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|Kinematics of the Open Cluster System in the Galaxy|
Absolute proper motions and radial velocities of 202 open clusters inthe solar neighborhood, which can be used as tracers of the Galacticdisk, are used to investigate the kinematics of the Galaxy in the solarvicinity, including the mean heliocentric velocity components(u1,u2,u3) of the open cluster system,the characteristic velocity dispersions(σ1,σ2,σ3), Oortconstants (A,B) and the large-scale radial motion parameters (C,D) ofthe Galaxy. The results derived from the observational data of propermotions and radial velocities of a subgroup of 117 thin disk young openclusters by means of a maximum likelihood algorithm are:(u1,u2,u3) =(-16.1+/-1.0,-7.9+/-1.4,-10.4+/-1.5) km s-1,(σ1,σ2,σ3) =(17.0+/-0.7,12.2+/-0.9,8.0+/-1.3) km s-1,(A,B) =(14.8+/-1.0,-13.0+/-2.7) km s-1 kpc-1, and (C,D) =(1.5+/-0.7,-1.2+/-1.5) km s-1 k pc-1. A discussionon the results and comparisons with what was obtained by other authorsis given.
|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.
|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.
|Gamma-ray line emission from OB associations and young open clusters. II. The Cygnus region|
Gamma-ray and microwave observations of the Cygnus region reveal anintense signal of 1.809 Me line emission, attributed to radioactivedecay of 26, that is closely correlated with 53 GHz free-freeemission, originating from the ionised interstellar medium. We modelledboth emissions using a multi-wavelength evolutionary synthesis code formassive star associations that we applied to the known massive starpopulations in Cygnus. For all OB associations and young open clustersin the field, we determined the population age, distance, and richnessas well as the uncertainties in all these quantities from publishedphotometric and spectroscopic data. We propagate the populationuncertainties in model uncertainties by means of a Bayesian method. Theyoung globular cluster Cyg OB2 turns out to be the dominant26 nucleosynthesis and ionisation source in Cygnus. Our modelreproduces the ionising luminosity of the Cygnus region very well, yetit underestimates 26 production by about a factor of 2. Weattribute this underestimation to shortcomings of currentnucleosynthesis models, and suggest the inclusion of stellar rotationas possible mechanism to enhance 26 production. We alsomodelled 60Fe nucleosynthesis in the Cygnus region, yet thesmall number of recent supernova events suggests only little60Fe production. Consequently, a detection of the 1.137 Meand 1.332 Me decay lines of 60Fe from Cygnus by the upcomingINTEGRAL observatory is not expected. Appendices A and B, and Tables 1,2, and 5 are only available in electronic form athttp://www.edpsciences.org
|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 CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. IV. NGC663|
We present results of the variability search in the field of the youngopen cluster NGC663. In addition to the one beta Cep-type variable knownin this cluster, we found another one. It is a mono-periodic pulsatorchanging brightness with a period of 0.27640 d. In total, 19 newvariables were discovered and the variability of 5 other ones wasconfirmed. Out of all 24 variables in the observed field, 21 areprobable cluster members. One SPB candidate and three eclipsing orellipsoidal variables could be classified. Moreover, ten out of fourteenBe stars we observed vary in brightness. Only one of them shows periodicvariations of the lambda Eri-type, while the remaining ones exhibitirregular changes with the range up to 0.4 mag in the I_C band. We alsoprovide new VI_C photometry of 477 stars in the field of the cluster andcheck the consistence of the present photometry with cluster parametersderived earlier. The average cluster E(V-I_C) color excess amounts toabout 0.92mag.
|Fundamental parameters and new variables of the galactic open cluster NGC 7128|
CCD photometry in Johnson UBV and Strömgren uvby systems andmedium-resolution spectroscopy of the galactic open cluster NGC 7128 arepresented. Spectral types of the brightest 12 stars in the cluster fieldwere determined based on equivalent widths of the Hα and the Hei6678-Å line. The spectroscopic observations also revealed twoobvious and one probable Be-type stars showing Hα emission. Theanalysis of the photometric diagrams gave a colour excess ofE(B-V)=1.03+/-0.06mag, a distance modulus DM=13.0+/-0.2mag and an ageabove 10Myr. Time-resolved photometric observations obtained on onenight resulted in the detection of short time-scale light variations ofseven new and three already known variable stars in the cluster field.
|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 (188.8.131.52) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|Search for Pre-Main-Sequence Stars in the Young Galactic Cluster NGC 6910|
Photometric CCD UBV measurements have been obtained in the field of theyoung Cygnus cluster NGC 6910. The observations reach down to magnitudeV~=18 for 206 stars measured in all three UBV bands, uncovering theregion of the color-magnitude diagram where pre-main-sequence (PMS)stars are expected. The transformation of our instrumental magnitudes tothe standard system is discussed on the basis of two different sets ofstandard stars: 22 stars from six fields in the Landolt catalogs and 48stars with published photoelectric photometry in common with ours in thefour clusters observed in this campaign. The latter set is preferred,since it enables the effect of systematic errors in the U-B colors to beminimized. The adopted cluster parameters are E(B-V)=1.02+/-0.13,V0-MV=11.2+/-0.2, and age=(6.5+/-3)x106yr. The search for PMS cluster members on the basis of the calculatedcolor excess and distance modulus results in the proposed membership for11 PMS stars of spectral types from A to G.
|A CCD Search for Variable Stars of Spectral TypeB in the Northern Hemisphere Open Clusters. III. NGC 6823|
We present the results of variability search in the field of a veryyoung open cluster NGC 6823. Two delta Sct stars, still at the pre-mainsequence (PMS) stage of evolution, were found. These objects could beused for future testing of the evolutionary period changes in this classof variable stars. In addition, we found 13 other variables including abright cluster eclipsing binary and an SPB candidate. A few othervariables could be PMS stars of the UX Ori type. The H alpha photometry,which we made for 69 brightest stars, revealed only one object withstrong emission, discovered recently by the photographic methods. Twoother stars announced to have H alpha emission, do not show any evidencefor its presence. For a number of stars in the search field, we alsoprovide the BV(RI)_C photometry. We explain how the distribution ofabsorbing matter along the line of sight results in the unusualmorphology of the cluster color-magnitude (CM) diagram. The dereddenedCM diagram is used in the calculation of the extinction map for theobserved field, in which the E(R-I)_C color excess varies from 0.54 to0.72 mag, with the average value equal to 0.62 mag. It is also shownthat all cluster stars with spectral types later than A0 are PMSobjects. We use these stars to estimate the cluster age: 3+/-1 Myr.Using the cluster CM diagram, we compare and discuss the position of thetwo discovered delta Sct stars with respect to the theoreticalinstability strip for PMS stars of this type.
|Pre-Main-Sequence Stars in the Young Galactic Cluster IC 4996: A CCD Photometric Study|
The results of a UBV CCD photometric study of the cluster IC 4996 arepresented. We obtain new values for the cluster parameters: E(B-V) =0.71 +/- 0.08, V_0 - M_V = 11.9 +/- 0.1, and age = (7.5 +/- 3) x 10^6yr. The combined evidence from the photometric diagrams suggests thepresence of a number of pre-main-sequence (PMS) cluster members withspectral types ~A0 to F5. The interpretation of these objects as PMScandidates is further supported by independent results from CCD uvbyHβ observations. If confirmed, these stars would bridge theexisting gap in the sample of PMS stars, between the coolest Herbig AeBestars (HAeBe), and the hottest T Tauri stars. These PMS candidates arelocated some 0.5 and 1 mag above the main sequence in the V-(B-V)diagram, around the location of spectral types AF. This feature,together with their locations in the (U-B)-(B-V) diagram and theinterpretation that they are PMS members, suggest an additionalreddening law with a slope alpha = E(U-B)/E(B-V) ~= 0.55, probablycaused by circumstellar material.
|Infrared imaging and millimetre continuum mapping of Herbig Ae/Be and FU Orionis stars|
The goal of this paper is a detailed analysis of the dusty environmentof Herbig Ae/Be stars and FU Orionis objects. For this purpose we mapped22 regions at 1.3 mm wavelength containing 25 target objects. We foundthat it is indispensable to perform mapping in contrast to pointed On-Onmeasurements in order to obtain the correct distribution of coldmaterial around young stellar objects and to relate 1.3 mm fluxdensities to individual sources. To get reliable information about thestructure and shape of the dust configurations and their relation to thestellar sources, we superimposed the millimetre maps on near-infraredimages. The comparison of the data demonstrated that some of the HerbigAe/Be stars are not associated with the peak of the millimetre emission.This is obviously the case for V 376 Cas/LkHα 198, MWC 137,CoD-42(deg) 11721, and V 1685 Cyg/V 1686 Cyg. We found two differentmorphologies of the dust envelopes: 6 regions show a compact structure,whereas 12 regions are characterized by a core/envelope structure. The``disk'' objects AB Aur and HD 163296 show only a compact core and arenot surrounded by an extended envelope. We did not detect HK Ori, HD250550, LkHα 25, and V 1515 Cyg which all have low IRASluminosities. Based on the flux densities derived from the millimetremaps, we estimated characteristic physical parameters like density andmass assuming optically thin emission. The total masses of thecircumstellar regions around the Herbig Ae/Be stars with core/envelopestructure and with ``genuine" point-like millimetre sources are 80+/-60Msun\ and 0.15+/-0.15 Msun, respectively. Thelowest and highest masses of the circumstellar material were foundaround AB Aur (0.03 Msun) and CoD-42(deg) 11721 (1100Msun), respectively. The average densities in the cores rangefrom 10(5) to 10(8) cm(-3) . The densities of the extended envelopes areof the order of 10(4) to 10(5) cm(-3) . In addition, we combined themeasured millimetre flux densities with infrared and optical data andmodelled the broad-band spectral energy distributions using sphericallysymmetric models. We found good fits for both the core sources (AB Aur,V 1331 Cyg) and the core/envelope objects (VY Mon, LkHα 234) weconsidered for modelling. The parameters derived this way are generallyin good agreement with data directly derived from the maps. However, thepossibility to fit the spectral energy distribution of AB Aur which isknown to be associated with a disk clearly demonstrates that a good``spherical'' fit cannot be used as an argument against the presence ofa disk. Partially based on observations collected at the EuropeanSouthern Observatory, La Silla, Chile
|Close binary systems in the regions of open clusters. V1481 CYG in NGC 7128.|
|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: email@example.com.
|Binary stars in the vicinity of the open cluster NGC 6913.|
|Photometry of the Eclipsing Binary V1481 Cyg in the Open Cluster NGC 7128|
New ephemeris and lightcurve characteristics are given for the eclipsingbinary V1481 Cygni.
|Absolute proper motions of 181 young open clusters.|
|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.
|Estimates of geometric and dynamic parameters of star-gas complexes in the Galaxy|
Parameters of geometric models of 11 gas-star complexes (GSCs) wereobtained. We used information about GSC projections onto the celestialsphere and the Galactic plane and about GSC extension along the line ofsight. GSCs were represented as triaxial ellipsoids. To estimate thesemiminor axis of the GSC ellipsoidal model and GSC slope angle to theGalactic plane, we used data on spatial location of open stellarclusters (OSCs) entering GSCs. GSC slopes to the Galactic plane varybetween 2.5 and 20.5 deg. Their semiminor axes are between 11 and 164pc. GSC total masses are estimated from GSC tidal effect on OSCs thatare members of the corresponding GSCs. The effect manifests itself insmaller sizes of young OSCs as compared to their tidal sizes in theforce field of the Galaxy. We used studies of stability of an OSC movingin the joint force field of the Galaxy and spheroidal stationary GSC, aswell as studies of evolution of a virialized cluster located at thecenter of a nonstationary ellipsoidal GSC. Estimated total masses fordifferent GSCs lie between 0.65 x 10 exp 5 solar masses and 11.5 x 10exp 7 solar masses.
|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.
|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.
|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|
|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.
|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.
|The classification of open clusters by the centroid method of cluster analysis|
The distribution of open clusters in the Galaxy are considered, withspace coordinates including mass, absolute magnitude, integrated colorindex, diameter, metallicity, and age. It is shown that the majority ofclusters belong to several classes which have parameter values in asufficiently narrow range. The classes form a linear sequence by age andmonotonic sequence on a color-magnitude diagram. They are not isolated,but move into each other continuously. This suggests that the process ofcluster formation contains no significant gaps. The bifurcation of theage sequence of classes depending on the mass and diameter values isfound. This bifucation makes an evolutionary interpretation possible.
|Catalog of open clusters and associated interstellar matter.|
|Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)|
|The absolute masses of 72 galactic clusters and 12 OB associations|
The Reddish (1978) relative masses for 72 open clusters and 12 OBassociations are presently converted to absolute masses, within an errormargin of about 25 percent, using three calibration clusters of knownmass whose average mass is 300 solar masses. The Reddish techniqueassumes the initial stellar mass distribution function to be valid forall aggregates, together with a universal relationship between stellarmass and stellar luminosity.
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