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β Cephei stars in the ASAS-3 data. I. Long-term variations of periods and amplitudes
Aims.We analyse V-filter ASAS-3 photometry of 41 known βCephei-type stars. The ASAS-3 photometry is combined with the archivaldata, if available, to determine long-term stability of periods andamplitudes of excited modes. Methods: Frequencies of modes are derivedby means of Fourier periodograms with consecutive prewhitening. Theresults are examined in the context of detection threshold. Results: Wedetected amplitude changes in three β Cephei stars, BW Cru, V836Cen, and V348 Nor. Period changes were found in KK Vel and V836 Cen. Ouranalysis shows that intrinsic period changes are more common amongmultiperiodic stars, apparently because they are caused by some kind ofmode interaction. In addition, we found new modes for seven stars, andfor ten others we provide new solutions or remove ambiguities in thedetected frequencies. One candidate hybrid β Cephei/SPB star, HD133823, is discovered.Appendix A, Figs. 2-6 and Tables 2-6 are only available in electronicform at http://www.aanda.org Table V photometry for all 41 stars is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/477/907
| 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.
| 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.
| Catalog of Galactic β Cephei Stars
We present an extensive and up-to-date catalog of Galactic β Cepheistars. This catalog is intended to give a comprehensive overview ofobservational characteristics of all known β Cephei stars, coveringinformation until 2004 June. Ninety-three stars could be confirmed to beβ Cephei stars. We use data from more than 250 papers publishedover the last nearly 100 years, and we provide over 45 notes onindividual stars. For some stars we reanalyzed published data orconducted our own analyses. Sixty-one stars were rejected from the finalβ Cephei list, and 77 stars are suspected to be β Cepheistars. A list of critically selected pulsation frequencies for confirmedβ Cephei stars is also presented.We analyze the β Cephei stars as a group, such as the distributionsof their spectral types, projected rotational velocities, radialvelocities, pulsation periods, and Galactic coordinates. We confirm thatthe majority of the β Cephei stars are multiperiodic pulsators. Weshow that, besides two exceptions, the β Cephei stars with highpulsation amplitudes are slow rotators. Those higher amplitude starshave angular rotational velocities in the same range as thehigh-amplitude δ Scuti stars (Prot>~3 days).We construct a theoretical HR diagram that suggests that almost all 93β Cephei stars are main-sequence objects. We discuss theobservational boundaries of β Cephei pulsation and the physicalparameters of the stars. We corroborate that the excited pulsation modesare near to the radial fundamental mode in frequency and we show thatthe mass distribution of the stars peaks at 12 Msolar. Wepoint out that the theoretical instability strip of the β Cepheistars is filled neither at the cool nor at the hot end and attempt toexplain this observation.
| 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.
| Radio emission models of colliding-wind binary systems
We present calculations of the spatial and spectral distribution of theradio emission from a wide WR+OB colliding-wind binary system based onhigh-resolution hydrodynamical simulations and solutions to theradiative transfer equation. We account for both thermal and synchrotronradio emission, free-free absorption in both the unshocked stellar windenvelopes and the shocked gas, synchrotron self-absorption, and theRazin effect. To calculate the synchrotron emission several simplifyingassumptions are adopted: the relativistic particle energy density is asimple fraction of the thermal particle energy density, in equipartitionwith the magnetic energy density, and a power-law in energy. We alsoassume that the magnetic field is tangled such that the resultingemission is isotropic. The applicability of these calculations tomodelling radio images and spectra of colliding-wind systems isdemonstrated with models of the radio emission from the wide WR+OBbinary WR 147. Its synchrotron spectrum follows apower-law between 5 and 15 GHz but turns down to below this at lower andhigher frequencies. We find that while free-free opacity from thecircum-binary stellar winds can potentially account for thelow-frequency turnover, models that also include a combination ofsynchrotron self-absorption and Razin effect are favoured. We argue thatthe high-frequency turn down is a consequence of inverse-Comptoncooling. We present our resulting spectra and intensity distributions,along with simulated MERLIN observations of these intensitydistributions. From these we argue that the inclination of theWR 147 system to the plane of the sky is low. Wesummarise by considering extensions of the current model that areimportant for models of the emission from closer colliding windbinaries, in particular the dramatically varying radio emission ofWR 140.
| 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.
| Metallicity and binarity in WC and WO stars
Not Available
| The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| 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.
| High-resolution X-ray imaging of the colliding wind shock in WR 147
We analyze new high-resolution Chandra X-ray images of the Wolf-Rayetbinary system WR147. This system contains a WN8 star with an early-typecompanion located 0.6'' to its north, and is the only known early-typebinary with a separation on the sky large enough for the wind-windcollision between the stars to currently be resolved at X-ray energies.The 5 ksec Chandra HRC-I image provides the first direct evidence forspatially extended X-ray emission in an early-type binary system. TheX-ray emission peaks close to the position of the radio bow shock andnorth of the WN8 star. A deeper X-ray image is needed to accuratelydetermine the degree of spatial extension, to exactly align the X-rayand optical/radio frames, and to determine whether part of the detectedX-ray emission arises in the individual stellar winds. Simulated X-rayimages of the wind-wind collision have a FWHM consistent with the data,and maximum likelihood fits suggest that a deeper observation may alsoconstrain the inclination and wind momentum ratio of this system.However, as the WR wind dominates the colliding wind X-ray emission itappears unlikely that M?OB andvinfty_OB can be separately determined from X-rayobservations. We also note an inconsistency between numerical andanalytical estimates of the X-ray luminosity ratio of the stronger andweaker wind components, and conclude that the analytical results are inerror.
| 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.
| On the variability of the visual binary WR86. WC7 with a β-Cephei companion.
We discuss the variability of WR 86 (WC7 (+B0 III)), a known visualbinary, confirmed by Hubble Space Telescope observations (Niemela et al.\cite{niemela}). Photometric observations show a fairly smooth lightcurve with a time scale of ~3.5 h and a light amplitude of ~0.01m.Because of the spectral classification of the visual companion (B0 III)it might well be a β-Cephei star. From observations taken in 1989,1990 and 1995 we derive two photometric frequencies, 6.914:cd-1 and 7.236: cd-1, where only the latter isgiven in the recent VIIth catalogue of galactic Wolf-Rayet stars (vander Hucht \cite{hucht}). Our spectroscopy reveals a slightly variable WRstar and almost certainly a pulsating companion. Comparison with stellarmodels suggests that WR 86 consists of a 20 Msolarβ-Cephei star in combination with a WR star of initial mass 40Msolar, at Z=0.04. We derive a distance to WR 86 of 2.1± 0.8 kpc.
| Spatially Resolved STIS Spectra of WR+OB Binaries with Colliding Winds
We present spatially resolved spectra of the visual WR+OB massivebinaries WR 86, WR 146, and WR 147, obtained with the Space TelescopeImaging Spectrograph on board the Hubble Space Telescope. The systemsare classified as follows: WR 86=WC 7+B0 III, WR 146=WC 6+O8 I-IIf, WR147=WN 8+O5-7 I-II(f). Both WR 146 and WR 147 are known to have strongnonthermal radio emission arising in a wind-wind collision shock zonebetween the WR and OB components. We find that the spectra of their Ocompanions show Hα profiles in emission, indicative of largemass-loss rates and consistent with the colliding-wind model. Ourspectra indicate that the B component in WR 86 has a low mass-loss rate,which possibly explains the fact that WR 86, despite being a long-periodWR+OB binary, was not found to be a strong nonthermal radio emitter.Because of the small mass-loss rate of the B-star component in WR 86,the wind collision region must be closer to the B star and smaller ineffective area, hence generating smaller amounts of nonthermal radioemission. Absolute magnitudes for all the stars are estimated based onthe spectral types of the components (based on the tables bySchmidt-Kaler for OB stars and van der Hucht for WR stars) and comparedwith actual, observed magnitude differences. While the derivedluminosities for the WC 7 and B0 III stars in WR 86 are consistent withthe observed magnitude difference, we find a discrepancy of at least 1.5mag between the observed luminosities of the components in each of WR146 and WR 147 and the absolute magnitudes expected from their spectraltypes. In both cases, it looks as though either the WR components areabout 2 mag too bright for their spectral types or that the O componentsare about 2 mag too faint. We discuss possible explanations for thisapparent discrepancy. Based on observations with the NASA/ESA HubbleSpace Telescope, obtained at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS 5-26555.
| Episodic dust formation by HD 192641 (WR 137) - II
We present new infrared photometry of the WC7-type Wolf-Rayet star HD192641 (WR137) from 1985 to 1999. These data track the cooling of thedust cloud formed in the 1982-84 dust-formation episode from 1985 to1991, the increase of the infrared flux from 1994.5 to a newdust-formation maximum in 1997 and its subsequent fading. From these andearlier data we derive a period of 4765+/-50d (13.05+/-0.15yr) for thedust-formation episodes. Between dust-emission episodes, the infraredspectral energy distribution has the form of a power law,?F?~?-1.86. The rising branchof the infrared light curve (1994-97) differs in form from that of theepisodic dust-maker WR125. Time-dependent modelling shows that thisdifference can be attributed to a different time dependence of dustformation in WR137, which occurred approximately ~t2 untilmaximum, whereas that of WR125 could be described by a step function,akin to a threshold effect. For an adopted distance of 1.6kpc, the rateof dust formation was found to be5.0×10-8Msolaryr-1 at maximum,accounting for a fraction fC~1.5×10-3 of thecarbon flowing in the stellar wind. The fading branches of the lightcurves show evidence for secondary `mini-eruptions' in 1987, 1988 and1990, behaviour very different from that of the prototypical episodicdust-maker HD 193793 (WR140), and suggesting the presence in the WR137stellar wind of large-scale structures that are crossed by the wind-windcollision region.
| 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.
| Non-thermal emission in Wolf-Rayet stars: are massive companions required?
We examine the radio spectral indices of 23 Wolf-Rayet (WR) stars toidentify the nature of their radio emission. We identify nine systems asnon-thermal emitters. In seven of these systems the non-thermal emissiondominates the radio spectrum, while in the remaining two it is ofcomparable strength to the thermal, stellar wind emission, giving`composite' spectra. Among these nine systems, seven have knownspectroscopic or visual binary companions. The companions are allmassive O or early B-type stars, strongly supporting a connectionbetween the appearance of non-thermal emission in WR stars and thepresence of a massive companion. In three of these binaries, the originof non-thermal emission in a wind-collision region between the stars hasbeen well established in earlier work. The binary systems that exhibitonly thermal emission are all short-period systems where awind-collision zone is deep within the opaque region of the stellar windof the WR star. To detect non-thermal emission in these systems requiresoptically thin lines of sight to the wind-collision region.
| 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.
| A search for nonthermal radio emission from OB and WR stars with RATAN-600
We have searched for nonthermal radio emission from 40 OB and WR stars.Enhanced nonthermal radio emission from an early-type star could beevidence for the presence of a collapsed companion, and thus for itsorigin as the result of a supernova explosion in a massive binary. Asshown in the evolutionary calculations of joint evolution of a neutronstar and a normal star in binaries (Lipunov & Prokhorov \cite{lp}),a considerable fraction of neutron stars in binary systems having anoptical companion must be in the ejector state. A neutron star in thisstate generates a relativistic wind like an isolated radio pulsar. Mostejectors in binary systems can not be identified as radio pulsarsbecause of absorption of radiowaves in the stellar wind of the normalcompanion, but instead, they may appear as sources of high-energy quantadue to the synchrotron radiation of relativistic particles (ejected bythe radio pulsar) in the magnetic field of a normal star (Lipunov &Prokhorov \cite{lp2}; Lipunov & Nazin \cite{naz}). In this case asource of nonthermal radiation in a wide range from radio to hardgamma-ray may appear as a result of a specific reflection effect in themagnetic field of the optical companion. Cyg X-3 and the periodicradioburster LS I +610303 may be examples of just this kind.To test this idea, measurements of radio flux densities in the rangefrom 0.96 to 21.7 GHz from selected OB and WR stars were made with theRATAN-600. No nonthermal radio emission from the selected stars weredetected.
| 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
| Wolf-Rayet stars before and after Hipparcos.
Not Available
| A dedicated photometric system for the classification of Wolf-Rayet stars
We present here tests of a five-filter photometric system aimed at WRclassification. In addition to the well-known easy separation betweenthe WN and WC spectral types, these tests indicate interestingpotentialities in the discrimination of subgroups among the WN and theWC which look well related to the classical subtypes. The proposedcombinations of filters (or derived ones) bear enough discriminatingpower to satisfy some evolutionary studies in crowded fields wherespectroscopic follow-up is not possible. Based on observations collectedat the European Southern Observatory, La Silla, Chile.
| Quantitative classification of WC and WO stars
We present a quantitative classification scheme for carbon and oxygensequence Wolf-Rayet stars. Our scheme uses new high-quality optical AATand INT observations of 20 stars for which we provide narrow-bandphotometry and estimates of interstellar reddenings. In increasing orderof excitation, our spectral classes range from WC11 to WC4 forWolf-Rayet stars with a dominant carbon line visual spectrum, andsubsequently from WO4 to WO1 for those with predominantly oxygen lines.We refine existing WC and WO schemes to incorporate stars with higherand lower excitation spectral features. Both massive stars and centralstars of planetary nebulae (CSPNe) can be classified with the unifiedsystem. We have found no criterion that cleanly separates spectra of thetwo types of star, including elemental abundances (C/O or C/He).However, CSPNe show a wider range of line strength and width thanmassive stars in the same ionization subclass. Systematically lowerFWHM(Civ lambda5808) values are observed from WO-type CSPNe than frommassive WO stars. For WC4-11 stars, our primary diagnostic is theequivalent width or line flux ratio Civlambdalambda5801-12/Ciiilambda5696. We extend the use of this as theprincipal criterion throughout the WC sequence, with fewreclassifications necessary relative to Smith, Shara & Moffat. ForWO stars, Ciii is absent and our new criteria, using primarily oxygenlines, take over smoothly. We define subclasses WO4-1, using Ovilambdalambda3811-34/Ov lambda5590 as our primary diagnostic. Thecontinuation in spectral sequence from WC to WO is used to indicate thatthe sequence is a result primarily of excitation effects, rather thansignificant abundance differences. Our scheme allows us to confirm thatmassive stars and CSPNe are differently distributed over the subclasses.Around 3/5 of massive WC stars lie within the range WC5-8, while<=1/5 of CSPNe are found within these spectral types. Stars withinboth the highest (WO1) and lowest (WC10-11) excitation spectral classesare unique to CSPNe. A WC classification for the hot RCrB star V348 Sgris excluded (previously [WC12]) since both Ciii lambda5696 and Civlambda5808 are absent in its optical spectrum. Additional criteria allowus to distinguish between WC-type, `weak emission line' CSPNe, and Ostars, allowing us to reclassify the central star of IRAS 21282+5050(previously [WC11]) as an O star.
| Hubble Space Telescope Detection of Optical Companions of WR 86, WR 146, and WR 147: Wind Collision Model Confirmed
Hubble Space Telescope (HST) Wide Field Planetary Camera 2 images of therado-binary Wolf-Rayet stars WR 146 and WR 147, as well as the 0.2"visual binary WR 86, resolve each of them into two very close opticalcomponents. The colors of these optical pairs are similar, indicatingthat they are likely to be physically bound WR + OB systems at the samedistance. Comparison of the locations of the optical components of WR146 and WR 147 with high-resolution radio maps strikingly demonstratesthat the nonthermal radio components arise between the optical binarycomponents, closer to the OB component than the WR. This is as expectedif the nonthermal radio emission results from the collision of thestellar winds of the binary components seen in the HST images. Thesimilar magnitudes and colors determined for the components of WR 86from our HST images, combined with an analysis of the unresolved,combined WC7 + OB optical spectrum, indicates an absolute magnitude forthe WC7 component of about M_V ~ -5. Based on observations with theNASA/ESA Hubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.
| 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
| The 73rd Name-List of Variable Stars
Not Available
| Large IRAS Shells Around Galactic Wolf-Rayet Stars and the O Star Phase of Wolf-Rayet Evolution
Abstract image available at:http://adsabs.harvard.edu/abs/1996AJ....112.2828M
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | עקרב |
| התרוממות ימנית: | 17h18m23.06s |
| סירוב: | -34°24'30.6" |
| גודל גלוי: | 9.328 |
| תנועה נכונה: | -2.1 |
| תנועה נכונה: | -2.4 |
| B-T magnitude: | 10.223 |
| V-T magnitude: | 9.402 |
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