|UBVRI CCDphotometric studyoftheopen clusters Basel 4 and NGC 7067|
In this paper we present UBVRI CCD photometry in the region of twoyoung open star clusters Basel 4 and NGC 7067 for the first time. Oursample consists of ~4000 stars down to V~ 21 mag. Stellar surfacedensity profile indicates that radii of Basel 4 and NGC 7067 are about1.8 and 3.0 arcmin respectively. The (U-B) versus (B-V) diagramsindicate that the metallicity of NGC 7067 is solar while that of Basel 4is Z~ 0.008. We estimate the mean value of E(B-V) = 0.45 +/- 0.05 and0.75 +/- 0.05 mag for Basel 4 and NGC 7067, respectively. The analysisof 2MASS JHK data in combination with the optical data in both theclusters yields E(J-K) = 0.30 +/- 0.20 mag and E(V-K) = 1.60 +/- 0.20mag for Basel 4 while E(J-K) = 0.40 +/- 0.20 mag and E(V-K) = 2.10 +/-0.20 mag for NGC 7067. Furthermore, colour excess diagrams show a normalinterstellar extinction law towards both the clusters.Using the intrinsic colour-magnitude diagrams of the cluster members, weestimated the distances of the clusters as 3.0 +/- 0.2 and 3.6 +/- 0.2kpc for Basel 4 and NGC 7067, respectively. By fitting the propermetallicity isochrones to the bright cluster members we estimated theage of the clusters as 200 +/- 50 and 100 +/- 25 Myr for Basel 4 and NGC7067, respectively. The mass function slopes that are derived byapplying the corrections of field star contamination and dataincompleteness are 1.55 +/- 0.25 and 1.68 +/- 0.47 for Basel 4 and NGC7067, respectively. The values of the mass function slope are thus notvery different from Salpeter's value. Mass segregation is observed inboth the clusters, which may be caused by the dynamical evolution or theimprint of star formation processes or both.
|Studies of Young Stellar Objects|
We present a detailed study of four young open star clusters and two OBassociations using deep CCD U B V R I and 2MASS J H Ks measurements.Physical parameters of the clusters have been estimated using optical aswell as near-IR data. Ages of objects under study range 10-100 Myr. Massfunction slope of the sample of clusters are in agreement with theSalpeter (1955) value. From a comparison of mass function slope ofclusters and OB associations in our Galaxy with those in externalgalaxies, we urgue that the star formation processes are such that theyyield almost similar stellar mass distribution in vastly different starforming environments. Mass segregation suggests that the clusters understudy are dynamically relaxed and hence mass segregation may be due todynamical evolution or imprint of star formation or both. The extinctionproperties of a sample of 18 young star clusters have been investigatedutilizing recent data available in literature. The study suggests thatthere is no uniformity in extinction properties amongst these clusters.A non-uniform extinction has been noticed for the first time in NGC 1502and Tr 37 along with the existence of circumstellar shell around someearly type stars in NGC 884, NGC 2264, Tr 14 and Tr 16.
|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.
|Gamma-ray line emission from OB associations and young open clusters. II. The Cygnus region|
Gamma-ray and microwave observations of the Cygnus region reveal anintense signal of 1.809 Me line emission, attributed to radioactivedecay of 26, that is closely correlated with 53 GHz free-freeemission, originating from the ionised interstellar medium. We modelledboth emissions using a multi-wavelength evolutionary synthesis code formassive star associations that we applied to the known massive starpopulations in Cygnus. For all OB associations and young open clustersin the field, we determined the population age, distance, and richnessas well as the uncertainties in all these quantities from publishedphotometric and spectroscopic data. We propagate the populationuncertainties in model uncertainties by means of a Bayesian method. Theyoung globular cluster Cyg OB2 turns out to be the dominant26 nucleosynthesis and ionisation source in Cygnus. Our modelreproduces the ionising luminosity of the Cygnus region very well, yetit underestimates 26 production by about a factor of 2. Weattribute this underestimation to shortcomings of currentnucleosynthesis models, and suggest the inclusion of stellar rotationas possible mechanism to enhance 26 production. We alsomodelled 60Fe nucleosynthesis in the Cygnus region, yet thesmall number of recent supernova events suggests only little60Fe production. Consequently, a detection of the 1.137 Meand 1.332 Me decay lines of 60Fe from Cygnus by the upcomingINTEGRAL observatory is not expected. Appendices A and B, and Tables 1,2, and 5 are only available in electronic form athttp://www.edpsciences.org
|Fundamental parameters and new variables of the galactic open cluster NGC 7128|
CCD photometry in Johnson UBV and Strömgren uvby systems andmedium-resolution spectroscopy of the galactic open cluster NGC 7128 arepresented. Spectral types of the brightest 12 stars in the cluster fieldwere determined based on equivalent widths of the Hα and the Hei6678-Å line. The spectroscopic observations also revealed twoobvious and one probable Be-type stars showing Hα emission. Theanalysis of the photometric diagrams gave a colour excess ofE(B-V)=1.03+/-0.06mag, a distance modulus DM=13.0+/-0.2mag and an ageabove 10Myr. Time-resolved photometric observations obtained on onenight resulted in the detection of short time-scale light variations ofseven new and three already known variable stars in the cluster field.
|Search for Pre-Main-Sequence Stars in the Young Galactic Cluster NGC 6910|
Photometric CCD UBV measurements have been obtained in the field of theyoung Cygnus cluster NGC 6910. The observations reach down to magnitudeV~=18 for 206 stars measured in all three UBV bands, uncovering theregion of the color-magnitude diagram where pre-main-sequence (PMS)stars are expected. The transformation of our instrumental magnitudes tothe standard system is discussed on the basis of two different sets ofstandard stars: 22 stars from six fields in the Landolt catalogs and 48stars with published photoelectric photometry in common with ours in thefour clusters observed in this campaign. The latter set is preferred,since it enables the effect of systematic errors in the U-B colors to beminimized. The adopted cluster parameters are E(B-V)=1.02+/-0.13,V0-MV=11.2+/-0.2, and age=(6.5+/-3)x106yr. The search for PMS cluster members on the basis of the calculatedcolor excess and distance modulus results in the proposed membership for11 PMS stars of spectral types from A to G.
|Pre-Main-Sequence Stars in the Young Galactic Cluster IC 4996: A CCD Photometric Study|
The results of a UBV CCD photometric study of the cluster IC 4996 arepresented. We obtain new values for the cluster parameters: E(B-V) =0.71 +/- 0.08, V_0 - M_V = 11.9 +/- 0.1, and age = (7.5 +/- 3) x 10^6yr. The combined evidence from the photometric diagrams suggests thepresence of a number of pre-main-sequence (PMS) cluster members withspectral types ~A0 to F5. The interpretation of these objects as PMScandidates is further supported by independent results from CCD uvbyHβ observations. If confirmed, these stars would bridge theexisting gap in the sample of PMS stars, between the coolest Herbig AeBestars (HAeBe), and the hottest T Tauri stars. These PMS candidates arelocated some 0.5 and 1 mag above the main sequence in the V-(B-V)diagram, around the location of spectral types AF. This feature,together with their locations in the (U-B)-(B-V) diagram and theinterpretation that they are PMS members, suggest an additionalreddening law with a slope alpha = E(U-B)/E(B-V) ~= 0.55, probablycaused by circumstellar material.
|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.
|Galactic clusters with associated Cepheid variables. 4: C2128+488 (Anon. Platais) and V1726 Cygni|
New photoelectric UBV photometry of 32 stars, photographic UBVphotometry of 120 stars, and spectroscopic observations of 8 stars arepresented for C 2128+488 (Anon. Platais), the cluster associated withthe 4d.237 s-Cepheid V1726 Cygni. The resulting photometry,spectral classifications, and radial velocities are used withspectroscopic and proper motion data previously published by Platais andothers for the Cepheid and other stars in this field in a detailedcluster analysis. The newly obtained cluster distance modulus isVzero - MV = 10.98 +/- 0.02s.e. (d = 1568 +/- 13pc), and a value of R = AV/EV-V = 3.07 +/- 0.27s.e. is found to describe the dust extinction in the field. A spacereddening of EB-V = 0.43 +/- 0.02 is derived for V1726 Cygfrom two late B-type companions which bracket the Cepheid, as well asfrom the reddenings of other stars in the field. Its resultingluminosity as a probable cluster member is (MV) = -3.42 +/-0.07. A cluster radial velocity of -15.4 +/-0.2 km/sec and a clusterturnoff point at spectral type B7 are both consistent with the likelymembership of V1726 Cyg, as are the available proper motion data. Thesmall amplitude, sinusoidal light curve, and location of V1726 Cyg onthe blue edge of the Cepheid instability strip are consistent with theproperties expected for overtone pulsation, although such a possibilityappears to imply an unrealistically small value (beta = 0.5 +/- 0.2) forthe color coefficient in the PLC relation. A more reasonable value ofbeta = 2.1 +/- 0.2 is derived for the color term applicable to galacticcluster Cepheids in this program when V1726 Cyg is assumed to bepulsating in the fundamental mode.
|A CO survey of regions around 34 open clusters. II - Physical properties of cataloged molecular clouds|
The physical properties of the 148 molecular clouds found in a CO surveyof regions around 34 young open clusters have been examined. Expressionsare given for the cloud size spectrum and the mass spectrum. Themass-radius relation implies that clouds of all size larger than a fewpc have about the same mean volume density. Power laws with slopes of0.6 and 3 describe, respectively, the relations of CO linewidth andcloud mass to cloud size. The clouds are distinctly nonspherical andappear to be randomly oriented with respect to the Galactic plane. Theobservations can be explained by a model for molecular clouds in whichclouds are ensembles of dense clumps of gas. Based on such a model, itis shown that molecular clouds are perturbed on a time scale shortcompared to the time required for them to reestablish virialequilibrium.
|A CO survey of regions around 34 open clusters|
Results are presented from a systematic search for CO emission fromregions around 34 young open clusters in the outer Galaxy. The clustershave well-determined distances ranging from about 1 to 5 kpc and agesnot greater than about 100 Myr. It was found that some moderately youngclusters have no associated CO emission. All the surveyed clustersyounger than about 5 Myr have associated with them at least onemolecular cloud more massive than 10,000 solar mass, while the molecularclouds associated with clusters older than about 10 Myr are not moremassive than a few thousands solar masses. It was also found thatmolecular clouds are receding from young clusters at a rate of about 10km/sec, and that they seem to be destroyed by their interaction with thestars. Sites of ongoing star formation were identified in a number ofclouds associated with young clusters.
|An optical spiral arm beyond the Perseus arm|
In the second galactic quadrant, optical spiral arm tracers have beencollected in a systematic literature search. A uniform reduction of thedata led to the detection of a distinct structure (probably a spiralarm) beyond the Perseus arm that is separated by a statisticallysignificant gap from the latter.
|Component Analysis of Open Clusters|
|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.
|Catalog of open clusters and associated interstellar matter.|
|Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)|
|Interstellare Extinktion entlang (1,b) = (88°.5, -0°.5)|
|Search for Faint Halos of Planetary Nebulae|
|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.
|The absolute masses of 72 galactic clusters and 12 OB associations|
The Reddish (1978) relative masses for 72 open clusters and 12 OBassociations are presently converted to absolute masses, within an errormargin of about 25 percent, using three calibration clusters of knownmass whose average mass is 300 solar masses. The Reddish techniqueassumes the initial stellar mass distribution function to be valid forall aggregates, together with a universal relationship between stellarmass and stellar luminosity.
|Integrated Photometric Parameters of Open and Globular Clusters|
|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.
|The Extinction and the HI Content of the Dark Cloud Complex KHAVTASI:141|
Abstract image available at:http://adsabs.harvard.edu/abs/1981PASJ...33..327S
|Three colour photometry of the five open clusters NGC 7039, NGC 7062, NGC 7067, NGC 7082, IC 1369|
Abstract image available at:http://adsabs.harvard.edu/abs/1973A&AS....9..261H
|First Supplement to the list of transit tables for star numberings in open clusters.|
|Application of the Density-Wave Theory of Spiral Structure: Shock Formation Along the Perseus Arm|
Abstract image available at:http://adsabs.harvard.edu/abs/1972ApJ...173..259R
|A catalogue of galactic star clusters observed in three colours|
Abstract image available at:http://adsabs.harvard.edu/abs/1971A&AS....4..241B
|An atlas of open cluster colour-magnitude diagrams|
|The ages of open clusters|
|Die photometrische Genauigkeit des Palomar Sky Survey bei Anwendung der Durchmessermethode|