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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}
| Spectral Classification of Stars in A Supplement to the Bright Star Catalogue
MK spectral types are given for about 584 stars in A Supplement to theBright Star Catalogue. These are compared with Hipparcos parallaxes tocheck the reliability of those classifications. The estimated errors are+/-1.2 subtypes, and 10% of the luminosity classes may be wrong.
| An Ultraviolet/Optical Atlas of Bright Galaxies
We present wide-field imagery and photometry of 43 selected nearbygalaxies of all morphological types at ultraviolet and opticalwavelengths. The ultraviolet (UV) images, in two broad bands at 1500 and2500 Å, were obtained using the Ultraviolet Imaging Telescope(UIT) during the Astro-1 Spacelab mission. The UV images have ~3"resolution, and the comparison sets of ground-based CCD images (in oneor more of B, V, R, and Hα) have pixel scales and fields of viewclosely matching the UV frames. The atlas consists of multiband imagesand plots of UV/optical surface brightness and color profiles. Otherassociated parameters, such as integrated photometry and half-lightradii, are tabulated. In an appendix, we discuss the sensitivity ofdifferent wavebands to a galaxy's star formation history in the form of``history weighting functions'' and emphasize the importance of UVobservations as probes of evolution during the past 10-1000 Myr. We findthat UV galaxy morphologies are usually significantly different fromvisible band morphologies as a consequence of spatially inhomogeneousstellar populations. Differences are quite pronounced for systems in themiddle range of Hubble types, Sa through Sc, but less so for ellipticalsor late-type disks. Normal ellipticals and large spiral bulges arefainter and more compact in the UV. However, they typically exhibitsmooth UV profiles with far-UV/optical color gradients which are largerthan any at optical/IR wavelengths. The far-UV light in these cases isprobably produced by extreme horizontal branch stars and theirdescendants in the dominant, low-mass, metal-rich population. The coolstars in the large bulges of Sa and Sb spirals fade in the UV while hotOB stars in their disks brighten, such that their Hubble classificationsbecome significantly later. In the far-UV, early-type spirals oftenappear as peculiar, ringlike systems. In some spiral disks, UV-brightstructures closely outline the spiral pattern; in others, the disks canbe much more fragmented and chaotic than at optical wavelengths.Contributions by bright active galactic nuclei (AGNs) to the integratedUV light in our sample range from less than 10% to nearly 100%. A numberof systems have unusual UV-bright structures in their inner disks,including rings, compact knots, and starburst nuclei, which could easilydominate the UV light in high-redshift analogs. A significant butvariable fraction of the far-UV light in spiral disks is diffuse ratherthan closely concentrated to star-forming regions. Dust in normal spiraldisks does not control UV morphologies, even in some highly inclineddisk systems. The heaviest extinction is apparently confined to thinlayers and the immediate vicinity of young H II complexes; the UV lightemerges from thicker star distributions, regions evacuated of dust byphotodestruction or winds, or by virtue of strong dust clumpiness. Onlyin cases where the dust layers are disturbed does dust appear to be amajor factor in UV morphology. The UV-bright plume of M82 indicates thatdust scattering of UV photons can be important in some cases. In acompanion paper, we discuss far-UV data from the Astro-2 mission andoptical comparisons for another 35 galaxies, emphasizing face-onspirals.
| Third preliminary catalogue of stars observed with the photoelectric astrolabe of the Beijing Astronomical Observatory.
Not Available
| U, V, W velocity components for the old disk using radial velocities of 1295 stars in the three cardinal Galactic directions
New radial velocities are presented for 1295 stars chosen at random nearthe three cardinal Galactic directions of l = 180 deg, b = 0; l = 90deg, b = 0 deg; and b = 90 deg, giving the distribution in U, V, and W,respectively, from the radial velocities alone. The measurements weremade with the coude spectrograph of the Mount Wilson 100 in. Hookerreflector. The purpose of the program is to set limits on the densitynormalization in the solar neighborhood of the old thin disk, the oldthick disk, and the halo. Many more high-velocity stars are present inthe unbiased sample than expected from previous estimates of thenormalization. The data suggest the density ratios in the solarneighborhood to be about 90 percent, 10 percent, and about 0.5 percentfor the thin disk, thick disk, and halo populations, respectively.
| Stars with large proper motions in the astrographic zones +32° and + 33° (List V)
Not Available
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | עגלון |
| התרוממות ימנית: | 05h45m29.60s |
| סירוב: | +31°19'29.4" |
| גודל גלוי: | 6.51 |
| מרחק: | 307.692 פארסק |
| תנועה נכונה: | 6.2 |
| תנועה נכונה: | -19.2 |
| B-T magnitude: | 7.941 |
| V-T magnitude: | 6.629 |
קטלוגים וכינוים:
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