Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
A Systematic Search for Corotating Interaction Regions in Apparently Single Galactic Wolf-Rayet Stars. I. Characterizing the Variability
We present the results of a systematic search for large-scalespectroscopic variability in apparently single Wolf-Rayet (WR) starsbrighter than v ~ 12.5. In this first paper we characterize the variousforms of variability detected and distinguish several separate groups.For each star in our sample, we obtained 4-5 high-resolution spectrawith signal-to-noise ratio ~100. Our ultimate goal is to identify newcandidates presenting variability that potentially comes from corotatinginteraction regions (CIRs). Out of a sample of 25 stars, 10 were foundto display large-scale changes of which four are of CIR-type (WR 1,WR 115, WR 120, and WR 134). The star WR 134 wasalready known to show such changes from previous studies. Three WN8stars present a different type of large-scale variability and we believedeserve a group of their own. Also, all three WC9d stars in our samplepresent large-scale variability, but it remains to be checked if theseare binaries, as many dust-making WR stars are double. Finally, of theremaining stars, 10 were found to show small-amplitude spectral changes,which we attribute to normal line-profile variability due toinhomogeneities in the wind, and five were found to show no spectralvariability, as far as can be concluded from the data in hand. Follow-upstudies are required to identify potential periods for our candidatesshowing CIR-type changes and eventually estimate a rotation rate forthese WR stars.
| Eclipsing Binaries as Calibrators of the Extragalactic Distance Scale and Probes of the Most Massive Stars
Masses, radii and luminosities of distant stars can only be measuredaccurately in eclipsing binaries. These systems further provide anindependent method for calibrating the extragalactic distance scale andthus determining the Hubble constant. They have been used as distanceindicators to the Magellanic Clouds, the Andromeda Galaxy and mostrecently to the Triangulum Galaxy by the DIRECT Project, pushing thelimit of our current observational capabilities. Despite their greatpotential for furthering our understanding of massive stars, the mostmassive stars in eclipsing binaries remain unexplored. A systematicstudy of such systems is currently underway. I present results from aphotometric survey of the massive Westerlund 1 cluster, a likely host tosome of the most massive stars in eclipsing binaries in our Galaxy.
| MOST Finds No Coherent Oscillations in the Hot Carbon-rich Wolf-Rayet Star HD 165763 (WR 111)
We have photometrically monitored the V = 8 mag Galactic Population IWC5 star WR 111 for 3 weeks nonstop using the MOST microsatellite. Eachof the ~27,000 data points has a precision of ~3 mmag. We find nocoherent Fourier components above the 50 part per million level over thewhole interval for frequencies f>10 cd-1 (periods P <2.4 hr). This limit is nearly 2 orders of magnitude below recentpredictions for early-type WR stars based on strange-mode pulsationsimulations, with expected periods in the range 10-30 minutes.Simultaneous spectroscopic observations of WR 111 reveal a normal levelof stochastic clumps propagating in the wind, which possibly manifestthemselves in the slow 1/f rise in the MOST power spectrum below f~10cd-1. Time-frequency analysis of the MOST data shows noobvious short-lived frequencies above the 1 mmag level, in starkcontrast to the highly variable cool WR stars WR 123 (WN8) and WR 103(WC9d), monitored previously by MOST. Radiation pressure thereforeappears to be the main, if not sole, driver of WR 111's strong wind.Based on data from the MOST satellite, a Canadian Space Agency mission,jointly operated by Dynacon, Inc., the University of Toronto Instituteof Aerospace Studies, and the University of British Columbia with theassistance of the University of Vienna.
| Theoretical Aspects of Massive Stars
From numerical simulations of massive and luminous stars, we often findregular radial pulsations for a large variety of stellar parameters. Thepulsation periods are typically around one day. Such pulsations areencountered during the core hydrogen burning as well as during the earlycore helium burning stage of evolution. The numerical results arediscussed with the aim to guide observations to identify and monitorsuch regularly pulsating variable massive stars in nature. We emphasisethat mass loss events generating circumstellar shells, complexatmospherical motions and angular variations due to stellar rotation canstrongly modify the actually observable light curves.
| Near Infrared Spectra of Galactic Wolf-Rayet Stars
Spectra of 37 Galactic WR stars were observed and reduced in thespectral range 790--895 nm. The main spectral features are identifiedand the equivalent widths and FWHMs of the strongest emission lines aremeasured. The equivalent width of the diffuse interstellar band at 862nm is also measured and the new estimates of color excessesE(B-V) are derived by using an empirical relationship betweenthe equivalent width and the color excess. The equivalent width ratiosfor the lines C III 850 nm, C IV 886 nm and C II 880 nm were found tocorrelate well with the WC subtype.
| Variability of Young Massive Stars in the Galactic Super Star Cluster Westerlund 1
This paper presents the first optical variability study of theWesterlund 1 super star cluster in search of massive eclipsing binarysystems. A total of 129 new variable stars have been identified,including the discovery of 4 eclipsing binaries that are clustermembers, 1 additional candidate, 8 field binaries, 19 field δScuti stars, 3 field W UMa eclipsing binaries, 13 other periodicvariables, and 81 long-period or nonperiodic variables. These includethe known luminous blue variable, the B[e] star, 11 Wolf-Rayet stars,several supergiants, and other reddened stars that are likely members ofWesterlund 1. The bright X-ray source corresponding to the Wolf-Rayetstar WR 77o (B) is found to be a 3.51 day eclipsing binary. Thediscovery of a reddened detached eclipsing binary system implies thefirst identification of main-sequence stars in Westerlund 1.
| Spectral Analysis of the Pre-WN Candidate HD 326823
We present a spectral analysis of the peculiar emission-line star HD326823. As has been reported in the literature, this object seems to bea rare, massive star entering the Wolf-Rayet (W-R) phase. In order toconfirm its evolutionary status, we used the radiative transfer codeCMFGEN to obtain its physical parameters and chemical abundances for thefirst time. By analyzing ultraviolet to optical observations of HD326823, we were able to obtain the following parameters:L=2×105 Lsolar, R*=30Rsolar, T*=22,280 K,M˙=5.2×10-6 Msolar yr-1, andv∞=200 km s-1. In addition, we demonstratedthat this star is severely hydrogen-depleted and helium-rich, withXH~3% and XHe~96% (mass fractions), confirmingprevious qualitative claims of a hydrogen deficiency. From the N IIλ5754 transition, we estimated an upper limit for the nitrogenabundance that is compatible with the idea that HD 326823 is a pre-WNstar (XN<~1%). Our models indicate that the Fe II linespresent in the optical spectrum are not formed in a sphericallysymmetric wind. We found that the iron ionization structure is dominatedby Fe III and Fe IV, and that these ions dominate the UV. By comparingour results with WNE and WNL stars in the H-R diagram, we suggest thatHD 326823 is a pre-WN8 star. The use of the transformedradius-temperature diagram also confirms a pre-WNL status. The idea thatstars may enter the W-R stage with a very low hydrogen mass fraction issupported by our results.
| 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.
| A MOST probable explanation of the pulsation of WR 123
Aims.Resorting to the observed period of the cyclic part of WR 123'sphotometric variability we constrain its stellar parameters.Methods: .Radiation hydrodynamic simulations were performed on selectedstellar envelope models for which also linear stability analyses werecomputed. Results: .Pulsations of massive hydrogen-rich stellarenvelopes subject to sufficiently high luminosity-to-mass ratios areexcited with periods that conform with the observed one by MOST inWR123.
| Excitation of g modes in Wolf-Rayet stars by a deep opacity bump
We examine the stability of l= 1 and l= 2 g modes in a pair ofnitrogen-rich Wolf-Rayet stellar models characterized by differinghydrogen abundances. We find that modes with intermediate radial ordersare destabilized by a ? mechanism operating on an opacity bump atan envelope temperature of logT~ 6.25. This `deep opacity bump' is dueprimarily to L-shell bound-free transitions of iron. Periods of theunstable modes span ~11-21h in the model containing some hydrogen, and~3-12h in the hydrogen-depleted model. Based on the latter finding, wesuggest that self-excited g modes may be the source of the 9.8-hperiodic variation of WR 123 recently reported by Lefèvre et al.
| Oscillations in the Massive Wolf-Rayet Star WR 123 with the MOST Satellite
We present the results of intensive visual-broadband photometricmonitoring of the highly variable WN8 Wolf-Rayet star WR 123, obtainedby the MOST (Microvariability and Oscillations of STars) satellite. Thisfirst Canadian astronomical space telescope observed WR 123 for 38 daysnonstop during 2004 June and July. Fourier analysis shows that noperiodic signal is stable for more than several days in thelow-frequency domain (f< 1 day-1), where most of thestochastic power is contained. Also, no significant variability is seenin the high-frequency domain (10 day-1 < f < 1400day-1) down to the level of 0.2 mmag, an order of magnitudelower than theoretical predictions for strange-mode pulsations. On theother hand, there seems to be a relatively stable 9.8 hr periodic signalpresent throughout the whole run. This period is probably too short torepresent the axial rotation of the star, unless it is related tomultiple substructures equidistantly spread along the stellar equator.It is also too short to be orbital in nature; it is more likely to berelated to pulsational instablilities (although with a much longerperiod than expected), thus finally revealing a possible fundamentaldriver behind the highly variable wind of this object, and others ofsimilar type.
| 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.
| Observing massive stars with the MOST satellite: the enigmatic WN8 star WR 123.
Not Available
| Canada's Little Space Telescope That Could: Another Year of Scientific Surprises From the MOST Microsatellite
At CASCA 2004 in Winnipeg, I announced the first scientific results fromthe MOST (Microvariability & Oscillations of STars) mission,launched in summer 2003. These included the controversial null detectionof acoustic oscillations in the light output of Procyon, at odds withtheory and groundbased spectroscopy, and the first direct measurement ofdifferential rotation in a star other than the Sun, kappa 1 Ceti. A yearlater, by CASCA 2005 in Montreal, I'll be able to share even moreexciting astrophysics, including: ultraprecise photometric studies ofexoplanetary systems like 51 Pegasi, tau Bootis, and HD 209458; newperspectives on massive stars like zeta Oph and the Wolf-Rayet star WR123; the definitive eigenfrequency spectrum of a pulsating chemicallypeculiar star (HR 1217), which provides an acid test for theories ofmagneto-acoustic coupling; and seismology of pulsating protostars in theopen cluster NGC 2264. I'll also return to Procyon, shedding more lighton the oscillation controversy by showing how MOST observations compareto 3-D hydrodynamical simulations of granulation in that star. Andbetween February and May, MOST will monitor a G dwarf and a K dwarf tosearch for true analogues of the solar 5-min oscillations. Too much tofit into 50 minutes, but I'll try to convey a broad flavour of thediverse MOST science (and, as usual, I'll talk really, really fast).
| 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.
| The influence of binaries on galactic chemical evolution
Understanding the galaxy in which we live is one of the greatintellectual challenges facing modern science. With the advent of highquality observational data, the chemical evolution modeling of ourgalaxy has been the subject of numerous studies in the last years.However, all these studies have one missing element which is theevolution of close binaries. Reason: their evolution is very complex andsingle stars only perhaps can do the job. (Un)Fortunately at present weknow that the majority of the observed stars are members of a binary ormultiple system and that certain objects can only be formed throughbinary evolution. Therefore galactic studies that do not account forclose binary evolution may be far from realistic.Because of the large expertise developed through the years in stellarevolution in general and binary evolution in particular at the BrusselsAstrophysical Institute, we found ourselves in a privileged position tobe the first to do chemical evolutionary simulations with the inclusionof detailed binary evolution. The complexity of close binary evolutionhas kept many astronomers from including binary stars into theirstudies. However, it is not always the easiest way of living that givesyou the most excitement and satisfaction.
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
| The neutral gas in the environs of the Wolf Rayet stars in the Circinus OB1 association
We have investigated the neutral hydrogen in the direction of theCircinus OB1 association with particular emphasis in the study of thevicinity of the WR stars WR 65 and WR 67. The HI line data were obtainedwith the Australia Telescope Compact Array with a synthesized beam of4\farcm0 × 2\farcm7 and a velocity resolution of 1.1 kms-1. These data led to the discovery of a large cavitysurrounded by an almost complete shell in agreement with the locationsand distances of the two WR stars. We propose that the HI featuresconstitute an interstellar bubble created by the powerful winds of theWR stars and their progenitors. By assuming a distance of 3 kpc, wecalculate for this HI bubble a linear radius of 22 pc, a swept-up massof 1600 M_ȯ and an expansion velocity of more than 7 kms-1. High angular resolution IRAS infrared data (HIRES)reveal the presence of a ring with good spatial correlation with the HIshell. Eight IRAS protostellar candidates located around the HI cavitysuggest that star formation may be taking place in the shell. Furtherinvestigation is required to confirm this proposition.
| The chemical evolution of the Galaxy: the importance of stars with an initial mass larger than 40 Msolar
In the present paper we investigate in how far stars with an initialmass larger than 40 Msolar affect the chemical enrichment ofthe Galaxy. We illustrate the importance for chemical yields of a mostup-to-date treatment of the various stellar wind mass loss episodes instellar evolutionary codes and we discuss the effects of a possiblesupernova-like outburst prior to massive black hole formation.
| 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 effects of binaries on the evolution of Wolf-Rayet type spectral features in starbursts
In the present paper we investigate in detail the effects of binarieswith initial period between 1 day and 10 years on theoreticalsimulations of Wolf-Rayet (WR) type spectral features in starbursts. Wefocus on the evolution of the nebular Hbeta line instarburst in general, on the intensity ratios I(nebular He II;lambda4686)/I(Hbeta ), I(blue bump)/I(Hbeta ), and I(redbump)/I(Hbeta ) as a function of the equivalent width ofHbeta of WR galaxies in particular. The binary evolutionaryprocesses that dominate the evolution of the considered spectralfeatures are the Roche lobe overflow in case Br systems, the masstransfer efficiency, and the merger rate. We show that the predictionson nebular He II depend critically on the uncertainties in the theory ofWR atmospheres and particularly on uncertainties in the treatment of thesubsonic velocity region of the WR wind. The observations of lowmetallicity starbursts are best reproduced by a theoretical model with asignificant number of binaries and with a metallicity-dependent WR wind.
| 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.
| MASSIVE STARS IN THE LOCAL GROUP: Implications for Stellar Evolution and Star Formation
The galaxies of the Local Group serve as important laboratories forunderstanding the physics of massive stars. Here I discuss what isinvolved in identifying various kinds of massive stars in nearbygalaxies: the hydrogen-burning O-type stars and their evolved He-burningevolutionary descendants, the luminous blue variables, red supergiants,and Wolf-Rayet stars. Primarily I review what our knowledge of themassive star population in nearby galaxies has taught us about stellarevolution and star formation. I show that the current generation ofstellar evolutionary models do well at matching some of the observedfeatures and provide a look at the sort of new observational data thatwill provide a benchmark against which new models can be evaluated.
| 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.
| 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.
| 2 Micron Narrowband Adaptive Optics Imaging in the Arches Cluster
Canada-France-Hawaii-Telescope adaptive optics bonnette images throughnarrowband filters in the K band are presented for the Arches cluster.Continuum fluxes, line fluxes, and equivalent widths are derived fromhigh angular resolution images, some nearly diffraction limited, for thewell-known massive stars in the Arches cluster. Images were obtained inthe lines He I 2.06 μm, H I Brγ (2.17 μm), and He II 2.19μm, as well as continuum positions at 2.03, 2.14, and 2.26 μm. Inaddition, fluxes are presented for H I Pα (1.87 μm) and anearby continuum position (1.90 μm) from Hubble Space Telescopearchival data.2 The 2 μm and Pαdata reveal two new emission-line stars and three fainter candidateemission-line objects. Indications for a spectral change of one objectbetween earlier observations in 1992-1993 and our data from 1999 arefound. The ratio of He II 2.19 μm to Brγ emission exhibits anarrow distribution among the stars, suggesting a narrow evolutionaryspread centered predominantly on spectral types O4 If or Wolf-Rayetstars of the WN7 subtype. From the approximate spectral types of theidentified emission-line stars and comparisons with evolutionary modelswe infer a cluster age between ~2 and 4.5 Myr.
| A Mid-Infrared Spectral Survey of Galactic Wolf-Rayet Stars
We present 8-13 μm spectra at resolution R~600 of 29 northernGalactic Wolf-Rayet stars, including the first ever reportedmid-infrared (MIR) spectrum for many. Among the subtypes of the starsstudied were 14 WC, 13 WN, 1 WN/WC, and an additional reclassified WN.Lines of He I and He II, along with fine-structure lines of Ne II and SIV, are strongly present in 22 of the sources observed, while six of thesources exhibit the powerful emission of heated circumstellar carbondust. We point out similarities between our spectra and Infrared SpaceObservatory (ISO) observations of several of the same sources and notean unresolved discrepancy between the two data sets for the WC6 star WR146. We investigate the diagnostic power of MIR He I and He II lines forsubtype discrimination and find the line ratio Wλ(9.7μm He II)/Wλ(11.3 μm He I+He II) can providemoderate discrimination within the WN and WC types, though the smallnumber of stars with corresponding line pairs detected made suchassessment difficult.
| The VIIth catalogue of galactic Wolf-Rayet stars
The VIIth catalogue of galactic PopulationI Wolf-Rayet stars providesimproved coordinates, spectral types and /bv photometry of known WRstars and adds 71 new WR stars to the previous WR catalogue. This censusof galactic WR stars reaches 227 stars, comprising 127 WN stars, 87 WCstars, 10 WN/WC stars and 3 WO stars. This includes 15 WNL and 11 WCLstars within 30 pc of the Galactic Center. We compile and discuss WRspectral classification, variability, periodicity, binarity, terminalwind velocities, correlation with open clusters and OB associations, andcorrelation with Hi bubbles, Hii regions and ring nebulae. Intrinsiccolours and absolute visual magnitudes per subtype are re-assessed for are-determination of optical photometric distances and galacticdistribution of WR stars. In the solar neighbourhood we find projectedon the galactic plane a surface density of 3.3 WR stars perkpc2, with a WC/WN number ratio of 1.5, and a WR binaryfrequency (including probable binaries) of 39%. The galactocentricdistance (RWR) distribution per subtype shows RWRincreasing with decreasing WR subtype, both for the WN and WC subtypes.This RWR distribution allows for the possibility ofWNE-->WCE and WNL-->WCL subtype evolution.
| Wolf-Rayet Stars and Relativistic Objects: Distinctions between the Mass Distributions in Close Binary Systems
The observed properties of Wolf-Rayet stars and relativistic objects inclose binary systems are analyzed. The final masses M CO f for thecarbon-oxygen cores of WR stars in WR + O binaries are calculated takinginto account the radial loss of matter via stellar wind, which dependson the mass of the star. The analysis includes new data on the clumpystructure of WR winds, which appreciably decreases the requiredmass-loss rates for the WR stars. The masses M CO f lie in the range (12)M ȯ (20 44)M ȯ and have a continuous distribution. Themasses of the relativistic objects M x are 1 20M ȯ and have abimodal distribution: the mean masses for neutron stars and black holesare 1.35 ± 0.15M ȯ and 8 10M ȯ, respectively, with agap from 2 4M ȯ in which no neutron stars or black holes areobserved in close binaries. The mean final CO-core mass is &$/line M _{CO}(f) = 7.4 - 10.3M_ ȯ$; , close to the mean mass for the black holes. This suggests that it isnot only the mass of the progenitor that determines the nature of therelativistic object, but other parameters as well-rotation, magneticfield, etc. One SB1R Wolf-Rayet binary and 11 suspected WR + C binariesthat may have low-mass companions (main-sequence or subgiant M-A stars)are identified; these could be the progenitors of low-mass X-raybinaries with neutron stars and black holes.
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
| Constelación: | Águila |
| Ascensión Recta: | 19h03m59.02s |
| Declinación: | -04°19'01.9" |
| Magnitud Aparente: | 11.378 |
| Movimiento Propio en Ascensión Recta: | -0.4 |
| Movimiento Propio en Declinación: | -3.8 |
| B-T magnitude: | 11.521 |
| V-T magnitude: | 11.39 |
Catálogos y designaciones:
|
