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The outskirts of Cygnus OB2
Context: Cygnus OB2 is one of the richest OB associations in the localGalaxy, and is located in a vast complex containing several otherassociations, clusters, molecular clouds, and HII regions. However, thestellar content of Cygnus OB2 and its surroundings remains rather poorlyknown largely due to the considerable reddening in its direction atvisible wavelength. Aims: We investigate the possible existence of anextended halo of early-type stars around Cygnus OB2, which is hinted atby near-infrared color-color diagrams, and its relationship to CygnusOB2 itself, as well as to the nearby association Cygnus OB9 and to thestar forming regions in the Cygnus X North complex. Methods: Candidateselection is made with photometry in the 2MASS all-sky point sourcecatalog. The early-type nature of the selected candidates is confirmedor discarded through our infrared spectroscopy at low resolution. Inaddition, spectral classifications in the visible are presented for manylightly-reddened stars. Results: A total of 96 early-type stars areidentified in the targeted region, which amounts to nearly half of theobserved sample. Most of them have featureless near-infrared spectra asexpected from OB stars at the available resolution. Another 18 starsthat display Brackett emission lines can be divided between evolvedmassive stars (most likely Be stars) and Herbig Ae/Be stars based ontheir infrared excesses. A component associated with Cygnus OB9/NGC 6910is clearly identified, as well as an enhancement in the surface densityof early-type stars at Cygnus X North. We also find a field population,consisting largely of early B giants and supergiants, which is probablythe same as identified in recent studies of the inner 1° circlearound Cygnus OB2. The age and large extension of this populationdiscards a direct relationship with Cygnus OB2 or any other particularassociation. Conclusions: Earlier claims of the possible large extentof Cygnus OB2 beyond its central, very massive aggregate seem to bedismissed by our findings. The existence of a nearly ubiquitouspopulation of evolved stars with massive precursors suggests a massivestar formation history in Cygnus having started long before theformation of the currently observed OB associations in the region.Based on observations collected at the Centro AstronómicoHispano-Alemán (CAHA) at Calar Alto, operated jointly by theMax-Planck Institut für Astronomie and the Instituto deAstrofísica de Andalucía (CSIC).Tables 1-9 are only available in electronic form at http://www.aanda.org
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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}
| Classification of Population II Stars in the Vilnius Photometric System. II. Results
The results of photometric classification of 848 true and suspectedPopulation II stars, some of which were found to belong to Population I,are presented. The stars were classified using a new calibrationdescribed in Paper I (Bartkevicius & Lazauskaite 1996). We combinethese results with our results from Paper I and discuss in greaterdetail the following groups of stars: UU Herculis-type stars and otherhigh-galactic-latitude supergiants, field red horizontal-branch stars,metal-deficient visual binaries, metal-deficient subgiants, stars fromthe Catalogue of Metal-deficient F--M Stars Classified Photometrically(MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs(Bartkevicius 1994a). It is confirmed that high galactic latitudesupergiants from the Bartaya (1979) catalog are giants or even dwarfs.Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as fieldRHB stars, appear to be ordinary giants according to our classification.Some of the visual binaries studied can be considered as physical pairs.Quite a large fraction of stars from the MDPH catalog are found to havesolar metallicity. A number of new possible UU Herculis-type stars, RHBstars and metal-deficient subgiants are identified.
| First radial velocities for 146 bright F- and G-type stars
We have obtained an average of 5.7 radial velocities for 146 northernstars of types F and G (all luminosity classes) listed in 'A Supplementto the Bright Star Catalogue' as having no previously known radialvelocity measures. Those were obtained with charge coupled devices(CCDs) and a cross-correlation technique; the intrinsic velocityaccuracy, based on stars of apparently constant velocity, is probablyless than +/- 0.3 km/s per mean. Of those stars 14% are newly discoveredSB2 stars. The prevelance of rapid profile variations (in minutes orhours) in most of the broad-lined F-type stars makes it difficult toobtain accurate measures for them.
| Interstellar extinction in the vicinity of the North America and Pelican Nebulae. II
The results of photoelectric photometry of 564 stars in the Vilniusseven-color system in three areas near the North America and PelicanNebulae are given. Photometric spectral types, absolute magnitudes,color excesses, interstellar extinction,s and distances to the stars aredetermined. We find that the dark cloud separating both nebulae is at580 pc distance. A number of stars immersed in the dark cloud have beenfound. It seems that the dark cloud extends south down to 40 degdeclination. The area southwest of alpha Cygni in the declination zones42 deg and 43 deg is comparatively transparent at least up to 1 kpc.
| Possible young stellar objects in the region of the Cygnus OB2 (VI Cygni) association from IRAS observations
Several massive young stellar objects are found from an analysis of the12- to 100-micron flux data of IRAS sources in the region of the Cyg OB2association. Sixty-four sources with positive spectral indices andsteeply increasing FIR flux distribution similar to that found in knownyoung stellar objects are identified. Some of these sources have massivecold dust shells with FIR luminosities of the order of 1000 to 10,000solar luminosities and are most likely massive young stellar objectswhich may show bipolar structure and molecular outflows. The luminosityfunction for the IRAS sources in the Cyg OB2 suggests that most of thesources with positive spectral indices are most likely members of theCyg OB2 association. It is suggested that there may be a few hundredlow-mass young stellar objects in the Cyg OB2 association.
| Third preliminary catalogue of stars observed with the photoelectric astrolabe of the Beijing Astronomical Observatory.
Not Available
| VI photometry of selected SAO stars
Johnson V- and I-band photoelectric photometry has been obtained for 158SAO stars in a continuing program in support of the Near InfraredPhotographic Sky Survey. These data are utilized in the calibration ofthe survey photographs and are presented here to assist other programsreliant upon access to photometry in the photographic infrared.
| Kinematical data of two samples of late-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...27..267G&db_key=AST
| Narrow-band photometry of late-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&AS....1..199H&db_key=AST
| KURZE MITTEILUNG. Zur Expansion der Assoziation Cep III
Not Available
| Spectral Classification of Stars Noted on Case Objective Prism Plates. II
Not Available
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Membre dels grups següents:
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Dades d'Observació i Astrometria
| Constel·lació: | Cygnus |
| Ascensió Recta: | 20h35m18.02s |
| Declinació: | +41°53'24.6" |
| Magnitud Aparent: | 6.631 |
| Distancia: | 180.832 parsecs |
| Moviment propi RA: | 4.1 |
| Moviment propi Dec: | 19.4 |
| B-T magnitude: | 7.833 |
| V-T magnitude: | 6.731 |
Catàlegs i designacions:
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