Contents
Images
Upload your image
DSS Images Other Images
Related articles
Unveiling the molecular environment of the ring nebula RCW 78
Aims. We present a study of the ionized, neutral atomic, and moleculargas associated with the ring nebula RCW 78 around the WR star HD 117688(=WR 55) with the aim of analyzing the distribution of the associatedgas and investigating its energetics. Methods: We base our studyon 12CO(1-0) and 12CO(2-1) observations of thebrightest section of the nebula carried out with the SEST telescope withangular resolutions of 45´´ and 22´´,respectively; and on complementary 12CO(1-0) data of a largerarea obtained with the NANTEN telescope with an angular resolution of 2arcmin 7, Hi 21-cm line data taken from the ATCA survey, IRAS HIRESdata, and radio continuum data at 4.85 GHz from the Parkes survey. Results: We report the detection of molecular gas having velocitiesin the range -56 to -33 km s-1 associated with the westernregion of RCW 78. A few patches of molecular gas possibly linked to theeastern faint section are detected. The CO emission appears concentratedin a region of 23 arcmin×18 arcmin in size, with a total molecularmass of (1.3±0.5)×105 M_?, mainly connectedto the western section. The analysis of the neutral atomic gasdistribution reveals the H i envelope of the molecular cloud, while theradio continuum emission shows a ring-like structure, which is the radiocounterpart of the optical nebula. The gas distribution is compatiblewith the western section of RCW 78 having originated in thephotodissociation and ionization of the molecular gas by the UV photonsof the WN7 star HD 117688, and with the action of the stellar winds ofthe WR star on the surrounding gas. In this scenario, the interstellarbubble expanded more easily towards the east than towards the west dueto the lack of dense molecular gas in the eastern section. The proposedscenario also explains the off center location of WR 55. A number ofinfrared point sources classified as YSO candidates showed that starformation activity is present in the molecular gas linked to the nebula.The possibility that the expansion of the bubble triggered starformation in this region cannot be discarded. Member of Carrera del Investigador, CONICET, Argentina.
| A Near-Infrared Survey of the Inner Galactic Plane for Wolf-Rayet Stars. I. Methods and First Results: 41 New WR Stars
The discovery of new Wolf-Rayet (WR) stars in our Galaxy via large-scalenarrowband optical surveys has been severely limited by dust extinction.Recent improvements in infrared technology have madenarrowband-broadband imaging surveys viable again. We report a new J, K,and narrowband imaging survey of 300 deg2 of the plane of theGalaxy, spanning 150 degrees in Galactic longitude and reaching 1 degreeabove and below the Galactic plane. The survey has a useful limitingmagnitude of K = 15 over most of the observed Galactic plane, and K = 14within a few degrees of the Galactic center. Thousands of emission linecandidates have been detected. In spectrographic follow-ups of 173 WRstar candidates we have discovered 41 new WR stars, 15 of type WN and 26of type WC. Star subtype assignments have been confirmed with K-bandspectra, and distances approximated using the method of spectroscopicparallax. A few of the new WR stars are among the most distant known inour Galaxy. The distribution of these new WR stars is seen to followthat of previously known WR stars along the spiral arms of the Galaxy.Tentative radial velocities were also measured for most of the new WRstars.
| 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.
| Conference Summary
In this summary we will first talk a little bit about the woman whosework so inspired us and brought us here. We will then describe what wefeel we learned this week, and finally we will pose some of the bigquestions that we are left with.
| β Cephei stars in the ASAS-3 data. II. 103 new β Cephei stars and a discussion of low-frequency modes
Context: The β Cephei stars have been studied for over a hundredyears. Despite this, many interesting problems related to this class ofvariable stars remain unsolved. Fortunately, these stars seem to bewell-suited to asteroseismology. Hence, the results of seismic analysisof β Cephei stars should help us to better understand pulsationsand the main sequence evolution of massive stars, particularly theeffect of rotation on mode excitation and internal structure. It istherefore extremely important to increase the sample of known βCephei stars and select targets that are useful for asteroseismology. Aims: We analysed ASAS-3 photometry of bright early-type stars with thegoal of finding new β Cephei stars. We were particularly interestedin β Cephei stars that would be good for seismic analysis, i.e.,stars that (i) have a large number of excited modes; (ii) showrotationally split modes; (iii) are components of eclipsing binarysystems; (iv) have low-frequency modes, that is, are hybrid βCephei/SPB stars. Methods: Our study was made with a homogeneous sampleof over 4100 stars having MK spectral type B5 or earlier. For thesestars, the ASAS-3 photometry was analysed by means of a Fourierperiodogram. Results: We have discovered 103 β Cephei stars,nearly doubling the number of previously known stars of this type. Amongthese stars, four are components of eclipsing binaries, seven have modesequidistant or nearly equidistant in frequency. In addition, we foundfive β Cephei stars that show low-frequency periodic variations,very likely due to pulsations. We therefore regard them as candidatehybrid β Cephei/SPB pulsators. All these stars are potentially veryuseful for seismic modeling. Moreover, we found β Cephei-typepulsations in three late O-type stars and fast period changes in one, HD168050.Table 2 and Figs. 2-14 are only available in electronic form athttp://www.aanda.org The V photometry for all 103 stars is available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/477/917
| The Galactic WN stars. Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation
Context: .Very massive stars pass through the Wolf-Rayet (WR) stagebefore they finally explode. Details of their evolution have not yetbeen safely established, and their physics are not well understood.Their spectral analysis requires adequate model atmospheres, which havebeen developed step by step during the past decades and account in theirrecent version for line blanketing by the millions of lines from ironand iron-group elements. However, only very few WN stars have beenre-analyzed by means of line-blanketed models yet. Aims: .Thequantitative spectral analysis of a large sample of Galactic WN starswith the most advanced generation of model atmospheres should provide anempirical basis for various studies about the origin, evolution, andphysics of the Wolf-Rayet stars and their powerful winds. Methods:.We analyze a large sample of Galactic WN stars by means of the PotsdamWolf-Rayet (PoWR) model atmospheres, which account for iron lineblanketing and clumping. The results are compared with a syntheticpopulation, generated from the Geneva tracks for massive starevolution. Results: .We obtain a homogeneous set of stellar andatmospheric parameters for the Galactic WN stars, partly revisingearlier results. Conclusions: .Comparing the results of ourspectral analyses of the Galactic WN stars with the predictions of theGeneva evolutionary calculations, we conclude that there is roughqualitative agreement. However, the quantitative discrepancies are stillsevere, and there is no preference for the tracks that account for theeffects of rotation. It seems that the evolution of massive stars isstill not satisfactorily understood.
| HI and molecular gas related to RCW 78
We analyze the atomic neutral and molecular gas associated with the ringnebula RCW 78 around the Wolf-Rayet star HD 117688 (WN7). The CO(1-0)data were obtained with the SEST telescope of the ESO, located at LaSilla, Chile, with an angular resolution of 45 arcsec. The neutralhydrogen data belong to the Southern Galactic Plane Survey with asynthesized beam of 2.1 arcmin.The CO emission distribution reveals the presence of molecular gas withvelocities in the range -66 to -32 km s^{-1} associated with thebrightest part of the nebula.The study of the HI gas emission distribution allowed the identificationof a void and shell linked to the nebula, which was interpreted as theneutral gas counterpart of the optical ring nebula.The analysis suggests that RCW 78 has probably developped at the surfaceof the molecular cloud, where the UV stellar photons havephotodissociated and ionized the dense gas.
| 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.
| The Stars Surrounding WR 55
Photoelectric UBV photometry is presented for stars in a field closelyadjacent to the Wolf-Rayet star WR 55 (WN7) in a search for a possibleparent cluster. There is a group of at least eight stars ~7'south-southeast of the WR star forming a newly discovered, sparselypopulated open cluster (designated C1331-622), but the stars are only819+/-26 pc distant, less than a quarter of the predicted distance to WR55.
| Kinematical Structure of Wolf-Rayet Winds. II. Internal Velocity Scatter in WN Stars
The shortward edge of the absorption core velocities - v_black asdetermined from low resolution archived IUE spectra from the INESdatabase are presented for three P Cyg profiles of NV 1240, HeII 1640and NIV 1720 for 51 Galactic and 64 LMC Wolf-Rayet stars of the WNsubtype. These data, together with v_black of CIV 1550 line presented inNiedzielski and Skorzynski (2002) are discussed. Evidences are presentedthat v_black of CIV 1550 rarely displays the largest wind velocity amongthe four lines studied in detail and therefore its application as anestimator of the terminal wind velocity in WN stars is questioned. Anaverage v_black of several lines is suggested instead but it is pointedout that v_black of HeII 1640 usually reveals the highest observablewind velocity in Galactic and LMC WN stars. It is shown that thestratification strength decreases from WNL to WNE stars and that for WNLstars there exists a positive relation between v_black and theIonization Potential. The velocity scatter between v_black obtained fromdifferent UV lines is found to correlate well with the X-ray luminosityof single WN stars (correlation coefficient R=0.82 for the data obtainedfrom the high resolution IUE spectra) and therefore two clumpy windmodels of single WN stars are presented that allow the velocity scatterto persist up to very large distances from the stellar surface (r approx500-1000 R_*). These models are used to explain the specific features ofsingle WN stars like broad absorption troughs of strong lines havingdifferent v_black, X-ray fluxes, IR/radio continua and stratificationrelations.
| 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.
| The orbit of the double-lined Wolf-Rayet binary HDE 318016 (=WR 98)
We present the discovery of OB type absorption lines superimposed to theemission line spectrum and the first double-lined orbital elements forthe massive Wolf-Rayet binary HDE 318016 (=WR 98), a spectroscopicbinary in a circular orbit with a period of 47.825 days. Thesemiamplitudes of the orbital motion of the emission lines differ fromline to line, indicating mass ratios between 1 and 1.7 forMWR/MOB.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| 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.
| 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.
| 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.
| The nitrogen spectra of Wolf-Rayet stars. A grid of models and its application to the Galactic WN sample
Adopting the ``standard model'' for Wolf-Rayet atmospheres, non-LTEradiation transfer calculations are performed which account for heliumand nitrogen. Grids of theoretical models are presented for the wholerelevant parameter range. The WN classification criteria are employed inorder to identify the subtype domains, and inconsistencies arediscussed. The (almost complete) sample of known Galactic WN stars isanalyzed by comparing the observed spectra with the synthetic spectra ofthe grid models. This is the first time that nitrogen line analyses areperformed for the whole WN sample, while previous comprehensive studieswere restricted to helium models. The obtained parameters roughlyconfirm the results from the previous helium analyses, as far as latesubtypes (WNL) and early subtypes with strong lines (WNE-s) areconcerned. For early subtypes with weak lines (WNE-w), however, theparameters are substantially revised. The hottest WN star, with astellar (effective) temperature of 140kK, is WR2, which could not beanalyzed previously from its helium lines due to the lack of He I. Theother members of the WNE-w subgroup have stellar temperatures between 40and 90kK, thus populating the same temperature range as the strong-linedWNE-w, but with less dense winds. The luminosities are revised accordingto the new parameters. Moreover, reddening corrections are newlydetermined form comparing IUE data with the UV model fluxes. The averageluminosity is now log L/Lsun = 5.5 for WNE stars (both,strong and weak lined), and log L/Lsun = 5.9 for WNL (notsignificantly revised). The empirical minimum WN luminosity is10(5.0}L_{sun) , reducing former incompatibilities with predictions fromevolutionary calculations. The ratio between mechanical and radiativemomentum flow is slightly affected by the revisions, but remains muchhigher than unity: 9, 9 and 29 for the WNL, WNE-w and WNE-s subclass,respectively. Partly based on observations collected at the EuropeanSouthern Observatory (ESO), La Silla, Chile, and on archival data fromthe International Ultraviolet Explorer (IUE)
| 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. II. Photometry
Abundant {HIPPARCOS photometry over 3 years of 141 O and Wolf-Rayetstars, including 8 massive X-ray binaries, provides a magnificentvariety of light curves at the sigma ~ 1-5% level. Among the mostinteresting results, we mention: optical outbursts in HD 102567 (MXRB),coinciding with periastron passages; drastic changes in the light curveshape of HD 153919 (MXRB); previously unknown long-term variability ofHD 39680 (O6V:[n]pe var) and WR 46 (WN3p); unusual flaring of HDE 308399(O9V); ellipsoidal variations of HD 64315, HD 115071 and HD 160641;rotationally modulated variations in HD 66811=zeta Pup (O4Inf) and HD210839=lambda Cep (O6I(n)fp); dust formation episode in WR 121 (WC9). Ina statistical sense, the incidence of variability is slightly higheramong the WR stars, which might be explained by the higher percentage ofknown binary systems. Among the presumably single WR stars, thecandidate runaways appear to be more variable then the rest. Based ondata from the ESA Hipparcos astrometry satellite
| 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
| 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
| A Survey of Nebulae around Galactic Wolf-Rayet Stars in the Southern Sky. III. Survey Completion and Conclusions
We present the conclusion of a narrow-band optical CCD survey ofWolf-Rayet stars in the southern portion of the Milky Way. In this partof the survey we complete our survey of the southern Galaxy and reportthe detection of 10 new optical nebulae associated with Wolf-Rayetstars. This brings the final survey total to 40 Wolf-Rayet stars withassociated nebulae in 114 southern Galactic fields for a 35% detectionrate. Our results suggest that the Galactic environment has littleapparent effect on the detection rate of nebulae associated withWolf-Rayet stars. Indeed, a more important role in the production ofnebulae is likely to be played by the evolution of the central star. Thesurvey results also suggest a slightly higher incidence of nebuladetection around WN stars over WC stars, although nebulae associatedwith WC stars are noted as being generally larger and some may have beenmissed through being larger than the CCD array used. Indeed, theincreased rate of nebula detection compared to that of a northernGalactic survey can be accounted for solely through the fact that alarger region of sky around the Wolf-Rayet stars was imaged in oursouthern survey as compared to the northern survey. Larger nebulaeexisting around WC as opposed to WN stars are also consistent with thecurrent theory of the evolution of Wolf-Rayet stars from WN to WC.
| Stationary hydrodynamic models of Wolf-Rayet stars with optically thick winds.
We investigate the influence of a grey, optically thick wind on thesurface and internal structure of Wolf-Rayet (WR) stars. We calculatehydrodynamic models of chemically homogeneous helium stars withstationary outflows, solving the full set of stellar structure equationsfrom the stellar center up to well beyond the sonic point of the wind,including the line force originating from absorption lines in aparameterized way. For specific assumptions about mass loss rate andwind opacity above our outer boundary, we find that the iron opacitypeak may lead to local super-Eddington luminosities at the sonic point.By varying the stellar wind parameters over the whole physicallyplausible range, we show that the radius of the sonic point of the windflow is always very close to the hydrostatic stellar radius obtained inWR star models which ignore the wind. However, our models confirm thepossibility of large values for observable WR radii and correspondinglysmall effective temperatures found in earlier models. We show furtherthat the energy which is contained in a typical WR wind can not beneglected. The stellar luminosity may be reduced by several 10%, whichhas a pronounced effect on the mass-luminosity relation, i. e., the WRmasses derived for a given luminosity may be considerably larger.Thereby, also the momentum problem of WR winds is considerably reduced,as well as the scatter in the ˙(M) vs. M diagram for observedhydrogen-free WN stars.
| A three-dimensional classification for WN stars
A three-dimensional classification for WN stars is presented using (1)the HeII 5411/HeI 5875 ratio as a primary indicator of ionization, (2)FWHM 4686 and EW 5411 as indicators of line width and strength, and (3)an oscillating Pickering decrement as an indicator of the presence ofhydrogen. All WN stars in the Galaxy and two-thirds of the LMC stars areclassified on the new system. Almost all spectra inspected fall smoothlyinto categories within which the spectra are very similar. Allionization subclasses show a tight correlation between line strength andwidth, with stars containing hydrogen at the weak, narrow end, and WN/Cstars near the strong, broad end. H^+/He^++ correlates with strength andwidth with a cut-off for the presence of hydrogen, which is slightlydependent on ionization subclass, at about FWHM 4686=30A and EW5411=25A. The correlations found indicate that high (initial) mass starsevolve as narrow-line stars from late to early ionization subclass.Lower (initial) mass stars evolve with increasing line strength andwidth, probably to earlier ionization subclass. The HeII 4686/NV,III4604-40 ratio shows a clear correlation with Galactocentric radius,presumably an effect of the Z gradient. CIV 5808/HeII 5411 shows no suchcorrelation. LMC WN stars can be classified without difficulty by thecriteria established for Galactic WN stars. While individual spectra ofa given subtype are similar in the two galaxies, the frequencydistributions over ionization subclass, over EW and FWHM in subclassesWN4 and WN5, and hydrogen content in subclasses WN6-8 are different. Theeffects are presumably due to metallicity, but the causal connection isunclear.
| Existence of a short period (3.5-4 hours) in the photometric variability of WR66.
We report here on an independent detection of a short period (~4hours)in the photometric variations of WR66, thus confirming in broad termsthe discovery by Antokhin et al.. In addition, we present the firstspectroscopic variability analysis for this star. A few peculiarities ofthe spectrum of WR66 are also discussed. Finally, we perform a briefexamination of different possible origins of the phenomenon.
| Spectral atlas of the Galactic Wolf-Rayet stars (WN sequence).
Spectra of 62 (i.e. almost all) Galactic single Wolf-Rayet stars of theWN sequence are compiled. These data provided the empirical basis forour comprehensive spectral analyses of these stars published recently.The observations cover wide parts of the visual range and have aspectral resolution λ/{DELTA} λ between 2000 and 3600 inmost cases. Infrared observations around 10830A are included for 18stars. The spectra are preliminary ``rectified'' by division through anestimated stellar continuum. The whole material is displayed in conciseplots sorted by spectral subtype in order to provide an overview. Accessto the full digital data is offered via anonymous file transfer.
| 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
| Chemical composition of Wolf-Rayet stars. II. Hydrogen-to-helium ratio.
The formation of HeII, HeI and HI lines in the winds of somerepresentative WN stars of different spectral subtypes has been modeled.Two different types of models were studied: the clumped winds and smoothwinds for both of which the standard velocity lawv=v_0_+(vinfinity_-v_0_) (1-R_*_/r)beta^ withβ=1 was assumed. The smooth winds model predicts about two timeslower IR fluxes than observed if one determines the matter density inthe winds through the observed values of radio fluxes. The increaseddensity smooth wind models with 1.5 times higher density as compared tothe radio-flux scaling are in reasonable agreement with IR fluxes andHeII and HeI line fluxes in the case of WN 5, WN 6 and WN 8 stars butfor other subtypes these models predict discrepant line fluxes. Theclumped wind models agree quite well with the most importantobservational data whereas somewhat lower mass loss rates are nowderived as compared to the smooth wind models. Theoretical line fluxeswere found by summing of the contributions from different layers of thewind. The statistical equilibria equations for level populations weresolved in the Sobolev approximation by taking into account the overlapof HeII and HI lines in the expanding medium. We used 40, 20 and 52level atomic models for HeII, HI and HeI respectively, whereas theinfluence of higher levels was taken into account through the correctionterms. On the basis of our modelling study we derived a simple formulafor the determination of hydrogen-to-helium ratios for WN stars whichwas used for concrete estimates for 28 stars. In all cases thehydrogen-to-helium ratios are lower than the mean cosmic value. Byinspection of the line fluxes of the neighboring HeII lines of (n-4),(n-6) and (n-8) series in the spectra of two WC stars we concluded thatno hydrogen seems to be present in their winds. The hydrogen-to-heliumratio is decreasing when going from late to early WN subtypes withstrong scatter existing among the stars of WN 6 and later subtypes.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | ケンタウルス座 |
| Right ascension: | 13h33m30.11s |
| Declination: | -62°19'01.2" |
| Apparent magnitude: | 10.422 |
| Proper motion RA: | -6.8 |
| Proper motion Dec: | -1.8 |
| B-T magnitude: | 10.884 |
| V-T magnitude: | 10.461 |
Catalogs and designations:
|
