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Open clusters in the Third Galactic Quadrant III. Alleged binary clusters
Aims: We aim to determine accurate distances and ages of eightopen clusters in order to: (1) assess their possible binarity (2)provide probes to trace the structure of the Third Galactic Quadrant. Methods: Cluster reddenings, distances, ages and metallicitiesare derived from ZAMS and isochrone fits in UBVRI photometric diagrams.Field contamination is reduced by restricting analysis to stars withinthe cluster limits derived from star counts. Further membership controlis done by requiring that stars have consistent positions in severaldiagrams and by using published spectral types. Results: Thederived distances, ages and metallicities have shown that none of theanalysed clusters compose binary/double systems. Of the four candidatepairs, only NGC 2383/NGC 2384 are close to each other, but havedifferent metallicities and ages. Ruprecht 72 and Ruprecht 158 are notclusters but fluctuations of the field stellar density. Haffner 18 isfound to be the superposition of two stellar groups at differentdistances: Haffner 18(1) at 4.5 kpc and Haffner 18(2) between 9.5 and11.4 kpc from the Sun. The derived distances and ages have been used tosituate the clusters in the Galactic context. In particular, youngstellar groups trace spiral structure at large Galactocentric radii. Atleast two clusters formed during the last few 108 yr in aninterstellar medium with less than solar abundances. Conclusions:In contrast with the LMC, double clusters are apparently rare, or evennon existent, in the undisturbed environment of the Third GalacticQuadrant. This leaves open the question of whether binary clusters formmore easily toward denser and more violent regions of the Milky Way suchas the inner Galaxy.The original photometry is only available in electronic form at CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/511/A38onleave from Dipartimento di Astronomia, Università di Padova,Vicolo Osservatorio 2, 35122 Padova, Italy
| Red giants in open clusters. XIV. Mean radial velocities for 1309 stars and 166 open clusters
Context: Radial velocities have proved to be an efficient method formembership determination if there are at least 2 or 3 red giants in acluster. They are necessary for galactic studies, but are still missingfor many open clusters. Aims: We present the final catalogues of along-term observing programme performed with the two coravelspectrovelocimeters for red giants in open clusters. The main aims wereto detect spectroscopic binaries and determine their orbital parameters,determine the membership, and compute mean velocities for the stars andopen clusters. Methods: We computed weighted mean radial velocities for1309 stars from 10 517 individual observations, including the systemicradial velocities from spectroscopic orbits and for cepheids. Results:The final results are contained in three catalogues collecting 10 517individual radial velocities, mean radial velocities for 1309 redgiants, and mean radial velocities for 166 open clusters among whichthere are 57 new determinations. We identified 891 members and 418non-members. We discovered a total of 288 spectroscopic binaries, amongwhich 57 are classified as non-members. In addition 27 stars were judgedto be variable in radial velocities and they are all red supergiants. Conclusions: The present material, combined with recent absolute propermotions, will permit various investigation of the galactic distributionand space motions of a large sample of open clusters. However, thedistance estimates still remain the weakest part of the necessary data.This paper is the last one in this series devoted to the study of redgiants in open clusters based on radial velocities obtained with thecoravel instruments.Based on observations collected at the Haute-Provence Observatory(France) and on observations collected with the Danish 1.54-m telescopesat the European Southern Observatory, La Silla, Chile. Full Tables [seefull textsee full textsee full textsee full textsee full text] to [seefull textsee full textsee full textsee full textsee full text] are onlyavailable and Tables [see full textsee full textsee full textsee fulltextsee full text] and [see full textsee full textsee full textsee fulltextsee full text] are also available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/485/303
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Multicolor CCD Photometry and Stellar Evolutionary Analysis of NGC 1907, NGC 1912, NGC 2383, NGC 2384, and NGC 6709 Using Synthetic Color-Magnitude Diagrams
We present the first CCD photometric observations of NGC 2383 and NGC2384 in B, V, R, and I, NGC 1912, NGC 6709 in B, V, and I and NGC 1907in B and V passbands, reaching down to a limiting magnitude of V~20 magfor ~3300 stars put together. The results of the spectroscopicobservations of 43 bright stars in the field of NGC 1912, NGC 2383, NGC2384, and NGC 6709 are also presented. The color-magnitude diagrams(CMDs) of the clusters in V versus B-V, V versus V-R, and V versus V-Iare presented. The distances and reddening to these clusters aredetermined using the cluster CMDs. The distances to the clusters NGC1907, NGC 1912, NGC 2383, NGC 2384, and NGC 6709 are 1785+/-260,1820+/-265, 3340+/-490, 2925+/-430, and 1190+/-175 pc, respectively.Some gaps in the cluster main sequence have been identified. We havecompared the observed color-magnitude diagrams of these four openclusters with the synthetic ones derived from one classical and twoovershoot stellar evolutionary models. Overshoot models estimate olderages for clusters when compared to the classical models. The age of theclusters estimated using the isochrones of Bertelli et al. are 400, 250,400, 20, and 315 Myr for the clusters NGC 1907, NGC 1912, NGC 2383, NGC2384, and NGC 6709, respectively. A comparison of the syntheticcolor-magnitude diagrams with the observed ones indicates that theovershoot models should be preferred. The comparison of integratedluminosity functions do not clearly indicate as to which model is to bepreferred. The values of the mass function slopes estimated for theclusters are x=1.7+/-0.15 for NGC 1912 (mass range: 1.7-3.9 M_solar) andNGC 6709 (1.7-3.4 M_solar), x=1.3+/-0.15 for NGC 2383 (1.7-3.1 M_solar),and x=1.0+/-0.15 for NGC 2384 (2.0-14.0). The present age estimates showthat the closely located cluster pair NGC 1912 + NGC 1907 have similarages, indicating that they may have born together, making them a goodcandidate to be a binary open cluster.
| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| Photometric metal abundances of high-luminosity red stars in young and intermediate-age open clusters
UBV, DDO, and Washinton photometry has been obtained for G and K starslocated in or near 22 young and intermediate-age open clusters. Nearly65 percent of the observed stars are found to have a high probability ofbeing cluster members, while the remaining 35 percent are likely to bered field stars. Five clusters (NGC 2383, NGC 3033, Ruprecht 20, NGC5168, and NGC 6249) probably do not contain any red giants. Sixteenclusters are found to be nearly solar in composition; three are slightlymetal-poor or metal-rich; one (Ruprecht 20) is moderately metal-poor(Fe/H = -0.3); and another (NGC 5617) is moderately metal-rich (Fe/H =0.3). None of the clusters with derived Washington abundances appear tobe enriched in elements of the CNO group.
| Analysis of the results of MK classification of 176 stars in 37 southern open clusters
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979A&AS...37..345F&db_key=AST
| Southern open clusters I. UBV and Hbeta photometry of 15 clusters between galactic longitudes 231d and 256d
Abstract image available at:http://adsabs.harvard.edu/abs/1972A&AS....7..133V
| Estrellas Rojas entre Popa y Cruz.
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