CCD BV survey of 42 open clusters
Aims.We present results of a photometric survey whose aim was to derivestructural and astrophysical parameters for 42 open clusters. While oursample is definitively not representative of the total open clustersample in the Galaxy, it does cover a wide range of cluster parametersand is uniform enough to allow for simple statistical considerations. Methods: BV wide-field CCD photometry was obtained for open clusters forwhich photometric, structural, and dynamical evolution parameters weredetermined. The limiting and core radii were determined by analyzingradial density profiles. The ages, reddenings, and distances wereobtained from the solar metallicity isochrone fitting. The mass functionwas used to study the dynamical state of the systems, mass segregationeffect and to estimate the total mass and number of cluster members. Results: This study reports on the first determination of basicparameters for 11 out of 42 observed open clusters. The angular sizesfor the majority of the observed clusters appear to be several timeslarger than the catalogue data indicate. The core and limiting clusterradii are correlated and the latter parameter is 3.2 times larger onaverage. The limiting radius increases with the cluster's mass, and boththe limiting and core radii decrease in the course of dynamicalevolution. For dynamically not advanced clusters, the mass functionslope is similar to the universal IMF slope. For more evolved systems,the effect of evaporation of low-mass members is clearly visible. Theinitial mass segregation is present in all the observed young clusters,whereas the dynamical mass segregation appears in clusters older thanabout log({age}) = 8. Low-mass stars are deficient in the cores ofclusters older than log({age}) = 8.5 and not younger than one relaxationtime.Tables 1-5 are only available in electronic form at http://www.aanda.org
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Radio observations and spectrum of the SNR G127.1+0.5 and its central source 0125+628
We present new images of the Supernova Remnant (SNR) G127.1+0.5 (R5),based on the 408 MHz and 1420 MHz continuum emission and the HI-lineemission data of the Canadian Galactic Plane Survey (CGPS). The radiospectrum of the central compact source (0125+628) is analyzed in therange 178 MHz-8.7 GHz, indicating a flat spectrum with synchrotronself-absorption below 800 MHz. The SNR's flux density at 408 MHz is 17.1± 1.7 Jy and at 1420 MHz is 10.0 ± 0.8 Jy, corrected forflux densities from compact sources within the SNR. The SNR's integratedflux density based spectral index (Sν ∝ν-α) is 0.43 ± 0.10. The respective T-T plotspectral index (derived from the relative size of brightness temperaturevariations between two frequencies, see text for details) is 0.46± 0.01. There is no evidence at 1σ for spatial variationsin spectral index within G127.1+0.5. In particular, we compared thenorthern shell, southern shell and central diffuse region. HIobservations show structures associated with the SNR in the radialvelocity range of -12 to -16 km s-1, suggesting G127.1+0.5'sdistance is 1.15 kpc. The estimated Sedov age is 2-3 ×104 yr.
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Limits on Enhanced Radio Wave Scattering by Supernova Remnants
We report multifrequency observations with the NRAO Very Long BaselineArray (VLBA) of the compact radio sources J0128+6306 and J0547+2721,which are viewed through the supernova remnants G127.1+0.5 and S147,respectively. Observations were made at frequencies of 1.427, 1.667,2.271, and 4.987 GHz. The lines of sight to these sources pass throughthe shock wave and upstream and downstream turbulent layers of theirrespective supernova remnants and thus might detect cosmic-ray-generatedturbulence produced during the Fermi acceleration process. For bothsources, we detect interstellar scattering, characterized by a componentof the angular size that scales as the square of the observingwavelength. The magnitude of the scattering is characterized by aneffective scattering angular size θS0 at a frequencyof 1 GHz of 13.2+/-2.6 mas for J0128+6306 and 6.7+/-2.2 mas forJ0547+2721. These angular sizes are consistent with the incidentalscattering for any line of sight out of the galaxy at similar Galacticlatitudes and longitudes. There is therefore no evidence for enhancedturbulence at these supernova remnants. We establish upper limits to thesupernova remnant-associated scattering measures of 8.1-14.8m-20/3 pc for J0128+6306 and 3.0 m-20/3 pc forJ0547+2721.
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The association of IRAS sources and 12CO emission in the outer Galaxy
We have revisited the question of the association of CO emission withIRAS sources in the outer Galaxy using data from the FCRAO Outer GalaxySurvey (OGS). The availability of a large-scale high-resolution COsurvey allows us to approach the question of IRAS-CO associations from anew direction - namely we examined all of the IRAS sources within theOGS region for associated molecular material. By investigating theassociation of molecular material with random lines of sight in the OGSregion we were able to construct a quantitative means to judge thelikelihood that any given IRAS-CO association is valid and todisentangle multiple emission components along the line of sight. Thepaper presents a list of all of the IRAS-CO associations in the OGSregion. We show that, within the OGS region, there is a significantincrease ( ~ 22%) in the number of probable star forming regions overprevious targeted CO surveys towards IRAS sources. As a demonstration ofthe utility of the IRAS-CO association table we present the results ofthree brief studies on candidate zone-of-avoidance galaxies with IRAScounterparts, far outer Galaxy CO clouds, and very bright CO clouds withno associated IRAS sources. We find that ~ 25% of such candidate ZOAGsare Galactic objects. We have discovered two new far outer Galaxystar-forming regions, and have discovered six bright molecular cloudsthat we believe are ideal targets for the investigation of the earlieststages of sequential star formation around HII regions. Finally, thispaper provides readers with the necessary data to compare othercatalogued data sets with the OGS data.Tables 1, 2 and A1 are only available in electronic form at the 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/399/1083
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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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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
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The STACC Open Cluster Target List
Observations of variable stars offer a potential to test stellarstructure and evolution. The observations can be either of single,isolated stars, or of variable stars in clusters. The STACC group(Frandsen 1992) has for the last several years searched for openclusters with a population of delta Scuti stars. To make this searchmore efficient, we have produced a target list with a number ofpromising open clusters. The list includes parameters, finding charts,Colour-Magnitude diagrams (CM diagrams) and references for the clusters.This target list is presented here, and is thus made available toobservers interested in participating in the search for variable starsin open clusters. In this paper we describe the motivation, contents anduse of the STACC Open Cluster Target List. We also give some guidelineson how to make CCD observations of open clusters in order to search forvariable stars.
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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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Detection of optical emission in the area of G127.1+0.5
Diffuse optical emission has been detected around the area of thegalactic SNR G127.1+0.5 for the first time. Deep H-alpha CCD images havebeen used to identify the nebulosity that correlates with both the IRemission evident on the IRAS maps and the radio contours of the galacticremnant G127.1+0.5. The optical filaments of the known nearby remnant G126.2+1.6 have also been observed in order to evaluate the detectionability of our instrumental set-up. The intensity of the opticalemission from the nebulosity has been determined by comparison with thestandard star BD +28 deg 4211. The detection of the diffuse opticalemission is established beyond doubt. The structure of the surroundingarea is discussed and an attempt is made to identify the origin of thedetected emission by studying this area at other wavelengths.
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An observational age-metallicity relation for the Galaxy
An observational Age-Metallicity Diagram for the Galaxy has beenconstructed on the base of star cluster data available in theliterature. This diagram exhibits two independent and simultaneousmetallicity enhancement processes identified with two dynamical galacticsubstructures: the thin and the thick disks. Within the observationaluncertainties both these processes can be satisfactory approximated byInfall-Inflow models of the chemical evolution with different high,although rapidly decaying with time, Star Formation and Infall Rates.The comparison of the galactic age-metallicity relations with that forthe Large Magellanic Cloud shows some similarities between processes ofthe chemical enhancement in the Large Magellanic Cloud and the Thin Disksubsystem in the Galaxy.
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Metallicities of open clusters
An examination is conducted of available metallicity data on openclusters, gathering the largest possible set of homogeneous estimationsof this parameter and determining whether open cluster metallicities arerelated to the spatial and age distributions of such objects. The'composite' C-M diagrams for the two metallicity groups discussedexhibit interesting morphological differences which may be characterizedas the presence of numbered blue stragglers at the two metal-richclusters and a lack of such members in two metal-poor ones.
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Two populations of open clusters
The paper proposes a division of the local open clusters into twodifferent dislike subpopulations on the base of the metallicityenhancement history, spatial distribution in the Galaxy and morphologyof their C-M diagrams. The thin disk population objects exhibit highermetallicities and are more closely concentrated to the center and thedisk of the Galaxy than the thick disk clusters. The former contain alsofrequently blue stragglers while the later exhibit the presence of Clumpgiant members, typical for the thick disk globular clusters. Kinematicalproperties of the two considered open cluster subpopulations remainunknown due to the lack of observational data.
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Component Analysis of Open Clusters
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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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The classification of open clusters by the centroid method of cluster analysis
The distribution of open clusters in the Galaxy are considered, withspace coordinates including mass, absolute magnitude, integrated colorindex, diameter, metallicity, and age. It is shown that the majority ofclusters belong to several classes which have parameter values in asufficiently narrow range. The classes form a linear sequence by age andmonotonic sequence on a color-magnitude diagram. They are not isolated,but move into each other continuously. This suggests that the process ofcluster formation contains no significant gaps. The bifurcation of theage sequence of classes depending on the mass and diameter values isfound. This bifucation makes an evolutionary interpretation possible.
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Properties of the open cluster system
A system of weights corresponding to the precision of open cluster datais described. Using these weights, some properties of open clusters canbe studied more accurately than was possible earlier. It is clear thatthere are three types of objects: unbound clusters, bound clusters inthe thin disk, and older bound clusters. Galactic gradients ofmetallicity, longevity, and linear diameter are studied. Distributionsat right angles to the galactic plane are discussed in the light of thedifferent cluster types. The clumping of clusters in complexes isstudied. An estimate of the selection effects influencing the presentmaterial of open cluster data is made in order to evaluate the roleplayed by open clusters in the history of the galactic disk.
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Catalog of open clusters and associated interstellar matter.
Not Available
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Yellow evolved stars in open clusters
This paper describes a program in which Galactic cluster post-AGBcandidates were first identified and then analyzed for clustermembership via radial velocities, monitored for possible photometricvariations, examined for evidence of mass loss, and classified ascompletely as possible in terms of their basic stellar parameters. Theintrinsically brightest supergiants are found in the youngest clusters.With increasing cluster age, the absolute luminosities attained by thesupergiants decline. It appears that the evolutionary tracks ofluminosity class II stars are more similar to those of class I than ofclass III. Only two superluminous giant star candidates are found inopen clusters.
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Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)
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The effect of main-sequence stars on age estimates of open clusters
Existing methods for age estimation of open clusters are discussed. Mostof the observed open clusters (except extremely young and old) contain50-90 percent unevolved Main-Sequence stars. Possible difficultiesencountered in estimating the actual age of an unevolved Main-Sequencestar are discussed. For a relatively reliable cluster age estimationonly a small percentage of cluster members are suitable. The effect ofunevolved Main-Sequence stars on open cluster age estimates using themodified method of isochrones is analyzed.
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Proper motion studies of stars in and around open clusters
A compilation of proper motion studies of stars in and around openclusters is presented. It can serve as a reference to cluster memberselections, studies of cluster dynamics, or as a guide to furtherimprovement of the data presently available. The present paper is only apreliminary version.
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Investigation of the initial mass spectrum of open star clusters
The mass spectra of 228 open star clusters were derived by comparison ofcolor-magnitude diagrams with evolutionary tracks. The application tobinary stars showed the reliability of the mass determination. Thederived mass spectra were fitted by power laws as well as exponentiallaws. It could be shown that both approximate the mass spectra of openstar clusters on the same average significance level. The presentinvestigation revealed a correlation of the slope of the mass spectrawith the cluster age, whereas a detected correlation of the slope withgalactocentric distance is slight. The results suggest that the slope ofthe mass spectrum increases with increasing cluster and galactocentricdistance. These findings are discussed with respect to their reasons andprevious results concerning open clusters and field stars.
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A Radial Velocity Study of Open Clusters Containing Blue Stragglers
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Integrated Photometric Parameters of Open and Globular Clusters
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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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Photoelectric sequences for three open clusters: C0126+630 (NGC 559), C2137+572 (Tr 37), C2152+623 (NGC 7160).
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Catalogue of Masses and Ages of Stars in 68 Open Clusters
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Astrometric criteria for selecting "physical members" of open clusters with low astrometric precision : application to NGC 559
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A possible supernova remnant in an open cluster
The extended radio source G 127.3+0.7 coincides in position with theopen cluster NGC 559. The source may be a supernova remnant which isphysically associated with the cluster. An improved estimate of thedistance to the cluster might make the supernova remnant a usefulcalibrator of the surface-brightness - diameter relation.
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