The VLT-FLAMES survey of massive stars: stellar parameters and rotational velocities in NGC 3293, NGC 4755 and NGC 6611
An analysis is presented of VLT-FLAMES spectroscopy for three Galacticclusters, NGC 3293, NGC 4755 and NGC 6611. Non-LTE model atmospherecalculations have been used to estimate effective temperatures (fromeither the helium spectrum or the silicon ionization equilibrium) andgravities (from the hydrogen spectrum). Projected rotational velocitieshave been deduced from the helium spectrum (for fast and moderaterotators) or the metal line spectrum (for slow rotators). The origin ofthe low gravity estimates for apparently near main sequence objects isdiscussed and is related to the stellar rotational velocity. Theatmospheric parameters have been used to estimate cluster distances(which are generally in good agreement with previous determinations) andthese have been used to estimate stellar luminosities and evolutionarymasses. The observed Hertzsprung-Russell diagrams are compared withtheoretical predictions and some discrepancies including differences inthe main sequence luminosities are discussed. Cluster ages have beendeduced and evidence for non-coeval star formation is found for allthree of the clusters. Projected rotational velocities for targets inthe older clusters, NGC 3293 and NGC 4755, have been found to besystematically larger than those for the field, confirming recentresults in other similar age clusters. The distribution of projectedrotational velocities are consistent with a Gaussian distribution ofintrinsic rotational velocities. For the relatively unevolved targets inthe older clusters, NGC 3293 and NGC 4755, the peak of the velocitydistribution would be 250 km s-1 with afull-width-half-maximum of approximately 180 km s-1. For NGC6611, the sample size is relatively small but implies a lower meanrotational velocity. This may be evidence for the spin-down effect dueto angular momentum loss through stellar winds, although our results areconsistent with those found for very young high mass stars. For allthree clusters we deduce present day mass functions with Γ-valuesin the range of -1.5 to -1.8, which are similar to other young stellarclusters in the Milky Way.
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The VLT-FLAMES survey of massive stars: Observations in the Galactic clusters NGC 3293, NGC 4755 and NGC 6611
We introduce a new survey of massive stars in the Galaxy and theMagellanic Clouds using the Fibre Large Array Multi-Element Spectrograph(FLAMES) instrument at the Very Large Telescope (VLT). Here we presentobservations of 269 Galactic stars with the FLAMES-Giraffe Spectrograph(R ≃ 25 000), in fields centered on the open clusters NGC 3293,NGC 4755 and NGC 6611. These data are supplemented by a further 50targets observed with the Fibre-Fed Extended Range Optical Spectrograph(FEROS, R = 48 000). Following a description of our scientificmotivations and target selection criteria, the data reduction methodsare described; of critical importance the FLAMES reduction pipeline isfound to yield spectra that are in excellent agreement with lessautomated methods. Spectral classifications and radial velocitymeasurements are presented for each star, with particular attention paidto morphological peculiarities and evidence of binarity. Theseobservations represent a significant increase in the known spectralcontent of NGC 3293 and NGC 4755, and will serve as standards againstwhich our subsequent FLAMES observations in the Magellanic Clouds willbe compared.
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Metallicity of mono- and multiperiodic β Cephei stars
Analyzing IUE ultraviolet spectra of β Cep pulsating stars wenoticed that multiperiodic variables have a larger mean metal abundancein the photosphere, [ m/H] , than monoperiodic ones. We applystatistical tests to verify this dichotomy. We obtain that, with a largeprobability, the multiperiodic β Cep stars have greater values of [m/H] . This result is consistent with the linear non-adiabatic theory ofpulsation of early B-type stars.
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Metallicities of the β Cephei stars from low-resolution ultraviolet spectra
We derive basic stellar parameters (angular diameters, effectivetemperatures, metallicities) and interstellar reddening for all βCephei stars observed during the IUE satellite mission, including thosebelonging to three open clusters. The parameters are derived by means ofan algorithmic procedure of fitting theoretical flux distributions tothe low-resolution IUE spectra and ground-based spectrophotometricobservations. Since the metallicity has a special importance forpulsating B-type stars, we focus our attention in particular on thisparameter.Tables 1, 2, 4 and 5 are only available in electronic form athttp://www.edpsciences.org
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Misidentifications of Stars in NGC 4755 (κ Crucis)
Erroneous cross-identifications appearing in the literature and in theSIMBAD database for stars in the Jewel Box cluster, NGC 4755, arecorrected. These errors concern mistaken cross-references for CPD,Bright Star Catalog, and Luminous Stars in the Southern Milky Waynumbers to stars identified in the analysis of this cluster carried outby Arp & van Sant.
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β Cephei and new pulsating stars in NGC 4755
We present the results of a photometric multi-colour, two-site observingcampaign of β Cephei stars in the young open cluster NGC 4755. Morethan 260 h of time-series U, B, V filter data of the cluster wereacquired on two continents during 1999 and 2000. We list the detectedpulsation frequencies and discuss the results of their analysis. Modeidentification of the detected modes is performed as well. In addition,we present the detection of four new variable stars in NGC 4755. We givefrequency solutions as indicators of the time-scales and amplitudes ofthe pulsations. NGC 4755-116 is probably a B2 dwarf with a period of 4.2d whose variability is caused by a spot or g-mode pulsation. NGC4755-405 can be considered as a new β Cephei star with twopulsation frequencies. For NGC 4755-215 we found one frequency and forNGC 4755-316 three pulsation frequencies; we suggest that both are newslowly pulsating B stars of short period.
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Light element abundances in the young open clusters NGC 3293, NGC 4755 and NGC 6231: Tracers of stellar evolution
The abundances of He (LTE), C, N, and O (NLTE) were derived for 21 Bstars in three young open clusters. Almost all the stars show subsolarCNO abundances. However, the mean oxygen abundance for each programmecluster appears to be in marginal agreement with the most recentrevisions of the solar value. After consideration of the CN abundancesin this sample, there is no clear evidence of internal mixing. Onlythree stars among the non-supergiants seem to show a nitrogenenhancement. Two of them have a fairly low projected equatorial velocity(admittedly, they may be rapid rotators seen pole-on); the third one isa definite fast rotator. In the lower gravity stars (three stars in thissample with log g < 3.0) some kind of mixing has apparently occurred.The supergiants do not differ significantly from the other programmestars in their respective helium contents. The mean helium abundance foreach cluster is close to the standard value, (He/H) ~ 11.0. Based onspectra collected at the European Southern Observatory, La Silla, Chile,as part of programme 47.7-045.
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Photometric and kinematic studies of open star clusters. III. NGC 4103, NGC 5281, and NGC 4755
We present CCD photometry and proper motion studies of the three openstar clusters NGC 4103, NGC 5281, and NGC 4755 (kappa Cru). By fittingisochrones to the colour magnitude diagrams, we found that all threeobjects are young open star clusters with ages of at most t=45 Myr. Theyare located at distances from approx. 1600 pc to 2200 pc, derived fromdistance moduli (m-M)_0 ranging from 11 mag to 12 mag. We combinedmembership determinations based on proper motions and statistical fieldstar subtraction to derive the initial mass function (IMF) of theclusters. The shape of the IMFs could be represented by power laws withexponents of Gamma =-1.46 +/- 0.22 for NGC 4103, Gamma =-1.60 +/- 0.50for NGC 5281, and Gamma =-1.68 +/- 0.14 for NGC 4755, when - as areference - Salpeter's (\cite{salpeter}) value would be Gamma =-1.35.These results agree well with other IMF studies of open star clusters.Partly based on observations from ESO, La Silla.
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Preliminary New Results on Beta Cephei Stars in NGC 4755
In this poster we present the results from observations of the youngopen southern cluster NGC 4755. The observations were carried out inMarch 1999. The 40arcsec telescope in Siding Spring, Australia was usedto collect CCD photometric data for nine beta Cephei stars in NGC 4755.We describe the observations, data reduction methods applied and dataanalysis.
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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
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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.
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The structure of the instability strip and mode identification for beta CEP stars in three young open clusters
We use a grid of stellar models to calculate isochrones. These are usedto determine the ages of NGC 3293, NGC 4755 and NGC 6231. Using anon-adiabatic pulsation code, we compute the instability strip for betaCep variables. We find that there is a correlation between thefrequencies of the excited modes and the mass for stars of a given age.A calibration is presented which allows age determination of beta Cepstars in clusters with greater accuracy than isochrone fitting. Thestrong dependence of the frequency-mass relationship on age explains thetemperature difference between the instability strips in NGC 3293 andNGC 4755. The second part of the paper examines the question of modeidentification for beta Cep stars in NGC 3293 and NGC 4755. We presentnew uvby observations for these stars and use the dependence of theamplitude on wavelength to estimate the modes. We are able to isolate afew radial pulsators in the two clusters and to deduce their masses,effective temperatures and luminosities.
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A Radial Velocity Database for Stephenson-Sanduleak Southern Luminous Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113..823R&db_key=AST
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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.
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Observational status and excitation mechanisms of beta-Cephei variables.
Not Available
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A spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
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The Open Cluster NGC4755 and its Shortperiod B-Type Variables
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.267.1071B&db_key=AST
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A photometric study of β Cephei stars. II. Determination of the degrees L of pulsation modes
The wavelength dependence of photometric amplitudes is used as a meansof identifying the degrees l of pulsation modes of β Cephei starsstudied in an earlier paper. To this end, an expression for thephotometric amplitude of a non-rotating pulsating star is derived interms of the wavelength of the radiation received and the degree of thepulsation mode involved. The derivation differs from earlier derivationsin that the specific radiation intensity is considered instead of theoutward normal radiation flux. Furthermore, the effects of thenon-radial components of the Lagrangian displacement on the localsurface element of the star are taken into account. The angulardependence of the specific radiation intensity is determined by alimb-darkening function. The relative Lagrangian perturbation of thespecific radiation intensity is set equal to the relative Lagrangianperturbation of the outward normal radiation flux. The physicalparameters of the β Cephei stars are estimated by means ofcalibrations of photometric systems. From a comparison of thecalibrations of the Walraven, the Geneva, and the Stroemgren system forearly-type stars, it appears that the most reliable values are obtainedby means of the Walraven system. The influence of the uncertainties onthe physical parameters on the determination of the degrees l ofpulsation modes in β Cephei stars is examined. The expression forthe photometric amplitude of a pulsating star is used for thedetermination of the degree l of a pulsation mode by fitting curves ofthe wavelength dependences of theoretical photometric amplitudes forvarious degrees l to the wavelength dependence of observationallydetermined photometric amplitudes. In this way, values for the degrees lof most of the pulsation modes of the β Cephei stars considered arefound. It appears that not all β Cephei stars pulsate in at leastone radial mode and that multiperiodic β Cephei stars pulsate in avariety of combinations of pulsation modes.
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Beta Cephei stars from a photometric point of view
This is an observational review, with an emphasis on photometric dataand their interpretation. Two lists are presented, one containing BetaCephei stars and the other Beta Cephei suspects. These lists then serveas a basis for discussing such topics as the location of Beta Cepheistars in the observational and theoretical H-R diagrams, theevolutionary state of these stars, the period-luminosity andperiod-luminosity-color relations, and observational identification ofpulsation modes. The paper also includes references to recent workconnected with the theoretical discovery that an opacity mechanism isresponsible for the excitation of Beta Cephei-star pulsations. Finally,observational programs for verifying the consequences of this discoveryare suggested.
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Observation of Beta-Cephei Candidates in the Jewel-Box
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993MNRAS.264..165K&db_key=AST
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Trapezium-type wide systems
On the basis of the Smithsonian Observatory Catalogues 15 Trapezium-typesystems are found. Photometric distances are determined for theTrapezium components. A conclusion is drawn on physical relations of thecomponents in the systems. The fact of existence of Trapezium-type largestellar systems confirms the existence of Trapezia with positive totalenergy.
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Uvby-beta photometry of southern clusters. IV - The lower main sequence of NGC 4755
uvby-beta photometry is presented for a total of 46 stars in the youngsouthern galactic cluster NGC 4755, 29 of which have not previously beenmeasured in this photometric system. Most of these 29 are fainter than V= 11 and clearly define the mid-to-late B star ZAMS. Distance estimatesare made of the cluster using hydrogen line luminosity calibrations anduvby and UBV ZAMS fitting. The agreement between the methods isgenerally good and the distance modulus finally adopted is 11.4,corresponding to a distance of 1.9 kpc. Comparison of the V(O)/C(O)diagrams of NGC 4755 and h and CHi Per indicates that the southerncluster is slightly younger. Comparison of several methods of distancedetermination for four young clusters reveals generally very goodagreement, particularly if the methods are applied to the unevolvedstars in the clusters.
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UBV photometry of the southern galactic cluster NGC 4755 = Kappa Crucis
UBV photoelectric magnitudes and colors are presented for 86 starstogether with photographic magnitudes and colors for 553 stars in thevicinity of the southern young open cluster NGC 4755. A true distancemodulus of 11.82 m is derived corresponding to a linear distance of 2.3kpc. The evolutionary age is determined to be between 8 and 11.5 x 10 tothe 6th years, depending on the assumed chemical composition of thecluster stars. The mean interstellar reddening E(B-V) across the clusterincreases with galactic latitude and angular distance from the Coalsackfrom about 0.40 m to 0.48 m with an average value of 0.44 m. The totalnumber of probable cluster members detected in the field down to alimiting visual magnitude of V = 16.0 m is 203. The linear gravitationalradius of the cluster obtained from star strip counts down to visualmagnitude 14.5 m is found to be 3.4 pc. The luminosity function derivedfor NGC 4755 is in good agreement with the initial luminosity functionas given by Sandage (1957). The cluster contains six supergiants andthree variable Be stars.
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Catalog of Luminous Stars in the Southern Coalsack Zone
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982RMxAA...5..183M&db_key=AST
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Variable Stars in the LSS Catalogue
Not Available
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65th Name-List of Variable Stars
Not Available
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Balmer-line photometry of NGC 4755
To discriminate between emission and nonemission objects in the analysisof a number of polarization observations of stars in the southern opencluster NGC 4755, a comparison of the H alpha and H beta line strengthsis made. H alpha and H beta photometric observations are presented for28 and 33 stars, respectively, in NGC 4755; eight emission line starsare identified. V-magnitude, spectral type, and alpha and beta indicestogether with standard deviations are included. In general, nosignificant deviations of the beta indices from those measured by Perryet al. (1976) are found.
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A search for Beta Cephei stars. II - NGC 4755
This paper reports the result of a search for Beta Cephei stars in thecluster NGC 4755. Three were found. New evidence about the evolutionarystage of Beta Cephei stars is put forward, which supports the hypothesisthat they are going through the core-hydrogen burning phase.
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Evolved stars in open clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976ApJS...30..451H&db_key=AST
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Multicolor photometry of the open cluster NGC 4755.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976AJ.....81..632P&db_key=AST
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INHABITED SKY
