Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
A census of the Carina Nebula - I. Cumulative energy input from massive stars
The Carina Nebula (NGC 3372) is our richest nearby laboratory in whichto study feedback through ultraviolet radiation and stellar winds fromvery massive stars during the formation of an OB association, at anearly phase in the evolution of the surrounding proto-superbubble beforesupernova explosions have influenced the environment. This feedback istriggering successive generations of new star formation around theperiphery of the nebula, while simultaneously evaporating the gas anddust reservoirs out of which young stars are trying to accrete material.This paper takes inventory of the combined effect from all the knownmassive stars that power the Carina Nebula through their total ionizingflux and integrated mechanical energy from their stellar winds. Carinais close enough and accessible enough that spectral types for individualstars are available, and many close binary and multiple systems haverecently been spatially resolved, so that one can simply add them.Adopting values from the literature for corresponding spectral types,the present-day total ionizing photon luminosity produced by the 65 Ostars and three WNL stars in Carina is QH~=1051s-1, the total bolometric luminosity of allstars earlier than B2 is 2.5 × 107Lsolar,and the total mechanical luminosity of stellar winds is LSW~=105Lsolar. The total QH was about 25per cent higher when η Carinae was on the main sequence, before itand its companion were surrounded by its obscuring dust shell; for thefirst 3Myr, the net ionizing flux of the 70 O stars in Carina was about150 times greater than in the Orion Nebula. About400-500Msolar has been contributed to the HII region bystellar wind mass-loss during the past 3Myr. Values for QHand LSW are also given for the individual clusters Tr14, 15and 16, and Bo10 and 11, which are more relevant on smaller spatialscales than the total values for the whole nebula.
| Sous le vent des étoiles massives
Not Available
| Evolution of X-ray emission from young massive star clusters
The evolution of X-ray emission from young massive star clusters ismodelled, taking into account the emission from the stars as well asfrom the cluster wind. It is shown that the level and character of thesoft (0.2-10 keV) X-ray emission change drastically with cluster age andare tightly linked with stellar evolution. Using the modern X-rayobservations of massive stars, we show that the correlation betweenbolometric and X-ray luminosity known for single O stars also holds forO+O and (Wolf-Rayet) WR+O binaries. The diffuse emission originates fromthe cluster wind heated by the kinetic energy of stellar winds andsupernova explosions. To model the evolution of the cluster wind, themass and energy yields from a population synthesis are used as input toa hydrodynamic model. It is shown that in a very young cluster theemission from the cluster wind is low. When the cluster evolves, WRstars are formed. Their strong stellar winds power an increasing X-rayemission of the cluster wind. Subsequent supernova explosions pump thelevel of diffuse emission even higher. Clusters at this evolutionarystage may have no X-ray-bright stellar point sources, but a relativelyhigh level of diffuse emission. A supernova remnant may become adominant X-ray source, but only for a short time interval of a fewthousand years. We retrieve and analyse Chandra and XMM-Newtonobservations of six massive star clusters located in the LargeMagellanic Cloud (LMC). Our model reproduces the observed diffuse andpoint-source emission from these LMC clusters, as well as from theGalactic clusters Arches, Quintuplet and NGC 3603.
| A phase-resolved XMM-Newton campaign on the colliding-wind binary HD 152248
We report the first results of an XMM-Newton monitoring campaign of theopen cluster NGC 6231 in the Sco OB 1 association. This first paperfocuses on the massive colliding-wind binary HD 152248, which is thebrightest X-ray source of the cluster. The campaign, with a totalduration of 180 ks, was split into six separate observations, followingthe orbital motion of HD 152248. The X-ray flux from this systempresents a clear, asymmetric modulation with the phase and ranges from0.73 to 1.18 × 10-12 erg s-1 cm-2in the 0.5-10.0 keV energy band. The maximum of the emission is reachedslightly after apastron. The EPIC spectra are quite soft, and peakaround 0.8-0.9 keV. We characterize their shape using severalcombinations of MEKAL models and power-law spectra and we detectsignificant spectral variability in the 0.5-2.5 keV energy band.We also perform 2D hydrodynamical simulations using different sets ofparameters that closely reproduce the physical and orbital configurationof the HD 152248 system at the time of the six XMM-Newton pointings.This allows a direct confrontation of the model predictions with theconstraints deduced from the X-ray observations of the system. We showthat the observed variation of the flux can be explained by a variationof the X-ray emission from the colliding-wind zone, diluted by thesofter X-ray contribution of the two O-type stars of the system. Oursimulations also reveal that the interaction region of HD 152248 shouldbe highly unstable, giving rise to shells of dense gas that areseparated by low-density regions.Finally, we perform a search for short-term variability in the lightcurves of the system and we show that trends are present within severalof the 30-ks exposures of our campaign. Further, most of these trendsare in good agreement with the orbital motion and provide a directconstraint on the first-order derivative of the flux. In the samecontext, we also search for long-range correlations in the X-ray data ofthe system, but we only marginally detect them in the high-energy tailof the signal.
| CO-to-H2 Abundance Ratio of the Foreground Gas of the Carina Nebula
We analyze CO and H2 absorption lines of the foregroundmolecular cloud in the Carina nebula. We use HST-STIS(Hubble SpaceTelescope - Space Telescope Imaging Spectrograph) & IUE(International Ultraviolet Explorer) INES data to analyze the A-X(v=0→2) absorption band of CO for several hot stars toward theCarina nebula, while 9 stars of them have FUSE (Far UltravioletSpectroscopic Explorer) spectra to analyze the (v=0→4) vibrationalband in the Lyman series of H2. The column densities of COand H2 varies in the vicinity of N(CO) 1013cm-2 and N(H2) 1019cm-2, respectively. The resultant CO-to-H2abundance ratio is about 10-6. We investigate the variationof the abundance ratio according to the relative position of the targetstars to morphology the molecular cloud in the Carina nebula.
| 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.
| Resolving OB Systems in the Carina Nebula with the Hubble Space Telescope Fine Guidance Sensor
We observed 23 OB stars in the Carina Nebula (NGC 3372) with the HubbleSpace Telescope's Fine Guidance Sensor 1r (FGS1r) in its high angularresolution mode. Five of these OB stars are newly resolved binaries withprojected separations ranging from 0.015" to 0.352" (37 to 880 AU at adistance of 2.5 kpc), and V-band magnitude differences ranging from 0.9to 2.8. The most important astrophysical result is the unexpectedresolution of the prototype O2 If* star HD 93129A as a 55 milliarcsecond(mas) double with a ΔmV of 0.9. This object has servedas a spectroscopic benchmark for the analysis of the most massive hotstars and their winds on the prior assumption that it is a single star.This discovery supports the interpretation of recent radio and X-rayobservations as evidence of colliding-wind phenomena in HD 93129A.Another interesting result is the determination of an upper limit ofabout 35 AU for the projected separation of the binary pairs in thehierarchical double spectroscopic binary HD 93206. The high incidence ofresolved binaries provides motivation for a more thorough, statisticallymeaningful study of multiplicity among the most massive stars in theyoung ionizing clusters of the nebula to obtain a complete sample of thelong-period systems that have evaded spectroscopic detection. However,considering that the nine spectroscopic binaries with accurate orbits inthe Carina Nebula have orbital dimensions <~1 AU, which at a distanceof 2.5 kpc subtends an angle of only 0.4 mas, well below the ~=10 masangular resolution of FGS1r, there remains a significant range oforbital periods and separations over which it is very difficult todetect multiplicity in the nebula with currently available instruments.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy (AURA), Inc.,under NASA contract NAS 5-26555.
| 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.
| Preliminary results from XMM-Newton observations of the massive Wolf-Rayet binary WR 22 (WN7h+O9III-V)
We present preliminary results from observations of the massive WR+Obinary WR 22 performed with the XMM observatory. The star is brighterin the X-ray domain near apastron and fainter at periastron. The changein brightness is very progressive and mainly corresponds to a loweringof the soft part of the spectrum.
| 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.
| eta Car: the optical features at the 2003.5 low-excitation event
UBV and BVR photometry of eta Car during the 2003.5 low-excitationevent - the considered periastron passage of a binary - is presented.The light and colour curves show a number of features, which were alsoseen at previous periastron passages: a light maximum of long durationwith a superimposed flare-like event which is temporarily interrupted byan eclipse-like dip, and a steep decline in the U-B color index. The Rbrightness reached a minimum at the time of mid X-ray totality, probablyimplying that the Hα emission line reached a minimum. The sourceof the optical flare-like event is probably not the same as the onecausing the the X-ray radiation. It is tempting to consider the epoch ofthe R minimum and the mid- X ray totality - which roughly coincides withthe UBV minimum - as the central moment of the 2003.5 low-excitationevent.
| The Carina Spiral Feature: Strömgren-Hβ photometry approach. I. The photometric data-base
A data-base collating all uvbybeta photometry available at present forO-B9 stars brighter than 10th visual magnitude in the field of theCarina Spiral Feature is presented. The completeness and homogeneity ofthe data-base are discussed.Based on CDS data.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/cgi-bin/qcat?J/A+A/410/523
| XMM-Newton high-resolution X-ray spectroscopy of the Wolf-Rayet object WR 25 in the Carina OB1 association
We report the analysis of the first high-resolution X-ray spectra of theWolf-Rayet (WR) object WR 25 (HD 93162, WN6ha+O4f) obtained with theReflection Grating Spectrometers (RGS) and the European Photon ImagingCameras (EPIC-MOS and PN) CCD spectrometers on board the XMM-Newtonsatellite. The spectrum exhibits bright emission lines of the H- andHe-like ions of Ne, Mg, Si and S, as well as Fe XVII i to Fe XX and FeXXV lines. Line fluxes have been measured. The RGS and EPIC spectrahave been simultaneously fitted to obtain self-consistent temperatures,emission measures, and elemental abundances. Strong absorption by thedense WR stellar wind and the interstellar medium (ISM) is observedequivalent to NH = 7 x 1021 cm-2.Multi-temperature (DEM) fitting yields two dominant components aroundtemperatures of 7.0 and 32 MK, respectively. The XMM intrinsic (i.e.unabsorbed, corrected for the stellar wind absorption and the absorptionof ISM) X-ray luminosity of WR 25 is Lx(0.5-10 keV) = 1.3 x1034 erg s-1, and Lx(0.5-10 keV) = 0.85x 1034 erg s-1, (when correcting for the ISM only)assuming d=3.24 kpc. The obtained chemical abundances are subsolar,except for S. This may be real, but could equally well be due to a weakcoupling to the continuum, which is strongly influenced by theabsorption column density and the subtracted background. The expectedhigh N-abundance, as observed in the optical wavelength region, couldnot be confirmed due to the strong wind absorption, blocking out itsspectral signature. The presence of the Fe XXV emission-line complex at~ 6.7 keV is argued as being indicative for colliding winds inside aWR+O binary system.Based on observations obtained with XMM-Newton, an ESA science missionwith instruments and contributions directly funded by ESA Member Statesand the USA (NASA).
| 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%).
| Phase-resolved X-ray and optical spectroscopy of the massive binary HD 93403
We report the first results of a campaign aimed at the study ofearly-type binaries with the XMM-Newton observatory. Phase-resolved EPICspectroscopy of the eccentric binary HD 93403 reveals a clear orbitalmodulation of the X-ray luminosity as a function of the orbital phase.Below 1.0 keV, the observed X-ray flux is modulated by the opacity ofthe primary wind. Above 1.0 keV, the observed variation of the X-rayflux is roughly consistent with a 1/r dependence expected for anadiabatic colliding wind interaction. HD 93403 appears lessoverluminuous in X-rays than previously thought and a significantfraction of the total X-ray emission arises probably within the winds ofthe individual components of the binary. Optical monitoring of thesystem reveals strong variability of the He {II} lambda 4686 andHα line profiles. The He {II} lambda 4686 line displays a broadasymmetrical emission component which is found to be significantlystronger between phases 0.80 and 0.15 than around apastron. Thissuggests that part of the emission arises in the interaction region andmost probably in the trailing arm of a shock cone wrapped around thesecondary. Some absorption lines of the secondary's spectrum displayequivalent width variations reminiscent of the so-called Struve-Sahadeeffect. The differences in behaviour between individual lines suggestthat the temperature may not be the only relevant parameter thatcontrols this effect. Based on observations with XMM-Newton, an ESAScience Mission with instruments and contributions directly funded byESA Member states and the USA (NASA). Also based on observationscollected at the European Southern Observatory (La Silla, Chile).
| BeppoSAX broad X-ray range observations of eta Carinae during high and low spectroscopic states
We present BeppoSAX spectra of the extremely luminous and massive objecteta Car observed in a very broad X-ray range (0.1-200 keV) during highstate (December 1996) and egress from the last low state (March 1998).Both spectra are composed of at least two components, a soft one withkTs < 0.7 keV, and a hard with kTh =4.7 keV. Wefound in March 1998 a large flux defect in the 1.5-4 keV range, whilethe flux remained constant below 1.5 keV and above 5 keV. We attributethis defect to a x3.5 increase of the absorbing matter in front of thehard component, while its temperature and unabsorbed luminosity werenearly the same in the two epochs. In December 1996 the PDS X-ray fluxin the 13-20 keV range is larger than the extrapolated hard spectrum,indicating the presence of an even harder additional component, whichpossibly declined during the March 1998 low state. Conversely, we findthat at that time, the flux of the 6.7 keV iron line was 40% stronger.Coordinated optical and NIR spectroscopic observations indicate that inMarch 1998 eta Car was still in a state of low excitation of theemission line spectrum, with extended P Cygni absorptions. These resultsindicate that after the X-ray flux minimum, the hard component recoveredits high state luminosity more rapidly than the high ionization spectrallines, but in the meantime it was partly occulted by a large amount ofabsorbing matter placed in front of the source. These results arediscussed in the framework of the proposed binary model of eta Car.Based on space observations collected with the BeppoSAX X-Ray AstronomySatellite which is a program of the Agenzia Spaziale Italiana withparticipation of the Netherlands Agency for Aerospace Programs, and onspectroscopic observations obtained at the Laboratório Nacionalde Astrofísica (LNA/MCT), Brazil, and at the Complejo AstronomicoEl Leoncito (CASLEO), Argentina.
| O Iiject{HD 152248}: Evidence for a colliding wind interaction
We present the results of a four year spectroscopic campaign on theearly-type binary system HD 152248. Our analysis yields a newclassification as O7.5III(f) + O7III(f), in contradiction with previousclassifications of the components as supergiants. We derive improvedorbital elements and the corresponding masses (M_1=29.6 Msunand M_2=29.9 Msun) are somewhat larger than previouslyreported in the literature, although they are still significantly lowerthan the ones expected from evolutionary tracks. Both components of thesystem are close to filling their Roche lobe at periastron passage. Wealso investigate the equivalent width variations of the lines of the twocomponents and we discuss their relation to the Struve-Sahade effect.Finally, we show that the line profile variability of the He Iil4686 andHα lines is consistent with a strong wind interaction between thetwo stars, quite as predicted by current colliding wind models. Based ondata collected at the European Southern Observatory (La Silla, Chile)and at the Cerro Tololo Inter-American Observatory (Cerro Tololo,Chile).
| 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
| 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.
| A new orbital solution for the massive binary system HD 93403
We present a spectroscopic analysis of the early-type massive binarysystem HD 93403. Using high resolution optical spectra, we clearlyseparate the primary and secondary components. For the first time, weare able to provide an orbital solution for both stars. Our new orbitalparameters show discrepancies with the previous solution published byThackeray & Emerson (?). We further discuss several spectralfeatures of HD 93403. We finally derive qualitative constraints on theinclination of the system and we discuss its evolutionary status and theposition of both components in the Hertzsprung-Russell diagram. Based onobservations collected at the European Southern Observatory (La Silla,Chile) and the Cerro Tololo Inter-American Observatory (CTIO).
| Five-colour photometry of OB-stars in the Southern Hemisphere
Observations of OB-stars, made in 1959 and 1960 at the Leiden SouthernStation near Hartebeespoortdam, South Africa, with the VBLUW photometerattached to the 90 cm light-collector, are given in this paper. They arecompared with photometry obtained by \cite[Graham (1968),]{gra68}\cite[Walraven & Walraven (1977),]{wal77} \cite[Lub & Pel(1977)]{lub77} and \cite[Van Genderen et al. (1984).]{gen84} Formulaefor the transformation of the present observations to those of\cite[Walraven & Walraven (1977)]{wal77} and \cite[Lub & Pel(1977)]{lub77} are given. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| On the possible explosion in the Carina nebula.
Not Available
| 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.
| Stromgren and Hβ photometry of OB stars in the region of the Carina Spiral Feature
Stromgren and Hβ photometry of 130 stars in the Carina section ofthe Milky Way is presented. The color excesses and the distances of allstars are obtained. A good agreement is found between the CM and HRdiagrams and the spatial distribution of these stars. Tables 1, 2, 4 and5 are only available in electronic form at the CDS via anonymous ftp to130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html
| Tomographic Separation of Spectra of O-Type Binary Systems
Knowledge about the individual components of O-type binaries isdifficult to obtain because of the severe line blending present in theirspectra. An important new method is Doppler tomography, an iterativescheme that uses a set of orbital phase distributed spectra and bothradial velocity curves to reconstruct the individual component spectra(see Bagnuolo, Gies & Wiggs 1992, ApJ, 385, 708). These individualspectra can then be analyzed to determine various physical properties ofthe stars. The spectral types and luminosity classes obtained provideindicators of the temperatures and gravities. The individual projectedrotational velocities can be used to test for rotational synchronizationof the orbit or rapid spin-up due to mass transfer. For stars that arecluster members, an estimate of the magnitude difference together withthe combined absolute magnitude results in individual luminosityestimates. Finally, it is possible to search for abundance differencesdue to mass transfer or loss. Here I present results of a program ofDoppler tomography of O-binaries observed with the InternationalUltraviolet Explorer (IUE). I describe cross-correlation methods thatuse narrow-lined spectral templates to obtain precise radial velocitiesand orbital velocity curves which are used in the tomography algorithm.I present results for six systems: DH Cep, HD 165052, HD 93403, HD93205,HD 149404, and HD 152248. (SECTION: Dissertation Summaries)
| 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.
| Cross-correlation characteristics of OB stars from IUE spectroscopy
We present a catalogue of homogeneous measures of the linewidthparameter, v_esin i, for 373 O-type stars and early B supergiants(including the separate components of 25 binary and three triplesystems), produced by cross-correlating high-resolution,short-wavelength IUE spectra against a `template' spectrum of tauSco. Wealso tabulate terminal velocities. There are no O supergiants in oursample with v_esin i<65 km s^-1, and only one supergiant earlier thanB5 has v_esin i<50 km s^-1, confirming that an important linebroadening mechanism in addition to rotation must be present in theseobjects. A calibration of the area under the cross-correlation peakagainst spectral type is used to obtain estimates of continuum intensityratios of the components in 28 spectroscopically binary or multiplesystems. At least seven SB2 systems show evidence for the `Struve-Sahadeeffect', a systematic variation in relative line strength as a functionof orbital phase. The stellar wind profiles of the most rapid rotator inour sample, the O9III:n* star HD 191423 (v_esin i=436km s^-1), show itto have a `wind-compressed disc' similar to that of HD 93521; this starand other rapid rotators are good candidates for studies of non-radialpulsation.
| A Survey for H alpha Emission in Massive Binaries: The Search for Colliding Wind Candidates
I report the results of the first all-sky survey of H alpha emission inthe spectra of O-type binaries. The survey includes 26 systems, of which10 have emission that extends clearly above the continuum. This is thefirst report of emission for four of these. An additional three systemsshow small distortions in the H alpha profile that may result from weakemission. I compare the distribution of emission systems in H-R diagramsfor both binary and single stars, using a survey of single O-type starsdone by Conti (1974). Emission in main-sequence systems is extremelyrare and is completely absent in my sample of binary stars. Among binarystars, 78% of the systems containing giants show some emission, while nosingle giants in Conti's sample do. In the case of supergiants, 78% ofsingle stars show emission, while all supergiant binaries show strongemission. H alpha emission may come from a variety sources, but the factthat binaries have a higher incidence and strength of emission inpost--main-sequence stages may indicate that wind interactions are acommon source of emission in massive binaries. To ascertain whether ornot colliding winds have been observed, it will be necessary to studythe H alpha line profile throughout several orbits of each candidatecolliding wind system and look for recurring orbital-phase--relatedvariations. Such a study is underway.
| A Radial Velocity Database for Stephenson-Sanduleak Southern Luminous Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113..823R&db_key=AST
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Carina |
| Ascensió Recta: | 10h45m44.12s |
| Declinació: | -59°24'28.2" |
| Magnitud Aparent: | 7.308 |
| Distancia: | 884.956 parsecs |
| Moviment propi RA: | -5.7 |
| Moviment propi Dec: | 1.8 |
| B-T magnitude: | 7.512 |
| V-T magnitude: | 7.325 |
Catàlegs i designacions:
|
