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A revisit to agglomerates of early-type Hipparcos stars
% We study the spatial structure and sub-structure of regions rich in{Hipparcos} stars with blue B_T-V_T colours. These regions, whichcomprise large stellar complexes, OB associations, and young openclusters, are tracers of on-going star formation in the Galaxy. TheDBSCAN (Density-Based Spatial Clustering of Applications with Noise)data clustering algorithm is used to look for spatial overdensities ofearly-type stars. Once an overdensity, ``agglomerate'', is identified,we carry out a data and bibliographic compilation of their star membercandidates. The actual membership in agglomerate of each early-type staris studied based on its heliocentric distance, proper motion, andprevious spectro-photometric information. We identify 35 agglomerates ofearly-type {Hipparcos} stars. Most of them are associated to previouslyknown clusters and OB associations. The previously unknown P Puppisagglomerate is subject of a dedicated study with Virtual Observatorytools. It is actually a new, nearby, young open cluster (d ˜ 470pc, age ˜ 20 Ma) with a clear radial density gradient. We list PPuppis and other six agglomerates (including NGC 2451 A, vdBH 23, andTrumpler 10) as new sites for substellar searches because of theiryouth, closeness, and spatial density. We investigate in detail thesub-structure in the Orion, CMa-Pup and Pup-Vel OB complexes(``super-agglomerates''). We confirm or discover some stellaroverdensities in the Orion complex, like the 25 Ori group, the Horseheadregion (including the σ Orionis cluster), and the η Orionisagglomerate. Finally, we derive accurate parallactic distances to thePleiades, NGC 2451 A, and IC 2391, describe several field early-typestars at d < 200 pc, and discuss the incompleteness of our search.
| 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
| Open clusters with Hipparcos. I. Mean astrometric parameters
New memberships, mean parallaxes and proper motions of all 9 openclusters closer than 300 pc (except the Hyades) and 9rich clusters between 300 and 500 pc have been computed using Hipparcosdata. Precisions, ranging from 0.2 to 0.5 mas for parallaxes and 0.1 to0.5 mas/yr for proper motions, are of great interest for calibratingphotometric parallaxes as well as for kinematical studies. Carefulinvestigations of possible biases have been performed and no evidence ofsignificant systematic errors on the mean cluster parallaxes has beenfound. The distances and proper motions of 32 more distant clusters,which may be used statistically, are also indicated. Based onobservations made with the ESA Hipparcos astrometry satellite
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| Photoelectric search for CP2-stars in open clusters. X - NGC 2232, NGC 2343, CR 140, and TR 10
One hundred stars in the regions of the four open clusters NGC 2232, NGC2343, Cr 140, and Tr 10 were measured in the Delta(a)-system (Maitzen,1976) in order to detect photometric peculiarity indicating CP2-stars.Of the total of 63 cluster member and probable member stars, only oneturned out to be photometrically peculiar (NGC 2232-9), while Cr 140-60is peculiar, but most likely a nonmember. Tr 10-19, a spectroscopicallypeculiar star according to one source (in disagreement with another),appears to be normal in the present observations.
| The common origin of some open clusters
Eight open clusters have been observed with uvby-beta photometry and forseven of them the metal abundances have been determined. Six of thesehave similar metallicities. They are close in space and are also knownto have similar ages and radial velocities. These clusters are suspectedof having a common origin. Some studies are made of the reliability ofthe photometric system. A large gain in limiting magnitude can beachieved against an unimportant loss of accuracy if interference filtersare removed.
| Six clusters in Puppis-Vela
Intermediate band and H-beta observations of stars in the clusters NGC2451, Cr 140, Cr 135, Cr 173, IC 2391, and Cr 132 in Puppis-Vela arediscussed. Photometric and astrometric parameters for the stars areshown and discussed, along with light and color curves, color-luminosityarrays, histograms for reddening and luminosity, and stellardistributions. Cr 132 consists mainly of members of CMa OB2 plus a fewstars that may be an extension of Cr 140. The latter is an elongatedcluster of some 20 stars, 450 pc distant, 30 million years old, and with(U,V,W) = (+27,-6,-16) km/s. Cr 135 has only eight members, including aK2 Ib star, some 30 million years old, 310 pc distant, and (U,V,W) =(+13,-11,-12) km/s. For NGC 2451, extensive photometry reveals nocluster. Cr 173 is in the Vela sheet and may contain Gamma Vel and thecepheid AH Vel. IC 2391 is a very extended cluster including about twodozen stars brighter than the sun, some 30 million years old and 165 pcdistant, with (U,V,W) = (+20,-19,-3) km/s.
| VY Carinae, S Normae, and photometric luminosities for bright giants and supergiants of types G and K
Observations in the modified Stromgren system of the Cepheids VY Carinaeand S Normae with their associated early-type stars are discussed. Theluminosities of the Cepheids, together with the bright giants R Puppis,HR 2834, HR 4180, and HDE 269953 in the Large Magellanic Cloud (LMC),are used for calibration of photometric luminosities.
| A spectroscopic and statistical study of Collinder 140
Results of a spectroscopic and statistical study of 140 stars in a 1.36sq deg area surrounding the extended open cluster Collinder 140 and intwo neighboring fields are presented. Stars were classified in the MKsystem based on prism and slit spectra to a completeness limit of V =14.35 - 0.65 S, where S is a numerical representation of spectral class.A statistically significant H-R diagram of Cr 140 is obtained by thesubtraction of the H-R diagrams of the neighboring field stars, and itis shown that most cluster members are of type B9 or earlier, between A0and A4 with V less than or equal to 10.3 or between F8 and K4 with Vless than 7.2 + 0.65 S, with a well-defined main sequence down to A3 anda significant number of F8 to K4 giants. The H-R diagram, B-V and U-Vcolors and membership properties of the cluster are then used toestimate a distance of 410 + or - 30 pc and an age of 20 + or - 6 Myrfor the cluster. The presence of a significant concentration of yellowgiants in the cluster is pointed out, and proper motion and radialvelocity studies are suggested as a means of confirming the clustermembership of the evolutionarily anomalous group.
| The open cluster CR 140 revisited.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978MNRAS.183...49W&db_key=AST
| The nearby open cluster Collinder 140.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978AJ.....83..278C&db_key=AST
| The Open Cluster Cr 140
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