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On the current status of open-cluster parameters
We aim to characterize the current status of knowledge on the accuracyof open-cluster parameters such as the age, reddening and distance.These astrophysical quantities are often used to study the globalcharacteristics of the Milky Way down to the very local stellarphenomena. In general, the errors of these quantities are neglected orset to some kind of heuristic standard value. We attempt to give somerealistic estimates for the accuracy of available cluster parameters byusing the independently derived values published in the literature. Intotal, 6437 individual estimates for 395 open clusters were used in ourstatistical analysis. We discuss the error sources depending ontheoretical as well as observational methods and compare our resultswith those parameters listed in the widely used catalogue by Dias et al.In addition, we establish a list of 72 open clusters with the mostaccurate known parameters which should serve as a standard table in thefuture for testing isochrones and stellar models.
| Calibration of a UBVRI sequence around Nova Cyg 2006
A highly accurate UBV(RI)c photometric sequence around Nova Cyg 2006 ispresented. The photometric stability of the stars in the sequence hasbeen checked on 12 different nights. The sequence is linked to theLandolt's equatorial standards for (RI)c bands and to UBV photoelectricphotometry of selected open clusters by Hoag et al. (1961).
| 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.
| Revisiting the population of Galactic open clusters
We present results of a study of the galactic open cluster populationbased on the all-sky catalogue ASCC-2.5 (I/280A) compiled from Tycho-2,Hipparcos and other catalogues. The sample of optical clusters fromASCC-2.5 is complete up to about 850 pc from the Sun. The symmetry planeof the clusters' distribution is determined to be at Z_0=-22±4pc, and the scale height of open clusters is only 56±3 pc. Thetotal surface density and volume density in the symmetry plane areΣ= 114 kpc-2 and D(Z_0)=1015 kpc-3,respectively. We find the total number of open clusters in the Galacticdisk to be of order of 105 at present. Fluctuations in thespatial and velocity distributions are attributed to the existence offour open cluster complexes (OCCs) of different ages containing up to afew tens of clusters. Members in an OCC show the same kinematicbehaviour, and a narrow age spread. We find, that the youngest clustercomplex, OCC 1 (log t<7.9), with 19 deg inclination to the Galacticplane, is apparently a signature of Gould's Belt. The most abundant OCC2 complex has moderate age (log t≈8.45). The clusters of thePerseus-Auriga group, having the same age as OCC 2, but differentkinematics are seen in breaks between Perseus-Auriga clouds. The oldest(log t≈8.85) and sparsest group was identified due to a large motionin the Galactic anticentre direction. Formation rate and lifetime ofopen clusters are found to be 0.23±0.03 kpc-2Myr-1 and 322±31 Myr, respectively. This implies atotal number of cluster generations in the history of the Galaxy between30 to 40. We estimate that less than about 10% of the total Galacticstellar disk population has ever passed an open cluster membership.
| 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.
| Catalogue of the orbital elements, masses, and luminosities for short-periodic RS CVn-type eclipsing systems
New data on the orbital elements, masses, and luminosities werecollected for 31 pre-contact binary systems of short-periodic {RS}{CVn}-type. We treat the catalogued data statistically in order toaccurately define the properties and evolutionary status of each classsystem. The ages of pre-contact systems were estimated by the isochronemethod. Numerous comments and bibliographic references to the catalogueare also included.
| 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.
| A Spectroscopic Search for λ Bootis and Other Peculiar A-Type Stars in Intermediate-Age Open Clusters
As part of our continuing search for peculiar A-type stars, especiallyλ Bootis stars, in open clusters of all ages, we have obtainedclassification spectra of 130 late B, A, and early F-type stars in 12intermediate-age open clusters, including NGC 1039, 2281, 2548, 6633,7039, 7063, 7092, and 7209, IC 4665, IC 4756, Stock 2, and Praesepe. Thespectra were obtained with resolutions of 1.8 and 3.6 Å on the 0.8m telescope of Appalachian State University and were classified on theMK system. Numerous classical Ap and Am stars were found among the 130,including two new Ap stars in NGC 7092. In addition, three emission-linestars and two candidate λ Bootis stars were found. Neither ofthese λ Bootis candidates turned out to be members of theirrespective clusters. Combined with 184 stars previously classified in 10other intermediate-age open clusters, also devoid of λ Bootisstars, a statistically significant null result is obtained. We discussthe implications of this null result for our understanding of theλ Bootis mechanism.
| 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
| A spectroscopic survey for lambda Bootis stars. III. Final results
In the third paper of a series dedicated to the spectroscopic survey fornew lambda Bootis stars, we present all new and confirmed members of thegroup as well as a detailed analysis of the observed sample. The natureof this small group of chemically peculiar stars of the upper mainsequence still challenges our understanding of processes like diffusion,mass-loss and accretion. The typical abundances pattern (nearly solarvalues for C, N, O and S whereas the Fe-peak elements are moderate tostrong underabundant) can still not be explained by any proposed theory.Hence, the significant increase of new members gives the opportunity toinvestigate the group properties in more detail. We report the discoveryof 26 new members of the group and the confirmation of 18 candidatesfrom the literature. This almost triples the number of known lambdaBootis stars. The existence of one member in the young open cluster NGC2264 and four members in the Orion OB1 association proves that thelambda Bootis phenomenon already works at very early stages of stellarevolution. Recent results from the Hipparcos mission have shown that thewell established lambda Bootis stars of the Galactic field comprise thewhole area from the Zero Age Main Sequence to the Terminal Age MainSequence (~ 109 yr for an A-type star). There is a continuoustransition between very young and rather evolved evolutionary stages. Wefind that the overall percentage of lambda Bootis type among all normaltype stars in the spectral range from B8 to F4 is 2% in the Galacticfield as well as in open clusters. Furthermore, 44 metal-weak objectsare listed which might be connected with the lambda Bootis phenomenon.Our biased sample (chosen by photometric boxes) is not distinguishedfrom all A-type stars in the corresponding spectral region by therotational velocity distribution. Only for the luminosity classes IV andIII (especially for the cooler program stars) the determined mean v sini values are very high compared to those of the literature. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
| The Change in the Inclination Angle of the Noneclipsing Binary SS Lacertae: Future Eclipses
Eclipses in the 14.4 day-period double-lined binary SS Lac were observedphotographically and visually early in the twentieth century but stoppedsome 50 or 60 yr ago. This has been explained by the presence of adistant third star in the system, which has now been detectedspectroscopically, with a period of 679 days. The plane of the orbit ofthe binary is changing relative to the line of sight in response toperturbations from this third object. A recent analysis by Milone et al.of all photometric material available for the system, including aremeasurement of original Harvard plates, has confirmed earlier reportsof changes in the depth of the eclipses as a function of time, which aredue to the third star. In this paper we discuss our detailed analysis ofthe eclipse amplitude measurements and extract from them information onthe change in the inclination angle of the binary over the last century.Our use of a much improved ephemeris for the system by Torres &Stefanik was found to be crucial, and it prompted us to redetermine allthe amplitudes from the historical data at our disposal, including theHarvard material used by Milone et al. Systematically lower measurementson the branches of the minima were properly accounted for, and we madeuse of both a linear approximation to the time variation of theinclination angle and a more realistic model based on the theory ofthree-body interactions (``regression of the nodes'' effect). The nodalcycle is found to be ~600 yr, within which two eclipse ``seasons''occur, each lasting about 100 yr. The noneclipsing status of the systemis expected to continue until the beginning of the twenty-third century.
| Aus der Litteratur.
Not Available
| 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 Cessation of Eclipses in SS Lacertae: The Mystery Solved
The 14.4 day period eclipsing binary SS Lacertae in the open cluster NGC7209 is unusual in that the eclipses stopped completely about the middleof this century, giving rise to considerable speculation as to thecause. Disruption of the binary through a collision with another memberof the cluster and, more likely, gravitational perturbations from athird star in the system have been proposed to explain the phenomenon.We present here the results of our intensive radial velocity monitoringof the object, which show clearly that there is indeed a third star inthe system in a slightly eccentric orbit with a period of about 679days. We also reanalyze the historical light curves of SS Lac todetermine the properties of the system early in the century. We discussthe implications of our findings in terms of changes in the inclinationangle of the close pair. An analysis of available times of eclipse forSS Lac together with the new velocity information has also revealedapsidal motion in the system, ω=0.0137d cycle-1,corresponding to an apsidal period of about 1000 yr. We argue that thethird star is probably responsible for this effect also. Some of theobservations reported here were obtained with the Multiple MirrorTelescope, a joint facility of the Smithsonian Institution and theUniversity of Arizona.
| Analyses of the Currently Noneclipsing Binary SS Lacertae or SS Lacertae's Eclipses
Confirmatory evidence for changing light-curve amplitude of the formereclipsing and current SB2 system SS Lac in the Open Cluster NGC 7209 hasbeen uncovered. Remeasured Harvard plate data and published and compileddata sets reveal that the depth of the primary minimum increased betweenthe 1890s and 1902 and decreased in the 1920s and 1930s. A parabolicfitting of the amplitude with phase predicts a maximum at 1911.5, withan eclipse onset at 1885.3 and eclipse cessation at 1937.8. We confirmthe finding of Lehmann, that the system's inclination varies with timeand that a central eclipse occurred ~1912, and we concur withMossakovskaya that eclipses effectively ceased ~1940. Estimates of SSLac on plates taken at Tashkent between 1937 and 1940 further serve toconfirm the result. Thus, SS Lac belongs to a small but elite class oftriple systems in which changes due to dynamical effects can be seenover a single human lifetime. In order to explore the properties of theSS Lac system, recent radial velocity curves and archival photographicand visual light curves have been analyzed with versions of theWilson-Devinney code, augmented with a simplex routine to test solutionuniqueness. The modeling solutions for the Dugan-Wright light curvesostensibly indicate that the former eclipsing system is composed of twoearly A stars of only slightly differing masses (2.57+/-0.16 and2.59+/-0.19 Msolar) and effective surface temperatures(8750+/-300 [assumed for component 1] and 8542+/-309 K), butsignificantly different radii (2.38+/-0.02 and 3.63+/-0.07Rsolar) and luminosities (30+/-4 and 63+/-9Lsolar) for the hotter and cooler components, respectively.The light-curve solutions are compromised somewhat by variable eclipsedepths over the ranges of dates of the data sets. This is especiallytrue of the most complete light curve, that of Dugan & Wright; theothers also suffer from incompleteness (that of Wachmann) and highscatter (that of Kordylewski, Pagaczewski, & Szafraniec). As aconsequence, small, temporal variations in such system properties as theeccentricity, argument of periastron, modified Roche potentials,luminosities, and third light level, cannot be ruled out from currentlyavailable data. However, solutions with WD95, a self-iterating,damped-least squares version of the Wilson-Devinney program, revealoptimized inclinations for the data sets that project an inclinationvariation of 0.16d yr-1, but no evidence of apsidal motion.We find a distance for the system of 898+/-95 pc, consistent with thevalue of Vansevičius et al. of 1040+/-10 pc, and finally, on thebases of location on the sky, proper motion, radial velocity,photometry, and properties deduced in the present study, we confirm itsmembership in the cluster NGC 7209. Publications of the RothneyAstrophysical Observatory, No. 73.
| Close binary systems in star-forming regions: KV Cyg, V435 Cyg, and V699 Cyg in the OB association Cyg OB1
We carried out photoelectric UBVR observations of three eclipsingsystems in the OB association Cyg OB1. The ephemerides of minima and theamplitudes of light variations in the observed bands are refined. Wesolve all light curves of KV Cyg and V435 Cyg by Lavrov's method anddetermine their photometric orbital elements. Absolute parameters of thecomponents of KV Cyg are estimated by using standard relations betweenthe fundamental stellar parameters. By applying the same procedure toV435 Cyg, we failed to obtain the expected parameters of its components.The light curve of V699 Cyg underwent a significant change, and thequestion of its interpretation remains an open question. All threevariables are probable members of the OB association Cyg OB1. Weobtained UBVR photometry for 78 stars in the region of the association,41 of which belong to Cyg OB1.
| 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.
| Spectroscopic orbit of the ex-eclipsing binary SS Lacertae in the young open cluster NGC 7209
The no-longer-eclipsing system SS Lac in the young open cluster NGC 7209has been recently announced to show a constant radial velocity. Puzzledby this finding, we have monitored the system during 1997 obtaining 24Echelle+CCD spectra over 8 orbital revolutions. Our spectra reveal anice orbital motion with periodic splitting and merging of spectrallines from both components. An accurate orbit has been derived, togetherwith individual masses of the stars. SS Lac presents a moderatelyeccentric orbit and a probably full synchronization between stellarrotation and orbital revolution.
| 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
| A study of the open cluster NGC 7209 in the Vilnius photometric system
Photoelectric photometry in the Vilnius seven-colour system is presentedfor the open cluster NGC 7209. In total 96 probable cluster members havebeen measured down to V~14.0. For all stars their spectral types,absolute magnitudes, colour excesses, interstellar reddening anddistances are derived from the Vilnius photometry. The metallicity isestimated to be [Fe/H]=-0.07. In addition, a list of suspected binariesis provided. The reddening across the cluster shows a slight trend alongthe north-south direction. The mean reddening equals E(Y-V)=0.121 [inthe UBV system E(B-V)=0.171] which corresponds to A_V=0.54. The derivedmedian distance for NGC 7209 is 1026+/-30pc (equivalent to the distancemodulus V_0-M_V=10.06+/-0.06). Theoretical isochrone fits to thecolour-magnitude diagram yield an age estimate of 0.45Gyr.
| Parameters of open star clusters from uvby-beta photometry.
Not Available
| Cluster membership determinations from proper motion surveys
Not Available
| 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)
| Divorce stellaire dans le Lezard.
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
| 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 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
| The disappearance of eclipses in the eclipsing variable star SS Lacertae
The photographic observations of the eclipsing variable SS Lac conductedby Mossakovskaya in 1989 failed to show eclipses at the time predictedfrom the ephemerides of Dugan and Wright (1935). From a compositephotographic light curve of SS Lac constructed on the basis ofliterature data and observations based on plates from the SternbergInstitute in Moscow, it is suggested that the eclipses in SS Lacdisappeared as early as the period between 1935 and 1940, and not during1949-1950, as argued by Zakirov and Azimov (1990). The depth of the SSLac maxima changed from 0.6 m pg in 1898 to 0.4 m pg in 1935.
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