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Blue Straggler Stars in Galactic Open Clusters and the Simple Stellar Population Model
The presence of blue straggler stars (BSs) as secure members of Galacticopen clusters (OCs) poses a major challenge to the conventional pictureof simple stellar population (SSP) models. These are based on thestellar evolution theory of single stars, whereas the major formationmechanisms of BSs are all correlated with stellar interactions. We haveillustrated this in a previous study based on a small sample of old (age>=1 Gyr) Galactic OCs. However, for the purpose of demonstrating thecontributions of BSs to the conventional SSP models statistically andsystematically, a large database with sufficient coverage of age andmetallicity is definitely needed. The working sample now includes 100Galactic OCs with ages ranging from 0.1 to 10 Gyr. The contributions ofBSs to the integrated light of their host clusters are calculated on anindividual cluster basis. The general existence of BSs in our starcluster sample dramatically alters the predictions of conventional SSPmodels in terms of their integrated properties. Neglecting theconsequences of nonstandard evolutionary products, such as BSs, instellar populations, very large uncertainties can be made in analyzingtheir integrated spectral energy distributions at unresolvableconditions. The current work strongly suggests that when evolutionarypopulation synthesis technique is used to study the properties ofunresolved stellar populations in galaxies, the contributions of BSsshould be taken into account.
| 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
| The Overall Properties of Open Clusters Located Towards The Galactic Anticenter Direction: Washington Photometry of NGC 1817 and NGC 2251
We present Washington photometry for red giant candidates in the openclusters NGC 1817 and NGC 2251. Coravel radial velocities are used toseparate field stars from cluster giants. Effective temperatures andmetallicities are derived for each giant star. From new UBV and DDOdata, we also derive reddening and metal content for NGC 2251. We find[Fe/H] = -0.33+/-0.08 and -0.20+/-0.05 for NGC 1817 and NGC 2251,respectively. We reexamine the overall properties of a sample of 30clusters in the Galactic anticenter direction with distances, ages andmetallicities available. No evidence for an age-metallicity relation isfound. However, a radial abundance gradient of -0.093 dex kpc^{-1} isderived over a Galactocentric distance of 14 kpc. This value practicallydoes not change when all clusters with basic parameters known up to thisdate are considered.
| 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.
| Washington photometry of open cluster giants: two moderately metal-poor anticentre clusters
New photometric data in the Washington system are presented for redgiant candidates in NGC 1817 and 2251, two open clusters located towardsthe Galactic anticentre direction. In the case of NGC 2251, theWashington data are supplemented with new UBV and David DunlapObservatory (DDO) photoelectric photometry. Published radial velocitiesare used to separate field stars from cluster giants. The photometricdata yield an effective temperature and metal abundance for each clustermember. Five independent Washington abundance indices yield meanmetallicities of [Fe/H]= 0.25 +/- 0.04 for NGC 1817 and 2251,respectively. From combined BV and DDO data, we also derive E(B-V) =0.21 +/- 0.03 and [Fe/H]DDO=-0.14 +/- 0.05 for NGC 2251. Bothobjects are then found to be on the metal-poor side of the distributionof open clusters, their metallicities being compatible with theexistence of a radial abundance gradient in the disc. Using the WEBDAOpen Cluster data base and the available literature, we re-examined theoverall properties of a sample of 30 clusters located towards theGalactic anticentre with the distances, ages and metallicitiesavailable. This cluster sample presents no evidence of an abundancegradient perpendicular to the Galactic plane, nor is an age-metallicityrelation found. However, a radial abundance gradient of -0.093 dexkpc-1 is derived over a Galactocentric distance of 14 kpc, agradient which is in keeping with most recent determinations. This valuepractically does not change when all clusters with basic parametersknown up to this date are considered.
| 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.
| 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.
| The relatively young and metal-poor Galactic open cluster NGC 2194
We present CCD VIKC photometry down to V~ 21 mag in the fieldof the rich open cluster NGC 2194, which is projected towards theGalactic anticentre direction. We measured V magnitudes and V-I coloursfor a total of 2515 stars in a field of 13.6 × 13.6arcmin2. These data are supplemented with CCD photometry inthe C, M and T1 filters of the Washington system andphotoelectric CMT1T2 photometry of 20 red giantcandidates. Based on the best fits of isochrones computed by the Genevaand Padova groups to the (V, V-I) colour-magnitude diagram, we derive acolour excess E(V-I) = 0.75, a cluster distance of 3.2 kpc and an age of400 Myr. Five independent Washington abundance indices yield a meancluster metallicity of [Fe/H]=-0.27 +/- 0.06, which is compatible withthe existence of both a radial and Z gradient in the Galactic disc. NGC2194 is a relatively young open cluster, whose deficiency in metalcontent can be accounted for by the fact that it was born not only farfrom the Galactic centre in the outer disc, but also at a relativelyhigh Z value.
| On the Galactic Disk Metallicity Distribution from Open Clusters. I. New Catalogs and Abundance Gradient
We have compiled two new open cluster catalogs. In the first one, thereare 119 objects with ages, distances, and metallicities available, whilein the second one, 144 objects have both absolute proper motion andradial velocity data, of which 45 clusters also have metallicity dataavailable. Taking advantage of the large number of objects included inour sample, we present an iron radial gradient of about -0.063+/-0.008dex kpc-1 from the first sample, which is quite consistentwith the most recent determination of the oxygen gradient from nebulaeand young stars, about -0.07 dex kpc-1. By dividing clustersinto age groups, we show that the iron gradient was steeper in the past,which is consistent with the recent result from Galactic planetarynebulae data, and also consistent with inside-out galactic diskformation scenarios. Based on the cluster sample, we also discuss themetallicity distribution, cluster kinematics, and space distribution. Adisk age-metallicity relation could be implied by those properties,although we cannot give conclusive result from the age- metallicitydiagram based on the current sample. More observations are needed formetal-poor clusters. From the second catalog, we have calculated thevelocity components in cylindrical coordinates with respect to theGalactic standard of rest for 144 open clusters. The velocitydispersions of the older clusters are larger than those of youngclusters, but they are all much smaller than that of the Galactic thickdisk stars.
| 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.
| Abundance Gradient from Open Clusters and Implications for the Galactic Disk Evolution
We compile a new sample of 89 open clusters with ages, distances andmetallicities available. We derive a radial iron gradient of about-0.099±0.008 dexkpc (unweighted) for the whole sample, which issomewhat greater than the most recent determination of oxygen gradientfrom nebulae and young stars. By dividing the clusters into age groups,we show that the iron gradient was steeper in the past and has evolvedslowly in time. Current data show a substantial scatter of the clustermetallicities indicating that the Galactic disk has undergone a veryrapid, inhomogeneous enrichment.Also, based on a simple, but quitesuccessful model of chemical evolution of the Milky Way disk, we make adetailed calculation of the iron abundance gradient and its timeevolution. The predicted current iron gradient is about -0.072 dexkpc.The model also predicts a steady flattening of the iron gradient withtime, which agrees with the result from our open cluster sample.
| The CFHT Open Star Cluster Survey. I. Cluster Selection and Data Reduction
We present this paper in conjunction with a companion paper as the firstresults in the Canada-France-Hawaii Telescope Open Star Cluster Survey.This survey is a large BVR imaging data set of 19 open star clusters inour Galaxy. This data set was taken with the CFH12K mosaic CCD(42'×28'), and the majority of the clusters were imaged underexcellent photometric, subarcsecond seeing, conditions. The combinationof multiple exposures extending to deep (V~25) magnitudes with short(<=10 s) frames allows for studies ranging from faint white dwarfstars to bright turnoff, variable, and red giant stars. The primary aimof this survey is to catalog the white dwarf stars in these clusters andestablish observational constraints on the initial-final massrelationship for these stars and the upper mass limit to white dwarfproduction. Additionally, we hope to better determine the properties ofthe clusters, such as age and distance, and also test evolution anddynamical theories by analyzing luminosity and mass functions. In orderto more easily incorporate these data in further studies, we haveproduced a catalog of positions, magnitudes, colors, and stellarityconfidence for all stars in each cluster of the survey. This reduction,along with the computed calibration parameters for all three nights ofthe observing run will encourage others to use these data in differentastrophysical studies outside of our goals. Additionally, the data setis reduced using the new TERAPIX photometric reduction package, PSFex,which is found to compare well with other packages. This paper isintended both as a source for the astronomical community to obtaininformation on the clusters in the survey and as a detailed reference ofreduction procedures for further publications of individual clusters. Wediscuss the methods employed to reduce the data and compute thephotometric catalog. We reserve both the scientific results for eachindividual cluster and global results from the study of the entiresurvey for future publications. The first of these further publicationsis devoted to the old rich open star cluster, NGC 6819, and appears as acompanion paper in the same issue of the Journal.
| 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.
| Baldone Schmidt Telescope Plate Archive and Catalogue
The article presents information on the archive and catalogue of theastrophotos taken with the Schmidt telescope of the Institute ofAstronomy of the University of Latvia (until July 1, 1997 --Radioastrophysical Observatory of the Latvian Academy of Sciences) inthe period 1967--1998. The archive and catalogue contain more than 22000direct and 2300 spectral photos of various sky regions. Information onthe types of photo materials and color filters used as well as on mostfrequently photographed sky fields or objects is given. The catalogue isavailable in a computer readable form at the Institute of Astronomy ofthe University of Latvia and at the Astrophysical Observatory in Baldone(Riekstukalns, Baldone, LV-2125, Latvia), e-mail: astra@latnet.lv.
| Some Revised Observational Constraints on the Formation and Evolution of the Galactic Disk
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.2556T&db_key=AST
| Thirty years of research with the Baldone Schmidt Telescope
We describe the research done with the Baldone Schmidt telescope(80/120/240 cm) of the Radioastrophysical Observatory. The telescope hastwo objective prisms with reciprocal dispersions of 600 and 1130 A/mm atH-gamma. One of the main research projects is the search for andphotometric study of galactic carbon stars. The telescope has also beenused for novae studies in M 31 and stellar photometry in open clustersand fields of special interest. Comet studies, particularly during theInternational Halley Watch, proved to be another successful applicationof the telescope. The archive of the Baldone Schmidt telescope containsnearly 20,000 direct and 2000 spectral plates and films.
| Be stars in open clusters I. uvbyβ photometry.
We present uvbyβ photometry for Be stars in eight open clusters andtwo OB associations. It is shown that Be stars occupy anomalouspositions in the photometric diagrams, which can be explained in termsof the circumstellar continuum radiation contribution to the photometricindices. In the (b-y)_0_-M_V_ plane Be stars appear redder than the nonemission B stars, due to the additional reddening caused by the hydrogenfree-bound and free-free recombination in the circumstellar envelope. Inthe c_0_-M_V_ plane the earlier Be stars present lower c_0_ values thanabsorption-line B stars, which is caused by emission in the Balmerdiscontinuity, while the later Be stars deviate towards higher c_0_values, indicating absorption in the Balmer discontinuity ofcircumstellar origin.
| Chemical Evolution of the Galactic Disk: Evidence for a Gradient Perpendicular to the Galactic Plane
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2813P&db_key=AST
| Probable binary open star clusters in the Galaxy.
The existence of double/binary clusters in the Magellanic Clouds isfairly well established, whereas only one such pair, h + χ Persei,is known in the Galaxy. From the catalogues of open clusters of theGalaxy, we have identified 18 probable pairs of clusters (with knowndistances), with spatial separations less than 20pc. The tidaldisruption timescales for these pairs, due to Galactic differentialrotation are calculated, using cluster data where available or byassuming typical values. In some cases, these timescales are larger thanthe average open cluster lifetime, =~10^8^yr. About 8% of open clustersappear to be members of binary systems, and hence binary cluster systemsmay not be very uncommon in the Galaxy.
| 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.
| The young open clusters NGC 2244 and NGC 2264
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1991RMxAA..22...99P&db_key=AST
| Radial velocities of stars in open clusters
A CORAVEL type spectrometer was used to measure precise radialvelocities of 116 late-type stars of spectral classes F5 - M5 in thefields of 18 open clusters. Probable cluster members were selected onthe basis of kinematic and photometric data. New or improved radialvelocities for 12 open clusters were thus obtained.
| The formation of Be stars through close binary evolution
The possibility that Be stars are the remnants of case B mass transferin intermediate-mass close binaries is investigated. It is shown thatonly progenitors with mass ratios greater than a certain minimum valueq-min are capable of producing a Be star after the mass transfer. Thevalue of q-min lies between 0.3 and 0.5, depending on the evolutionparameters as well as on the observationally determined lower mass limitof Be/X-ray binaries. In more than 80 percent of the predicted systems,the evolved companion is an He star, particularly among the late-type Bstars; these systems may be detectable as XUV sources.
| Liste des étoiles Ap et Am dans les amas ouverts (Edition révisée)
Not Available
| Photographic photometry of DP Mon.
Not Available
| On the universality of initial mass function of open star clusters
The luminosity functions of 23 open star clusters of age less than 1 Gyrare determined by the method of star counts on astronegatives obtainedwith the Schmidt telescope at the Radioastrophysical Observatory of theAcademy of Sciences of the Latvian SSR. The differential and integralluminosity functions are then used to calculate the initial luminosity(mass) functions, and the results are presented in tables. It isconcluded that, for time intervals up to 1 Gyr and distances up to 2kpc, the process of star formation leads to identical mass distributionsin different protoclouds, confirming the hypothesis that theopen-cluster zero-age luminosity function is universally valid.
| Component Analysis of Open Clusters
Not Available
| Catalog of AP and AM stars in open clusters
The previous results of Raab (1922), Markarian (1951), and Collinder(1931) have been used to catalog Ap and Am stars that are in the fieldof open clusters. Tabular data are presented for the clusterdesignation, the HD or HDE number, the right ascension (1900), thedeclination (1900), and the magnitude. Also listed are the spectraltypes and, for certain stars, the probability of cluster membership.
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