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|Effects of metallicity, star-formation conditions, and evolution in B and Be stars. II. Small Magellanic Cloud, field of NGC 330|
Aims.We search for the effects of metallicity on B and Be stars in theSmall and Large Magellanic Clouds (SMC and LMC) and in the Milky Way(MW), by extending our previous analysis of B and Be star populations inthe LMC to the SMC. The rotational velocities of massive stars and theevolutionary status of Be stars are examined with respect to theirenvironments. Methods: Spectroscopic observations of hot starsbelonging to the young cluster SMC-NGC 330 and its surrounding regionwere obtained with the VLT-GIRAFFE facilities in MEDUSA mode. Wedetermined fundamental parameters for B and Be stars with the GIRFITcode, taking the effect of fast rotation and the age of observedclusters into account. We compared the mean V sin i obtained by spectraltype- and mass-selection for field and cluster B and Be stars in the SMCwith the one in the LMC and MW. Results: We find that (i) B and Bestars rotate faster in the SMC than in the LMC and in the LMC than inthe MW; (ii) at a given metallicity, Be stars begin their main sequencelife with a higher initial rotational velocity than B stars.Consequently, only a fraction of the B stars that reach the ZAMS with asufficiently high initial rotational velocity can become Be stars; (iii)the distributions of initial rotational velocities at the ZAMS for Bestars in the SMC, LMC, and MW are mass- and metallicity-dependent; (iv)the angular velocities of B and Be stars are higher in the SMC than inthe LMC and MW; (v) in the SMC and LMC, massive Be stars appear in thesecond part of the main sequence, in contrast to massive Be stars in theMW.Tables 1-6, 8 and 11 are only available in electronic form athttp://www.aanda.org
|The Star Clusters of the Small Magellanic Cloud: Age Distribution|
We present age measurements for 195 star clusters in the SmallMagellanic Cloud based on comparison of integrated colors measured fromthe Magellanic Clouds Photometric Survey with models of simple stellarpopulations. We find that the modeled nonuniform changes of clustercolors with age can lead to spurious age peaks in the cluster agedistribution; that the observed numbers of clusters with age t declinessmoothly as t-2.1 that for an assumed initial cluster massfunction scaling as M-2, the dependence of the clusterdisruption time on mass is proportional to M0.48; thatdespite the apparent abundance of young clusters, the dominant epoch ofcluster formation was the initial one; and that there are significantdifferences in the spatial distribution of clusters of different ages.Because of limited precision in our age measurements, we cannot addressthe question of detailed correspondence between the cluster age functionand the field star formation history. However, this sample provides aninitial guide as to which clusters to target in more detailed studies ofspecific age intervals.
|Dating star clusters in the Small Magellanic Cloud by means of integrated spectra|
In this study flux-calibrated integrated spectra in the range(3600-6800) Å are presented for 16 concentrated star clusters inthe Small Magellanic Cloud (SMC), approximately half of which constituteunstudied objects. We have estimated ages and foreground interstellarreddening values from the comparison of the line strengths and continuumdistribution of the cluster spectra with those of template clusterspectra with known parameters. Most of the sample clusters are youngblue clusters (6-50 Myr), while L 28, NGC 643 and L 114 are found to beintermediate-age clusters (1-6 Gyr). One well known SMC cluster (NGC416) was observed for comparison purposes. The sample includes clustersin the surroundings and main body of the SMC, and the derived foregroundreddening values are in the range 0.00 <= E(B-V) <= 0.15. Thepresent data also make up a cluster spectral library at SMC metallicity.Based on observations made at Complejo Astronómico El Leoncito,which is operated under agreement between the Consejo Nacional deInvestigaciones Científicas y Técnicas de laRepública Argentina and the National Universities of La Plata,Córdoba and San Juan, Argentina.
|ESO imaging survey. Pre-FLAMES survey: Observations of selected stellar fields|
This paper presents the first set of fully calibrated images andassociated stellar catalogs of the Pre-FLAMES survey being carried outby the ESO Imaging Survey (EIS) project. The primary goal of this surveyis to provide the ESO community with data sets from which suitabletarget lists can be extracted for follow-up observations with the newVLT facility FLAMES (Fiber Large Array Multi Element Spectrograph). Forthis purpose, 160 stellar fields have been selected for observations inB, V and I using the 8kx8k Wide Field Imager (WFI) at the MPG/ESO 2.2 mtelescope at La Silla. Out of those, over 100 fields have already beenobserved. The list of selected fields includes open clusters, globularclusters, regions in the Galaxy bulge, dwarf spheroidal galaxies in thevicinity of the Milky Way, contiguous regions of SMC and LMC and fewnearby clusters of galaxies. The present paper discusses the resultsobtained for a small subset of these data, which include four openclusters (M 67, NGC 2477, NGC 2506 and Berkeley 20) and two regions ofthe SMC. These data have been used to assess the observing strategyadopted, a combination of short- and long-exposures, and to definesuitable reduction techniques and procedures for the preparation ofinput catalogs for FLAMES. In order to minimize light losses due tomisplacements of FLAMES fibers, the astrometric calibration of crowdedstellar fields is a critical issue. The impact of different swarpingtechniques and different reference catalogs on the astrometriccalibration of the images is evaluated and compared to those of otherauthors. From this comparison, one finds that both USNO 2.0 and therecently released GSC 2.2 yield comparable results with the positionaldifferences having a rms of about 0.15 arcsec, well within therequirements (0.2 arcsec) specified by the FLAMES science team. Theinternal accuracy of the astrometry is estimated to be <~ 0.1 arcsec,primarily limited by the reference catalog used. The major differencebetween these catalogs is the systematic variation of the positionalresiduals as a function of the apparent magnitude of the objects, withthe GSC 2.2 yielding by far the best results. The astrometriccalibration of the images presented here is based on the USNO 2.0catalog because not all fields considered are covered by the currentrelease of the GSC 2.2. Future EIS calibrations will be done using theGSC 2.2 catalog. The extraction and photometric measurements of stellarsources are carried out using a PSF fitting technique. Comparison withresults available in the literature shows that the photometricmeasurements are in good agreement, apart from possible zero-pointoffsets, with the magnitude differences having a scatter of ~ 0.06 magat V=20 mag. This demonstrates that the data allow for the selection ofrobust targets down to the expected spectroscopic limit of FLAMES. Thecombination of catalogs extracted from the short and long-exposuresallows one to produce color-magnitude diagrams (CMD) spanning ~ 13 magin V and reaching a limiting magnitude of V ~ 22-23. These data havealso been combined with data from the Two Micron All Sky Survey (2MASS)survey allowing for a better color-based object classification andtarget selection. The Pre-Flames (PF) survey data meet the requirementsof FLAMES, and provide a good starting point for detailed studies of theexamined systems. The images and catalogs presented here are publiclyavailable and can be requested from the URL address``http://www.eso.org/eis''. Based on observations collected at theEuropean Southern Observatory, La Silla, Chile within program ESO164.O-O561.
|The EIS Pre-FLAMES Survey: observations of selected stellar fields|
|A radio continuum study of the Magellanic Clouds V. Catalogues of radio sources in the Small Magellanic Cloud at 1.42, 2.45, 4.75, 4.85 and 8.55 GHz|
We present catalogues of radio sources in the Small Magellanic Cloudfrom observations with the Parkes radio telescope at 1.42, 2.45, 4.75and 8.55 GHz, and an additional catalogue from the Parkes-MIT-NRAOsurvey at 4.85 GHz. A total of 224 sources were detected at at least oneof these frequencies, 60 of which are reported here for the first timeas radio sources. We compare positions and flux densities of thesesources with previously published results and find no significantpositional displacement or flux discrepancies. Tables 2-7 are onlyavailable electronically at the CDS via ftp 184.108.40.206 or athttp://cdsweb.u-strasbg.fr/Abstract.html
|A Revised and Extended Catalog of Magellanic System Clusters, Associations, and Emission Nebulae. I. Small Magellanic Cloud and Bridge|
A survey of extended objects in the Magellanic System was carried out onthe ESO/SERC R and J Sky Survey Atlases. The present work is dedicatedto the Small Magellanic Cloud and to the inter-Magellanic Cloud region("Bridge") totaling 1188 objects, of which 554 are classified as starclusters, 343 are emissionless associations, and 291 are related toemission nebulae. The survey includes cross-identifications amongcatalogs, and we present 284 new objects. We provide accurate positions,classification, homogeneous sizes, and position angles, as well asinformation on cluster pairs and hierarchical relation for superimposedobjects. Two clumps of extended objects in the Bridge and one at theSmall Magellanic Cloud wing tip might be currently forming dwarfspheroidal galaxies.
|A New Catalogue of Hα Emission Line Stars and Small Nebulae in the Small Magellanic Cloud|
An objective-prism survey of the Small Magellanic Cloud has beenperformed through an Hα + [N II] interference filter, using the0.90 m Curtis Schmidt telescope of Cerro Tololo. 1898 emission-lineobjects have been detected in the main body of this galaxy, almostquadrupling the number of those found, in the same region, by theprevious objective-prism surveys. Among these objects are newlydiscovered planetary nebulae, compact HII regions and late-type stars.Continuum intensity, as well as the shape and relative strength of theHα emission-line have been estimated; coordinates, cross-identifications for the listed objects and 2.25 arcmin square findingcharts for all the objects are provided.
|Accurate positions for SMC clusters|
Positions of 203 SMC clusters accurate to + or - 5 arcsec are reported.The astrometry method used is briefly described. Plans for futureMagellanic Cloud cluster astrometry are summarized.
|The asymptotic giant branch of Magellanic Cloud clusters|
The present search for carbon and M-type asymptotic giant branch (AGB)stars in the 39 clusters of the Magellanic Clouds has yieldedidentifications and near-IR photometry for about 400 such stars. TheSearle et al. (1980) cluster-age-related classification scheme is abasic element of the present analysis of these data. In a C-M diagram,the cluster M stars shift steadily redward as one proceeds from clustersof SWB type I to VI, due to the increasing age of the clusters along thesequence. Luminous carbon stars are present only in SWB IV-VI clusters,and are easily distinguished from M stars by their color and luminosity.
|The interacting system MKN 305306.|
|Age calibration and age distribution for rich star clusters in the Large Magellanic Cloud|
An empirical relation is presented for estimating the ages of rich starclusters in the Large Magellanic Cloud (LMC), to within a factor ofabout 2, from their integrated UBV colors. The calibration is based onpublished ages for 58 LMC clusters derived from main-sequencephotometry, integrated spectra, or the extent of the asymptotic giantbranches. Using stellar population models, a sample of LMC clusters moremassive than about 10,000 solar masses is isolated, which is correctedfor incompleteness as a function of magnitude. An unbiased agedistribution for three clusters is then determined. The number ofclusters decreases with increasing age in a manner that is qualitativelysimilar to the age distribution for the open clusters in our Galaxy. TheLMC age distribution is, however, flatter, and the median age of theclusters is greater. If the formation rate has been approximatelyconstant over the history of the two galaxies, then the age distributionobtained here implies that clusters are disrupted more slowly in theLMC. The results contain no evidence for bursts in the formation ofclusters, although fluctuations on small time scales and slow variationsover the lifetime of the LMC cannot be ruled out.
|Arecibo H I data for 136 spiral galaxies|
The results of observations of the neutral hydrogen emission of 136spiral galaxies observed using the 21 cm spectral-line system of theArecibo Observatory are presented. Most of the 114 detected objects havebeen mapped along the major axis, and cumulative spectra andposition-velocity contour maps for each of them are presented. The dataare used to determine the overall H I content, systemic velocity, linewidths, and scale-length H I diameters. Data are also presented, indetailed tabular form, for each of the positions observed on thedetected objects.
|Integrated magnitudes and colors of clusters in the magellanic clouds and Fornax system|
Data from PV, six-color, and four-color photometric observations ofclusters (38 in the Small Magellanic Cloud, 16 in the Large MagellanicCloud, four in the Fornax system, and NGC 1841) are reported. Theobservations were made in 1951, 1960-1961, 1959-1966, and 1974-1975using various telescopes and photometer setups at Mount StromloObservatory in Australia. Tables of integrated magnitudes and colors(both as originally observed and as reduced to the BV system) arepresented, and comparable published data are shown. The combined V dataare fitted to the theoretical luminosity profiles of King (1966) toestimate the total magnitudes and surface brightness distributions of 33of the clusters. Several sample profile fits are shown. A color-colorplot (V-B vs. G-R) is discussed in terms of identification of clustertypes by color: it is found that globular clusters can be separated fromother types, if all have the same amount of reddening.
|Magnitudes of Clusters in the Small Magellanic Cloud|
|The cluster system of the Small Magellanic Cloud|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1958MNRAS.118..172L&db_key=AST
|Star Clusters in the Small Magellanic Cloud: I. Identification of 69 Clusters|
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