Detection of double stars with the use of Kyiv database of lunar occultations
On the basis of 40-year series of observations of occultations of starsby the Moon from the Kyiv database, we found 83 stars which are likelyto be double ones. Additional components close to basic stars arerevealed for four known wide pair.
| Surface inhomogeneities and line variability on DF Tau
We have mapped surface inhomogeneities on the classical T Tauri star DFTau, using the Lii doublet at 670.8 nm, the Cai lines at 612.2 nm and643.9 nm and a calcium and iron blend at 646.3 nm. We find compellingevidence that there are hotspots with temperatures of more than 5000 K.Two of the hotspots produce line-profile deformations that can be tracedas they move through the cross-correlated profiles. When one of thehotspots crosses the stellar disc, redshifted absorption componentsappear in the Na D lines. As these redshifted absorption features areusually tracers for mass-infall we interpret this hotspot as anaccretion shock close to the stellar surface. Parts of the surface of DFTau are covered with a hot chromosphere that is visible in the Caiiinfrared triplet lines and the narrow component of Hei. We find nocorrelation between the veiling and the lines that originate from thehot chromosphere, suggesting that the veiling and the chromosphericemission are produced in physically distinct regions.
| Library of high-resolution UES echelle spectra of F, G, K and M field dwarf stars
We present a library of Utrecht echelle spectrograph (UES) observationsof a sample of F, G, K and M field dwarf stars covering the spectralrange from 4800 \ Angstroms to 10600 \ Angstroms with a resolution of55000. These spectra include some of the spectral lines most widely usedas optical and near-infrared indicators of chromospheric activity suchas Hβ , Mg i b triplet, Na i D1, D2, He iD3, Hα , and Ca ii IRT lines, as well as a large numberof photospheric lines which can also be affected by chromosphericactivity. The spectra have been compiled with the aim of providing a setof standards observed at high-resolution to be used in the applicationof the spectral subtraction technique to obtain the active-chromospherecontribution to these lines in chromospherically active single andbinary stars. This library can also be used for spectral classificationpurposes. A digital version with all the spectra is available via ftpand the World Wide Web (WWW) in both ASCII and FITS formats. Based onobservations made with the William Herschel Telescope operated on theisland of La Palma by the Isaac Newton Group at the Spanish Observatoriodel Roque de Los Muchachos of the Instituto de Astrof\'{\i
| UBV photometry of stars whose positions are accurately known.
Photometric indices V, B-V, and U-B were measured for about 560 stars ofthe AGK3R and NPZT catalogs between BD declinations 11 deg and 23 deg,using the 40-cm Cassegrain telescope of the Kvistaberg Observatory fromApril 1986 to May 1987. The observation procedure and the reductiontechnique were the same as in the earlier papers of this series by Oja(1984, 1985, 1986, and 1987). The mean errors were calculated from theinternal consistency of the data. The accuracy was found to be the sameas for the earlier parts of the survey.
| Photoelectric observations of lunar occultations. XV
The last (or possibly penultimate) paper in a series on lunaroccultations presents observations of 404 phenomena, preceded by somegeneral remarks of a retrospective nature. The series of observationsbegan in 1968. Data for 20 doubles or suspected doubles are presented,ranked in order of certainty, with designation 3 representing thesurest. Thirteen of the cases refer to stars not previously noted asdoubles. Seven determinations of angular diameters are presented, ofwhich three have been previously observed.
| On the homogeneity of the spectral-energy distribution among giant E and SO galaxies and other results.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75...21L&db_key=AST
| Spectral and Luminosity Classification of the Bright Sequence Stars in the C Regions.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1955ApJ...121...32N&db_key=AST
| The Transfer of the North Polar Standards to the Southern Hemisphere.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1953ApJ...117...83C&db_key=AST
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Ован |
| Ректацензија: | 03h03m33.32s |
| Deклинација: | +14°28'14.6" |
| Apparent магнитуда: | 7.885 |
| Даљина: | 149.925 parsecs |
| Proper motion RA: | -22.8 |
| Proper motion Dec: | -34.7 |
| B-T magnitude: | 9.212 |
| V-T magnitude: | 7.995 |
Каталог и designations:
|
