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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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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Variable Stars in the Field of NGC 6882/6885: The Case of V381 Vulpeculae and V382 Vulpeculae
We present photometric and spectroscopic results for two reportedδ Scuti stars in the field of NGC 6882/6885. We find that V381 Vulhas a period of 0.1185 days and is a δ Scuti variable, aspreviously reported. The spectra of V382 Vul shows it to be a B3 starand therefore not a δ Scuti. All evidence points to V382 Vul beinga β Cephei star with a period of 0.1808 days. Additionally, wereport five new variables and eight suspected variable stars. Of thefive new variables, two are pulsators and three are eclipsing binarysystems. In our search for new variable stars, we use a ``robust medianstatistic'' that is proven to be better at finding low-amplitudevariables than the traditional error curve approach.
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Delta Scuti Variables in the Field of NGC 6882/85
In the constellation Vulpecula reside two open clusters NGC 6882 and NGC6885. The smaller cluster NGC 6885 is superimposed onto NGC 6882. Recentobservations of the field have led to discoveries that challenge thecurrent classification of these two clusters. We present the resultsfrom a variable star campaign of regions surrounding the heart of thecluster that resulted in the discovery of four new δ Scuti starsand five other candidates. Of the four, one star was found to be a highamplitude pulsator with a period of about 0.205557 days. The remainingcandidates consist of low amplitude stars of which two were found toundergo rapid pulsations. The observations were performed utilizing anapplication of time series CCD photometry using VRI Bessel filters. Datawere obtained using the 0.4-m David Derrick Telescope.Funding for this research was provided by the National ScienceFoundation Research Experience for Undergraduates program hosted by theDept. of Physics and Astronomy at Brigham Young University.
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tex2html_wrap_inlineuvbyb#beta; Photoelectric Photometry of the Open Cluster NGC823
Absolute uvby beta photoelectric photometry of the brightest stars inthe direction of the Open Cluster NGC823 has been secured and ispresented. From the data analysis, reddening, distance, temperature andgravity are determined for the B, A, F stars and, from these, reddeningand a mean distance modulus ( 12.475+/-0.414) to the cluster aredetermined. Also, their membership in the cluster has been establishedand a numerical value of the age is determined through direct comparisonwith theoretical models. A brief analysis of the short period variablestars in the direction of NGC823 is made. We have concluded that theymight not be pre-MS delta Scuti stars.
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Membership in the Region of the Double Cluster h and χ Persei Working from Proper Motions and Positions: Distance Moduli and Extinction in That Galactic Direction
A segregation between cluster members and field stars in the region ofthe double cluster h and χ Persei is accomplished working fromproper motions and positions as kinematic random variables. Theextinction RV and the distance moduli are determined once thephysical cluster members are found.
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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
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Open cluster chemical composition. 1: Later type stars in eight clusters
Abundance analyses of 36 stars associated with eight open clusters (IC2581, NGC 3532, NGC 5822, NGC 6067, NGC 6087, IC 4725 (M25), IC 4756,and NGC 6882/6885) are presented. The stars are primarily evolved G andK giants and supergiants. Cepheids in NGC 6067, NGC 6087, and IC 4725are included as are non-cluster Cepheids near the clusters NGC 3532, NGC6067, and IC 4725. With the addition of a background K giant in IC 4725,the total number of stars is 40. Elemental abundances derived includeLi, C, N, O, the alpha-elements, the Fe peak, and limited data on theheavy elements. The Na abundances of the sample show a gravitydependence in the sense of an increase in the abundance as the gravitydecreases. The CNO abundances indicate that these objects are processed(on the whole), and that they show the O deficiency previously noted inintermediate mass stars by Luck & Lambert (1981, 1985). There arefour stars in the sample which appear to be unprocessed: two giants andtwo supergiants. There are also two super-Li stars in the sample, one ofwhich is most likely a weak G-band star. It is suggested that thesuper-Li F supergiants could be evolved blue stragglers. The moststriking result of the study is the finding that the (O/Na) ratiocorrelates strongly with the gravity and the stellar mass, thus implyingthat there is a nonstandard additional mixing process affecting thesurface abundances of these stars. A promising candidate for the mixingprocess is the turbulent diffusive mixing process proposed byDenissenkov (1993) which brings Na to the surface and which could alsolead to a modification of the oxygen content.
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Development of the Galactic disk: A search for the oldest open clusters
In an extensive charge coupled devices (CCD) photometric survey ofpotential old open clusters, we have identified a number of systems thatare indeed old; some of them are among the oldest of the open clusters.Using our versions of two well-known morphological age indices, onebased on the luminosity difference between the main sequence turnoff andthe horizontal branch and the other on the color difference between theturnoff and the giant branch, we have ranked the open clusters inapproximate order of age. Our data together with previously publishedphotometry of other old open clusters, yields a catalogue of 72 clustersof the age of Hyades or older with 19 of the clusters as old or olderthan M67 (about 5 Gyr). Among the oldest open clusters are Be 17, Cr261, NGC 6791, Be 54, and AM 2. Be 17 and another old cluster, Lynga 7,are possibly as old as the youngest globulars. The data also suggestthat the formation rate of open clusters may have been higher early inthe history of the disk than at intermediate times since numerousclusters have survived from that time.
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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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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.
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Groups of open clusters with common motion in the Galaxy
A method of identifying star groups with common motion in space isapplied to a sample of 66 open clusters with known space velocitycomponents. Eight groups are obtained; out of these, five are probablyreal. It is shown that the motions of the cepheids and the open clustersare analogous in the vicinity of the sun.
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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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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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Radial velocities of stars in five old open clusters
Radial velocities are derived from 76 medium-resolution spectra of 57stars in the old open clusters NGC 2158, NGC 6791 NGC 6882/5, NGC 6939,and NGC 6940. The mean cluster radial velocities are determined to lessthan about 3 km/s. Cluster membership is discussed, and the results arecompared to previous investigations.
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A catalog of some observational data and elements of the galactic orbits of open star clusters
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A Possible Rotation of the System of Open Cluster Complexes
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Star-forming loops in the IRAS sky images
Loops containing diffuse and discrete emission are a feature of the IRASsky images. Some of these loops are limb-brightened shells resultingfrom supernovae or stellar winds acting on the interstellar medium.Secondary star formation appears to have occurred at the surface ofthese shells. A significant proportion of the early-type stars in thesolar neighborhood appear to have formed in stellar loops.
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A photometric study of short period variable stars in open clusters
The photoelectric photometry of known Delta Scuti variable stars inselected open clusters (Coma, Praesepe, Pleiades, Alpha Per, and NGC2264) was carried out in order to determine the periods of pulsation.Multicolor uvby-beta photometry and a search for new variables in otheropen clusters (NGC 2539, NGC 6494, NGC 6882-5, NGC 7062, NGC 7063 andNGC 7686) were also performed.
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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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Washington photometry of open cluster giants - The metal-rich clusters
Abundances of more than one hundred giants in a large sample ofmetal-rich open clusters in the Galaxy are investigated with Washingtonphotometry. Most of these clusters have no high-dispersion spectroscopicabundance determinations. A revision of the empirical abundancecalibrations for Population I giants, based on a much improved data setover previous calibrations, is first presented. The M-T(1) (Feabundance) calibration changes slightly for stars with Fe/H of about-0.5. The C-M (Fe + CN abundance) calibration is substantially alteredfor abundances above solar. The net effect brings the two abundanceindices into close agreement and eliminates the apparent CN enhancementspreviously determined for several open clusters. An enhanced sensitivityto Fe abundance is found for both the M - T(1) and especially the C - Mindex over that determined in previous investigations. Indeed, Delta(C -M) has an Fe abundance sensitivity that exceeds any other photometricabundance index. In view of the relative rarity of CN strengthvariations in Pop I giants, this index is most useful as a metallicityindicator for these stars. Abundances with an uncertainty of about 0.1dex are derived for a total of 18 open clusters observed with theWashington system. The abundances are generally in good agreement withprior abundance analyses. No strong evidence is found for CN variationsor anomalies in any of the clusters. A comparison with Population Ifield giants shows that the open cluster giants have normal CNabundances for their FE abundances.
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On determining membership of open clusters from relative proper motion
We discuss the determination of membership of 42 open clusters. Ouranalysis shows that Vasilevskis' mathematical model can be reasonablyapplied to this case. Our improved version of Sanders' method and ourdefinition of cluster member based on the principles of discriminatoryanalysis effectively exclude stars of low probabilities. It is importantin the study of open cluster to use only those with high probabilities.The effectiveness of the statistical method is closely related to thevelocity distributions of the member and field stars. For fields wherethe error rate is high, it is better to combine other data than propermotion in determining membership.
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On determining membership of open clusters from relative proper motion
The determination of membership of 42 open clusters is discussed. Theanalysis shows that Vasilevskis' (1962) mathematical model can bereasonably applied to this case. The improved version of Sanders' methodand the definition of cluster member based on the principles ofdiscriminatory analysis effectively exclude stars of low probabilities.It is important in the study of open cluster to use only those with highprobabilities. The effectiveness of the statistical method is closelyrelated to the velocity distributions of the member and field stars. Forfields where the error rate is high, it is better to combine other datathan proper motion in determining membership.
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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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Magnesium, silicon, and iron abundances and the cluster metallicity scale
Abundances have been determined for a number of giant stars in open andglobular clusters on the basis of broadband Washington photometry, andhigh-resolution echelle spectroscopy. The photometric observations weremade with the CTIO 91-nm and 1.5 m reflectors, and the KPNO 1.3 mreflector during 44 consecutive nights between May 1980 and September1982. The spectrographic observations were carried out between 1981 andJanuary 1982, with the KNO KPNO 4-m echelle spectrograph. The spectralresolution was approximately 0.3 A and the wavelength coverage was from5500 to 7000 A. The classical metal-rich globular clusters NGC 6352,M69, and M71 are found to have Fe/H values of less than -1. Themetal-poor open clusters NGC 2141, 2158, 2506, and Melotte 66 have Fe/Hvalues ranging from -0.5 to -1.2. Mg and Si were significantly enhancedrelative to Fe in many of the clusters, and a much better correlation isfound between the color of the cluster giant branch and the mean (Mg +Si + Fe) abundance than with the Fe abundance alone. The data for thecluster abundances are presented in a table.
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A radial-velocity study of open clusters containing blue stragglers.
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A Radial Velocity Study of Open Clusters Containing Blue Stragglers
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Catalogue of Eclipsing and Spectroscopic Binary Stars in the Regions of Open Clusters
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