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Detection of Magnetic Massive Stars in the Open Cluster NGC 3766
A growing number of observations indicate that magnetic fields arepresent among a small fraction of massive O- and B-type stars, yet theorigin of these fields remains unclear. Here we present the results of aVLT/FORS1 spectropolarimetric survey of 15 B-type members of the opencluster NGC 3766. We have detected two magnetic B stars in the cluster,including one with a large field of nearly 2 kG, and we find marginaldetections of two additional stars. There is no correlation between theobserved longitudinal field strengths and the projected rotationalvelocity, suggesting that a dynamo origin for the fields is unlikely. Wealso use the oblique dipole rotator model to simulate populations ofmagnetic stars with uniform or slightly varying magnetic flux on theZAMS. None of the models successfully reproduces our observed range inBl and the expected number of field detections, and we ruleout a purely fossil origin for the observed fields.
| The B and Be Star Population of NGC 3766
We present multiple epochs of H? spectroscopy for 47 members ofthe open cluster NGC 3766 to investigate the long-term variability ofits Be stars. Sixteen of the stars in this sample are Be stars,including one new discovery. Of these, we observe an unprecedented 11 Bestars that undergo disk appearances and/or near disappearances in ourH? spectra, making this the most variable population of Be starsknown to date. NGC 3766 is therefore an excellent location to study theformation mechanism of Be star disks. From blue optical spectra of 38cluster members and existing Strömgren photometry of the cluster,we also measure rotational velocities, effective temperatures, and polarsurface gravities to investigate the physical and evolutionary factorsthat may contribute to the Be phenomenon. Our analysis also providesimprovements to the reddening and distance of NGC 3766, and we findE(B-V)=0.22+/-0.03 and (V-MV)0=11.6+/-0.2,respectively. The Be stars are not associated with a particular stage ofmain-sequence evolution, but they are a population of rapidly rotatingstars with a velocity distribution generally consistent with rotation at70%-80% of the critical velocity, although systematic effects probablyunderestimate the true rotational velocities, so that the rotation ismuch closer to critical. Our measurements of the changing disk sizes areconsistent with the idea that transitory, nonradial pulsationscontribute to the formation of these highly variable disks.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| A Photometric Method to Search for Be Stars in Open Clusters
We describe a technique to identify Be stars in open clusters usingStrömgren b, y, and narrowband Hα photometry. We firstidentify the B-type stars of the cluster using a theoretical isochronefit to the (b-y, y) color-magnitude diagram. The strongest Be stars areeasily identified in a (b-y, y-Hα) color-color diagram, but thosewith weaker Hα emission (classified as possible Be stardetections) may be confused with evolved or foreground stars. Here wepresent such photometry plus Hα spectroscopy of members of thecluster NGC 3766 to demonstrate the accuracy of our technique.Statistical results on the relative numbers of Be and B-type stars inadditional clusters will be presented in a future paper.
| The Carina Spiral Feature: Strömgren-Hβ photometry approach. I. The photometric data-base
A data-base collating all uvbybeta photometry available at present forO-B9 stars brighter than 10th visual magnitude in the field of theCarina Spiral Feature is presented. The completeness and homogeneity ofthe data-base are discussed.Based on CDS data.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/410/523
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| 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 (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Five-colour photometry of OB-stars in the Southern Hemisphere
Observations of OB-stars, made in 1959 and 1960 at the Leiden SouthernStation near Hartebeespoortdam, South Africa, with the VBLUW photometerattached to the 90 cm light-collector, are given in this paper. They arecompared with photometry obtained by \cite[Graham (1968),]{gra68}\cite[Walraven & Walraven (1977),]{wal77} \cite[Lub & Pel(1977)]{lub77} and \cite[Van Genderen et al. (1984).]{gen84} Formulaefor the transformation of the present observations to those of\cite[Walraven & Walraven (1977)]{wal77} and \cite[Lub & Pel(1977)]{lub77} are given. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| OB Stellar Associations in the Direction of Centaurus OB2
One hundred eighty-five mostly OB and some early A-type stars aredetected at 1640 Å with the ultraviolet telescope Glazar aboardthe Mir space station in an area of about 8 deg^2 in the directiontoward the stellar association Cen OB2. The limiting stellar magnitudem_1640 of the observations is about 8.5 mag. Stellar associations atdistances of 360, 850, 1500, 2300, 2700, 4000, and 6700 pc are detectedby the study of the space distribution of 111 of the observed stars withknown spectral types. It was shown that the cluster IC 2944 is locatedat a distance of 2200 pc. It is suggested that the extinction ofemission of stars in the content of the cluster is due to small dustclouds or even to circumstellar dust shells. It is shown also that thedust matter is practically absent in the space between stellarassociations and that the extinction of some stars within stellarassociations is caused by relatively small dust clouds, in which thestars are embedded. Two of the detected stars, HD 101316 and HD 101967,are of relatively late spectral types and therefore probably have hotdwarf or subdwarf companions.
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
| Short-period variability in Be stars
A highly significant correlation is found between the projectedrotational velocities and the photometric periods of Be stars. It isshown that this correlation may be readily understood if the photometricperiod is equated with the rotational period. If the nonradial pulsationhypothesis (NRP) is correct, g-modes with radial order exceeding 50 mustbe involved. According to current NRP theory, these results indicatethat the Be stars rotate like solid bodies. On the basis of some recentobservations which show that considerable magnetic activity is presentand a particular episode in the Be star Kappa CMa, it is suggested thatNRP is unlikely to be the cause of low-order periodic variations in Bestars. A model of rotational modulation caused by active areas isproposed.
| Periodic Be stars in NGC 3766
Results of a continuous four-week photometric campaign on 14 Be stars inthe galactic cluster NGC 3766 are presented. Comparisons are made withresults from a similar campaign in 1985 on four of the stars. These arealso now monitored in three colors to determine possible temperaturevariations. Of the remaining 10 Be stars, only two show signs ofperiodic variability. The amplitudes of these stars and the shapes ofthe light curves differ considerably over the two-yr interval, but theperiods have remained the same. A double-wave light curve in one seasonmay change to a single-wave of the same period, and vice versa. Thenature of the short-period variations in the light of these findings isdiscussed.
| UVBY beta photometry of southern clusters. VI - NGC 3766
Stromgren four color and H-beta photometry has been obtained for 39early to mid-B stars in the young southern cluster NGC 3766. The clustercontains an unusually large number of Be stars, the proportion betweenmagnitudes 6.5 and 11.5 being about 30 per cent. Estimates from bothuvby beta and UBV data indicate a reddening E(b-y) of 0.15 mag,corresponding to E(B-V) 0.20. The distance modulus obtained from bothphotometric systems is 11.4, giving a distance of 1.9 kpc.
| Stellar Content of Young Open Clusters - Part Two - Be-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982A&A...109...48M&db_key=AST
| Be stars in two open clusters
Slit spectra at 60 A/mm covering H alpha have revealed Be stars in NGC3766 and IC 2581. NGC 3766 is found to contain the largest number of Bestars of any single cluster studied in the Galaxy, and the highproportion of Be stars in NGC 3766 around V equal to 9 supports thefinding of Schild and Romanishin (1976) that Be stars are most likely toappear in the core contraction stage of evolution. Also discussed arethree giant or supergiant stars, HD 90706, HD 90707 and HD 100943, withat least incipient emission.
| Observations of southern emission-line stars
A catalog of 1929 stars showing H-alpha emission on photographic platesis presented which covers the entire southern sky south of declination-25 deg to a red limiting magnitude of about 11.0. The catalog providesprevious designations of known emission-line stars equatorial (1900) andgalactic coordinates, visual and photographic magnitudes, H-alphaemission parameters, spectral types, and notes on unusual spectralfeatures. The objects listed include 16 M stars, 25 S stars, 37 carbonstars, 20 symbiotic stars, 40 confirmed or suspected T Tauri stars, 16novae, 14 planetary nebulae, 11 P Cygni stars, 9 Bep stars, 87 confirmedor suspected Wolf-Rayet stars, and 26 'peculiar' stars. Two new Tassociations are discovered, one in Lupus and one in Chamaeleon. Objectswith variations in continuum or H-alpha intensity are noted, and thedistribution by spectral type is analyzed. It is found that the skydistribution of these emission-line stars shows significantconcentrations in the region of the small Sagittarius cloud and in theCarina region.
| Photometric standards for the southern hemisphere.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74.1125B&db_key=AST
| Distances of five open cluster near Eta Carinae
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1965MNRAS.129..237S&db_key=AST
| Estrellas de alta luminosidad entre Vela y Cruz. II.
Not Available
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | קנטאור |
| התרוממות ימנית: | 11h36m09.37s |
| סירוב: | -61°41'41.5" |
| גודל גלוי: | 9.264 |
| תנועה נכונה: | -7.9 |
| תנועה נכונה: | 7.7 |
| B-T magnitude: | 9.288 |
| V-T magnitude: | 9.266 |
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