目录
图像
上传图像
DSS Images Other Images
相关文章
An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium
We present a survey of diffuse O VI emission in the interstellar medium(ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).Spanning 5.5 yr of FUSE observations, from launch through 2004 December,our data set consists of 2925 exposures along 183 sight lines, includingall of those with previously published O VI detections. The data wereprocessed using an implementation of CalFUSE version 3.1 modified tooptimize the signal-to-noise ratio and velocity scale of spectra from anaperture-filling source. Of our 183 sight lines, 73 show O VIλ1032 emission, 29 at >3 σ significance. Six of the 3σ features have velocities |vLSR|>120 kms-1, while the others have |vLSR|<=50 kms-1. Measured intensities range from 1800 to 9100 LU (lineunit; 1 photon cm-2 s-1 sr-1), with amedian of 3300 LU. Combining our results with published O VI absorptiondata, we find that an O VI-bearing interface in the local ISM yields anelectron density ne=0.2-0.3 cm-3 and a path lengthof 0.1 pc, while O VI-emitting regions associated with high-velocityclouds in the Galactic halo have densities an order of magnitude lowerand path lengths 2 orders of magnitude longer. Although the O VIintensities along these sight lines are similar, the emission isproduced by gas with very different properties.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Observations of the Diffuse Far-Ultraviolet Background with the Far Ultraviolet Spectroscopic Explorer
We have used observations taken under the Far Ultraviolet SpectroscopicExplorer (FUSE) S405/505 channel realignment program to explore thediffuse far-ultraviolet (FUV; 1000-1200 Å) radiation field. Of the71 independent locations in that program, we have observed a diffusesignal in 32, ranging in brightness from 1600 to a maximum of2.9×105 photons cm-2 sr-1s-1 Å-1 in Orion. The FUSE data confirm thatthe diffuse FUV sky is patchy with regions of intense emission, usuallynear bright stars, but also with dark regions, even at low Galacticlatitudes. We find a weak correlation between the FUV flux and the 100μm ratio but with wide variations, perhaps due to differences in thelocal radiation field.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by The Johns HopkinsUniversity under NASA contract NAS5-32985.
| Far Ultraviolet Spectroscopic Explorer Snapshot Survey of O VI Variability in the Winds of 66 OB-Type Stars
We have used the Far Ultraviolet Spectroscopic Explorer to conduct asnapshot survey of O VI variability in the winds of 66 OB-type stars inthe Galaxy and the Magellanic Clouds. These time series consist of twoor three observations separated by intervals ranging from a few days toseveral months. Although these time series provide the bare minimum ofinformation required to detect variations, this survey demonstrates thatthe O VI doublet in the winds of OB-type stars is variable on variousscales in both time and velocity. For spectral types from O3 to B1, 64%vary in time. At spectral types later than B1, no wind variability isobserved. In view of the limitations of this survey, this fractionrepresents a lower limit on the true incidence of variability in the OVI wind lines, which is very common and probably ubiquitous. Incontrast, for S IV and P V, only a small percentage of the whole sampleshows wind variations, although this may be principally due to selectioneffects. The observed variations extend over several hundreds ofkilometers per second of the wind profile and can be strong. The widthover which the wind O VI profile varies is only weakly correlated withthe terminal velocity (v&infy;), but a significantcorrelation (close to a 1:1 relationship) is derived between the maximumvelocity of the variation and v&infy;. High-velocity O VIwind absorption features (possibly related to the discrete absorptioncomponents seen in other wind lines) are also observed in 46% of thecases for spectral types from O3 to B0.5. These features are variable,but the nature of their propagation cannot be determined from thissurvey. If X-rays can produce sufficient O VI by Auger ionization of OIV and the X-rays originate from strong shocks in the wind, this studysuggests that stronger shocks occur more frequently nearv&infy;, causing an enhancement of O VI nearv&infy;.
| Apsidal Motion in Binaries: Rotation of the Components
A sample of 51 separated binary systems with measured apsidal periodsand rotational velocities of the components is examined. The ranges ofthe angles of inclination of the equatorial planes of the components tothe orbital plane are estimated for these systems. The observed apsidalvelocities can be explained by assuming that the axes of rotation of thestars are nonorthogonal to the orbital plane in roughly 47% of thesystems (24 of the 51) and the rotation of the components is notsynchronized with the orbital motion in roughly 59% of the systems (30of 51). Nonorthogonality and nonsynchrony are defined as deviations from90° and a synchronized angular velocity, respectively, at levels of1 or more.
| Grey extinction in the solar neighbourhood?
Some of the close O and B dwarfs appear to be fainter than indicated bytheir Hipparcos distances, intrinsic absolute magnitudes attributed totheir spectral types, and estimated selective interstellar extinction.This discrepancy is explained in the paper by the grey (neutral)interstellar extinction in the visual range of spectrum. The measure ofsuch an effect is related to discrete features of the interstellarmatter.
| A search for O VI in the winds of B-type stars
We have conducted a survey of FUSE spectra of 235 Galactic B-type starsin order to determine the boundaries in the H-R diagram for theproduction of the superion {O Vi} in their winds. By comparing thelocations and morphology of otherwise unidentified absorption featuresin the vicinity of the {O Vi} resonance doublet with the bona fide windprofiles seen in archival IUE spectra of the resonance lines of {N V},{Si Iv} and {C Iv}, we were able to detect blueshifted {O Vi} lines inthe spectra of giant and supergiant stars with temperature classes aslate as B1. No features attributable to {O Vi} were detected in dwarfslater than B0, or in stars of any luminosity class later than B1,although our ability to recognize weak absorption features in thesestars is severely restricted by blending with photospheric andinterstellar features. We discuss evidence that the ratio of the ionfractions of {O Vi} and {N V} is substantially different in the winds ofearly B-type stars than O-type stars.
| The massive and evolved EBS V380 Cygni: A case of critical evolution
The evolution and the internal structure of the double-lined eclipsingbinary V380 Cyg showing apsidal motion is investigated. The systemconsists of an evolved massive primary with a mass of 11.1 +/- 0.5Msun and a secondary which is still close to the ZAMS and hasa mass of 6.95 +/- 0.25 Msun. The core overshooting parameteralphaov was recently determined for this star as 0.6 +/- 0.1.However, such a value was derived using error bars in the effectivetemperature which seem to be unrealistically small. In addition, thereis no independent support for this value of alphaov eitherfrom Colour-Magnitude Diagrams of clusters or from double-linedeclipsing binaries. Therefore, we decided to compute stellar models withseveral values of core-overshooting parameter in order to try todisentangle this apparent disagreement. In order to compare theobservations with the theoretical predictions, we decided to use theratio of the effective temperatures,TR=Teff2/Teff1, rather than the effectivetemperatures themselves to avoid problems with calibrations and/or modelatmosphere dependencies. Contrary to what has been previouslyestablished, we have found acceptable common ages foralphaov= 0.2, 0.4, and 0.6 which fit the TR, the masses, theradii and the apsidal-motion rate simultaneously. Such indeterminationin alphaov should not be interpretated as a negative result.Instead, it indicates that errors in alphaov cannot bedetermined with a precision of 0.1 if realistic observational error barsare used; we are dealing with an EBS in a very critical phase ofevolution. Moreover, these new inferred values of alphaovimply that the dependency of convective core overshooting on the stellarmass, if it exists, is more uncertain and less pronounced than previousinvestigations suggested.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| Apsidal Motion in Detached Binary Stars: Comparison of Theory and Observations
A list of 62 detached binaries having reliable data on the rotation ofthe line of apsides is considered. Theoretical estimates of the rate ofapsidal motion are obtained. These estimates are compared withobservational data. It is shown that cases in which the theoreticalestimate exceeds the observed value are several times more frequent thancases in which the theoretical value is lower than the observed one.This discrepancy increases when systems with more reliable observationaldata are considered.
| New results on the apsidal-motion test to stellar structure and evolution including the effects of dynamic tides
We revised the current status of the apsidal-motion test to stellarstructure and evolution. The observational sample was increased by about50% in comparison to previous studies. Classical and relativisticsystems were analyzed simultaneously and only systems with accurateabsolute dimensions were considered. New interior models incorporatingrecent opacity tables, stellar rotation, mass loss, and moderate coreovershooting were used as theoretical tools to compare the predictedwith the observed shifts of the position of the periastron. The stellarmodels were computed for the precise observed masses and the adoptedchemical compositions are consistent with the corresponding tables ofopacities to avoid the inherent problems of interpolation in mass and in(X, Z). The derived chemical composition for each individual system wasused to infer the primordial helium content as well as a law ofenrichment. The values found are in good agreement with those obtainedfrom various independent sources. For the first time, the effects ofdynamic tides are taken into account systematically to determine thecontribution of the tidal distortion to the predicted apsidal-motionrate. The deviations between the apsidal-motion rates resulting from theclassical formula and those determined by taking into account theeffects of dynamic tides are presented as a function of the level ofsynchronism. For systems close to synchronisation, dynamic tides causedeviations with respect to the classical apsidal-motion formula due tothe effects of the compressibility of the stellar fluid. For systemswith higher rotational angular velocities, additional deviations due toresonances arise when the forcing frequencies of the dynamic tides comeinto the range of the free oscillation modes of the component stars. Theresulting comparison shows a good agreement between the observed andtheoretical apsidal-motion rates. No systematic effects in the sensethat models are less mass concentrated than real stars and nocorrelations with the evolutionary status of the systems were detected.
| 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
| Intrinsically-Variable B Stars in Eclipsing Binary Systems
We have investigated the use of Hipparcos epoch photometry for studyingpossible intrinsic variability in B0-B3 stars in eclipsing binarysystems with well-determined masses.
| CQ Cep - a close Wolf-Rayet binary system + a third body ?
Not Available
| Eclipsing Binaries as Astrophysical Laboratories: Internal Structure, Core Convection, and Evolution of the B-Star Components of V380 Cygni
New photometric solutions have been carried out on the importanteccentric eclipsing system V380 Cygni (B1.5 II-III+B2 V) from UBVdifferential photoelectric photometry obtained by us. The photometricelements obtained from the analysis of the light curves have beencombined with the spectroscopic solution recently published by Popper& Guinan and have led to the physical properties of the systemcomponents. The effective temperature of the stars has been determinedby fitting IUE UV spectrophotometry to Kurucz model atmospheres andcompared with other determinations from broadband and intermediate-bandstandard photometry. The values of mass, absolute radius, and effectivetemperature for the primary and secondary stars are 11.1+/-0.5Msolar, 14.7+/-0.2 Rsolar, 21,350+/-400 K, and6.95+/-0.25 Msolar, 3.74+/-0.07 Rsolar,20,500+/-500 K, respectively. In addition, a redetermination of thesystem's apsidal motion rate has been done from the analysis of 12eclipse timings obtained from 1923 to 1995. The apsidal motion studyyields the internal mass distribution of the more luminous component.Using stellar structure and evolutionary models with modern inputphysics, tests on the extent of convection in the core of the moremassive B1.5 II-III star of the system have been carried out. Both theanalysis of the logg-logTeff diagram and the apsidal motionstudy indicate a star with a larger convective core, and thus morecentrally condensed, than currently assumed. This has been quantified inform of an overshooting parameter with a value ofαov~0.6+/-0.1. Finally, the tidal evolution of thesystem (synchronization and circularization times) has also beenstudied.
| Polycyclic Aromatic Hydrocarbons and the Diffuse Interstellar Bands: A Survey
We discuss the proposal relating the origin of some of the diffuseinterstellar bands (DIBs) to neutral and ionized polycyclic aromatichydrocarbons (PAHs) present in interstellar clouds. Laboratory spectraof several PAHs, isolated at low temperature in inert gas matrices, arecompared with the spectra of five reddened early-type stars selectedfrom an extensive set of astronomical spectra. From this comparison, itis concluded that PAH ions are good candidates to explain some of theDIBs. Unambiguous assignments are difficult, however, because of theshift in wavelengths and the band broadening induced in the laboratoryspectra by the solid matrix. This situation is illustrated by acomparison with the gas-phase spectra made available recently for twoPAH ions. Definitive band assignments and, ultimately, the test of theproposal that PAH ions carry some of the DIBs must await theavailability of a larger set of gas-phase measurements in thelaboratory. The present assessment offers a guideline for futurelaboratory experiments by allowing the preselection of promising PAHmolecules to be studied in jet expansions.
| 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.
| On the relation between diffuse interstellar bands and simple molecular species
We present observations of the major diffuse interstellar bands (DIBs)at 5780 and 5797 Ä as well as literature data and our ownobservations of the violet lines of CH and CH(+) , in the lines of sighttoward some 70 stars representing various degrees of the interstellarreddening. The correlations are shown and discussed in the context ofindicators such as far-UV extinction parameters and neutral molecularabundances. The results show that the DIBs in question (lambda lambda5797 and 5780) both probably form in diffuse cloud interiors, in arelated regime where CH and H_2 form. The ratio of the two DIBscorrelates with CH abundance, confirming that the lambda 5797 carrier isfavoured in enhanced molecular gas regions over the lambda 5780 carrier.The ratio of the two DIBs correlates poorly with CH(+) abundance. Ourcompilation of observational data also suggests that the DIB ratio maybe equally useful as a cloud type indicator as is R_V, the ratio oftotal to selective extinction, and much more readily observed. Based onobservations obtained at the Russian Special Astrophysical Observatory(SAO), Terskol Observatory (TER), Canada France Hawaii Telescope (CFHT),European Southern Observatory (ESO), Observatoire de Haute-Provence(OHP)
| Determination of empirical mass-luminosity and mass-radius relations for main-sequence stars that are the components of eclipsing binary systems
Based on a new catalog of photometric, geometrical, and absoluteelements for 112 eclipsing binary systems with both components on themain sequence and with known photometric and spectroscopic orbitalelements, we redetermined the mass-luminosity and mass-radius relations:M_bol = 4.46 - 9.52 lg M (lg M > -0.4), M_bol = 6.58 - 5.00 lg M (lgM <= -0.4), lg R = 0.096 + 0.652 lg M (lg M > 0.14), lg R = 0.049+ 0.993 lg M (lg M <= 0.14). For most systems, the masses and radiiof the components are determined with an accuracy of 2-3% and 2-4%,respectively. We estimated the parameters of these relations by theleast-squares method using the procedure for correcting the estimatesthus obtained for noise in the argument.
| 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.
| Kinematic signatures of violent formation of galactic OB associations from HIPPARCOS measurements
Proper motions measured by Hipparcos confirm the large anomalousvelocities of the OB associations located around the Cygnus Superbubble(Cygnus OB1, OB3, OB7, and OB9), and reveal a clearly organizedexpanding pattern in Canis Major OB1. At the distances of theseassociations, the organized velocity patterns imply LSR velocities of upto ~ 60 km s(-1) for the associations in Cygnus, and about ~ 15 km s(-1)in Canis Major OB1. The magnitude and spatial arrangement of theexpanding motions suggests that very energetic phenomena are responsiblefor the formation of the present OB associations. This is independentlysupported by observations of the associated interstellar medium carriedout in other wavelengths. The gravitational instability scenarioproposed by Comeron & Torra 1994 (ApJ 423, 652) to account for theformation of the stars in the Cygnus Superbubble region is reviewed inthe light of the new kinematic data. It is found that the energeticrequirements set by the highest velocities on the OB associationpowering the Superbubble, Cygnus OB2, are too large by orders ofmagnitude. However, the scenario can still account for the formation ofmost of the stars if, as can be reasonably expected, the stars with thehighest measured velocities are actually runaways from Cygnus OB2itself. As for Canis Major OB1, we consider their formation in asupernova remnant, as suggested by Herbst & Assousa 1977 (ApJ, 217,473). The detection of a new runaway star, HIC 35707 (=HD 57682), whosemotion is directed away from the derived center of expansion, supportsthis scenario and provides an independent age for the supernova remnant,assuming that the runaway star was the binary companion of thesupernova. Based on a number of arguments, however, we find it unlikelythat the stars are a direct consequence of instabilities in theexpanding shell. We propose instead that their formation was triggeredin preexisting clouds, accelerated and compressed by the supernovaexplosion.
| 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.
| Determination of the internal structure constants of the components of the WR type eclipsing binary CQ Cep.
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 Catalogue of Correlations Between Eclipsing Binaries and Other Categories of Double Stars
Among the 9110 stars in The Bright Star Catalogue, there are 225eclipsing or ellipsoidal variables. A search has been made for these incatalogues of spectroscopic binaries, visual double or multiple stars,speckle interferometry, occulation binaries, and galatic clusters. Themajority of the photometric binaries are also members of groups ofhigher multiplicity. The variables are in systems ranging from one to 91stars, five on the average. 199 are either spectroscopic binaries (SB)or stars with variable radial velocity, with orbital periods known for160. Photometric periods are lacking for 48 while SB periods areavailable for 23 of these. Observers with photoelectric equipment areencouraged to plan observations to test if the SB periods are consistentwith photometric data. Observers are likewise encouraged to examinethose stars for which the photometric and SB periods appear to beinconsistent. Parallaxes are available for 86 of the stars, 41 of themindicating distances nearer than 50 parsecs.
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| The Light Curve of V1765 Cygni: A Close Binary System With a Supergiant Component
Not Available
| Eclipse Monitoring of Eccentric Binary Systems
Not Available
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Circularization and synchronization times in the main sequence of detached eclipsing binaries.I. Using the formalism by Tassoul.
We have studied a sample of selected eclipsing binaries with eccentricorbits and accurate absolute dimensions in order to analyse the validityof available theories of tidal evolution concerning synchronization andcircularization time scales. In the present investigation we pay specialattention to stars with radiative envelopes though some stars with outerlayers in convective equilibrium have been included to show differentaspects of tidal evolution. In the present paper, we have adopted forthe comparison with observational parameters, the tidal theory byTasssoul (1987, 1988). The formalism introduced by Zahn (1977, 1989)will be the subject of a separate paper. The critical values of the age,log g and R for circularization and synchronization have been computedusing a set of stellar models which include recent opacity libraries,core overshooting and mass loss. These values can be computed as afunction of the orbital period for different masses. In this way, it isrelatively simple to compare them with observational values and,therefore, to analyse the behaviour of parameters which indicate theactual situation, namely, the eccentricity and the rotationalvelocities. The comparison of observed rotational velocities withexpected values for each binary system configuration has shown thatnearly all systems in our sample are actually pseudo-synchronized withtheir orbital periods (i.e. with the fastest orbital velocity ineccentric systems) in good agreement with theoretical predictions. Theseresults, however, should be taken with some caution since the rotationof the stellar interior may be decoupled from that of the surfacelayers. With respect to circularization, a cutoff value around log t=logt_cri_(or log g_obs_=log g_cri_) shows a satisfactory agreement forobservational values of the eccentricity. Furthermore, we concluded thatthe circularization process is still active during the main sequencestage for early-type binaries.
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
