Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
Neon Abundances from a Spitzer/IRS Survey of Wolf-Rayet Stars
We report on neon abundances derived from Spitzer high resolutionspectral data of eight Wolf-Rayet (WR) stars using the forbidden line of[Ne III] 15.56 μm. Our targets include four WN stars of subtypes 4-7,and four WC stars of subtypes 4-7. We derive ion fraction abundancesγ of Ne2+ for the winds of each star. The ion fractionabundance is a product of the ionization fraction Qi in stagei and the abundance by number AE of element E relativeto all nuclei. Values generally consistent with solar are obtained forthe WN stars, and values in excess of solar are obtained for the WCstars.
| Automatic Detection of Expanding H I Shells in the Canadian Galactic Plane Survey Data
The identification of expanding H I shells is difficult because of theirvariable morphology. In this paper we present an automatic detector forH I shells, based on the more stable dynamical characteristics ofexpanding bubbles with radii <40 pc. The detection is performed intwo stages. First, artificial neural networks are trained to recognizethe dynamical signature of an expanding bubble in the velocity spectraof 21 cm data. The second stage consists of subsequent validations basedon the potential bubble's morphology. The technique is tested on 11known bubbles, and 10 of them are successfully detected. Conducting asystematic detection on a 48deg×9deg regionin the Perseus arm, we obtain 7100 detections with spatial distributionfollowing the stellar distribution of the Galactic disk. The estimatedradius and expansion velocity distributions for objects with R<=10 pcagree with the distributions predicted by models of adiabaticallyexpanding bubble populations. The fraction of the Perseus arm volumeoccupied by the detected objects, which can be interpreted as the smallbubbles' contribution to the Galactic porosity Q, is calculated toQR<40pc=0.007+0.025-0.003. Four newbubble cases and eight serious candidates, related to known progenitors,are proposed.
| An Unusual System of H I Filaments near WR 5 and HD 17603
We report the discovery of a system of unusual H I filaments that appearto be associated with molecular clouds in the Perseus spiral arm of ourGalaxy. We investigate the hypothesis that this system is the result ofa directed flow of dissociated gas from clouds trapped within anextended wind flow from massive stars. The Wolf-Rayet star WR 5 and theO Ib(f) star HD 17603 are identified as candidate driving sources.However, an examination of this hypothesis within the context of thetheory of mass-loaded winds shows that these two stars alone cannotaccount for the energetics and kinematics of the required sphericallysymmetric wind flow. Unless the apparent association between H I,molecular gas, and stars is an accidental one, we suggest that other asyet unidentified stars must have contributed to driving the filaments.
| A Very Large Array 3.6 Centimeter Continuum Survey of Galactic Wolf-Rayet Stars
We report the results of a survey of radio continuum emission ofGalactic Wolf-Rayet (WR) stars north of δ=-46°. Theobservations were obtained at 8.46 GHz (3.6 cm) using the Very LargeArray, with an angular resolution of ~6"×9" and typical rms noiseof ~0.04 mJy beam-1. Our survey of 34 WR stars resulted in 15definite and five probable detections, 13 of these for the first time atradio wavelengths. All detections are unresolved (θ<~5"). Timevariations in flux are confirmed in the cases of WR 98a, 104, 105, and125. WR 79a and WR 89 are also variable in flux, and we suspect they arealso nonthermal emitters. Thus, of our sample 20%-30% of the detectedstars are nonthermal emitters. Average mass-loss rate determinationsobtained excluding definite and suspected nonthermal cases give similarvalues for WN (all subtypes) and WC5-7 stars[M(WN)=(4+/-3)×10-5 Msolar yr-1and M(WC5-7)=(4+/-2)×10-5 Msolaryr-1], while a lower value was obtained for WC8-9 stars[M(WC8-9)=(2+/-1)×10-5 Msolaryr-1]. Uncertainties in stellar distances largely contributeto the observed scatter in mass-loss rates. Upper limits to themass-loss rates were obtained in cases of undetected sources and forsources that probably show additional nonthermal emission.
| Morphological Analysis of H I Features. I. Metric Space Technique
This is the first of two papers on the morphological analysis of H Ifeatures. In this first paper, we use the so-called metric spacetechnique, developed by F. C. Adams and J. Wiseman. The metric spacetechnique is an image analysis, mathematical formalism used toquantitatively compare astrophysical maps according to complexity.Instead of comparing maps on a pixel-by-pixel basis, we compare themaps' one-dimensional ``output functions,'' which characterize specificmorphological/physical aspects of the maps. The tool is used to analyze28 H I features of known origin taken from the Canadian Galactic PlaneSurvey (CGPS), where the maps are scaled at 18" per pixel (resolution of1cosδ arcmin). Technical and mathematical improvements to theformalism are presented. After classifying the 28 maps according tocomplexity, we searched for correlations between this complexity rankingand other quantifiable aspects of the H I features such as age, area, HI area, distance, flux from the ionizing star(s), fractal dimension, H Imass, and |z| (the absolute value of the height of the objects, above orbelow the Galactic plane). The most interesting correlations are (1) thehigher the flux of UV photons, the more complex is the photodissociatedH I feature, and (2) the older the supernova remnant, the more complexthe H I associated with it. There is no correlation between the fractaldimension of the maps and their complexity or their physicalcharacteristics, thus showing that the metric space technique could beused as a solution to the degeneracy of the fractal dimension.
| The neutral gas in the environs of the Wolf Rayet stars in the Circinus OB1 association
We have investigated the neutral hydrogen in the direction of theCircinus OB1 association with particular emphasis in the study of thevicinity of the WR stars WR 65 and WR 67. The HI line data were obtainedwith the Australia Telescope Compact Array with a synthesized beam of4\farcm0 × 2\farcm7 and a velocity resolution of 1.1 kms-1. These data led to the discovery of a large cavitysurrounded by an almost complete shell in agreement with the locationsand distances of the two WR stars. We propose that the HI featuresconstitute an interstellar bubble created by the powerful winds of theWR stars and their progenitors. By assuming a distance of 3 kpc, wecalculate for this HI bubble a linear radius of 22 pc, a swept-up massof 1600 M_ȯ and an expansion velocity of more than 7 kms-1. High angular resolution IRAS infrared data (HIRES)reveal the presence of a ring with good spatial correlation with the HIshell. Eight IRAS protostellar candidates located around the HI cavitysuggest that star formation may be taking place in the shell. Furtherinvestigation is required to confirm this proposition.
| The conspicuous absence of X-ray emission from carbon-enriched Wolf-Rayet stars
The carbon-rich WC5 star WR 114 was not detected during a 15.9 ksecXMM-Newton, observation, implying an upper limit to the X-ray luminosityof LX < 2.5x 1030 erg s-1 andto the X-ray to bolometric luminosity ratio ofLX/Lbol < 4*E-9. This confirmsindications from earlier less sensitive measurements that there has beenno convincing X-ray detection of any single WC star. This lack ofdetections is reinforced by XMM-Newton, and CHANDRA observations of WCstars. Thus the conclusion has to be drawn that the stars withradiatively-driven stellar winds of this particular class areinsignificant X-ray sources. We attribute this to photoelectronicabsorption by the stellar wind. The high opacity of the metal-rich anddense winds from WC stars puts the radius of optical depth unity athundreds or thousands of stellar radii for much of the X-ray band. Webelieve that the essential absence of hot plasma so far out in the windexacerbated by the large distances and correspondingly high ISM columndensities makes the WC stars too faint to be detectable with currenttechnology. The result also applies to many WC stars in binary systems,of which only about 20% are identified X-ray sources, presumably due tocolliding winds.
| H I Tails from Molecular Clouds near HD 17603 and Wolf-Rayet 5
We report the detection of long, thin H I tails emanating from molecularclouds in the Perseus Arm of the Galaxy. The hypothesis that they aredriven by stellar winds from one or both of the massive stars HD 17603and WR 5 places strong constraints on the stellar wind environment: wefind that a heavily mass-loaded wind bubble is required.
| Radio observations of interstellar bubbles surrounding massive stars}
We show radio continuum observations of the WR ring nebulae around WR101 and WR 113 obtained using the VLA and HI 21 cm line data of theinterstellar bubble around the O type stars BD +24 deg 3866 and BD+25deg 3952 obtained with the DRAO Synthesis Telescope. We review previousradio continuum and HI line results toward WR and O-type stars.
| Wolf-Rayet star parameters from spectral analyses
The Potsdam non-LTE code for expanding atmospheres, which accounts forclumping and iron-line blanketing, has been used to establish a grid ofmodel atmospheres for WC stars. A parameter degeneracy is discovered forearly-type WC models which do not depend on the `stellar temperature'.15 Galactic WC4-7 stars are analyzed, showing a very uniform carbonabundance (He:C = 55:40) with only few exceptions.
| Kinematical Structure of Wolf-Rayet Winds. I.Terminal Wind Velocity
New terminal wind velocities for 164 Wolf-Rayet stars (from the Galaxyand LMC) based on PCyg profiles of lambda1550 CIV resonance line werederived from the archive high and low resolution IUE spectra availableform the INES database. The high resolution data on 59 WR stars (39 fromthe Galaxy and 20 from LMC) were used to calibrate the empiricalrelation lambda_min^Abs- lambda_peak^Emis vs terminal wind velocity,which was then used for determinations of the terminal wind velocitiesfrom the low resolution IUE data. We almost doubled the previous mostextended sample of such measurements. Our new measurements, based onhigh resolution data, are precise within 5-7%. Measurements, based onthe low resolution spectra have the formal errors of approx 40-60%. Acomparison of the present results with other determinations suggestshigher precision of approx 20%. We found that the terminal windvelocities for the Galactic WC and WN stars correlate with the WRspectral subtype. We also found that the LMC WN stars have winds slowerthan their Galactic counterparts, up to two times in the case of the WNEstars. No influence of binarity on terminal wind velocities was found.Our extended set of measurements allowed us to test application of theradiation driven wind theory to the WR stars. We found that, contrary toOB stars, terminal wind velocities of the WR stars correlate only weaklywith stellar temperature. We also note that the terminal to escapevelocity ratio for the WR stars is relatively low: 2.55 pm 1.14 for theGalactic WN stars and 1.78 pm 0.70 for the Galactic WCs. This ratiodecreases with temperature of WR stars, contrary to what is observed inthe case of OB stars. The presented results show complex influence ofchemical composition on the WR winds driving mechanism efficiency. Ourkinematical data on WR winds suggest evolutionary sequence: WNL -->WNE --> WCE --> WCL.
| A Mid-Infrared Spectral Survey of Galactic Wolf-Rayet Stars
We present 8-13 μm spectra at resolution R~600 of 29 northernGalactic Wolf-Rayet stars, including the first ever reportedmid-infrared (MIR) spectrum for many. Among the subtypes of the starsstudied were 14 WC, 13 WN, 1 WN/WC, and an additional reclassified WN.Lines of He I and He II, along with fine-structure lines of Ne II and SIV, are strongly present in 22 of the sources observed, while six of thesources exhibit the powerful emission of heated circumstellar carbondust. We point out similarities between our spectra and Infrared SpaceObservatory (ISO) observations of several of the same sources and notean unresolved discrepancy between the two data sets for the WC6 star WR146. We investigate the diagnostic power of MIR He I and He II lines forsubtype discrimination and find the line ratio Wλ(9.7μm He II)/Wλ(11.3 μm He I+He II) can providemoderate discrimination within the WN and WC types, though the smallnumber of stars with corresponding line pairs detected made suchassessment difficult.
| The VIIth catalogue of galactic Wolf-Rayet stars
The VIIth catalogue of galactic PopulationI Wolf-Rayet stars providesimproved coordinates, spectral types and /bv photometry of known WRstars and adds 71 new WR stars to the previous WR catalogue. This censusof galactic WR stars reaches 227 stars, comprising 127 WN stars, 87 WCstars, 10 WN/WC stars and 3 WO stars. This includes 15 WNL and 11 WCLstars within 30 pc of the Galactic Center. We compile and discuss WRspectral classification, variability, periodicity, binarity, terminalwind velocities, correlation with open clusters and OB associations, andcorrelation with Hi bubbles, Hii regions and ring nebulae. Intrinsiccolours and absolute visual magnitudes per subtype are re-assessed for are-determination of optical photometric distances and galacticdistribution of WR stars. In the solar neighbourhood we find projectedon the galactic plane a surface density of 3.3 WR stars perkpc2, with a WC/WN number ratio of 1.5, and a WR binaryfrequency (including probable binaries) of 39%. The galactocentricdistance (RWR) distribution per subtype shows RWRincreasing with decreasing WR subtype, both for the WN and WC subtypes.This RWR distribution allows for the possibility ofWNE-->WCE and WNL-->WCL subtype evolution.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| The Interstellar Environment of the Wolf-Rayet Star WR 143
As part of a systematic study of the environment of Galactic WR stars, aregion along the line of sight to Cygnus (l=77.5°,b=0°) has beenstudied. The neutral hydrogen 21 cm line distribution shows theexistence of a cavity expanding from the Wolf-Rayet star WR 143. Thiscavity, created by the stellar wind of the star, has a mean radius of 7pc (assuming a distance of about 1 kpc), an expansion velocity of morethan 8 km s-1, and a missing mass of some 150Msolar and seems to be surrounded by an H I shell, likelymade up of the gas pushed by the star. Although this hole (also calledbubble) is quite conspicuous in H I, there seems to be no trace of it atthe other wavelengths studied (radio continuum and infrared). All radioobservations were obtained at the Dominion Radio AstrophysicalObservatory as part of the Canadian Galactic Plane Survey.
| Exospheric models for the X-ray emission from single Wolf-Rayet stars
We review existing ROSAT detections of single Galactic Wolf-Rayet (WR)stars and develop wind models to interpret the X-ray emission. The ROSATdata, consisting of bandpass detections from the ROSAT All-Sky Survey(RASS) and some pointed observations, exhibit no correlations of the WRX-ray luminosity (LX) with any star or wind parameters ofinterest (e.g. bolometric luminosity, mass-loss rate or wind kineticenergy), although the dispersion in the measurements is quite large. Thelack of correlation between X-ray luminosity and wind parameters amongthe WR stars is unlike that of their progenitors, the O stars, whichshow trends with such parameters. In this paper we seek to (i) test byhow much the X-ray properties of the WR stars differ from the O starsand (ii) place limits on the temperature TX and fillingfactor fX of the X-ray-emitting gas in the WR winds. Adoptingempirically derived relationships for TX and fXfrom O-star winds, the predicted X-ray emission from WR stars is muchsmaller than observed with ROSAT. Abandoning the TX relationfrom O stars, we maximize the cooling from a single-temperature hot gasto derive lower limits for the filling factors in WR winds. Althoughthese filling factors are consistently found to be an order of magnitudegreater than those for O stars, we find that the data are consistent(albeit the data are noisy) with a trend of fx ∝(Mν&infy;)-1 in WR stars, as is also the casefor O stars.
| Mass-loss rates of Wolf-Rayet stars as a function of stellar parameters
Clumping-corrected mass-loss rates of 64 Galactic Wolf-Rayet (WR) starsare used to study the dependence of mass-loss rates, momentum transferefficiencies and terminal velocities on the basic stellar parameters andchemical composition. The luminosities of the WR stars have beendetermined either directly from the masses, using the dependence of L onmass predicted by stellar evolution theory, or they were determined fromthe absolute visual magnitudes and the bolometric corrections. For thispurpose we improved the relation between the bolometric correction andthe spectral subclass. (1) The momentum transfer efficiencies η(i.e. the ratio between the wind momentum loss and radiative momentumloss) of WR stars are found to lie in the range of 1.4 to 17.6, with themean value of 6.2 for the 64 program stars. Such values can probably beexplained by radiative driving due to multiple scattering of photons ina WR wind with an ionization stratification. However, there may be aproblem in explaining the driving at low velocities. (2) We derived thelinear regression relations for the dependence of the terminal velocity,the momentum transfer efficiency and the mass-loss rates on luminosityand chemical composition. We found a tight relation between the terminalvelocity of the wind and the parameters of the hydrostatic core. Thisrelation enables the determination of the mass of the WR stars fromtheir observed terminal velocities and chemical composition with anaccuracy of about 0.1 dex for WN and WC stars. Using evolutionary modelsof WR stars, the luminosity can then be determined with an accuracy of0.25 dex or better. (3) We found that the mass-loss rates(&mathaccent "705Frelax dot;) of WR stars depend strongly onluminosity and also quite strongly on chemical composition. For thecombined sample of WN and WC stars we found that &mathaccent"705Frelax dot; in Mȯyr-1 can be expressed as&mathaccent "705Frelax dot; ≃ 1.0 ×10-11(L/L ȯ)1.29Y1.7Z0.5 (1) with an uncertainty of σ = 0.19dex (4) The new mass-loss rates are significantly smaller than adoptedin evolutionary calculations, by about 0.2 to 0.6 dex, depending on thecomposition and on the evolutionary calculations. For H-rich WN starsthe new mass-loss rates are 0.3 dex smaller than adopted in theevolutionary calculations of Meynet et al. (1994). (5) The lowermass-loss rates, derived in this paper compared to previously adoptedvalues, facilitate the formation of black holes as end points of theevolution of massive stars. However they might create a problem inexplaining the observed WN/WC ratios, unless rotational mixing ormass-loss due to eruptions is important.
| Physical Structure of Small Wolf-Rayet Ring Nebulae
We have selected the seven most well-defined Wolf-Rayet (WR) ringnebulae in the Large Magellanic Cloud (LMC), Br 2, 10, 13, 40a, 48, 52,and 100, to study their physical nature and evolutionary stages. New CCDimaging and echelle observations have been obtained for five of thesenebulae; previous photographic imaging and echelle observations areavailable for the remaining two nebulae. Using the nebular dynamics andabundances, we find that the Br 13 nebula is a circumstellar bubble, andthat the Br 2 nebula may represent a circumstellar bubble merging with afossil main-sequence interstellar bubble. The nebulae around Br 10, 52,and 100 all show influence of the ambient interstellar medium. Theirregular expansion patterns suggest that they still contain significantamounts of circumstellar material. Their nebular abundances would beextremely interesting, as their central stars are WC5 and WN3-WN4 starswhose nebular abundances have not been derived previously. Intriguingand tantalizing implications are obtained from comparisons of the LMC WRring nebulae with ring nebulae around Galactic WR stars, Galactic LBVs,LMC LBVs, and LMC BSGs; however, these implications may be limited bysmall-number statistics. A SNR candidate close to Br 2 is diagnosed byits large expansion velocity and nonthermal radio emission. There is noindication that Br 2's ring nebula interacts dynamically with this SNRcandidate.
| Catalogue of H-alpha emission stars in the Northern Milky Way
The ``Catalogue of Stars in the Northern Milky Way Having H-alpha inEmission" appears in Abhandlungen aus der Hamburger Sternwarte, Band XIin the year 1997. It contains 4174 stars, range {32degr <= l() II< 214degr , -10degr < b() II < +10degr } having the Hαline in emission. HBH stars and stars of further 99 lists taken from theliterature till the end of 1994 were included in the catalogue. We givethe cross-identification of stars from all lists used. The catalogue isalso available in the Centre de Données, Strasbourg ftp130.79.128.5 or http://cdsweb.u-strasbg.fr and at the HamburgObservatory via internet.
| 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.
| Wolf-Rayet stars and O-star runaways with HIPPARCOS. I. Kinematics
Reliable systemic radial velocities are almost impossible to secure forWolf-Rayet stars, difficult for O stars. Therefore, to study the motions- both systematic in the Galaxy and peculiar - of these two relatedtypes of hot, luminous star, we have examined the Hipparcos propermotions of some 70 stars of each type. We find that (a) both groupsfollow Galactic rotation in the same way, (b) both have a similarfraction of ``runaways'', (c) mean kinetic ages based on displacementand motion away from the Galactic plane tend to slightly favour thecluster ejection over the the binary supernova hypothesis for theirformation, and (d) those with significant peculiar supersonic motionrelative to the ambient ISM, tend to form bow shocks in the direction ofthe motion. Based on data from the ESA Hipparcos astrometry satellite.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/Abstract.html
| Catalogue of stars in the northern Milky Way having H-alpha in emission
Not Available
| Large IRAS Shells Around Galactic Wolf-Rayet Stars and the O Star Phase of Wolf-Rayet Evolution
Abstract image available at:http://adsabs.harvard.edu/abs/1996AJ....112.2828M
| The Wolf-Rayet counterpart of Cygnus X-3.
We present orbital-phase resolved I and K-band spectroscopy of CygnusX-3. All spectra show emission lines characteristic of Wolf-Rayet starsof the WN subclass. On time scales longer than about one day, the linestrengths show large changes, both in flux and in equivalent width. Inaddition, the line ratios change, corresponding to a variation inspectral subtype of WN6/7 to WN4/5. We confirm the finding that at timeswhen the emission lines are weak, they shift in wavelength as a functionof orbital phase, with maximum blueshift coinciding with infrared andX-ray minimum, and maximum redshift half an orbit later. Furthermore, weconfirm the prediction - made on the basis of previous observations -that at times when the emission lines are strong, no clear wavelengthshifts are observed. We describe a simplified, but detailed model forthe system, in which the companion of the X-ray source is a Wolf-Rayetstar whose wind is at times ionised by the X-ray source, except for thepart in the star's shadow. With this model, the observed spectralvariations can be reproduced with only a small number of freeparameters. We discuss and verify the ramifications of this model, andfind that, in general, the observed properties can be understood. Weconclude that Cyg X-3 is a Wolf-Rayet/X-ray binary.
| Star counts in southern dark clouds: Corona Australis and Lupus.
Star counts technique is used towards southern dark globular filamentssituated in the cloud complexes of Corona Australis and Lupus. Tablesand maps of the distribution of visual extinction are presented for eachfilament. Lower limit masses for the filaments and condensations havebeen estimated and the central coordinates of the condensations are alsogiven. R CrA is the most active star forming region among the filamentsstudied in this work whereas Lupus 1, with almost the same lower limitof mass, has only a few T Tauri stars and just one young embeddedobject. The distribution of direction of the magnetic field in thecondensations of Lupus, suggests that the condensation morphologies doesnot have any apparent relation with the magnetic field orientation.
| An IRAS-based Search for New Dusty Late-Type WC Wolf-Rayet Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS..100..413C&db_key=AST
| An atlas of the infrared spectral region. I. The early type stars (O-G0).
The Atlas illustrates the behavior of early type stars (O, B, A and Ftype) in the near infrared 8375-8770A region at a resolution of aboutone A. Intensity tracings of 76 stars are presented. Of these 51 starscover the spectral range O to G0 and luminosity classes V, III, Ib andIa. The influence of the rotational velocity is also illustrated as wellas the spectra of 19 stars with spectral peculiarities. The completeAtlas is also available under catalog number 3183 from the CDSStrasbourg and other data centers.
| Spectral analyses of 25 Galactic Wolf-Rayet stars of the carbon sequence.
We present a grid of helium-carbon models for Wolf-Rayet (WR) stars ofthe carbon sequence (WC) with β_ C_=0.2 (carbon mass fraction),thus extending our previously released grid with β_C_=0.6 to adifferent chemical composition. The WR model atmospheres are based onthe so-called standard assumptions. The calculations account for non-LTEradiation transfer in spherically expanding atmospheres. Helium andcarbon are represented by detailed model atoms, especially concerningthe ions Ciii and Civ. Using the model grids 25 Galactic WC stars ofintermediate subtype (WC5 to WC8) are analyzed. Subsequently we performfine analyses by calculating several individual models for each of theprogram stars. Temperatures, radii, mass-loss rates and terminalvelocities are determined together with the carbon to helium ratio. Theanalyzed WC stars are found to form two groups, which can bedistinguished by the strength of their emission lines. Stars with weaklines (WC-w) have effective temperatures close to 50kK and their windsare relatively thin, forming the continuous spectrum in regions withsmall expansion velocities. WC stars with strong lines (WC-s) havehigher effective temperatures (60 to 100kK, referring to the coreradius) and thick winds. Thus there is a strong analogy to thedistribution of the early-type WN stars (WNE-w and WNE-s, respectively).For the WC stars we determine luminosities between 10^4.7^ and10^5.5^Lsun_ and mass-loss rates from 10^-4.8^ to10^-3.9^Mȯ/yr. The carbon mass fraction varies from 0.2 to 0.6. Nocorrelation is found between the carbon abundance and any of the stellarparameters (e.g. temperature, luminosity) or the spectral subtype. Theevolution of WR stars is discussed by comparing the results of ouranalyses with evolutionary tracks.
| A Large Bubble External to the Wolf-Rayet Ring Nebula NGC 6888
Abstract image available at:http://adsabs.harvard.edu/abs/1995AJ....109.2257M
| Terminal Velocities of Wolf-Rayet Star Winds from Low Resolution IUE Spectra
Attracted by the simplicity of the recently published by Prinja (1994)method of determination of terminal wind velocities in hot stars fromlow resolution IUE spectra we investigate its application to WR stars.With a large sample of low resolution IUE spectra of WR stars we foundeven simpler, that is linear instead of square, empirical relationbetween Delta lambda as defined by Prinja (1994) and terminal windvelocity -- vinfty. Using this new empirical relation wepresent vinfty for a sample of 85 galactic and LMC stars, 19of them determined for the first time. We almost tripled the number ofterminal velocity determinations for LMC WR stars. The comparison withother determinations shows that this simple method is accurate to within10-20%. We confirm the correlation between terminal velocity and WCsubtype. We also show that terminal velocities of WN stars are lowerthan that of WCE. A comparison between galactic and LMC stars shows thatthe LMC WN stars have slower winds in most of WN subtypes.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Kahraman |
| Sað Açýklýk: | 02h52m11.67s |
| Yükselim: | +56°56'07.2" |
| Görünürdeki Parlaklýk: | 10.497 |
| özdevim Sað Açýklýk: | 3.8 |
| özdevim Yükselim: | 0.3 |
| B-T magnitude: | 11.214 |
| V-T magnitude: | 10.557 |
Kataloglar ve belirtme:
|
INHABITED SKY
