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.
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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.
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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.
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The Evolutionary Status of Be Stars: Results from a Photometric Study of Southern Open Clusters
Be stars are a class of rapidly rotating B stars with circumstellardisks that cause Balmer and other line emission. There are threepossible reasons for the rapid rotation of Be stars: they may have beenborn as rapid rotators, spun up by binary mass transfer, or spun upduring the main-sequence (MS) evolution of B stars. To test the variousformation scenarios, we have conducted a photometric survey of 55 openclusters in the southern sky. Of these, five clusters are probably notphysically associated groups and our results for two other clusters arenot reliable, but we identify 52 definite Be stars and an additional 129Be candidates in the remaining clusters. We use our results to examinethe age and evolutionary dependence of the Be phenomenon. We find anoverall increase in the fraction of Be stars with age until 100 Myr, andBe stars are most common among the brightest, most massive B-type starsabove the zero-age main sequence (ZAMS). We show that a spin-up phase atthe terminal-age main sequence (TAMS) cannot produce the observeddistribution of Be stars, but up to 73% of the Be stars detected mayhave been spun-up by binary mass transfer. Most of the remaining Bestars were likely rapid rotators at birth. Previous studies havesuggested that low metallicity and high cluster density may also favorBe star formation. Our results indicate a possible increase in thefraction of Be stars with increasing cluster distance from the Galacticcenter (in environments of decreasing metallicity). However, the trendis not significant and could be ruled out due to the intrinsic scatterin our data. We also find no relationship between the fraction of Bestars and cluster density.
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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.
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Pulsating Stars in the ASAS-3 Database. I. beta Cephei Stars
We present results of an analysis of the ASAS-3 data for short-periodvariables from the recently published catalog of over 38000 stars. Usingthe data available in the literature we verify the results of theautomatic classification related to \beta Cep pulsators. In particular,we find that 14 stars in the catalog can be classified unambiguously asnew beta Cep stars. By means of periodogram analysis we derive thefrequencies and amplitudes of the excited modes. The main modes in thenew beta Cep stars have large semi-amplitudes, between 35 and 80 mmag.Up to four modes were found in some stars. Two (maybe three) new betaCep stars are members of southern young open clusters: ASAS164409-4719.1 belongs to NGC 6200, ASAS 164630-4701.2 is a member ofHogg 22, and ASAS 164939-4431.7 could be a member of NGC 6216.We also analyze the photometry of four known beta Cep stars in theASAS-3 catalog, namely IL Vel, NSV 24078, V1449 Aql and SY Equ. Finally,we discuss the distribution of beta Cep stars in the Galaxy.
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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.
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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
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Proper motions of open clusters based on the TYCHO2 Catalogue. II. Clusters farther than 1 kpc
We determined the mean absolute proper motion of 94 open clusterssituated farther than 1 kpc from the Sun. The results are derived fromthe stellar proper motion data given in the Tycho2 Catalogue. The meanproper motion of the clusters and membership probability of individualstars were obtained from the proper motion data by applying thestatistical method proposed by Sanders (\cite{Sanders1971}). Themeasurements made use of a large number of stars, usually several tens,for each cluster. The total number of stars investigated in the fieldsof the clusters is 4864 of which 2021 were considered members. For 55clusters, this is the first determination of the proper motion. Based onobservations of the ESA Hipparcos satellite. Tables 1 to 95 are onlyavailable 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/388/168
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Broad-band X-ray/gamma-ray spectra and binary parameters of GX 339-4 and their astrophysical implications
We present X-ray/gamma-ray spectra of the binary GX 339-4 observed inthe hard state simultaneously by Ginga and CGRO OSSE during an outburstin 1991 September. The Ginga X-ray spectra are well represented by apower law with a photon spectral index of Gamma~=1.75 and a Comptonreflection component with a fluorescent Fe Kalpha line corresponding toa solid angle of an optically thick, ionized medium of ~0.4x2pi. TheOSSE data (>=50 keV) require a sharp high-energy cut-off in thepower-law spectrum. The broad-band spectra are very well modelled byrepeated Compton scattering in a thermal plasma with an optical depth oftau~1 and kT~=50 keV. We also study the distance to the system and findit to be >~3 kpc, ruling out earlier determinations of ~1 kpc. Usingthis limit, the observed reddening and the orbital period, we find theallowed range of the mass of the primary is consistent with it being ablack hole. We find the data are inconsistent with models of eitherhomogenous or patchy coronae above the surface of an accretion disc.Rather, they are consistent with the presence of an inner hot disc withthe viscosity parameter of alpha~1 accreting at a rate close to themaximum set by advection. The hot disc is surrounded by a cold outerdisc, which gives rise to the reflection component and a soft X-rayexcess, also present in the data. The seed photons for Comptonizationare unlikely to be due to thermal synchrotron radiation. Rather, theyare supplied by the outer cold disc and/or cold clouds within the hotdisc. e^+/- pair production is negligible if electrons are thermal. Thehot disc model, for which scaled parameters are independent of the blackhole mass, is supported by the similarity of the spectrum of GX 339-4 tothose of other black hole binaries and Seyfert 1s. On the other hand,their spectra in the soft gamma-ray regime are significantly harder thanthose of weakly magnetized neutron stars. Based on this difference, wepropose that the presence of broad-band spectra corresponding to thermalComptonization with kT>~50 keV represents a black hole signature.
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Absolute proper motions of 181 young open clusters.
Not Available
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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.
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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.
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Topography of the Galactic disk - Z-structure and large-scale star formation
A 3D morphological description of the Galactic disk defined by the youngstellar population is delineated using a sample of young open clusterswith cataloged distances and treated with Kriging techniques. The valuesof the positional variable Z for the cluster sample are considered asprospectings of the displacement of the Galactic disk in respect to theequator in the plane. The Kriging technique is described with emphasison its application to the automatic cartography problem. A view of theGalactic disk in a region of about 3 kpc around the sun emerges fromthis treatment and shows a trough-peak structure with four maindepressions as the more striking features. The most prominentdepression, named Big Dent, is apparent at about 1.8 kpc in anapproximately 240-deg direction. It has an elliptical shape with axissizes of 1.5 and 3 kpc, reaching a Z value of 200 pc below the formalGalactic plane. Two-dimensional sections across some selected directionsof the topography show profiles in good agreement with previousobservational studies based on different object samples.
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Component Analysis of Open Clusters
Not Available
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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.
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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.
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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.
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Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)
Not Available
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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.
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Open clusters and galactic structure
A total of 610 references to 434 clusters are employed in thecompilation of a catalog of open clusters with color-magnitude diagramson the UBV or RGU systems. Estimates of reddening, distance modulus, ageand number of cluster members are included. Although the sample isconsidered representative of the discoverable clusters in the galaxy,the observed distribution is nonuniform because of interstellarobscuration. Cluster distribution in the galactic plane is found to bedominated by the locations of dust clouds rather than by spiralstructure. The distributions of clusters as a function of age andrichness class show that the lifetimes of poor clusters are much shorterthan rich ones, and that clusters in the outer disk survive longer thanthose in the inner disk. An outer disk age which is only about 50% theage of the globular clusters is indicated by cluster statistics. Thethickening of the galactic disk with increasing galactocentric distancemay be due to either a younger dynamical age or a lower gravitationalpotential in the outer regions.
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A catalogue of galactic clusters observed in three colours
This catalogue contains photometric data for 190 galactic clusters, allobserved in UBV or RGU. The distances of the young clusters (with spless than b3) have been calculated or recalculated according to method Aof Becker (1963). The galactic distribution of these clusters confirmstheir role of being good spiral tracers.
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NGC 6200, a loose young open cluster in the Sagittarius-I arm extension
Not Available
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