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An Analysis of the Shapes of Interstellar Extinction Curves. V. The IR-through-UV Curve Morphology
We study the IR-through-UV interstellar extinction curves towards 328Galactic B and late-O stars. We use a new technique which employsstellar atmosphere models in lieu of unreddened "standard" stars. Thistechnique is capable of virtually eliminating spectral mismatch errorsin the curves. It also allows a quantitative assessment of the errorsand enables a rigorous testing of the significance of relationshipsbetween various curve parameters, regardless of whether theiruncertainties are correlated. Analysis of the curves gives the followingresults: (1) In accord with our previous findings, the central positionof the 2175 A extinction bump is mildly variable, its width is highlyvariable, and the two variations are unrelated. (2) Strong correlationsare found among some extinction properties within the UV region, andwithin the IR region. (3) With the exception of a few curves withextreme (i.e., large) values of R(V), the UV and IR portions of Galacticextinction curves are not correlated with each other. (4) The largesightline-to-sightline variation seen in our sample implies that anyaverage Galactic extinction curve will always reflect the biases of itsparent sample. (5) The use of an average curve to deredden a spectralenergy distribution (SED) will result in significant errors, and arealistic error budget for the dereddened SED must include the observedvariance of Galactic curves. While the observed largesightline-to-sightline variations, and the lack of correlation among thevarious features of the curves, make it difficult to meaningfullycharacterize average extinction properties, they demonstrate thatextinction curves respond sensitively to local conditions. Thus, eachcurve contains potentially unique information about the grains along itssightline.
| CCD BV survey of 42 open clusters
Aims.We present results of a photometric survey whose aim was to derivestructural and astrophysical parameters for 42 open clusters. While oursample is definitively not representative of the total open clustersample in the Galaxy, it does cover a wide range of cluster parametersand is uniform enough to allow for simple statistical considerations. Methods: BV wide-field CCD photometry was obtained for open clusters forwhich photometric, structural, and dynamical evolution parameters weredetermined. The limiting and core radii were determined by analyzingradial density profiles. The ages, reddenings, and distances wereobtained from the solar metallicity isochrone fitting. The mass functionwas used to study the dynamical state of the systems, mass segregationeffect and to estimate the total mass and number of cluster members. Results: This study reports on the first determination of basicparameters for 11 out of 42 observed open clusters. The angular sizesfor the majority of the observed clusters appear to be several timeslarger than the catalogue data indicate. The core and limiting clusterradii are correlated and the latter parameter is 3.2 times larger onaverage. The limiting radius increases with the cluster's mass, and boththe limiting and core radii decrease in the course of dynamicalevolution. For dynamically not advanced clusters, the mass functionslope is similar to the universal IMF slope. For more evolved systems,the effect of evaporation of low-mass members is clearly visible. Theinitial mass segregation is present in all the observed young clusters,whereas the dynamical mass segregation appears in clusters older thanabout log({age}) = 8. Low-mass stars are deficient in the cores ofclusters older than log({age}) = 8.5 and not younger than one relaxationtime.Tables 1-5 are only available in electronic form at http://www.aanda.org
| 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
| Open cluster remnants: an observational overview
The state of the art in the current research on the final stages of OpenStar Clusters dynamical evolution is presented. The focus will be onobservational studies and their achievements. By combining togetherphotometric, spectroscopic and astrometric material, a new look at thisexciting topic is now possible, thus providing a solid observationalfoundation for a new generation of theoretical studies on the subject.
| 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.
| The intermediate-age open cluster NGC 2112
We report on BVI charge-coupled device photometry of a field centred onthe region of the intermediate-age open cluster NGC 2112 down to V= 21.Owing to the smaller field coverage, we are able to limit the effect offield star contamination that, in the past, hampered precisedeterminations of the cluster age and distance. In this way, we provideupdated estimates of the fundamental parameters for NGC 2112. Havingextended the photometry to the I passband, we are able to construct acolour-colour diagram, from which we infer a reddening E(B-V) = 0.63 +/-0.14 mag. The comparison of the colour-magnitude diagram withtheoretical isochrones leads to a distance of 850 +/- 100 pc and an ageof 2.0 +/- 0.3 Gyr. While the distance is in agreement with previousdeterminations, the age turns out to be much better constrained andsignificantly lower than previous estimates.
| 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.
| The intermediate-age open cluster NGC 2158
We report on UBVRI CCD photometry of two overlapping fields in theregion of the intermediate-age open cluster NGC 2158 down to V =21. Byanalysing colour-colour (CC) and colour-magnitude diagrams (CMDs) weinfer a reddening E (B -V )=0.55+/-0.10, a distance of 3600+/-400pc, andan age of about 2Gyr. Synthetic CMDs constructed with these parameters(but fixing E (B -V )=0.60 and [Fe/H]=-0.60), and including binaries,field contamination and photometric errors, yield a good description ofthe observed CMD. The elongated shape of the clump of red giants in theCMD is interpreted as resulting from a differential reddening of aboutΔE (B -V )=0.06 across the cluster, in the direction perpendicularto the Galactic plane. NGC 2158 turns out to be an intermediate-age opencluster with an anomalously low metal content. The combination of theseparameters, together with the analysis of the cluster orbit, suggeststhat the cluster belongs to the old thin disc population.
| Photometry of dissolving star cluster candidates. The cases of NGC 7036 and NGC 7772
We present CCD UBVI observations obtained in the field of the twopreviously unstudied dissolving open cluster candidates NGC 7036 and NGC7772. Our analysis suggests that both the objects are Open ClusterRemnants (OCR). NGC 7036 is an open cluster remnant with a core radiusof about 3-4 arcmin. We derive for the first time estimates of itsfundamental parameters. We identify 17 likely members that define agroup of stars at 1 kpc from the Sun, with a low reddening E(B-V) ~ 0.1,and with an age of about 3-4 Gyr. As for NGC 7772, we identify 14 likelymembers, that define a group of stars with a very low reddening (E(B-V)~ 0.03), are 1.5 Gyr old and are located about 1.5 kpc from the Sun.Based on observations carried out at Mt Ekar, Asiago, Italy. Photometryis only available 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/385/471
| The Galactic System of Open Star Clusters: A Personal Perspective
Technology is now allowing for the investigation of star clustersoutside of the Milky Way. As attention turns to the extragalactic starclusters, a perception that the system of star clusters in the Milky Wayis well understood may grow, resulting in the neglect of these importantobjects. In this review, the status of our understanding of the MilkyWay's open star cluster population will be discussed. Specifically, Iwill attempt to illustrate not only the important information that canand must be learned from these nearby star clusters, but also the degreeto which our understanding of the Galactic open clusters remainsincomplete.
| 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
| 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].
| Classification of Red Stars with Spectral Absorption Bands Observed in the Near-Infrared Range
The results of a spectral classification of 257 M stars observed in theCepheus region are given. Their equatorial coordinates, photographicstellar magnitudes, and spectral subtypes were determined. These starsare giants and supergiants, in all probability. None of them appear in acatalog of variable stars. It is assumed that variability might bedetected in many of them upon further study. Fifty-two of the stars havebeen identified with infrared sources.
| On the stellar content of the open clusters Melotte 105, Hogg 15, Pismis 21 and Ruprecht 140
CCD observations in the B, V and I passbands have been used to generatecolour-magnitude diagrams reaching down to V ~ 19 mag for two slightlycharacterized (Melotte 105 and Hogg 15) and two almost unstudied (Pismis21 and Ruprecht 140) open clusters. The sample consists of about 1300stars observed in fields of about 4arcmin x4arcmin . Our analysis showsthat neither Pismis 21 nor Ruprecht 140 are genuine open clusters sinceno clear main sequences or other meaningful features can be seen intheir colour-magnitude diagrams. Melotte 105 and Hogg 15 are openclusters affected by E(B-V) = 0.42 +/- 0.03 and 0.95 +/- 0.05,respectively. Their distances to the Sun have been estimated as 2.2 +/-0.3 and 2.6 +/- 0.08 kpc, respectively, while the corresponding agesestimated from empirical isochrones fitted to the Main Sequence clustermembers are ~ 350 Myr and 300 Myr, respectively. The present data arenot consistent with the membership of the WN6 star HDE 311884 to Hogg15. Tables 2 to 5 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.793.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/370/931
| 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.
| New variable stars in NGC 7762
We have discovered three new variable stars in NGC 7762, a northern opencluster. We present here the Johnsons V light curves of these stars.
| 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.
| Thirty years of research with the Baldone Schmidt Telescope
We describe the research done with the Baldone Schmidt telescope(80/120/240 cm) of the Radioastrophysical Observatory. The telescope hastwo objective prisms with reciprocal dispersions of 600 and 1130 A/mm atH-gamma. One of the main research projects is the search for andphotometric study of galactic carbon stars. The telescope has also beenused for novae studies in M 31 and stellar photometry in open clustersand fields of special interest. Comet studies, particularly during theInternational Halley Watch, proved to be another successful applicationof the telescope. The archive of the Baldone Schmidt telescope containsnearly 20,000 direct and 2000 spectral plates and films.
| The Old Open Cluster, Berkeley 66
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1604P&db_key=AST
| NGC 7762: A forgotten moderate age open cluster.
We report CCD B and V photometry for the central region of the old opencluster NGC 7762. The cluster appears very loose and occupies a largesky area. The Colour Magnitude Diagram (CMD) shows a distinct MainSequence (MS) down to V=~16.5, and a couple of evolved stars. The bottomof the sequence is characterized by a large spread, much greater thanthe expected broadness due to photometric errors, and probably relatedto low mass stars evaporation. The analysis here carried out allows usto conclude that NGC 7762 in an intermediate age cluster about 1.8Gyrold. The comparison with theoretical isochrones from the Padova groupconstrains colour excess and apparent distance modulus in the range0.85-0.90 and 12.00-12.20, respectively. The distance to the Sun comesout to be 800 pc, somewhat lower than Chincarini's (1966) estimate.
| 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%.
| 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.
| Searching for embedded clusters in the Cepheus-Cassiopeia region
A relatively extended galactic region in the upper Cep/Cas was searchedfor extremely young embedded star clusters with the aid of a multistageclustering method developed by us. Even if some of the stages haveheuristic nature, the method that we worked out and describe here provedto be an effective tool for pattern analysis of distribution of pointsources selected from the IRAS Point Source Catalog (IPSC). We used itsuccessfully in studying star forming regions to locate significantenhancements (clusters) in the point source surface densitydistribution. We applied our nearest neighbors statistics basedalgorithm to a subsample of IRAS point sources resulting from a set ofselection criteria formed in order to extract cold and young stellar andprotostellar candidates from IPSC. We succeeded in identifying smallgroups among these cold sources which we think to be embedded groups ofprotostellar or young stellar objects.
| Integrated parameters of open clusters
Integrated magnitudes and colors of population I synthetic clusters havebeen derived using theoretical evolutionary tracks and an age-dependedntinitial mass function. A comparison of the theoretically obtainedintegrated parameters with the observational data of open clusters inthe Milky Way and clusters in the LMC has also been made. It is foundthat the observed dependences show a better agreement with thetheoretical dependences obtained in the present work than thetheoretical dependences obtained by earlier authors. It is alsoconcluded that the clusters in the LMC in general show a mean reddeningof E(B-V) = 0.12 mag.
| On the universality of initial mass function of open star clusters
The luminosity functions of 23 open star clusters of age less than 1 Gyrare determined by the method of star counts on astronegatives obtainedwith the Schmidt telescope at the Radioastrophysical Observatory of theAcademy of Sciences of the Latvian SSR. The differential and integralluminosity functions are then used to calculate the initial luminosity(mass) functions, and the results are presented in tables. It isconcluded that, for time intervals up to 1 Gyr and distances up to 2kpc, the process of star formation leads to identical mass distributionsin different protoclouds, confirming the hypothesis that theopen-cluster zero-age luminosity function is universally valid.
| The Guide Star Photometric Catalog.
This paper presents data and finding charts for the Guide StarPhotometric Catalog (GSPC), which is an all-sky set of 1477pohotoelectrically determined BV sequences covering the magnitude rangefrom 9 to 15. The GSPC was created to provide photometric calibratorsfor the Guide Star Catalog, which is a catalog of approximately 2 x 10to the 7th objects needed to support the pointing of the Hubble SpaceTelescope. For declinations greater than +3 deg, the sequences generallylie near the centers of the original (Palomar Observatory-NationalGeographic Society) Sky Atlas, while for smaller declinations they lienear the centers for the ESO/SERC Southern Sky Atlas. The sequencesnominally contain (at least) six stars, each with a photometricprecision of 0.05 mag. In practice, a small number of sequences containsfewer stars, and the precisions achieved for the faintest stars are morenearly 0.1 mag.
| Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)
Not Available
| Red giants in old open clusters - A test for stellar evolution
A group of 38 among the oldest open clusters has been analyzed usingtheoretical isochrones derived by Ciardullo and Demarque (1977) andevolutionary tracks for central He-burning of Sweigart and Gross (1976).This analysis has been performed in two steps: - comparison of HRdiagrams with isochrones statistical check of the fit between observedluminosity distributions of red giant stars and the theoretical ones.The following conclusions have been reached: - clusters older than 2 or3 billion years (B-V) equal to or greater than 0.35 at MS turnoff pointgenerally agree with theoretical description and allow the determinationof reliable ages from the distribution of red giants, - for clustersyounger than 2 or 3 billion years, the theory fails in theinterpretation of their red giant stars and the statistical analysisrejects all the tested distributions. In fact, their behavior is similarto that of even younger clusters, in which the evolved stars, duringshell H-burning, have non-degenerate cores and therefore do not undergothe helium flash. It is suggested that such behavior could be attributedto overshooting from the convective core during central H-burning in themass range 1.3-2.2 solar masses.
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