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Wolf Rayets: Interferometry of Hot Dust
Wolf Rayets (WRs) are hot massive stars at a late stage of evolution.They are prominent signposts for high mass star formation and theirmassive winds have significant influence on the interstellar medium. Asmall but significant number of these stars in the Galaxy are known toproduce copious amounts of dust. Given the hostile circumstellarenvironment, this raises interesting questions. Interferometric andaperture masking observations strongly indicate that binarity plays apivotal role in the dust formation. I will briefly review high angularresolution observations in the near- and mid-infrared which shed somelight on dusty WRs.
| Dust formation by colliding-wind binaries
The recent high-resolution infrared images of the enigmatic cocoon starsin the Quintuplet cluster showing them to have ``pinwheel'' tails, andthe deduction that they are colliding-wind Wolf-Rayet binaries, showshow far the study of colliding-wind dust formation has come since thefirst discovery of heated carbon dust around the classical WC9 starVe2-45 (WR 104) in the early days of infrared astronomy. The formationof dust is the least expected, and hardest to understand, processattributed to colliding stellar winds, and direct evidence of theconnection is only now becoming available. I will review recent work andconsider systems showing a range of dust-formation phenomena, includingthe prototypical epsiodic dust-maker WR 140 and the variable dust-makerWR 70, also long studied by Virpi Niemela and her colleagues.
| 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.
| Chromospheric Ca II Emission in Nearby F, G, K, and M Stars
We present chromospheric Ca II H and K activity measurements, rotationperiods, and ages for ~1200 F, G, K, and M type main-sequence stars from~18,000 archival spectra taken at Keck and Lick Observatories as a partof the California and Carnegie Planet Search Project. We have calibratedour chromospheric S-values against the Mount Wilson chromosphericactivity data. From these measurements we have calculated medianactivity levels and derived R'HK, stellar ages,and rotation periods from general parameterizations for 1228 stars,~1000 of which have no previously published S-values. We also presentprecise time series of activity measurements for these stars.Based on observations obtained at Lick Observatory, which is operated bythe University of California, and on observations obtained at the W. M.Keck Observatory, which is operated jointly by the University ofCalifornia and the California Institute of Technology. The KeckObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| 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 Asiago Database on Photometric Systems (ADPS). II. Band and reddening parameters
The Asiago Database on Photometric Systems (ADPS) is a compilation ofbasic information and reference data on 201 photometric systems (bothground-based and space-born), available in printed form (Moro &Munari \cite{Moro00}, hereafter Paper I) and electronically(http://ulisse.pd.astro.it/ADPS). Seventeen new systems have been addedto ADPS since its publication, bringing the total to 218. In this PaperII, band and reddening parameters are homogeneously computed viasynthetic photometry for the censed photometric systems with known bandtransmission profiles (179 systems). Band parameters include varioustypes of wavelengths (mean, peak, Gaussian, and effective according to aseries of representative spectral types), widths (width at half maximum,at 80% and 10% of transmission's peak, FWHM of the fitting Gaussian,equivalent, and effective for representative spectral types), moment ofthe 2nd order, skewness and kurtosis indices, and polynomial expressionsfor the behavior of effective wavelength and effective width as functionof black-body temperature. Reddening parameters include A(lambda )/A(V)for three reddening laws (characterized by RV=5.0, 3.1 and2.1) and its range of variability over the HR diagram, the Cardelli etal. (\cite{Cardelli89}) a(x) and b(x) coefficients, second order fits toA(lambda )/ EB-V for three representative spectral types, andpolynomial expressions for the behavior of effective wavelength andeffective width as function of reddening (for the RV=3.1law).Figures 9-187 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/401/781}\fnmsep\thanks{Thesource spectra used in the computations are available via the webinterface to ADPS: http://ulisse.pd.astro.it/ADPS/}
| A HST imaging survey of a sample of 61 Galactic Wolf-Rayet stars --- the WC8-9 subsample
A HST-WFPC2 survey of Galactic Wolf-Rayet stars was undertaken over afive year period, in an effort to discover new close visual companions,tight clusters, and/or association memberships. In total, 61 GalacticWR stars were observed, with nine objects being members of thesubclasses WC8 and WC9, which are associated with dust production. Forthese nine, we present images of WR 11, WR 48a, WR 69, WR 70, WR 81, andWR 92. We refer to Wallace et al. (2002) for discussion of WR 98a, WR104, and WR 112. Overall, we find for separations of approximately >=150 mas, that the binary/association properties of the WC8/WC9 sampleare statistically indistinguishable from the overall WR population. These statistics are limited, however, by the small numbers of each WRsubclass observed.Based on observations with the NASA/ESA HST obtained at the SpaceTelescope Science Institute, which is operated by AURA, Inc., under NASAcontract NAS5-26555.}
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| 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.
| A multi-epoch spectrophotometric atlas of symbiotic stars
A multi-epoch, absolute-fluxed spectral atlas extending from about 3200to 9000 Å is presented for 130 symbiotic stars, including membersof the LMC, SMC and Draco dwarf galaxies. The fluxes are accurate tobetter than 5% as shown by comparison with Tycho and ground-basedphotometric data. The spectra of 40 reference objects (MKK cool giantstandards, Mira and Carbon stars, planetary nebulae, white dwarfs, hotsub-dwarfs, Wolf-Rayet stars, classical novae, VV Cep and Herbig Ae/Beobjects) are provided to assist the interpretation of symbiotic starspectra. Astrometric positions and counterparts in astrometriccatalogues are derived for all program symbiotic stars. The spectra areavailable in electronic form from the authors. Based on observationscollected with the telescopes of the European Southern Observatory (ESO,Chile) and of the Padova & Asiago Astronomical Observatories(Italy). Tables 2 and 3 are only available in electronic form (a) at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/383/188, and (b) from thepersonal home page http://ulisse.pd.astro.it/symbio_atlas/ Figures 4-256are only available in electronic form (a) at http://www.edpsciences.organd (b) from the personal home pagehttp://ulisse.pd.astro.it/symbio_atlas/
| 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.
| Spectroscopy of WC9 Wolf-Rayet stars: a search for companions
A spectroscopic search for luminous companions to WC9-type Wolf-Rayetstars making circumstellar dust reveals the presence of absorption linesattributable to companions in the blue spectra of WR69 (HD136488) andWR104 (Ve2-45). Comparison of spectra of WR104 observed in 1995 and 1997showed the absorption lines to be more conspicuous in the latterobservation and the emission lines weaker, suggesting a selectiveeclipse of the WC9 star similar to that observed by Crowther in 1996.The WC9 emission-line spectra are shown to be less uniform thanpreviously thought, showing a significant range of Oii line strengths.The only two WC9 stars in the observed sample that do not makecircumstellar dust, WR81 (He3-1316) and WR92 (HD 157451), are found tohave anomalously weak Oii and strong Heii lines. We suggest that thesespectroscopic differences may reflect a compositional difference thatplays a role in determining which of the WC9 stars make dust.
| 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
| 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.
| On the physical model of dust around Wolf-Rayet stars
The observational infrared spectra of a number of Wolf-Rayet stars ofWC8-9 spectral classes are shown to be quite satisfactorily explained bymaking use of the detailed theoretical model of a dust shell made up ofspherical amorphous carbon grains, the dynamics, growth-destruction,thermal and electrical charge balance of which are taken into account.The dust grains acquire mainly positive electrical charge, move withsuprathermal drift velocities, and may grow up to 100-200 A as a resultof implantation of impinging carbon ions. For most of the stars, thefraction of condensed carbon does not exceed 1 percent. While the natureof the grain nucleation remains unknown, the condensation distances andthe grain seed production can be estimated by fitting the observationalspectra with theoretical ones.
| Wolf-Rayet stars and O-star runaways with HIPPARCOS. II. Photometry
Abundant {HIPPARCOS photometry over 3 years of 141 O and Wolf-Rayetstars, including 8 massive X-ray binaries, provides a magnificentvariety of light curves at the sigma ~ 1-5% level. Among the mostinteresting results, we mention: optical outbursts in HD 102567 (MXRB),coinciding with periastron passages; drastic changes in the light curveshape of HD 153919 (MXRB); previously unknown long-term variability ofHD 39680 (O6V:[n]pe var) and WR 46 (WN3p); unusual flaring of HDE 308399(O9V); ellipsoidal variations of HD 64315, HD 115071 and HD 160641;rotationally modulated variations in HD 66811=zeta Pup (O4Inf) and HD210839=lambda Cep (O6I(n)fp); dust formation episode in WR 121 (WC9). Ina statistical sense, the incidence of variability is slightly higheramong the WR stars, which might be explained by the higher percentage ofknown binary systems. Among the presumably single WR stars, thecandidate runaways appear to be more variable then the rest. Based ondata from the ESA Hipparcos astrometry satellite
| 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
| Ultraviolet Ionization Stratification in Wolf-Rayet Winds
Ionization stratification can be used to study the structure of WRwinds. In an accelerated outflow the stratification is observablethrough the Doppler effect as an inverse correlation of ionizationpotential (IP) with line width (FWHM). However, not only the averageline widths of different ions, but also the line widths of one series ofHeII show stratification. The evidence of both effects is demonstratedhere as a part of ongoing study. The ultraviolet spectra of WR starsobtained from the IUE archive are used to get the IP vs FWHM diagrams aswell as the principal quantum number n of HeII (n-3) transitions vs FWHMvelocity relations. A systematic insight into stratification in HeIIlines is provided on the basis of observations.
| Radio Continuum Measurements of Southern Early-Type Stars. II. A Distance-limited Sample of Wolf-Rayet Stars
A distance-limited sample of southern Wolf-Rayet stars within 3 kpc ofthe Sun has been observed with the Australia Telescope Compact Array at8.64 and 4.80 GHz. Radio continuum flux densities at one or bothfrequencies were obtained for 10 sources and upper limits for 20; foursources are found to be thermal emitters on the basis of the observedspectral index. Five sources are classified as nonthermal. One sourcecould not be classified. We derive mass-loss rates for the thermalsources. After combining them with all existing radio mass-loss rates ofWolf-Rayet stars in the northern and southern hemisphere, we perform acomparison with mass-loss rates derived from optical emission lines. Thetwo methods lead to consistent results, which suggests either that theassumption of a spherically symmetric, stationary, homogeneous stellarwind is correct or that deviations from this assumption affect bothmethods in the same way. Wolf-Rayet mass-loss rates are surprisinglyuniform across spectral type. We find an average mass-loss rate of 4 x10-5 Mȯ yr-1 for all types observed, except for WC9 stars, whichhave rates that are lower by at least a factor of 2. An alternativeexplanation could be partial recombination of helium from He+ to He0 inthe radio region, which would lead to a reduced number of freeelectrons, and therefore reduced radio flux for WC9 stars. Mass-lossrates of 8 x 10-5 Mȯ yr-1 for late WN stars favored in recentstellar evolution models disagree with the observations of thesesubtypes. The results of this survey suggest that ~40% of all Wolf-Rayetstars with measured spectral index are nonthermal emitters at centimeterwavelengths. This percentage is nearly twice as high as that ofnonthermal emitters among OB stars and is higher than that previouslyestimated for WR stars. The nature of the nonthermal emission is stillnot fully understood. Possible causes of nonthermal emission arediscussed. In particular, we speculate that nonthermal emission mayarise from an interaction between a thermal WR wind and surroundingmaterial owing to a shell ejected during a previous evolutionary stageor owing the wind of a companion star.
| A Radial Velocity Database for Stephenson-Sanduleak Southern Luminous Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113..823R&db_key=AST
| UBV Photometry of Southern Luminous Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2855R&db_key=AST
| 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
| Existence of a short period (3.5-4 hours) in the photometric variability of WR66.
We report here on an independent detection of a short period (~4hours)in the photometric variations of WR66, thus confirming in broad termsthe discovery by Antokhin et al.. In addition, we present the firstspectroscopic variability analysis for this star. A few peculiarities ofthe spectrum of WR66 are also discussed. Finally, we perform a briefexamination of different possible origins of the phenomenon.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| An IRAS-based Search for New Dusty Late-Type WC Wolf-Rayet Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS..100..413C&db_key=AST
| A spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
| Discovery of a possible Wolf-Rayet star at the galactic center
We report the discovery of a possible Wolf-Rayet satr located at 0.5 pcprojected radius from the center of the Galaxy. A K-band (2.2 micron)spectrum of the Galactic center object shows strong similarities withpublished K-band spectra of WC9 stars, including emission lines due toHe I at 2.06 micron, the C IV3d2D-3p2P0 multiplet with componentsbetween 2.071 and 2.084 micron, and a blend of two C III lines and He Inear 2.11 micron.
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