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The Discordance of Mass-Loss Estimates for Galactic O-Type Stars
We have determined accurate values of the product of the mass-loss rateand the ion fraction of P+4, M˙q(P+4), for asample of 40 Galactic O-type stars by fitting stellar wind profiles toobservations of the P V resonance doublet obtained with FUSE, ORFEUSBEFS, and Copernicus. When P+4 is the dominant ion in thewind [i.e., 0.5<~q(P+4)<=1], M˙q(P+4)approximates the mass-loss rate to within a factor of <~2. Theorypredicts that P+4 is the dominant ion in the winds of O7-O9.7stars, although an empirical estimator suggests that the range O4-O7 maybe more appropriate. However, we find that the mass-loss rates obtainedfrom P V wind profiles are systematically smaller than those obtainedfrom fits to Hα emission profiles or radio free-free emission bymedian factors of ~130 (if P+4 is dominant between O7 andO9.7) or ~20 (if P+4 is dominant between O4 and O7). Thesediscordant measurements can be reconciled if the winds of O stars in therelevant temperature range are strongly clumped on small spatial scales.We use a simplified two-component model to investigate the volumefilling factors of the denser regions. This clumping implies thatmass-loss rates determined from ``ρ2'' diagnostics havebeen systematically overestimated by factors of 10 or more, at least fora subset of O stars. Reductions in the mass-loss rates of this size haveimportant implications for the evolution of massive stars andquantitative estimates of the feedback that hot-star winds provide totheir interstellar environments.
| 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.
| The spectrum of the very massive binary system WR 20a (WN6ha + WN6ha): Fundamental parameters and wind interactions
We analyse the optical spectrum of the very massive binary system WR 20a(WN6ha + WN6ha). The most prominent emission lines, Hα and He iiλ 4686, display strong phase-locked profile variability. From thevariations of their equivalent widths and from a tomographic analysis,we find that part of the line emission probably arises in a windinteraction region between the stars. Our analysis of the opticalspectrum of WR 20a indicates a reddening of AV ≃ 6.0mag and a distance of 7.9 kpc, suggesting that the star actuallybelongs to the open cluster Westerlund 2. The location of the system at 1.1 pc from the cluster core could indicate that WR 20a was gentlyejected from the core via dynamical interactions. Using a non-LTE modelatmosphere code, we derive the fundamental parameters of each component:Teff = 43 000 ± 2000 K,log{Lbol/Lȯ} ≃ 6.0, dot{M} = 8.5× 10-6 Mȯ yr-1 (assuming aclumped wind with a volume filling factor f = 0.1). Nitrogen is enhancedin the atmospheres of the components of WR 20a, while carbon isdefinitely depleted. Finally, the position of the binary components inthe Hertzsprung-Russell diagram suggests that they are core hydrogenburning stars in a pre-LBV stage and their current atmospheric chemicalcomposition probably results from rotational mixing that might beenhanced in a close binary compared to a single star of same age.Based on observations collected at the European Southern Observatory, LaSilla, Chile.
| 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.
| 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.
| High-Resolution Observations of Interstellar Ca I Absorption-Implications for Depletions and Electron Densities in Diffuse Clouds
We present high-resolution (FWHM~0.3-1.5 km s-1) spectra,obtained with the AAT UHRF, the McDonald Observatory 2.7 m coudéspectrograph, and/or the KPNO coudé feed, of interstellar Ca Iabsorption toward 30 Galactic stars. Comparisons of the column densitiesof Ca I, Ca II, K I, and other species-for individual componentsidentified in the line profiles and also when integrated over entirelines of sight-yield information on relative electron densities anddepletions (dependent on assumptions regarding the ionizationequilibrium). There is no obvious relationship between the ratio N(CaI)/N(Ca II) [equal to ne/(Γ/αr) forphotoionization equilibrium] and the fraction of hydrogen in molecularform f(H2) (often taken to be indicative of the local densitynH). For a smaller sample of sight lines for which thethermal pressure (nHT) and local density can be estimated viaanalysis of the C I fine-structure excitation, the average electrondensity inferred from C, Na, and K (assuming photoionizationequilibrium) seems to be independent of nH andnHT. While the electron density (ne) obtained fromthe ratio N(Ca I)/N(Ca II) is often significantly higher than the valuesderived from other elements, the patterns of relative nederived from different elements show both similarities and differencesfor different lines of sight-suggesting that additional processesbesides photoionization and radiative recombination commonly andsignificantly affect the ionization balance of heavy elements in diffuseinterstellar clouds. Such additional processes may also contribute tothe (apparently) larger than expected fractional ionizations(ne/nH) found for some lines of sight withindependent determinations of nH. In general, inclusion of``grain-assisted'' recombination does reduce the inferred ne,but it does not reconcile the ne estimated from differentelements; it may, however, suggest some dependence of ne onnH. The depletion of calcium may have a much weakerdependence on density than was suggested by earlier comparisons with CHand CN. Two appendices present similar high-resolution spectra of Fe Ifor a few stars and give a compilation of column density data for Ca I,Ca II, Fe I, and S I.
| Spectropolarimetry of O supergiants
We present medium-resolution spectropolarimetry at high signal-to-noiseratio of the Hα emission line of 20 O-type supergiants. Five stars(25 per cent) of the sample show a statistically significant change inpolarization through the line. We combine our Hα data with newK-band spectropolarimetry and archival low-resolution opticalspectropolarimetry to determine the polarigenic mechanism in the starsthat show a line effect. We show that the line polarization change inthe binary systems is caused by the classical `dilution' mechanism, inwhich the Hα emission is essentially unpolarized and the continuumpolarization is caused by intrabinary scattering. We find that the lineeffect in HD 108 is also well modelled by pure dilution, but suggestthat the continuum polarization is the result of stochastic windclumping. A similar description applies to the continuum polarization ofHD 188001, although the line effect cannot be reproduced by puredilution. We use low-resolution spectropolarimetry to determine theinterstellar polarization vector to λ Cephei, and confirm thatthe intrinsic polarization of the object is very low (<0.1 per cent,corresponding to an equator:pole density ratio of <1.25). The linepolarization of this star is modelled using the TORUS three-dimensionalradiative-transfer code. We show that the line effect is a consequenceof symmetry breaking caused by the rapid rotation of the system (>200km s-1), and that the system is similar polarimetrically tothe O4 supergiant ζ Puppis. Finally, we note that the precision ofcurrent photo- and spectro-polarimetric observations is insufficient totest structured wind models, which predict a continuum polarization of~0.1 per cent.
| A Spectroscopic Search for Colliding Stellar Winds in O-Type Close Binary Systems. V. HD 149404
We present new Hα emission-line spectra and an analysis of themass outflow for the massive close binary HD 149404. Spectra obtainedbetween 1995 and 1997 show evidence of coherent orbital phase-relatedvariations superimposed on both long-term and short-term emissionstrength variations. We use a Doppler tomography algorithm to constructvelocity maps of the emission intensity, and these demonstrate thatemission displays two broad peaks that follow sinusoidal radial velocitycurves that are significantly different from the orbital velocity curvesof either star. We present a model for the kinematics and distributionof the emitting circumstellar gas, and we argue that most of theemission comes from wind flows from both stars into a shock regionbetween them. The binary appears to be in a post-mass transfer stage inwhich systemic mass loss dominates the evolutionary processes.
| The strange case of the massive binary HD 149404
We report the analysis of an extensive set of high-resolutionspectroscopic observations of the massive binary system HD 149404. Wecompare different techniques to measure the radial velocities of theheavily blended absorption lines and we derive a new orbital solution.The absorption lines display strong variability that slightly affectsthe orbital solution and the determination of the spectral types of thecomponents of the binary. We find that the primary is probably ofspectral type O7.5 I(f), while the secondary is most likely an ON9.7 Isupergiant. The secondary seems to be the most evolved component of thesystem and its current evolutionary status could best be explained ifthe system has undergone a Roche lobe overflow episode during the past.The secondary could actually still be rather close to filling itscritical volume and this could lead to an enhanced mass loss of thesecondary. The spectrum of HD 149404 displays many emission lines someof which show phase-locked line profile variations. In particular, theHα line displays a double-peaked morphology at orbital phases nearconjunction. We investigate the radial velocity behaviour of theemission lines and we find that some of them must be formed in aninteraction region. We propose a simple model where some of the opticalemission lines arise in a heavily bended shock region. Based onobservations collected at the European Southern Observatory (La Silla,Chile) and at the Cerro Tololo Inter-American Observatory (CTIO).
| 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
| The Ionization in the Winds of O Stars and the Determination of Mass-Loss Rates from Ultraviolet Lines
Empirical ionization fractions of C IV, N V, Si IV, and empiricalionization plus excitation fractions of C III* and N iv^* in the windsof 34 O stars and one B star have been derived. We combine the mass-lossrates derived from radio measurements and Hα with the line fittingof ultraviolet resonance lines and subordinate lines using the Sobolevplus exact integration (SEI) method. The dependence of the empiricalionization fractions, q, on the stellar effective temperature and on themean wind density is discussed. This sets constraints for the models ofionization in the winds of hot stars. The ionization and excitationfractions can be expressed in terms of an empirical radiationtemperature. This radiation temperature scales with T_eff, and we deriveempirical relations for T_rad as a function of T_eff. The radiationtemperatures are on the order of 0.5-0.9 T_eff, with significantdifferences between the ions. The derived relations between theionization fractions and the stellar parameters have an uncertainty of0.2 dex forSi IV, N V, and C iii^*, and about 0.26 dex for N iv^*. For CIV, we can only derive an expression for the mean ionization fraction inthe wind if the mass-loss rate is small, M<10^-6 M_solar yr^-1,because the C IV lines are usually saturated for higher mass-loss rates.The resulting expressions for T_rad can be used to derive the mass-lossrates from studies of ultraviolet P Cygni profiles in the range ofstellar parameters studied here: 30,000 K<~T_eff<~50,500 K,5.2<~logL/L_*<~6.4, and -7.5 M_solar<~logM<~-4.6 M_solaryr^-1. An accuracy of about a factor of 2 or better can be reached,depending on the lines that are used and the accuracy of the line fitsand the stellar parameters. The Si IV lines give the most reliablemass-loss rates, because the abundance is about the same for all Ostars, the lines saturate only for high mass-loss rates, the doubletlines only partly overlap, and the mass-loss rate is proportional to thesquare root of the column density. The radiation temperature of N Vshows a surprisingly strict relation with T_eff, with a scatter of onlyDeltaT_rad/T_eff=0.01. The mass-loss rate cannot be derived from the N Vlines, because the column density of the N V ions in the wind isindependent of M. A consistency check and a test of the method for thestars HD 14749 and HD 190429 show that the mass-loss rate derived fromthe UV lines with the ionization fractions of this paper agree very wellwith the mass-loss rate derived from new radio flux measurements.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| The FIRST Unbiased Survey for Radio Stars
Comparison of the VLA FIRST survey with various catalogs of bright starsallows an examination of the prevalence of stellar radio emissionindependent of optical selection criteria. This FIRST unbiased surveyfor radio stars covers nearly 5000 deg^2 of the northern sky to a fluxdensity limit of 0.7 mJy at 20 cm. Using astrometric catalogs thatinclude proper-motion information, we have detected 26 stellar radiosources, doubling the number of such objects previously known in thisregion of high-latitude sky. We also show that, in the absence of goodproper motions, even the 1" precision of the FIRST positions isinsufficient to avoid crippling chance coincidence rates. We calculatethe fraction of radio detections as a function of stellar magnitude andshow that, when proper motions from the Guide Star Catalog II becomeavailable, the number of stellar radio source detections should increasefourfold.
| Strömgren and Hβ photometry of O and B type stars in star-forming regions. I. Canis Major - Puppis - Vela
Strömgren and Hβ photometry of OB-stars generally brighterthan 9.5 mag in the Canis Major - Puppis - Vela region of Milky Way isreported. The observations are based on the Milky Way luminous-star (LS)identifications and are designed to create a complete, magnitude-limitedsample of LS for this field. We present new uvby photometry for 127 LSand Hβ photometry for 25 of them. These observations are part of anongoing effort to improve the completeness of the existing uvbybetadata-base for the bright OB-type stars in the Milky Way, with the aim toinvestigate the structure of selected star-forming regions. Based ondata from the Strömgren Automatic Telescope of the CopenhagenAstronomical Observatory, La Silla. Tables 3 and 4 are only available inelectronic form at the CDS via anonymous ftp to 130.79.128.5 or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Colliding Winds in Massive Binary Systems
Not Available
| A common resonance of delta SCT stars and ellipsoidal binaries.
Not Available
| 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.
| 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.
| UV Spectral Classification of O and B Stars in the Small Magellanic =
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1951N&db_key=AST
| 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)
| Three massive binaries and the Struve-Sahade effect
Not Available
| 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.
| On rotation of ellipsoidal binary systems.
Not Available
| 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.
| 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.
| Photospheric Heating in Colliding-Wind Binaries
The spectra of many massive binaries show secondary line depths that aredeeper when the secondary is approaching, a phenomenon we refer to asthe Struve-Sahade effect. Such systems are expected to contain collidingstellar winds, and we show how the X-ray flux from the bow shock thatwraps around the secondary will preferentially heat one hemisphere ofthe secondary. If the bow shock suffers any significant Coriolisdeflection due to orbital motion, then the heated surface of thesecondary will be best seen during orbital phases of secondary approach.We present model calculations for the system AO Cassiopeiae thatillustrate how the secondary's light curve appears brighter during theseorbital phases (as observed). We find that the model profiles ofspectral lines that are insensitive to or that strengthen with heatingwill appear deeper when the secondary is approaching, but the sameheating effects may be nulled or even reversed in lines that weaken withincreased temperature. This differing response of lines to heating maybe at odds with reports of systematic deepening of UV and optical lines,and thus the connection between such heating and the Struve-Sahadeeffect needs further observational and theoretical investigation.
| On the wind momentum problem of O-type stars in the galaxy
We have examined the wind momentum problem of O-type stars in theGalaxy. It is shown that the discrepancy between theoretical andempirical mass loss rates and terminal velocities can be reversed byusing recently updated values of force multiplier parameters. With thesenew values, the momentum problem found by former investigators isreversed so that there now appears to be more than enough radiationforce in order to accelerate the stellar winds of a sample of GalacticO-type stars.
| 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
| Spectroscopic binary orbits from ultraviolet radial velocities. Paper 20: HD 149404
Not Available
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