Contents
Images
Upload your image
DSS Images Other Images
Related articles
Photometric and Coravel observations of red giant candidates in three open clusters: membership, binarity, reddening and metallicity
Aims.We present new CORAVEL radial-velocity observations andphotoelectric photometry in the UBV and DDO systems for a sample ofpotential members of the red-giant branches of NGC 6192, NGC 6208 andNGC 6268, three open clusters projected close to the Galactic centerdirection. We also examine the properties of a sample of 42 inner diskopen clusters projected towards almost the same direction as the threeclusters. Methods: .Cluster members and red field giants werediscriminated by using the CORAVEL radial-velocity data and by applyingtwo photometric criteria. Interstellar reddening and metal content ofthe clusters were derived from combined BV and DDO data. Results:.Cluster membership for five red giants in NGC 6192, three in NGC 6208and three in NGC 6268 has been confirmed by the analysis of thephotometric and kinematic data. Photometric membership probabilitiesshow very good agreement with those obtained from CORAVEL radialvelocities. Three new spectroscopic binaries were discovered among thered giants of NGC 6192 and NGC 6208. Mean radial velocities and E(B-V)colour excesses were derived. Conclusions: .The overallmetallicities were found to be nearly solar for NGC 6208 and above solarfor NGC 6192 and NGC 6268. Most of the clusters located closer than 2kpc from the Sun in the considered direction are slightly more reddenedthan the absorption resulting from the Baade's window absorption law.
| Kinematics of the Open Cluster System in the Galaxy
Absolute proper motions and radial velocities of 202 open clusters inthe solar neighborhood, which can be used as tracers of the Galacticdisk, are used to investigate the kinematics of the Galaxy in the solarvicinity, including the mean heliocentric velocity components(u1,u2,u3) of the open cluster system,the characteristic velocity dispersions(σ1,σ2,σ3), Oortconstants (A,B) and the large-scale radial motion parameters (C,D) ofthe Galaxy. The results derived from the observational data of propermotions and radial velocities of a subgroup of 117 thin disk young openclusters by means of a maximum likelihood algorithm are:(u1,u2,u3) =(-16.1+/-1.0,-7.9+/-1.4,-10.4+/-1.5) km s-1,(σ1,σ2,σ3) =(17.0+/-0.7,12.2+/-0.9,8.0+/-1.3) km s-1,(A,B) =(14.8+/-1.0,-13.0+/-2.7) km s-1 kpc-1, and (C,D) =(1.5+/-0.7,-1.2+/-1.5) km s-1 k pc-1. A discussionon the results and comparisons with what was obtained by other authorsis given.
| Proper motion determination of open clusters based on the UCAC2 catalogue
We present the kinematics of hundreds of open clusters, based on theUCAC2 Catalogue positions and proper motions. Membership probabilitieswere obtained for the stars in the cluster fields by applying astatistical method uses stellar proper motions. All open clusters withknown distance were investigated, and for 75 clusters this is the firstdetermination of the mean proper motion. The results, including the DSSimages of the cluster's fields with the kinematic members marked, areincorporated in the Open Clusters Catalogue supported on line by ourgroup.
| New fundamental parameters for the inner disk open cluster Lyngå 11
We have obtained CCD BVIKC photometry down to V ˜ 21.5for the open cluster Lyngå 11 and its surrounding field. Thispreviously unstudied object appears to be rich and highly absorbed. Acluster angular radius of 4.5′ ± 0.5′, equivalent to(3.0 ± 0.3) pc, is estimated from star counts in 100-pixel a sideboxes distributed throughout the whole observed field. Our analysissuggests that Lyngå 11 is moderately young and probably of solarmetallicity. Adopting the theoretical metal content Z = 0.02, whichprovides the best global fit, we derive an age of (630 ± 70) Myr.Simultaneously, colour excesses E(B ‑ V) = 0.70 and E(V ‑ I)= 0.85 and an apparent distance modulus V ‑ MV = 14.0are obtained. These results place Lyngå 11 at a distance of (2.3± 0.5) kpc from the Sun and ˜6.5 kpc from the Galacticcentre. The properties of a sample of clusters aligned along theline-of-sight of Lyngå 11 are examined as well.
| Astrophysical parameters of Galactic open clusters
We present a catalogue of astrophysical data for 520 Galactic openclusters. These are the clusters for which at least three most probablemembers (18 on average) could be identified in the ASCC-2.5, a catalogueof stars based on the Tycho-2 observations from the Hipparcos mission.We applied homogeneous methods and algorithms to determine angular sizesof cluster cores and coronae, heliocentric distances, mean propermotions, mean radial velocities, and ages. For the first time we derivedistances for 200 clusters, radial velocities for 94 clusters, and agesof 196 clusters. This homogeneous new parameter set is compared withearlier determinations, where we find, in particular, that the angularsizes were systematically underestimated in the literature.
| Deepsky delights.
Not Available
| A 12CO (J = 1 -> 0) study towards the Ara OB1 region
Intermediate angular resolution (HPBW=8\farcm7 ) carbon monoxide(12CO J=1->0) line observations towards the OB associationAra OB1 are reported. The molecular line observations cover an area of2\fdg75 x 3\fdg00 , and disclose a rich and complex distribution of themolecular line emission. The molecular features likely to be associatedwith the OB-association Ara OB1 span the velocity range from -28 to -20km s-1. The most negative radial velocities are observedalong NGC 6188 (equiv Rim nebula). This nebula marks the interfacebetween the HII region RCW 108 and the highly absorbing molecularmaterial located westwards of the ionised region. The dominant COstructures, labeled E and F, have a radial velocity of about -23.5 and-21.8 km s-1, respectively. The former harbours a brightoptical knot, the infrared cluster RCW-108 and the strong IRAS source16362-4845. IRAS point sources are also seen in projection onto12CO concentrations F and H. This may indicate that the starforming process is a widespread phenomenon in this molecular complex.Extended continuum emission, having a high degree of spatial correlationwith both the infrared and molecular emission, is observed in theregion. We believe that this emission, thermal in nature, arises fromthe ionised surface layers of the molecular complex. The ionising agentsare the high mass stars of NGC 6193, the nucleus of Ara OB1. The totalamount of molecular gas related to Ara OB1 is about ~ 1.4x104 Msun.
| Optical Polarization Observations of NGC 6231: Evidence for a Past Supernova Fingerprint
We present the first linear multicolor polarization observations for asample of 35 stars in the direction of the Galactic cluster NGC 6231. Wehave found a complex pattern in the angles of the polarimetric vectors.Near the core of this cluster the structure shows a semicircular patternthat we have interpreted as a reorientation of the dust particlesshowing the morphology of the magnetic field. We propose that asupernova event occurred some time ago and produced a shock on the localISM. We discuss in this paper independent confirmations of this event,both from the studies on the diffuse interstellar absorptions and theresults of the pre-main-sequence stars. We also show that a supernova issupported by the evolutionary status of the cluster.Based on observations obtained at Complejo Astronómico ElLeoncito (CASLEO), operated under agreement between the CONICET and theNational Universities of La Plata, Córdoba, and San Juan,Argentina.
| Proper Motions of Open Star Clusters and the Rotation Rate of the Galaxy
The mean proper motions of 167 Galactic open clusters withradial-velocity measurements are computed from the data of the Tycho-2catalog using kinematic and photometric cluster membership criteria. Theresulting catalog is compared to the results of other studies. The newproper motions are used to infer the Galactic rotation rate at the solarcircle, which is found to be ω0=+24.6±0.8 km s-1 kpc-1.Analysis of the dependence of the dispersion of ω0 estimates onheliocentric velocity showed that even the proper motions of clusterswith distances r>3 kpc contain enough useful information to be usedin kinematic studies demonstrating that the determination of propermotions is quite justified even for very distant clusters.
| Two highly reddened young open clusters located beyond the Sagittarius arm
We present the results of CCD BVI Johnson-Cousins photometry down to V ~19 mag in the regions of the unstudied stellar groups Pismis 23 and BH222, both projected close to the direction towards the Galactic centre.We measured V magnitude and B-V and V-I colours for a total of 928 starsin fields of about 4arcmin x4arcmin . Pismis 23 is conclusively aphysical system, since a clear main sequence and other meaningfulfeatures can be seen in the colour-magnitude diagrams. The reality ofthis cluster is also supported by star counts carried out within andoutside the cluster field. For Pismis 23 we derive colour excessesE(B-V) = 2.0 +/- 0.1 and E(V-I) = 2.6 +/- 0.1, a distance from the Sunof 2.6 +/- 0.6 kpc (Z = -19 pc) and an age of 300 +/- 100 Myr (assumingsolar metal content). BH 222 appears to be a young open cluster formedby a vertical main sequence and by a conspicuous group of luminous,typically red supergiant stars. We derived for this cluster a colourexcess of E(V-I) = 2.4 +/- 0.2, a distance from the Sun of 6.0 +/- 2.7kpc (Z = -46 pc) and an age of 60 +/- 30 Myr. The resulting reddeningand distance estimates place these two young objects among the mostreddened and distant open clusters known in the direction towards theGalactic centre. They are located beyond the Sagittarius arm, close tothe direction where this arm probably bifurcates into two arms. Based onobservations made at the University of Toronto (David DunlapObservatory) 24-inch telescope, Las Campanas, Chile. Tables \ref{t2} and3 are only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/388/179
| Proper motions of open clusters within 1 kpc based on the TYCHO2 Catalogue
We present mean absolute proper motions of 112 open clusters, determinedusing the data from the Tycho2 Catalogue. For 28 clusters, this is thefirst determination of proper motion. The measurements made use of alarge number of stars (usually several tens) for each cluster. The totalnumber of stars studied in the fields of the 164 open clusters is 5016,of which 4006 were considered members. The mean proper motions of theclusters and membership probability of individual stars were obtainedfrom the proper motion data by applying the statistical method proposedby Sanders (\cite{Sanders71}). Based on observations of the ESAHipparcos satellite. Tables 1, 2 and 5 to 117 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/376/441
| Spectroscopic Binaries in Young Open Clusters
We have analysed the binarity and multiplicity characteristics of 120O-type stars in 22 very young open clusters and found marked differencesbetween the "rich" (N >= 6 O-type stars and primaries) and "poor" (N= 1) clusters. In the rich clusters, the binary frequencies vary between14% (1 SB among 7 stars) and 80% (8 SBs among 10 stars). Multiplesystems seem not to be frequent and stars are spread all over thecluster area. In poor clusters, the binary frequency of the O-typeobjects is nearly 100%, with orbital periods around 3 days. Severalbinaries are also eclipsing. Additional companions are always present.They form either hierarchical multiple stars or trapezium systems. Thesemassive multiple systems are generally found close to the clustercenter, although there are exceptions.
| The Highly Polarized Open Cluster Trumpler 27
We have carried out multicolor linear polarimetry (UBVRI) of thebrightest stars in the area of the open cluster Trumpler 27. Our datashow a high level of polarization in the stellar light with aconsiderable dispersion, from P=4% to P=9.5%. The polarization vectorsof the cluster members appear to be aligned. Foreground polarization wasestimated from the data of some nonmember objects, for which twodifferent components were resolved: the first one associated with a dustcloud close to the Sun producing Pλmax=1.3% andθ=146°, and a second component, the main source ofpolarization for the cluster members, originating in another dust cloud,which polarizes the light in the direction of θ=29.5d. From adetailed analysis, we found that the two components have associatedvalues EB-V<0.45 for the first one andEB-V>0.75 for the other. Due the difference in theorientation of both polarization vectors, almost 90° (180° atthe Stokes representation), the first cloud (θ~146°)depolarizes the light strongly polarized by the second one(θ~29.5d). Based on observations obtanined at ComplejoAstronómico El Leoncito (CASLEO), operated under agreementbetween CONICET and the National Universities of La Plata,Córdoba, and San Juan, Argentina.
| 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 Polarization Study of ARA OB1
We present the results of a multicolor polarimetric study of stars inthe association Ara OB1. Several objects belonging to the clusters NGC6204, 6193, and 6167 and the local field were observed as part of aglobal study of the region. The polarimetry shows that the orientationof the polarimetric vectors of each star is very similar within eachcluster. The average values are 35.5d+/-15.1d and 52.2d+/-16 deg for NGC6204 and 6193, respectively. An average value of 106.5d+/-9.9d is foundfor NGC 6167, but the angle distribution is asymmetric, and a secondcomponent can be fitted to the angle histogram (P.A.~120.8d+/-11.6d),showing a behavior not observed in NGC 6204 and 6193. So, we suggestthat some of the observed stars perhaps belong to another starsgrouping, located behind NGC 6167 and between a dust layer with adifferent orientation of the grains. The large difference in thepolarization angle between NGC 6167 and the other two clusters couldalso be explained because NGC 6167 is supposed to be at the center of agas-expanding structure and it is possible that this cluster was theorigin of the star formation process in the Ara OB1 association,triggered by stellar winds or supernova explosions.
| Multicolor polarization study of Ara OB1.
Not Available
| Absolute proper motions of 181 young open clusters.
Not Available
| Deep Hα survey of the Milky Way. III. The l=338deg area.
The Galactic plane has been observed between l=337deg and l=342deg inthe frame of an Hα Survey of the Southern Milky Way. This area isknown to be rich in radio sources but poor in Hα emission. Theanalysis of high resolution profiles of the Hα emission observedin this direction nevertheless enabled to distinguish 6 differentvelocity components: 2 faint layers of diffuse ionized hydrogen at 0 and-12km/s (V_LSR_), 2 brighter layers at -28 and -39km/s includingindividual HII regions, a faint patch at -50km/s and two isolated brightHII regions at -61km/s. Combining these Hα observations withstellar and radio data we conclude about the most probable distances forthe different components.
| Catalogue of blue stragglers in open clusters.
An extensive survey of blue straggler candidates in galactic openclusters of both hemispheres is presented. The blue stragglers wereselected considering their positions in the cluster colour-magnitudediagrams.They were categorized according to the accuracy of thephotometric measurements and membership probabilities. An amount of 959blue straggler candidates in 390 open clusters of all ages wereidentified and classified. A set of basic data is given for everycluster and blue straggler. The information is arranged in the form of acatalogue. Blue stragglers are found in clusters of all ages. Thepercentage of clusters with blue stragglers generally grows with age andrichness of the clusters. The mean ratio of the number of bluestragglers to the number of cluster main sequence stars is approximatelyconstant up to a cluster age of about 10^8.6^ yr and rises for olderclusters. In general, the blue stragglers show a remarkable degree ofcentral concentration.
| The interstellar medium in the ARA OB1 field
We report here the results of a detailed study of two surveys of H I, atlambda = 21 cm, in the field of the stellar association Ara OB1.Subtracting the background with a procedure developed here, we were ableto identify two H I shell-like features, at roughly the same positionbut at different velocities, whose parameters were determined. On thebasis of their kinematical distances, two concentrations of OB stars(one at 1400 pc, belonging to Ara OB1, and another at 2500 pc) might bethe progenitors of these shells. The nearest H I shell may havetriggered a process of star formation.
| Integrated photometric properties of open clusters
Galactic open clusters provide an abundant sample of stellar aggregatesof various sizes, ages and metal abundances, apt to constitute atemplate for comparison with star systems in other galaxies. In thispaper we present and discuss a standard methodology to synthesize U,B,Vfluxes and colours, and apply it to a set of 138 open clusters. Resultsare compared with previous ones available in the literature. We wereable to calibrate a mass-luminosity relation by which we evaluated themass of ~400 open clusters, leading to a well defined present-day massfunction. The number-complete sample of galactic open clusters presentedin Battinelli & Capuzzo-Dolcetta (1991) is enlarged of a 15%.
| Formation and evolutionary properties of the Galactic open cluster system
Results are reported from a statistical analysis of observational dataon 100 open clusters within 2 kpc of the sun, selected from the catalogof Lynga (1987). The selection criteria and the completeness of thesample are discussed; the data are compiled in a table; and the analysisresults are presented in a series of graphs and characterized in detail.A cluster formation rate of 0.45 clusters/kpc Myr is found,significantly lower than the rates determined previously (using clusterswithin 1 kpc of the sun) and corresponding to a cluster star-formationefficiency of 0.0063. The low average cluster lifetime (about 10 Myr)suggests that clusters are formed as unstable systems.
| Component Analysis of Open Clusters
Not Available
| The Sagittarius-Carina Arm Structure and Parameters of Spiral Pattern
Not Available
| Young stellar-gas complexes in the Galaxy
It is found that about 90 percent of OB-associations and o-b2 clusterssituated within 3 kpc of the sun can be united into complexes withdiameters of 150-700 pc. Almost all of these clusters contain giantmolecular clouds with a mass greater than about 100,000 solar masses. Anumber of complexes are associated with giant H I clouds; a few of thesmall complexes are situated in the HI caverns. The concentration ofOB-associations and young clusters in star complexes attests to theircommon origin in the supergiant gaseous clouds.
| A cluster analysis of open clusters
The Galactic distribution of 361 open clusters is studied using acluster analysis method. It is shown that more than half of the clustersenter groups with characteristic dimensions of several hundred parsecs.To distinguish physical clusters from random condensations, criteriabased on age similarity, the color of the main-sequence blue end, andthe integrated color and radial velocity of the clusters are used. Theproximity of these values suggests a physical unity and common origin ofclusters in a group.
| A cluster analysis of young open clusters
Cluster analysis methods are used to consider the galactic distributionof 224 open clusters with an age up to 10 to the 8th yrs. Most of theseclusters enter condensations with characteristic dimensions of a fewhundred parsecs. Some condensations are so similar in terms of the age,integrated color, and radial velocity of their components, that thiscannot be considered a coincidence. This suggests that each condensationis a physical entity consisting of clusters apparently linked by acommon origin.
| ARA OB1 - A stellar association formed by the action of an energetic event?
Neutral hydrogen (at the wavelength of 21 cm) and carbon monoxide (at2.6 mm) line observations of the interstellar medium in the neighborhoodof the association Ara OB1 are reported. The observed H I distributionindicates the presence of an expanding structure. The total H I massassociated with such feature amounts to 4800 solar masses, and itsmomentum and kinetic energy are about 40,000 solar mass km/s and 3 x 10to the 48th erg, respectively. The H I structure, 42 pc in diameter,expands at a speed of 10 km/s. A possible origin for the expanding H Istructure, and a genetic link between such structure and Ara OB1 areproposed.
| Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)
Not Available
| Interstellar NaI absorption towards the stellar association ARA OB1
Observations have been made of the interstellar D-line absorption of NaI towards a loose grouping of OB stars (containing the association AraOB1 and probably the H-alpha emission regions RCW 107 and 108) centeredat 1 = 337.5 deg and b = - 0.5 deg. The individual absorption spectracontain several velocity components which show well-defined groupings at- 37, -18 and 0 km/s. The corresponding median optical depths are 2, 7and 6. The evidence indicates that both the -37 and -18 km/s Na I cloudsare located in the Carina-Sagittarius spiral arm. Several H II regionsare located at similar longitudes, but most are close to zero latitudeand are more distant than the arm. The association contains the galacticcluster NGC 61993. The results suggest that the turbulence seenoptically towards this cluster has been caused by the interactionbetween two cloud groups moving towards each other at velocities of 10to 15 km/s.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
