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NGC 7419: a young open cluster with a number of very young intermediate mass pre-MS stars
We present a photometric and spectroscopic study of the young opencluster NGC 7419, which is known to host a large number of classical Bestars for reasons not well understood. Based on CCD photometricobservations of 327 stars in UBV passbands, we estimated the clusterparameters as, reddening [E(B - V)] = 1.65 +/- 0.15 mag and distance =2900 +/- 400 pc. The turn-off age of the cluster was estimated as 25 +/-5 Myr using isochrone fits. UBV data of the stars were combined with theJHK data from Two-Micron All-Sky Survey (2MASS) and were used to createthe near-infrared (NIR) (J - H) versus (H - K) colour-colour diagram. Alarge fraction of stars (42 per cent) was found to have NIR excess andtheir location in the diagram was used to identify them as intermediatemass pre-main-sequence (MS) stars. The isochrone fits to pre-MS stars inthe optical colour-magnitude diagram showed that the turn-on age of thecluster is 0.3-3 Myr. This indicates that there has been a recentepisode of star formation in the vicinity of the cluster.Slitless spectra were used to identify 27 stars which showed Hα inemission in the field of the cluster, of which six are newidentifications. All these stars were found to show NIR excess and arelocated closer to the region populated by Herbig Ae/Be stars in the (J -H) versus (H - K) diagram. Slit spectra of 25 stars were obtained in theregion 3700-9000 Å. The spectral features were found to be verysimilar to those of Herbig Be stars. These stars were found to be morereddened than the main-sequence stars by 0.4 mag, on an average. Thus,the emission-line stars found in this cluster are more similar to theHerbig Be-type stars where the circumstellar material is the remnant ofthe accretion disc. We conclude that the second episode of starformation has led to the formation of a large number of Herbig Be starsas well as intermediate mass pre-MS stars in the field of NGC 7419, thusexplaining the presence of emission-line stars in this cluster. Thiscould be one of the young open clusters with the largest number ofHerbig Be stars.
| CCD photometric search for peculiar stars in open clusters. VI. NGC 1502, NGC 3105, Stock 16, NGC 6268, NGC 7235 and NGC 7510
In a sample of six young open clusters (NGC 1502, NGC 3105, Stock 16,NGC 6268, NGC 7235, and NGC 7510) we investigated 1753 objects using thenarrow band, three filter Δ a photometric system resulting in thedetection of eleven bona-fide magnetic chemically peculiar (CP) starsand five Be or metal-weak stars. The results for the distant cluster NGC3105 is most important because of the still unknown influence of theglobal metallicity gradient of the Milky Way. These findings confirmthat CP stars are present in open clusters of very young ages (log t≥ 6.90) at galactocentric distances up to 11.4 kpc. For all programmeclusters the age, reddening, and distance modulus were derived using thecorresponding isochrones. Some additional variable stars within Stock 16could be identified by comparing different photometric studies.
| NGC 146: a young open cluster with a Herbig Be star and intermediate mass pre-main sequence stars
We present UBV CCD photometry and low-resolution spectra of stars in thefield of the young open cluster NGC 146. UBV photometry of 434 starswere used to estimate the E(B-V) reddening of 0.55 ± 0.04 mag andBV photometry of 976 stars were used to estimate a distance modulus of(m-M)0 = 12.7 ± 0.2 mag, corresponding to a distanceof 3470+335-305 pc. We estimated 10-16 Myr as theturn-off age for the upper main sequence of the cluster using isochronesand synthetic colour magnitude diagrams. We identified two B type starswith Hα in emission and located on the MS using slit-less spectra.A higher resolution spectrum of the brighter Be star indicated thepresence of a number of emission lines, with some lines showing thesignature of gas infall. This star was found to be located in the regionof Herbig Ae/Be stars in the (J-H) vs. (H-K) colour-colour diagram.Thus, we identify this star as a Herbig Be star. On the other hand, 54stars were found to show near infrared excess, of which 17 were found tobe located in the region of Herbig Ae/Be stars and 18 stars were foundto be located in the region of Be stars in the NIR colour-colourdiagram. Thus NGC 146 is a young cluster with a large number ofintermediate mass pre-main sequence stars. The turn-on age of thecluster is found to be ~3 Myr. Though NGC 146 shows an older turn off,the bulk of stars in this cluster seems to belong to the youngerpopulation of 3 Myr.
| 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.
| The young open cluster Markarian 50
We report on a deep CCD UBV(RI)C photometric survey in theregion of the young open cluster Markarian 50. The new photometric dataallow us to extend the cluster membership down to V~ 17.5, about 2 magdeeper than any previous investigation. On the basis of these data wederive a distance d= 3460 +/- 350 pc (VO-MV= 12.7+/- 0.2), which turns out to be only slightly lower than previousestimates. The cluster presents differential reddening, with E(B-V)values ranging from 0.69 to 1.1. The brightest member (HD 219460) is adouble star, which we separate photometrically for the first time,providing individual magnitudes and colours for each component. One ofthem is a Wolf-Rayet (WR) star and, according to evolutionary models,the mass of its progenitor should be greater than ~20 Msolar.The age obtained for the cluster is 7.5 +/- 2 Myr and the mass functionfor the most massive stars (M > 1 Msolar) presents a slopex~ 1.0.
| Comparison of the Luminosity Functions of Open Clusters Based on USNO-A1 Data
The luminosity and mass functions of a group of Galactic open clustersare constructed by applying a statistical method to photometric datafrom the USNO-A1 catalog. Despite some limitations, this catalog can beused for statistical analyses in Galactic astronomy. Pairwisecomparisons of the derived cluster luminosity functions are performedfor five age intervals. The differences between the luminosity functionsof the open clusters are not statistically significant in most cases. Itis concluded that the luminosity functions are approximately universalthroughout a large volume in the solar neighborhood. Combined luminosityand mass functions are constructed for six age intervals. The slope ofthe mass spectrum may vary somewhat from cluster to cluster, and themean slope may be somewhat higher than the Salpetervalue.
| On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions
We construct the observed luminosity functions of the remote young openclusters NGC 2383, 2384, 4103, 4755, 7510 and Hogg 15 from CCDobservations of them. The observed LFs are corrected for field starcontamination determined with the help of a Galactic star count model.In the case of Hogg 15 and NGC 2383 we also consider the additionalcontamination from neighbouring clusters NGC 4609 and 2384,respectively. These corrections provide a realistic pattern of clusterLF in the vicinity of the main-sequence (MS) turn-on point and atfainter magnitudes reveal the so-called H-feature arising as a result ofthe transition of the pre-MS phase to the MS, which is dependent on thecluster age. The theoretical LFs are constructed representing a clusterpopulation model with continuous star formation for a short time-scaleand a power-law initial mass function (IMF), and these are fitted to theobserved LF. As a result, we are able to determine for each cluster aset of parameters describing the cluster population (the age, durationof star formation, IMF slope and percentage of field starcontamination). It is found that in spite of the non-monotonic behaviourof observed LFs, cluster IMFs can be described as power-law functionswith slopes similar to Salpeter's value. The present main-sequenceturn-on cluster ages are several times lower than those derived from thefitting of theoretical isochrones to the turn-off region of the uppermain sequences.
| 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.
| Estimation of Errors in the Distances to Intrinsically Reddened Stars
Not Available
| 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].
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| On the evolutionary status of Be stars
We present a study of the incidence of Be stars in open clusters as afunction of the cluster age, using whenever possible ages determinedthrough Strömgren uvby photometry. For the first time in studies ofthis kind we have considered separately classical and Herbig Be stars.The main results can be summarized as follows: Clusters associated toemitting nebulosities and undergoing stellar formation are rich inemission line objects, which most likely are all pre main-sequencestars. No bona fide classical Be star has yet been identified amongthem. Clusters younger than 10 Myr and without associated nebulosity arealmost completely lacking Be stars, although they have a completeunevolved B main sequence. Classical Be stars appear at an age of 10Myr, and reach the maximum abundance in the age interval 13-25 Myr. Weinterpret our results in the sense that the Be phenomenon is anevolutionary effect which appears in the second half of the mainsequence lifetime of a B star. We propose that it can be related to mainstructural changes happening at this evolutionary phase, which also leadto the recently discovered non-monotonic helium abundance enhancement.The semiconvection or turbulent diffusion responsible of the surfacehelium enrichment, coupled with the high rotational velocity, cangenerate magnetic fields via the dynamo effect and thereby originate theBe phenomenon. Observational tests to this hypothesis are proposed.
| 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.
| Corridors in the regions of young open stellar clusters.
Not Available
| A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters I. NGC 7128
In 1994 we started a program of looking for variable stars in young openclusters. Our main goal is finding pulsating stars of spectral type B.The equipment we use consists of a 60-cm reflecting telescope and a CCDcamera. In this paper, intended as the first one in a series, we detailthe equipment, describe the reductions and present results for NGC 7128.For stars with instrumental magnitudes corresponding to early B spectraltypes on the cluster's main-sequence, the photometric accuracy weachieved allows detection of short-period variables with amplitudesexceeding 5mmag. The results include confirmation of the variability oftwo and discovery of six variables in the cluster. The variables wediscovered comprise two eclipsing binaries, one irregular red variable,and three small-amplitude periodic variables. No B-type pulsators arepresent in NGC 7128.
| A new study of the young open cluster NGC 7510.
Three-colour photographic photometry of the young open cluster NGC 7510based upon UBV observations made with the 122cm and 182cm Asiagoreflectors is presented here. A mean colour excess E(B-V)=1.12, adistance of 3.09kpc could be achieved for this cluster and 31 starscould be identified as photometric physical members. An age of10^7^years has been derived by comparison with standard isochrones. Thediscrepancy between the photometric and spectroscopic distances obtainedfor some stars is discussed and comparisons with recent investigationsof the same object are also given.
| Chemical Evolution of the Galactic Disk: Evidence for a Gradient Perpendicular to the Galactic Plane
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2813P&db_key=AST
| Catalogue of blue stragglers in open clusters.
An extensive survey of blue straggler candidates in galactic openclusters of both hemispheres is presented. The blue stragglers wereselected considering their positions in the cluster colour-magnitudediagrams.They were categorized according to the accuracy of thephotometric measurements and membership probabilities. An amount of 959blue straggler candidates in 390 open clusters of all ages wereidentified and classified. A set of basic data is given for everycluster and blue straggler. The information is arranged in the form of acatalogue. Blue stragglers are found in clusters of all ages. Thepercentage of clusters with blue stragglers generally grows with age andrichness of the clusters. The mean ratio of the number of bluestragglers to the number of cluster main sequence stars is approximatelyconstant up to a cluster age of about 10^8.6^ yr and rises for olderclusters. In general, the blue stragglers show a remarkable degree ofcentral concentration.
| The galactic open cluster NGC 7419 and its five red supergiants
UBV CCD photometry has been carried out on the heavily reddened(Av = 6.7) Cepheus open cluster NGC 7419. An age of 14 +/- 2million yr and a distance of 2.3 kpc have been derived using theisochrones of Maeder. The mass function of the cluster satisfies theSalpeter form N(M) is approximately M(-gamma) with gamma = 2.25. Thecluster is dynamically relaxed. Radial velocities of the five redsupergiants and the six brightest blue stars (mean approximately equals-74 km/s) confirm their membership. However, the radial velocity of thenearby carbon star (MZ Cep) is a factor of 2 too low for it to be amember. There is at most one blue supergiant member; this is much lessthan the number of red supergiants, in contrast with theoreticalpredictions. The red supergiants range in type from M2Iab to M7.5I, thecoolest (MY Cep) -- an OH/IR source -- being strongly variable in thevisible, but not in the IR. The two supergiants cooler than M2 do notfit the theoretical isochrones.
| Be stars in young clusters
Photometric H(alpha) and H(beta) line indices for 71 B stars in sevengalactic clusters are presented. Some stars in three of the clusterswere observed at two epochs. Using these data nine Be stars wereidentified. Three of them were previously detected as emission-linestars, while six do not appear to have been previously recognized assuch. Of the 62 stars for which we find no indication of emission, threewere previously found to exhibit emission. We find that emission-lineobjects are absent among the most luminous early B giants.
| Topography of the Galactic disk - Z-structure and large-scale star formation
A 3D morphological description of the Galactic disk defined by the youngstellar population is delineated using a sample of young open clusterswith cataloged distances and treated with Kriging techniques. The valuesof the positional variable Z for the cluster sample are considered asprospectings of the displacement of the Galactic disk in respect to theequator in the plane. The Kriging technique is described with emphasison its application to the automatic cartography problem. A view of theGalactic disk in a region of about 3 kpc around the sun emerges fromthis treatment and shows a trough-peak structure with four maindepressions as the more striking features. The most prominentdepression, named Big Dent, is apparent at about 1.8 kpc in anapproximately 240-deg direction. It has an elliptical shape with axissizes of 1.5 and 3 kpc, reaching a Z value of 200 pc below the formalGalactic plane. Two-dimensional sections across some selected directionsof the topography show profiles in good agreement with previousobservational studies based on different object samples.
| CCD photometry of the distant young open cluster NGC 7510
CCD observations in B, V, and I passbands have been used to generatedeep V, (B-V), and V,(V-I) color-magnitude diagrams for the open clusterNGC 7510. The sample consists of 592 stars reaching down to V = 21 mag.There appears to be nonuniform extinction over the face of the clusterwith the value of color excess, E(B-V), ranging from 1.0 to 1.3 mag. Thelaw of interstellar extinction in the direction of the cluster is foundto be normal. A broad main sequence is clearly visible in bothcolor-magnitude diagrams. From the bluest part of the color-magnitudediagrams, the true distance modulus to the cluster has been estimated as12.5 = or - 0.3 mag and an upper limit of 10 Myr has been assigned forthe cluster age.
| Numerical taxonomy for open clusters.
Abstract image available at:http://adsabs.harvard.edu/abs/1990RMxAA..21..305T
| IRAS sources beyond the solar circle. I - CO observations
C-12O (J = 1-0) has been observed with the 15-m SEST and the 30-m IRAMtelescope in the direction of 1302 IRAS sources with colors of starforming regions located within 10 deg of the galactic plane in theinterval between 85 and 280 deg. Emission components with line profilesthat are non-Gaussian (showing, e.g., possible self-absorption or wings)are identified; this information may serve as a basis for selectingsources for future research. For all components, kinematic heliocentricand galactocentric distances, and distances from the galactic plane arederived. For those components which may be associated with the IRASsources, bolometric luminosities are derived. These data will beanalyzed and compared with HI data in subsequent papers.
| An optical spiral arm beyond the Perseus arm
In the second galactic quadrant, optical spiral arm tracers have beencollected in a systematic literature search. A uniform reduction of thedata led to the detection of a distinct structure (probably a spiralarm) beyond the Perseus arm that is separated by a statisticallysignificant gap from the latter.
| Component Analysis of Open Clusters
Not Available
| Young stellar-gas complexes in the Galaxy
It is found that about 90 percent of OB-associations and o-b2 clusterssituated within 3 kpc of the sun can be united into complexes withdiameters of 150-700 pc. Almost all of these clusters contain giantmolecular clouds with a mass greater than about 100,000 solar masses. Anumber of complexes are associated with giant H I clouds; a few of thesmall complexes are situated in the HI caverns. The concentration ofOB-associations and young clusters in star complexes attests to theircommon origin in the supergiant gaseous clouds.
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