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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.
|Proper motion determination of open clusters based on the UCAC2 catalogue|
We present the kinematics of hundreds of open clusters, based on theUCAC2 Catalogue positions and proper motions. Membership probabilitieswere obtained for the stars in the cluster fields by applying astatistical method uses stellar proper motions. All open clusters withknown distance were investigated, and for 75 clusters this is the firstdetermination of the mean proper motion. The results, including the DSSimages of the cluster's fields with the kinematic members marked, areincorporated in the Open Clusters Catalogue supported on line by ourgroup.
|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 Galactic Constants and Rotation Curve from Molecular-Gas Observations|
We obtained the photometric distances and radial velocities for themolecular gas for 270 star-forming regions and estimated the distance tothe Galactic center from ten tangent points to be R 0 = 8.01 ±0.44 kpc. Estimates of R 0 derived over the last decade are summarizedand discussed; the average value is R 0 = 7.80 ± 0.33 kpc. Weanalyze deviations from axial symmetry of the gas motion around theGalactic center in the solar neighborhood. Assuming a flat rotationcurve, we obtain Θ0 ˜ 200 km/s for the circular velocity ofthe Sun from regions beyond the Perseus arm. We used these Galacticconstants to construct the Galactic rotation curve. This rotation curveis flat along virtually its total extent from the central bar to theperiphery. The velocity jump in the corotation region of the central barin the first quadrant is 20 km/s. We present analytical formulas for therotation curves of the Northern and Southern hemispheres of the Galaxyfor R 0 = 8.0 kpc and Θ0 = 200 km/s.
|Carina's defiant Finger: HST observations of a photoevaporating globule in NGC 3372*|
We present Hubble Space Telescope Wide Field Planetary Camera 2 imagesof a prominent externally ionized molecular globule in the Carina Nebula(NGC 3372), supplemented with ground-based infrared images andvisual-wavelength spectra. This molecular globule has a shape resemblinga human hand, with an extended finger that points toward its likelysource of ionizing radiation. Following an analysis of the spatiallyresolved ionization structure and spectrum of the photoevaporative flowfrom the Finger, we conclude that the dominant ionizing source is eitherthe WNL star WR25 (HD 93162), the adjacent O4 If-type star Tr16-244, orperhaps both. We estimate a mass-loss rate of ~2 × 10-5Msolar yr-1 from the main evaporating surface ofthe globule, suggesting a remaining lifetime of105.3-106 yr. We find a total mass for the entireglobule of more than 6 Msolar, in agreement with previousestimates. The hydrogen column density through the globule derived fromextinction measurements is a few times 1022 cm-2,so the photodissociation region behind the ionization front should belimited to a thin layer compared to the size of the globule, inagreement with the morphology seen in H2 images. Although afew reddened stars are seen within the boundary of the globule innear-infrared continuum images, these may be background stars. We do notdetect a reddened star at the apex of the finger, for example, down to alimiting magnitude of mK~= 17. However, considering thephysical properties of the globule and the advancing ionization front,it appears that future star formation is likely in the Finger globule,induced by radiation-driven implosion.
|GLIMPSE. I. An SIRTF Legacy Project to Map the Inner Galaxy|
The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE),a Space Infrared Telescope Facility (SIRTF) Legacy Science Program, willbe a fully sampled, confusion-limited infrared survey of 2/3 of theinner Galactic disk with a pixel resolution of ~1.2" using the InfraredArray Camera at 3.6, 4.5, 5.8, and 8.0 μm. The survey will coverGalactic latitudes |b|<=1deg and longitudes|l|=10deg-65° (both sides of the Galactic center). Thesurvey area contains the outer ends of the Galactic bar, the Galacticmolecular ring, and the inner spiral arms. The GLIMPSE team will processthese data to produce a point-source catalog, a point-source dataarchive, and a set of mosaicked images. We summarize our observingstrategy, give details of our data products, and summarize some of theprincipal science questions that will be addressed using GLIMPSE data.Up-to-date documentation, survey progress, and information oncomplementary data sets are available on the GLIMPSE Web site.
|The Mysterious Ring in the Open Cluster NGC 3572: Planetary Nebula or Photoevaporating Globule?|
We discuss optical and infrared emission from the putative planetarynebula in the young open cluster NGC 3572. Velocity images of [N II]λ6583 obtained with the Rutgers/CTIO Fabry-Perot interferometerreveal that most gas in the nebula is expanding at velocities <~5 kms-1, with marginal evidence for bipolar expansion. A fewouter condensations are seen at faster redshifted velocities, but theirorigin is uncertain. Optical spectra reveal a spatial excitationgradient, with higher excitation in a diffuse outer halo and lowexcitation in the bright inner nebula, suggesting that the nebula isexternally ionized by hot stars in the open cluster and that the nebulaand cluster are therefore equidistant. The nebula coincides with aninfrared source detected by the MSX and IRAS satellites and has aspectral energy distribution implying a total mass of 5-10Msolar. MSX also reveals diffuse infrared emission associatedwith the cluster, and its morphology implies a connection with the ringnebula. We discuss two very different interpretations of this object-itis either a strange planetary nebula or (more probably) a youngphotoevaporating globule left over from the molecular cloud that formedthe cluster.
|New infrared star clusters in the southern Milky Way with 2MASS|
We carried out a 2MASS J, H and Ks survey of infrared starclusters in the Milky Way sector 230deg< l <350deg. This zone was the least studied in the literature,previously including only 12 infrared clusters or stellar groups with|b|< 10deg, according to the recent catalogue by Bica etal. (2003). We concentrated efforts on embedded clusters, which arethose expected in the areas of known radio and optical nebulae. Thepresent study provides 179 new infrared clusters and stellar groups,which are interesting targets for detailed future infrared studies. Thesample of catalogued infrared clusters and stellar groups in the Galaxyis now increased by 63%.
|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.
|Reddening and age for 13 southern Galactic open clusters determined from integrated spectra|
In this study we present flux-calibrated integrated spectra in the range3800-6800 Å for 13 concentrated open clusters with Galacticlongitudes between 219deg and 316deg, nine ofwhich have not been previously studied. Using the equivalent widths ofthe Balmer lines and comparing the cluster spectra with template spectraof Magellanic Clouds and Galactic star clusters with known parameters,we derive both foreground interstellar reddening values and age. Fornine clusters these two parameters have been determined for the firsttime, while for the rest of the sample the results show good agreementwith previous studies. The present analysis indicates four very young(Hogg 11, NGC 5606, vdB-RN 80 and Pismis 17), seven moderately young(ESO 429-SC13, Hogg 3, Hogg 12, Haffner 7, BH 87, NGC 2368 and Bochum12) and two intermediate-age (Berkeley 75 and NGC 2635) open clusters.The derived foreground interstellar reddening values are in the range0.00 <= E(B-V) <= 0.38. The age and reddening distributions of thepresent sample of relatively faint open clusters match those of openclusters with known parameters in a 90deg sector centered atl = 270deg. Based on observations made at ComplejoAstronómico El Leoncito, which is operated under agreementbetween the Consejo Nacional de Investigaciones Científicas yTécnicas de la República Argentina and the NationalUniversities of La Plata, Córdoba and San Juan, Argentina.
|Spectroscopic Binaries in Young Open Clusters|
We have analysed the binarity and multiplicity characteristics of 120O-type stars in 22 very young open clusters and found marked differencesbetween the "rich" (N >= 6 O-type stars and primaries) and "poor" (N= 1) clusters. In the rich clusters, the binary frequencies vary between14% (1 SB among 7 stars) and 80% (8 SBs among 10 stars). Multiplesystems seem not to be frequent and stars are spread all over thecluster area. In poor clusters, the binary frequency of the O-typeobjects is nearly 100%, with orbital periods around 3 days. Severalbinaries are also eclipsing. Additional companions are always present.They form either hierarchical multiple stars or trapezium systems. Thesemassive multiple systems are generally found close to the clustercenter, although there are exceptions.
|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 (18.104.22.168) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|Deep Hα survey of the Milky Way. V. The l=289o to 295o area|
An Hα study of the ionized hydrogen in the Galactic planedirection l = 290o has been undertaken. We describe anddiscuss the characteristics of the numerous filaments and emissionpatches observed. These appear linked to a major expanding HI bubble orshell over an area of several degrees. Thanks to morphological,kinematical and stellar distance considerations we have linked observedHII regions and molecular clouds into star-forming complexes whichmainly trace the Carina arm. We show particularly that the HII regionsGum35 (G289.8-1.3), Gum38b (G291.6-0.5, NGC 3603) and Hf 58 (G291.9-0.7)can be directly linked to the farthest complexes at a distance `d' of 8and 9 kpc, while HII regions Gum37 (G290.6+0.3), Gum38a (G291.3-0.7) andthe expanding shell can be linked to the closest complexes locatedbetween 2.6 and 2.9 kpc. Important internal motions have been identifiedin the Gum35, Gum37, Gum38a and Gum38b HII regions. The identificationand analysis of these motions are essential for a good systemic velocitydetermination. We have also identified and delineated that part of theGalactic plane exhibiting velocity departures of Delta Theta = 7 kms-1 (between 285o and 295o and d = 2.5and 3 kpc). Based on observations collected at the European SouthernObservatory.}
|Statistical parallaxes and kinematical parameters of classical Cepheids and young star clusters|
The statistical-parallax method is applied for the first time to spacevelocities of 270 classical Cepheids with proper motions adopted fromHIPPARCOS (1997) and TRC (Hog et al. 1998) catalogs and distances basedon the period-luminosity relation by Berdnikov et al. (1996). Thedistance scale of short-period Cepheids (with periods less than 9 days)is shown to require an average correction of 15-20%, whereas statisticalparallaxes of Cepheids with periods > 9 days are found to agree wellwith photometric distances. It is shown that the luminosities ofshort-period Cepheids must have been underestimated partly due to thecontamination of this subsample by a substantial (20 to 40%) fraction offirst-overtone pulsators. The statistical-parallax technique is alsoapplied for the first time to 117 open clusters younger than 100 millionyears and with proper motions reduced to the HIPPARCOS reference system.It is concluded that a 0.12-0.15 mag increase of the distance scales ofopen clusters and Cepheids would be sufficient to reconcile thestatistical-parallax results inferred for these two types of objects.Such approach leads to an LMC distance modulus of less than 18.40 mag,which agrees, within the errors, with the short distance scale for RRLyrae variables and is at variance with the conclusions by Feast andCatchpole (1998) and Feast et al. (1998), who argue that the LMCdistance modulus should be increased to 18.70 mag. The distance scalebased on the Cepheid period-luminosity relation by Berdnikov and Efremov(1985) seems to be a good compromise. Extragalactic distances, whichrely on long-period Cepheids, seem to require no substantial correction.In addition to statistical parallaxes, kinematical parameters have beeninferred for the combined sample consisting of Cepheids andopen-clusters: solar-motion components (U0 ,V0,W0) = (9, 12, 7) km/s (+/- 1 km/s); velocity-ellipsoid axes(σU; σV; σW) = (15.0,10.3, 8.5) km/s (+/- 1 km/s); the angular velocity of rotation of thesubsystem, ω0 = 28.7 +/- 1 km/s/kpc, the Oort constantA = 17.4 +/- 1.5 km/s, and the second derivative of angular velocity,⋰ω0= 1.15 +/- 0.2 km/s/kpc3.
|A study of the interstellar gas surrounding Carina OB2|
A huge Hi cavity delimited by a large and ellipsoidal Hi feature, hasbeen found toward the stellar association Car OB2. Based on the goodagreement found between the mean radial velocity of the Hi feature (V_HI~ -27+/-5 km s(-1) ) and the radial velocity of the OB association (V_*~ -33+/-8 km s(-1) ), and the coincidence in position between thebarycentral position of the Hi feature and the optical position of CarOB2, a physical link between the neutral gas and the stellar associationis suggested. The interaction of the stellar winds of the most massivemembers of Car OB2 with its local ISM could have given rise to both theHi low emissivity region and the surrounding \HI\ shell. The \HI\ shellappears to be expanding at ~ 22 km s(-1) . The Hi feature has acounterpart in the CO emission. The size and kinematical parameters ofthe molecular gas almost mimic those of the atomic gas. Based on theevidence presented in this paper, the anomalous behavior of the Hi alongl~ 290degr , first noticed by Humphreys & Kerr (1974), would merelybe a perturbation of the Hi local to Car OB2, and would not represent aphenomenon on a galactic scale.
|Long-Slit Spectrophotometry of the H II Regions GUM 38a and GUM 38b|
We present new long-slit spectrophotometric observations in the range3700--7200 Angstroms of the H II regions Gum 38a and Gum 38b (RCW 57).We study the spatial distribution of reddening and excitation throughoutthe complex by means of emission-line intensities. From the strongreddening difference, we confirm that Gum 38a and Gum 38b are twoindividual complexes, the former being in the foreground. We derivechemical abundances in both nebulae, the results of which are similar tothose of the Orion Nebula. This is consistent with the fact that thethree nebulae are located at similar Galactocentric distances. We alsodiscuss the general ionization structure of the complexes based on thespectral properties of several filaments and diffuse emission around thecentral bright knots of Gum 38a and beyond. In particular, we found aninteresting filament with strong [O I] lambda lambda 6300, 6364 lines.
|Absolute proper motions of 181 young open clusters.|
|The LS stars at 25 years|
Since its publication in 1971, Stephenson and Sanduleak's Luminous Starsin the Southern Milky Way has served as a starting point for a wholegeneration of investigations of galactic structure and thecharacteristics of massive, early-type stars. This paper presents asilver-anniversary review of the Stephenson-Sanduleak "LS" stars: theirdistribution on the sky, observed magnitudes, colors and spectral types,their distribution in space, and the characteristics of some of the moreunique individual objects. While much has been learned of and from theseobjects, much fundamental data remain to be acquired.
|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.
|A study of Carina OB2 association. 2: Analysis and discussion of the data|
UBV photometric data and accurate MK spectral types of stars in theregion of Carina OB2 association, presented in Paper I, are used to showthat Carina OB2 is a genuine stellar association located at a distanceof 3.1 kpc from the Sun, and with an age of about 4 x 106 yr,in accordance with the bluest star on the main sequence. From thecomplete sample, a total of 91 O and B stars were retained as members ofCarina OB2, while 66 stars were considered probable members. Among themembers, there are two- early supergiant stars, three O-type stars, an12 giants or subgiant B-type stars. For 37 stars in the field of theassociation we obtained between 3 and 10 spectrograms per star, and withthese data we were able to derive preliminary orbital elements for threespectroscopic binaries and probable periods for two other stars. Theratio of average projected rotational velocity of the cluster members tothat of field stars is 0.87 +/- 0.05. The average radial velocity forthe group is -23 +/- 2(p.e.) km/s. We call attention to several peculiarstars, early-type SB1, and SB2 systems of potential astrophysicalinterest. Finally, we propose a global picture of the region whereCarina OB2 is located and a preliminary analysis of the possiblerelation between the association and the other clusters present in thiswonderful region of the southern sky.
|Ubvy-Beta Photometry of 100 Stars in the Region of Eta-Carinae|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.269..857S&db_key=AST
|Spectroscopy of the ringlike nebula toward the open cluster NGC 3572|
Low-dispersion spectroscopy has been obtained for the ringlike nebulawhich Phelps and Janes (1991) found in the direction of the young opencluster NGC 3572 and suspected as a planetary nebula. Some nearbynebulosities have also been observed. Analyses of these data indicatethat all of them, including the NGC 3572 ring, are H II regions.Morphological considerations of the region show that the nearbynebulosities are bright rims which are associated with the H II regionBBW 342 and are partly hidden by the obscuring matter lying on thisside. The NGC 3572 ring could be of the same nature. However, as thealternative interpretation, it could be a ring nebula (probably awind-blown bubble) around a massive star (WR/Of star or LBV).
|A probable planetary nebula in the direction of the young open cluster NGC 3572|
The discovery of a ringlike emission feature located along the time ofsight toward the young open cluster NGC 3572 is reported. The smallfeature is prominent in H-alpha but has no central star brighter thanmagnitude V about 20 and is barely detectable in U, B, and V frames. Theappearance of the ring is consistent with it being a PN at an unknowndistance.
|The Gould plates|
Most of the 1200 photographs of southern galactic star clusters anddouble stars taken by Benjamin A. Gould at Cordoba, Argentina, in1872-1882 are in the Harvard College Observatory plate collection. Arecent evaluation of these plates shows many to be in usable condition.Details of the characteristics of Gould's plates of galactic clusters,including limiting magnitudes, are presented.
|Colour excesses and absolute magnitudes for non-Cepheid F-G supergiants from uvbybeta photometry|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990A&A...239..205A&db_key=AST
|Infrared circumstellar shells - Origins, and clues to the evolution of massive stars|
The infrared fluxes, spatial and spectral characteristics for a sampleof 111 supergiant stars of spectral types F0 through M5 are tabulated,and correlations examined with respect to the nature of theircircumstellar envelopes. One-fourth of these objects were spatialyresolved by IRAS at 60 microns and possess extended circumstellar shellmaterial, with implied expansion ages of about 10 to the 5th yr.Inferences about the production of dust, mass loss, and the relation ofthese characteristics of the evolution of massive stars, are discussed.
|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.
|A cluster analysis of open clusters|
The Galactic distribution of 361 open clusters is studied using acluster analysis method. It is shown that more than half of the clustersenter groups with characteristic dimensions of several hundred parsecs.To distinguish physical clusters from random condensations, criteriabased on age similarity, the color of the main-sequence blue end, andthe integrated color and radial velocity of the clusters are used. Theproximity of these values suggests a physical unity and common origin ofclusters in a group.
|A cluster analysis of young open clusters|
Cluster analysis methods are used to consider the galactic distributionof 224 open clusters with an age up to 10 to the 8th yrs. Most of theseclusters enter condensations with characteristic dimensions of a fewhundred parsecs. Some condensations are so similar in terms of the age,integrated color, and radial velocity of their components, that thiscannot be considered a coincidence. This suggests that each condensationis a physical entity consisting of clusters apparently linked by acommon origin.
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