New magnetic chemically peculiar stars
Spectropolarimetric observations of 96 chemically peculiar (CP)main-sequence stars have been carried out at the 6-m telescope at theSpecial Astrophysical Observatory of the Russian Academy of Sciences(SAO RAS) with the aim of searching for the presence of stellar magneticfields. The stars selected for investigation were CP stars known to havestrong anomalies in the wavelength region of the continuum fluxdepression around λ 5200Å. This selection was conductedwith the aid of low-resolution spectral observations, made with the SAORAS 1-m telescope, and of published differential photometric data.Magnetic fields have been successfully detected in 72 stars of whichonly three stars were previously known to have magnetic fields. For twostars, the longitudinal component of the magnetic field Beexceeds 5 kG: HD178892 - 7.4 kG, and HD258686 - 6.7 kG. We failed toreliably detect the magnetic field in the other 24 CP stars. These starsare mostly fast rotators, a feature which hampers accurate measurementsof Be. It is demonstrated in this paper that selectingcandidate magnetic stars by considering their photometric indices Z orΔa, or alternatively, by inspecting low-resolution spectra aroundthe λ5200Å flux depression, considerably increases thedetection rate.This paper is based on data obtained at the 6-m telescope of the RussianAcademy of Sciences.E-mail: dkudr@sao.ru
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Searching for links between magnetic fields and stellar evolution. I. A survey of magnetic fields in open cluster A- and B-type stars with FORS1
Context: .About 5% of upper main sequence stars are permeated by astrong magnetic field, the origin of which is still matter of debate. Aims: . With this work we provide observational material to studyhow magnetic fields change with the evolution of stars on the mainsequence, and to constrain theory explaining the presence of magneticfields in A and B-type stars. Methods: . Using FORS1 inspectropolarimetric mode at the ESO VLT, we have carried out a survey ofmagnetic fields in early-type stars belonging to open clusters andassociations of various ages. Results: . We have measured themagnetic field of 235 early-type stars with a typical uncertainty of 100 G. In our sample, 97 stars are Ap or Bp stars. For thesetargets, the median error bar of our field measurements was 80 G.A field has been detected in about 41 of these stars, 37 of which werenot previously known as magnetic stars. For the 138 normal A and B-typestars, the median error bar was 136 G, and no field was detected in anyof them.
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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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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.
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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.
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Searching for unknown open clusters in the Tycho-2 catalog
We present 11 new open cluster candidates found in a systematic searchfor unknown star clusters using the astrometric and photometric dataincluded in the Tycho 2 catalog. The possible existence of these stellaraggregates is supported by the analysis of proper motions,color-magnitude diagrams, stellar density distributions, and by thevisual inspection of the Digitized Sky Survey (DSS) plates. With thesetools we were able to determine mean absolute proper motions as well aspreliminary reddenings, distances and ages for the majority of thecandidates. We found that most of them are possibly nearby (closer than~ 600 pc) open clusters never studied before.Based on observations of the ESA Hipparcos satellite.Figures 1 and 2 are only available in electronic form athttp://www.edpsciences.org
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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.
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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.
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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.
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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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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
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Proper motion and membership determination in the young open cluster NGC 1662
Relative proper motions and cluster membership probabilities of 30 starswithin an area of 14' of diameter centered in the opencluster NGC 1662 (alpha =04h48m, delta=+10o56') are determined by combining positions ofstars observed by the Valinhos CCD meridian circle with those from otherastrometric catalogues. Our basic source for first epoch of starsbrighter than B=13 magnitudes is the AC2000 Catalogue, which provides atime baseline of about 90 years, whereas the USNO-A2.0 Catalogue is usedfor fainter stars, providing a time baseline of about 40 years in thisregion. Average accuracies in proper motion of 2 mas/yr and 7 mas/yr areachieved, respectively, when the AC2000 or the USNO-A2.0 is used.Membership determination is obtained by applying the Zhao & He(\cite{zha}) method. The cluster proper motion was found to be (-3.2+/-0.6) mas/yr in right ascension and (-1.6+/- 0.6) mas/yr in declination.
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Corridors in the regions of young open stellar clusters.
Not Available
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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
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Parameters of open star clusters from uvby-beta photometry.
Not Available
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DDO Metal Abundances of High-Luminosity Late-Type Stars in Galactic Open Clusters
Results from UBV and DDO photometry are presented for 54 high-luminositylate-type stars in the fields of 23 open clusters. The probability ofcluster membership for each observed star is evaluated using twoindependent photometric criteria. It is found that 32 stars are verylikely cluster members, the remaining ones being almost certainly fieldobjects. The recently improved calibrations of the DDO system have beenused to derive MK spectral types, effective temperatures, andmetallicities, while E(B-V) color excesses have been determined throughknown photometric and spectroscopic procedures. The DDO metallicitiesrange between values typical of moderately metal-poor ([Fe/H]=~ -0.3) tomoderately metal-rich ([Fe/H] =~ 0.2) clusters. The masses of thecluster giants range between 1 and 4 solar masses, with the scatterwithin a cluster being less than 1 solar mass. (SECTION: StellarClusters and Associations)
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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
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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.
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Uvby-beta photometry of open clusters. IV. NGC 1444, NGC 1662, NGC 2129, NGC 2169 and NGC 7209.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994RMxAA..28..139P&db_key=AST
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UVBY-beta photometry of the open clusters NGC 1662 and NGC 2129.
Abstract image available at:http://adsabs.harvard.edu/abs/1994RMxAA..29..125P
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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.
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Fundamental characteristics of cool giant stars
Methods are suggested for determining the fundamental characteristics ofcool giant stars from photometry in the Geneva and Gildenkern system,using a large number of standard stars for the calibration. The catalogsof T(eff), lg g, and Fe/H are obtained for 1000 and 600 stars in theGeneva Observatory and Gildenkern systems, respectively. Effectivetemperature scales and gravity accelerations are determined. Themetallicity distribution is obtained according to spectral types. Themetallicity data of stars belong to dynamical groups, and open clustersdo not confirm the presence of a linear metallicity-age relationship. Aconclusion on the existence of two age groups among disk giants isdrawn.
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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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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.
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Liste des étoiles Ap et Am dans les amas ouverts (Edition révisée)
Not Available
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Carbon isotope ratios and lithium abundances in open cluster giants
New high-resolution, high S/N spectra of CN lines at 8000 A and Li linesat 6707 A have been obtained for giants in about 20 Galactic openclusters and C-12/C-13 ratios and Li abundances determined for thesestars. The ages of the clusters vary from about 50 million years to 5billion years, and their turn-off masses vary from 1 solar mass to about6 solar masses. The ages and turn-off masses were determined by fittingtheoretical isochrones to the cluster color-magnitude diagrams.Correlation of the isotope ratio and the Li abundances with the clusterturn-off masses indicates the following: (1) the C-12/C-13 ratioincreases steeply with the turn-off mass until a mass of approximately2.2 solar masses when the ratio levels off abruptly to a value near 26;(2) older clusters with turn-off masses lower than about 2.2 solarmasses in general exhibit C-12/C-13 ratios that are considerably lowerthan the theoretically predicted values while those with larger turn-offmasses show ratios close to standard predictions; and (3) no strongcorrelation exists between the Li abundances and the cluster turn-offmass, and the Li abundances in giants are, in general, lower thantheoretically predicted values. Various theories to explain the observedabundance trends are discussed.
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The late stages of stellar evolution : from AGB stars to planetary nebulae.
Not Available
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The European Working Group on chemically peculiar stars of the upper main sequence : the first 10 years.
Not Available
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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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