תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
The Wolf-Rayet Stars HD 4004 and HD 50896: Two of a Kind
We present the results of the analysis of 151 spectra of the Wolf-Rayetstar HD 4004 (WR1) obtained in 1999 and in 2005. The line-profilevariability is found to be periodic, with P=7.684 days, and to havecharacteristics that are very similar to those of another variable WRstar, HD 50896 (WR6). The similarities point toward a common physicalphenomenon in both systems. Of the scenarios that can explain theobservations, such as colliding winds in two stars with similar windmomenta and the ejection of streams or jets from two opposite locationson the stellar surface, the latter seems more likely due to the lack ofobservational evidence for a strong wind-bearing companion.
| 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.
| Models of forbidden line emission profiles from axisymmetric stellar winds
A number of strong infrared forbidden lines have been observed inseveral evolved Wolf-Rayet (WR) star winds, and these are important forderiving metal abundances and testing stellar evolution models. Inaddition, because these optically thin lines form at large radius in thewind, their resolved profiles carry an imprint of the asymptoticstructure of the wind flow. This work presents model forbidden lineprofile shapes formed in axisymmetric winds. It is well known that anoptically thin emission line formed in a spherical wind expanding atconstant velocity yields a flat-topped emission profile shape. Simulatedforbidden lines are produced for a model stellar wind with anaxisymmetric density distribution that treats the latitudinal ionizationself-consistently and examines the influence of the ion stage on theprofile shape. The resulting line profiles are symmetric about linecentre. Within a given atomic species, profile shapes can vary betweencentrally peaked, doubly peaked, and approximately flat-topped inappearance depending on the ion stage (relative to the dominant ion) andviewing inclination. Although application to WR star winds isemphasized, the concepts are also relevant to other classes of hot starssuch as luminous blue variables and Be/B[e] stars.
| Cleaning Up η Carinae: Detection of Ammonia in the Homunculus Nebula
We report the first detection of ammonia in the Homunculus Nebula aroundη Carinae, which is also the first detection of emission from apolyatomic molecule in this or any other luminous blue variable (LBV)nebula. Observations of the NH3 (J,K)=(3,3) inversiontransition made with the Australia Telescope Compact Array revealemission at locations where infrared H2 emission had beendetected previously, near the strongest dust emission in the core of theHomunculus. We also detect ammonia emission from the so-called strontiumfilament in the equatorial disk. The presence of NH3 aroundη Car hints that molecular shells around some Wolf-Rayet stars couldhave originated in prior LBV eruptions, rather than in cool redsupergiant winds or the ambient interstellar medium. Combined with thelack of any CO detection, NH3 seems to suggest that theHomunculus is nitrogen-rich like the ionized ejecta around η Car. Italso indicates that the Homunculus is a unique laboratory in which tostudy unusual molecule and dust chemistry, as well as their rapidformation in a nitrogen-rich environment around a hot star. We encouragefuture observations of other transitions like NH 3 (1, 1) and(2, 2), related molecules like N2H+, and renewedattempts to detect CO.
| 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.
| An Extreme Case of a Misaligned Highly Flattened Wind in the Wolf-Rayet Binary CX Cephei
CX Cep (WR 151) is the WR+O binary (WN5+O5 V) with the second shortestperiod known in our Galaxy. To examine the circumstellar matterdistribution and to better constraint the orbital parameters andmass-loss rate of the W-R star, we obtained broadband and multiband(i.e., UBVRI) linear polarization observations of the system. Ouranalysis of the phase-locked polarimetric modulation confirms the highorbital inclination of the system (i.e., i=65deg). Using theorbital solution of Lewis et al. (1993), we obtain masses of 33.9 and23.9 Msolar for the O and W-R stars, respectively, whichagree with their spectral types. A simple polarimetric model accountingfor finite stellar size effects allowed us to derive a mass-loss ratefor the W-R star of (0.3-0.5)×10-5 Msolaryr-1. This result was remarkably independent of the model'sinput parameters and favors an earlier spectral type for the W-Rcomponent (i.e., WN4). Finally, using our multiband observations, wefitted and subtracted from our data the interstellar polarization. Theresulting constant intrinsic polarization of 3%-4% is misaligned inrelation to the orbital plane (i.e.,θCIP=26deg vs. Ω=75deg)and is the highest intrinsic polarization ever observed for a W-R star.This misalignment points toward a rotational (or magnetic) origin forthe asymmetry and contradicts the most recent evolutionary models formassive stars (Meynet & Maeder 2003) that predict sphericallysymmetric winds during the W-R phase (i.e., CIP=0%).
| 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.
| 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.
| CQ Cephei - The most mysterious of Wolf-Rayet type binary systems.
Not Available
| Cygnus X-3 and the problem of the missing Wolf-Rayet X-ray binaries
Cygnus X-3 is a strong X-ray source (LX ≈ 1038erg s-1) which is thought to consist of a compact objectaccreting matter from a helium star. We analytically find that theestimated ranges of mass-loss rate and orbital-period derivative for CygX-3 are consistent with two models: i) the system is detached and themass loss from the system comes from the stellar wind of a massivehelium star, of which only a fraction that allows for the observed X-rayluminosity is accreted, or ii) the system is semidetached and aRoche-lobe-overflowing low- or moderate-mass helium donor transfers massto the compact object, followed by ejection of its excess over theEddington rate from the system. These analytical results appear to beconsistent with evolutionary calculations. By means of populationsynthesis we find that currently in the Galaxy there may exist ~1 X-raybinary with a black hole that accretes from a ⪆7~M_ȯ Wolf-Rayetstar and ~1 X-ray binary in which a neutron star accretes matter from aRoche-lobe-overflowing helium star with mass ⪉1.5~M_ȯ. Cyg X-3is probably one of these systems.
| Spectroscopic study of the long-period dust-producing WC7pd+O9 binary HD192641
We present the results of an optical spectroscopic study of the massiveWolf-Rayet (WR) binary HD192641 = WR137. These 1986-2000 data cover thedust-formation maximum in 1997. Combining all available measurements ofradial velocities, we derive, for the first time, a spectroscopic orbitwith period 4766 +/- 66 d (13.05 +/- 0.18 yr). The resulting masses,adopting i= 67 °, are MO= 20 +/- 2Msolar forthe O component and MWR= 4.4 +/- 1.5Msolar for theWR component. These appear, respectively, approximately normal and onthe low side for the given spectral types. Analysis of the intensemultisite spectroscopic monitoring in 1999 shows that theCIIIλ5696 and CIVλλ5802/12 lines have the highestintrinsic variability levels. The periodogram analysis yields asmall-amplitude modulation in the absorption troughs of theCIVλλ5802/12 and HeIλ5876 lines with a period of0.83 d, which could be related either to pulsations or large-scalerotating structures as seen in the WN4 star EZ Canis Majoris (WR6).Wavelet analysis of the strong emission lines of CIIIλ5696 andCIVλλ5802/12 enabled us to isolate and follow for severalhours small structures (emission subpeaks) associated with densityenhancements within the wind of the Wolf-Rayet star. Cross-correlatingthe variability patterns seen in different lines, we find a weak butsignificant correlation between the variability in emission lines withdifferent ionization potentials, i.e. in lines formed at differentdistances from the WR stellar core. Adopting a β wind-velocity law,from the motion of individual subpeaks we find β~ 5, which issignificantly larger than the canonical value β~= 1 found in O starwinds.
| 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.
| An Atlas of Far-Ultraviolet Spectra of Wolf-Rayet Stars from the FUSE Satellite
We present an atlas of far-ultraviolet spectra of 21 Wolf-Rayet (WR)stars in the Galaxy and Large and Small Magellanic Clouds, secured withthe Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. The datacover the wavelength range of 912-1190 Å at a spectral resolutionof 0.1 Å and span examples of most subtypes in the WN and WCsequences. We discuss the FUV spectral morphology of the different WRsequences, emphasizing the wide range of ions and chemical speciesexhibiting well-developed P Cygni profiles and emission lines in thiswavelength range. For WN stars the relative strengths of C IV/C III, NIII/N II, P V/P IV, and Si IV/Si III show a decrease in strength of thehigh ions from WN3 to WN11 complemented by an increase in the lower ionsat later types. The ``super ions'' of O VI and S VI are consideredphotoionized wind features for WN3-WN6 stars, probably the result ofAuger ionization in WN7-WN9 stars, and probably absent at WN10-WN11. TheWN5h star Sk 41 in the SMC shows relatively weaker features, which canbe ascribed to the effects of a global galaxy metal deficiency. For theWC stars, a similar pattern of wind ionization-linked strengths in theemissions and P Cygni profiles is present, particularly evident in therelative strengths of lines in P V, S IV, Si IV, and Si III. O VI, and SVI features are only seen in the earliest WC subtypes. The high carbonabundance in WC stars is reflected by the presence of strong C IV and CIII lines throughout the sequence. We present new estimates of the windterminal velocities from measurements of saturated absorption componentsobserved in a wide range of I.P. species. Considerable revisions tov&infy; for the WN3 and WN5 (SMC) stars in our sample and,in particular for the WN10 and WN11 stars are found. The latter make useof the unique availability of the N II resonance line in the FUSEwaveband.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by The Johns HopkinsUniversity under NASA contract NAS5-32985.
| 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.
| Shocked gas layers surrounding the WR nebula NGC 2359
NGC 2359 is a Wolf-Rayet (W-R) nebula partially bound by a rather denseand warm molecular cloud. We present the results derived from CO and13CO fully sampled maps of the molecular material withangular resolutions up to 12arcsec . We have detected three differentvelocity components, and determined their spatial distribution andphysical properties. The kinematics, morphology, mass and density areclearly stratified with respect to the W-R star. These features allow usto learn about the recent evolutionary history of HD 56925, because themultiple layers could be associated to several energetic events whichhave acted upon the surrounding circumstellar medium. Hence, a carefulstudy of the different shockfronts contain clues in determining thepresent and past interaction of this evolved massive star with itssurroundings. From the analysis of the mass-loss history in massivestars like HD 56925, we suggest that the multiple layers of shockedmolecular gas are likely to be produced during the earlier LBV phaseand/or the actual W-R stage of HD 56925.
| The interstellar medium local to HD 10125
Based on an HI line and 408- and 1420-MHz radio continuum survey carriedout at the Dominion Radio Astrophysical Observatory (DRAO), theenvironment of the O star HD 10125 has been studied. In addition,complementary radio continuum images, as well as infrared data of thesame region have been analysed. An arc-like structure is found in allthe radio continuum data. From the 21-cm line data, an HI minimum isfound in the velocity range -27 to -32 km s-1. Although HD10125 is not at the centre of the HI cavity, its eccentric position isconsistent with the observed stellar proper motion. The HI cavity andthe continuum arc-like structure show an excellent morphologicalcorrelation. The radio continuum emission has a spectral index(Sν~να) α= 0.0 +/- 0.1, whichestablishes the thermal nature of the arc-like feature. The dusttemperature obtained from the infrared data is higher in the area wherethe continuum emission is present. A distance of 3 kpc is derived forthe star, the HI cavity and the radio continuum structure. We concludethat all the features we have found are physically related to eachother. The O star has enough energetic photons to both ionize thesurrounding gas and heat up the dust and, through its powerful wind,also sweep up the HI and HII gas.
| Automatic Detection of Expanding H I Shells Using Artificial Neural Networks
The identification of expanding H I shells is difficult because of theirvariable morphological characteristics. The detection of H I bubbles ona global scale has therefore never been attempted. In this paper, anautomatic detector for expanding H I shells is presented. The detectionis based on the more stable dynamical characteristics of expandingshells and is performed in two stages. The first one is the recognitionof the dynamical signature of an expanding bubble in the velocityspectra, based on the classification of an artificial neural network.The pixels associated with these recognized spectra are identified oneach velocity channel. The second stage consists of looking forconcentrations of those pixels that were first pointed out and decidingif they are potential detections by morphological and 21 cm emissionvariation considerations. Two test bubbles are correctly detected, and apotentially new case of a shell that is visually very convincing isdiscovered. About 0.6% of the surveyed pixels are identified as part ofa bubble. These may be false detections but still constitute regions ofspace with high probability of finding an expanding shell. Thesubsequent search field is thus significantly reduced. In the nearfuture, we intend to conduct a large-scale H I shell detection over thePerseus arm using our detector.
| Dust Formation Events in Colliding Winds: An Application to Eta Car
Recent IR observations indicate that many massive binary systems presentdust formation episodes in regions close to the stars during theperiastron passage. These systems are known to be high-energy sources,and it is believed that wind collisions are the origin of the emission.In this work we show that wind collisions not only increase the X-rayemission but also allow dust formation. As an application we study etaCar, which presents, near periastron, an increase in the X-ray emissionfollowed by a sudden decrease that lasts for about a month. We reproducethis feature calculating the optical depth due to dust formation alongthe orbital period.
| Wolf-Rayet binaries in the Magellanic Clouds and implications for massive-star evolution - I. Small Magellanic Cloud
We have carried out an intensive spectroscopic campaign to search forbinaries via periodic radial velocity (RV) variations among all thenitrogen-rich WN Wolf-Rayet (WR) stars in the Small Magellanic Cloud(SMC), and all WNE stars in the Large Magellanic Cloud (LMC). We presentin this first paper the results for the SMC. Along with the results ofBartzakos et al. on the only carbon/oxygen-rich WR star (AB8, WO4+O4),the whole WR population of the SMC (11 stars) has now been investigatedintensively for periodic RV variability. We have also retrievedtime-dependent photometric data in the public domain from the OGLE andMACHO projects, and X-ray data from the ROSAT and Chandra archives, toprovide additional constraints on the binary character. Contrary totheoretical expectations that predict a virtually 100 per cent binaryfrequency in the SMC, we find a normal (~40 per cent) WR binaryfrequency in this galaxy. We also find the clear presence of hydrogen inthe winds of the single WR stars in the SMC, even for the stars with anearly spectral subtype. We discuss the possible reasons and implicationsof this for stellar evolution of massive stars in such a low-metallicityenvironment, e.g. the influence of rotation versus the necessity of avery high initial mass of the progenitors for single stars, and thepossible past occurrence of Roche lobe overflow for binaries.
| Optical line emission from the supernova remnant G 73.9+0.9
Flux calibrated images of the field around the known supernova remnant G73.9+0.9 in the Hiα+[N Ii], [S Ii], [O Ii], and [O Iii] emissionlines are presented. The low ionization images are characterized bydiffuse emission both within and outside the extent of the remnant. Theflux calibrated images revealed a few small scale structures in the eastareas of G 73.9+0.9. The long-slit spectra identify the emission fromone of them as emission from shock heated gas. This patchy structure is 3 arcmin long and emits Hα flux at a level of 33× 10-17 erg s-1 cm-2arcsec-2. The bright diffuse arc-like structure in the centerof the field seems to be associated to G 73.9+0.9 given its spectralsignature and positional relation with the non-thermal radio emission. A8 arcmin long filamentary structure with an absolute Hα fluxof 9 × 10-17 erg s-1 cm-2arcsec-2 is detected in the [O Iii] emission line to thesouth of G 73.9+0.9 but is probably unrelated. The deep long-slitspectra suggest complete recombination zones, shock velocities below 90km s-1, low electron densities (<50 cm-3) andnon-negligible magnetic field strengths.
| 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.
| Shocked CO and 13CO around Wolf-Rayet ring nebulae
We show CO and 13CO maps toward the WR nebulae NGC 2359, NGC6888 and Anon (WR 134). We determine global parameters and discuss theprobable origin of this gas. Nowadays it is becoming clear thatmolecule formation and survival is be possible around massive evolvedstars.
| 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.
| Ring nebulae around massive stars throughout the Hertzsprung-Russell diagram
Massive stars evolve across the H-R diagram, losing mass along the wayand forming a variety of ring nebulae. During the main sequence stage,the fast stellar wind sweeps up the ambient interstellar medium to forman interstellar bubble. After a massive star evolves into a red giantor a luminous blue variable, it loses mass copiously to form acircumstellar nebula. As it evolves further into a WR star, the fast WRwind sweeps up the previous mass loss and forms a circumstellar bubble.Observations of ring nebulae around massive stars not only arefascinating, but also are useful in providing templates to diagnose theprogenitors of supernovae from their circumstellar nebulae. In thisreview, I will summarize the characteristics of ring nebulae aroundmassive stars throughout the H-R diagram, show recent advances in X-rayobservations of bubble interiors, and compare supernovae's circumstellarnebulae with known types of ring nebulae around massive 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.
| Neutral Hydrogen around the Oxygen-Sequence Wolf-Rayet Star WR 102 and the Nebula G2.4 + 1.4
Not Available
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | ברבור |
| התרוממות ימנית: | 20h10m14.19s |
| סירוב: | +36°10'35.1" |
| גודל גלוי: | 8.004 |
| מרחק: | 10000000 פארסק |
| תנועה נכונה: | -4.2 |
| תנועה נכונה: | -9 |
| B-T magnitude: | 8.26 |
| V-T magnitude: | 8.026 |
קטלוגים וכינוים:
|
INHABITED SKY
