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מאמרים קשורים
Monitor: transiting planets and brown dwarfs in star forming regions and young open clusters
The Monitor project is a large scale photometric monitoring survey often star forming regions and open clusters aged between 1 and 200 Myrusing wide-field optical cameras on 2-4 m telescopes worldwide. Theprimary goal of the project is to search for close-in planets and browndwarfs at young ages through the detection of transit events. Suchdetections would provide unprecedented constraints on planet formationand migration time-scales, as well as on evolutionary models of planetsand brown dwarfs in an age range where such constraints are very scarce.Additional science goals include rotation period measurements and theanalysis of flares and accretion-related variability.Workshop ``Ultralow-mass star formation and evolution'', see AN 326, No. 10www.ast.cam.ac.uk/suz/monitor/monitor.php
| The Bologna Open Cluster Chemical Evolution Project: Midterm Results from the Photometric Sample
We describe a long-term project aimed at deriving information on thechemical evolution of the Galactic disk from a large sample of openclusters. The main property of this project is that all clusters areanalyzed in a homogeneous way to guarantee the robustness of the rankingin age, distance, and metallicity. Special emphasis is devoted to theevolution of the earliest phases of the Galactic disk evolution, forwhich clusters have superior reliability with respect to other types ofevolution indicators. The project is twofold: on one hand we derive theage, distance, and reddening (and indicative metallicity) byinterpreting deep and accurate photometric data with stellar evolutionmodels, and on the other hand, we derive the chemical abundances fromhigh-resolution spectroscopy. Here we describe our overall goals andapproaches and report on the midterm project status of the photometricpart, with 16 clusters already studied, covering an age interval from0.1 to 6 Gyr and galactocentric distances from 6.6 to 21 kpc. Theimportance of quantifying the theoretical uncertainties by deriving thecluster parameters with various sets of stellar models is emphasized.Stellar evolution models assuming overshooting from convective regionsappear to better reproduce the photometric properties of the clusterstars. The examined clusters show a clear metallicity dependence on thegalactocentric distance and no dependence on age. The tight relationbetween cluster age and magnitude difference between the main-sequenceturnoff and the red clump is confirmed.
| Toward the Detection of Transiting Hot Earths and Hot Neptunes in Open Clusters
Radial velocity searches for extrasolar planets have recently detectedseveral very low mass (7-20 M_oplus) planets in close orbits withperiods less than 10 days. We consider the prospects for detecting theanalogs of these planets in Galactic open clusters via transits. Weoutline the requirements for constructing a transit survey that wouldallow one to probe such ``Hot Earths'' and ``Hot Neptunes.''Specifically, we present a simple criterion for detection that definesthe minimum aperture required to detect planets of a given radius in acluster at a given distance. Adopting photometric precisions that havebeen demonstrated in state-of-the-art variability surveys, we thenpredict the number of planets one could potentially detect withambitious transit surveys toward several open clusters. Dedicatedsurveys lasting more than 20 nights with Pan-STARRS toward the Hyadesand Praesepe could detect a handful of Hot Earths, if the majority ofstars host such planets. Similar surveys with larger aperture telescopes(eg CFHT, MMT), toward M67, M35, M50, and M37 could detect Hot Neptunes,provided that their frequency is greater than 1%. The majority ofplanets will be detected around M dwarfs; detecting Hot Neptunes aroundsuch primaries requires photometric precisions of approx 1%, whereas HotEarths require approx 0.1 %. We discuss potential hurdles in detectingand confirming small planets in ground-based surveys, includingcorrelated noise, false positives, and intrinsic stellar variability.
| 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.
| 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.
| On the distance, reddening and progenitor of V838 Mon
Extensive optical and infrared photometry as well as low and highresolution spectroscopy are used as inputs in deriving robust estimatesof the reddening, distance and nature of the progenitor of V838 Mon, the2002 outbursting event that produced a most spectacular light-echo. Thereddening affecting V838 Mon is found to obey the R_V=3.1 law andamounts to (i) EB-V=0.86 from the interstellar NaI and KIlines; (ii) EB-V=0.88 from the energy distribution of the B3V component; and (iii) EB-V=0.87 from the progression ofextinction along the line of sight. The adoptedEB-V=0.87±0.01 is also the amount required by fittingthe progenitor with theoretical isochrones of appropriate metallicity.The distance is estimated from (a) the galactic kinematics of the threecomponents of the interstellar lines; (b) the amount of extinction vs.the HI column density and vs. the dust emission through the whole Galaxyin that direction; from (c) spectrophotometric parallax to the B3 Vcompanion; from (d) comparison of the observed color-magnitude diagramof field stars with 3D stellar population models of the Galaxy; from (e)comparison of theoretical isochrones with the components of the binarysystem in quiescence and found to be around 10 kpc. Pre-outburst opticaland IR energy distributions show that the component erupting in 2002 wasbrighter and hotter than the B3 V companion. The best fit is obtainedfor a 50 000 K source, 0.5 mag brighter than the B3 V companion. Thelatter passed unaffected through the outburst, which implies an orbitalseparation wide enough to avoid mass exchange during the evolution ofthe binary system, and to allow a safe comparison with theoreticalisochrones for single stars. Such a comparison suggests that theprogenitor of the outbursting component had an initial mass ~65M_ȯ, that it was approaching the carbon ignition stage in its coreat the time it erupted in 2002 and that the age of the V838 Mon binarysystem is close to 4 million yr. The 2002 event is probably just a shellthermonuclear event in the outer envelope of the star.
| Interpreting the colour-magnitude diagrams of open star clusters through numerical simulations
We present detailed comparisons between high quality observationalcolour-magnitude diagrams (CMDs) of open star clusters and syntheticCMDs based on Monte Carlo numerical simulations. The comparisons accountfor all of the main parameters which determine the shape of the CMD fora stellar population. For the four clusters studied, NGC 6819, 2099(M37), 2168 (M35) and 2323 (M50), we derive reddening, distance, age,binary fraction, star formation rate and indicative metallicity bycomparing the locations and density of points in the observed CMDs tothe simulated CMDs. We estimate the uncertainties related to stellarevolution theories by adopting various sets of stellar models for all ofthe synthetic CMDs and discuss which stellar models provide thetheoretical CMDs that best reproduce the observations.
| 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.
| Astrophysical supplements to the ASCC-2.5. II. Membership probabilities in 520 Galactic open cluster sky areas
We present a catalogue (CSOCA ) of stars residing in 520 Galactic opencluster sky areas which is the result of the kinematic (proper motion)and photometric member selection of stars listed in the homogeneousAll-sky Compiled Catalogue of 2.5 Million Stars (ASCC-2.5). We describethe structure and contents of the catalogue, the selection procedureapplied, and the proper motion and photometric membership constraintsadopted. In every cluster area the CSOCA contains the complete list ofthe ASCC-2.5 stars regardless of their membership probability. Forevery star the CSOCA includes accurate J2000 equatorial coordinates,proper motions in the Hipparcos system, BV photometric data in theJohnson system, proper motion and photometric membership probabilities,as well as angular distances from the cluster centers for about 166 000ASCC-2.5 stars. If available, trigonometric parallaxes, spectral types,multiplicity and variability flags from the ASCC-2.5, and radialvelocities with their errors from the Catalogue of Radial Velocities ofGalactic Stars with high precision Astrometric Data (CRVAD) are alsogiven.
| 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.
| The CFHT Open Star Cluster Survey. IV. Two Rich, Young Open Star Clusters: NGC 2168 (M35) and NGC 2323 (M50)
We continue our study of rich Galactic clusters by presenting deep CCDobservations of both NGC 2168 (M35) and NGC 2323 (M50). Both clustersare found to be rich (NGC 2168 contains at least 1000 stars brighterthan V=22, and NGC 2323 contains ~2100 stars brighter than ourphotometric limit of V~23) and young (NGC 2168 age=180 Myr and for NGC2323 age=130 Myr). The color-magnitude diagrams for the clusters exhibitclear main sequences stretching over 14 mag in the (V, B-V)-plane.Comparing these long main sequences with those of earlier clusters inthe survey, as well as with the Hyades, has allowed for accuratedistances to be established for each cluster (for NGC 2168d=912+70-65 pc and for NGC 2323d=1000+81-75 pc). Analysis of the luminosity andmass functions suggests that, despite their young ages, both clustersare somewhat dynamically relaxed, exhibiting signs of mass segregation.This is especially interesting in the case of NGC 2323, which has an ageof only 1.3 times the dynamical relaxation time. The present photometryis also deep enough to detect all of the white dwarfs in both clusters.We discuss some interesting candidates that may be the remnants of quitemassive (M>=5Msolar) progenitor stars. The white dwarfcooling age of NGC 2168 is found to be in good agreement with themain-sequence turnoff age. These objects are potentially very importantfor setting constraints on the white dwarf initial-final massrelationship and the upper mass limit for white dwarf production.
| 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.
| Urban Astronomy: Observing the Messier Objects from the City
Not Available
| A study of spatial structure of galactic open star clusters
In order to study the relation between the core and corona in galacticstar clusters, the spatial structure of 38 rich open star clusters hasbeen studied using radial density profiles derived from the photometricdata of the Digital Sky Survey. The shape of the radial density profileindicates that the corona, most probably, is the outer region around thecluster. It can exist from the very beginning of the cluster formationand dynamical evolution is not the reason for its occurrence. The studydoes not find any relation between cluster size and age but indicatesthat the clusters with galacto-centric distances >9.5 kpc have largersizes. Further, we find that the average value of the core radius is1.3+/- 0.7 pc and that of annular width of the corona is 5.6+/- 1.9 pc,while average values of densities of cluster members in the core andcorona are 15.4+/- 9.9 star/pc2 and 1.6+/- 0.99star/pc2 respectively. Average field star contaminations inthe core and corona are ~ 35% and 80% respectively. In spite of smallerdensities in the coronal region, it contains ~ 75% of the clustermembers due to its larger area in comparison to the core region. Thisclearly demonstrates the importance of the coronal region in studiesdealing with the entire stellar contents of open star clusters as wellas their dynamical evolution. In contrast to the cluster cores, thestructure of coronal regions differs significantly from one cluster toother.
| Hipparcos Trigonometric Parallaxes and the Distance Scale for Open Star Clusters
Hipparcos trigonometric parallaxes are used to estimate the distances tothe maximum possible number of open star clusters (OSC); distance moduliare estimated for 45 clusters with maximum heliocentric distances ofabout 1000 pc. The latter value can serve as an estimate of the limit towhich it still makes sense to use Hipparcos trigonometric parallaxes todetermine the distances to small groups composed of 6-10 sufficientlybright stars. A systematic correction to the distance moduli of clustersfrom the homogeneous catalog of OSC parameters (Loktin et al. 1997,2000) is estimated, which turns out to be independent of the clusterage.
| 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.
| 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
| Open clusters in the third galactic quadrant. I. Photometry
We have performed a photometric survey of open clusters in the thirdGalactic quadrant in order to study the star formation history andspatial structure in the Canis Major-Puppis-Vela region. In this paperwe describe a catalogue of CCD U BV RI photometry of approximately 65000 stars in the fields of 30 open clusters. The data were obtained andreduced using the same telescope, the same reduction procedures, and thesame standard photometric system, which makes this catalogue the largesthomogeneous source of open cluster photometry so far. In subsequentpapers of this series, colour-colour and colour-magnitude diagrams willbe presented which, amongst other uses, will allow the determination ofan homogeneous set of cluster reddenings, distances, and ages that willconstitute the observational basis for our studies of the spatialstructure and star formation history in the third Galactic quadrant.
| The IMF of open star clusters with Tycho-2
We studied the fields of nine nearby open star clusters based on theTycho-2 catalogue. We determined membership probabilities for the starsin the cluster fields from the stellar proper motions and used theTycho-2 photometry to compute the initial mass function (IMF) of theclusters from the main sequence turn-off point down to approx. 1 M_sun.We found IMF slopes ranging from Gamma =-0.69 down to Gamma =-2.27 (whenthe Salpeter \cite{salpeter} value would be Gamma =-1.35). We alsostudied the membership of individual stars of special astrophysicalinterest. In some cases previous results had to be revised. As aby-product, we investigated some general properties of the Tycho-2catalogue; we confirmed that the Tycho-2 proper motions show onlymarginal deviations from the Hipparcos catalogue. On the other hand, insome regions the completeness of the catalogue seems to decrease atmagnitudes brighter than claimed by Høg et al. (\cite{tycho2}).Based on observations of the ESA Hipparcos satellite.
| Spectroscopic investigations of classical Cepheids and main-sequence stars in galactic open clusters and associations. I. Association Cas OB2 and the small-amplitude Cepheid SU Cassiopeae
The small-amplitude Cepheid SU Cas and four membersof the association Cas OB2 (HD 16893, HD17327a and b, HD 17443) were investigated,using high-resolution CCD spectra. The following results were obtained:1) All these objects have the same metallicity values, close to that ofthe Sun; 2) Elemental abundance indicates that SU Cas is a post firstdredge-up star with an age from 1 108 to 1.45 108yr, and it is not crossing the Cepheid instability strip for the firsttime. The mean value of log g = 2.35 corresponds to pulsations in thefundamental tone, although errors in gravity estimations provideovertone pulsations. The questions about its pulsational mode andmembership in Cas OB2 remained open; 3) HD17327a is a slowly rotating HgMn-star with the highest heliumcontent among such objects, while HD 16893 also has a manganeseoverabundance and might be classified as an Am-star; 4) HD17327b and HD 17443 are rapidly rotating main-sequence stars,while HD 17443 has a helium content comparable with that of the Sun.
| 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
| Statistical parallaxes and kinematical parameters of classical Cepheids and young star clusters
The statistical-parallax method is applied for the first time to spacevelocities of 270 classical Cepheids with proper motions adopted fromHIPPARCOS (1997) and TRC (Hog et al. 1998) catalogs and distances basedon the period-luminosity relation by Berdnikov et al. (1996). Thedistance scale of short-period Cepheids (with periods less than 9 days)is shown to require an average correction of 15-20%, whereas statisticalparallaxes of Cepheids with periods > 9 days are found to agree wellwith photometric distances. It is shown that the luminosities ofshort-period Cepheids must have been underestimated partly due to thecontamination of this subsample by a substantial (20 to 40%) fraction offirst-overtone pulsators. The statistical-parallax technique is alsoapplied for the first time to 117 open clusters younger than 100 millionyears and with proper motions reduced to the HIPPARCOS reference system.It is concluded that a 0.12-0.15 mag increase of the distance scales ofopen clusters and Cepheids would be sufficient to reconcile thestatistical-parallax results inferred for these two types of objects.Such approach leads to an LMC distance modulus of less than 18.40 mag,which agrees, within the errors, with the short distance scale for RRLyrae variables and is at variance with the conclusions by Feast andCatchpole (1998) and Feast et al. (1998), who argue that the LMCdistance modulus should be increased to 18.70 mag. The distance scalebased on the Cepheid period-luminosity relation by Berdnikov and Efremov(1985) seems to be a good compromise. Extragalactic distances, whichrely on long-period Cepheids, seem to require no substantial correction.In addition to statistical parallaxes, kinematical parameters have beeninferred for the combined sample consisting of Cepheids andopen-clusters: solar-motion components (U0 ,V0,W0) = (9, 12, 7) km/s (+/- 1 km/s); velocity-ellipsoid axes(σU; σV; σW) = (15.0,10.3, 8.5) km/s (+/- 1 km/s); the angular velocity of rotation of thesubsystem, ω0 = 28.7 +/- 1 km/s/kpc, the Oort constantA = 17.4 +/- 1.5 km/s, and the second derivative of angular velocity,⋰ω0= 1.15 +/- 0.2 km/s/kpc3.
| Photometric study of the open cluster NGC2323
UBV photoelectric photometry for 175 stars in the field of the southernopen cluster NGC2323, supplemented by DDO photometry of 5 probablegiants, is presented. The analysis of the photometric data yields 109probable members; one of them being a red giant, and 3 possible members.The reddening across the cluster is slightly variable and the mean valueE(B-V)=0.25. The apparent cluster distance modulus is 10.62,corresponding to a distance of 940 pc. The age, determined by fittingisochrones with core overshooting, turns out to be 100+/- 20 Myr. Otherfundamental cluster parameters are also determined. NGC2323 appears notto be physically connected to the CMa OB1 association. Based onobservations made at Cerro Tololo Inter-American Observatory (Chile) andat Las Campanas Observatory (Chile).
| Parameters of open star clusters from uvby-beta photometry.
Not Available
| Absolute proper motions of 181 young open clusters.
Not Available
| Be stars in open clusters. II. Balmer line spectroscopy
We present Hα line profiles (R ~= 3x103, S/N ~=102 at continuum level, ~= 50 for some objects) for 58 starsin 8 northern open clusters and associations, complemented with Hβand Hγ profiles for 36 of them as well as Hdelta and Hepsilon for16 programme stars. Our observations, though lower in resolution, yieldresults which are in good agreement with those obtained in earlier worksbased mainly on field Be stars. Our data suggest a similar spectroscopicbehavior for both field and cluster Be stars. The line parameters (EW,FWHM, Delta vp) have been obtained for each line. Nearly thewhole set of stars have previously published quasi-simultaneousuvby\beta photometry, so a study of reliable correlations betweenphotometric and spectroscopic data can be undertaken. Based onobservations made at the German-Spanish Astronomical Center, Calar Alto,Spain which is operated by the Max Planck Institut fuer Astronomie,Heidelberg, jointly with the spanish National Commission for Astronomy.
| 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.
| Integrated photometric properties of open clusters
Galactic open clusters provide an abundant sample of stellar aggregatesof various sizes, ages and metal abundances, apt to constitute atemplate for comparison with star systems in other galaxies. In thispaper we present and discuss a standard methodology to synthesize U,B,Vfluxes and colours, and apply it to a set of 138 open clusters. Resultsare compared with previous ones available in the literature. We wereable to calibrate a mass-luminosity relation by which we evaluated themass of ~400 open clusters, leading to a well defined present-day massfunction. The number-complete sample of galactic open clusters presentedin Battinelli & Capuzzo-Dolcetta (1991) is enlarged of a 15%.
| 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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