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New catalogue of blue stragglers in open clusters
We present a catalogue of blue-straggler candidates in galactic openclusters. It is based on the inspection of the colour-magnitude diagramsof the clusters, and it updates and supersedesthe first version(Ahumada & Lapasset 1995). A new bibliographical search was made foreach cluster, and the resulting information is organised into twotables. Some methodological aspects have been revised, in particularthose concerning the delimitation of the area in the diagrams where thestragglers are selected.A total of 1887 blue-straggler candidates have been found in 427 openclusters of all ages, doubling the original number. The catalogued starsare classified into two categories mainly according to membershipinformation.The whole catalogue (Tables 8, 9, notes, and references) is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/463/789
| First estimates of the fundamental parameters of the relatively bright Galactic open cluster NGC 5288
In this paper we present charge-coupled device (CCD) images in theJohnson B and V and Kron-Cousins I passbands for the previouslyunstudied open cluster NGC 5288. The sample consists of 15688 starsreaching down to V~ 20.5. The cluster appears to have a relatively smallbut conspicuous nucleus and a low-density extended coronal region. Starcounts carried out in 25 × 25 pixel2 boxes distributedthroughout the whole observed field allowed us to estimate the angularcore and corona radii as ~1.3 and 6.3arcmin, respectively. Our analysissuggests that NGC 5288 is moderately young and probably more metal-richthan the Sun. Adopting the theoretical metal content Z= 0.040, whichprovides the best global fit, we derive an age of130+40-30Myr. Simultaneously, we have obtainedcolour excesses E(B-V) = 0.75 and E(V-I) = 0.95 and an apparent distancemodulus V-MV= 14.00. The law of interstellar extinction inthe cluster direction is found to be normal. NGC 5288 is located at 2.1+/- 0.3kpc from the Sun beyond the Carina spiral feature and ~7.4kpcfrom the Galactic Centre. The cluster metallicity seems to be compatiblewith the cluster position in the Galaxy, given the recognized radialabundance gradient in the disc. For the first time, in this paper wedetermine the basic parameters for the open cluster NGC 5381, situatedin the same direction as NGC 5288. This determination was reached byusing CCD VI data published almost a decade ago by Pietrzyński etal. (1997) for NGC 5381. The properties of some open clusters alignedalong the line of sight of NGC 5288 are examined. The properties ofclusters of similar ages to NGC 5288 are also looked into. Evidence ispresented that these did not form mainly along the spiral arms butrather in the thin Galactic disc (Z~+/-100pc).
| 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.
| New fundamental parameters for the inner disk open cluster Lyngå 11
We have obtained CCD BVIKC photometry down to V ˜ 21.5for the open cluster Lyngå 11 and its surrounding field. Thispreviously unstudied object appears to be rich and highly absorbed. Acluster angular radius of 4.5′ ± 0.5′, equivalent to(3.0 ± 0.3) pc, is estimated from star counts in 100-pixel a sideboxes distributed throughout the whole observed field. Our analysissuggests that Lyngå 11 is moderately young and probably of solarmetallicity. Adopting the theoretical metal content Z = 0.02, whichprovides the best global fit, we derive an age of (630 ± 70) Myr.Simultaneously, colour excesses E(B ‑ V) = 0.70 and E(V ‑ I)= 0.85 and an apparent distance modulus V ‑ MV = 14.0are obtained. These results place Lyngå 11 at a distance of (2.3± 0.5) kpc from the Sun and ˜6.5 kpc from the Galacticcentre. The properties of a sample of clusters aligned along theline-of-sight of Lyngå 11 are examined as well.
| 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.
| CCD photometry of the open clusters NGC 2627, NGC 5617, Pismis 7, and Ruprecht 75
We present broad-band, optical CCD photometry of the galactic openclusters NGC 2627, NGC 5617, Pismis 7, and Ruprecht 75. By means of thecomparison between the observed cluster sequences and the theoreticalisochrones of Girardi et al. (2000, A&AS 141, 371), we derive thefollowing parameters. For NGC 2627,E(B-V)=0.04-0.02+0.10, log(age)=9.25+0.10-0.05, and (m-M)_0 =11.33±0.31; for NGC 5617,E(B-V)=0.54-0.08+0.09 , log (age)=8.15-0.15+0.25, and (m-M)_0 =11.53-0.43+0.36; for Pismis 7, E(B-V)=0.69-0.16+0.18, log (age)= 8.70±0.10, and(m-M)_0 =13.46±0.56; and for Ruprecht 75, E(B-V)=0.24-0.13+0.18, log (age)= 9.15± 0.05, and(m-M)_0 =13.16-0.57+0.60. The isochrones have beenrenormalized to the solar values (B-V)_ȯ=0.65 and M_V=4.84, alongthe lines established in Ahumada (2003, RMxAA 39, 41), and following,for instance, Twarog, Ashman & Anthony-Twarog (1997, AJ 114, 2556).Besides, a comparison is made between the isochrones by Girardi et al.(2000) and those, also renormalized, by Castellani, Degl'Innocenti &Marconi (1999, MNRAS 303, 265) in the range of ages and metallicities ofinterest. It is noted that discrepancies arise mainly for the amount ofcore overshooting incorporated into the models, which implies differentages for a given cluster.
| Improvements on the fundamental parameters of the open cluster Tombaugh 1 through Washington system photometry
We present CCD photometry in the Washington system C and T1passbands down to T1 ˜ 18.5 mag in the field ofTombaugh 1, a little studied open cluster located in the third Galacticquadrant. We measured T1 magnitudes and C-T1colours for a total of 1351 stars distributed throughout an area of 13.6arcmin × 13.6 arcmin. A cluster radius of 4.3 arcmin ± 0.3arcmin was estimated from star counts in 100-pixel a side boxesdistributed throughout the entire observed field. Based on the best fitsof isochrones computed by the Geneva group for Z = 0.008 to theT1 vs. C-T1 colour-magnitude diagram, we derive acolour excess E(C-T1) = 0.55 ± 0.10, equivalent toE(B-V) = 0.30 ± 0.05, a distance of (2.2 ± 0.5) kpc fromthe Sun and an age of 1.3 +0.1-0.2 Gyr. The lattervalue is in good agreement with that derived from the independentmetallicity δT1 index defined in Geisler et al. (1997,AJ, 114, 1920). An independent metallicity estimation using the[MT_1, (C-T1)0] plane with the standardgiant branches of Geisler & Sarajedini (1999, AJ, 117, 308) yields[Fe/H] = -0.30 ± 0.25 dex, a value which lends support to the oneobtained from the isochrone fit. Tombaugh 1 is then found to be arelatively metal-poor intermediate-age open cluster.
| The relatively young, metal-poor and distant open cluster NGC 2324
We have obtained CCD photometry in the Johnson V, Kron-Cousins I andCT1 Washington systems for NGC 2324, a rich open clusterlocated 35° from the Galactic anticentre direction. We measuredV magnitudes and V-I colours for 2865 stars and T1 magnitudesand C-T1 colours for 1815 stars in an area of 13.6 arcmin× 13.6 arcmin. The comparison of the cluster colour-magnitudediagrams with isochrones of the Geneva group yield E(V-I) = 0.33± 0.07 and V-MV = 13.70 ± 0.15 for log t = 8.65(t = 440 Myr) and Z = 0.008 ([Fe/H] = -0.40), and E(C-T1) =0.40 ± 0.10 and T1-MT1 = 13.65 ±0.15 for the same age and metallicity level. The resulting E(V-I)reddening value implies E(B-V) = 0.25 ± 0.05 and a distance fromthe Sun of (3.8 ± 0.5) kpc. Star counts carried out within andoutside the cluster region allowed us to estimate the cluster angularradius as 5.3 arcmin ± 0.3 arcmin (5.9 pc). When using the E(B-V)reddening value here derived and the original Washington photometricdata of \citet{gcm91} for the stars confirmed as red cluster giants fromCoravel radial velocities, we found [Fe/H] = -0.31 ± 0.04, whichis in good agreement with the best fits of isochrones. Therefore, NGC2324 is found to be a relatively young, metal-poor and distant opencluster located beyond the Perseus spiral arm. A comparison of NGC 2324with 10 well-known open clusters of nearly the same age shows that thecluster metal abundance and its position in the Galaxy are consistentwith the existence of a radial abundance gradient of -0.07 dexkpc-1 in the Galactic disc.
| The old open cluster Trumpler 5: a reddened, metal-poor anticentre cluster
CCD observations in the Johnson V, Kron-Cousins I and the Washingtonsystem C and T1 passbands have been used to generatecolour-magnitude diagrams (CMDs) reaching down to V~ 21.0 mag andT1~ 19.0 for Trumpler 5, an old open cluster located towardsthe Galactic anticentre. Our data analysis confirms the existence ofnon-uniform extinction over the face of the cluster, the mean E(V-I) andE(C-T1) values being 0.80 +/- 0.05 and 1.17 +/- 0.15,respectively. Through comparison of the cluster CMDs with theoreticalisochrones of the Geneva group, Washington Standard Giant Branches andmeasures of δV and δT1 indices, we derive thefollowing values for the cluster apparent distance modulus, age, andmetallicity: V-MV= 13.80 +/- 0.30 (corresponding to adistance from the Sun of 2.4 +/- 0.5 kpc and 0.04 kpc above the Galacticplane), t= 5.0 +/- 0.5 Gyr and [Fe/H]=-0.30 +/- 0.15. We estimate thecluster angular radius to be about 7.7 arcmin (=5.4 pc) from star countscarried out within and outside the cluster field.
| The age of the oldest Open Clusters
We determine ages of 71 old Open Clusters by a two-step method: we usemain-squence fitting to 10 selected clusters, in order to obtain theirdistances, and derive their ages from comparison with our own isochronesused before for Globular Clusters. We then calibrate the morphologicalage indicator δ(V), which can be obtained for all remainingclusters, in terms of age and metallicity. Particular care is taken toensure consistency in the whole procedure. The resulting Open Clusterages connect well to our previous Globular Cluster results. From theOpen Cluster sample, as well as from the combined sample, questionsregarding the formation process of Galactic components are addressed.The age of the oldest open clusters (NGC 6791 and Be 17) is of the orderof 10 Gyr. We determine a delay by 2.0±1.5 Gyr between the startof the halo and thin disk formation, whereas thin and thick disk startedto form approximately at the same time. We do not find any significantage-metallicity relationship for the open cluster sample. The cumulativeage distribution of the whole open cluster sample shows a moderatelysignificant (˜ 2σ level) departure from the predictions foran exponentially declining dissolution rate with timescale of 2.5 Gyr.The cumulative age distribution does not show any trend withgalactocentric distance, but the clusters with larger height to theGalactic plane have an excess of objects between 2-4 and 6 Gyr withrespect to their counterpart closer to the plane of the Galaxy.
| Intermediate-age Galactic open clusters: fundamental parameters of NGC 2627
Charge-coupled device (CCD) photometry in the Johnson V, Kron-Cousins Iand Washington CMT1 systems is presented in the field of thepoorly known open cluster NGC 2627. Four independent Washingtonabundance indices yield a mean cluster metallicity of [Fe/H]=-0.12 +/-0.08, which is compatible with the existence of a radial gradient in theGalactic disc. The resultant colour-magnitude diagrams indicate that thecluster is an intermediate-age object of 1.4 Gyr. Based on the best fitsof the Geneva group's isochrones to the (V, V-I) and (T1,C-T1) diagrams, we estimate E(V-I) = 0.25 +/- 0.05 andV-MV= 11.80 +/- 0.25 for logt= 9.15, and E(C-T1) =0.23 +/- 0.07 and T1-MT1= 11.85 +/-0.25 for logt= 9.10, respectively, assuming solar metal content. Thederived reddening value E(C-T1) implies E(B-V) = 0.12 +/-0.07 and a distance from the Sun of 2.0 +/- 0.4 kpc. Using the WEBDAdata base and the available literature, we re-examined the overallproperties of all the open clusters with ages between 0.6 and 2.5 Gyr.We identified peaks of cluster formation at 0.7-0.8, 1.0-1.1, 1.6-1.7and 2.0-2.1 Gyr, separated by relative quiescent epochs of ~0.2-0.3 Gyr.We also estimated a radial abundance gradient of -0.08 +/- 0.02, whichis consistent with the most recent determinations for the Galactic disc,but no clear evidence for a gradient perpendicular to the Galactic planeis found.
| 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.
| 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.
| 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.
| 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].
| Foreground and background dust in star cluster directions
This paper compares reddening values E(B-V) derived from the stellarcontent of 103 old open clusters and 147 globular clusters of the MilkyWay with those derived from DIRBE/IRAS 100 mu m dust emission in thesame directions. Star clusters at |b|> 20deg showcomparable reddening values between the two methods, in agreement withthe fact that most of them are located beyond the disk dust layer. Forvery low galactic latitude lines of sight, differences occur in thesense that DIRBE/IRAS reddening values can be substantially larger,suggesting effects due to the depth distribution of the dust. Thedifferences appear to arise from dust in the background of the clustersconsistent with a dust layer where important extinction occurs up todistances from the Plane of ~ 300 pc. For 3 % of the sample asignificant background dust contribution might be explained by higherdust clouds. We find evidence that the Milky Way dust lane and higherdust clouds are similar to those of several edge-on spiral galaxiesrecently studied in detail by means of CCD imaging.
| Upper main sequence and blue stragglers in galactic open clusters.
Not Available
| The Old Open Clusters Of The Milky Way
The Galactic open clusters, in particular the oldest members, serve asexcellent probes of the structure and evolution of the Galactic disk.Individual clusters provide excellent tests of stellar and dynamicalevolution. Cluster spatial and age distributions provide insight intothe processes of cluster formation and destruction that have allowedsubstantial numbers of old open clusters to survive.Spectroscopic andphotometric data for the old clusters yield kinematic, abundance, andage information that clarifies the relationship between the old opencluster population and other Galactic populations. New samples of oldopen clusters, which span a large range in distance and age, are used todefine disk abundance gradients and the cluster age-metallicityrelationship, and they point to a complex history of chemical enrichmentand mixing in the disk.
| The galactic system of old star clusters: The development of the galactic disk
The vast majority of open clusters persist as clusters for no more thana few hundred million years, but the few which survive for much longerperiods constitute a unique sample for probing the evolution of thegalactic disk. In a charge coupled device (CCD) photometric survey forpossible old open clusters combined with previously publishedphotometry, we have developed a list of 72 clusters of the age of theHyades or older (Phelps (1994). Using our version of parameters based onthe luminosity difference between the main sequence turnoff and thehorizontal branch and on the color difference between the turnoff andthe giant branch, we have calculated a 'Morphological Age Index' (MAI)for the clusters in our list and for a sample of globular clusters. Wefind that the MAI is well correlated with the logarithm of cluster ages,as determined by fitting to theoretical isochrones. We conclude that theindex is a good measure of the relative ages of both globular and openclusters, although uncertainties in the models and residual metallicityeffects prevent the use of the MAI as a definitive calibration of actualcluster ages. The age distribution of the open clusters overlaps that ofthe globular clusters, indicating that the galactic disk began todevelop toward the end of the period of star formation in the galactichalo. The open cluster age distribution can be fit approximately with atwo-component exponential decay function; one component can beidentified as the tail of the dominant population of thin disk openclusters with an age scale factor of 200 Myr, and the other consists oflonger-lived clusters with an age scale of 4 Gyr. The young openclusters are distributed on the galactic plane almost symmetricallyabout the Sun with a scale height perpendicular to the galactic plane of55 pc. The old population consists of rich clusters found only in theouter disk, nore than RGC = 7.5 kpc from the galactic center;this population has a scale height of 375 pc. After accounting for thetwo exponential distributions of cluster ages, there are indications ofan excess of clusters in the age range of 5-7 Gyr; there may have beenlarge bursts of star formation in that period, or perhaps a largerproportion of the clusters forming at that time had advantageous orbitsfor survival. Either circumstance is consistent with the idea that thegalactic disk has been repeatedly disturbed, possibly in collisions orother interactions with external systems, resulting in the occasionalformation of clusters with relatively large velocities perpendicular tothe plane; these are the clusters that have survived until the present.Finally, the repeated accretion of low angular momentum material ontothe disk from the halo or beyond would also explain the observed radialcomposition gradient and the lack of a correlation between open clustermetallicity and age found by Friel & Janes (1993).
| Development of the Galactic disk: A search for the oldest open clusters
In an extensive charge coupled devices (CCD) photometric survey ofpotential old open clusters, we have identified a number of systems thatare indeed old; some of them are among the oldest of the open clusters.Using our versions of two well-known morphological age indices, onebased on the luminosity difference between the main sequence turnoff andthe horizontal branch and the other on the color difference between theturnoff and the giant branch, we have ranked the open clusters inapproximate order of age. Our data together with previously publishedphotometry of other old open clusters, yields a catalogue of 72 clustersof the age of Hyades or older with 19 of the clusters as old or olderthan M67 (about 5 Gyr). Among the oldest open clusters are Be 17, Cr261, NGC 6791, Be 54, and AM 2. Be 17 and another old cluster, Lynga 7,are possibly as old as the youngest globulars. The data also suggestthat the formation rate of open clusters may have been higher early inthe history of the disk than at intermediate times since numerousclusters have survived from that time.
| CCD observations in 7 open clusters - NGC2421, NGC2439, NGC2489, NGC2567, NGC2627, NGC2658 and NGC2910
Photometric UBVIc data are presented for the open clusters NGC2439,NGC2489, NGC2567, NGC2627, NGC2658, and NGC2910. From a combination ofthe new BVIc technique and the analysis of the CMDs, the color excessE(B-V), the distance modulus, and approximate age are given for theseclusters and NGC2421.
| Uniform survey of clusters in the southern Milky Way.
Abstract image available at:http://adsabs.harvard.edu/abs/1975AJ.....80...11V
| A list of clusters that may be old.
Not Available
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