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|Pre-main sequence stars in open clusters. I. The DAY-I catalogue|
Context: We present the basic ideas and first results from the projectwe are carrying out at present, the search for and characterisation ofpre-main sequence (PMS) stars among the members of Galactic youngclusters. The observations of 10 southern clusters, nine of them locatedin the Carina-Sagittarius spiral arm of the Milky Way are presented. Aims: We aim at listing candidate PMS member stars in young clusters.The catalogued stars will serve as a basis for future spectroscopicstudies of individual objects to determine the properties of stellarformation in the last phases before the main sequence stage. Propertiessuch as the presence of residual envelopes or disks, age spread amongPMS members, and the possible presence of several episodes of starformation in the clusters, are to be addressed. Methods: Multicolourphotometry in the UBVR_CIC system has been obtained for 10southern young clusters in the fourth Galactic quadrant, located betweenGalactic longitudes l = 238° and l = 310°. For six clusters inthe sample, the observations presented here provide the first publishedstudy based on CCD photometry. A quantitative comparison is performedwith post-MS isochrones, and PMS isochrones from three differentevolutionary models are used in the photometric membership analysis forpossible PMS stars. Results: The observations produce photometricindices in the Johnson-Cousins photometric systems for a total of 26 962stars. The matching of our pixel coordinates with corresponding fieldsin the 2MASS data base provides astrometric calibration for allcataloged stars and JHK 2MASS photometric indices for 60% of them.Post-MS cluster ages range from 4 to 60 Myr, whereas the photometricmembership analysis assigns PMS membership to a total of 842 stars,covering an age range between 1 and 10 Myr. This information on the PMScandidate members has been collected into a catalogue, named DAY-I,which contains 16 entries for 842 stars in the field of 10 southernclusters.Catalog is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (18.104.22.168) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/467/1397
|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.
|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.
|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).
|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.
|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.|
|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
|Integrated photometric properties of open clusters|
Galactic open clusters provide an abundant sample of stellar aggregatesof various sizes, ages and metal abundances, apt to constitute atemplate for comparison with star systems in other galaxies. In thispaper we present and discuss a standard methodology to synthesize U,B,Vfluxes and colours, and apply it to a set of 138 open clusters. Resultsare compared with previous ones available in the literature. We wereable to calibrate a mass-luminosity relation by which we evaluated themass of ~400 open clusters, leading to a well defined present-day massfunction. The number-complete sample of galactic open clusters presentedin Battinelli & Capuzzo-Dolcetta (1991) is enlarged of a 15%.
|Discovery of two Herbig-Haro objects in the small dark cloud D291.4-0.2 in Carina|
The discovery of two Herbig-Haro (HH) objects, designated HH 137 and138, towards eastern Carina in a dark small cloud is reported. Theirstructure is investigated on the basis of narrow-band CCD imagesobtained in red forbidden S II lines, the H-alpha + forbidden N IIemission, and the adjacent continuum. HH 137 consists of many knotsdistributed roughly in the east-west direction, while HH 138 has fewerknots in a similar elongation. HH 138 is located roughly on theextension of the axis of HH 137, but it is not clear whether they make aphysically associated HH pair. The westernmost part of HH 137 appears tocorrespond to the working surface of the outflow, and one of the knots,which is bright in H-alpha + forbidden N II, is probably the Mach disk.
|Formation and evolutionary properties of the Galactic open cluster system|
Results are reported from a statistical analysis of observational dataon 100 open clusters within 2 kpc of the sun, selected from the catalogof Lynga (1987). The selection criteria and the completeness of thesample are discussed; the data are compiled in a table; and the analysisresults are presented in a series of graphs and characterized in detail.A cluster formation rate of 0.45 clusters/kpc Myr is found,significantly lower than the rates determined previously (using clusterswithin 1 kpc of the sun) and corresponding to a cluster star-formationefficiency of 0.0063. The low average cluster lifetime (about 10 Myr)suggests that clusters are formed as unstable systems.
|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 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.
|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)|
|Evolution of massive stars - Comparison of cluster sequences and models with mass loss|
A comparison between theoretical isochrones of models with mass loss andobserved sequences of 25 clusters younger than 25 million years, ismade. The number counts are compared with the theoretically expectedstar numbers in various parts of the isochrones, and the effects ofdifferences in mass loss rates and stellar opacities are considered. Thestudy indicates that the theoretical main sequence band with mass lossis wider than the observed main sequence band for very young clusterswith turnoff at type earlier or equal to B0, and is smaller for olderclusters. A discrepancy of 1.0-1.5 mag is found for clusters with an ageof 10-21 million years. It is suggested that some extra-mixing,overshooting, or turbulent diffusion is at the origin of the observeddifferences, with an overshooting distance to pressure scale height atthe edge of the classical convective core ratio of about 0.3 for massivestars in the range of 9-15 solar masses.
|IDAM - A catalogue of DM, HD(E) and other cross-identifications for stars in open clusters (magnetic tape)|
This catalogue presents cross-identifications between usual numberingsystems for stars in open clusters and several astronomical catalogues:BS, HD-HDE, DM, NLS, LLS, GCVS, IDS, ADS, SAO and miscellaneous lists orcatalogues. It concerns 345 open clusters, for a total of 9543 entries.Inverse tables are given for each catalogue. The present cataloguecompletely supersedes the 1976 version.
|Star Complexes as Superclusters of Clusters and Associations Originated from the same Supercloud|
|Investigation of the initial mass spectrum of open star clusters|
The mass spectra of 228 open star clusters were derived by comparison ofcolor-magnitude diagrams with evolutionary tracks. The application tobinary stars showed the reliability of the mass determination. Thederived mass spectra were fitted by power laws as well as exponentiallaws. It could be shown that both approximate the mass spectra of openstar clusters on the same average significance level. The presentinvestigation revealed a correlation of the slope of the mass spectrawith the cluster age, whereas a detected correlation of the slope withgalactocentric distance is slight. The results suggest that the slope ofthe mass spectrum increases with increasing cluster and galactocentricdistance. These findings are discussed with respect to their reasons andprevious results concerning open clusters and field stars.
|RGU photometry of a field in the Carina region near the cluster IC 2581|
A field of 0.21 sq deg containing 2099 stars in the Carina region nearthe cluster IC 2581, has been measured on 14 plates in the RGU system.The reddening is caused by a thin absorbing cloud at 770 pc with E(G-R)= 0.23 mag, as well as an interstellar absorption free zone followed bya moderate gradient which increases with distance. The density gradientscorresponding to late-type giants and main sequence stars of the sameabsolute magnitude do not display the same behavior. Assuming that theouter edge of the arm of Carina is being observed, the present resultsseem to corroborate the existence of external spiral features between 12and 13 kpc. The distribution of F0-F5 stars seems to confirm predictionsof the theory of density waves.
|Integrated Photometric Parameters of Open and Globular Clusters|
|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.
|Analysis of UBV Data in Open Clusters|
|Comparative Studies of Young Open Clusters - Part Two - an Atlas of Composite Colour-Magnitude Diagrams|
Abstract image available at:http://adsabs.harvard.edu/abs/1981A&AS...44..467M
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