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Blue and yellow long-period variables in the direction of the Small Magellanic Cloud
Aims.We investigate the nature of a sample of 17 long-term periodicvariables in the direction of the Small Magellanic Cloud. Methods:.Based on new spectroscopic data, we determined spectral types, radialvelocities, absolute magnitudes, and colors for these stars. We presenta refined discussion of their OGLE light curves along with an analysisof their 2MASS photometry. Results: .Most stars turned out to beB-A giants members of the Small Magellanic Cloud. We find a newinteracting eclipsing binary with a period of 184 days and two newearly-type ellipsoidal variables. One of our objects is the ROSAT sourceRX J0058.2-7231. We analyzed 11-years of data forthis Be X-ray binary finding that their photometric period varies by ~4%quasiperiodically, on a time scale of ~1200 days. We find evidence ofmultiple photometric periods in 2 Ae-type and 1 late-Be type stars. Thecase of OGLE00445466-7328029 is especiallyinteresting, as this late-type Be star shows a beating phenomenonprimarily caused by two closely-spaced frequencies, 0.05733 c/d (17.44d) and 0.06347 c/d (15.76 d). Four other emission-line objects showstable long-term periodicities and probably correspond to Be-starbinaries. Transient photometric periods are only found in 4 non-emissionearly-type stars.
| A Very Large Array 3.6 Centimeter Continuum Survey of Galactic Wolf-Rayet Stars
We report the results of a survey of radio continuum emission ofGalactic Wolf-Rayet (WR) stars north of δ=-46°. Theobservations were obtained at 8.46 GHz (3.6 cm) using the Very LargeArray, with an angular resolution of ~6"×9" and typical rms noiseof ~0.04 mJy beam-1. Our survey of 34 WR stars resulted in 15definite and five probable detections, 13 of these for the first time atradio wavelengths. All detections are unresolved (θ<~5"). Timevariations in flux are confirmed in the cases of WR 98a, 104, 105, and125. WR 79a and WR 89 are also variable in flux, and we suspect they arealso nonthermal emitters. Thus, of our sample 20%-30% of the detectedstars are nonthermal emitters. Average mass-loss rate determinationsobtained excluding definite and suspected nonthermal cases give similarvalues for WN (all subtypes) and WC5-7 stars[M(WN)=(4+/-3)×10-5 Msolar yr-1and M(WC5-7)=(4+/-2)×10-5 Msolaryr-1], while a lower value was obtained for WC8-9 stars[M(WC8-9)=(2+/-1)×10-5 Msolaryr-1]. Uncertainties in stellar distances largely contributeto the observed scatter in mass-loss rates. Upper limits to themass-loss rates were obtained in cases of undetected sources and forsources that probably show additional nonthermal emission.
| Morphological Analysis of H I Features. I. Metric Space Technique
This is the first of two papers on the morphological analysis of H Ifeatures. In this first paper, we use the so-called metric spacetechnique, developed by F. C. Adams and J. Wiseman. The metric spacetechnique is an image analysis, mathematical formalism used toquantitatively compare astrophysical maps according to complexity.Instead of comparing maps on a pixel-by-pixel basis, we compare themaps' one-dimensional ``output functions,'' which characterize specificmorphological/physical aspects of the maps. The tool is used to analyze28 H I features of known origin taken from the Canadian Galactic PlaneSurvey (CGPS), where the maps are scaled at 18" per pixel (resolution of1cosδ arcmin). Technical and mathematical improvements to theformalism are presented. After classifying the 28 maps according tocomplexity, we searched for correlations between this complexity rankingand other quantifiable aspects of the H I features such as age, area, HI area, distance, flux from the ionizing star(s), fractal dimension, H Imass, and |z| (the absolute value of the height of the objects, above orbelow the Galactic plane). The most interesting correlations are (1) thehigher the flux of UV photons, the more complex is the photodissociatedH I feature, and (2) the older the supernova remnant, the more complexthe H I associated with it. There is no correlation between the fractaldimension of the maps and their complexity or their physicalcharacteristics, thus showing that the metric space technique could beused as a solution to the degeneracy of the fractal dimension.
| 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.
| Radio observations of interstellar bubbles surrounding massive stars}
We show radio continuum observations of the WR ring nebulae around WR101 and WR 113 obtained using the VLA and HI 21 cm line data of theinterstellar bubble around the O type stars BD +24 deg 3866 and BD+25deg 3952 obtained with the DRAO Synthesis Telescope. We review previousradio continuum and HI line results toward WR and O-type stars.
| 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.
| 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.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable 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/qcar?J/A+A/367/521
| Exospheric models for the X-ray emission from single Wolf-Rayet stars
We review existing ROSAT detections of single Galactic Wolf-Rayet (WR)stars and develop wind models to interpret the X-ray emission. The ROSATdata, consisting of bandpass detections from the ROSAT All-Sky Survey(RASS) and some pointed observations, exhibit no correlations of the WRX-ray luminosity (LX) with any star or wind parameters ofinterest (e.g. bolometric luminosity, mass-loss rate or wind kineticenergy), although the dispersion in the measurements is quite large. Thelack of correlation between X-ray luminosity and wind parameters amongthe WR stars is unlike that of their progenitors, the O stars, whichshow trends with such parameters. In this paper we seek to (i) test byhow much the X-ray properties of the WR stars differ from the O starsand (ii) place limits on the temperature TX and fillingfactor fX of the X-ray-emitting gas in the WR winds. Adoptingempirically derived relationships for TX and fXfrom O-star winds, the predicted X-ray emission from WR stars is muchsmaller than observed with ROSAT. Abandoning the TX relationfrom O stars, we maximize the cooling from a single-temperature hot gasto derive lower limits for the filling factors in WR winds. Althoughthese filling factors are consistently found to be an order of magnitudegreater than those for O stars, we find that the data are consistent(albeit the data are noisy) with a trend of fx ∝(Mν&infy;)-1 in WR stars, as is also the casefor O stars.
| X-ray Nova Binary Systems
The physical properties of X-ray novae as close binary systems areanalysed. Observational data in X-ray, UV, optical, IR and radio rangesare summarized. Modern theoretical considerations of the problem ofX-ray novae, taking into account some new ideas and results, aredescribed. Properties of optical stars in X-ray novae are analysed. Dataabout the masses of black holes in X-ray binary systems are summarized.Possible evolutionary links between WR stars in close binary systems andX-ray novae are analysed.
| Catalogue of H-alpha emission stars in the Northern Milky Way
The ``Catalogue of Stars in the Northern Milky Way Having H-alpha inEmission" appears in Abhandlungen aus der Hamburger Sternwarte, Band XIin the year 1997. It contains 4174 stars, range {32degr <= l() II< 214degr , -10degr < b() II < +10degr } having the Hαline in emission. HBH stars and stars of further 99 lists taken from theliterature till the end of 1994 were included in the catalogue. We givethe cross-identification of stars from all lists used. The catalogue isalso available in the Centre de Données, Strasbourg ftp130.79.128.5 or http://cdsweb.u-strasbg.fr and at the HamburgObservatory via internet.
| 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
| Catalogue of stars in the northern Milky Way having H-alpha in emission
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
| The Structure of Wolf-Rayet Winds. I. Observation of Ionization Stratification in WR 6 and WR 111
Abstract image available at:http://adsabs.harvard.edu/abs/1995ApJ...454..917S
| 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
| Spectral analyses of 25 Galactic Wolf-Rayet stars of the carbon sequence.
We present a grid of helium-carbon models for Wolf-Rayet (WR) stars ofthe carbon sequence (WC) with β_ C_=0.2 (carbon mass fraction),thus extending our previously released grid with β_C_=0.6 to adifferent chemical composition. The WR model atmospheres are based onthe so-called standard assumptions. The calculations account for non-LTEradiation transfer in spherically expanding atmospheres. Helium andcarbon are represented by detailed model atoms, especially concerningthe ions Ciii and Civ. Using the model grids 25 Galactic WC stars ofintermediate subtype (WC5 to WC8) are analyzed. Subsequently we performfine analyses by calculating several individual models for each of theprogram stars. Temperatures, radii, mass-loss rates and terminalvelocities are determined together with the carbon to helium ratio. Theanalyzed WC stars are found to form two groups, which can bedistinguished by the strength of their emission lines. Stars with weaklines (WC-w) have effective temperatures close to 50kK and their windsare relatively thin, forming the continuous spectrum in regions withsmall expansion velocities. WC stars with strong lines (WC-s) havehigher effective temperatures (60 to 100kK, referring to the coreradius) and thick winds. Thus there is a strong analogy to thedistribution of the early-type WN stars (WNE-w and WNE-s, respectively).For the WC stars we determine luminosities between 10^4.7^ and10^5.5^Lsun_ and mass-loss rates from 10^-4.8^ to10^-3.9^Mȯ/yr. The carbon mass fraction varies from 0.2 to 0.6. Nocorrelation is found between the carbon abundance and any of the stellarparameters (e.g. temperature, luminosity) or the spectral subtype. Theevolution of WR stars is discussed by comparing the results of ouranalyses with evolutionary tracks.
| A Large Bubble External to the Wolf-Rayet Ring Nebula NGC 6888
Abstract image available at:http://adsabs.harvard.edu/abs/1995AJ....109.2257M
| Terminal Velocities of Wolf-Rayet Star Winds from Low Resolution IUE Spectra
Attracted by the simplicity of the recently published by Prinja (1994)method of determination of terminal wind velocities in hot stars fromlow resolution IUE spectra we investigate its application to WR stars.With a large sample of low resolution IUE spectra of WR stars we foundeven simpler, that is linear instead of square, empirical relationbetween Delta lambda as defined by Prinja (1994) and terminal windvelocity -- vinfty. Using this new empirical relation wepresent vinfty for a sample of 85 galactic and LMC stars, 19of them determined for the first time. We almost tripled the number ofterminal velocity determinations for LMC WR stars. The comparison withother determinations shows that this simple method is accurate to within10-20%. We confirm the correlation between terminal velocity and WCsubtype. We also show that terminal velocities of WN stars are lowerthan that of WCE. A comparison between galactic and LMC stars shows thatthe LMC WN stars have slower winds in most of WN subtypes.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| The ROSAT PSPC survey of the Wolf-Rayet stars
Not Available
| Low resolution IUE spectra of Wolf-Rayet stars.
We present uniformly reduced and measured equivalent widths, FWHM andobserved line fluxes for 94 "single" WR stars (34 galactic WN, 22galactic WC, 31 LMC WN and 7 LMC WC) based on the archive IUE spectra ofWR stars gathered from different observational runs and from differentepochs. The spectra are used for spectral classification in theultraviolet region and for searching correlations among the strength andwidths of emission lines of different ions. Some correlations withoptical and near IR lines observed by other authors are given as well.The set of spectra we use is almost complete to 12 magnitude andrepresentative according to spectral subtype of WR stars.
| Spectrophotometry of Wolf-Rayet stars. I - Continuum energy distributions
All available low-resolution IUE spectra are assembled for Galactic,LMC, and SMC W-R stars and are merged with ground-based optical and NIRspectra in order to collate in a systematic fashion the shapes of theseenergy distributions over the wavelength range 0.1-1 micron. They can beconsistently fitted by a power law of the form F(lambda) isapproximately equal to lambda exp -alpha over the range 1500-9000 A toderive color excesses E(B-V) and spectral indices by removing the 2175-Ainterstellar absorption feature. The WN star color excesses derived arefound to be in good agreement with those of Schmutz and Vacca (1991) andKoesterke et al. (1991). Significant heterogeneity in spectral indexvalues was generally seen with any given subtype, but the groupsconsisting of the combined set of Galactic and LMC W-R stars, theseparate WN and WC sequences, and the Galactic and LMC W-R stars allshowed a striking and consistent Gaussian-like frequency distribution ofvalues.
| A new survey of nebulae around Galactic Wolf-Rayet stars in the northern sky
Interference filter CCD images have been obtained in H-alpha andforbidden O III 5007 A for 62 Wolf-Rayet (W-R) stars, representing acomplete survey of nebulae around Galactic W-R stars in the northernsky. We find probable new ring nebulae around W-R stars number 113, 116and 132, and possible new ring nebulae around W-R stars number 133 and153. All survey images showing nebulosities around W-R stars arepresented in this paper. New physical information is derived from theimproved images of known ring nebulae. The absence of ring nebulaearound most W-R stars is discussed.
| Interpretation of Wolf-Rayet Stars - C.S. Beal's Contribution
Not Available
| Cavities around Progenitors of Ibsne - Effelsberg HI Observations Towards Six Galactic Wolf-Rayet Stars
Abstract image available at:http://adsabs.harvard.edu/abs/1992A&A...254..305A
| Chemical composition of Wolf-Rayet stars. I - Line intensities in 7 galactic WR stars
Detailed optical spectrophotometry of seven WR stars based on mediumdispersion spectra are presented. Equivalent widths and FWHM of almostall lines in the optical region are measured, absolute continua aredetermined, dereddened line fluxes are presented, the ionizationpotential versus 1/2 FWHM graphs are constructed, and new tentativeidentifications of S VI lines are proposed.
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