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New X-Ray Detections of WNL Stars
Previous studies have demonstrated that putatively single nitrogen-typeWolf-Rayet stars (WN stars) without known companions are X-ray sources.However, almost all WN star X-ray detections so far have been of earlierWN2-WN6 spectral subtypes. Later WN7-WN9 subtypes (also known as WNLstars) have proved more difficult to detect, an important exceptionbeing WR 79a (WN9ha). We present here new X-ray detections of the WNLstars WR 16 (WN8h) and WR 78 (WN7h). These new results, when combinedwith previous detections, demonstrate that X-ray emission is present inWN stars across the full range of spectral types, including later WNLstars. The two WN8 stars observed to date (WR 16 and WR 40) showunusually low X-ray luminosities (Lx ) compared to other WNstars, and it is noteworthy that they also have the lowest terminal windspeeds (v ?). Existing X-ray detections of about adozen WN stars reveal a trend of increasing Lx with windluminosity Lwind =(1/2)?v2?, suggesting that wind kineticenergy may play a key role in establishing X-ray luminosity levels in WNstars.
| A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun
Traditionally, runaway stars are O- and B-type stars with large peculiarvelocities. We would like to extend this definition to young stars (upto ?50 Myr) of any spectral type and to identify those present in theHipparcos catalogue by applying different selection criteria, such aspeculiar space velocities or peculiar one-dimensional velocities.Runaway stars are important for studying the evolution of multiple starsystems or star clusters, as well as for identifying the origins ofneutron stars. We compile the distances, proper motions, spectral types,luminosity classes, V magnitudes and B-V colours, and we utilizeevolutionary models from different authors to obtain star ages. We studya sample of 7663 young Hipparcos stars within 3 kpc from the Sun. Theradial velocities are obtained from the literature. We investigate thedistributions of the peculiar spatial velocity and the peculiar radialvelocity as well as the peculiar tangential velocity and itsone-dimensional components and we obtain runaway star probabilities foreach star in the sample. In addition, we look for stars that aresituated outside any OB association or OB cluster and the Galactic planeas well as stars for which the velocity vector points away from themedian velocity vector of neighbouring stars or the surrounding local OBassociation/cluster (although the absolute velocity might be small). Wefind a total of 2547 runaway star candidates (with a contamination ofnormal Population I stars of 20 per cent at most). Thus, aftersubtracting these 20 per cent, the runaway frequency among young starsis about 27 per cent. We compile a catalogue of runaway stars, which isavailable via VizieR.
| Spectral Variability of Romano's Star
We combine archival spectral observations of the LBV star V532 (Romano'sstar) together with existing photometric data in the B band.Spectroscopic data cover 15 years of observations (from 1992 to 2007).We show that the object in maximum of brightness behaves as an emissionline supergiant while in minimum V532 moves along the sequence of lateWN stars. In this sense, the object behaves similarly to the well-knownLuminous Blue Variable (LBV) stars AG Car and R127, but is somewhathotter at the minima. We identify about 100 spectral lines in the3700-7300Å range. As of today, our spectroscopy is the mostcomprehensive for this object. The velocity of the wind is derived usingthe He I triplet lines (360±30 km s(-1) ). Physical parameters ofthe nebula around V532 are estimated.
| AKARI's infrared view on nearby stars. Using AKARI infrared camera all-sky survey, 2MASS, and Hipparcos catalogs
Context. The AKARI, a Japanese infrared space mission, has performed anAll-Sky Survey in six infrared-bands from 9 to 180 ?m with higherspatial resolutions and better sensitivities than IRAS. Aims: Weinvestigate the mid-infrared (9 and 18 ?m) point source catalog (PSC)obtained with the infrared camera (IRC) onboard AKARI, in order tounderstand the infrared nature of the known objects and to identifypreviously unknown objects. Methods: Color-color diagramsand a color-magnitude diagram were plotted with the AKARI-IRC PSCand other available all-sky survey catalogs. We combined the Hipparcosastrometric catalog and the 2MASS all-sky survey catalog with theAKARI-IRC PSC. We furthermore searched literature and SIMBADastronomical database for object types, spectral types, and luminosityclasses. We identified the locations of representative stars and objectson the color-magnitude and color-color diagram schemes. Theproperties of unclassified sources can be inferred from their locationson these diagrams. Results: We found that the (B-V) vs.(V-S9W) color-color diagram is useful for identifying thestars with infrared excess emerged from circumstellar envelopes ordisks. Be stars with infrared excess are separated well from other typesof stars in this diagram. Whereas (J-L18W) vs. (S9W-L18W)diagram is a powerful tool for classifying several object types.Carbon-rich asymptotic giant branch (AGB) stars and OH/IR stars formdistinct sequences in this color-color diagram. Young stellarobjects (YSOs), pre-main sequence (PMS) stars, post-AGB stars, andplanetary nebulae (PNe) have the largest mid-infrared color excess andcan be identified in the infrared catalog. Finally, we plot the L18W vs.(S9W-L18W) color-magnitude diagram, using the AKARI data togetherwith Hipparcos parallaxes. This diagram can be used to identify low-massYSOs and AGB stars. We found that this diagram is comparable to the [24]vs. ([8.0]-[24]) diagram of Large Magellanic Cloud sources usingthe Spitzer Space Telescope data. Our understanding of Galactic objectswill be used to interpret color-magnitude diagram of stellar populationsin the nearby galaxies that Spitzer Space Telescope observed. Conclusions: Our study of the AKARI color-color andcolor-magnitude diagrams will be used to explore properties ofunknown objects in the future. In addition, our analysis highlights afuture key project to understand stellar evolution with a circumstellarenvelope, once the forthcoming astronometrical data with GAIA areavailable.Catalog (full Tables 3 and 4) are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/514/A2
| Disentangling the Nature of the Radio Emission in Wolf-Rayet Stars
We present quasi-simultaneous, multi-frequency Very Large Arrayobservations at 4.8, 8.4, and 22.5 GHz of a sample of 13 Wolf-Rayet (WR)stars, aimed at disentangling the nature of their radio emission and thepossible detection of a non-thermal behavior in close binary systems. Wedetected 12 stars from our sample, for which we derived spectralinformation and estimated their mass-loss rates. From our data, weidentified four thermal sources (WR 89, 113, 138, and 141), and threesources with a composite spectrum (similar contribution of thermal andnon-thermal emission; WR 8, 98, and 156). On the other hand, from thecomparison with previous observations, we confirm the non-thermalspectrum of one (WR 105), and also found evidence of a compositespectrum for WR 79a, 98a, 104, and 133. Finally, we discuss the possiblescenarios to explain the nature of the emission for the observedobjects.
| A Systematic Search for Corotating Interaction Regions in Apparently Single Galactic Wolf-Rayet Stars. I. Characterizing the Variability
We present the results of a systematic search for large-scalespectroscopic variability in apparently single Wolf-Rayet (WR) starsbrighter than v ~ 12.5. In this first paper we characterize the variousforms of variability detected and distinguish several separate groups.For each star in our sample, we obtained 4-5 high-resolution spectrawith signal-to-noise ratio ~100. Our ultimate goal is to identify newcandidates presenting variability that potentially comes from corotatinginteraction regions (CIRs). Out of a sample of 25 stars, 10 were foundto display large-scale changes of which four are of CIR-type (WR 1,WR 115, WR 120, and WR 134). The star WR 134 wasalready known to show such changes from previous studies. Three WN8stars present a different type of large-scale variability and we believedeserve a group of their own. Also, all three WC9d stars in our samplepresent large-scale variability, but it remains to be checked if theseare binaries, as many dust-making WR stars are double. Finally, of theremaining stars, 10 were found to show small-amplitude spectral changes,which we attribute to normal line-profile variability due toinhomogeneities in the wind, and five were found to show no spectralvariability, as far as can be concluded from the data in hand. Follow-upstudies are required to identify potential periods for our candidatesshowing CIR-type changes and eventually estimate a rotation rate forthese WR stars.
| Near-Infrared Spectra of 21 Wolf-Rayet Stars: Wind Clumping and Mass-Loss Rates
We present 0.9-2.4?m spectra of 21 galactic Wolf-Rayet (WR) starsthat were obtained by using an echelle spectrograph attached to the 1.5minfrared telescope in Tokyo. The observed Wolf-Rayet stars contain12WNE, 3WNL, and 6WC stars. The near-infrared continuum spectra can befitted by the superposition of stellar blackbody radiation with astellar effective temperatures, T*, of 30-60kK and free-freeradiation from the stellar wind with an electron temperature,Te, of ˜15kK. However, these calculated spectra showan excess at cm wavelength compared with the cm data for almost allstars. This may be interpreted by an infrared excess flux possibly dueto the clumping of the stellar wind gas. Assuming an ``enhancementfactor'' that depends on the distance from the center of the stars as˜r?, we can reproduce both our near-infraredspectra and the cm data by this clump-corrected free-free radiationwith mass-loss rates similar to those derived by Nugis et al. On theother hand, we also estimated the mass-loss rates from our HeI 1.083and HeII 1.012 fluxes without a consideration of clumping, although amore detailed consideration should be necessary in order to estimatemore reliable values of the mass-loss rates from the He line fluxes.
| The Galactic WN stars. Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation
Context: .Very massive stars pass through the Wolf-Rayet (WR) stagebefore they finally explode. Details of their evolution have not yetbeen safely established, and their physics are not well understood.Their spectral analysis requires adequate model atmospheres, which havebeen developed step by step during the past decades and account in theirrecent version for line blanketing by the millions of lines from ironand iron-group elements. However, only very few WN stars have beenre-analyzed by means of line-blanketed models yet. Aims: .Thequantitative spectral analysis of a large sample of Galactic WN starswith the most advanced generation of model atmospheres should provide anempirical basis for various studies about the origin, evolution, andphysics of the Wolf-Rayet stars and their powerful winds. Methods:.We analyze a large sample of Galactic WN stars by means of the PotsdamWolf-Rayet (PoWR) model atmospheres, which account for iron lineblanketing and clumping. The results are compared with a syntheticpopulation, generated from the Geneva tracks for massive starevolution. Results: .We obtain a homogeneous set of stellar andatmospheric parameters for the Galactic WN stars, partly revisingearlier results. Conclusions: .Comparing the results of ourspectral analyses of the Galactic WN stars with the predictions of theGeneva evolutionary calculations, we conclude that there is roughqualitative agreement. However, the quantitative discrepancies are stillsevere, and there is no preference for the tracks that account for theeffects of rotation. It seems that the evolution of massive stars isstill not satisfactorily understood.
| Tycho-2 stars with infrared excess in the MSX Point Source Catalogue
Stars of all evolutionary phases have been found to have excess infraredemission due to the presence of circumstellar material. To identify suchstars, we have positionally correlated the infrared Mid-Course SpaceExperiment (MSX) Point Source Catalogue and the Tycho-2 opticalcatalogue. Near-mid-infrared colour criteria have been developed toselect infrared excess stars. The search yielded 1938 excess stars; overhalf (979) have never previously been detected by IRAS. The excess starswere found to be young objects such as Herbig Ae/Be and Be stars, andevolved objects such as OH/IR (infrared) and carbon stars. A number ofB-type excess stars were also discovered whose infrared colours couldnot be readily explained by known catalogued objects.
| 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.
| Kinematical Structure of Wolf-Rayet Winds. II. Internal Velocity Scatter in WN Stars
The shortward edge of the absorption core velocities - v_black asdetermined from low resolution archived IUE spectra from the INESdatabase are presented for three P Cyg profiles of NV 1240, HeII 1640and NIV 1720 for 51 Galactic and 64 LMC Wolf-Rayet stars of the WNsubtype. These data, together with v_black of CIV 1550 line presented inNiedzielski and Skorzynski (2002) are discussed. Evidences are presentedthat v_black of CIV 1550 rarely displays the largest wind velocity amongthe four lines studied in detail and therefore its application as anestimator of the terminal wind velocity in WN stars is questioned. Anaverage v_black of several lines is suggested instead but it is pointedout that v_black of HeII 1640 usually reveals the highest observablewind velocity in Galactic and LMC WN stars. It is shown that thestratification strength decreases from WNL to WNE stars and that for WNLstars there exists a positive relation between v_black and theIonization Potential. The velocity scatter between v_black obtained fromdifferent UV lines is found to correlate well with the X-ray luminosityof single WN stars (correlation coefficient R=0.82 for the data obtainedfrom the high resolution IUE spectra) and therefore two clumpy windmodels of single WN stars are presented that allow the velocity scatterto persist up to very large distances from the stellar surface (r approx500-1000 R_*). These models are used to explain the specific features ofsingle WN stars like broad absorption troughs of strong lines havingdifferent v_black, X-ray fluxes, IR/radio continua and stratificationrelations.
| 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.
| 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.
| 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 Mid-Infrared Spectral Survey of Galactic Wolf-Rayet Stars
We present 8-13 μm spectra at resolution R~600 of 29 northernGalactic Wolf-Rayet stars, including the first ever reportedmid-infrared (MIR) spectrum for many. Among the subtypes of the starsstudied were 14 WC, 13 WN, 1 WN/WC, and an additional reclassified WN.Lines of He I and He II, along with fine-structure lines of Ne II and SIV, are strongly present in 22 of the sources observed, while six of thesources exhibit the powerful emission of heated circumstellar carbondust. We point out similarities between our spectra and Infrared SpaceObservatory (ISO) observations of several of the same sources and notean unresolved discrepancy between the two data sets for the WC6 star WR146. We investigate the diagnostic power of MIR He I and He II lines forsubtype discrimination and find the line ratio Wλ(9.7μm He II)/Wλ(11.3 μm He I+He II) can providemoderate discrimination within the WN and WC types, though the smallnumber of stars with corresponding line pairs detected made suchassessment difficult.
| Hα Emission Stars in the Cepheus OB3 Region
Hα emission objects were searched for, using the objective-prismSchmidt plates in a 36 deg^2 sky area covering the Cepheus OB3association. Hundred and eight emission stars have been found, 68 ofwhich are new findings to our knowledge. The properties of the IRASpoint sources identified with Hα emission stars indicate that mostof the Hα emission stars are T Tauri stars or related objects.Hα emission stars associated with IRAS sources and thoseunassociated have different distributions, suggesting an age sequenceamong them. Altogether, they show a ring- or shell-like surfacedistribution, which almost coincides with that of heated dusts, andthese distributions appear to be encompassed by an HI shell.
| 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.
| 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.
| Observational constraints on the efficiency of acceleration in the optically thin parts of Wolf-Rayet winds
Wolf-Rayet stars have such strong winds that their inner regions areoptically thick, preventing us from seeing the hydrostatic stellarcores. One might expect considerable acceleration of the wind to occurin the optically thick part. However, we show empirically that at least50%, and in some cases up to 100%, of the wind's acceleration occurs inthe optically thin part of the WR wind.
| A spectropolarimetric survey of northern hemisphere Wolf-Rayet stars
We present a homogeneous, high signal-to-noise spectropolarimetricsurvey of 16 northern hemisphere Wolf-Rayet (WR) stars. A reduction inpolarization at emission-line wavelengths - the `line effect' - isidentified in four stars: WRs 134, 137, 139, and 141. The magnitude ofthe effect in WR 139 (V444 Cyg) is variable, while WR 136, previouslyreported to show the line effect, does not show it in our data. Assumingthe line effect generally to arise from axisymmetric distortions ofstellar winds, we show that a model in which all WRs have the sameintrinsic (equator-on) polarization, with the observed variations solelya result of inclination effects, is inconsistent with the observations.A model in which the intrinsic polarizations are uniformly distributedis more plausible, but best-fitting results are obtained if thedistribution of polarizations is biased towards small values, with only~20 per cent of stars having intrinsic polarizations greater than ~0.3per cent. Radiative transfer calculations indicate that the observedcontinuum polarizations can be matched by models with equator:poledensity ratios of 2-3. The model spectra have electron-scattering wingsthat are significantly stronger than observed (in both intensity andpolarized flux), confirming that the winds of stars showing intrinsicpolarization must be clumped on small scales as well as being distortedon large scales. We combine the results of our survey with observationsfrom the literature to give a sample of 29 stars which have bothaccurate spectropolarimetric observations and physical parametersderived from standard-model analyses. We find that the line-effect starsare clustered at high M, L in the luminosity-mass-loss rate plane(although they are unexceptional in the terminal velocity-subtype andthe surface-mass-flux-temperature planes). The mass-loss rates derivedfrom radio-continuum observations for these stars are in good accordwith the results of optical emission-line analyses, suggesting that (i)the wind structure of line-effect stars has a density contrast which iseffectively constant with radius, and (ii) the high M values may beartefacts of large-scale wind structure. Assuming that observedspectroscopic and photometric variability of the line-effect stars isrelated to the WR rotation period, we compute equatorial rotationvelocities. These velocities correspond to ~10 per cent of the corebreakup rates, and may be large enough to produce significantwind-compression effects according to the models of Ignace, Cassinelli& Bjorkman.
| The nitrogen spectra of Wolf-Rayet stars. A grid of models and its application to the Galactic WN sample
Adopting the ``standard model'' for Wolf-Rayet atmospheres, non-LTEradiation transfer calculations are performed which account for heliumand nitrogen. Grids of theoretical models are presented for the wholerelevant parameter range. The WN classification criteria are employed inorder to identify the subtype domains, and inconsistencies arediscussed. The (almost complete) sample of known Galactic WN stars isanalyzed by comparing the observed spectra with the synthetic spectra ofthe grid models. This is the first time that nitrogen line analyses areperformed for the whole WN sample, while previous comprehensive studieswere restricted to helium models. The obtained parameters roughlyconfirm the results from the previous helium analyses, as far as latesubtypes (WNL) and early subtypes with strong lines (WNE-s) areconcerned. For early subtypes with weak lines (WNE-w), however, theparameters are substantially revised. The hottest WN star, with astellar (effective) temperature of 140kK, is WR2, which could not beanalyzed previously from its helium lines due to the lack of He I. Theother members of the WNE-w subgroup have stellar temperatures between 40and 90kK, thus populating the same temperature range as the strong-linedWNE-w, but with less dense winds. The luminosities are revised accordingto the new parameters. Moreover, reddening corrections are newlydetermined form comparing IUE data with the UV model fluxes. The averageluminosity is now log L/Lsun = 5.5 for WNE stars (both,strong and weak lined), and log L/Lsun = 5.9 for WNL (notsignificantly revised). The empirical minimum WN luminosity is10(5.0}L_{sun) , reducing former incompatibilities with predictions fromevolutionary calculations. The ratio between mechanical and radiativemomentum flow is slightly affected by the revisions, but remains muchhigher than unity: 9, 9 and 29 for the WNL, WNE-w and WNE-s subclass,respectively. Partly based on observations collected at the EuropeanSouthern Observatory (ESO), La Silla, Chile, and on archival data fromthe International Ultraviolet Explorer (IUE)
| 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.
| A comprehensive variability study of the enigmatic WN8 stars - Final results
As a conclusion of our all-sky variability survey of the 'enigmatic'variable WN8 stars, we have carried out coordinated multisitephotometric and spectroscopic observations of WN8 stars in 1989 and1994-1995. We confirm the leading role of the stellar core inrestructuring the whole wind. This emerges as a statistical trend: thehigher the level of the continuum (i.e., core) light variations, thehigher the variability of the P Cygni edges of the optical emissionlines. However, the form of the correlation between the light andprofile variations is generally different for each individual star. Thehigh level of activity of WN8 stars may be supported/induced bypulsational instability.
| 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
| Catalogue of stars in the Northern Milky Way having H-alpha in emission.
The catalogue contains 4174 stars in the Northern Milky Way, range32° ? lII< 214°, -10° < bII< +10°, having the H? line in emission. The HBH list (mainlist, Schmidt camera Hamburg-Bergedorf, red plates taken in the years1964-70) contains 1979 objects partly identical with those in otherlists of H? emission-line stars given in the literature up till1994. Non-stellar objects (e.g. H II regions, planetary nebulae) havenot been included in this catalogue except for those objects containingcentral stars which have the H? line in emission, and also forsome doubtful cases. In Part 1 the authors give the equatorial (2000.0)and galactic coordinates, the brightness and the spectrum (if existingin the literature), the membership of HBH, the estimation of continuumand H?-line intensity, the reference to the finding chart in Part2 and the cross-identification of 100 lists mostly of H? emissionline stars. In Part 2 the authors present the finding charts for morethan half of the objects; they have the "normal" orientation and mainlysize 7 arcmin square. At the end they give elementary statistics of thepresent data showing also gaps in the material.
| Infrared Spectra of Massive Stars in Transition: WNL, Of, Of/WN, Be, B[e], and Luminous Blue Variable Stars
Abstract image available at:http://adsabs.harvard.edu/abs/1996ApJ...470..597M
| A three-dimensional classification for WN stars
A three-dimensional classification for WN stars is presented using (1)the HeII 5411/HeI 5875 ratio as a primary indicator of ionization, (2)FWHM 4686 and EW 5411 as indicators of line width and strength, and (3)an oscillating Pickering decrement as an indicator of the presence ofhydrogen. All WN stars in the Galaxy and two-thirds of the LMC stars areclassified on the new system. Almost all spectra inspected fall smoothlyinto categories within which the spectra are very similar. Allionization subclasses show a tight correlation between line strength andwidth, with stars containing hydrogen at the weak, narrow end, and WN/Cstars near the strong, broad end. H^+/He^++ correlates with strength andwidth with a cut-off for the presence of hydrogen, which is slightlydependent on ionization subclass, at about FWHM 4686=30A and EW5411=25A. The correlations found indicate that high (initial) mass starsevolve as narrow-line stars from late to early ionization subclass.Lower (initial) mass stars evolve with increasing line strength andwidth, probably to earlier ionization subclass. The HeII 4686/NV,III4604-40 ratio shows a clear correlation with Galactocentric radius,presumably an effect of the Z gradient. CIV 5808/HeII 5411 shows no suchcorrelation. LMC WN stars can be classified without difficulty by thecriteria established for Galactic WN stars. While individual spectra ofa given subtype are similar in the two galaxies, the frequencydistributions over ionization subclass, over EW and FWHM in subclassesWN4 and WN5, and hydrogen content in subclasses WN6-8 are different. Theeffects are presumably due to metallicity, but the causal connection isunclear.
| Spectral atlas of the Galactic Wolf-Rayet stars (WN sequence).
Spectra of 62 (i.e. almost all) Galactic single Wolf-Rayet stars of theWN sequence are compiled. These data provided the empirical basis forour comprehensive spectral analyses of these stars published recently.The observations cover wide parts of the visual range and have aspectral resolution λ/{DELTA} λ between 2000 and 3600 inmost cases. Infrared observations around 10830A are included for 18stars. The spectra are preliminary ``rectified'' by division through anestimated stellar continuum. The whole material is displayed in conciseplots sorted by spectral subtype in order to provide an overview. Accessto the full digital data is offered via anonymous file transfer.
| 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
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Membro dei seguenti gruppi:
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Osservazione e dati astrometrici
| Costellazione: | Cefeo |
| Ascensione retta: | 23h00m10.15s |
| Declinazione: | +60°55'38.7" |
| Magnitudine apparente: | 11.013 |
| Moto proprio RA: | -4 |
| Moto proprio Dec: | 0.2 |
| B-T magnitude: | 12.521 |
| V-T magnitude: | 11.138 |
Cataloghi e designazioni:
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