Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
Computing Limb-darkening Coefficients from Stellar Atmosphere Models
We explore the sensitivity of limb-darkening coefficients computed fromstellar atmosphere models to different least-squares fitting methods. Wedemonstrate that conventional methods are strongly biased to fitting thestellar limb. Our suggested method of fitting by minimizing the radiallyintegrated squared residual yields improved fits with better fluxconservation. The differences of the obtained coefficients from commonlyused values are observationally significant. We show that the new valuesare in better agreement with solar limb-darkening measurements, as wellas with coefficients reported from analyses of eclipsing binary lightcurves.
| New CCD Times of Minima of Eclipsing Binary Systems
We present a total of 208 CCD timings for 103 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.
| Evaluating Gaia performances on eclipsing binaries. IV. Orbits and stellar parameters for SV Cam, BS Dra and HP Dra
This is the fourth in a series of papers that aim both to providereasonable orbits for a number of eclipsing binaries and to evaluate theexpected performance of Gaia of these objects and the accuracy that isachievable in the determination of such fundamental stellar parametersas mass and radius. In this paper, we attempt to derive the orbits andphysical parameters for three eclipsing binaries in the mid-F to mid-Gspectral range. As for previous papers, only the H_P, V_T, BTphotometry from the Hipparcos/Tycho mission and ground-based radialvelocities from spectroscopy in the region 8480-8740 Å are used inthe analyses. These data sets simulate the photometric and spectroscopicdata that are expected to be obtained by Gaia, the approved ESACornerstone mission to be launched in 2011. The systems targeted in thispaper are SV Cam, BS Dra and HP Dra. SV Cam and BS Dra have been studiedpreviously, allowing comparisons of the derived parameters with thosefrom full scale and devoted ground-based investigations. HP Dra has nopublished orbital solution. SV Cam has a β Lyrae type light curveand the others have Algol-like light curves. SV Cam has the complicationof light curve anomalies, usually attributed to spots; BS Dra hasnon-solar metallicity, and HP Dra appears to have a small eccentricityand a sizeable time derivative in the argument of the periastron. Thusall three provide interesting and different test cases.
| Evaluating the Performance of the GAIA Space Mission on and with Eclipsing Binaries: Three Problematic Systems, SV Cam, BS Dra, HP Dra
GAIA is a reconfirmed Cornerstone Mission of ESA, with an anticipatedlaunch date of 2011. Its primary purpose is to study the kinematics andstructure of the galaxy for which it will be equipped to domicroarcsecond astrometry, multi-band photometry, and radial-velocityspectroscopy on a billion of the brightest stars. GAIA will carry outits five-year survey mission from the L2 point of the Earth's orbit. Itis expected to discover of order one million eclipsing binaries, whichalone may keep ground-based observatories busy on follow-up programs fordecades to follow. Here we will review the general benefits of GAIA forstellar and galactic astronomy, and discuss its potential for SB2eclipsing binaries in particular. A group headed by U. Munari (Univ.Padova) has demonstrated GAIA's importance in a series of tests of theprecision and accuracy of fundamental stellar parameters from analysesof light and RV curves of selected systems. The trials conservativelymake use only of Hipparcos-Tycho photometry and ground-based echellespectroscopy matching GAIA's spectral (Ca triplet) region andapproximate resolution (~12,000). Here, we describe the determinationsof fundamental parameters for three of the most recently studiedsystems: SV Cam with complicated light curves and, in the data analyzedin this study, only 1 RV curve; BS Dra with nonsolar metallicity; and HPDra with a small eccentricity and a significant time derivative of theargument of periastron. The latter two systems have partial, sparselyobserved eclipses, which make the radiative properties difficult todetermine. Although the three systems represent limiting cases, theresults are nevertheless encouraging, with uncertainties in one or morecomponents approaching 2% in some parameters, and derived distancesfalling close to or within the errors of the Hipparcos determinations,for all three systems. Some of the work described here was supported byNSERC grants to EFM.
| Studies of Intermediate-Mass Stellar Models Using Eclipsing Binaries
Evolutionary computations for intermediate-mass stars are analyzed usingobserved parameters for eclipsing SB2 binaries and theoreticalparameters based on evolutionary tracks. Modern observations cannot beused to distinguish between models with and without convectiveovershooting for stars in the vicinity of the main sequence.Statistically significant discrepancies between the observed andcomputed stellar parameters are associated with systematic errors inphotometric effective temperatures. After taking into account systematiceffects, the theoretical computations fit the observational datauniformly well throughout the entire mass interval studied. Empiricaland semiempirical (i.e., reduced to the ZAMS and with solar elementalabundances) formulas for the mass-luminosity, mass-effectivetemperature, and mass-radius relations are proposed.
| Age and Metallicity Estimates for Moderate-Mass Stars in Eclipsing Binaries
We estimate the ages and metallicities for the components of 43 binarysystems using a compilation of accurate observational data on eclipsingbinaries for which lines of both components are visible in theirspectra, together with two independent modern sets of stellar evolutionmodels computed for a wide range of masses and chemical abundances. Theuncertainties of the resulting values are computed, and their stabilityis demonstrated. The ages and metallicity are compared with thosederived in other studies using different methods, as well as withindependent estimates from photometric observations and observations ofclusters. These comparisons con firm the reliability of our ageestimates. The resulting metallicities depend significantly on thechoice of theoretical model. Comparison with independent estimatesfavors the estimates based on the evolutionary tracks of the Genevagroup.
| 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.
| Accurate Positions for 45 Variables in Five Fields
Accurate positions of 45 variables in 5 fields, determined fromphotographic astrometry, are presented.
| 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.
| The active dynamo stars: RS CVn, BY Dra, FK Com, Algol, W UMa, and T Tau
Not Available
| Catalogue of astrophysical parameters of binary systems
Not Available
| Eclipsing binaries with eccentric orbits
Two groups of eclipsing binaries are dealt with: the first consists ofall binaries with enough data in the General Catalog of Variable Stars(GCVS; Cholopov et al, 1987), the other of those for which accurateparameters are known. In the first group, problems with classificationin GCVS are noticed and several examples of binaries with unexpectedparameters are named. For binaries of the second group, their fractionalradii, ages, and initial radii are used to discuss the relation of theirevolutionary status and orbital eccentricity. Dependence of eccentricityon spectral type and age is observed, and no peak in the initialeccentricity distribution at e = 0 seems to be present. It is suggestedthat binary origin by fragmentation followed by disruption of initialmultiple systems can explain all observed binaries, perhaps with theexception of contact systems in the main sequence. In several cases thecircularization must be due to mass transfer in the eccentric orbit.
| A Study of the DM and SD Type Eclipsing Variables by Means of the Cluster Analysis Technique
Not Available
| Reexamination of the mass-radius relation of main sequence in binary systems
The mass-radius relation of the main sequence was reexamined using 171components of 88 double-lined detached binary systems with welldetermined absolute dimensions and masses. Empirical relations for theZAMS were obtained and compared with the theoretical models. Thepositions of the other 27 semidetached binaries in the log M - log Rdiagram are also discussed.
| Stellar masses and radii based on modern binary data
Accurate data on absolute dimensions of eclipsing binaries published inthe astronomical literature since 1980 are collected and analyzed.Simple approximation formulas relating the effective temperature withother basic physical parameters (mass, radius, bolometric magnitude) arederived. Mean and extreme values of these parameters for each spectraltype are also tabulated. The implication of improved data for theproblem of critical rotational periods and equatorial velocities ofearly-type stars is discussed.
| Angular momenta in binary systems
The correlations of angular momenta L to masses M are studied fordifferent types of spectroscopic binaries. Postulates about equivalentstates of angular momenta for different orbital parameters areintroduced. From comparisons with galaxies and single stars, it isevidenced that there is not a unique universal function L = AM exp b,when the finite structure of the relation is analyzed: each object hasits own coefficients A, b. It seems that there are an upper and a lowerlimit for all the possible functions.
| Nonstationary Phenomena in Eclipsing Detached Main Sequence Binaries
Not Available
| Close binary mass anomalies and metallicity
Direct (radial velocity) and indirect (spectral type, luminosity class)mass determinations for luminosity class V binaries are compared. Theexistence of statistical biases or apparently irreconcilable individualdiscrepancies, or both, in the data is examined, and their explanationby astrophysical effects such as chemical composition and agedifferences is considered. The existence of residual discrepancies,after correction for chemical composition effects and statisticalallowance for age effects, which could only be due to otherastrophysical effects, to instrumental effects, or to selection effects,is investigated. A need for at least one additional astrophysicaleffect, suspected to be fast core rotation, is found in a few binaries.It is argued that some remaining evidence for systematic observationalerrors is more likely to be the result of selection effects rather thanan instrumental effect.
| The period distribution of unevolved close binary systems
Period distributions have been examined for various spectral types ofabout 600 (eclipsing and spectroscopic) close binaries, which are likelyto be substantially unevolved. The comparison with the previouscorresponding analyses of extensive (but heterogeneous) binary samplesallows a clarification of the extent of the evolutionary andobservational selection effects. Remarkably, this analysis reveals agreat deficiency of short period binaries (with periods corresponding tocase A mass transfer) in the whole spectral range. For the late spectraltypes, this result may be connected with postformation angular momentumloss caused by stellar wind magnetic braking; at least for the late Band A spectral range, a ready interpretation of this finding is thatclose binaries of corresponding periods and spectral types are rarelyformed.
| The mass-spectrum relation for main-sequence stars
A mass-spectrum relation is obtained for 240 main-sequence stars withknown masses; in several intervals of spectral class it differs markedlyfrom the analogous relations of Allen and Trimble. Its accuracy indetermining the masses of component stars of eclipsing binary systems ofvarious types from their spectra given in the General Catalog ofVariable stars III and supplements to it is estimated.
| Statistics of categorized eclipsing binary systems Lightcurve shapes, periods, and spectral types
The statistics of the light curve morphologies, eclipse depths, orbitalperiods, and spectral types of about 1000 eclipsing binary systems areexamined, after attempting to subdivide these binaries into variousbasic evolutionary categories. The applicability of statisticalcriteria, based on light curve morphologies and eclipse depths, for thecategorization of eclipsing binaries has been found more limited thanpreviously believed. In particular, EW-type light curves turn out to begood indicators of contact systems (though not conversely), while EA-and EB-type light curves have little physical significance. Moreover,the study reveals a strong deficit of short-period noncontact systems inthe whole spectral range, together with an underabundance of early-typecontact binaries (compared with the number of late-type contact pairs).Interestingly, the distribution of evolved Algol-type systems isshifted, on average, to periods longer than those of unevolved detachedsystems in the OB and early A spectral range (and to shorter periods inthe F spectral range).
| The masses of the main-sequence stars
The methods used to calculate the masses of nearby visual double starsand of the components of eclipsing binaries are discussed, taking theaccuracy of the orbital measurements and distance estimates intoaccount. The spectral type, absolute magnitude, luminosity, and mass arelisted for a number of stars, in tables based on the survey of Popper(1980). The empirical mass-luminosity relationship is illustrated with aHertzsprung-Russell diagram.
| Photoelectric Minima of Eclipsing Binaries
Not Available
| A supercritical accretion disk model for SS 433
A model for SS 433 based on an accretion disk around a black hole isdescribed. Due to the very high mass transfer rate in the system, thedisk must be geometrically thick. Two narrow funnels are formed aroundthe rotation axis and radiation pressure in the funnels acceleratesmatter to relativistic velocities in the form of two opposite jets. TheX-ray and optical luminosities are evaluated and they agree well withthe experimental data.
| Revised Photometric Elements of the Eclipsing Systems Bs-Draconis and Cd-Tauri
The recently published two-colour photoelectric light curves of thedouble-lined spectroscopic binaries CD Tauri and BS Draconis have beenanalysed using the Wilson and Devinney (1971) method of solution. Withrespect to previous solutions, CD Tau shows small but appreciabledifferences, while for BS Dra the old elements are confirmed. Theabsolute elements, computed using Popper's spectroscopic data, show thatboth binaries have normal Main Sequence components, and the comparisonof their relative radii with the Roche lobes allows us to classify themas geometrically detached
| Photometric orbits of seven detached eclipsing binaries
Photoelectric light curves of the detached eclipsing binaries V805 Aql,TV Cet, MY Cyg, V478 Cyg, V1143 Cyg, BS Dra, and BK Peg are analyzed.The systems are among those with good spectrographic orbits of bothcomponents that are in need of good photometric solutions in order toobtain the absolute properties of the components. The analyses arecarried out with a computer program valid for detached systems ofspherical or slightly oblate stars in orbits of arbitrary eccentricity.A range of solutions much greater than implied by the internal meanerrors of the parameters, is found to give satisfactory fits to theobservations. Some of the fits are displayed for a variety of solutionsfor each system. For the three systems with measurable light variationbetween eclipses - V478 Cyg, V805 Aql, and MY Cyg - the effect ofreflection appears to be substantially less than predicted. Very small,but nonzero, orbital eccentricities are found for four of the systems.The variations of limb darkening with wavelength and with spectral typeare found to be in reasonable agreement with predictions fromatmospheric theory.
| Observational results of the Berliner Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V. /BAV/
Results of observations of variable stars derived from 10,000 individualevaluations are presented for the years 1978 and 1979. Included are 172minima of 75 eclipsing binaries; 70 maxima of 17 RR Lyrae stars; 309results on 93 Mira stars; 90 results on 19 long-period, semi-regular,irregular and RV Tauri stars; and 6 results on 5 eruptive variablestars.
| Determinations of Six Times of Minima, and a New Ephemeris for BS Dra
Not Available
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Draco |
| Ascensió Recta: | 19h56m28.77s |
| Declinació: | +73°36'57.5" |
| Magnitud Aparent: | 9.151 |
| Moviment propi RA: | -8.2 |
| Moviment propi Dec: | -3.8 |
| B-T magnitude: | 9.662 |
| V-T magnitude: | 9.194 |
Catàlegs i designacions:
|
INHABITED SKY
