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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
| On the Distance to the Bright Nonthermal Radio Sources in the Direction of an Extraordinarily Massive Cluster of Red Supergiants
An extraordinarily massive cluster of red supergiants has been recentlyreported in the direction of the galactic coordinates l = 25.3°; b =-0.2°. This cluster is associated with an X-ray source, a veryhigh-energy γ-ray source, and three bright non-thermal radiosources. The a priori probability of these associations being onlyline-of-sight coincidences is very small. However, we have analyzed VLAarchive data taken toward these three radio sources and find from theirHI absorption spectra that they are extragalactic and thus not directlyassociated with the galactic cluster.
| 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.
| Discovery of an Extraordinarily Massive Cluster of Red Supergiants
We report the discovery of an extraordinarily massive young cluster ofstars in the Galaxy, having an inferred total initial cluster masscomparable to the most massive young clusters in the Galaxy. UsingIRMOS, 2MASS, and Spitzer observations, we conclude that there are 14red supergiants in the cluster, compared with five, in what waspreviously thought to be the richest Galactic cluster of such stars. Weinfer spectral types from near-infrared spectra that reveal deep CObandhead absorption that can only be fit by red supergiants. We identifya gap of ΔKs~4 mag between the stars and the bulk ofthe other stars in the region that can only be fit by models if thebrightest stars in the cluster are red supergiants. We estimate adistance of 5.8 kpc to the cluster by associating an OH maser with theenvelope of one of the stars. We also identify a ``yellow'' supergiantof G6 I type in the cluster. Assuming a Salpeter IMF, we infer aninitial cluster mass of 20,000-40,000 Msolar for cluster agesof 7-12 Myr. Continuing with these assumptions, we find that 80% of theinitial mass and 99% of the number of stars remain at the present time.We associate the cluster with an X-ray source (detected by ASCA andEinstein), a recently discovered very high energy γ-ray source(detected by INTEGRAL and HESS), and several nonthermal radio sources,finding that these objects are likely related to recent supernovae inthe cluster. In particular, we claim that the cluster has produced atleast one recent supernova remnant with properties similar to the CrabNebula.
| 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.
| 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.
| The Lack of Blue Supergiants in NGC 7419, a Red Supergiant-rich Galactic Open Cluster with Rapidly Rotating Stars
According to previous studies based on photometry alone, NGC 7419reveals a surprisingly low ratio of blue to red supergiants: only oneblue supergiant (BSG) along with a record number of five red supergiants(RSGs). However, for a cluster like NGC 7419 with solar metallicity, oneexpects twice as many BSGs as RSGs. To verify the small ratio of BSGs toRSGs, we have obtained spectroscopic observations of the seven mostluminous blue member stars using the 1.6 m telescope of the MountMégantic Observatory. (The RSGs have already been studiedspectroscopically.) To classify the stars, we have developed a systemespecially adapted for these heavily reddened stars in a spectral regionfrom 8400 to 8920 Å, near the hydrogen Paschen series limit. Thisclassification system is based on standard stars of known MK spectraltype extending over O9-B5 and all luminosity classes and is linkedthrough a grid of synthetic spectra to the atmospheric physicalparameters Teff and logg. We also include Be stars. Among theseven blue stars observed in NGC 7419, four have red spectra that aredominated by absorption lines and three by emission lines. The spectraltypes for the former are B2.5 II-III, B2.5 III, B0 III, and B4 III (e),while those for the latter are Be, B1 III-Ve, and Be, respectively. Theaverage heliocentric radial velocity of these stars is -66+/-6 kms-1, compatible with the value of -74+/-9 km s-1measured for the five RSG members. A distance of 1.7+/-0.4 kpc for thiscluster was estimated using the blue-star spectral types, in agreementwith the value of 2.3+/-0.3 kpc found by Beauchamp and coworkers, basedon isochrone fitting in the color-magnitude diagram. With no BSG starsdetected spectroscopically, we confirm the low number, in this caseabsence, of BSGs in this cluster. The high fraction of Be stars detectedby us and others among the bright blue member stars could be explainedby an average rotational velocity for the stars in NGC 7419, which issignificantly higher than in other clusters of similar age andmetallicity. Since higher stellar rotation rates shorten the BSG phase,we suggest that this explains why the evolved stars in NGC 7419 havebecome RSGs. Thus, NGC 7419 is an exceptional case, since high stellarrotation normally tends to occur at lower metallicity.
| 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.
| The blue to red supergiant ratio in young clusters at various metallicities
We present new determinations of the blue to red supergiant ratio (B/R)in young open clusters at various metallicities. For this purpose, weexamine the HR diagrams of 45 clusters in the Galaxy and of 4 clustersin the Magellanic Clouds. The identification of supergiants is based onspectroscopic measurements (with photometric counts to check theresults). The new counts confirm the increase of the B/R ratio when themetallicity increases with the following normalized relation:(B/R)/((B/R)sun) =~ 0.05* e3(Z)/(Zsun)}, where Zsun=0.02 and(B/R)sun is the value of B/R at Zsun which dependson the definition of B and R and on the age interval considered (e.g.for spectroscopic counts including clusters with log age between 6.8 and7.5, (B/R)sun =~ 3 when B includes O, B and A supergiants).
| The young open cluster NGC 663 and its Be stars
We present new BV(RI)CHα photometry of the young opencluster NGC 663. The Hα photometry is complete down to magnitudeRC = 15.4, corresponding to spectral type A5 for the clustermembers. This allows detection of mild and strong Hα emission inall B-type stars in the cluster. In addition to the 22 Be stars known inthe observed field of NGC 663, we discovered four new faint stars ofthis type. We find that Be stars in NGC 663 cover the whole range of theB spectral type. They are, however, most populous among stars withspectral types falling in the range between B0 and B3, where theirfraction amounts to 31 +/- 8%. Among B-type stars later than B3, Bestars are much less abundant: only 7 out of 101 observed stars, that is,7 +/- 3%, were detected. About 70% of the observed Be stars in NGC 663show detectable variations of light. In the time interval covered by ourobservations, the ranges of the largest variations reach 0.4 mag in theIC band. By means of the isochrone fitting, we derived thecluster distance of 2.1 kpc, age of 20-25 Myr, and the mean colourexcess E(R-I)C = 0.54 mag, with a ~ 0.1 mag scatter due todifferential reddening. Tables 2 and 3 are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/376/144
| 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].
| Hα Emission Stars in the Cepheus OB3 Region
Hα emission objects were searched for, using the objective-prismSchmidt plates in a 36 deg^2 sky area covering the Cepheus OB3association. Hundred and eight emission stars have been found, 68 ofwhich are new findings to our knowledge. The properties of the IRASpoint sources identified with Hα emission stars indicate that mostof the Hα emission stars are T Tauri stars or related objects.Hα emission stars associated with IRAS sources and thoseunassociated have different distributions, suggesting an age sequenceamong them. Altogether, they show a ring- or shell-like surfacedistribution, which almost coincides with that of heated dusts, andthese distributions appear to be encompassed by an HI shell.
| NGC 7419: An open cluster rich in Be stars
The results of our CCD photometric Hα observations of NGC7419 are presented. The observations resulted in a discoveryof 17 new Be stars and two other emission-line objects. In consequence,the number of known Be stars in this young cluster increased more thantwofold and equals now to 31. This is at present the largest number ofBe stars known in any galactic open cluster. Moreover, we estimate thatthese 31 Be stars constitute 36 +/- 7% of all cluster B-type starsbrighter than R_C = 16.1 mag. This locates NGC 7419 among these openclusters which are richest in Be stars such as galactic NGC663, NGC 330 in SMC, and NGC1818A in LMC.
| A report on the studies of star clusters with the UPSO 104-cm Sampurnanand telescope during last 25 years
Not Available
| Baldone Schmidt Telescope Plate Archive and Catalogue
The article presents information on the archive and catalogue of theastrophotos taken with the Schmidt telescope of the Institute ofAstronomy of the University of Latvia (until July 1, 1997 --Radioastrophysical Observatory of the Latvian Academy of Sciences) inthe period 1967--1998. The archive and catalogue contain more than 22000direct and 2300 spectral photos of various sky regions. Information onthe types of photo materials and color filters used as well as on mostfrequently photographed sky fields or objects is given. The catalogue isavailable in a computer readable form at the Institute of Astronomy ofthe University of Latvia and at the Astrophysical Observatory in Baldone(Riekstukalns, Baldone, LV-2125, Latvia), e-mail: astra@latnet.lv.
| 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.
| CCD photometry of galactic open star clusters IV. NGC 366
Not Available
| CCD photometry of galactic open star clusters-III. NGC 1931
Not Available
| 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.
| 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.
| On the behaviour of the IR CA II triplet in normal and active galaxies
The strength of the Ca II triplet in absorption at 8498/8542/8662 A hasbeen found to serve as a good luminosity indicator for metal-richstellar populations; high S/N near-IR spectroscopic data are presentedfor the nuclear regions of 42 normal and active galaxies. The normalgalaxies' Ca II triplet strengths exhibit a small spread around a meanvalue of 7 A. The large equivalent width of the IR Ca II triplet inSeyfert nuclei furnishes a unique means for probing the gravitationalpotential close to the central engine. Nuclear velocity dispersions in'active' galaxies are comparable to those in normal ones of similarluminosity.
| 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.
| Self-regulating star formation in isolated galaxies - Thermal instabilities in the interstellar medium
Using the Parravano (1987) hypothesis, the influence of dust content, UVradiation, primary cosmic ray ionization rate, and metal abundance uponthe conditions for cool cloud condensation are investigated. Thehypothesis is tested for several isolated and interacting galaxies. Itis suggested that the UV radiation regulates star formation and that thedust content plays an important role in determining the star formationrate.
| Kinematics of young open clusters and the rotation curve of our Galaxy
Published observational data on a sample of 105 kinematically andspatially distinct open clusters of early spectral type (up to B3) arecompiled in tables, graphs, and diagrams and characterizedstatistically. Findings reported include (1) solar motion expanding atLSR velocity 3 km/s or less (with no noncircular motion in the directionof rotation), (2) Oort constant A = 17.0 + or - 1.5 km/s kpc andsecond-order rotation term alpha = -2.0 + or - 0.6 km/s sq kpc at R-R0between -3 and 5 kpc, (3) maximum rotation-curve deviation + or - 10km/s at R-R0 about - or + 2 kpc, and (4) nondecreasing rotationalvelocities beyond about R-R0 = 3 kpc. The rotational velocities of H IIregions and molecular clouds in the Perseus arm are found to besignificantly lower than those of the open clusters.
| Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)
Not Available
| UBV photometry of the young open cluster Berkeley 96
Photoelectric UBV measurements of 10 stars have been made in the regionof Be 96. A distance of 5.3 kpc and an earliest spectral type of B0Vwere derived. This cluster could be considered a new spiral structuretracer belonging to the arm beyond the Perseus arm.
| Open clusters and galactic structure
A total of 610 references to 434 clusters are employed in thecompilation of a catalog of open clusters with color-magnitude diagramson the UBV or RGU systems. Estimates of reddening, distance modulus, ageand number of cluster members are included. Although the sample isconsidered representative of the discoverable clusters in the galaxy,the observed distribution is nonuniform because of interstellarobscuration. Cluster distribution in the galactic plane is found to bedominated by the locations of dust clouds rather than by spiralstructure. The distributions of clusters as a function of age andrichness class show that the lifetimes of poor clusters are much shorterthan rich ones, and that clusters in the outer disk survive longer thanthose in the inner disk. An outer disk age which is only about 50% theage of the globular clusters is indicated by cluster statistics. Thethickening of the galactic disk with increasing galactocentric distancemay be due to either a younger dynamical age or a lower gravitationalpotential in the outer regions.
| An up-to-date picture of galactic spiral features based on young open star clusters.
Abstract image available at:http://adsabs.harvard.edu/abs/1973A&A....23..317M
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