Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
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.
| 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 early-type semidetached binary system V716 Centaurus
New high-resolution spectra of V716 Cen revealed for the first timelines of the secondary component and its radial velocities. Thesimultaneous solution of the new radial velocity curves and theHipparcos light curve yield the reliable absolute dimensions of thissemidetached system. The masses for the primary and secondary areM1 = 5.68 +/- 0.07Msolar and M2 = 2.39+/- 0.05Msolar, respectively, and the radii are R1= 4.08 +/- 0.07Rsolar and R2 = 3.36 +/-0.02Rsolar. We derive also effective temperatures ofTeff1 = 15500 +/- 50 K and Teff2 = 9000 +/- 80 K,and equatorial rotational velocities of vrot sini = 137 +/- 2km s-1 and vrot sini = 116 +/- 7 kms-1. These rotational velocities imply that the componentsrotate synchronously. The distance to the system is d = 339 +/- 8 pc, ingood agreement with the less accurate Hipparcos distance (337 +/- 72pc). The primary is underluminous and the secondary overluminouscompared to normal main-sequence stars of the same mass. This impliesthat the secondary component of the semidetached system is in slow masstransferring stage after mass ratio reversal, although the Hα-lineprofiles do not show clear evidence for this.
| B.R.N.O. Contributions #34
Not Available
| Visual Minima Timings of Eclipsing Binaries Observed in the Years 1992 - 1996
The paper contains a list of 283 new times of minima and 77 revisedtimes of minima for 63 eclipsing binaries derived by the author fromhis visual observations.
| New Minimum Times of Eclipsing Binaries
I report 16 visual minimum times of eclipsing binaries.
| 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.
| Analysis of photoelectric light curves of V448 CYG taking the Roche geometry into account
Three-color photoelectric UBV light curves of the close binary systemV448 Cyg obtained at the Abastumani Astrophysical Observatory areanalyzed using a new code by Djurasevi. A new value for the ratio of themasses of the components, which is the fundamental parameter fordetermining the absolute elements of the system, has recently beenpublished. The parameters obtained in our analysis differ substantiallyfrom those published previously because the new mass ratio has beenemployed. The location of the components of V448 Cyg on a mass-logg plotshows that this system, similarly to XZ Cep and V382 Cyg, is in a phasesubsequent to a rapid transfer of mass.
| 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.
| 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/.
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
Not Available
| 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.
| Masses and other parameters of massive binaries
Binary stars provide us with the means to measure stellar mass. Here Ipresent several lists of known O-type stars with reliable mass estimatesthat are members of eclipsing, double-lined spectroscopic binaries. Themasses of young, unevolved stars in binaries are suitable for testingthe predictions of evolutionary codes, and there is good agreementbetween the observed and predicted masses (based upon temperature andluminosity) if the lower temperature scale from line-blanketed modelatmospheres is adopted. A final table lists masses for systems in awide variety of advanced evolutionary stages.
| Tomographic Separation of Composite Spectra. IX. The Massive Close Binary HD 115071
We present the first orbital elements for the massive close binary HD115071, a double-lined spectroscopic binary in a circular orbit with aperiod of 2.73135+/-0.00003 days. The orbital semiamplitudes indicate amass ratio of M2/M1=0.58+/-0.02, and yet the starshave similar luminosities. We used a Doppler tomography algorithm toreconstruct the individual component optical spectra, and we appliedwell-known criteria to arrive at classifications of O9.5 V and B0.2 IIIfor the primary and secondary, respectively. We present models of theHipparcos light curve of the ellipsoidal variations caused by the tidaldistortion of the secondary, and the best-fit model for a Roche-fillingsecondary occurs for an inclination of i=48.7d+/-2.1d. The resultingmasses are 11.6+/-1.1 and 6.7+/-0.7Msolar for the primary andsecondary, respectively, so both stars are very overluminous for theirmass. The system is one of only a few known semidetached, Algol-typebinaries that contain O stars. We suggest that the binary has recentlyemerged from extensive mass transfer (possibly through a delayed contactand common-envelope process).
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
Not Available
| Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald Observatory
The Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos ``problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos ``problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission.
| 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
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| A Probable Variation in the Polarization of The Early-Type Eclipsing Binary System XZ Cep
The early-type eclipsing binary system XZ Cep are observedspectro-polarimetrically. We report a probable detection of temporalvariations in the polarization.
| V606 Centauri: an early-type eclipsing contact binary
We present a spectroscopic and photometric analysis of the early-typeeclipsing binary V606 Cen. Based on new high-resolution CCD spectra thefirst radial velocity curve of this system is given, which allows for anaccurate determination of radial velocity amplitudes (K_1=181.8 km s(-1), K_2=345.2 km s(-1) ) and the spectroscopic mass ratio q_spec=0.527.Moreover, equivalent widths are listed. The line strengths of He i 4922show strong variations with the orbital phase, related to the so-called(and hitherto unexplained) ``Struve-Sahade effect". In this context,some aspects concerning the determination of equivalent widths in closebinary systems are discussed, with special reference to the influence ofthe ellipsoidal light variations. For the first time, photoelectric UBVlight curves of V606 Cen are presented, which were solved with the MOROcode, based on the Wilson-Devinney model. The first set of solutions wasachieved with effective temperatures according to the previous spectralclassification B1-2 Ib/IIb, but the derived absolute dimensions, surfacegravities, as well as an investigation of the equivalent widths led to arevision of the spectral type. We now suggest B0-0.5 V for the primary,and B2-3 V for the secondary component, respectively. Using thecorresponding effective temperatures, another light curve analysis wasperformed, yielding the following absolute dimensions: M_1=14.7 M_sun,M_2=8.0 M_sun, R_1=6.8 R_sun, R_2=5.2 R_sun, log L_1/L_sun=4.48, and logL_2/L_sun=3.74. In all cases, a contact configuration is found. Theevolutionary state of V606 Cen is discussed in the light of modernevolutionary grids. It turns out that this contact system was formedduring the slow phase of case A mass transfer after reversal of its massratio. In this respect it is similar to other early-type contactbinaries such as V382 Cyg, V701 Sco or RZ Pyx. Based on observationscollected at the European Southern Observatory, La Silla, Chile
| Variations of the orbital periods in semi-detached binary stars with radiative outer layers
A detailed analysis of the period changes of sixteen semi-detachedbinaries which contain only stars with radiative outer layers(ET-systems) has been performed and their respective O-C diagrams arebrought and discussed. It was found that the course of the periodvariations is monotonic and in some systems the period is even constant.This detailed analysis of extensive sets of timings covering severaldecades brings a strong support to an earlier finding of te[Hall(1989)]{hal89} and develops it further. We show that all systems withthe orbital periods shorter than nine days display constant period orits increase, with the exception of an uncertain case of V 337 Aql. Thecourse of the period variations in TT Aur appears more complex but thecyclic term can be plausibly explained by the third body. A search forgeneral relations between the parameters of the systems and the periodchanges was undertaken. The mass ratio q appears to play a role in theperiod variations. Clear changes in systems with orbital periods shorterthan 9 days were detected only for q>0.4 while constant periods arecommon in systems with q<0.4 in this period range. The sense of thesecular changes in most systems is in accordance with the dominantconservative mass transfer in evolved binary and corresponds to the slowphase. The role of the evolutionary scenarios (case A versus B) and theinfluence of changes of the rotational angular momenta of the componentsare discussed.
| Orbital circularization in detached binaries with early-type primaries
Extending our previous study, the present paper reports on thediscussion of the orbital circularization in 37 detached binaries withearly-type primaries. From comparison of the theoretical predictionswith the orbital eccentricities of our binary systems, we find thatZahn's circularization theories are substantially consistent with theobserved data for overwhelming majority of our samples. However, we alsonote that three binaries of whom both components are asynchronizedrotators possess circular orbits. How to understand the circularism ofthe three systems remains a problem not only to Zahn's theories, but toall other present circularization mechanisms.We think that studies onthe circularization of pre-main-sequence binary systems could providesome clues for the problem.
| Interacting OB star binaries: LZ Cep, SZ Cam and IU AUR
New spectroscopic observations of three O+O binary stars (LZ Cep, SZ Camand IU Aur), obtained over a number of years at the DominionAstrophysical Observatory, are analysed using state-of-the-artcross-correlation techniques to produce radial velocity curves. Theseresults are combined with new (LZ Cep) and published (SZ Cam and IU Aur)photometry to yield masses, temperatures, radii and luminosities. Wefind that LZ Cep is a semi-detached system, in agreement with theresults of Howarth et al., with the secondary star filling its Rochelobe. We find a distance modulus of 9.6+/-0.2, which is slightly smallerthan the distance modulus to Cep OB2 (=9.9).The reddening of LZ Cep isalso at the lower end of the cluster range, suggesting that the binaryis located on the near side of the cluster. SZ Cam is a triple system,and we are able to measure the radial velocities of the three componentsthat are observed in the absorption lines. A light-curve solutionemploying our new mass ratio shows that the short-period binary isdetached. The third body emits about 40 per cent of the radiation fromthe system, and is probably a binary itself. The distance modulus for SZCam (=9.88) is in good agreement with that of its parent cluster NGC1502 (=9.71). IU Aur is another triple system, although we are unable tofind spectroscopic evidence for the tertiary. The close binary issemi-detached, with the secondary filling its Roche lobe. The distancemodulus of the system is 11.0, which is in approximate agreement withthat of the Aur OB1 association (=10.6+/-0.2). We note that the currentmodels for interacting massive binaries all assume case B mass transfer,in which the mass-loser becomes a Wolf-Rayet star. Case A mass-transfermodels (in which the mass-loser fills its Roche lobe while still on themain sequence) are required in order to see whether or not they canexplain the observed properties of these interacting systems.
| 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.
| The calculation of critical rotational periods in three typical close binary systems based on synchronization theory.
Not Available
| Measurement and study of rotation in close binary stars. (V) Orbital circularization.
Not Available
| Synchronization in the early-type detached binary stars.
With a set of homogeneous and refined rotational velocities, we discussthe synchronism in the "normal" (all the particular stars, such as Ap,Am and Of, are excluded) early-type detached binaries. Being differentfrom previous statistical studies, the present paper not onlyinvestigates the rotational synchronism of each component, but alsoestimates its age from new stellar evolutionary grids, and calculatesits synchronization time scale with Zahn's dynamically tidal theory.Significantly, we find that the dynamically tidal synchronizationmechanism is substantially compatible with the observed data from thecomparison of the rotational properties of our components with thetheoretical predictions.
| Interacting O-star binaries: V382 Cyg, V448 CYG and XZ CEP
New spectroscopic observations of three interacting O+O-star binaries(V382 Cyg, V448 Cyg and XZ Cep), obtained at the Dominion AstrophysicalObservatory, are analysed in conjunction with published photometry, toyield masses, temperatures and radii. We determine masses of 26.0+/-0.7and 1903+/-0.4Msolar for V382 Cyg, 25.2+/-0.7 and 14.0+/-0.7Msolar forV448 Cyg, and 15.8+/-0.4 and 6.4+/-0.3 Msolar for XZ Cep. We find thatV382 Cyg is a contact system, resulting from evolutionary expansion ofthe components during their main-sequence lifetimes (case A masstransfer). V448 Cyg is an evolved binary that has undergone late case Aor early case B mass transfer, with the mass loser now filling its Rochelobe and transferring mass more slowly to the gainer. The distancemodulus for V448 Cyg of 11.4 agrees well with that of its parent clusterNGC 6871, while the cluster age (7Myr) places a tight constraint on theevolutionary status of this system. XZ Cep closely resembles V448 Cyg,although its mass is somewhat lower.
| Measurement and study of rotation in close binary stars (IV) Comparison between observation and predictions of two theories.
Not Available
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Kral-Sefe |
| Sað Açýklýk: | 22h32m25.08s |
| Yükselim: | +67°09'02.5" |
| Görünürdeki Parlaklýk: | 8.519 |
| Uzaklýk: | 574.713 parsek |
| özdevim Sað Açýklýk: | -3.2 |
| özdevim Yükselim: | -1.4 |
| B-T magnitude: | 9.383 |
| V-T magnitude: | 8.591 |
Kataloglar ve belirtme:
|
