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New catalogue of blue stragglers in open clusters
We present a catalogue of blue-straggler candidates in galactic openclusters. It is based on the inspection of the colour-magnitude diagramsof the clusters, and it updates and supersedesthe first version(Ahumada & Lapasset 1995). A new bibliographical search was made foreach cluster, and the resulting information is organised into twotables. Some methodological aspects have been revised, in particularthose concerning the delimitation of the area in the diagrams where thestragglers are selected.A total of 1887 blue-straggler candidates have been found in 427 openclusters of all ages, doubling the original number. The catalogued starsare classified into two categories mainly according to membershipinformation.The whole catalogue (Tables 8, 9, notes, and references) is 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/463/789
| Calibration of a UBVRI sequence around Nova Cyg 2006
A highly accurate UBV(RI)c photometric sequence around Nova Cyg 2006 ispresented. The photometric stability of the stars in the sequence hasbeen checked on 12 different nights. The sequence is linked to theLandolt's equatorial standards for (RI)c bands and to UBV photoelectricphotometry of selected open clusters by Hoag et al. (1961).
| A Dozen δ Scuti Stars in the Open Cluster NGC 1817
We obtained high-precision time-series observations of stars in the opencluster NGC 1817 in order to find δ Scuti stars among the clustermembers. The detection of 12 δ Scuti stars, of which our datasuggest that 11 are cluster members, makes NGC 1817 a key target forasteroseismology of 1.5-2.5 Msolar stars. One of the clustermember δ Scuti stars is also an eclipsing binary, potentiallyoffering very strong constraints for theoretical modeling. In addition,we find one δ Scuti star candidate, a γ Dor candidate, twovariables of currently unknown type, and two eclipsing binary systems.We also describe a method for combining the oscillation frequencies ofseveral δ Scuti stars in a single cluster to obtain informationabout the order n of the excited modes. This method will eventually beused to constrain the theoretical models to be compared with preciseoscillation frequencies determined from a future multisite campaign(asteroseismology).
| Comparison of the Luminosity Functions of Open Clusters Based on USNO-A1 Data
The luminosity and mass functions of a group of Galactic open clustersare constructed by applying a statistical method to photometric datafrom the USNO-A1 catalog. Despite some limitations, this catalog can beused for statistical analyses in Galactic astronomy. Pairwisecomparisons of the derived cluster luminosity functions are performedfor five age intervals. The differences between the luminosity functionsof the open clusters are not statistically significant in most cases. Itis concluded that the luminosity functions are approximately universalthroughout a large volume in the solar neighborhood. Combined luminosityand mass functions are constructed for six age intervals. The slope ofthe mass spectrum may vary somewhat from cluster to cluster, and themean slope may be somewhat higher than the Salpetervalue.
| A search for variable stars in Trumpler 24
Trumpler 24 is a comparatively poorly-studied young open cluster. Toinvestigate the correlation between the Be phenomenon and the clusterage, and to study the stellar variability in Trumpler 24, CCDtime-series observations were made in 2001, and spectra were obtained in2002. The results reveal 21 new variable stars, including 3 eclipsingbinaries, no Be stars.
| Search for variable stars in the open cluster NGC 2539
We present UBVI absolute and V-band time-series CCD photometric resultsfor the intermediate-age open cluster NGC 2539. From the empiricalzero-age main sequence and theoretical isochrone fitting in color-colorand color-magnitude diagrams, we estimated the physical parameters ofthis cluster as follows: the color excess of E(B-V)=0.06 +/- 0.03, thedistance modulus of (V-MV)0=10.2 +/- 0.1 and theage of log t = 8.8 ( ~ 630 Myr). By carefully examining the time-seriesimages, we discovered seven new variable stars in the observed clusterfield. Considering the light curves, periods and positions on thecolor-magnitude diagram, we classified them as five eclipsing binarystars, one delta Scuti star and one gamma Doradus candidate. The gammaDoradus candidate might not be a cluster member because it is locatedredder by about Delta (B-V) = 0.2 than the cool edge of gamma Doradusinstability strip.
| 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.
| Cluster Distances using Delta Scuti Stars; The Open Clusters Praesepe and NGC 7062
Asteroseismology of multiperiodic δ Scuti stars is a powerful toolfor providing estimates of distances to the stars being analyzed.Especially δ Scuti stars in clusters offer good possibilities fordetermining asteroseismic distances, as the stellar models areconstrained by assuming common values for chemical composition, age anddistance. Recently, we detected a large population of δ Scutistars in the open cluster NGC 7062. On the basis of these results, wediscuss the potential of extending the asteroseismic distance scale forδ Scuti stars to include extra-galactic stellar clusters.Especially high--amplitude δ Scuti stars, pulsating in at least 2radial modes, offer promising possibilities for doing this.
| Multimode delta Scuti stars in the open cluster NGC 7062
The central field of NGC 7062 was observed intensively with the maingoal of finding delta Scuti stars suitable for use inasteroseismological tests of stellar structure and evolution theory. BVtime series photometry was obtained for this northern open cluster,which has a large population of stars inside the delta Scuti instabilitystrip, making it a probable host of several such variables. We reportfindings of 15 pulsating stars, including at least 13 delta Scuti stars.Ten variables oscillate in two or more frequencies. Only one of thesevariables was known before, for which we detected 9 frequencies. Fiveprobable variables are mentioned, and period analysis is given for all20 stars. Based on observations obtained at the Nordic OpticalTelescope, operated on the island of La Palma jointly by Denmark,Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio delRoque de los Muchachos of the Instituto de Astrofisíca deCanarias.
| delta Scuti and related stars: Analysis of the R00 Catalogue
We present a comprehensive analysis of the properties of the pulsatingdelta Scuti and related variables based mainly on the content of therecently published catalogue by Rodríguez et al.(\cite{retal00a}, hereafter R00). In particular, the primaryobservational properties such as visual amplitude, period and visualmagnitude and the contributions from the Hipparcos, OGLE and MACHOlong-term monitoring projects are examined. The membership of thesevariables in open clusters and multiple systems is also analyzed, withspecial attention given to the delta Scuti pulsators situated ineclipsing binary systems. The location of the delta Scuti variables inthe H-R diagram is discussed on the basis of HIPPARCOS parallaxes anduvbybeta photometry. New borders of the classical instability arepresented. In particular, the properties of the delta Scuti pulsatorswith nonsolar surface abundances (SX Phe, lambda Boo, rho Pup, delta Deland classical Am stars subgroups) are examined. The Hipparcos parallaxesshow that the available photometric uvbybeta absolute magnitudecalibrations by Crawford can be applied correctly to delta Scutivariables rotating faster than v sin i ~ 100 km s{-1} withnormal spectra. It is shown that systematic deviations exist for thephotometrically determined absolute magnitudes, which correlate with vsin i and delta m1. The photometric calibrations are found tofit the lambda Boo stars, but should not be used for the group ofevolved metallic-line A stars. The related gamma Dor variables and thepre-main-sequence delta Scuti variables are also discussed. Finally, thevariables catalogued with periods longer than 0fd 25 are examined on astar-by-star basis in order to assign them to the proper delta Scuti, RRLyrae or gamma Dor class. A search for massive, long-period delta Scutistars similar to the triple-mode variable AC And is also carried out.
| 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
| 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.
| A search for delta Scuti stars in northern open clusters. I. CCD photometry of NGC 7245, NGC 7062, NGC 7226 and NGC 7654
In an effort to test stellar structure and evolution models, analysis ofoscillations in A and F stars in open clusters is carried out by theSTACC network (Frandsen \cite{stacc}). In this paper we describe oureffort to locate a suitable open cluster in the northern hemisphere fora future multi-site campaign. We present BV Johnson and time series CCDphotometry of four poorly studied open clusters: NGC 7245, NGC 7062, NGC7226 and NGC 7654. New improved colour-magnitude diagrams for these fournorthern hemisphere clusters, together with the results from the searchfor variable stars in the clusters are presented. The cluster reddening,distance and age are estimated from isochrone fitting. In the fourclusters, we discovered a total of two delta Scuti stars, one eclipsingbinary, one variable of unknown type and evidence for 3 potentialvariables all situated within the delta Scuti instability strip. We findthat the fraction of delta Scuti stars in these four open clusters ismuch lower than among field stars and in other open clusters suggestingthat some additional parameters control the pulsation, parameters thatwe do not understand at this moment.
| Parameters of open star clusters from uvby-beta photometry.
Not Available
| 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.
| UVBY-beta photometry of the open clusters NGC 1662 and NGC 2129.
Abstract image available at:http://adsabs.harvard.edu/abs/1994RMxAA..29..125P
| A seven-year northern sky survey of AP stars for rapid variability
A high-speed photometric survey of 120 Ap stars in the northern sky, hasbeen conducted, between 1985 and 1991, in order to search for rapidvariability. Stars of spectral types, namely from B8 to F4, have beenselected for the survey. The selected pulsational variable stars occupythe hotter regions of the instability strip of the Hertzsprung-Russeldiagram. Noted is the absence of pulsations in the hotter B8-A3 Apstars; this does not, however, preclude the existence of pulsations,since HD 218495 was recently discovered to be a rapidly oscillating Ap(roAp) star. The primary result of this study is that variouscombinations of photometric indices, while pointing towards roAp starshaving the characteristic signatures of cool, SrCrEu stars, still failto isolate the roAp phenomenon from similar nonpulsating Ap stars.Color-magnitude and color-color diagrams are presented in order tocomplete this survey.
| Uvby-beta photoelectric photometry of the open cluster NGC 7062.
Abstract image available at:http://adsabs.harvard.edu/abs/1990RMxAA..20..127P
| Numerical taxonomy for open clusters.
Abstract image available at:http://adsabs.harvard.edu/abs/1990RMxAA..21..305T
| 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.
| 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.
| Catalog of open clusters and associated interstellar matter.
Not Available
| The distribution of interstellar dust in nine regions near the Galactic plane
Not Available
| A spiral model of the Galaxy from observations of interstellar light extinction
A model of the two-arm spiral structure of the Galaxy is constructedfrom observations of the spatial distribution of interstellar dust. Themodel is a logarithmic spiral with a characteristic angle of 6.5 deg.
| 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.
| Age distribution of open clusters as a function of their linear diameter and age-dependence of cluster masses
From the well-observed data of star clusters, the age distribution ofgalactic clusters is obtianed as a function of their linear diameter andit is concluded that the observed age distribution of clusters fordifferent linear diameter intervals within 1500 pc, is not seriouslyaffected by the selection effects. If we assume that the rate offormation of clusters is constant, the lifetimes r112 of the clustersfor different linear diameter intervals have been obtained and it isfound that the clusters with a linear diameter in the range 0-1.9 Pchave longer lifetimes than the clusters having linear diameters largerthan 2.0 Pc. Total masses of 57 clusters have been obtained using thecatalogues of Piskunov (1983) and Myakutin et al. (1984). A study ofage-dependence of cluster masses, based on the total masses of theclusters obtained in the present study and the cluster masses given byBruch and Sanders (1983) and Lynga (1983b), shows that there is adecreasing trend in the total mass with the age, however, there is anincreasing trend after the age of about 108 yr. It is also concludedthat the initial rate of formation of rich clusters was relativelyhigher than the present rate of formation
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