Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
A Multiwavelength Optical Emission Line Survey of Warm Ionized Gas in the Galaxy
We report on observations of several optical emission lines toward avariety of newly revealed faint, large-scale Hα-emitting regionsin the Galaxy. The lines include [N II] λ6583, [N II]λ5755, [S II] λ6716, [O III] λ5007, and He Iλ5876 obtained with the Wisconsin Hα Mapper (WHAM) towardsight lines that probe superbubbles, high-latitude filamentary features,and the more diffuse warm ionized medium (WIM). Our observations includemaps covering thousands of square degrees toward the well-knownOrion-Eridanus bubble, a recently discovered60deg×20deg bipolar superbubble centered inPerseus, plus several classical H II regions surrounding OB stars andhot evolved stellar cores. We use the emission-line data to explore thetemperature and ionization conditions within the emitting gas and theirvariations between the different emission regions. We find that in thediffuse WIM and in the faint high-latitude filamentary structures theline ratios of [N II]/Hα and [S II]/Hα are generally high,while [O III]/Hα and He I/Hα are generally low compared tothe bright classical H II regions. This suggests that the gas producingthis faint widespread emission is warmer, in a lower ionization state,and ionized by a softer spectrum than gas in classical H II regionssurrounding O stars, the presumed ionization source for the WIM. Inaddition, we find differences in physical conditions between the largebubble structures and the more diffuse WIM, suggesting that theionization of superbubble walls by radiation from interior Oassociations does not account entirely for the range of conditions foundwithin the WIM, particularly the highest values of [N II]/Hα and[S II]/Hα.
| Spectroscopic and Photometric Analysis of the O-Type Binary V1182 Aquilae: A Close Eclipsing System with a Luminous Third Body
We obtained high-resolution spectroscopy and UBV photometry of theO-type eclipsing binary V1182 Aql. In the spectra lines of a thirdcomponent were found; the presence of third light is also supported bythe solution of the light curves. New masses for both components of thebinary were derived: M1=31.0 and M2=16.6Msolar. These values differ considerably from those given byBell et al., which were obtained by neglecting the presence of a thirdbody. With Teff~43,000 K the primary component is much hotterthan expected for the previously assumed spectral type O8. Itsclassification has to be revised to O5.5, which makes V1182 Aql probablythe earliest eclipsing binary in the Galaxy. The mass of the primary issmaller than suggested by evolutionary models, while the secondaryparameters agree with a position close to the zero-age main sequence(ZAMS). The third body, which manifests itself by strong lines in theoptical spectrum and by a third light contribution of ~17% as deducedfrom the light curve solution might be detectable by interferometricmeasurements.Based on observations collected at the European Southern Observatory, LaSilla, Chile, and at the German-Spanish Astronomical Centre, Calar Alto,operated by the Max-Planck-Institut für Astronomie, Heidelberg,jointly with the Spanish National Commission for Astronomy; also basedon spectral data retrieved from the ELODIE archive at Observatoire deHaute Provence (OHP).
| On the Hipparcos parallaxes of O stars
We compare the absolute visual magnitude of the majority of bright Ostars in the sky as predicted from their spectral type with the absolutemagnitude calculated from their apparent magnitude and the Hipparcosparallax. We find that many stars appear to be much fainter thanexpected, up to five magnitudes. We find no evidence for a correlationbetween magnitude differences and the stellar rotational velocity assuggested for OB stars by Lamers et al. (1997, A&A, 325, L25), whosesmall sample of stars is partly included in ours. Instead, by means of asimulation we show how these differences arise naturally from the largedistances at which O stars are located, and the level of precision ofthe parallax measurements achieved by Hipparcos. Straightforwardlyderiving a distance from the Hipparcos parallax yields reliable resultsfor one or two O stars only. We discuss several types of bias reportedin the literature in connection with parallax samples (Lutz-Kelker,Malmquist) and investigate how they affect the O star sample. Inaddition, we test three absolute magnitude calibrations from theliterature (Schmidt-Kaler et al. 1982, Landolt-Börnstein; Howarth& Prinja 1989, ApJS, 69, 527; Vacca et al. 1996, ApJ, 460, 914) andfind that they are consistent with the Hipparcos measurements. AlthoughO stars conform nicely to the simulation, we notice that some B stars inthe sample of \citeauthor{La97} have a magnitude difference larger thanexpected.
| A radio and mid-infrared survey of northern bright-rimmed clouds
We have carried out an archival radio, optical and infrared wavelengthimaging survey of 44 Bright-Rimmed Clouds (BRCs) using the NRAO/VLA SkySurvey (NVSS) archive, images from the Digitised Sky Survey (DSS) andthe Midcourse Space eXperiment (MSX). The data characterise the physicalproperties of the Ionised Boundary Layer (IBL) of the BRCs. We haveclassified the radio detections as: that associated with the ionisedcloud rims; that associated with possible embedded Young Stellar Objects(YSOs); and that unlikely to be associated with the clouds at all. Thestars responsible for ionising each cloud are identified and acomparison of the expected ionising flux to that measured at the cloudrims is presented. A total of 25 clouds display 20 cm radio continuumemission that is associated with their bright optical rims. The ionisingphoton flux illuminating these clouds, the ionised gas pressure and theelectron density of the IBL are determined. We derive internal molecularpressures for 9 clouds using molecular line data from the literature andcompare these pressures to the IBL pressures to determine the pressurebalance of the clouds. We find three clouds in which the pressureexerted by their IBLs is much greater than that measured in the internalmolecular material. A comparison of external pressures around theremaining clouds to a global mean internal pressure shows that themajority of clouds can be expected to be in pressure equilibrium withtheir IBLs and hence are likely to be currently shocked byphotoionisation shocks. We identify one source which shows 20 cmemission consistent with that of an embedded high-mass YSO and confirmits association with a known infrared stellar cluster. This embeddedcluster is shown to contain early-type B stars, implying that at leastsome BRCs are intimately involved in intermediate to high mass starformation.Figure \ref{fig:images} and Table \ref{tbl:istars1} are only availablein electronic form at http://www.edpsciences.org
| Close binary stars in ob-association regions i. preliminary investigation
We performed a sample of O- and B-eclipsing binary stars inOB-association regions and obtained the preliminary list of 147 binariesin 45 OB-association regions. We tried to elucidate the question whether(or not) the close binaries belong to corresponding OB-associations,from the commonness of their proper motions, radial velocities anddistances. Based on the completeness of the data,the binaries aredevided into three groups and the scheme for calculation of degree ofbelonging of stars to OB-associations is developed. Necessary data arenot available for nine systems and they are given in a specific table.For 12 cases, the binaries project onto the regions of two associations.We show that 33 (22.3%) close binary stars are members, 65 (43.9%) areprobable members and 39 (26.4%) are less probable members of theOB-associations. We find that 11 binaries belong to the Galaxybackground. The comparison of the distributions of orbital periods forthe binaries in OB-associations and for O-, B-binaries of the Galaxybackground shows their considerable differences in the vicinity of thetwo-day period.
| A Galactic O Star Catalog
We have produced a catalog of 378 Galactic O stars with accuratespectral classifications that is complete for V<8 but includes manyfainter stars. The catalog provides cross-identifications with othersources; coordinates (obtained in most cases from Tycho-2 data);astrometric distances for 24 of the nearest stars; optical (Tycho-2,Johnson, and Strömgren) and NIR photometry; group membership,runaway character, and multiplicity information; and a Web-based versionwith links to on-line services.
| Masses and other parameters of massive binaries
Binary stars provide us with the means to measure stellar mass. Here Ipresent several lists of known O-type stars with reliable mass estimatesthat are members of eclipsing, double-lined spectroscopic binaries. Themasses of young, unevolved stars in binaries are suitable for testingthe predictions of evolutionary codes, and there is good agreementbetween the observed and predicted masses (based upon temperature andluminosity) if the lower temperature scale from line-blanketed modelatmospheres is adopted. A final table lists masses for systems in awide variety of advanced evolutionary stages.
| Detached double-lined eclipsing binaries as critical tests of stellar evolution. Age and metallicity determinations from the HR diagram
Detached, double-lined spectroscopic binaries that are also eclipsingprovide the most accurate determinations of stellar mass, radius,temperature and distance-independent luminosity for each of theirindividual components, and hence constitute a stringent test ofsingle-star stellar evolution theory. We compile a large sample of 60non-interacting, well-detached systems mostly with typical errorssmaller than 2% for mass and radius and smaller than 5% for effectivetemperature, and compare them with the properties predicted by stellarevolutionary tracks from a minimization method. To assess the systematicerrors introduced by a given set of tracks, we compare the resultsobtained using three widely-used independent sets of tracks, computedwith different physical ingredients (the Geneva, Padova and Granadamodels). We also test the hypothesis that the components of thesesystems are coeval and have the same metallicity, and compare thederived ages and metallicities with the ones obtained by fitting asingle isochrone to the system. Overall, there is a good agreement amongthe different determinations, and we provide a comprehensive discussionon the sub-sample of systems which either present problems or haveestimated metallicities. Although within the errors the published trackscan fit most of the systems, a large degeneracy between age andmetallicity remains. The power of the test is thus limited because themetallicities of most of the systems are unknown. The full version ofTable 6 is only available in the electronic form athttp://www.edpsciences.org
| A Dozen Colliding-Wind X-Ray Binaries in the Star Cluster R136 in the 30 Doradus Region
We analyzed archival Chandra X-ray observations of the central portionof the 30 Doradus region in the Large Magellanic Cloud. The imagecontains 20 X-ray point sources with luminosities between5×1032 and 2×1035 ergs s-1(0.2-3.5 keV). A dozen sources have bright WN Wolf-Rayet or spectraltype O stars as optical counterparts. Nine of these are within ~3.4 pcof R136, the central star cluster of NGC 2070. We derive an empiricalrelation between the X-ray luminosity and the parameters for the stellarwind of the optical counterpart. The relation gives good agreement forknown colliding-wind binaries in the Milky Way Galaxy and for theidentified X-ray sources in NGC 2070. We conclude that probably allidentified X-ray sources in NGC 2070 are colliding-wind binaries andthat they are not associated with compact objects. This conclusioncontradicts earlier studies where it was argued, using ROSAT data, thattwo earlier discovered X-ray sources are accreting black hole binaries.Five of the 18 brightest stars in R136 are not visible in our X-rayobservations. These stars either are single, have low-mass companions,or have very wide orbits. The resulting binary fraction among early-typestars is then unusually high (at least 70%).
| The dominant X-ray wind in massive star binaries
We investigate which shocked wind is responsible for the majority of theX-ray emission in colliding wind binaries, an issue where there is someconfusion in the literature, and which we show is more complicated thanhas been assumed. We find that where both winds rapidly cool (typicallyclose binaries), the ratio of the wind speeds is often more importantthan the momentum ratio, because it controls the energy flux ratio, andthe faster wind is generally the dominant emitter. When both winds arelargely adiabatic (typically long-period binaries), the slower anddenser wind will cool faster and the stronger wind generally dominatesthe X-ray luminosity.
| Wind Accretion and Binary Evolution of the Microquasar LS 5039
There is much evidence to suggest that stellar wind capture, rather thanRoche lobe overflow, serves as the mechanism for accretion onto thecompact secondary object in the massive X-ray binary LS 5039. The lackof significant emission combined with only a modest X-ray flux providesobservational evidence that no large-scale mass transfer is occurring(consistent with our estimate of the radius of the O6.5 V((f)) opticalstar that is smaller than its critical Roche radius). Here we determinethe mass-loss rate of the optical star from the broad, residual emissionin the Hα profile. Using a stellar wind accretion model for arange in assumed primary mass, we compute the predicted X-ray luminosityfor the system. We compare our results to the observed X-ray luminosityto determine the mass of the compact object for each case. The companionappears to be a neutron star with a mass between 1 and 3Msolar. With our new constraints on the masses of bothcomponents, we discuss their implications on the evolution of the systembefore and after the supernova event that created the compact companion.The binary experienced significant mass loss during the supernova, andwe find that the predictions for the resulting runaway velocity agreewell with the observed peculiar space velocity. LS 5039 may be thefastest runaway object among known massive X-ray binaries.
| High-mass binaries in the very young open cluster NGC 6231. Implication for cluster and star formation
New radial-velocity observations of 37 O- and B stars in the very youngopen cluster NGC 6231 confirm the high frequency of short-periodspectroscopic binaries on the upper main sequence. Among the 14 O-typestars, covering all luminosity classes from dwarfs to supergiants, 8 aredefinitively double-lined systems and all periods but one are shorterthan 7 days. Several additional binaries have been detected among theearly B-type stars. NGC 6231 is an exceptional cluster to constrain thescenarios of cluster- and binary-star formation over a large range ofstellar masses. We discuss the evidences, based on NGC 6231 and 21 otherclusters, with a total of 120 O-type stars, for a clear dichotomy in themultiplicity rate and structure of very young open clusters containingO-type stars in function of the number of massive stars. However, wecannot answer the question whether the observed characteristics resultfrom the formation processes or from the early dynamical evolution.
| Tomographic Separation of Composite Spectra. VII. The Physical Properties of the Massive Triple System HD 135240 (δ Circini)
We present the results of a radial velocity study of the massive,double-lined, O binary HD 135240 based primarily on UV spectroscopy fromthe International Ultraviolet Explorer. Cross-correlation methodsindicate the presence of a third stationary spectral line componentwhich indicates that the system is a triple consisting of a central 3.9day close binary with a distant companion. We measured radial velocitiesfrom the cross-correlation functions after removal of the thirdcomponent, and we combined these with velocities obtained from Hαspectroscopy to reassess the orbital elements. We applied a Dopplertomography algorithm to reconstruct the individual UV spectra of allthree stars, and we determine spectral classifications of O7 III-V, O9.5V, and B0.5 V for the primary, secondary, and tertiary, respectively,using UV criteria defined by Penny, Gies, & Bagnuolo. We comparethese reconstructed spectra to standard single-star spectra to find theUV flux ratios of the components(F2/F1=0.239+/-0.022, andF3/F1=0.179+/-0.021). Hipparcos photometry revealsthat the central pair is an eclipsing binary, and we present the firstmodel fit of the light curve from which we derive an orbitalinclination, i=74deg+/-3deg. This analysisindicates that neither star is currently experiencing Roche lobeoverflow. We place the individual components in the theoretical H-Rdiagram, and we show that the masses derived from the combinedspectroscopic and photometric analysis(Mp/Msolar=21.6+/-2.0 andMs/Msolar=12.4+/-1.0) are significantly lower thanthose computed from evolutionary tracks for single stars.
| 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
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| On the Correlation between CO Absorption and Far-Ultraviolet Nonlinear Extinction toward Galactic OB Stars
A sample of 59 sight lines to reddened Galactic OB stars was examinedfor correlations of the strength of the CO Fourth Positive(A1Π-X1Σ+) absorption bandsystem with the ultraviolet interstellar extinction curve parameters. Weused archival high-dispersion NEWSIPS IUE spectra to measure the COabsorption for comparison with parametric fits of the extinction curvesfrom the literature. A strong correlation with the nonlinear far-UVcurvature term was found with greater absorption, normalized to E(B-V),being associated with more curvature. A weaker trend with the linearextinction term was also found. Mechanisms for enhancing CO in dustenvironments exhibiting high nonlinear curvature are discussed.
| Oxygen and helium abundances in Galactic Hii regions - I. Observations
Absolute integrated line fluxes of Hii regions have been measured usinga Fabry-Perot spectrophotometer. We describe the observations andcalibration procedures. Fluxes are given for 36 Hii regions withGalactocentric distances ranging from 6.6 to 17.7kpc. Several emissionlines have been measured, mainly [Oii] λλ3726 and 3629,Hβ, [Oiii] λ5007, Hei λ5876 and Hα. The veryfaint [Oiii] λ4363 line has been measured in six regions,allowing a direct determination of the electron temperature. Newphotometric distances have been derived based on data from theliterature. A discussion of these results in terms of extinction,electron density and temperature, and oxygen and helium abundances isgiven in Paper II.
| Limb-darkening coefficients of illuminated atmospheres. I. Results for illuminated line-blanketed models with 3 700 K < T_eff < 7 000 K
The effect of mutual illumination in a close binary on thelimb-darkening coefficients is studied using the UMA (Uppsala ModelAtmosphere) code in convective line-blanketed atmospheres illuminated byline-blanketed fluxes, for 3 700 K
| 1-m spectroscopy of normal OB stars
We have obtained spectra of 70 normal OB stars in the near-IR I(1-μm) band. The strongest features are those due to lines of thehydrogen Paschen series and neutral and ionized helium, which are, forthe most part, in absorption. The information content in this spectralrange is sufficient for only a rough classification of hot stars into`early O', `late O' and `B' types. Curiously, the leading He i tripletline, He i λ1.0830 μm, is usually not detectable, although ina few stars it is in emission; its behaviour generally correlates withthe leading helium singlet line, He i λ 2.058 μ m. These twofeatures appear to be present in emission only in stars with extremes ofmass loss or wind extension.
| Apsidal Motion in Double Stars. I. Catalog
A catalog of 128 double stars with measured periods of apsidal motion iscompiled. Besides the apsidal periods, the orbital elements of binariesand physical parameters of components (masses, radii, effectivetemperatures, surface gravities) are given. The agreement of the apsidalperiods found by various authors is discussed.
| The binary system V373 Cas: orbital elements, parameters of the components, and helium abundance
CCD spectra with high resolution and large signal-to-noise ratio areused to study the binary system V373 Cas, which includes two early Bstars, and is apparently undergoing a very early phase of mass exchangebetween the components. The new radial velocity measurements made itpossible to improve the system's orbital elements and to refine the massestimates for the components: M_orb = 18.6 +/- 2.4 M for the primary(star A) and 14.2 +/- 1.9M_solar for the secondary (star B). Aself-consistent method for estimation of the effective temperature andgravitational acceleration yields T_eff = 23,200 +/- 600 K and lg g= 3.0+/- 0.2 for component A and T_eff = 26,800 +/- 1500 K and lg g = 3.5 +/-0.2 for component B. These parameters correspond to the spectral typesB0.5-B1 (II-Ib) for A and B0.5 III for B. The helium abundance isenhanced in the atmospheres of both components: He/H = 0.23 +/- 0.03 and0.18 +/- 0.02 for A and B, respectively. This helium abundance excessconfirms that He/H depends on age, and is consistent with the fact thatboth the components of V373 Cas are near the end of the main sequencestage. The magnesium abundance for the primary is close to the solarvalue, suggesting that its metallicity may be normal. The rotationvelocities sin i = 130 +/- 10 km/s (A) and 60 +/- 5 km/s (B) are derivedfrom the He I lines. These confirm the conclusion of Hill and Fisherthat the rotation of the components in their orbital motion isasynchronous. The masses M_ev estimated using evolutionary tracks areoverestimated by 34% for the both components, compared to the moreaccurate values M_orb determined from the orbit analysis. This is thelargest known discrepancy between M_ev and M_orb for a binary system ofthis type. The age of the system is 7-8 million years.
| 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.
| Astrophysics in 1997
Martian marvels, a gamma-ray burster with a redshift, Galileo converseswith Ganymede, a record galactic redshift of 4.92, and much else. Fiscal1997 was definitely an exciting year for astronomers. We have tried hardto hit all the obvious highlights, but also to report more gradualprogress on traditional problems of understanding planets, stars,galaxies, and the universe. Though the year was saddened by the loss ofmany valued colleagues, we nevertheless indulge in occasionalsoupçons of frivolity.
| A critique of disentangling as a method of deriving spectroscopic orbits
Multiple sets of synthetic spectra of OB-binary stars are used to testthe suitability of disentangling for deriving accurate spectroscopicorbits. Given a set of spectra with broad phase coverage and sufficienttotal integration time (almost independent of the number of spectra), itappears that disentangling yields accurate and reliable semi-amplitudesof the spectroscopic orbits (other parameters being fixed). Methods forestimating the uncertainties on the derived semi-amplitudes areinvestigated.
| ICCD speckle observations of binary stars. XIX - an astrometric/spectroscopic survey of O stars
We present the results of a speckle interferometric survey made with theCHARA speckle camera and 4 m class telescopes of Galactic O-type starswith V less than 8. We can detect with the speckle camera binaries inthe angular separation range 0.035-1.5 arcsec with delta M less than 3,and we have discovered 15 binaries among 227 O-type systems. We combinedour results on visual binaries with measurements of wider pairs from theWashington Double Star Catalog and fainter pairs from the HipparcosCatalog, and we made a literature survey of the spectroscopic binariesamong the sample. We then investigated the overall binary frequency ofthe sample and the orbital characteristics of the known binaries.Binaries are common among O stars in clusters and associations but lessso among field and especially runaway stars. There are many triplesystems among the speckle binaries, and we discuss their possible rolein the ejection of stars from clusters. The period distribution of thebinaries is bimodal in log P, but we suggest that binaries with periodsof years and decades may eventually be found to fill the gap. The massratio distribution of the visual binaries increases toward lower massratios, but low mass ratio companions are rare among close,spectroscopic binaries. We present distributions of the eccentricity andlongitude of periastron for spectroscopic binaries with ellipticalorbits, and we find strong evidence of a bias in the longitude ofperiastron distribution.
| Helium Enrichment of the Atmospheres of B and O Stars: New Aspects of the 20-Year-Old Problem
An analysis of the latest data for close binary systems consisting of Oand early B stars shows that during the first half of the lifetime onthe main sequence, the components of such systems retain the initialhelium abundance He/H = 0.08-0.09 in their atmospheres. Subsequently,He/H abruptly increases approximately twofold in a short interval ofrelative ages t/t_MS between 0.5 and 0.7, and this enhanced He/H remainsconstant until the main-sequence stage is complete. Single O starsexhibit a similar nonmonotonic dependence of He/H on t/t_MS with adiscontinuity at t/t_MS ~ 0.6. A preliminary analysis performed forsingle early B stars leads us to conclude that in this case He/H mayalso increase steeply at t/tMS 0.6. The data available for early B starsreveal no correlation of He/H with the observed projected rotationalvelocity vsini and with the equatorial rotational velocity v. Nor isthere any correlation when changing to the values of v_0sini and v_0corresponding to the initial time t = 0. It is noted that the currenttheoretical models of mixing on the main sequence can explain neitherthe abrupt increase in He/H at t/t_MS ~ 0.6 nor the lack of correlationwith rotation. New high-quality spectroscopic observations of early Bstars and new helium-abundance determinations are needed to increase theaccuracy of the initial data. In particular, of interest is to obtainaccurate values of He/H for pulsating Beta Cep stars, because most ofthem have relative ages t/t_MS > 0.5.
| A common resonance of delta SCT stars and ellipsoidal binaries.
Not Available
| Theoretical X-ray properties of colliding stellar winds in O+O star binaries
This paper on colliding wind binaries presents a detailed andquantitative comparison between theoretical models of colliding windsand X-ray observations. We concentrate on colliding stellar winds in O+Ostar binaries. We calculate the expected X-ray spectra and orbital lightcurves, and investigate the effect of different parameters (mass-lossrate, orbital separation, system inclination, etc.) on the expectedX-ray properties. In particular we investigate three model systems; onerepresenting HD 165052 with equal winds, another representing HD 57060with very unequal winds, and a third representing an intermediate case.We demonstrate the sensitive relationship between system wind parametersand the shape of the X-ray light curve, and discuss these models inrelation to recent ROSAT results on O+O star colliding wind systems. Wefind that the variation in X-ray luminosity during the orbit isprimarily a result of varying extinction of the intrinsic X-rayluminosity by the more massive wind in the system. We also present theresults of spectral fitting to our synthetic spectra.
| Time-series spectropolarimetry of the short-period Wolf-Rayet+O star binary CQ Cephei
We present time-resolved, very precise linear spectropolarimetry of theshort-period WR+O star binary CQ Cephei. We find that the N IV 4058 Aline is the best spectral diagnostic of the WR orbital motion, and wederive a semiamplitude K(WR) = 290 +/- 1 km/s and a systemic velocitygamma = -72 +/- 1 km/s. We identify an antiphase spectral feature thatwe attribute to He I 4143 A absorption by the O star. A semiamplitude of360 +/- 18 km/s is found for the O star, giving a mass ratio (WR:O) of1.24 +/- 0.06. Spectropolarimetric measurements, combined with publishedphotopolarimetry, enable a determination of the orbital inclination. Theemission-line polarization vectors allow us to separate the intrinsicand interstellar polarizations, and we find that the polarizationattributable to scattering of the WR radiation in the expanding wind issmall but may be increasing towards the UV. We note that theinclinations derived from photometric analyses of eclipsing WR+Obinaries are systematically lower than those computed from polarimetricmeasurements. The light curves from Hiltner are analyzed with LIGHT2 toconfirm that the system is in a near-contact state. The resultant massesand astrophysical parameters show a normal main-sequence O star with aWR star that has parameters typical of the WN 6 type. The distancemodulus for CQ Cep derived from our results is (V0 - MV) = 12.0.
| The ``Mass Discrepancy'' for Massive Stars: Tests of Models Using Spectroscopic Binaries
Stellar evolutionary models are often used to infer a star's mass viaits luminosity, but empirical checks on the accuracy of the theoreticalmass-luminosity relation for very massive stars have been lacking. Thisis of particular concern given that modern atmosphere models yieldsystematically smaller masses for massive stars than do evolutionarymodels, with the discrepancy being a factor of 2 for Of stars. Weattempt to resolve this mass discrepancy by obtaining new,high-resolution optical data on seven early-type spectroscopic binaries:V453 Cyg, HD 191201, V382 Cyg, Y Cyg, HD 206267, DH Cep, and AH Cep. Ourstudy produces improved spectral subtypes for the components of thesesystems, which are crucial for evaluating their luminosities andlocations in the H-R diagram. Our radial velocity study utilizes ameasuring method that explicitly accounts for the effects of pairblending. We combine our new orbit solutions with existing data oninclinations and distances when available to compare the orbital masseswith evolutionary models, and we find good agreement in all cases wherethe stars are noninteracting. (The components of V382 Cyg and DH Cepfill their Roche lobes, and in both cases we find masses substantiallylower than the masses inferred from evolutionary tracks, suggesting thatsignificant material has been lost rather than transferred. We confirmthat this same trend exists for other systems drawn from theliterature.) Our own data extends to only 15 Mȯ, althoughphotometric inclination determinations for HD 191201 and HD 206267should prove possible and will provide examples of higher mass systems.We briefly discuss suitable systems from the literature and concludethat orbit solutions provide good agreement with the evolutionary modelsto 25 Mȯ. Beyond this, most known binaries either fill their Rochelobes or have other complications. We also discuss five systems forwhich our improved data and analysis failed to yield acceptable orbitsolutions: EO Aur, IU Aur, V640 Mon (Plaskett's star), LY Aur, and 29 UWCMa all remained intractable, despite improved data.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Kral-Sefe |
| Sað Açýklýk: | 22h46m54.11s |
| Yükselim: | +58°05'03.6" |
| Görünürdeki Parlaklýk: | 8.62 |
| Uzaklýk: | 10000000 parsek |
| özdevim Sað Açýklýk: | -1.7 |
| özdevim Yükselim: | -0.8 |
| B-T magnitude: | 8.922 |
| V-T magnitude: | 8.645 |
Kataloglar ve belirtme:
|
