Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
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}
| Chromospheric Ca II Emission in Nearby F, G, K, and M Stars
We present chromospheric Ca II H and K activity measurements, rotationperiods, and ages for ~1200 F, G, K, and M type main-sequence stars from~18,000 archival spectra taken at Keck and Lick Observatories as a partof the California and Carnegie Planet Search Project. We have calibratedour chromospheric S-values against the Mount Wilson chromosphericactivity data. From these measurements we have calculated medianactivity levels and derived R'HK, stellar ages,and rotation periods from general parameterizations for 1228 stars,~1000 of which have no previously published S-values. We also presentprecise time series of activity measurements for these stars.Based on observations obtained at Lick Observatory, which is operated bythe University of California, and on observations obtained at the W. M.Keck Observatory, which is operated jointly by the University ofCalifornia and the California Institute of Technology. The KeckObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| 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.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| The luminosity function at the end of the main sequence: Results of a deep, large-area, CCD survey for cool dwarfs
The luminosity function at the end of the main sequence is determinedfrom V, R, and I data taken by the charge coupled devices (CCD)/TransitInstrument, a dedicated telescope surveying an 8.25 min wide strip ofsky centered at delta = +28 deg, thus sampling Galactic latitudes of +90deg down to -35 deg. A selection of 133 objects chosen via R - I and V -I colors has been observed spectroscopically at the 4.5 m MultipleMirror Telescope to assess contributions by giants and subdwarfs and toverify that the reddest targets are objects of extremely late spectralclass. Eighteen dwarfs of type M6 or later have been discovered, withthe latest being of type M8.5. Data used for the determination of theluminosity function cover 27.3 sq. deg down to a completeness limit of R= 19.0. This luminosity function, computed at V, I, and bolometricmagnitudes, shows an increase at the lowest luminosities, correspondingto spectral types later than M6- an effect suggested in earlier work byReid & Gilmore and Legget & Hawkins. When the luminosityfunction is segregated into north Galactic and south Galactic portions,it is found that the upturn at faint magnitudes exists only in thesouthern sample. In fact, no dwarfs with MI is greater thanor equal to 12.0 are found within the limiting volume of the 19.4 sq degnorthern sample, in stark contrast to the smaller 7.9 sq deg area atsoutherly latitudes where seven such dwarfs are found. This fact,combined with the fact that the Sun is located approximately 10-40 pcnorth of the midplane, suggests that the latest dwarfs are part of ayoung population with a scale height much smaller than the 350 pc valuegenerally adopted for other M dwarfs. These objects comprise a youngpopulation either because the lower metallicities prevelant at earlierepochs inhibited the formation of late M dwarfs or because the oldercounterparts of this population have cooled beyond current detectionlimits. The latter scenario would hold if these late-type M dwarfs aresubstellar. The luminosity function data together with an empiricalderivation of the mass-luminosity relation (from Henry & McCarthy)are used to compute a mass function independent of theory. This massfunction increases toward the end of the main sequence, but the observeddensity of M dwarfs is still insufficient to account for the missingmass. If the increases seen in the luminosity and mass functions areindicative of a large, unseen, substellar population, brown dwarfs mayyet add significantly to the mass of the Galaxy.
| Photoelectric UBV photometry in four areas of intermediate-high galactic latitude
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973A&AS....9..163A&db_key=AST
| Photoelectric photometry of selected AG stars in the 25D to 30D zone.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..187B&db_key=AST
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Kucuk Aslan |
| Sað Açýklýk: | 10h34m50.02s |
| Yükselim: | +27°57'41.7" |
| Görünürdeki Parlaklýk: | 6.817 |
| Uzaklýk: | 62.15 parsek |
| özdevim Sað Açýklýk: | 152.2 |
| özdevim Yükselim: | -86.4 |
| B-T magnitude: | 8.169 |
| V-T magnitude: | 6.929 |
Kataloglar ve belirtme:
|
INHABITED SKY
