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The Bologna Open Cluster Chemical Evolution Project: Midterm Results from the Photometric Sample
We describe a long-term project aimed at deriving information on thechemical evolution of the Galactic disk from a large sample of openclusters. The main property of this project is that all clusters areanalyzed in a homogeneous way to guarantee the robustness of the rankingin age, distance, and metallicity. Special emphasis is devoted to theevolution of the earliest phases of the Galactic disk evolution, forwhich clusters have superior reliability with respect to other types ofevolution indicators. The project is twofold: on one hand we derive theage, distance, and reddening (and indicative metallicity) byinterpreting deep and accurate photometric data with stellar evolutionmodels, and on the other hand, we derive the chemical abundances fromhigh-resolution spectroscopy. Here we describe our overall goals andapproaches and report on the midterm project status of the photometricpart, with 16 clusters already studied, covering an age interval from0.1 to 6 Gyr and galactocentric distances from 6.6 to 21 kpc. Theimportance of quantifying the theoretical uncertainties by deriving thecluster parameters with various sets of stellar models is emphasized.Stellar evolution models assuming overshooting from convective regionsappear to better reproduce the photometric properties of the clusterstars. The examined clusters show a clear metallicity dependence on thegalactocentric distance and no dependence on age. The tight relationbetween cluster age and magnitude difference between the main-sequenceturnoff and the red clump is confirmed.
| Deepsky delights.
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.
| Ages and metallicities of star clusters: New calibrations and diagnostic diagrams from visible integrated spectra
We present homogeneous scales of ages and metallicities for starclusters from very young objects, through intermediate-age ones up tothe oldest known clusters. All the selected clusters have integratedspectra in the visible range, as well as reliable determinations oftheir ages and metallicities. From these spectra equivalent widths (EWs)of K Ca II, G band (CH) and Mg I metallic, and Hδ, Hγ andHβ Balmer lines have been measured homogeneously. The analysis ofthese EWs shows that the EW sums of the metallic and Balmer H lines,separately, are good indicators of cluster age for objects younger than10 Gyr, and that the former is also sensitive to cluster metallicity forages greater than 10 Gyr. We propose an iterative procedure forestimating cluster ages by employing two new diagnostic diagrams and agecalibrations based on the above EW sums. For clusters older than 10 Gyr,we also provide a calibration to derive their overall metal contents.
| Urban Astronomy: Observing the Messier Objects from the City
Not Available
| 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 spectral evolution of Galactic open clusters
We present a library of 47 open-cluster integrated spectra, mostlyobtained at CASLEO (San Juan, Argentina) in the range 3600 < λ< 7400 Å, which are made available at CDS. The data arecombined with previous spectra to obtain 10 high signal-to-noise ratiobasic templates in the young and intermediate-age domains, which arealso provided in the library. These Galactic disc templates representthe increased time resolution spectral evolution of a stellar populationunit around the Solar metallicity level. The improved signal-to-noiseratio of the present templates with respect to previous template lists,together with their increased time resolution, allowed us to improve thefundamental parameters of some open clusters. The present spectrallibrary will be useful for several astrophysical applications,particularly for population syntheses of star-forming giant galaxies.
| 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.
| 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].
| A study of the old galactic star cluster Berkeley 32
We present new CCD photometry of the distant old open star clusterBerkeley 32 in Johnson V and Cousins I passbands. A total of ~ 3200stars have been observed in a field of about 13? x 13?. Thecolour-magnitude diagram (CMD) in V, (V - I) has been generated down toV = 22 mag. A broad but well defined main sequence is clearly visible.Some blue stragglers, a well developed subgiant branch and a Red Clumpare also seen. By fitting isochrones to this CMD as well as to otherCMDs available in the literature, and using the Red Clump location, thereddening, distance and age of the star cluster have been determined.The cluster has a distance of ~ 3.3 kpc, its radius is about 2.4 pc; thereddening E(B-V) is 0.08 mag and the age is ~ 6.3 Gyr. By comparisonwith theoretical isochrones, a metallicity of [Fe/H] ??-0.2 dex has beenestimated. Theoretical isochrones have been used to convert the observed clusterluminosity function into a mass function in the mass range ~ 0.6-1.1 M?.We find a much flatter mass function than what has been found for youngclusters. If the mass function is a power law dN ~ m?dm, then we get ??=-0.5 ± 0.3. This may be seen as a signature of the highly evolveddynamical state of the cluster.
| A photometric study of the intermediate age open cluster King 5
We report on near IR (J and K bands) observations of an 8' x8' region centered on the poorly studied open cluster King 5,for which only optical photometry existed. Photometry of two nearbyfields is also reported. We found that the cluster is of moderate age(1.0 Gyr old), intermediate in age between the Hyades and NGC 752.Combining optical and IR photometry we obtain estimates for the clusterparameters. The color excesses E(J-K), E(V-I) and E(V-K) are 0.50, 1.10and 2.45, respectively. The true distance modulus turns out to be(m-M)_0 = 11.40+/- 0.15. As a consequence, King 5 is 1.9 kpc far fromthe Sun. Based on observations taken at TIRGO.
| The Galactic disk: study of four low latitude Galactic fields
We present deep V and I photometry of stellar fields in four previouslyunstudied low latitude regions of the Galactic disk. All observed fieldsare located at the western side of the Galactic Center in the directionof the Coalsack-Carina region. They are chosen on the large scalesurface photometry of the Milky Way (Hoffmann et al., 1998 andKimeswenger et al., 1993) and corresponding term maps (Schlosser et al.,1995) as being affected by low interstellar absorption and havingintegrated colours typical of a very young population. Two of them aresuspected to cross the inner spiral arm. More than 105 starsare detected in total, down to a magnitude of V ~ 23.5. Theobservational colour-magnitude diagrams (CMDs) and luminosity functionsare analyzed using a revised version of the Padova software described inBertelli et al. (1995). The interstellar extinction along the line ofsight is derived and found to be in reasonable agreement with\cite{Men+98} maps. Due to the low galactic latitude of the studiedfields, the scale length and mainly the scale height of the thick diskare not strongly constrained by the observations. However a thin diskscale height of about 250+/- 60 pc seems to be favored. The data arevery sensitive to the star formation rate of the thin disk. A decreasingstar formation rate is necessary to reproduce the distribution of thestars in the colour-magnitude diagrams as well as the luminosityfunctions. A constant or a strongly increasing star formation rate asderived using Hipparcos data for the solar neighborhood (Bertelli et al.1999) are marginally in agreement with the luminosity functions but theyare at odds with the CMDs. The analysis of these data suggest that thesolar neighborhood star formation rate cannot be considered asrepresentative for the whole thin disk. To properly reproduce theluminosity functions a thick disk component having a local density ofabout 2-4% must be included. From the star-counts the local neighborhoodmass density in stars more massive than 0.1 Msun is found tobe 0.036-0.02 Msun pc -3. Finally, the location ofinner spiral arm is discussed. We find evidence of a population youngerthan 108 yr distributed in a spiral arm at a distance of1.3+/- 0.2 and 1.5 +/- 0.2 Kpc in the directions l ~ 292 and l ~ 305respectively. This result is consistent with the spiral arm patterndefined on the basis of pulsars and young associations (\cite{TayCor93};\cite{Hum76}). Due to the small field of view two of the studied fieldsdo not set strong constrains on the scale height and lenght of the disk.A larger field of view, see e.g. the WFI at the 2.2m ESO telescopehaving 30' x 30' would allow us to have goodstatistics down to faint magnitudes. Based on observations collected atthe European Southern Observatory, La Silla, Chile
| Old Open Clusters: Constraints on Disk age and Evolution
Not Available
| Mass functions of five distant northern open star clusters
We analyse BVI CCD data of five northern open star clusters in theGalaxy in order to determine their mass functions. The clusters areBerkeley 81, Berkeley 99, NGC 6603, NGC 7044 and NGC 7510. They aredistant (>= 3kpc) and compact (radius <=2.8 arcmin) objects.Except for NGC 7510 whose age is 10 Myr, all are intermediate-age andold star clusters with ages between 0.5 and 3.2 Gyr. The observedcluster luminosity function (LF) is corrected for both dataincompleteness and field star contamination. Theoretical stellarevolutionary isochrones are used to convert LFs into mass functions(MFs). The MF slope becomes flatter if a correction for dataincompleteness is not applied, while it becomes steeper if a correctionfor field star contamination is ignored; however, both correctionsincrease with decreasing stellar brightness. In the mass range ~1-14Msolar, the MF slope of NGC 7510 is 1.1+/-0.2. As the cluster is notdynamically evolved, its present-day MF can be considered as the initialMF. It is not too different from the Salpeter value (x=1.35). In anarrow mass range ~0.6-2 Msolar, the values of the MF slope in the fourintermediate-age and old clusters range from 0.3 to 2.5 and differsignificantly from each other. For Berkeley 99 and NGC 6603, the MFslopes are 1.4+/-0.6 and 1.1+/-0.4 respectively. They agree with theSalpeter value within the errors. However, significantly differentvalues of MF slopes, 2.5+/-0.2 and 0.3+/-0.2, are found for Berkeley 81and NGC 7044 respectively. We therefore conclude that the MF does varyamong this cluster sample. The effects of mass segregation are observedin all the four intermediate-age and old clusters; this segregation ismost probably due to dynamical evolution, as the ages of the clustersare much longer than the corresponding dynamical relaxation times. Thereis no obvious dependence of the MF slope on either Galactocentricdistance or age of the well-studied Galactic open clusters. Except forsome of the dynamically evolved older (age >=50 Myr) clusters, the MFslopes of the clusters are not too different from the Salpeter value.
| BVI CCD photometry of the distant open star clusters Berkeley 81, Berkeley 99, NGC 6603 and NGC 7044
We present CCD observations for the distant northern open star clustersBerkeley 81, Berkeley 99, NGC 6603 and NGC 7044 in BVI photometricpassbands. A total of 9900 stars have been observed in fields of about6x6 arcmin^2 of the sky around the clusters. Colour-magnitude diagramsin V, (B-V) and V, (V-I) have been generated down to V=22 mag and, forthe first time, such diagrams have been produced for the clustersBerkeley 81 and Berkeley 99. The data serve as a base for the study ofmass functions and for comparison with theoretical models. Analysis ofthe radial distribution of stellar surface density indicates that theradius values for Berkeley 81, Berkeley 99, NGC 6603 and NGC 7044 are2.7, 2.8, 2.8 and 2.2 arcmin respectively. By fitting the latestconvective core overshooting isochrones to the colour-magnitude diagramand using its morphological features, reddenings, distances and ages ofthe star clusters have been determined. Broad but well-defined mainsequences with stellar evolutionary effects in the brighter stars areclearly visible in colour-magnitude diagrams of all the clusters understudy. Some blue stragglers along with well-developed giant branches andred giant clumps are also clearly seen in all of them. The clustersstudied here are located at a distance of ~3 kpc, except for Berkeley 99which is located at a distance of 4.9 kpc. Their linear sizes liebetween 3.8 and 8.0 pc; E(B-V) values range from 0.3 to 1.0 mag, whiletheir ages are between 0.5 and 3.2 Gyr. Thus the star clusters studiedhere are of intermediate and high age but are compact and distantobjects.
| HP 1: a blue horizontal branch globular cluster in the bulge
We present V, I colour-magnitude diagrams of the globular cluster HP1obtained at the European Southern Observatory New Technology Telescopeunder exceptional seeing conditions. The cluster shows blue horizontalbranch (HB) and red giant branch morphologies very similar to clustersof intermediate metallicity such as NGC6752 we therefore estimate[Fe/H]ap-1.5 for HP1. The blue HB morphology is extended, which is notunusual for a post-core-collapse cluster. We derive a reddening ofE(B-V)=1.19 and a distance dsolar=6.85kpc. HP1 might be a halo clustercrossing the bulge or belong to the low-metallicity tail of the bulge.
| UBVRI CCD photometry of the old open cluster NGC 6253
We present UBVRI photometry for the old open cluster NGC 6253. Fromcomparison of the observed colour-magnitude diagrams with simulationsbased on stellar evolutionary models we derive in a self-consistent waythe reddening, the distance and the age of the cluster:E(B-V)=0.23-0.32, (m-M)_0=10.9+/-0.1, with metallicity approximatelydouble the solar value and age ~=3 Gyr. The cluster has a binarysequence, discernible even through the field contamination, suggestingthat about 1/3 of the cluster members belong to binary, or multiple,systems.
| Constraints on disk age and evolution from the study of old open clusters
Not Available
| CCD photometry of the old open cluster Collinder 261.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996MNRAS.283...66G&db_key=AST
| 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
| Where are the hot horizontal branch stars in the Galactic Bulge?
In the modern understanding of the nature of the UV excess in ellipticalgalaxies the main source of this radiation is identified with the hothorizontal branch (H-HB) stages of the old, high metallicity stars.Since bulges of galaxies can possess stars of very high metallicity, thequestion arises whether these type of stars can be detected in the mixof stellar populations. In particular, whether they are present in ourown Bulge. For this purpose we examine the Colour-Magnitude Diagram(CMD) of a field near the Galactic Centre in the projected sky region ofTerzan 1. In this CMD we notice a feature, which could be the trace ofan old, high metallicity component. The feature in question is a sort ofbow departing from the red clump located at about V=22.5mag andV-I=3.8mag, passing at V=21mag, and terminating in a group of blue faintobjects approximately located at V=23mag and V-I=2.2mag. The analysis ismade with the aid of single stellar populations (SSPs) and syntheticCMDs. We suggest that the bow of stars traces the core He-burning phaseof old (~13Gyr) stars of very high metallicity, and that the faint starsof very blue colour (V-I) are the observational counterpart of theirH-HB stages.
| Briefly noted: Irish astronomy (poem)
Not Available
| The stellar content of the open clusters Tombaugh 1 and Ruprecht 46
V and I CCD photometry has been carried out for two poorly known openclusters: Tombaugh 1 an Ruprecht 46. Photometry has also been obtainedfor nearby fields to correct for the effects of field starcontamination. Estimates of the cluster fundamental parameters(reddening, distance and age) are given for Tombaugh 1 from comparisonwith theoretical isochrones of the Padova group. We find that this is anintermediate-age open cluster about 1Gyr old, and probably of solarabundance. The colour excess E(B-V) and the apparent distance modulus(m-M) are about 0.40+/-0.05 and 13.60+/-0.20 mag, respectively. Theseresults improve on previous determinations of the distance, and putTombaugh 1 at about 3.0 kpc from the Sun. The high degree ofcontamination from field stars prevents us from obtaining firmerresults. We estimate the cluster radius to be about 4.0 arcmin. As forthe luminosity function (LF), there is satisfactory agreement with thatderived from the standard Salpeter (x=1.35) initial mass function (IMF),allowing for the uncertainties in the subtraction of field stars.Ruprecht 46 was poorly studied before. From our analysis it emerges thatthis object is not an open cluster, but simply a density fluctuationabove the background level.
| A ROSAT-detected, New Galactic Supernova Remnant in Sagittarius, G13.3-1.3
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...449..681S&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.
| The galactic structure towards the galactic centre. II. A study of the fields near the clusters NGC 6603, Lynga 7 and Terzan 1.
The results are presented from a study of Colour-Magnitude Diagrams inthree fields, located in the galactic plane towards the Galactic Centre.First the extinction is determined in the line of sight. In two fields asignificant increase in the absorption is found. For the field nearTerzan 1 the increase starts immediately at 0kpc in the line of sightand for the field near NGC 6603 it occurs between 3.5kpc and 4.0kpc. Thelatter apparently coincides with the position of the molecular ring. Theabrupt end in the steep increment in the absorption is likely the resultof gas consumption by star formation. In two fields a significantincrease in the number of stars with probably a contribution from astellar ring has been found. The stellar ring can be described with aGaussian centered around 3.5kpc from the Galactic Centre withσ_ring_=0.5kpc. Between 1.0 to about 3.0kpc in the line of sight astellar contribution is present from the Sagittarius spiral arm. In thefields near the clusters Lynga 7 and Terzan 1 relatively young stars arepresent from a recent burst of star formation. The field of NGC 6603crosses a patchy region in this arm where this recent burst is absent.In all fields the major contribution for V<22mag is due to discstars. Around 2.5kpc from the Galactic Centre we find a sharp drop inthe stellar density of the disc. The stellar density towards theGalactic Centre is still increasing due to the stellar contribution fromthe Bulge. Therefore we identify this as the disc/bulge transition. Forthe Bulge we suggest the presence of a super metal rich population.
| CMDs of Three Regions Toward the Galactic Center
Not Available
| 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.
| PISMIS 3: an unstudied old open cluster
We have obtained CCD Bv photometry for the open cluster Pismis 3 and anearby field. This previously unstudied object appears to be rich, looseand strongly absorbed. Our analysis suggests that Pismis 3 is ofintermediate age and probably metal poor. Adopting the theoretical metalcontent Z = 0.008, which provides the best global fit, we obtain an ageof about 2 Gyr. Simultaneously a color excess EB-V = 1.35 andan apparent distance modulus (m - M) = 14.70 are derived. These resultsput Pismis 3 about 1.5 Kpc distance from the Sun. The relation of thecluster with the surrounding field is also investigated.
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