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Spectral atlas of massive stars around He I 10 830 Å
We present a digital atlas of peculiar, high-luminosity massive stars inthe near-infrared region (10 470-11 000 Å) at medium resolution(R≃7000). The spectra are centered around He I 10 830 Å,which is formed in the wind of those stars, and is a crucial line toobtain their physical parameters. The instrumental configuration alsosampled a rich variety of emission lines of Fe II, Mg II, C I, N I, andPa γ. Secure identifications for most spectral lines are given,based on synthetic atmosphere models calculated by our group. We alsopropose that two unidentified absorption features have interstellarand/or circumstellar origin. For the strongest one (10 780 Å) anempirical calibration between E(B-V) and equivalent width is provided.The atlas displays the spectra of massive stars organized in fourcategories, namely Be stars, OBA Iape (or luminous blue variables, LBVcandidates and ex/dormant LBVs), OB supergiants and Wolf-Rayet stars.For comparison, the photospheric spectra of non emission-line stars arepresented. Selected LBVs were observed in different epochs from 2001 to2004, and their spectral variability reveals that some stars, such asη Car, AG Car and HR Car, suffered dramatic spectroscopic changesduring this time interval.Based on observations made at Observatório do Pico dos Dias/LNA(Brazil). Figures 5 to 18 are only available in electronic form athttp://www.aanda.org Electronic version of the spectra (fichiers FITS)is only available 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/qcat?J/A+A/465/993
| Searching for hidden Wolf-Rayet stars in the Galactic plane - 15 new Wolf-Rayet stars
We report the discovery of 15 previously unknown Wolf-Rayet (WR) starsfound as part of an infrared (IR) broad-band study of candidate WR starsin the Galaxy. We have derived an empirically based selection algorithmwhich has selected ~5000 WR candidate stars located within the Galacticplane drawn from the Galactic Legacy Infrared Mid-Plane SurveyExtraordinaire (mid-IR) and Two-Micron All-Sky Survey (near-IR)catalogues. Spectroscopic follow-up of 184 of these reveals 11nitrogen-rich (WN) and four carbon-rich (WC) WR stars. Early WC subtypesare absent from our sample and none shows evidence for circumstellardust emission. Of the candidates which are not WR stars, ~120 displayedhydrogen emission-line features in their spectra. Spectral featuressuggest that the majority of these are in fact Bsupergiants/hypergiants, ~40 of these are identified Be/B[e] candidates.Here, we present the optical spectra for six of the newly detected WRstars, and the near-IR spectra for the remaining nine of our sample.With a WR yield rate of ~7 per cent and a massive star detection rate of~65 per cent, initial results suggest that this method is one of themost successful means for locating evolved, massive stars in the Galaxy.
| The Abundance of Interstellar Fluorine and Its Implications
We report results from a survey of neutral fluorine (F I) in theinterstellar medium. Data from FUSE were used to analyze 26 lines ofsight lying in both the galactic disk and halo, including lines toWolf-Rayet stars and through known supernova remnants. The equivalentwidths of the fluorine resonance lines at 951.871 and 954.827 Åwere measured or assigned upper limits and combined with a nitrogencurve of growth to obtain F I column densities. These column densitieswere then used to calculate fluorine depletions. Comparisons are made tothe previous study of F I by Federman and coworkers and implications forF I formation and depletion are discussed.
| A census of the Wolf-Rayet content in Westerlund 1 from near-infrared imaging and spectroscopy
New Technology Telescope (NTT)/Son of Isaac (SOFI) imaging andspectroscopy of the Wolf-Rayet population in the massive clusterWesterlund 1 are presented. Narrow-band near-infrared (IR) imagingtogether with follow up spectroscopy reveals four new Wolf-Rayet stars,of which three were independently identified recently by Groh et al.,bringing the confirmed Wolf-Rayet content to 24 (23 excluding source S)- representing 8 per cent of the known Galactic Wolf-Rayet population -comprising eight WC stars and 16 (15) WN stars. Revised coordinates andnear-IR photometry are presented, whilst a quantitative near-IR spectralclassification scheme for Wolf-Rayet stars is presented and applied tomembers of Westerlund 1. Late subtypes are dominant, with no subtypesearlier than WN5 or WC8 for the nitrogen and carbon sequences,respectively. A qualitative inspection of the WN stars suggests thatmost (~75 per cent) are highly H deficient. The Wolf-Rayet binaryfraction is high (>=62 per cent), on the basis of dust emission fromWC stars, in addition to a significant WN binary fraction from hardX-ray detections according to Clark et al. We exploit the large WNpopulation of Westerlund 1 to reassess its distance (~5.0kpc) andextinction (AKS ~ 0.96mag), such that it islocated at the edge of the Galactic bar, with an oxygen metallicity ~60per cent higher than Orion. The observed ratio of WR stars to red andyellow hypergiants, N(WR)/N(RSG + YHG) ~3, favours an age of~4.5-5.0Myr, with individual Wolf-Rayet stars descended from progenitorsof initial mass ~40-55Msolar. Qualitative estimates ofcurrent masses for non-dusty, H-free WR stars are presented, revealing10-18Msolar, such that ~75 per cent of the initial stellarmass has been removed via stellar winds or close binary evolution. Wepresent a revision to the cluster turn-off mass for other Milky Wayclusters in which Wolf-Rayet stars are known, based upon the latesttemperature calibration for OB stars. Finally, comparisons between theobserved WR population and subtype distribution in Westerlund 1 andinstantaneous burst evolutionary synthesis models are presented.Based on observations made with ESO telescopes at the La SillaObservatory under programme IDs 073.D-0321 and 075.D-0469.E-mail: Paul.crowther@sheffield.ac.uk
| 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.
| Radio observations of Wolf-Rayet ring nebulae
The main physical characteristics of the optical ring nebulae around WRstars based on radio continuum, HI1 cm line and molecular observationsare summarized. The energetics of these structures is analyzed takinginto account predictions from evolutionary models of interstellarbubbles. The main open questions are also discussed.
| Stratification of optical emission from NGC 6888 as a trace of the interaction between Wolf-Rayet stellar wind and the shell of a red supergiant
We suggest a model that explains the stratification peculiarities of the[O III] and Hα line emission from some of the ring nebulae aroundWolf-Rayet stars. These peculiarities lie in the fact that the [O III]line emission regions are farther from the central star than theHα regions, with the distance between them reaching several tenthsof a parsec. We show that the radiative shock produced by a Wolf-Rayetstellar wind and propagating with a velocity of 100 km s-1 cannotexplain such large distances between these regions due to the lowvelocity of the gas outflow from the shock front. The suggested modeltakes into account the fact that the shock produced by a Wolf-Rayetstellar wind propagates in a two-phase medium: a rarefied medium anddense compact clouds. The gas downstream of a fast shock traveling in ararefied gas compresses the clouds. Slow radiative shocks are generatedin the clouds; these shocks heat the latter to temperatures at whichions of doubly ionized oxygen are formed. The clouds cool down,radiating in the lines of this ion, to temperatures at which Balmer lineemission begins. The distance between the [O III] and Hα lineemission regions is determined by the cooling time of the cloudsdownstream of the slow shock and by the velocity of the fast shock.Using the ring nebula NGC 6888 as an example, we show that the gasdownstream of the fast shock must be at the phase of adiabatic expansionrather than deceleration with radiative cooling, as assumed previously.
| The Origin of Structures in Wolf-Rayet Winds: FUSE Observations of WR 135
We report the detection with FUSE of strong, highly blueshiftedabsorption features appearing in the absorption troughs of practicallyall major P Cygni profiles in the presumably single Wolf-Rayet star WR135. These features also appear in the shock-sensitive O VIλλ1032, 1038 doublet, coincident both in time and invelocity space with the rest of the lower ionization species. Choosingbetween two alternative interpretations (large-scale, coherentstructures vs. localized, random shocks), we favor the latter. Theabsolute value of the velocity as well as the velocity dispersion in theshocked region, the density of the shocked gas, and the timescales ofthe observed variability allow us to relate the observed shocks to theincidence of numerous overdense clumps (blobs) in the wind of a hot,massive star.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
| Massive Stars and the Energy Balance of the Interstellar Medium. II. The 35 Msolar Star and a Solution to the ``Missing Wind Problem''
We continue our numerical analysis of the morphological and energeticinfluence of massive stars on their ambient interstellar medium for a 35Msolar star that evolves from the main-sequence through redsupergiant and Wolf-Rayet phases, until it ultimately explodes as asupernova. We find that structure formation in the circumstellar gasduring the early main-sequence evolution occurs as in the 60Msolar case but is much less pronounced because of the lowermechanical wind luminosity of the star. On the other hand, since theshell-like structure of the H II region is largely preserved, effectsthat rely on this symmetry become more important. At the end of thestellar lifetime 1% of the energy released as Lyman continuum radiationand stellar wind has been transferred to the circumstellar gas. Fromthis fraction 10% is kinetic energy of bulk motion, 36% is thermalenergy, and the remaining 54% is ionization energy of hydrogen. Thesweeping up of the slow red supergiant wind by the fast Wolf-Rayet windproduces remarkable morphological structures and emission signatures,which are compared with existing observations of the Wolf-Rayet bubbleS308, whose central star has probably evolved in a manner very similarto our model star. Our model reproduces the correct order of magnitudeof observed X-ray luminosity, the temperature of the emitting plasma,and the limb brightening of the intensity profile. This is remarkable,because current analytical and numerical models of Wolf-Rayet bubblesfail to consistently explain these features. A key result is that almostthe entire X-ray emission in this stage comes from the shell of redsupergiant wind swept up by the shocked Wolf-Rayet wind rather than fromthe shocked Wolf-Rayet wind itself as hitherto assumed and modeled. Thisoffers a possible solution to what is called the ``missing windproblem'' of Wolf-Rayet bubbles.
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| SS 433: a phenomenon imitating a Wolf-Rayet star
We present mid-infrared (2-12 μm) spectra of the microquasar SS 433obtained with the Infrared Space Observatory (spectroscopic mode ofISOPHOT and ISOCAM). We compare them to the spectra of four Wolf-Rayetstars: WR 78, WR 134, WR 136, and WR 147 in the same wavelength range.The mid-infrared spectrum of SS 433 mainly shows ion{H}{i} andion{He}{i} emission lines and is very similar to the spectrum of WR 147,a WN8(h)+B0.5V binary. The 2-12 μm continuum emission of SS 433corresponds to optically thin and partially optically thick free-freeemission, from which we calculate a mass loss rate of 2{-}3×10-4 M_ȯ yr-1 if the wind is homogeneousand a third of these values if it is clumped. This is consistent with astrong stellar wind from a WN star. However, following recent studiesconcluding that the mass donor star of SS 433 is not a Wolf-Rayet star,we propose that this strong wind out flows from a geometrically thickenvelope of material that surrounds the compact object like a stellaratmosphere, imitating the Wolf-Rayet phenomenon. This wind could alsowrap the mass donor star, and at larger distances ( 40 AU), it mightform a dust envelope from which the thermal emission, detected withISOPHOT at 25 μm and 60 μm, would originate. This wind alsoprobably feeds the material that is ejected in the orbital plane of thebinary system and that forms the equatorial outflow detected in radio atdistances >100 AU.
| X-Ray Emission from Wind-blown Bubbles. III. ASCA SIS Observations of NGC 6888
We present ASCA SIS observations of the wind-blown bubble NGC 6888.Owing to the higher sensitivity of the SIS for higher energy photonscompared to the ROSAT PSPC, we are able to detect aT~8×106 K plasma component in addition to theT~1.3×106 K component previously detected in PSPCobservations. No significant temperature variations are detected withinNGC 6888. García-Segura & Mac Low's analytical models of WRbubbles constrained by the observed size, expansion velocity, and massof the nebular shell underpredict the stellar wind luminosity and cannotreproduce simultaneously the observed X-ray luminosity, spectrum,surface brightness profile, and SIS count rate of NGC 6888's bubbleinterior. The agreement between observations and expectations frommodels may be improved if one or more of the following ad hocassumptions are made: (1) the stellar wind luminosity was weaker in thepast, (2) the bubble is at a special evolutionary stage and the nebularshell has recently been decelerated to 1/2 of its previous expansionvelocity, and (3) the heat conduction between the hot interior and thecool nebular shell is suppressed. Chandra and XMM-Newton observationswith high spatial resolution and high sensitivity are needed toaccurately determine the physical conditions of NGC 6888's interior hotgas for critical comparisons with bubble models.
| Evolution of X-ray emission from young massive star clusters
The evolution of X-ray emission from young massive star clusters ismodelled, taking into account the emission from the stars as well asfrom the cluster wind. It is shown that the level and character of thesoft (0.2-10 keV) X-ray emission change drastically with cluster age andare tightly linked with stellar evolution. Using the modern X-rayobservations of massive stars, we show that the correlation betweenbolometric and X-ray luminosity known for single O stars also holds forO+O and (Wolf-Rayet) WR+O binaries. The diffuse emission originates fromthe cluster wind heated by the kinetic energy of stellar winds andsupernova explosions. To model the evolution of the cluster wind, themass and energy yields from a population synthesis are used as input toa hydrodynamic model. It is shown that in a very young cluster theemission from the cluster wind is low. When the cluster evolves, WRstars are formed. Their strong stellar winds power an increasing X-rayemission of the cluster wind. Subsequent supernova explosions pump thelevel of diffuse emission even higher. Clusters at this evolutionarystage may have no X-ray-bright stellar point sources, but a relativelyhigh level of diffuse emission. A supernova remnant may become adominant X-ray source, but only for a short time interval of a fewthousand years. We retrieve and analyse Chandra and XMM-Newtonobservations of six massive star clusters located in the LargeMagellanic Cloud (LMC). Our model reproduces the observed diffuse andpoint-source emission from these LMC clusters, as well as from theGalactic clusters Arches, Quintuplet and NGC 3603.
| A new Wolf-Rayet star and its ring nebula: PCG11
In a search for new Galactic planetary nebulae from our systematic scansof the Anglo-Australian Observatory/United Kingdom Schmidt Telescope(AAO/UKST) Hα Survey of the Southern Galactic Plane, we haveidentified a Population I Wolf-Rayet star of type WN7h associated withan unusual ring nebula that has a fractured rim. We present imagery inHα, the 843-MHz continuum from the Molonglo Observatory SynthesisTelescope (MOST), the mid-infrared from the Midcourse Space Experiment(MSX), and confirmatory optical spectroscopy of the character of thenebula and of its central star. The inner edge of the Hα shellshows gravitational instabilities with a well-defined wavelength aroundits complete circumference.
| Sous le vent des étoiles massives
Not Available
| The Neon Abundance of Galactic Wolf-Rayet Stars
The fast, dense winds that characterize Wolf-Rayet (W-R) stars obscuretheir underlying cores and complicate the verification of evolving coreand nucleosynthesis models. Core evolution can be probed by measuringabundances of wind-borne nuclear-processed elements, partiallyovercoming this limitation. Using ground-based mid-infrared spectroscopyand the 12.81 μm [Ne II] emission line measured in four Galactic W-Rstars, we estimate neon abundances and compare them to long-standingpredictions from evolved-core models. For the WC star WR 121, thisabundance is found to be >~11 times the cosmic value, in goodagreement with predictions. For the three less-evolved WN stars, littleneon enhancement above cosmic values is measured, as expected. Wediscuss the impact of clumping in W-R winds on this measurement and thepromise of using metal abundance ratios to eliminate sensitivity to winddensity and ionization structure.
| Inferring hot-star-wind acceleration from Line Profile Variability
The migration of profile sub-peaks identified in time-monitored opticalemission lines of Wolf-Rayet (WR) star spectra provides a directdiagnostic of the dynamics of their stellar winds via a measured ΔvLOS/Δ t, a line-of-sight velocity change per unittime. Inferring the associated wind acceleration scale from such anapparent acceleration then relies on the adopted intrinsic velocity ofthe wind material at the origin of this variable pattern. Such acharacterization of the Line Emission Region (LER) is in principlesubject to inaccuracies arising from line optical depth effects andturbulence broadening. In this paper, we develop tools to quantify sucheffects and then apply these to reanalyze the LER properties oftime-monitored WR stars. We find that most program lines can be fittedwell with a pure optically thin formation mechanism, that the observedline-broadening is dominated by the finite velocity extent of the LER,and that the level of turbulence inferred through Line ProfileVariability (lpv) has only a minor broadening effect in the overallprofile. Our new estimates of LER velocity centroids are systematicallyshifted outwards closer to terminal velocity compared to previousdeterminations, now suggesting WR-wind acceleration length scales βR* of the order of 10-20 Rȯ, a factor of afew smaller than previously inferred. Based on radiation-hydrodynamicssimulations of the line-driven-instability mechanism, we computesynthetic lpv for Ciii5696 Å for WR 111. The results match wellthe measured observed migration of 20-30 m s-2, equivalent toβ R* 20 Rȯ. However, our modelstellar radius of 19 Rȯ, typical of an O-typesupergiant, is a factor 2-10 larger than generally expected for WR coreradii. Such small radii leave inferred acceleration scales to be moreextended than expected from dynamical models of line driving, whichtypically match a “beta” velocity lawv(r)=v&infy; (1-R*/r)β, withβ ≈ 1-2; but the severity of the discrepancy is substantiallyreduced compared to previous analyses. We conclude with a discussion ofhow using lines formed deeper in the wind would provide a strongerconstraint on the key wind dynamics in the peak acceleration region,while also potentially providing a diagnostic on the radial variation ofwind clumping, an issue that remains crucial for reliable determinationof O-star mass loss rates.
| 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.
| Observed Features of a Two-Phase Stellar Wind from WR 136 in the Vicinity of NGC 6888
A number of features are detected outside the nebula NGC 6888, within1.2° (30 pc) of the star WR 136, which can be explained in atwo-phase stellar-wind model. These include regions with finefilamentary gas structure that do not contain sources of stellar wind,extended radial “streams,” ultra-compact HII regions withhigh-velocity gas motions, and high-velocity gas motions outside theenvelope of NGC 6888. The two-phase wind consists of a rarefiedcomponent and dense compact condensations, or “bullets.” Thebullets generate cylindrical shocks in the interstellar gas, resultingin the presence of high-velocity gas up 20 30 pc from the star, outsidethe cavity formed by the rarified component of the wind.
| Cosmic Rays Acceleration in Wolf-Rayet Stellar Winds
Popescu et al (2004) gave a model for the observed cosmic rays between5×1015 and 3×1018 eV. Their source ispresumed to be the supernova of stars that explode in their winds. Theobserved cosmic rays abundance at the source are affected by spallationin the supernova shell, by the difference in ionization degree (beingone or two times ionized) at the injection in the supernova shock, thestars with initial masses 15MSun≤M≤30MSunhaving a different contribution to them than the stars with30MSun≤M≤50MSun, this being 2:1 for theelements with Z≥6. Still, the abundances after these corrections aredifferent by a factor Zi/ZHe, where Ziis the atomic number for the element i. This paper is dedicated to theexplanation of this factor and its physical meanings by consideringthat, prior to the shock injection, the wind particles are radiativeaccelerated.
| Constraints from Infrared Space Observatory Data on the Velocity Law and Clumpiness of WR 136
Observations with the Infrared Space Observatory (ISO) SWS spectrometerare used to constrain the velocity law and wind clumping of thewell-studied Wolf-Rayet (W-R) star WR 136 (HD 192163, WN6). Because thefree-free continuum opacity in W-R winds increases steadily withwavelength in the IR, each point in the continuous spectrum may beregarded as forming in a pseudophotosphere of larger radius for longerwavelength. Using this idea in combination with an analysis of theDoppler-broadened widths of several He II recombination lines, we canderive information about the velocity law and clumpiness of the stellarwind of WR 136. The observed line emission emerges from the regionexterior to the radius of optical depth unity in the free-free opacity,corresponding to v>~0.3v∞ for ourshortest-wavelength line. The ISO observations provide the continuumshape, flux level, and seven fairly strong He II emission profiles.Adopting a β-law distribution for the outflow velocity law, wecompute the continuous energy distribution and line profiles. We findthat there is a broad range of β-values consistent with thecontinuum data if we also allow the wind temperature to be a freeparameter. Interestingly, the continuum data are found to constrain thewind to have fairly low clumping values for the IR-forming region. Byusing the continuum results in conjunction with line profile modeling,the observational constraints are best satisfied with a clumping factorof Dc=<ρ2>/<ρ>2 of1-3 and a β-value of 2-3, although higher β-values are notstrongly ruled out for a modest wind temperature. The wavelength rangeof our ISO data allows us to probe only the outer wind accelerationzone, but in combination with radio observations, our finding that thewind clumping is fairly small suggests that the clumping in the wind ofWR 136 decreases with increasing radius.Based on observations with ISO, an ESA project with instruments fundedby ESA member states (especially the PI countries: France, Germany, theNetherlands, and the United Kingdom) and with the participation of ISASand NASA.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe 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/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| Stellar evolution with rotation. X. Wolf-Rayet star populations at solar metallicity
We examine the properties of Wolf-Rayet (WR) stars predicted by modelsof rotating stars taking account of the new mass loss rates for O-typestars and WR stars (Vink et al. \cite{Vink00}, \cite{Vink01}; Nugis& Lamers \cite{NuLa00}) and of the wind anisotropies induced byrotation. We find that the rotation velocities v of WR stars are modest,i.e. about 50 km s-1, not very dependent on the initial v andmasses. For the most massive stars, the evolution of v is very stronglyinfluenced by the values of the mass loss rates; below ~ 12 M_sun theevolution of rotation during the MS phase and later phases is dominatedby the internal coupling. Massive stars with extreme rotation may skipthe LBV phase.Models having a typical v for the O-type stars have WR lifetimes on theaverage two times longer than for non-rotating models. The increase ofthe WR lifetimes is mainly due to that of the H-rich eWNL phase.Rotation allows a transition WN/WC phase to be present for initialmasses lower than 60 M_sun. The durations of the other WR subphases areless affected by rotation. The mass threshold for forming WR stars islowered from 37 to 22 M_sun for typical rotation. The comparisons of thepredicted number ratios WR/O, WN/WC and of the number of transitionWN/WC stars show very good agreement with models with rotation, whilethis is not the case for models with the present-day mass loss rates andno rotation. As to the chemical abundances in WR stars, rotation bringsonly very small changes for WN stars, since they have equilibrium CNOvalues. However, WC stars with rotation have on average lower C/He andO/He ratios. The luminosity distribution of WC stars is also influencedby rotation.
| A near-infrared survey for Galactic Wolf-Rayet stars
Initial results, techniques, and rationale for a near-infrared survey ofevolved emission-line stars towards the Galactic Center are presented.We use images taken through narrow-band emission-line and continuumfilters to select candidates for spectroscopic follow-up. The filtersare optimized for the detection of Wolf-Rayet stars and other objectsthat exhibit emission-lines in the 2 mu m region. Approximately threesquare degrees along the Galactic plane have been analyzed in sevennarrow filters (four emission lines and three continuum). Four newWolf-Rayet stars have been found and are the subject of a followingpaper.
| 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.
| A 2.4-12 mu m spectrophotometric study with ISO of Cygnus X-3 in quiescence
We present mid-infrared spectrophotometric results obtained with the ISOon the peculiar X-ray binary Cygnus X-3 in quiescence, at orbital phases0.83 to 1.04. The 2.4-12 mu m continuum radiation observed withISOPHOT-S can be explained by thermal free-free emission in an expandingwind with, above 6.5 mu m, a possible additional black-body componentwith temperature T ~ 250 K and radius R ~ 5000 Rsun at 10kpc, likely due to thermal emission by circumstellar dust. The observedbrightness and continuum spectrum closely match that of the Wolf-Rayetstar WR 147, a WN8+B0.5 binary system, when rescaled at the same 10 kpcdistance as Cygnus X-3. A rough mass loss estimate assuming a WN windgives ~ 1.2 x 10-4 Msun yr-1. A line at~ 4.3 mu m with a more than 4.3 sigma ma detection level, and with adereddened flux of 126 mJy, is interpreted as the expected He I 3p-3sline at 4.295 μm, a prominent line in the WR 147 spectrum. Theseresults are consistent with a Wolf-Rayet-like companion to the compactobject in Cyg X-3 of WN8 type, a later type than suggested by earlierworks. Based on observations with ISO, an ESA project with instrumentsfunded by ESA Member States (especially the PI countries: France,Germany, The Netherlands and the UK) and with the participation of ISASand NASA.
| 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.
| An explanation for the curious mass loss history of massive stars: From OB stars, through Luminous Blue Variables to Wolf-Rayet stars
The stellar winds of massive stars show large changes in mass-loss ratesand terminal velocities during their evolution from O-star through theLuminous Blue Variable phase to the Wolf-Rayet phase. The luminosityremains approximately unchanged during these phases. These large changesin wind properties are explained in the context of the radiation drivenwind theory, of which we consider four different models. They are due tothe evolutionary changes in radius, gravity and surface composition andto the change from optically thin (in continuum) line driven winds tooptically thick radiation driven winds.
| Neutral Hydrogen around the Oxygen-Sequence Wolf-Rayet Star WR 102 and the Nebula G2.4 + 1.4
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| A Far Ultraviolet Spectroscopic Explorer Survey of Interstellar Molecular Hydrogen in Translucent Clouds
We report the first ensemble results from the Far UltravioletSpectroscopic Explorer survey of molecular hydrogen in lines of sightwith AV>~1 mag. We have developed techniques for fittingcomputed profiles to the low-J lines of H2, and thusdetermining column densities for J=0 and J=1, which contain >~99% ofthe total H2. From these column densities and ancillary datawe have derived the total H2 column densities, hydrogenmolecular fractions, and kinetic temperatures for 23 lines of sight.This is the first significant sample of molecular hydrogen columndensities of ~1021 cm-2, measured through UVabsorption bands. We have also compiled a set of extinction data forthese lines of sight, which sample a wide range of environments. We havesearched for correlations of our H2-related quantities withpreviously published column densities of other molecules and extinctionparameters. We find strong correlations between H2 andmolecules such as CH, CN, and CO, in general agreement with predictionsof chemical models. We also find the expected correlations betweenhydrogen molecular fraction and various density indicators such askinetic temperature, CN abundance, the steepness of the far-UVextinction rise, and the width of the 2175 Å bump. Despite therelatively large molecular fractions, we do not see the values greaterthan 0.8 expected in translucent clouds. With the exception of a fewlines of sight, we see little evidence for the presence of individualtranslucent clouds in our sample. We conclude that most of the lines ofsight are actually composed of two or more diffuse clouds similar tothose found toward targets like ζ Oph. We suggest a modification interminology to distinguish between a ``translucent line of sight'' and a``translucent cloud.''
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Membre dels grups següents:
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Dades d'Observació i Astrometria
| Constel·lació: | Cygnus |
| Ascensió Recta: | 20h12m06.54s |
| Declinació: | +38°21'17.8" |
| Magnitud Aparent: | 7.452 |
| Distancia: | 1639.344 parsecs |
| Moviment propi RA: | -7.8 |
| Moviment propi Dec: | -6.7 |
| B-T magnitude: | 7.657 |
| V-T magnitude: | 7.469 |
Catàlegs i designacions:
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INHABITED SKY
