Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium
We present a survey of diffuse O VI emission in the interstellar medium(ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).Spanning 5.5 yr of FUSE observations, from launch through 2004 December,our data set consists of 2925 exposures along 183 sight lines, includingall of those with previously published O VI detections. The data wereprocessed using an implementation of CalFUSE version 3.1 modified tooptimize the signal-to-noise ratio and velocity scale of spectra from anaperture-filling source. Of our 183 sight lines, 73 show O VIλ1032 emission, 29 at >3 σ significance. Six of the 3σ features have velocities |vLSR|>120 kms-1, while the others have |vLSR|<=50 kms-1. Measured intensities range from 1800 to 9100 LU (lineunit; 1 photon cm-2 s-1 sr-1), with amedian of 3300 LU. Combining our results with published O VI absorptiondata, we find that an O VI-bearing interface in the local ISM yields anelectron density ne=0.2-0.3 cm-3 and a path lengthof 0.1 pc, while O VI-emitting regions associated with high-velocityclouds in the Galactic halo have densities an order of magnitude lowerand path lengths 2 orders of magnitude longer. Although the O VIintensities along these sight lines are similar, the emission isproduced by gas with very different properties.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.
| First Ever Polarimetric Detection of a Wind-Wind Interaction Region and a Misaligned Flattening of the Wind in the Wolf-Rayet Binary CQ Cephei
In this paper we present unfiltered and multiband (i.e., UBVRI)polarimetric observations of the short-period Wolf-Rayet binary CQ Cep.Using the basic assumptions of an optically thin, corotating envelopeand pointlike sources (i.e., BME78 assumptions), we determined theorbital parameters of the system (i.e.,i=99deg+/-1deg andΩ=76deg+/-2deg at the 2 σ level) withan accuracy many times better than any previous work. Residual non-BME78variability around phase 0.0 was present in our data, which we associatewith the polarimetric eclipse of the dense central parts of theWolf-Rayet (W-R) wind by the orbiting O star. We attribute the observedphase lag of -0.15 between our residuals and those expected for astandard polarimetric eclipse to a wind-wind interaction (WWI) regiondistorted by Coriolis forces using the model presented by Marchenko etal. This model was also able to explain the strong wavelength dependenceof the polarimetric amplitudes in our multiband observations. Ouranalysis also reveals important epoch-dependent departures of the matterdistribution from spherical symmetry that were not related to theorbital plane and therefore cannot be the result of tidal interaction.We conclude that binarity is not playing an important role in drivingthe wind of the W-R star in CQ Cep and contributing to the observednonspherical matter distribution. On the other hand, this asymmetrycould be explained by a rotationally induced disk misaligned with theorbital plane.
| Observations of the Diffuse Far-Ultraviolet Background with the Far Ultraviolet Spectroscopic Explorer
We have used observations taken under the Far Ultraviolet SpectroscopicExplorer (FUSE) S405/505 channel realignment program to explore thediffuse far-ultraviolet (FUV; 1000-1200 Å) radiation field. Of the71 independent locations in that program, we have observed a diffusesignal in 32, ranging in brightness from 1600 to a maximum of2.9×105 photons cm-2 sr-1s-1 Å-1 in Orion. The FUSE data confirm thatthe diffuse FUV sky is patchy with regions of intense emission, usuallynear bright stars, but also with dark regions, even at low Galacticlatitudes. We find a weak correlation between the FUV flux and the 100μm ratio but with wide variations, perhaps due to differences in thelocal radiation field.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.
| The Unusual 2001 Periastron Passage in the ``Clockwork'' Colliding-Wind Binary WR 140
We follow, using both optical spectroscopy and photometry, the``textbook'' colliding-wind WR+O binary WR 140 through and between theperiastron passages of 1993 and 2001. An extensive collection ofhigh-quality spectra allows us to derive precise orbital elements forboth components simultaneously. We confirm the extremely higheccentricity of the system, e=0.881+/-0.005, find an excellent match ofthe newly derived period to the previous estimates, P=2899.0+/-1.3 days,and improve the accuracy of the time of periastron passage,T0=HJD2,446,147.4+/-3.7. Around periastron, at orbital phasesφ~0.995-1.015, additional emission components appear on the tops ofthe broad Wolf-Rayet emission lines of relatively low ionizationpotential. The phase-dependent behavior of these excess line emissionspoints to their origin in the wind-wind collision zone, which allows usto place some limits on the orbital inclination of the system,i=50deg+/-15deg, and half-opening angle of the bowshock cone, θ=40deg+/-15deg. The relativelysudden appearance and disappearance of the extra emission componentsprobably signify a rapid switch from an adiabatically to a radiativelydominated regime and back again. Multiyear UBV photometry provides onemore surprise: in 2001 at φ=0.02-0.06, the system went through aseries of rapid, eclipse-like events. Assuming these events to berelated to an episode of enhanced dust formation at periastron, weestimate the characteristic size of the dust grains to be a~0.07 μm.
| Wolf-Rayet Stars, Black Holes, and Gamma-Ray Bursters in Close Binaries
We consider the evolutionary status of observed close binary systemscontaining black holes and Wolf-Rayet (WR) stars. When the componentmasses and the orbital period of a system are known, the reason for theformation of a WR star in an initial massive system of two main-sequencestars can be established. Such WR stars can form due to the action ofthe stellar wind from a massive OB star (M OB≥50M ȯ),conservative mass transfer between components with close initial masses,or the loss of the common envelope in a system with a large (up to25) initial component mass ratio. The strong impact ofobservational selection effects on the creation of samples of closebinaries with black holes and WR stars is demonstrated. We estimatetheoretical mass-loss rates for WR stars, which are essential for ourunderstanding the observed ratio of the numbers of carbon and nitrogenWR stars in the Galaxy . We also estimate the minimum initial masses ofthe components in close binaries producing black holes and WR stars tobe 25M ȯ. The spatial velocities of systems with black holesindicate that, during the formation of a black hole from a WR star, themass loss reaches at least several solar masses. The rate of formationof rapidly rotating Kerr black holes in close binaries in the Galaxy is3×10-6 yr-1. Their formation may be accompanied by a burst ofgamma radiation, possibly providing clues to the nature of gamma-raybursts. The initial distribution of the component mass ratios for closebinaries is dNdq=dM 2/M 1 in the interval 0.04≲q 0≤1,suggesting a single mechanism for their formation.
| Evolution of Wolf-Rayet Stars in Binary Systems: An Analysis of the Mass and Orbital-Eccentricity Distributions
We have undertaken a statistical study of the component mass ratios andthe orbital eccentricities of WR + O close binary, detachedmain-sequence (DMS), contact early-type (CE), and semidetached (SD)systems. A comparison of the characteristics of WR + O systems and ofDMS, CE, and SD systems has enabled us to draw certain conclusions aboutthe evolutionary paths of WR + O binaries and to demonstrate that up to90% of all known WR + O binaries formed as a result of mass transfer inmassive close O + O binary systems. Since there is a clear correlationbetween the component masses in SD systems with subgiants, the absenceof an anticorrelation between the masses of the WR stars and O stars inWR + O binaries cannot be considered evidence against the formation ofWR + O binaries via mass transfer. The spectroscopic transitionalorbital period P tr sp corresponding to the transition from nearlycircular orbits (e sp<0.1) to elliptical orbits (e sp≥0.1) is14d for WR + O systems and 2d 3d for OB + OB systems. Theperiod range in which all WR + O orbits are circular &$(1mathop dlimits_. 6 ≤slant P ≤slant 14(d) ); is close to the range for SD systems with subgiants, &0mathop dlimits_. 7 ≤slant P ≤slant 15(d); . The large difference between the P tr sp values for WR + O and OB +OB systems suggests that a mechanism of orbit circularization additionalto that for OB + OB systems at the DMS stage (tidal dissipation of theorbital energy due to radiative damping of the dynamical tides) acts inWR + O binaries. It is natural to suggest mass transfer in the parent O+ O binaries as this supplementary orbit-circularization mechanism.Since the transitional period between circular and elliptical orbits forclose binaries with convective envelopes and ages of 5×109 yearsis &P_{tr} = 12mathop dlimits_. 4$; , the orbits of most known SD systems with subgiants had enough timeto circularize during the DMS stage, prior to the mass transfer. Thus,for most SD systems, mass transfer plays a secondary role incircularization of their orbits. In many cases, the initial orbitaleccentricities of the O + O binary progenitors of WR + O systems arepreserved, due to the low viscosity of the O-star envelopes and theshort timescale for their nuclear evolution until the primary O starfills its Roche lobe and the mass transfer begins. The mass transfer inthe parent O + O systems is short-lived, and the number of orbitalcycles during the early mass-transfer stage is relatively low (lowerthan for the progenitors of SD systems by three or four orders ofmagnitude). The continued transfer of mass from the less massive to themore massive star after the component masses have become equal leads tothe formation of a WR + O system, and the orbit's residual eccentricityincreases to the observed value. The increase of the orbitaleccentricity is also facilitated by variable radial mass loss via thewind from the WR star in the WR + O system during its motion in theelliptical orbit. The result is that WR + O binaries can haveconsiderable orbital eccentricities, despite their intense masstransfer. For this reason, the presence of appreciable eccentricitiesamong WR + O binaries with large orbital periods cannot be consideredfirm evidence against mass transfer in the parent O + O binary systems.Only for the WR + O binaries with the longest orbital periods (4 of 35known systems, or 11 %) can the evolution of the parent O + O binariesoccur without filling of the Roche lobe by the primary O star, beinggoverned by radial outflow in the form of the stellar wind and possiblyby the LBV phenomenon, as in the case of HD 5980.
| Colliding winds in the WR+OB binary θ Muscae (WR 48, WC5+O6-7V)
Spectra, providing full phase coverage, of the 19 d WC6+OB binaryθ Mus (WR 48, HD 113904), have been obtained and show dramaticvariations of the &CIIIλ5696 emission line profile. We havemodeled these line profile variations assuming the winds from the WRstar and its close OB companion are colliding and forming a shock regionfrom which extra emission originates.
| Sums of investigation of the linear polarization behaviour of binary systems with a Wolf-Rayet component
Analysis of the long-term (on a scale of years) behaviour of linearpolarization of four WR binary systems (CQ Cep, CX Cep, V444 Cyg and HD211853) is presented. Common features of the long-term polarizationvariations of CQ Cep, CX Cep and HD 211853 in combination with theresults of the harmonic analysis of their polarization curves allowed usto make assumptions on the causes of the found variability. The basicreason of the long-term polarization variability is likely to be thephysical activity of the WR components which manifests itself in theepisodic swelling of the WR envelopes and subsequent expulsion of theiroutermost layers. The involvement into the study of five wider "WR+O"pairs (HDE 311884, HD 90657, HD 97152, HD 152270 and HD 186943) allowedus to confirm these assumptions. The results of the analysis of thepolarization curves of nine WR binary systems are summed up. Threeconfirmations of high massiveness of the WR comnponent HDE 311884 havebeen derived.
| Modelling the colliding-winds spectra of the 19-d WR + OB binary in the massive triple system θ Muscae
High signal-to-noise ratio, moderate-resolution spectra, providing fullphase coverage of the 19-d WC6 + OB binary θ Mus (WR 48, HD113904), have been obtained and show dramatic variations of the CIIIλ5696 emission-line profile. We have modelled these lineprofile variations using a purely geometrical model which assumes thatthe emission arises from two regions, an optically thin spherical shellaround the WR star and a cone-shaped region that partially wraps aroundthe OB star. The cone-shaped region represents the shock front arisingfrom the collision between the winds of the two stars. This work buildsupon our earlier study of WR 42 and WR 79, and uses a completely newcode for the modelling, which includes the effects of turbulence. We nowfind much better agreement between the orbital inclination angles foundfor these stars with those determined using other methods. The fittingparameters found via modelling the C IIIλ5696 profile variationsof θ Mus are used to infer that the OB companion most likely hasa spectral type of O6V or O7V. The modelling presented here continues toshow the exciting promise of a better understanding of WR starfundamental parameters.
| Physical parameters of the high-mass X-ray binary 4U1700-37
We present the results of a detailed non-LTE analysis of the ultravioletand optical spectrum of the O6.5 Iaf+ star HD153919 - the mass donor in the high-mass X-ray binary4U1700-37. We find that the star has a luminositylog(L*/Lsun)=5.82 +/- 0.07, T_eff=35 000 +/- 1000K, radius R*=21.9+1.3-0.5Rsun, mass-loss rate dot {M}=9.5x 10-6Msun yr-1, and a significant overabundance ofnitrogen (and possibly carbon) relative to solar values. Given theeclipsing nature of the system these results allow us to determine themost likely masses of both components of the binary via Monte Carlosimulations. These suggest a mass for HD 153919 ofM* = 58 +/- 11 Msun - implying the initial mass ofthe companion was rather high (ga 60 Msun). The most likelymass for the compact companion is found to be M_x =2.44+/- 0.27Msun, with only 3.5 per cent of the trials resulting in amass less than 2.0 Msun and none less than 1.65Msun. Such a value is significantly in excess of the upperobservational limit to the masses of neutron stars of 1.45Msun found by Thorsett & Chakrabarthy (\cite{thorsett}),although a mass of 1.86 Msun has recently been reported forthe Vela X-1 pulsar (Barziv et al. \cite{barziv}).Our observational data is inconsistent with the canonical neutron starmass and the lowest black hole mass observed (ga 4.4 Msun;Nova Vel). Significantly changing observationalparameters can force the compact object mass into either of theseregimes but, given the strong proportionality between M* andM_x, the O-star mass changes by factors of greater than 2, well beyondthe limits determined from its evolutionary state and surface gravity.The low mass of the compact object implies that it is difficult to formhigh mass black holes through both the Case A & B mass transferchannels and, if the compact object is a neutron star, wouldsignificantly constrain the high density nuclear equation of state.Based on observations collected at the European Southern Observatory, LaSilla, Chile (64.H-0224).
| The mass-loss rates of Wolf-Rayet stars explained by optically thick radiation driven wind models
Observed, clumping-corrected mass-loss rates of Galactic Wolf-Rayet (WR)stars are compared with predictions of the optically thick radiationdriven wind models. We did not develop models for the whole wind, but westudied the conditions at the sonic point that would explain theobserved high mass-loss rates of WR-stars. We find that optically thickwind models can explain the observed values of the mass-loss rates onlyif two conditions are satisfied: (a) The sonic point (wherevflow=vsound) lies deep in the wind where thetemperature is either near 160 000 K, or in the range of 40 000 to 70000 K. (b) The flux-mean opacity must increase outward from the sonicpoint. With these conditions a simple approximate formula for themass-loss rates of WR-stars can be derived. The first condition impliesthat the sonic point is at an optical depth between about 3 and 30. Suchlarge optical depths require a slowly increasing velocity law in thesupersonic region, with a velocity-law index of beta =~ 5 for WR-stars,compared to beta =~ 1 for O-stars. The OPAL-opacity tables for thechemical composition of the WR-stars show that the opacity indeedincreases outward at the temperature range near 1.6 x 105 K,and between about 4 x 107 and 7 x 104 K, asrequired for the optically thick wind models. The opacity at the sonicpoints of the models is very similar to the OPAL-opacity at the sonicpoint temperature and density. The radius of the sonic point is abouthalf as large as the inner boundaries of the ``standard'' models forearly type WR-winds. Observational evidence, derived from line profilevariations and from the light-curves of WR-stars in eclipsing binarysystems, support the derived large values of beta and the small valuesof the sonic point radius. The models presented here show that the highmass-loss rates of WR-stars might be the result of optically thickradiation driven winds. The presence of two very distinct temperatureregimes for the sonic point implies a bifurcation in the wind models ofWR-stars.
| The Effect of Binarity and Metallicity in the Spectra of WC and WO Stars
A statistical analysis of the main emission lines common to the WC andWO stars is made based on an extensive set of spectral data. To definethe trends in equivalent width ( Wλ), line ratios, andline widths, median values are derived for single-spectrum stars ofdifferent spectral class. We find that in Galactic WO and WC4 stars,Wλ (C IV 581 nm) is smaller compared to inextragalactic objects. In both Galactic and extragalactic stars,Wλ (O V 559 nm) smoothly increases towards early WCand WO stars. It is argued that differences in stellar wind structure,in combination with the ambient metallicity, may be the cause of theanomalies. Variation of the profile of the 465 nm blend indicates asubstantial contribution of He II 468 nm for the WCE and WO stars. Inaddition, we comment on the carbon abundances in relation to theevolutionary status of these objects. We also give an estimate of theOB/WR continuum flux ratio in composite-spectrum systems.
| 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.
| High-Precision, Time-resolved Linear Polarimetry of Two Bright Dwarf Novae
We have monitored in broadband linear polarimetry two bright cataclysmicvariables (CVs) around complete 5-6 hr orbital cycles, with an order ofmagnitude better precision than any previous observations (save those ofNaylor and coworkers) for any CVs. No orbital double-wave modulation,nor flickering on a timescale of ~10 minutes, is seen above theinstrumental level of σP~0.03%, either in eruption forRX And (type: dwarf nova [DN]/ZC) or in quiescence or in eruption for SSCyg (type: DN). Furthermore, the level of (interstellar?) polarizationremained constant in both states for SS Cyg. This lack of detection ineither system is likely a consequence of the fact that there are simplynot enough polarizing free electrons available to allow detection atthis level.
| Multi-frequency variations of the Wolf-Rayet system HD193793 (WC7pd+O4-5) III. IUE observations
The colliding-wind binary system WR 140 (HD 193793, WC7pd+O4-5, P = 7.94yr) was monitored in the ultraviolet by IUE from 1979 to 1994 in 35short-wavelength high-resolution spectra. An absorption-lineradial-velocity solution is obtained from the photospheric lines of theO component, by comparison with a single O star. The resulting orbitalparameters, e = 0.87 +/- 0.05, omega = 31degr +/- 9degr andKO star = 25 +/- 15 km s-1, confirm the largeeccentricity of the orbit, within the uncertainties of previous opticalstudies. This brings the weighted mean UV-optical eccentricity to e =0.85 +/- 0.04. Occultation of the O-star light by the WC wind and theWC+O colliding-wind region results into orbital modulation of theP-Cygni profiles of the C ii, C iv and Si iv resonance lines. Nearperiastron passage, the absorption troughs of those resonance-lineprofiles increase abruptly in strength and width, followed by a gradualdecrease. In particular, near periastron the blue black-edges of theP-Cygni absorption troughs shift to larger outflow velocities. Wediscuss that the apparently larger wind velocity and velocity dispersionobserved at periastron could be explained by four phenomena: (i)geometrical resonance-line eclipse effects being the main cause of theobserved UV spectral variability, enhanced by sightline crossing of theturbulent wind-wind collision zone; (ii) the possibility of anorbital-plane enhanced WC7 stellar wind; (iii) possible common-envelopeacceleration by the combined WC and O stellar radiation fields; and (iv)possible enhanced radiatively driven mass loss due to tidal stresses,focused along the orbiting line of centers.
| Wolf-Rayet Stars and Cosmic Gamma-ray Bursts
The observational properties of cosmic gamma-ray bursts and ofWolf-Rayet (WR) stars and their CO cores at the end of their evolutionare analyzed. WR stars do not have hydrogen envelopes, facilitating thetransformation of the energy of collapse into observable gamma rays. Ofthe ≈90 well-localized gamma-ray bursts, 21 have opticalidentifications, of which 16 have measured redshifts (z=0.4 4.5). Thedistribution of gamma-ray bursts in energy N(ΔE) has a largescatter, from 3×1051 to 2×1054 erg. There is some evidencethat the distribution N(ΔE) is bimodal if we include the gamma-rayburst GRB 980425, which is associated with the peculiar type Icsupernova SN 1998bw in the nearby elliptical galaxy ESO 184-G82, forwhich ΔE γ≈1048erg. These characteristics of gamma-raybursts are reminiscent of the distribution of final masses for the COcores of WR stars, which uniformly covers a broad range: M CO=(1 2)Mȯ-(20 44)M ȯ. The possible bimodality of the gamma-ray burstenergy distribution (E 1=1048 erg; ΔE2=3×1051-2×1054erg) could be associated with the bimodalmass distribution for stellar relativistic objects (MNS=(1.35±0.15)M ȯ; M BH=4 15M ȯ). The fact that SN1998bw is a “peculiar” type Ic supernova, not typical forthe collapses of WR stars (which usually give rise to type Ib/csupernovae), could be related to the rotation of the collapsing CO core.This “drags out/rd the time for the collapse, leading to theformation of a neutron star, a decrease in the gamma-ray burst energy,and an increase in the fraction of kinetic energy transferred to thesupernova envelope. The expected rate of collapse of the CO cores of WRstars in the Galaxy is ≈10-3/yr. This is at least three orders ofmagnitude higher than the mean frequency of gamma-ray bursts per galaxy(≈10-6 10-7/yr). Two models for gamma-ray bursts with WR stars asprogenitors are considered: the hypernova model of Paczynski (1998) andthe pulsation instability CO-core collapse model proposed by Gershte&$/set{lower0.5emhbox{smashriptscriptstylesmile}}{l} $; n (2000). In both models, the rate of CO-core collapses can be broughtinto agreement with the observed rate of gamma-ray bursts by taking intoaccount the anisotropy of the gamma radiation, associated with either arelativistic jet or the random character of the initial CO-core collapsedue to instabilities. It is concluded that WR stars could be theprogenitors of gamma-ray bursts. This hypothesis predicts the existenceof two types of gamma-ray bursts, corresponding to the bimodal massdistribution for stellar relativistic objects, and of three types ofoptical afterglow, associated with collapses of the CO cores of WR starsthat are single, in WR+O binaries, and in hypothetical WR+(A-M) systems.The paper also briefly examines a model of gamma-ray bursts as transientphenomena in the early stages of the evolution of galaxies (z>1),when very massive stars (M>100M ȯ) weak in heavy elements couldform. Such massive stars should also lose their hydrogen envelopes andbe transformed into massive WR stars, whose collapses could beaccompanied by gamma-ray bursts. It is suggested that WR galaxies arethe most probable candidates for the host galaxies of gamma-ray bursts.
| Magellanic Cloud WC/WO Wolf-Rayet stars - II. Colliding winds in binaries
A search for evidence of colliding winds is undertaken among the fourcertain Magellanic Cloud WC/WO spectroscopic binaries found in thecompanion Paper I, as well as among two Galactic WC/WO binaries of verysimilar subtype. Two methods of analysis, which allow the determinationof orbital inclination and parameters relating to the shock cone fromspectroscopic studies of colliding winds, are attempted. In the firstmethod, Lührs' spectroscopic model is fitted to the moderatelystrong Ciii 5696-Å excess line emission arising in the shock conefor the stars Br22 and WR 9. The four other systems show only very weakCiii 5696-Å emission. Lührs' model follows well the meandisplacement of the line in velocity space, but is unable to reproducedetails in the line profile and fails to give a reliable estimate of theorbital inclination. In the second method, an alternative attempt isalso made to fit the variation of more global quantities, full width athalf-maximum and radial velocity of the excess emission, with phase.This method also gives satisfactory results in a qualitative way, butshows numerical degeneracy with orbital inclination. Colliding windeffects on the very strong Civ 5808-Å Wolf-Rayet emission line,present in all six binaries, are also found to behave qualitatively asexpected. After allowing for line enhancement in colliding windbinaries, it now appears that all Magellanic Cloud WC/WO stars occupy avery narrow range in spectral subclass: WC4/WO3.
| 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.
| Modelling the spectra of colliding winds in the Wolf-Rayet WC7+O binaries WR 42 and WR 79
We have obtained complete phase coverage of the WC7+O binaries WR 42=HD97152 and WR 79=HD 152270 with high signal-to-noise ratio (S/N),moderate-resolution spectra. Remarkable orbital phase-locked profilevariations of the Ciii λ5696 line are observed and interpreted asarising from colliding wind effects. Within this scenario, we havemodelled the spectra using a purely geometrical model that assumes acone-shaped wind-wind interaction region which partially wraps aroundthe O star. Such modelling holds the exciting promise of revealing anumber of interesting parameters for WR+O binaries, such as the orbitalinclination, the streaming velocity of material in the interactionregion and the ratio of wind momentum flux. Knowledge of theseparameters in turn leads to the possibility of a better understanding ofWR star masses, mass-loss rates and wind region characteristics.
| Mass-loss rates of Wolf-Rayet stars as a function of stellar parameters
Clumping-corrected mass-loss rates of 64 Galactic Wolf-Rayet (WR) starsare used to study the dependence of mass-loss rates, momentum transferefficiencies and terminal velocities on the basic stellar parameters andchemical composition. The luminosities of the WR stars have beendetermined either directly from the masses, using the dependence of L onmass predicted by stellar evolution theory, or they were determined fromthe absolute visual magnitudes and the bolometric corrections. For thispurpose we improved the relation between the bolometric correction andthe spectral subclass. (1) The momentum transfer efficiencies η(i.e. the ratio between the wind momentum loss and radiative momentumloss) of WR stars are found to lie in the range of 1.4 to 17.6, with themean value of 6.2 for the 64 program stars. Such values can probably beexplained by radiative driving due to multiple scattering of photons ina WR wind with an ionization stratification. However, there may be aproblem in explaining the driving at low velocities. (2) We derived thelinear regression relations for the dependence of the terminal velocity,the momentum transfer efficiency and the mass-loss rates on luminosityand chemical composition. We found a tight relation between the terminalvelocity of the wind and the parameters of the hydrostatic core. Thisrelation enables the determination of the mass of the WR stars fromtheir observed terminal velocities and chemical composition with anaccuracy of about 0.1 dex for WN and WC stars. Using evolutionary modelsof WR stars, the luminosity can then be determined with an accuracy of0.25 dex or better. (3) We found that the mass-loss rates(&mathaccent "705Frelax dot;) of WR stars depend strongly onluminosity and also quite strongly on chemical composition. For thecombined sample of WN and WC stars we found that &mathaccent"705Frelax dot; in Mȯyr-1 can be expressed as&mathaccent "705Frelax dot; ≃ 1.0 ×10-11(L/L ȯ)1.29Y1.7Z0.5 (1) with an uncertainty of σ = 0.19dex (4) The new mass-loss rates are significantly smaller than adoptedin evolutionary calculations, by about 0.2 to 0.6 dex, depending on thecomposition and on the evolutionary calculations. For H-rich WN starsthe new mass-loss rates are 0.3 dex smaller than adopted in theevolutionary calculations of Meynet et al. (1994). (5) The lowermass-loss rates, derived in this paper compared to previously adoptedvalues, facilitate the formation of black holes as end points of theevolution of massive stars. However they might create a problem inexplaining the observed WN/WC ratios, unless rotational mixing ormass-loss due to eruptions is important.
| Quantitative analysis of WC stars: constraints on neon abundances from ISO-SWS spectroscopy
Neon abundances are derived in four Galactic WC stars -γ2Vel (WR11, WC8+O7.5III), HD156385 (WR90, WC7),HD192103 (WR135, WC8) and WR146 (WC5+O8) - using mid-infraredfine-structure lines obtained with ISO-SWS. Stellar parameters for eachstar are derived using the non-local thermodynamic equilibrium modelatmospheric code of Hillier & Miller, together with ultraviolet(IUE), optical (INT, AAT) and infrared (UKIRT, ISO) spectroscopy. In thecase of γ2Vel, we adopt very recent results from DeMarco et al., who followed an identical approach. ISO-SWS data setsreveal the [Neiii] 15.5-μm line in each of our targets, while [Neii]12.8μm, [Siv] 10.5μm and [Siii] 18.7μm are observed solely inγ2Vel. Using a method updated from Barlow et al. toaccount for clumped winds, we derive Ne/He=(3-4)×10-3by number, plus S/He=6×10-5 for γ2Vel.Neon is highly enriched, such that Ne/S in γ2Vel iseight times higher than cosmic values. However, observed Ne/He ratiosare a factor of 2 lower than predictions of current evolutionary modelsof massive stars. An imprecise mass loss and distance were responsiblefor the much greater discrepancy in neon content identified by Barlow etal. Our sample of WC5-8 stars span a narrow range in T* (=55-71kK), withno trend towards higher temperature at earlier spectral type, supportingearlier results for a larger sample by Koesterke & Hamann. Stellarluminosities range from 100000 to 500000Lsolar, while10-5.1 <= M/(Msolar yr-1) <=10-4.5, adopting clumped winds, in which volume fillingfactors are 10per cent. In all cases, wind performance numbers are lessthan 10, significantly lower than recent estimates. Carbon abundancesspan 0.08<=C/He<=0.25 by number, while oxygen abundances remainpoorly constrained.
| ICCD Speckle Observations of Binary Stars. XXII. A Survey of Wolf-Rayet Starsfor Close Visual Companions
We present the results of a speckle interferometric survey for closevisual companions, mainly among 29 of the apparently brightestWolf-Rayet (W-R) stars. Only one target, WR 48 = theta Mus, was resolvedas a close astrometric binary (with a separation of 46+/-9 mas). Thissystem is probably a triple comprising a short-period W-R binary plus adistant O supergiant companion. Although our binary detection fractionis low, it is not an unexpected result given the selection effects thatmilitate against easy detection of binaries. New, higher resolutionobservations will almost certainly increase the fraction of binaries.There are four known binaries among the six W-R stars in our sample thathave nonthermal radio emission, and this connection supports the ideathat the nonthermal emission originates in the wind-wind collisionbetween components.
| Radio Continuum Measurements of Southern Early-Type Stars. III. Nonthermal Emission from Wolf-Rayet Stars
The Australia Telescope Compact Array (ATCA) has been used to search forradio continuum emission at 2.4 and 1.4 GHz from a sample of 36 southernWolf-Rayet stars. Seven Wolf-Rayet stars were detected at 2.4 GHz, ofwhich two were also detected at 1.4 GHz. We have identified sixWolf-Rayet stars, WR 14, 39, 48, 90, 105, and 112, that have nonthermalemission. The ATCA data confirm that at least 40% of Wolf-Rayet starswith measured spectral indices have nonthermal emission at centimeterwavelengths. Properties of each of the six sources are discussed. Themeasured spectral indices are between 0 and -1.0, and the radioluminosities are of order 10^29 ergs s^-1. So far 10 confirmed sourcesof nonthermal emission are known, including the six ATCA detections andfour previously known cases, WR 125, 140, 146, and 147. In all cases,the nonthermal radio emission almost certainly originates from aninteraction between the Wolf-Rayet stellar wind and the wind from amassive companion star. The radio observations agree well withtheoretical predictions for colliding winds. Synchrotron emission occursfrom relativistic electrons accelerated in strong shocks. The nonthermalspectral indices are likely to be close to -0.5. For WR 39, the detectedradio emission is offset by ~3" from the optical position of WR 39 andby ~2" from the optical position of WR 38B. We suggest that the radioemission may originate from a wind-wind interaction between WR 39 and WR38B, although this is not confirmed. For WR 11, the radio spectral indexincreases from +0.3 between 3 and 6 cm to +1.2 between 13 and 20 cm.This is interpreted as evidence for a highly attenuated nonthermalcomponent that originates well within the ionized wind of the W-R starfrom an interaction with the wind of the O9 companion star.
| Five-colour photometry of OB-stars in the Southern Hemisphere
Observations of OB-stars, made in 1959 and 1960 at the Leiden SouthernStation near Hartebeespoortdam, South Africa, with the VBLUW photometerattached to the 90 cm light-collector, are given in this paper. They arecompared with photometry obtained by \cite[Graham (1968),]{gra68}\cite[Walraven & Walraven (1977),]{wal77} \cite[Lub & Pel(1977)]{lub77} and \cite[Van Genderen et al. (1984).]{gen84} Formulaefor the transformation of the present observations to those of\cite[Walraven & Walraven (1977)]{wal77} and \cite[Lub & Pel(1977)]{lub77} are given. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| The WR and O-type star population predicted by massive star evolutionary synthesis
Evolutionary calculations of massive single stars and of massive closebinaries that we use in the population number synthesis (PNS) code arepresented. Special attention is given to the assumptions/uncertaintiesinfluencing these stellar evolutionary computations (and thus the PNSresults). A description is given of the PNS model together with theinitial statistical distributions of stellar parameters needed toperform number synthesis.We focus on the population of O-type stars andWR stars in regions where star formation was continuous in time and instarburst regions. We discuss the observations that have to be explainedby the model. These observations are then compared to the PNSpredictions.We conclude that: . probably the majority of the massivestars are formed as binary components with orbital period between 1 dayand 10 yr; most of them interact. . at most 8% of the O-type stars arerunaways due to a previous supernova explosion in a binary; recentstudies of pulsar space velocities and linking the latter to the effectof asymmetrical supernova explosions, reveal that only a smallpercentage of these runaways will have a neutron star companion. . withpresent day stellar evolutionary computations, it is difficult toexplain the observed WR/O number ratio in the solar neighbourhood and inthe inner Milky Way by assuming a constant star formation rate, with orwithout binaries. The observed ratio for the Magellanic Clouds is betterreproduced. . the majority of the single WR stars may have had a binarypast. . probably merely 2-3% (and certainly less than 8%) of all WRstars have a neutron star companion. . a comparison between theoreticalprediction and observations of young starbursts is meaningful only ifbinaries and the effect of binary evolution are correctly included. Themost stringent feature is the rejuvenation caused by mass transfer.
| Clumping-corrected mass-loss rates of Wolf-Rayet stars
Mass-loss rates of Galactic Wolf-Rayet stars have been determined fromtheir radio emission power and spectral index (alpha = dln {f_ν} /dln ν), accounting for the clumped structure and (potential) variableionization in their outer winds. The average spectral index between mm-and cm- wavelengths is ~ 0.77 for WN stars and ~ 0.75 for WC stars, incontrast with ~ 0.58 expected for smooth winds. The observed wavelengthdependence of alpha can be explained using clumped wind models in somecases, with shocks (at 30-100 stellar radii) producing a higherionization zone in the outer wind. We obtain an empirical formularelating mass-loss with observed optical emission line equivalentwidths, with application to stars without measured radio fluxes.Clumping-corrected mass-loss rates are generally lower than thoseobtained by current smooth wind models. Specifically we find log\mdot(clumpy)-log \mdot(smooth)=-0.19 (sigma=0.28) for WN stars, and log\mdot(clumpy)-log \mdot(smooth)=-0.62 (sigma=0.19) for WC stars. Newmass-loss rate estimates agree very well with (clumping independent)determinations of WR components in binary systems.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Wolf-Rayet stars and O-star runaways with HIPPARCOS. I. Kinematics
Reliable systemic radial velocities are almost impossible to secure forWolf-Rayet stars, difficult for O stars. Therefore, to study the motions- both systematic in the Galaxy and peculiar - of these two relatedtypes of hot, luminous star, we have examined the Hipparcos propermotions of some 70 stars of each type. We find that (a) both groupsfollow Galactic rotation in the same way, (b) both have a similarfraction of ``runaways'', (c) mean kinetic ages based on displacementand motion away from the Galactic plane tend to slightly favour thecluster ejection over the the binary supernova hypothesis for theirformation, and (d) those with significant peculiar supersonic motionrelative to the ambient ISM, tend to form bow shocks in the direction ofthe motion. Based on data from the ESA Hipparcos astrometry satellite.Table~1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Киль |
| Прямое восхождение: | 11h10m04.08s |
| Склонение: | -60°58'45.0" |
| Видимая звёздная величина: | 8.061 |
| Расстояние: | 769.231 парсек |
| Собственное движение RA: | -7.7 |
| Собственное движение Dec: | 1.9 |
| B-T magnitude: | 8.172 |
| V-T magnitude: | 8.071 |
Каталоги и обозначения:
|
