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CURious Variables Experiment (CURVE). CCD Photometry and Variable Stars in the Field of Open Cluster NGC637
We present VI photometry for the open cluster NGC 637 which is locatedin the Cassiopeia region. Morphology of cluster color-magnitude diagramindicates that it is a young object with age of a few million years. Theapparent distance modulus of the cluster is 13.9<(m-M)_V<14.3 mag,while reddening is 0.69
| 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.
| 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.
| Analysing the database for stars in open clusters. I. General methods and description of the data
We present an overview and statistical analysis of the data included inWEBDA. This database includes valuable information such as coordinates,rectangular positions, proper motions, photometric as well asspectroscopic data, radial and rotational velocities for objects of openclusters in our Milky Way. It also contains miscellaneous types of datalike membership probabilities, orbital elements of spectroscopicbinaries and periods of variability for different kinds of variablestars. Our final goal is to derive astrophysical parameters (reddening,distance and age) of open clusters based on the major photometric systemwhich will be presented in a follow-up paper. For this purpose we havechosen the Johnson UBV, Cousins VRI and Strömgren uvbybetaphotometric systems for a statistical analysis of published data setsincluded in WEBDA. Our final list contains photographic, photoelectricand CCD data for 469 820 objects in 573 open clusters. We have checkedthe internal (data sets within one photometric system and the samedetector technique) and external (different detector technique) accuracyand conclude that more than 97% of all investigated data exhibit asufficient accuracy for our analysis. The way of weighting and averagingthe data is described. In addition, we have compiled a list of deviatingmeasurements which is available to the community through WEBDA.
| Distances to Cepheid open clusters via optical and K-band imaging
We investigate the reddening and main-sequence-fitted distances to 11young, Galactic open clusters that contain Cepheids. Each clustercontains or is associated with at least one Cepheid variable star.Reddening to the clusters is estimated using the U-B:B-V colours of theOB stars and the distance modulus to the cluster is estimated via B-V:Vand V-K:V colour-magnitude diagrams. Our main-sequence fitting assumesthat the solar-metallicity zero-age main sequence of Allen appliesuniversally to all the open clusters, although this point iscontroversial at present. In this way we proceed to calibrate theCepheid period-luminosity (PL) relation and find MV=-2.87× logP- 1.243 +/- 0.09, MK=-3.44 × logP- 2.21 +/-0.10 and absolute distance moduli to the Large Magellanic Cloud (LMC) of18.54 +/- 0.10 from the V-band and 18.48 +/- 0.10 from the K-band givingan overall distance modulus to the LMC of μ0= 18.51 +/-0.10. This is in good agreement with the previous Cepheid PL-K result ofLaney & Stobie at μ0= 18.51 +/- 0.09 and with theHipparcos parallax-calibrated Cepheid PL-K estimate of Feast &Catchpole at μ0= 18.66 +/- 0.10 when no account is takenof the LMC metallicity.We also find that the two-colour U-B:B-V diagrams of two importantclusters are not well fitted by the standard main-sequence line. In onecase, NGC 7790, we find that the F stars show a UV excess and in thesecond case, NGC 6664, they are too red in U-B. Previous spectroscopicestimates of the metallicity of the Cepheids in these clusters appear tosuggest that the effects are not due to metallicity variations. Otherpossible explanations for these anomalies are positional variations inthe dust reddening law and contamination by foreground or backgroundstars.
| 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.
| Interstellar extinction in the open clusters towards galactic longitude around 130deg
In this paper we present a detailed study of the intra-cluster reddeningmaterial in the young open clusters located around l ~ 130degusing colour-excess diagrams and two-colour diagrams. The study supportsthe universality of the extinction curves for lambda >= lambdaJ, whereas for shorter wavelengths the curve depends upon thevalue of the Rcluster (total-to-selective absorption in thecluster region). The value of Rcluster in the case of NGC654, NGC 869 and NGC 884 is found to be normal, whereas the value ofRcluster in the cluster regions NGC 1502 and IC 1805indicates an anomalous reddening law in these regions. In the case ofNGC 1502 the value of Rcluster is found to be lower(2.57+/-0.27) whereas in the case of IC 1805 it is higher (3.56+/-0.29)than the normal value of 3.1. Although the intra-cluster materialindicates a higher value of Rcluster in the NGC 663 region,the error in the estimation of Rcluster is too large toconclude anything. It is also found that the extinction process in the Uband in the case of NGC 663 seems to be less efficient, whereas in thecase of NGC 869 the process is more efficient.
| Morphological analysis of open clusters' propertiesII. Relationships projected onto the galactic plane
A morphological analysis study of open clusters' properties has beenachieved for a sample of 160 UBVCCD open star clusters of approximately128,000 stars near the galactic plane. The data was obtained and reducedfrom using the same reduction procedures, which makes this catalogue thelargest homogeneous source of open clusters' parameters.
| Integrated photometric characteristics of galactic open star clusters
Integrated UBVRI photometric parameters of 140 galactic open clustershave been computed. Integrated I(V-R)0 and I(V-I)0colours as well as integrated parameters for 71 star clusters have beenobtained for the first time. These, in combination with published data,altogether 352 objects, are used to study the integrated photometriccharacteristics of the galactic open clusters. The I(MV)values range from -9.0 to -1.0 mag corresponding to a range in totalmass of the star clusters from ~ 25 to 4*E4 Msun.The integrated colours have a relatively narrow range, e.g., I(B-V){_0}varies from -0.4 to 1.2 mag. The scatter in integrated colours at agiven integrated magnitude can be understood in terms of differences infraction of red giants/supergiants in the clusters. The observedintegrated magnitudes and colours agree with the synthetic ones, exceptthe dependences of I(V-R)0 and I(V-I)0 colours forclusters younger than ~ 100 Myrs and also of the integrated magnitudesof oldest clusters. The large sample provides the most accurate agedependence of integrated magnitudes and colours determined so far. Theluminosity function of the I(MV) has a peak around -3.5 magand its slope indicates that only ~ 1% of the open clusters in thegalactic disc are brighter than I(MV)=-11 mag. No variationhas been found of integrated magnitude with galactocentric distance andmetallicity.
| BOAO Photometric Survey of Galactic Open Clusters. II. Physical Parameters of 12 Open Clusters
We have initiated a long-term project, the BOAO photometric survey ofopen clusters, to enlarge our understanding of Galactic structure usingUBVI CCD photometry of open clusters, which have been little studiedbefore. This is the second paper of the project, in which we present thephotometry of 12 open clusters. We have determined the clusterparameters by fitting the Padua isochrones to the color-magnitudediagrams of the clusters. All the clusters except for Be 60 and NGC 1348are found to be intermediate-age to old (0.2-4.0 Gyrs) open clusterswith a mean metallicity of [Fe/H]~0.0.
| NGC 2571: An intermediate-age open cluster with a White Dwarf candidate
CCD UBVI imaging photometry was carried out in the field of the opencluster NGC 2571. From the analysis of our data we state the cluster isat a distance of 1380 +/- 130 pc and its age is 50 +/- 10 x106 yr. The cluster mass function has a slope larger than atypical Salpeter's law. There are two notorious features in NGC 2571:the cluster contains a high proportion of stars located below thereference line that are serious candidates to be metallic line stars(probably Am-Fm), and shows also a sharp gap along its main sequencethat cannot be explained by a random process nor by a biased rejectionof cluster members. A striking blue object was detected in the clusterfield that could be a white dwarf candidate. Based on observationscollected at the European Southern Observatory ESO at La Silla, Chile.
| Morphological analysis of open clusters' propertiesI. Properties' estimations
A sample of 160 UBVCCD observations of open star clusters near thegalactic plane has been studied, and a catalogue of their propertiesobtained. The main photometrical properties have been re-estimated selfconsistently and the results have been compared with those of Lynga[Lynga, G., 1987. Catalog of Open Cluster Data, 5th Edition, StellarData Centers, Observatoire de Strasbourg, France].
| Statistical parallaxes and kinematical parameters of classical Cepheids and young star clusters
The statistical-parallax method is applied for the first time to spacevelocities of 270 classical Cepheids with proper motions adopted fromHIPPARCOS (1997) and TRC (Hog et al. 1998) catalogs and distances basedon the period-luminosity relation by Berdnikov et al. (1996). Thedistance scale of short-period Cepheids (with periods less than 9 days)is shown to require an average correction of 15-20%, whereas statisticalparallaxes of Cepheids with periods > 9 days are found to agree wellwith photometric distances. It is shown that the luminosities ofshort-period Cepheids must have been underestimated partly due to thecontamination of this subsample by a substantial (20 to 40%) fraction offirst-overtone pulsators. The statistical-parallax technique is alsoapplied for the first time to 117 open clusters younger than 100 millionyears and with proper motions reduced to the HIPPARCOS reference system.It is concluded that a 0.12-0.15 mag increase of the distance scales ofopen clusters and Cepheids would be sufficient to reconcile thestatistical-parallax results inferred for these two types of objects.Such approach leads to an LMC distance modulus of less than 18.40 mag,which agrees, within the errors, with the short distance scale for RRLyrae variables and is at variance with the conclusions by Feast andCatchpole (1998) and Feast et al. (1998), who argue that the LMCdistance modulus should be increased to 18.70 mag. The distance scalebased on the Cepheid period-luminosity relation by Berdnikov and Efremov(1985) seems to be a good compromise. Extragalactic distances, whichrely on long-period Cepheids, seem to require no substantial correction.In addition to statistical parallaxes, kinematical parameters have beeninferred for the combined sample consisting of Cepheids andopen-clusters: solar-motion components (U0 ,V0,W0) = (9, 12, 7) km/s (+/- 1 km/s); velocity-ellipsoid axes(σU; σV; σW) = (15.0,10.3, 8.5) km/s (+/- 1 km/s); the angular velocity of rotation of thesubsystem, ω0 = 28.7 +/- 1 km/s/kpc, the Oort constantA = 17.4 +/- 1.5 km/s, and the second derivative of angular velocity,⋰ω0= 1.15 +/- 0.2 km/s/kpc3.
| Absolute proper motions of 181 young open clusters.
Not Available
| Estimates of geometric and dynamic parameters of star-gas complexes in the Galaxy
Parameters of geometric models of 11 gas-star complexes (GSCs) wereobtained. We used information about GSC projections onto the celestialsphere and the Galactic plane and about GSC extension along the line ofsight. GSCs were represented as triaxial ellipsoids. To estimate thesemiminor axis of the GSC ellipsoidal model and GSC slope angle to theGalactic plane, we used data on spatial location of open stellarclusters (OSCs) entering GSCs. GSC slopes to the Galactic plane varybetween 2.5 and 20.5 deg. Their semiminor axes are between 11 and 164pc. GSC total masses are estimated from GSC tidal effect on OSCs thatare members of the corresponding GSCs. The effect manifests itself insmaller sizes of young OSCs as compared to their tidal sizes in theforce field of the Galaxy. We used studies of stability of an OSC movingin the joint force field of the Galaxy and spheroidal stationary GSC, aswell as studies of evolution of a virialized cluster located at thecenter of a nonstationary ellipsoidal GSC. Estimated total masses fordifferent GSCs lie between 0.65 x 10 exp 5 solar masses and 11.5 x 10exp 7 solar masses.
| 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.
| Young open clusters as probes of the star formation process. 1: an atlas of open cluster photometry
We have obtained charge coupled device (CCD) photometry, in the UBVsystem, for 23 open clusters in order to explore the star formationhistory of the Cassiopeia region of the Perseus spiral arm of ourGalaxy. Magnitudes and colors of 35,788 stars were measured, making thisthe most comprehensive, homogeneous single study of open clusterproperties in one part of the Galaxy. This paper presents an atlas ofopen cluster photometry that serves as the database for an investigationof cluster properties such as their ages, distances, reddenings, sizes,and richnesses. This information provides insight into the spatial andtemporal formation sequence of the clusters and allows an investigationof the stellar content of the clusters to be undertaken.
| New Color Magnitude Diagrams for NGC 637 and NGC 7245
We present new color-magnitude diagrams for the open clusters NGC 637and NCG 7245. CCD images were taken in the UBVR system for NGC 637 andin the BVR system for NGC 7245 at the Lowell Observatory 42-inchtelescope. The distance modulus and the age are determined for bothclusters; the color excess for NGC 637 is derived. NGC 7245 has notpreviously been measured in the BVR system, and neither cluster has beenanalyzed photometrically with a CCD. The improved accuracy ofphotometric measurement of CCD images over photographic methods givesincreased accuracy for the age and distance.
| More radial-velocity measurements in young open clusters
Further high resolution radial-velocity measurements are reported in 23young open clusters using the Kitt Peak CCD coude spectrograph on the0.9-m feed telescope. The radial velocities for the cluster stars arederived with the technique of cross correlation. The internal precisionof the velocity measurements is typically 2 km/s for early type stars.From these new data and previously published velocities, the observedstars in two clusters, NGC 663 and NGC 2287, were found to show arelatively small dispersion in the measured mean velocities. Furtherobservations of stars in young clusters will be useful in helping toestablish an early-type-star-velocity standard system.
| UBV photometry of open clusters in the Cassiopeia region. I - Photoelectric observations of NGC436 and 637
Abstract image available at:http://adsabs.harvard.edu/abs/1991A&AS...87..153H
| Some characteristics of complexes of open star clusters
Mean coordinates and velocities, phase sizes, mean elements of galacticorbits, mean ages, and metal abundances are given for 11 complexes ofopen clusters, and correlations between these characteristics arediscussed. The possible existence of a supercomplex encompassing 9 or 10complexes, and probably a number of individual clusters, is discussed.This rotates at an angular velocity of 10 to 13 km/s kpc.
| Radial-velocity measurements in 20 young open clusters
The further results of a program to determine the radial velocities ofyoung open clusters are presented. Using the KPNO coude spectrographcoupled with the 1-m feed and 2.1-m telescopes, radial velocities havebeen measured for nearly one hundred stars, most of which are ofspectral type B and A, in 20 young clusters. The combination ofinstruments and the use of cross-correlation techniques show that radialvelocities of B and A type stars as faint as 10th magnitude can bedetermined with an internal precision of less than about 2 km/s. Asexpected, the uncertainties in the velocity determination for the youngclusters are dominated by spectroscopic binary stars in these clusters.A third of the stars in the sample are found to be spectroscopicbinaries, but with a large variation in the frequency of binaries fromcluster to cluster. Because the time coverage is still limited, thisshould be considered a lower limit to the binary frequency. Clustervelocities are determined after eliminating binaries and known nonmemberstars. The new velocities are compared with a model galactic rotationcurve, as well as with previous velocity determinations.
| 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
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.
| 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.
| On Statistics of Star Complexes
Not Available
| 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.
| Stellar and molecular radial velocities for six young open clusters
Radial velocities for 24 stars in six young open clusters (Be 59, NGC581, NGC 637, NGC 654, NGC 1778, and NGC 2169) in the second and thirdgalactic-longitude quadrants have been obtained. Most of the observedstars are of spectral type B, and the present measurements have aninternal accuracy of about + or - 2 km/s. Mean cluster velocities werederived based on these velocity measurements. For Be 59 and NGC 1778,these are the first published cluster velocities. Radial velocities ofmolecular clouds near four of the six clusters - Be 59, NGC 581, NGC637, and NGC 654 - have also been determined by CO observations in orderto compare with the stellar velocities.
| Catalog of open clusters and associated interstellar matter.
Not Available
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