Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
Wolf Rayets: Interferometry of Hot Dust
Wolf Rayets (WRs) are hot massive stars at a late stage of evolution.They are prominent signposts for high mass star formation and theirmassive winds have significant influence on the interstellar medium. Asmall but significant number of these stars in the Galaxy are known toproduce copious amounts of dust. Given the hostile circumstellarenvironment, this raises interesting questions. Interferometric andaperture masking observations strongly indicate that binarity plays apivotal role in the dust formation. I will briefly review high angularresolution observations in the near- and mid-infrared which shed somelight on dusty WRs.
| Photometric variability of WC9 stars
Do some Wolf-Rayet stars owe their strong winds to something elsebesides radiation pressure? The answer to this question is still notentirely obvious, especially in certain Wolf-Rayet subclasses, mainlyWN8 and WC9. Both of these types of Wolf-Rayet stars are thought to behighly variable, as suggested by observations, possibly due topulsations. However, only the WN8 stars have so far been vigorously andsystematically investigated for variability. We present here the resultsof a systematic survey during three consecutive weeks of 19 Galactic WC9stars and one WC8 star for photometric variability in two optical bands,V and I. Of particular interest are the correlated variations inbrightness and colour index in the context of carbon dust formation,which occurs frequently in WC9 and some WC8 stars. In the most variablecase, WR76, we used this information to derive a typical dust grain sizeof ~ 0.1?m. However, most photometric variations occur atsurprisingly low levels, and in fact almost half of our sample shows nosignificant variability at all above the instrumental level (? ~0.005- 0.01 mag).
| Newly confirmed and candidate Galactic SNRs uncovered from the AAO/UKST H? survey
We present a catalogue of 18 new Galactic supernova remnants (SNRs)uncovered in the optical regime as filamentary emissions and extendednebulosities on images of the Anglo-Australian Observatory/UnitedKingdom Schmidt Telescope (AAO/UKST) H? survey of the southernGalactic plane. Our follow-up spectral observations confirmed classicaloptical SNR emission lines for these 18 structures via detection of verystrong [SII] at 6717 and 6731 Å relative to H?([SII]/H? > 0.5). Morphologically, 10 of these remnants havecoherent, extended arc or shell structures, while the remaining objectsare more irregular in form but clearly filamentary in nature, typical ofoptically detected SNRs.In 11 cases there was a clear if not complete match between the opticaland radio structures with H? filamentary structures registeredinside and along the presumed radio borders. Additionally, ROSAT X-raysources were detected inside the optical/radio borders of 11 of thesenew remnants and three may have an associated pulsar.The multiwavelength imaging data and spectroscopy together presentstrong evidence to confirm identification of 18 new, mostly senileGalactic SNRs. This includes G288.7-6.3, G315.1+2.7 and G332.5-5.6,identified only as possible remnants from preliminary radioobservations. We also confirm existence of radio-quiet but opticallyactive SNRs.
| The Neutral Counterpart of an Uncatalogued Nebula and a Probable Interstellar Bubble around WR 53 in the Centaurus Region
From the inspection of optical images at l = 307° we have found anuncatalogued nebula of about 9 arcmin in radius, which we namedG307.27+0.27. The analysis of the HI-21cm line emission distributionrevealed an expanding HI shell that encircles the optical emissionregion. The shell, placed at a kinematical distance of 4+/-1 kpc, issuggested to be the HI counterpart of the optical nebula. COobservations at radio wavelengths, and far and mid IR data, allowed usto detect molecular gas and interstellar dust associated with thestructures. The presence of an O6 star at a spectrophotometric distancecompatible with that of the shell supports a stellar wind/HII regionorigin for the whole structure. We also report a probable HIinterstellar bubble related to the Wolf-Rayet star WR 53. Its physicalparameters are similar to the parameters of other HI bubbles aroundmassive stars.
| 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.
| On the massive stellar population of the super star cluster Westerlund 1
We present new spectroscopic and photometric observations of the youngGalactic open cluster Westerlund 1 (Wd 1) that reveala unique population of massive evolved stars. We identify ~200 clustermembers and present spectroscopic classifications for ~25% of these. Wefind that all stars so classified are unambiguously post-Main Sequenceobjects, consistent with an apparent lack of an identifiable MainSequence in our photometric data to V 20. We are able to identifyrich populations of Wolf Rayet stars, OB supergiants and short livedtransitional objects. Of these, the latter group consists of both hot(Luminous Blue Variable and extreme B supergiant) and cool (YellowHypergiant and Red Supergiant) objects - we find that half the knownGalactic population of YHGs resides within Wd 1. We obtain a meanV-MV ~ 25 mag from the cluster Yellow Hypergiants, implying aMain Sequence turnoff at or below MV =-5 (O7 V or later).Based solely on the masses inferred for the 53 spectroscopicallyclassified stars, we determine an absolute minimum mass of ~1.5 ×10^3~Mȯ for Wd 1. However, considering the completephotometrically and spectroscopically selected cluster population andadopting a Kroupa IMF we infer a likely mass for Wd 1 of~10^5~Mȯ, noting that inevitable source confusion andincompleteness are likely to render this an underestimate. As such, Wd 1is the most massive compact young cluster yet identified in the LocalGroup, with a mass exceeding that of Galactic Centre clusters such asthe Arches and Quintuplet. Indeed, the luminosity, inferred mass andcompact nature of Wd 1 are comparable with those of Super Star Clusters- previously identified only in external galaxies - and is consistentwith expectations for a Globular Cluster progenitor.
| 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.
| A hidden population of Wolf-Rayet stars in the massive galactic cluster Westerlund 1
We report the discovery of a hitherto undetected population ofWolf-Rayet stars in the young galactic open cluster Westerlund1. Optical spectroscopy of the cluster identified 11 suchobjects; provisional classification suggests that 6 are nitrogen rich(WN) and 5 carbon rich (WC). Including the previously identified Blue,Yellow & Red Super- & Hypergiants, Westerlund1 clearly has a very rich population of massive post-MainSequence objects. To date, the post-MS population of Westerlund1 is significantly larger than that of any other galacticyoung open cluster - with the possible exception of theArches - implying that it is potentially amongst themost massive young clusters yet identified in the Local Group. Based onobservations collected at the European Southern Observatory, La Silla,Chile (ESO 67.D-0211).
| A new Wolf-Rayet star in Cygnus
We report the discovery of a new Wolf-Rayet star in the direction ofCygnus. The star is strongly reddened but quite bright in the infrared,with J = 9.22, H = 8.08 and KS = 7.09 (2MASS). On the basisof its H + K spectrum, we have classified WR 142a a WC8 star. We haveestimated its properties using as a reference those of other WC8 starsin the solar neighbourhood as well as those of WR 135, whosenear-infrared spectrum is remarkably similar. We thus obtain aforeground reddening of AV =~ 8.1 mag, MJ =~ -4.3,log (L/Lsun) ~ 5.0-5.2, R = 0.8 Rsun, T =~ 125 000K, M = 7.9-9.7 Msun, {dot M} = (1.4-2.3) x 10-5Msun yr-1. The derived distance modulus, DM = 11.2+/- 0.7 mag, places it in a region occupied by several OB associationsin the Cygnus arm, and particularly in the outskirts of both Cygnus OB2and Cygnus OB9. The position in the sky alone does not allow us tounambiguously assign the star to either association, but based on themuch richer massive star content of Cygnus OB2 membership in this latterassociation appears to be more likely. Based on observations collectedat the German-Spanish Astronomical Centre, Calar Alto, operated by theMax-Planck-Institut für Astronomie, Heidelberg, jointly with theSpanish National Commission for Astronomy.
| 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.
| 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.
| Quantitative analysis of WC stars: constraints on neon abundances from ISO-SWS spectroscopy
Neon abundances are derived in four Galactic WC stars -γ2Vel (WR11, WC8+O7.5III), HD156385 (WR90, WC7),HD192103 (WR135, WC8) and WR146 (WC5+O8) - using mid-infraredfine-structure lines obtained with ISO-SWS. Stellar parameters for eachstar are derived using the non-local thermodynamic equilibrium modelatmospheric code of Hillier & Miller, together with ultraviolet(IUE), optical (INT, AAT) and infrared (UKIRT, ISO) spectroscopy. In thecase of γ2Vel, we adopt very recent results from DeMarco et al., who followed an identical approach. ISO-SWS data setsreveal the [Neiii] 15.5-μm line in each of our targets, while [Neii]12.8μm, [Siv] 10.5μm and [Siii] 18.7μm are observed solely inγ2Vel. Using a method updated from Barlow et al. toaccount for clumped winds, we derive Ne/He=(3-4)×10-3by number, plus S/He=6×10-5 for γ2Vel.Neon is highly enriched, such that Ne/S in γ2Vel iseight times higher than cosmic values. However, observed Ne/He ratiosare a factor of 2 lower than predictions of current evolutionary modelsof massive stars. An imprecise mass loss and distance were responsiblefor the much greater discrepancy in neon content identified by Barlow etal. Our sample of WC5-8 stars span a narrow range in T* (=55-71kK), withno trend towards higher temperature at earlier spectral type, supportingearlier results for a larger sample by Koesterke & Hamann. Stellarluminosities range from 100000 to 500000Lsolar, while10-5.1 <= M/(Msolar yr-1) <=10-4.5, adopting clumped winds, in which volume fillingfactors are 10per cent. In all cases, wind performance numbers are lessthan 10, significantly lower than recent estimates. Carbon abundancesspan 0.08<=C/He<=0.25 by number, while oxygen abundances remainpoorly constrained.
| Spectroscopy of WC9 Wolf-Rayet stars: a search for companions
A spectroscopic search for luminous companions to WC9-type Wolf-Rayetstars making circumstellar dust reveals the presence of absorption linesattributable to companions in the blue spectra of WR69 (HD136488) andWR104 (Ve2-45). Comparison of spectra of WR104 observed in 1995 and 1997showed the absorption lines to be more conspicuous in the latterobservation and the emission lines weaker, suggesting a selectiveeclipse of the WC9 star similar to that observed by Crowther in 1996.The WC9 emission-line spectra are shown to be less uniform thanpreviously thought, showing a significant range of Oii line strengths.The only two WC9 stars in the observed sample that do not makecircumstellar dust, WR81 (He3-1316) and WR92 (HD 157451), are found tohave anomalously weak Oii and strong Heii lines. We suggest that thesespectroscopic differences may reflect a compositional difference thatplays a role in determining which of the WC9 stars make dust.
| 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 gamma Velorum binary system. I. O star parameters and light ratio
In this paper we demonstrate how previous determinations of the lightratio between the O and Wolf-Rayet stellar components of the gamma Velsystem are affected by large uncertainties. This is due, amongst otherthings, to the difficulty of measuring the equivalent widths of emissionand absorption lines. We then present a new technique to de-blend andmeasure spectral lines, in which we compensate for the observedabsorption features with synthetic profiles. From the new values of thediagnostic line strengths we determine a hotter spectral type for the Ostar companion (O7.5) than previously published. The light ratio is thendetermined, together with the stellar parameters, via a spectroscopicanalysis. We obtain Delta M_V=1.47+/-0.13 mag. From the light ratio andthe system's luminosity we find M_V(O) = -5.14 mag and M_V(WR) = -3.67mag. Simultaneously we determine ifmmode T_eff else T_efffi(O) = 35 000K, L(O) = 2.1x10(5) Lsun and cal M(O) = 30 Msun.An age of 3.59x10(6) yr is derived from these parameters andevolutionary tracks. We find that the H/He abundance ratio is solar.From a hydro-dynamical calculation of the radiation-driven wind weobtain dot{M}(O) = 1.8x10(-7) Msun yr(-1) and vinfty(O) =2500 km s(-1) . From the O star mass derived here and the mass ratiofrom the literature we derive the mass of the Wolf-Rayet star, cal M(WR)= 9 Msun. The mass-luminosity relation for Wolf-Rayet starsthen leads to L(WR) = 1.5x10(5) Lsun. We finally present thegamma Vel Wolf-Rayet spectrum de-convolved from the O star in the range3800-6700 Angstroms.
| Quantitative classification of WC and WO stars
We present a quantitative classification scheme for carbon and oxygensequence Wolf-Rayet stars. Our scheme uses new high-quality optical AATand INT observations of 20 stars for which we provide narrow-bandphotometry and estimates of interstellar reddenings. In increasing orderof excitation, our spectral classes range from WC11 to WC4 forWolf-Rayet stars with a dominant carbon line visual spectrum, andsubsequently from WO4 to WO1 for those with predominantly oxygen lines.We refine existing WC and WO schemes to incorporate stars with higherand lower excitation spectral features. Both massive stars and centralstars of planetary nebulae (CSPNe) can be classified with the unifiedsystem. We have found no criterion that cleanly separates spectra of thetwo types of star, including elemental abundances (C/O or C/He).However, CSPNe show a wider range of line strength and width thanmassive stars in the same ionization subclass. Systematically lowerFWHM(Civ lambda5808) values are observed from WO-type CSPNe than frommassive WO stars. For WC4-11 stars, our primary diagnostic is theequivalent width or line flux ratio Civlambdalambda5801-12/Ciiilambda5696. We extend the use of this as theprincipal criterion throughout the WC sequence, with fewreclassifications necessary relative to Smith, Shara & Moffat. ForWO stars, Ciii is absent and our new criteria, using primarily oxygenlines, take over smoothly. We define subclasses WO4-1, using Ovilambdalambda3811-34/Ov lambda5590 as our primary diagnostic. Thecontinuation in spectral sequence from WC to WO is used to indicate thatthe sequence is a result primarily of excitation effects, rather thansignificant abundance differences. Our scheme allows us to confirm thatmassive stars and CSPNe are differently distributed over the subclasses.Around 3/5 of massive WC stars lie within the range WC5-8, while<=1/5 of CSPNe are found within these spectral types. Stars withinboth the highest (WO1) and lowest (WC10-11) excitation spectral classesare unique to CSPNe. A WC classification for the hot RCrB star V348 Sgris excluded (previously [WC12]) since both Ciii lambda5696 and Civlambda5808 are absent in its optical spectrum. Additional criteria allowus to distinguish between WC-type, `weak emission line' CSPNe, and Ostars, allowing us to reclassify the central star of IRAS 21282+5050(previously [WC11]) as an O star.
| 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.
| On the physical model of dust around Wolf-Rayet stars
The observational infrared spectra of a number of Wolf-Rayet stars ofWC8-9 spectral classes are shown to be quite satisfactorily explained bymaking use of the detailed theoretical model of a dust shell made up ofspherical amorphous carbon grains, the dynamics, growth-destruction,thermal and electrical charge balance of which are taken into account.The dust grains acquire mainly positive electrical charge, move withsuprathermal drift velocities, and may grow up to 100-200 A as a resultof implantation of impinging carbon ions. For most of the stars, thefraction of condensed carbon does not exceed 1 percent. While the natureof the grain nucleation remains unknown, the condensation distances andthe grain seed production can be estimated by fitting the observationalspectra with theoretical ones.
| 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
| UBV Photometry of Southern Luminous Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2855R&db_key=AST
| 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
| 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.
| 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.
| The ROSAT PSPC survey of the Wolf-Rayet stars
Not Available
| Low resolution IUE spectra of Wolf-Rayet stars.
We present uniformly reduced and measured equivalent widths, FWHM andobserved line fluxes for 94 "single" WR stars (34 galactic WN, 22galactic WC, 31 LMC WN and 7 LMC WC) based on the archive IUE spectra ofWR stars gathered from different observational runs and from differentepochs. The spectra are used for spectral classification in theultraviolet region and for searching correlations among the strength andwidths of emission lines of different ions. Some correlations withoptical and near IR lines observed by other authors are given as well.The set of spectra we use is almost complete to 12 magnitude andrepresentative according to spectral subtype of WR stars.
| A new catalogue of members and candidate members of the Herbig Ae/Be (HAEBE) stellar group
A new up-to-date catalogue of Herbig Ae/Be (HAEBE) stars and relatedobjects is certainly needed, for both well-seasoned researchers and, inparticular, for new investigators starting to study the many interestingastrophysical properties of these very young objects. We present a briefdiscussion of the current observational characteristics that distinguishthis class from their main sequence counterparts. The HAEBE and relatedstars are listed in five tables, containing 287 objects. Table 1contains all Ae and Be stars which historically are recognized as trueHAEBE stars or potential candidate members. Table 2 gives the stars ofspectral type Fe, and emission line stars with very uncertain or unknownspectral type. In Table 3 are given all known Extreme Emission LineObjects (EELOs), of which most have not been identified to belong to anyspecific group. Table 4a and b list other Bep or B[e] stars with strongIR-excess and unknown spectral type. Table 5 contains the non-emissionline possible young objects. Furthermore, Table 6 contains 35 starsrejected from former published lists of HAEBE stars. In these tables weare including coordinates, spectral types, visual magnitudes, ranges inphotometric variability and references of several key publicationsrelated to each object. Relevant remarks, such as the presence of anebula in the vicinity of an object, are also given.
| Spectrophotometry of Wolf-Rayet stars. I - Continuum energy distributions
All available low-resolution IUE spectra are assembled for Galactic,LMC, and SMC W-R stars and are merged with ground-based optical and NIRspectra in order to collate in a systematic fashion the shapes of theseenergy distributions over the wavelength range 0.1-1 micron. They can beconsistently fitted by a power law of the form F(lambda) isapproximately equal to lambda exp -alpha over the range 1500-9000 A toderive color excesses E(B-V) and spectral indices by removing the 2175-Ainterstellar absorption feature. The WN star color excesses derived arefound to be in good agreement with those of Schmutz and Vacca (1991) andKoesterke et al. (1991). Significant heterogeneity in spectral indexvalues was generally seen with any given subtype, but the groupsconsisting of the combined set of Galactic and LMC W-R stars, theseparate WN and WC sequences, and the Galactic and LMC W-R stars allshowed a striking and consistent Gaussian-like frequency distribution ofvalues.
| Early-type emission-line stars with large infrared excesses
A catalog is presented of early-type emission-line stars obtained bycross-identification between Wackerling's catalog and the IRAS catalogof point sources. A study of the distribution in space of the starsshows that these stars belong to the extreme Population I; thus thepresent compilation provides a rather complete sample for further studyof the evolution of pre- and post-main sequence stars of medium and highmasses.
| Color excesses, intrinsic colors, and absolute magnitudes of Galactic and Large Magellanic Cloud Wolf-Rayet stars
A new method of determining the color excesses of WR stars in the Galaxyand the LMC has been developed and is used to determine the excesses for44 Galactic and 32 LMC WR stars. The excesses are combined withline-free, narrow-band spectrophotometry to derive intrinsic colors ofthe WR stars of nearly all spectral subtypes. No correlation of UVspectral index or intrinsic colors with spectral subtype is found forthe samples of single WN or WC stars. There is evidence that early WNstars in the LMC have flatter UV continua and redder intrinsic colorsthan early WN stars in the Galaxy. No separation is found between thevalues derived for Galactic WC stars and those obtained for LMC WCstars. The intrinsic colors are compared with those calculated frommodel atmospheres of WR stars and generally good agreement is found.Absolute magnitudes are derived for WR stars in the LMC and for thoseGalactic WR stars located in clusters and associations for which thereare reliable distance estimates.
| The distribution of massive stars in the Galaxy. I - The Wolf-Rayet stars
Using spectroscopic parallax, the heliocentric and Galactocentricdistances of nearly all of the 157 known Wolf-Rayet stars in the Galaxywere determined. Their distribution both within and perpendicular to theGalactic plane was investigated. The overall distribution within theplane reveals spiral features which are in accord with otherdeterminations of Galactic structure. In addition, it was found that theGalactocentric location of Wolf-Rayet stars is dependent on Wolf-Rayetsubtype, with late WC stars strongly confined to regions within thesolar circle. However, there is only a marginal variation in the WC/WNnumber ratio with distance from the Galactic center. The distribution ofWolf-Rayet stars in the direction perpendicular to the plane revealsthat these objects are closely confined to, but distributedasymmetrically about, the Galactic plane; the verical scale height ofthe distribution is about 45 pc. It is found that the sun is locatedabout 15 pc above the plane defined by these extreme Population Iobjects.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Kentaur |
| Rektaszcenzió: | 13h30m53.25s |
| Deklináció: | -62°04'51.9" |
| Vizuális fényesség: | 10.644 |
| RA sajátmozgás: | -7.1 |
| Dec sajátmozgás: | -3.9 |
| B-T magnitude: | 11.184 |
| V-T magnitude: | 10.689 |
Katalógusok és elnevezések:
|
