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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
| 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.
| 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.
| 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.
| The relatively young, metal-poor and distant open cluster NGC 2324
We have obtained CCD photometry in the Johnson V, Kron-Cousins I andCT1 Washington systems for NGC 2324, a rich open clusterlocated 35° from the Galactic anticentre direction. We measuredV magnitudes and V-I colours for 2865 stars and T1 magnitudesand C-T1 colours for 1815 stars in an area of 13.6 arcmin× 13.6 arcmin. The comparison of the cluster colour-magnitudediagrams with isochrones of the Geneva group yield E(V-I) = 0.33± 0.07 and V-MV = 13.70 ± 0.15 for log t = 8.65(t = 440 Myr) and Z = 0.008 ([Fe/H] = -0.40), and E(C-T1) =0.40 ± 0.10 and T1-MT1 = 13.65 ±0.15 for the same age and metallicity level. The resulting E(V-I)reddening value implies E(B-V) = 0.25 ± 0.05 and a distance fromthe Sun of (3.8 ± 0.5) kpc. Star counts carried out within andoutside the cluster region allowed us to estimate the cluster angularradius as 5.3 arcmin ± 0.3 arcmin (5.9 pc). When using the E(B-V)reddening value here derived and the original Washington photometricdata of \citet{gcm91} for the stars confirmed as red cluster giants fromCoravel radial velocities, we found [Fe/H] = -0.31 ± 0.04, whichis in good agreement with the best fits of isochrones. Therefore, NGC2324 is found to be a relatively young, metal-poor and distant opencluster located beyond the Perseus spiral arm. A comparison of NGC 2324with 10 well-known open clusters of nearly the same age shows that thecluster metal abundance and its position in the Galaxy are consistentwith the existence of a radial abundance gradient of -0.07 dexkpc-1 in the Galactic disc.
| 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.
| Study of the Per OB2 star forming complex. II. Structure and kinematics
The study of a sky area with a 20 degree diameter centered on the nearbyassociation Per OB2 has been carried out on the basis of the ``CompiledCatalogue of Astronomical Data in the Per OB2 Field'' presented in aprevious paper. The catalogue contains about 30 000 stars with accurateproper motions in the Hipparcos system as well as magnitudessupplemented with spectral classes and other relevant data. We appliedthe reduced proper motion technique to estimate individual distances foralmost all catalogue stars. The distributions of reddening andinterstellar extinction were determined on the basis of the spectralclassification of stars in the area. Proper motions were corrected fordifferential rotation of the Galactic disk and parallactic motioneffects and used for the evaluation of association membership. Theanalysis of a uniform subset of main sequence (MS) stars earlier than A7- which is complete within 500 pc - has clearly revealed the associationas an area of enhanced density with an angular size of about7o. In comparison to the previous results on Per OB2, we showthat the presently determined area extends the association from itsclassical position towards the California nebula and the Auriga darkcloud. There are 1025 MS proper motion members residing in this region.The distance to the association centre derived from a kinematiccalibration is found to be about 300 pc i.e., in perfect agreement withthe Hipparcos data. The shape of the association is almost spherical,and its diameter found from stellar counts is about 40 pc. Anexamination of internal systematic motions from proper motion data hasshown that there is no evidence of an expansion or a rotation of theassociation around the line of sight. The average tangential and spatialvelocity vectors of Per OB2 with respect to the LSR are determined as(Vl, Vb)=(+7.2+/-0.4,+2.0+/-0.3) km s-1and (U, V, W)=(+12.7+/- 1.6,-3.0+/- 0.6,-0.9+/- 0.8) km s-1.
| 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.
| 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
| 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.
| Luminosity and mass function of galactic open clusters I. NGC 4815
We present deep V and I photometry for the open cluster NGC 4815 andfour surrounding Galactic fields down to a limiting magnitude V ~ 25.These data are used to study cluster spatial extension by means of starcounts, and to derive the luminosity (LF) and mass function (MF). Theradius turns out to be 3.6+/-0.3 arcmin at V=19.0, whereas the mass is880+/-230 msun down to V=20.8. From the color-magnitudediagram, we obtain the LFs in the V and I bands, using both the standardhistogram and an adaptive kernel. After correction for incompletenessand field star contamination, the LFs were transformed into the presentday mass functions (PDMF). The PDMFs from the V and I photometry can berepresented as a power-law with a slope alpha = 3.1+/-0.3 and alpha =2.9+/-0.3 (the (Salpeter \cite{salp55}) MF in this notation has a slopealpha = 2.35) respectively, in the mass range 2.5 <=(m)/(msun) <= 0.8. Below this mass, the MF cannot beconsidered as representative of the cluster IMF, as it is the result ofthe combined effect of strong irregularities in the stellar background,probable internal dynamical evolution of the cluster and/or interactionof the cluster with the dense Galactic field. Unresolved binaries andmass segregation can only flatten the apparent derived IMF, so we expectthat the real IMF must be steeper than the quoted slope by an unknownamount. Based on observations made at the European Southern Observatory,La Silla, Chile.
| 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.
| Corridors in the regions of young open stellar clusters.
Not Available
| UBVR surface photometry of the late type galaxies NGC 523 and NGC 7678
Results of UBVR surface photometry of the two late type galaxies NGC 523and NGC 7678 are presented. The observations were made on the 1-mtelescope at Maidanak Observatory (Uzbekistan) using an electronic imageconverter. Regions of star formation in the galaxies are identified andstudied. The composition of the stellar population in the star-formingregions is estimated using (U_B)_0_(B_V)_0 two-color diagrams. Themechanisms stimulating star formation in NGC 523 and NGC 7678 arediscussed.
| Parameters of open star clusters from uvby-beta photometry.
Not Available
| Cluster membership determinations from proper motion surveys
Not Available
| 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
| On Coagulation and the Stellar Mass Spectrum
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...452..652A&db_key=AST
| CCD Photometry for the Open Cluster NGC 1342
We present BVI CCD color-magnitude diagrams for the Galactic opencluster NGC 1342. The photometry, which was obtained using the 0.9-mtelescope at Kitt Peak National Observatory, extends from the mainsequence turnoff at V ~ 9 to V ~ 18. We fit a theoretical zero-age mainsequence to the observed one in order to derive the cluster reddeningand distance. The age is derived via a comparison to theoreticalisochrones. We also investigate the effects of differential reddening onthe morphology of the color-magnitude diagram.
| 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
| CNO isotopes in red giants: theory versus observations
Evolutionary models in the mass range 1.7 to 15 Msun_ havingsolar-like initial composition are presented. The models are calculatedwith the latest opacities and with the Schwarzschild criterion forconvective instability. In test cases, core overshooting has beenincluded in a parameterized way. Up-dated nuclear reactions have beenused to follow the nucleosynthesis during the evolution which has beencarried out beyond core He-burning at masses > 2 Msun_.The 2 Msun_ model has been evolved through the core He-flash.The resulting surface CNO isotopic ratios after the first and seconddredge-up phases are compared with observations of field giants as wellas with data obtained for galactic open clusters. A comparison betweenrecent theoretical predictions of these ratios is also presented. Thegoal of this work is twofold: (i) to test mass estimations of theobserved giants on the basis of the predicted surface abundance ratiosof ^12^C/^13^C, ^16^O/^17^O and ^16^O/^18^O, and the evolutionarytracks, (ii) to show that ^16^O/^17^O ratio obtained in giant models atM>2 Msun_ is rather sensitive to the still uncertain^17^O(p,α)^14^N reaction. The main results of the present work areas follows: (i) our one-dimensional dynamical calculations show that the2 Msun_ model survives the core He-flash, (ii) we are able toestimate the masses of 6 observed giants out of 11. In addition, thesupergiant star α Sco is well described by a model of initially 15Msun_. (iii) the observed low ^12^C/^13^C ratios in manygiants with M>2 Msun_ cannot be explained in terms of asimple dredge-up scenario or by the variation of the initial value.These ratios are barely influenced by the effect of "moderate"overshooting, (iv) We find that the calculated Na enrichment resultingfrom the Ne-Na cycle does not match the values suggested by currentobservations.
| Uvby-beta photometry of open clusters. II. NGC 1342.
Abstract image available at:http://adsabs.harvard.edu/abs/1994RMxAA..28....7P
| The lithium abundance in stars
The lithium abundance determinations in premain-sequence (Population Iand II), subgiant, and giant stars are reviewed in order to show how Lican be used as a constraint on stellar hydrodynamics and in particularon particle transport processes in stars. Observations revealed thetight Li abundance dependence on Teff in the Hyades, the time dependenceof the Li abundance below Teff = 6000 K, the presence of an Li gap atTeff = 6700 K in young clusters, and the large Li abundance in somepeculiar giants. Models including progressively more physical propertiesare compared to the observed abundances. Li establishes the limits ofvalidity of the standard stellar evolution models. Evolutionary modelstaking into account diffusion and meridional circulation can clarifymost observations. The Li gap is considered to be due to gravitationalsettling with some probable contribution from meridional circulation.
| 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.
| 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.
| 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.
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