Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
UV emission line shifts of symbiotic binaries
Aims: Relative and absolute emission line shifts have beenpreviously found for symbiotic binaries, but their cause was not clear.This work aims to better understand the emission line shifts. Methods: Positions of strong emission lines were measured on archival UVspectra of Z And, AG Dra, RW Hya, SY Mus and AX Per and relative shiftsbetween the lines of different ions compared. Profiles of lines of RWHya and Z And were also examined. Results: The reality of therelative shift between resonance and intercombination lines of severaltimes ionised atoms was clearly shown except for AG Dra. This redshiftshows a well defined variation with orbital phase for Z And and RW Hya.In addition the intercombination lines from more ionised atoms andespecially O iv are redshifted with respect to those from less ionisedatoms. Other effects are seen in the profiles. Conclusions: Theresonance-intercombination line shift variation can be explained inquiescence by P Cygni shorter wavelength component absorption, due tothe wind of the cool component, which is specially strong in inferiorconjunction of this cool giant. The velocity stratification permitsabsorption of line emission. The relative intercombination line shiftsmay be connected with varying occultation of line emission near anaccretion disk, which is optically thick in the continuum.
| A giant planet in orbit around a magnetic-braking hibernating cataclysmic variable
Detections of Jupiter-like giant planets in orbit around short-periodwhite dwarf binaries should provide insight into the formation andevolution of circumbinary planets (planets orbiting both components ofshort-period binaries), as well as into the ultimate fate of planets andthe late evolutionary stage of binary stars (e.g. the evolution of thecommon envelope). However, to date no planets have been detected ascompanions to such close binaries. Here, we report the discovery of agiant planet orbiting the only known hibernating cataclysmic variable(CV), QS Vir, with a period of 7.86 yr. We analysed the variations ofthe orbital period of the eclipsing white dwarf-red dwarf binary, and avery small-amplitude cyclic change is found to be superimposed on along-term period decrease. The period oscillation has the smallestamplitude among close binary stars and can be plausibly interpreted asthe light-travel time effect via the presence of a third body. We foundthat the tertiary component is a giant planet with a mass of~6.4MJupiter at a distance of ~4.2 astronomical units (au)from the binary. The continuous decrease is explained as angularmomentum loss via magnetic braking which is driving the evolution of thehibernating CV into a normal cataclysmic binary.
| Masses and luminosities of O- and B-type stars and red supergiants
Massive stars are of interest as progenitors of supernovae, i.e.neutron stars and black holes, which can be sources of gravitationalwaves. Recent population synthesis models can predict neutron star andgravitational wave observations but deal with a fixed supernova rate oran assumed initial mass function for the population of massive stars. Here we investigate those massive stars, which are supernovaprogenitors, i.e. with O- and early B-type stars, and also allsupergiants within 3 kpc. We restrict our sample to those massive starsdetected both in 2MASS and observed by Hipparcos, i.e. only those starswith parallax and precise photometry. To determine the luminositieswe calculated the extinctions from published multi-colour photometry,spectral types, luminosity class, all corrected for multiplicity andrecently revised Hipparcos distances. We use luminosities andtemperatures to estimate the masses and ages of these stars usingdifferent models from different authors. Having estimated theluminosities of all our stars within 3 kpc, in particular for all O- andearly B-type stars, we have determined the median and mean luminositiesfor all spectral types for luminosity classes I, III, and V. Ourluminosity values for supergiants deviate from earlier results: Previouswork generally overestimates distances and luminosities compared to ourdata, this is likely due to Hipparcos parallaxes (generally moreaccurate and larger than previous ground-based data) and the fact thatmany massive stars have recently been resolved into multiples of lowermasses and luminosities. From luminosities and effective temperatureswe derived masses and ages using mass tracks and isochrones fromdifferent authors. From masses and ages we estimated lifetimes andderived a lower limit for the supernova rate of ?20 events/Myraveraged over the next 10 Myr within 600 pc from the sun. These data arethen used to search for areas in the sky with higher likelihood for asupernova or gravitational wave event (like OB associations).
| FUSE Measurements of Far-Ultraviolet Extinction. III. The Dependence on R(V) and Discrete Feature Limits from 75 Galactic Sightlines
We present a sample of 75 extinction curves derived from Far UltravioletSpectroscopic Explorer (FUSE) far-ultraviolet spectra supplemented byexisting International Ultraviolet Explorer (IUE) spectra. Theextinction curves were created using the standard pair method based on anew set of dereddened FUSE+IUE comparison stars. Molecular hydrogenabsorption features were removed using individualized H2models for each sightline. The general shape of the FUSE extinction (8.4μm-1 < λ-1 < 11μm-1) was found to be broadly consistent withextrapolations from the IUE extinction (3.3 μm-1< λ-1 < 8.6 μm-1)curve. Significant differences were seen in the strength of the far-UVrise and the width of the 2175 Å bump. All the FUSE+IUE extinctioncurves had positive far-UV slopes giving no indication that the far-UVrise was turning over at the shortest wavelengths. The dependence ofA(λ)/A(V) versus R(V)-1 in the far-UV using thesightlines in our sample was found to be stronger than tentativelyindicated by previous work. We present an updated R(V)-dependentrelationship for the full UV wavelength range (3.3μm-1 <= λ-1 <= 11μm-1). Finally, we searched for discrete absorptionfeatures in the far-ultraviolet. We found a 3σ upper limit of~0.12A(V) on features with a resolution of 250 (~4 Å width) and3σ upper limits of ~0.15A(V) for λ-1 <9.6 μm-1 and ~0.68A(V) forλ-1>9.6 μm-1 on featureswith a resolution of 104 (~0.1 Å width).
| A systematic study of variability among OB-stars based on HIPPARCOS photometry
Context: Variability is a key factor for understanding the nature of themost massive stars, the OB stars. Such stars lie closest to the unstableupper limit of star formation. Aims: In terms of statistics, thedata from the HIPPARCOS satellite are unique because of time coverageand uniformity. They are ideal to study variability in this large,uniform sample of OB stars. Methods: We used statisticaltechniques to determine an independant threshold of variabilitycorresponding to our sample of OB stars, and then applied an automaticalgorithm to search for periods in the data of stars that are locatedabove this threshold. We separated the sample stars into 4 maincategories of variability: 3 intrinsic and 1 extrinsic. The intrinsiccategories are: OB main sequence stars (~2/3 of the sample), OBe stars(~10%) and OB Supergiant stars (~1/4).The extrinsic category refers toeclipsing binaries. Results: We classified about 30% of the wholesample as variable, although the fraction depends on magnitude level dueto instrumental limitations. OBe stars tend to be much more variable(≈80%) than the average sample star, while OBMS stars are belowaverage and OBSG stars are average. Types of variables include αCyg, β Cep, slowly pulsating stars and other types from the generalcatalog of variable stars. As for eclipsing binaries, there arerelatively more contact than detached systems among the OBMS and OBestars, and about equal numbers among OBSG stars.
| The Extension of the Transition Temperature Plasma into the Lower Galactic Halo
Column densities for H I, Al III, Si IV, C IV, and O VI toward 109 starsand 30 extragalactic objects have been assembled to study the extensionsof these species away from the Galactic plane into the Galactic halo. HI and Al III mostly trace the warm neutral and warm ionized medium,respectively, while Si IV, C IV, and O VI trace a combination of warmphotoionized and collisionally ionized plasmas. The much larger objectsample compared to previous studies allows us to consider and correctfor the effects of the sample bias that has affected earlier but smallersurveys of the gas distributions. We find that Si IV and C IV havesimilar exponential scale heights of 3.2(+1.0, -0.6) and 3.6(+1.0,-0.8) kpc. The scale height of O VI is marginally smaller with h =2.6 ± 0.6 kpc. The transition temperature gas is ~3 times moreextended than the warm ionized medium traced by Al III with h =0.90(+0.62, -0.33) kpc and ~12 times more extended than the warmneutral medium traced by H I with h = 0.24 ± 0.06 kpc. There is afactor of 2 decrease in the dispersion of the log of the column densityratios for transition temperature gas for lines of sight in the Galacticdisk compared to extragalactic lines of sight through the entire halo.The observations are compared to the predictions of the various modelsfor the production of the transition temperature gas in the halo. Theappendix presents a revision to the electron scale height of Gaensler etal.'s 2008 study based on electron dispersion measures.
| Period Changes of DF Hydrae: Evidence of Mass Transfer and the Presence of a Cool Tertiary Companion
Combining our six new determined times of light minimum obtained from2001 to 2007 with others compiled from the literature, we investigatedthe period changes of DF Hydrae. The general trend of the O - C curvebased on all available data reveals that the period of the binary staris increasing continuously at a rate of dP/dt = + 1.11(±0.02)× 10-7dyr-1. After the long-term periodincrease was removed from the O - C diagram, it was discovered that theresiduals of the CCD and photoelectric observations suggest asmall-amplitude cyclic oscillation with a period of 21.5years. Thecontinuous period increase can be explained by mass transfer from thesecondary to the primary, indicating that DF Hydrae is on theTRO-controlled stage of the evolutionary scenario proposed by Qian. Thecyclic period variation suggests that DF Hydrae is a triple systemcontaining a cool tertiary component with a mass of M3sin i'= 0.21Modot in a 21.5-year orbit. By removing angularmomentum from the central binary system via Kozai oscillation or acombination of the Kozai cycle and tidal friction, the tertiarycompanion may play an important role for the formation and evolution ofthe contact system, which makes the eclipsing pair to have a shortinitial orbital period (i.e., P < 5d). In that case, thedetached progenitor of DF Hydrae evolves into the present contactconfiguration via a combination of magnetic braking and a case A masstransfer.
| An analysis of v sin (i) correlations in early-type binaries
We use information on the v sin(i) values of early-type binaries inorder to search for correlations which may constrain the relativeorientation of the stellar spin axes in binary systems. We findcorrelations in the case of close binaries which suggest that tidalsynchronization is effective for binaries whose separation exceeds thestellar radius by more than an order of magnitude, in line with thetheoretical predictions of Goldreich & Nicholson and the previousobservational analysis of Giuricin et al. In the case of wide binaries,the v sin(i) values are not well correlated, which requires that themagnitude of the spin speeds is not tightly correlated. Under thisassumption, we then find that the data provide no significantconstraints on the degree of alignment of spin axes. The data aretherefore compatible with scenarios (such as disc fragmentation orcapture) which differ widely in the expected degree of spin alignment.
| Magnetic Braking and the Evolution of the HW Vir-like Binary Stars
HW Vir-like close binaries are thought to be the progenitors ofcataclysmic variables. However, how this type of peculiar stars evolveinto cataclysmic variables is an unsolved problem in astrophysics. Herewe report the variations of the orbital period of HW Vir, the prototypeof this group of systems. A long-term period decrease is discovered tobe superimposed on the well-known cyclic change reported by previousinvestigators. It is suggested that the continuous decrease can beplausibly interpreted by angular momentum loss via magnetic braking ofthe completely convective star. This is driving the shrink of the orbitand will result in mass transfer between both components. We found thatthe binary will be undergoing mass transfer long before the sdB primarystar evolves into a white dwarf. This conclusion suggests that HWVir-like binaries do not directly evolve into cataclysmic variablesthrough angular momentum loss as astronomers previously thought. On theother hand, if the observed period decrease is only part of along-period cyclic variation, it may reveal the presence of anothersubstellar companion in a wide orbit. This makes HW Vir an importantsystem for future study of the formation and evolution of substellarobjects.
| A New Photometric Investigation of the W UMa-Type Binary BI CVn
New photometric observations and their investigation of the W UMa-typebinary, BI CVn, are presented. The variations of the orbital period wereanalyzed based on 12 new determined times of light minimum together withthe others compiled from the literature. It is discovered that theperiod of BI CVn shows a long-term period decrease at a rate of\dot{P}=-1.51(\pm 0.12)\times {10^{-7}} daysyear-1 while it undergoes a cyclic variation with aperiod of 27.0 years and an amplitude of 0fd0151. Photometricsolutions determined with the Wilson-Devinney method suggest that BI CVnis a contact binary with a degree of contact of 18.0(±1.7)%. Theasymmetry of the light curves was interpreted by the presence of darkspots on both components, and absolute parameters were determined bycombining the photometric elements with the spectroscopic solutionsgiven by Lu. The observed period decrease can be plausibly explained bya combination of the mass transfer from the primary to the secondary andangular momentum loss via magnetic braking. The cyclic periodoscillation suggests that BI CVn is a triple system containing atertiary component with a mass no less than 0.58 M sun in a27.0 year orbit. As in the cases of the other contact binaries (e.g., AHCnc, AP Leo, AD Cnc, and UX Eri), it is possible that this tertiarycompanion played an important role for the formation and evolution ofthe contact system by removing angular momentum from the central systemvia Kozai oscillation or a combination of Kozai cycle and tidalfriction, which causes the eclipsing pair to have a short initialorbital period (e.g., P < 5d). In that case, can theinitially detached system evolve into the present contact configurationvia a combination of magnetic torques from stellar winds and a case Amass transfer?
| High-resolution optical spectroscopy of Plaskett's star
Context: Plaskett's star (HD 47 129) is a verymassive O + O binary that belongs to the Mon OB2 association. Previouswork suggests that this system displays the Struve-Sahade effectalthough the measurements of the secondary radial velocities are verydifficult and give controversial results. Both components have powerfulstellar winds that collide and produce a strong X-ray emission. Aims: Our aim is to study the physical parameters of this system indetail and to investigate the relation between its spectral propertiesand its evolutionary status. Methods: We present here analysis ofan extensive set of high-resolution optical spectra of HD 47129. We used a disentangling method to separate the individualspectra of each star. We derived a new orbital solution and discuss thespectral classification of both components. A Doppler tomographytechnique applied to the emission lines H? and He II ? 4686yields a Doppler map that illustrates the wind interactions in thesystem. Finally, an atmosphere code is used to determine the differentchemical abundances of the system components and the wind parameters. Results: HD 47 129 appears to be an O8 III/I +O7.5 III binary system in a post RLOF evolutionary stage, where matterhas been transferred from the primary to the secondary star. The Heoverabundance of the secondary supports this scenario. In addition, theN overabundance and C underabundance of the primary component confirmprevious results based on X-ray spectroscopy and indicate that theprimary is an evolved massive star. We also determined a new orbitalsolution, with MP sin^3i = 45.4 ± 2.4M? and MS sin^3i = 47.3 ± 0.3M?. Furthermore, the secondary star has a highrotational velocity (v sin i ˜ 300 km s-1) that deformsits surface, leading to a non-uniform distribution in effectivetemperature. This could explain the variations in the equivalent widthsof the secondary lines with phase. We suggest that the wind of thesecondary star is confined near the equatorial plane because of its highrotational velocity, affecting the ram pressure equilibrium in the windinteraction zone.Based on observations made at the European Southern Observatory (LaSilla, Chile) and at the Observatoire de Haute Provence (France).
| Tomographic Separation of Composite Spectra. XI. The Physical Properties of the Massive Close Binary HD 100213 (TU Muscae)
We present the results of a Doppler tomographic reconstruction of the UVspectra of the double-lined, O binary HD 100213 based on observationsmade with the International Ultraviolet Explorer (IUE). We usedcross-correlation methods to obtain radial velocities, confirm theorbital elements, estimate the UV flux ratio, and determine projectedrotational velocities. The individual component spectra are classifiedas O7 V + O8 V using UV criteria defined by Penny, Gies, & Bagnuolo.We present a model fit of the eclipsing light curve from observationsfrom the Hipparcos satellite and published observations of Andersen& Gronbech. We derive an orbital inclination,i=77.7deg+/-1.0deg. This analysis indicates thatboth stars are currently experiencing Roche lobe overflow (RLOF), whichconfirms earlier results that this is one of only a few massive contactbinaries. Our derived masses, Mp/Msolar=16.7+/-0.4and Ms/Msolar=10.4+/-0.4, are significantly lowerthan those computed from the Doppler shifts of lines in the opticalspectrum. We suggest that the difference occurs because mutualirradiation decreases the upper atmospheric temperature gradient in theinward-facing hemispheres of both stars, which makes lower excitationlines appear weaker there and shifts their center of light away from thecenter of mass. We compare the current state of HD 100213 with predictedoutcomes of massive close binary evolutionary models, and suggest thatthe system is currently in a very slow case AA mass transfer stage.
| The Far Ultraviolet Spectroscopic Explorer Survey of O VI Absorption in the Disk of the Milky Way
To probe the distribution and physical characteristics of interstellargas at temperatures T~3×105 K in the disk of the MilkyWay, we have used the Far Ultraviolet Spectroscopic Explorer (FUSE) toobserve absorption lines of O VI λ1032 toward 148 early-typestars situated at distances >1 kpc. After subtracting off a mildexcess of O VI arising from the Local Bubble, combining our new resultswith earlier surveys of O VI, and eliminating stars that showconspicuous localized X-ray emission, we find an average O VI midplanedensity n0=1.3×10-8 cm-3. Thedensity decreases away from the plane of the Galaxy in a way that isconsistent with an exponential scale height of 3.2 kpc at negativelatitudes or 4.6 kpc at positive latitudes. Average volume densities ofO VI along different sight lines exhibit a dispersion of about 0.26 dex,irrespective of the distances to the target stars. This indicates that OVI does not arise in randomly situated clouds of a fixed size anddensity, but instead is distributed in regions that have a very broadrange of column densities, with the more strongly absorbing cloudshaving a lower space density. Line widths and centroid velocities aremuch larger than those expected from differential Galactic rotation, butthey are nevertheless correlated with distance and N(O VI), whichreinforces our picture of a diverse population of hot plasma regionsthat are ubiquitous over the entire Galactic disk. The velocity extremesof the O VI profiles show a loose correlation with those of very stronglines of less ionized species, supporting a picture of a turbulent,multiphase medium churned by shock-heated gas from multiple supernovaexplosions.
| Evolutionary states of the two shortest period O-type overcontact binaries V382 Cyg and TU Mus
Up to now, V382 Cyg and TU Mus are the only two discovered O-typeovercontact binary stars with periods less than two days (P = 1.8855 and1.3873 d). Both systems contain a visual companion. New eclipse timesand analyses of orbital period variations of the two systems arepresented. It is discovered that the periods of both binaries showcyclic oscillations with periods of 47.70 and 47.73yr, while theyundergo continuous increases at rates of dP/dt = +4.4 ×10-7 and +4.0 × 10-7dyr-1,respectively. The periodic variations can be interpreted as light traveltimes effects caused by the presence of invisible tertiary componentssuggesting that they may be quadruple systems. It is possible that theadditional bodies may play an important role in the formation andevolution of the two massive overcontact binaries by removing angularmomentum from the central systems, and causing the eclipsing pairs tohave lower angular momentum and shorter initial orbital periods. In thisway, the original detached systems can evolve into the presentovercontact configurations via a Case A mass transfer. This is inagreement with the observed long-term period increase of V382 Cyg and TUMus, which can be explained by mass transfers from the less massivecomponents to the more massive ones. It is found that the time-scales ofthe long-term period variations of both systems are much longer than thethermal time-scales of the secondary components, but are close to theirnuclear time-scales. This suggests that the two massive binaries havebeen through the rapid mass-transfer evolutionary stage on the thermaltime-scales of the secondaries, and they are now on the slow phase ofCase A mass transfer. It is shown that massive overcontact binaries aregoing through a short-lived overcontact configuration during theevolutionary phases of Case A mass transfer, which is different from thesituation of late-type overcontact binary stars where components remainin good overcontact configuration driving by a combination of thermalrelaxation oscillation and variable angular momentum loss via change inovercontact depth. This conclusion is in agreement with the distributionof overcontact binary stars along with the orbital period.
| The Struve-Sahade effect in the optical spectra of O-type binaries. I. Main-sequence systems
Aims:We present a spectroscopic analysis of four massive binary systemsthat are known or are good candidates to display the Struve-Sahadeeffect (defined as the apparent strengthening of the secondary spectrumof the binary when the star is approaching, and the correspondingweakening of the lines when it is receding). Methods: We use highresolution optical spectra to determine new orbital solutions andspectral types of HD 165 052, HD 100 213, HD 159 176 and DH Cep. As goodknowledge of the fundamental parameters of the considered systems isnecessary to examine the Struve-Sahade effect. We then study equivalentwidth variations in the lines of both components of these binariesduring their orbital cycle. Results: In the case of these foursystems, variations appear in the equivalent widths of some lines duringthe orbital cycle, but the definition given above can any longer bevalid, since it is now clear that the effect modifies the primaryspectrum as much as the secondary spectrum. Furthermore, the linesaffected, and the way in which they are affected, depend on theconsidered system. For at least two of them (HD 100 213 and HD 159 176)these variations probably reflect the ellipsoidal variable nature of thesystem.Based on observations made at the European Southern Observatory (LaSilla, Chile) and at the Observatoire de Haute Provence (France).
| Galactic distributions and statistics of the HD stars in the michigan spectral catalogue.
Not Available
| Third-Body Parameters from Whole Light and Velocity Curves
Eclipsing binaries can improve multiple system statistics via thelight-time effect and radial velocity shifts. Here an algorithm operateson data of mixed type to exploit these opportunities. Main reasons forenhanced reliability are that (1) combined light and velocity curvesgive better timewise coverage than either type alone, (2) properlyweighted solutions impersonally balance light and velocity information,and (3) the entire theory is within the computer model, so observationsare used directly without corrections. A brief history of mixedwhole-curve solutions is given and the relative importance of light-timeand radial velocity input for third-body parameters is discussed andquantified. Period sifting by power spectral analysis is essentiallyindispensable in preliminary work. Applications are to the Algol-typesystem DM Persei and the detached system VV Orionis. An assumption ofcoplanarity for DM Per's inner and outer orbits is tested and quantifiedby dynamical experiments. Derived third-body parameters for DM Per aremainly reasonable and self-consistent. For comparison with whole-curveresults, we also investigated DM Per's ephemeris in terms of eclipsetimings and found whole-curve solutions to give smaller standard errorsin reference epoch (T0), binary orbit period (P), and dP/dt,over a similar baseline in time. An astonishing outcome is lack ofevidence that can pass reasonable validity tests for VV Ori'swell-accepted third star with P~120 days. Estimates of third light doindicate a third star, but the correct period cannot now be established,so the star cannot be identified as the one heretofore recognized fromradial velocity evidence. The much cited 120 day period appears to be anartifact of the window function for VV Ori's historical velocityobservations.
| Mass-luminosity relation for massive stars
A catalog of massive (⩾10 M ȯ) stars in binary andmultiple systems with well-known masses and luminosities has beencompiled. The catalog is analyzed using a theoretical mass-luminosityrelation. This relation allows both normal main-sequence stars and starswith peculiarities: with clear manifestations of mass transfer, massaccretion, and axial rotation, to be identified. Least-squares fittingof the observational data in the range of stellar masses 10Mȯ ⩽ M ≲ 50 M ȯ yields therelation L ˜ M 2.76.
| Four-colour photometry of eclipsing binaries. XL. uvby light curves for the B-type systems DW Carinae, BF Centauri, AC Velorum, and NSV 5783
Aims.In order to increase the limited number of B-stars with accuratelyknown dimensions, and also the number of well studied eclipsing binariesin open clusters, we have undertaken observations and studies of foursouthern double-lined eclipsing B-type binaries; DW Car, BF Cen, AC Vel,and NSV 5783. Methods: .Complete {uvby} light curves were observedbetween January 1982 and April 1991 at the Danish 0.5 m telescope at ESOLa Silla, since 1985 known as the Strömgren Automatic Telescope(SAT). Standard indices for the systems and the comparison stars, aswell as additional minima observations for AC Vel, have been obtainedlater at SAT. For DW Car and AC Vel, high-resolution spectra fordefinitive spectroscopic orbits have also been obtained; they arepresented as part of the detailed analyses of these systems. A fewspectra of NSV 5783 are included in the present paper. Results:.For all four systems, the first modern accurate light curves have beenestablished. DW Car is a detached system consisting of two nearlyidentical components. It is member of the young open cluster Cr228. Adetailed analysis, based on the new light curves and 29 high-resolutionspectra, is published separately. BF Cen is semidetached and is memberof NGC 3766. Modern spectra are needed for a detailed study. AC Vel is adetached system with at least one more star. A full analysis, based onthe new light curves and 18 high-resolution spectra, is publishedseparately. NSV 5783 is discovered to be an eclipsing binary consistingof two well-detached components in an 11-day period eccentric (e = 0.18)orbit. Secondary eclipse is practically total. From the light curves anda few high-resolution spectra, accurate photometric elements andpreliminary absolute dimensions have been determined. The quite similarcomponents have masses of about 5 Mȯ and radii of about3.5 Rȯ, and they seem to have evolved just slightly offthe ZAMS. The measured rotational velocities (≈150 kms-1) are about 6 times those corresponding topseudosynchronization.
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Observational studies of early-type binary stars: MP Centauri
We present photometric and spectroscopic data on the early-type binaryMP Centauri. The photometric data are analysed simultaneously withradial velocities to derive preliminary absolute dimensions for thebinary components. Analysis of the spectra shows that the stars rotatesynchronously and that the line of sight to the system crosses twokinematically sharp and well-separated interstellar reddening sources.It is shown that MP Cen consists of a B3 primary with M1=11.4 +/- 0.4Msolar, R1= 7.7 +/-0.1Rsolar and a lobe-filling B6-B7 secondary withM2= 4.4 +/- 0.2Msolar, R2= 6.6 +/-0.1Rsolar.
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
| CX CMa - An Early-Type Detached Eclipsing Binary
We present new B and V photometry of CX CMa and solve these light curvesusing the Wilson-Devinney program.
| Up-to-Date Linear Elements of Eclipsing Binaries
About 1800 O-C diagrams of eclipsing binaries were analyzed and up-todate linear elements were computed. The regularly updated ephemerides(as a continuation of SAC) are available only in electronic form at theInternet address: http://www.as.ap.krakow.pl/ephem/.
| 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.
| The Database ASAS and the Periods of Several Early-Type Binaries
Using the database ASAS, new times of minima are calculated foreclipsing binaries EM Car, SV Cen, AQ Cir, TU Mus, V431 Pup and V701Sco. Periods of these stars are discussed.
| Observational Studies of Early-Type Overcontact Binaries: TU Muscae
We present new spectroscopic and photometric data on the early-typeovercontact binary TU Muscae. The analysis of the spectroscopic datashows that the line of sight to the system crosses three kinematicallysharp and well-separated interstellar reddening sources and that thestars rotate synchronously. We present new radial velocities that are ingood agreement with earlier optical velocities and, thus, do not confirmthe systematically smaller velocities obtained from IUE spectra. Theoptical velocities are analyzed simultaneously with the photometric datato derive accurate absolute dimensions for the binary components. Theresults show that TU Mus consists of an O7.5 primary withM1=23.5+/-0.8 Msolar and R1=7.48+/-0.08Rsolar and an O9.5 secondary with M2=15.3+/-0.4Msolar and R2=6.15+/-0.07 Rsolar in anovercontact configuration, and that the orbital period has remainedconstant over the three decades covered by the observations. Theseresults might imply that the mass transfer seen in late-type overcontactbinaries does not occur in their early-type counterparts.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| Evolution of Wolf-Rayet Stars in Binary Systems: An Analysis of the Mass and Orbital-Eccentricity Distributions
We have undertaken a statistical study of the component mass ratios andthe orbital eccentricities of WR + O close binary, detachedmain-sequence (DMS), contact early-type (CE), and semidetached (SD)systems. A comparison of the characteristics of WR + O systems and ofDMS, CE, and SD systems has enabled us to draw certain conclusions aboutthe evolutionary paths of WR + O binaries and to demonstrate that up to90% of all known WR + O binaries formed as a result of mass transfer inmassive close O + O binary systems. Since there is a clear correlationbetween the component masses in SD systems with subgiants, the absenceof an anticorrelation between the masses of the WR stars and O stars inWR + O binaries cannot be considered evidence against the formation ofWR + O binaries via mass transfer. The spectroscopic transitionalorbital period P tr sp corresponding to the transition from nearlycircular orbits (e sp<0.1) to elliptical orbits (e sp≥0.1) is14d for WR + O systems and 2d 3d for OB + OB systems. Theperiod range in which all WR + O orbits are circular &$(1mathop dlimits_. 6 ≤slant P ≤slant 14(d) ); is close to the range for SD systems with subgiants, &0mathop dlimits_. 7 ≤slant P ≤slant 15(d); . The large difference between the P tr sp values for WR + O and OB +OB systems suggests that a mechanism of orbit circularization additionalto that for OB + OB systems at the DMS stage (tidal dissipation of theorbital energy due to radiative damping of the dynamical tides) acts inWR + O binaries. It is natural to suggest mass transfer in the parent O+ O binaries as this supplementary orbit-circularization mechanism.Since the transitional period between circular and elliptical orbits forclose binaries with convective envelopes and ages of 5×109 yearsis &P_{tr} = 12mathop dlimits_. 4$; , the orbits of most known SD systems with subgiants had enough timeto circularize during the DMS stage, prior to the mass transfer. Thus,for most SD systems, mass transfer plays a secondary role incircularization of their orbits. In many cases, the initial orbitaleccentricities of the O + O binary progenitors of WR + O systems arepreserved, due to the low viscosity of the O-star envelopes and theshort timescale for their nuclear evolution until the primary O starfills its Roche lobe and the mass transfer begins. The mass transfer inthe parent O + O systems is short-lived, and the number of orbitalcycles during the early mass-transfer stage is relatively low (lowerthan for the progenitors of SD systems by three or four orders ofmagnitude). The continued transfer of mass from the less massive to themore massive star after the component masses have become equal leads tothe formation of a WR + O system, and the orbit's residual eccentricityincreases to the observed value. The increase of the orbitaleccentricity is also facilitated by variable radial mass loss via thewind from the WR star in the WR + O system during its motion in theelliptical orbit. The result is that WR + O binaries can haveconsiderable orbital eccentricities, despite their intense masstransfer. For this reason, the presence of appreciable eccentricitiesamong WR + O binaries with large orbital periods cannot be consideredfirm evidence against mass transfer in the parent O + O binary systems.Only for the WR + O binaries with the longest orbital periods (4 of 35known systems, or 11 %) can the evolution of the parent O + O binariesoccur without filling of the Roche lobe by the primary O star, beinggoverned by radial outflow in the form of the stellar wind and possiblyby the LBV phenomenon, as in the case of HD 5980.
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
| Constelación: | Mosca |
| Ascensión Recta: | 11h31m10.93s |
| Declinación: | -65°44'32.1" |
| Magnitud Aparente: | 8.398 |
| Distancia: | 10000000 parsecs |
| Movimiento Propio en Ascensión Recta: | -5.7 |
| Movimiento Propio en Declinación: | -1.1 |
| B-T magnitude: | 8.444 |
| V-T magnitude: | 8.402 |
Catálogos y designaciones:
|
