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A catalogue of close binaries located in the δ Scuti region of the Cepheid instability strip
A catalogue of close eclipsing binary systems (detached andsemidetached) with at least one of the components located in the δScuti region of the Cepheid instability strip is presented. Thepositions of the stars in the instability strip are determined by theiraccurate temperatures and luminosities. Observationally detectedbinaries (20 semidetached, four detached and one unclassified) withoscillating components were included in the catalogue as a separatetable. The primaries of the oscillating Algols tend to be located nearthe blue edge of the instability strip. Using reliable luminosities andtemperatures determined by recent photometric and spectroscopic studies,we have found that at least one or two components of 71 detached and 90semidetached systems are located in the δ Scuti region of theCepheid instability strip. In addition, 36 detached or semidetachedsystems discovered by the Hipparcos satellite were also given as aseparate list. One of their components is seen in the δ Scutiregion, according to their spectral type or B - V colours. They arepotential candidate binaries with the δ Scuti-type pulsatingcomponents which need further photometric and spectroscopic studies inbetter precision. This catalogue covers information and literaturereferences for 25 known and 197 candidate binaries with pulsatingcomponents.
| 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.
| Automatic classification of eclipsing binaries light curves using neural networks
In this work we present a system for the automatic classification of thelight curves of eclipsing binaries. This system is based on aclassification scheme that aims to separate eclipsing binary systemsaccording to their geometrical configuration in a modified version ofthe traditional classification scheme. The classification is performedby a Bayesian ensemble of neural networks trained with Hipparcos data ofseven different categories including eccentric binary systems and twotypes of pulsating light curve morphologies.
| Gravity-darkening exponents in semi-detached binary systems from their photometric observations. II.
This second part of our study concerning gravity-darkening presents theresults for 8 semi-detached close binary systems. From the light-curveanalysis of these systems the exponent of the gravity-darkening (GDE)for the Roche lobe filling components has been empirically derived. Themethod used for the light-curve analysis is based on Roche geometry, andenables simultaneous estimation of the systems' parameters and thegravity-darkening exponents. Our analysis is restricted to theblack-body approximation which can influence in some degree theparameter estimation. The results of our analysis are: 1) For four ofthe systems, namely: TX UMa, β Per, AW Cam and TW Cas, there is avery good agreement between empirically estimated and theoreticallypredicted values for purely convective envelopes. 2) For the AI Drasystem, the estimated value of gravity-darkening exponent is greater,and for UX Her, TW And and XZ Pup lesser than corresponding theoreticalpredictions, but for all mentioned systems the obtained values of thegravity-darkening exponent are quite close to the theoretically expectedvalues. 3) Our analysis has proved generally that with the correction ofthe previously estimated mass ratios of the components within some ofthe analysed systems, the theoretical predictions of thegravity-darkening exponents for stars with convective envelopes arehighly reliable. The anomalous values of the GDE found in some earlierstudies of these systems can be considered as the consequence of theinappropriate method used to estimate the GDE. 4) The empiricalestimations of GDE given in Paper I and in the present study indicatethat in the light-curve analysis one can apply the recent theoreticalpredictions of GDE with high confidence for stars with both convectiveand radiative envelopes.
| Catalogue of Algol type binary stars
A catalogue of (411) Algol-type (semi-detached) binary stars ispresented in the form of five separate tables of information. Thecatalogue has developed from an earlier version by including more recentinformation and an improved layout. A sixth table lists (1872) candidateAlgols, about which fewer details are known at present. Some issuesrelating to the classification and interpretation of Algol-like binariesare also discussed.Catalogue is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/417/263
| Gravity-darkening exponents in semi-detached binary systems from their photometric observations: Part I
From the light curve analysis of several semi-detached close binarysystems, the exponent of the gravity-darkening (GDE) for the Roche lobefilling components has been empirically estimated. The analysis, basedon Roche geometry, has been made using the latest improved version ofour computer programme. The present method of the light-curve analysisenables simultaneous estimation of the systems' parameters and thegravity-darkening exponents. The reliability of the method has beenconfirmed by its application to the artificial light curves obtainedwith a priori known parameters. Further tests with real observationshave shown that in the case of well defined light curves the parametersof the system and the value of the gravity-darkening exponent can bereliably estimated. This first part of our analysis presents the resultsfor 9 of the examined systems, that could be briefly summarised asfollows: 1) For four of the systems, namely: ZZ Cru, RZ Dra, XZ Sgr andW UMi, there is a very good agreement between empirically estimated andtheoretically predicted values for purely radiative and convectiveenvelopes. 2) For the rest five, namely: TT Aur, V Pup, TV Cas, LT Her,and VV UMa, the estimated values of the gravity-darkening exponents werededuced to be larger than theory expects for purely radiative orconvective envelopes, respectively. Moreover, it is worthwhile tomention that these values -although greater than theoreticalpredictions- are: a) Smaller compared to those found by others. b) Intwo cases, (TV Cas & LT Her), they are normal if some kind of solartype activity (i.e. by employing the Roche model involving a spottedarea on the surface of the secondary star) is assumed. 3) The largevalues derived for the two early type systems TT Aur & V Pup, arevery possibly connected with the effects of rotation laws, and in somedegree with the large contribution of the radiative pressure in thetotal potential, leading by that to considerable deviations of thestellar surfaces from the assumed classical Roche geometry. 4) Finally,in the VV UMa case, the estimated value of the gravity-darkeningexponent - although almost double than the expected for stars withconvective envelopes - still it is low in comparison with that estimatedby others who have analysed the same data. But, since for thisparticular binary the anomalous GDE is not supported by recentsimultaneous uvby observations (Lazaro et al. \cite{lazaro}), theestimated higher value may be due to the old observational materialused.
| 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
| Further discussion of binary star radio survey data
Statistical information on 8280 individual radio observations of binarystars, predominantly at 8.4 GHz using the Parkes 64 m antenna, ispresented. Three main groups are distinguished: (i) RS CVn stars, (ii)classical Algol binaries (EA2s) and (iii) detached pairs of generallyearly type (ETBs). The RS CVn stars more frequently gave rise todetectable fluxes, while the ETBs, in this data, are a small and ratherheterogeneous class. The Algols' emission appears to increase nearconjunction phases, though we cannot clearly distinguish any specialproperty of the Algols' phase-dependent behaviour which is not alsoshared by the RS CVn binaries. Both these categories' data show abimodal, phase-dependent pattern to the distribution of detections,suggesting both binary types share similar underlying physicalproperties, though there could also be other factors at play. The samplesizes of the Algols and particularly the ETB detections are too smallfor effective, discriminatory statistics, however.
| Magnetic activity and evolution of Algol-type stars - II
We examine the possibility of probing dynamo action in mass-losingstars, components of Algol-type binaries. Our analysis is based on thecalculation of non-conservative evolution of these systems. We model thesystems USge and betaPer where the more massive companion fills itsRoche lobe at the main sequence (case AB) and where it has a smallhelium core (early case B) respectively. We show that to maintainevolution of these systems at the late stages which are presumablydriven by stellar `magnetic braking', an efficient mechanism forproducing large-scale surface magnetic fields in the donor star isneeded. We discuss the relevance of dynamo operation in the donor starto the accelerated mass transfer during the late stages of evolution ofAlgol-type binaries. We suggest that the observed X-ray activity inAlgol-type systems may be a good indicator of their evolutionary statusand internal structure of the mass-losing stellar components.
| RS CVn Versus Algol-Type Binaries: A Comparative Study of Their X-Ray Emission
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.2415S&db_key=AST
| R Canis Majoris---Revisited
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...458..371S&db_key=AST
| 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| The active dynamo stars: RS CVn, BY Dra, FK Com, Algol, W UMa, and T Tau
Not Available
| Evidence of magnetic activity in short-period Algol binaries
The cool G- to K-type secondaries in short-period Algol-type binariesare expected to be magnetically active like the RS CVn binaries becauseof their rapid rotation and outer convective layers. There is nowgrowing evidence of such activity, primarily from radio and X-rayobservations, but there is still little or no information about most ofthe other indicators of magnetic activity. In this work, we havecollected the evidence for magnetic activity in a selected group of 15short-period Algols and have examined the possibility that part of theH-alpha emission detected in these systems may indeed arise from thechromosphere of the cool star and not exclusively from circumstellarmaterial.
| New rotational velocities for eclipsing binaries, and a comparison of spectroscopic and photometric rotations
Rotational velocities are determined spectroscopically for 38 eclipsingbinaries, including many long-period, nominally semidetached, systems.We note that spectroscopic rotations may differ from rotations derivedfrom light-curve modeling using the Wilson-Devinney program. In'direct-impact' mass-transferring systems, or in most systems withperiods smaller than about 7 days, observations suggest that the tworotations are usually about the same. In cases where the stream missesthe gainer and an accretion disk forms, however, photometric rotationestimates often exceed spectroscopic determinations. The possiblephysical significance of this situation is briefly discussed. Doubt iscast on the likelihood that the rotation of the hot component of U Sgehas changed detectably in the last 30 years.
| The determination of C/O and 12C/13C ratios from molecular indices in the atmospheres of the carbon stars.
Not Available
| An astrometric catalogue of radio stars
The first part is presented of a radio star catalog encompassing 186objects whose selection was guided by the priority criteria of theHipparchos Input Catalogue Consortium. Since these criteria are wellsuited to the need for linkage of ground-based optical systems to radioreference frames, this first selection is also considered a suitablebase for the catalog. Seventeen categories of stellar parameters arefurnished for each of the stars, including optical and radio positions,optical and radio parallax, radial velocity, type of variability, andoptical structure.
| Statistical study of semi-detached and near-contact semi-detached binaries
A statistical study was made of 107 semidetached with combined lightcurve solutions. An empirical period-dependent mass-radius relation wasderived, thereby revealing the impossibility of having evolvedsemidetached systems with very short periods. Statistically, thenear-contact semidetached systems have the common properties of nearlyequal mass densities of the components, larger mass-ratios, shorterperiods and smaller specific angular momenta, and their A- F-typesecondaries generally have greater densities than the secondaries ofclassical Algol systems of the same spectral types. A detaileddiscussion is also made in this paper on the evolution of near-contactsemidetached binaries.
| A Study of the DM and SD Type Eclipsing Variables by Means of the Cluster Analysis Technique
Not Available
| Radio emission from EA eclipsing binaries - Evidence for kilogauss surface fields on both early-type and late-type stars
Radio observations of a sample of EA eclipsing binaries, includingearly-type main-sequence pairs as well as classical Algol-type eclipsingbinaries, indicate the presence of a moderately strong coronal magneticfield, B of about 100 G, between the component stars. This translates toa surface magnetic field of about 1000-10,000 G on one or both stars.This is the first compelling evidence for magnetic fields on early-typestars, apart from the Ap and Bp magnetic stars first detected in 1947.
| Optical positions of radiostars.
Precise optical positions, relative to either the Perth 70 or the AGK3Rcatalogs, are presented for 38 radiostars which have been proposed ascandidates for the Hipparcos observing list. The observations wereobtained with the 70/100/210 cm Maksutov Astrograph at the EstacionAstronomica de Cerro El Roble. The precision levels are shown to beabout 0.2 arcsec in both coordinates.
| 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 radio luminosity and stellar rotation
Two measurements of the microwave surface brightness of 63 activechromospheric stars, one related to surface flux and one related to fluxratio, are correlated with rotational parameters. Although both methodsare found to provide similar results, the surface flux method accountsfor more of the variance in the regression. The consistency of theobserved surface brightnesses of the sun and three BY-Dra-type flarestars with the present rotational relationships is considered.
| Do all stars have magnetic fields?
The sun and other late-type stars have the ability to generate andmaintain strong localized magnetic field regions on and above thestellar surface. Recent observational results strongly suggest that amuch higher range of upper-main-sequence spectral types have appreciablesurface magnetic fields. The data refer to stars of spectral types B, A,and F in eclipsing binary systems.
| Statistical Study on the Semidetached and Near Contact Semidetached Binary Systems
Not Available
| An Updated List of Eclipsing Binaries Showing Apsidal Motion
Not Available
| A relation between radio luminosity and rotation for late-type stars
A relation is found between peak radio luminosities measured at 8 GHzand the rotational velocity of 51 late-type F, G, and K stars (includingthe sun). The sample includes both single stars and active components ofclose binary systems, with equatorial surface velocities ranging from 1to 100 km/s. A gyrosynchrotron source model originally developed toexplain solar microwave bursts could explain the relation. The mainparameter depending on rotation rate is the filling factor, i.e., thefraction of the stellar surface and corona occupied by intense magneticfields. As the rotation speed increases, the scale size of the coronalstructures emitting microwave gyrosynchrotron radiation increases, andthere is a corresponding increase in the area of the surface covered byintense starspot magnetic fields. However, the peak magnetic field ofthe starspots probably does not increase significantly above observedsunspot values.
| A microwave survey of southern active stars
The results of a survey of 153 active-chromosphere stars made with theParkes 64-m telescope at 5.0/8.4 GHz from 1981 to 1987 are reported.Microwave emission was detected from 70 stars on at least one occasion,with the highest detection rate of 68 percent from the RS CVn group. TheCa II stars and Algol-type binaries yielded detection rates of 44 and 30percent, respectively. The maximum powers emitted by the stars at5.0/8.4 GHz ranged over five orders of magnitude, with a median of 2.5 x10 to the 10th W/Hz. The maximum brightness temperatures had a smallerrange of three orders of magnitude, with a median of 3.6 x 10 to the 9thK.
| Semidetached systems - Evolutionary viewpoints and observational constraints
The present knowledge on the evolution of semidetached systems isreviewed. Characteristics of observed systems are discussed and generalproperties tested by the behavior of theoretical models. New models ofmass accreting companion stars are computed. The accretion phase isdivided into a fast and slow phase with an accretion rate depending onthe initial mass of the mass losing star and on the initial mass ratio,asssuming the systems are undergoing a case B of mass transfer. Theresults are compared with observed systems with masses of the gainerslocated within the theoretical range. Up to now no computations existfor the evolution of medium mass close binaries including overshootingof the convective core. However some of the influences of extendedconvective mixing on the interaction of close binaries are investigated.A larger probability for the occurrence of case A of mass exchange and alarger remnant mass at the end of the process are the most importantresults. Finally the investigation into the origin of individual systems(in mass, mass ratio and period) is discussed, showing that progressboth in observations and in theoretical models result in a more detailedand more restricted determination of the initial parameters of theindividual systems.
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Osservazione e dati astrometrici
| Costellazione: | Sagittario |
| Ascensione retta: | 18h22m06.77s |
| Declinazione: | -25°14'23.8" |
| Magnitudine apparente: | 8.951 |
| Distanza: | 234.192 parsec |
| Moto proprio RA: | -18 |
| Moto proprio Dec: | -14.4 |
| B-T magnitude: | 9.354 |
| V-T magnitude: | 8.985 |
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