Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
The population in the background of open clusters: tracer of the Norma-Cygnus arm
We present colour-magnitude diagrams of open clusters, located in therange 112° < l < 252°, manifesting stellar populations inthe background of clusters. Some of the populations are found to belocated beyond the Perseus arm and may be the part of the Norma-Cygnus(outer) arm. The outer arm seems to be continued from l ~ 120° to~235°. The background populations follow the downward warp of theGalactic plane around l ~ 240°.
| Caroline Herschel's catalogue of nebulae
Not Available
| 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 recent star formation history of the Milky Way disk
We have derived the star formation history of the Milky Way disk overthe last 2 Gyr from the age distribution diagram of a large sample ofopen clusters comprising more than 580 objects. By interpreting the agedistribution diagram using numerical results from an extensive libraryof N-body calculations carried out during the last ten years, wereconstruct the recent star formation history of the Milky Way disk.Under the assumption that the disk has never been polluted by anyextragalactic stellar populations, our analysis suggests thatsuperimposed on a relatively small level of constant star formationactivity mainly in small-N star clusters, the star formation rate hasexperienced at least five episodes of enhanced star formation lastingabout 0.2 Gyr with production of larger clusters. This cyclic behaviourshows a period of 0.4+/-0.1 Gyr and could be the result of density wavesand/or interactions with satellite galaxies. On the other hand, the starformation rate history from a volume-limited sample of open clusters inthe solar neighbourhood appears to be consistent with the overall starformation history obtained from the entire sample. Pure continuous starformation both in the solar neighbourhood and the entire Galactic diskis strongly ruled out. Our results also indicate that, in the Milky Waydisk, about 90% of open clusters are born with N<=150 and the slopein the power-law frequency distribution of their masses is about -2.7when quiescent star formation takes place. If the above results arere-interpreted taking into consideration accretion events onto the MilkyWay, it is found that a fraction of the unusually high number of openclusters with ages older than 0.6 Gyr may have been formed in disruptedsatellites. Problems arising from the selection effects and the ageerrors in the open cluster sample used are discussed in detail.
| Metallicity distribution on the galactic disk
Depending mainly on UBVCCD data, the metallicities of 91 open starclusters nearby the galactic disk have been estimated using Cameron's[A&A 147 (1985b) 39] method. The metallicity radial gradient alongthe galactic plane is found to be -0.09 dex/kpc; which is in a very goodagreement with Panagia and Tosi [A&A 96 (1981) 306] and Carraro etal. [MNRAS 296 (1998) 1045]. Vertically on the galactic disk, withinabout 800 pc, the metallicity gradient is found to be so trivial. Anaverage age-metallicity relation has been examined, which confirms theprevious suggestion that the metallicity of a cluster depending mainlyon its position on the galactic disk more than its age.
| 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.
| Morphological analysis of open clusters' propertiesII. Relationships projected onto the galactic plane
A morphological analysis study of open clusters' properties has beenachieved for a sample of 160 UBVCCD open star clusters of approximately128,000 stars near the galactic plane. The data was obtained and reducedfrom using the same reduction procedures, which makes this catalogue thelargest homogeneous source of open clusters' parameters.
| Proper motions of open clusters based on the TYCHO2 Catalogue. II. Clusters farther than 1 kpc
We determined the mean absolute proper motion of 94 open clusterssituated farther than 1 kpc from the Sun. The results are derived fromthe stellar proper motion data given in the Tycho2 Catalogue. The meanproper motion of the clusters and membership probability of individualstars were obtained from the proper motion data by applying thestatistical method proposed by Sanders (\cite{Sanders1971}). Themeasurements made use of a large number of stars, usually several tens,for each cluster. The total number of stars investigated in the fieldsof the clusters is 4864 of which 2021 were considered members. For 55clusters, this is the first determination of the proper motion. Based onobservations of the ESA Hipparcos satellite. Tables 1 to 95 are 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/388/168
| Integrated photometric characteristics of galactic open star clusters
Integrated UBVRI photometric parameters of 140 galactic open clustershave been computed. Integrated I(V-R)0 and I(V-I)0colours as well as integrated parameters for 71 star clusters have beenobtained for the first time. These, in combination with published data,altogether 352 objects, are used to study the integrated photometriccharacteristics of the galactic open clusters. The I(MV)values range from -9.0 to -1.0 mag corresponding to a range in totalmass of the star clusters from ~ 25 to 4*E4 Msun.The integrated colours have a relatively narrow range, e.g., I(B-V){_0}varies from -0.4 to 1.2 mag. The scatter in integrated colours at agiven integrated magnitude can be understood in terms of differences infraction of red giants/supergiants in the clusters. The observedintegrated magnitudes and colours agree with the synthetic ones, exceptthe dependences of I(V-R)0 and I(V-I)0 colours forclusters younger than ~ 100 Myrs and also of the integrated magnitudesof oldest clusters. The large sample provides the most accurate agedependence of integrated magnitudes and colours determined so far. Theluminosity function of the I(MV) has a peak around -3.5 magand its slope indicates that only ~ 1% of the open clusters in thegalactic disc are brighter than I(MV)=-11 mag. No variationhas been found of integrated magnitude with galactocentric distance andmetallicity.
| BOAO Photometric Survey of Galactic Open Clusters. II. Physical Parameters of 12 Open Clusters
We have initiated a long-term project, the BOAO photometric survey ofopen clusters, to enlarge our understanding of Galactic structure usingUBVI CCD photometry of open clusters, which have been little studiedbefore. This is the second paper of the project, in which we present thephotometry of 12 open clusters. We have determined the clusterparameters by fitting the Padua isochrones to the color-magnitudediagrams of the clusters. All the clusters except for Be 60 and NGC 1348are found to be intermediate-age to old (0.2-4.0 Gyrs) open clusterswith a mean metallicity of [Fe/H]~0.0.
| Morphological analysis of open clusters' propertiesI. Properties' estimations
A sample of 160 UBVCCD observations of open star clusters near thegalactic plane has been studied, and a catalogue of their propertiesobtained. The main photometrical properties have been re-estimated selfconsistently and the results have been compared with those of Lynga[Lynga, G., 1987. Catalog of Open Cluster Data, 5th Edition, StellarData Centers, Observatoire de Strasbourg, France].
| Apsidal motion in the eclipsing binary OX Cassiopeiae.
We report several new reliable times of minimum of the eccentriceclipsing binary OX Cas (P=2.48934days, e=0.04, V=9.92mag, B2V+B2V). TheO-C diagram is analyzed using all precise timings found in theliterature and improved values for the elements of the apsidal motionand the internal structure constant are computed. We have found a shortperiod of apsidal motion U=37.3+/-0.7yr and the internal structureconstant k_2,obs_=0.0060.
| 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.
| Young open clusters as probes of the star formation process. 1: an atlas of open cluster photometry
We have obtained charge coupled device (CCD) photometry, in the UBVsystem, for 23 open clusters in order to explore the star formationhistory of the Cassiopeia region of the Perseus spiral arm of ourGalaxy. Magnitudes and colors of 35,788 stars were measured, making thisthe most comprehensive, homogeneous single study of open clusterproperties in one part of the Galaxy. This paper presents an atlas ofopen cluster photometry that serves as the database for an investigationof cluster properties such as their ages, distances, reddenings, sizes,and richnesses. This information provides insight into the spatial andtemporal formation sequence of the clusters and allows an investigationof the stellar content of the clusters to be undertaken.
| A detailed study of the sparce open cluster Roslund 3 - A case for circumstellar extinction
A photometric study of the Roslund 3 cluster is presented whose B6-B9member stars exhibit the evidence for the presence of circumstellarextinction. The cluster is about 9 x 10 exp 7 yrs old, 2.29 +/-0.05 kpcdistant, with a radial velocity of -2.6 +/-1.1 km/s, and is estimated tocontain roughly 294 +/-36 solar masses of late B, A, and lower-massstars within its 10.0 +/-0.7 pc tidal radius. It is hypothesized that anexcess reddening for cluster B7-B9 stars originates in circumstellardust rings located around the equatorial regions of late B stars, whichare rotating at close to breakup velocity. The phenomenon may be relatedto beta Pictoris-type dust rings.
| A photometric analysis of the eclipsing binary OX Cassiopeiae
Photoelectric uvby, H-beta photometry is presented for the early B-typeeclipsing binary OX Cassiopeiae. A new ephemeris is determined.Photometric elements are derived using the WINK model and combined withrecent spectroscopic observations to determine the following absoluteparameters: for the primary star A-mass = 7.2 + or - 0.5 solar masses,R(A) = 4.69 + or - 0.3 solar radii, and T(e,A) = 24,000 K; and for thesecondary star B-mass = 6.3 + or - 0.5 solar masses, R(B) = 4.22 + or -0.3 solar radii, and T(e,B) = 23,400 K. The spectral types of bothcomponents are estimated photometrically to be B2 V. The system is foundto be detached. Rapid apsidal motion of the system is confirmed, and thepossible presence of a third source of light is explored. The distanceand (B-V) color excess are determined for the system to be 2.1 + or -0.2 kpc and 0.50 + or - 0.06, respectively, which preclude OX Cas frombeing a member of the nearby open cluster NGC 381.
| UBV photometry of the open cluster NGC 381
UBV photoelectric and photographic photometry of the field of NGC 381confirms the existence of an open cluster of some 60-plus stars,reddened by E(B-V) = 0.35 mag, at a distance of 950 pc. Cluster agedetermination from main-sequence turnoff point is similar to that of NGC2281 (about 320 million years). The distance and age of the clusterappear to preclude the nearby eclipsing binary OX Cas from membership.
| Catalogue of Eclipsing and Spectroscopic Binary Stars in the Regions of Open Clusters
Not Available
| A photographic survey of galactic clusters. V. NGC 189, I 1590, NGC 358, 366, 381, 433, 436, 457, 609, 637, I 166, NGC 743
Not Available
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
Cataloghi e designazioni:
|
