내용
사진
사진 업로드
DSS Images Other Images
관련 글
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.
| 163. List of Minima Timings of Eclipsing Binaries by BBSAG Observers
Not Available
| 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
| Doppler tomography of Algols
The technique of Doppler tomography has been influential in the study ofmass transfer in Algol-type interacting binaries. The Algols contain ahot blue dwarf star with a magnetically-active late-type companion. Inthe close Algols, the gas stream flows directly into the photosphere ofthe blue mass-gaining star because it does not have enough room to avoidimpact with that star. Doppler tomograms of the Algols have beenproduced from over 2500 time-resolved spectra at wavelengthscorresponding to Hα, Hβ, He I (6678 Å), Si II (6371Å) and Si IV (1394 Å). These tomograms display images ofaccretion structures that include a gas stream, accretion annulus,accretion disk, stream-star impact region, and occasionally a source ofchromospheric emission associated with the cool, mass-losing companion.Some Algol systems alternate between stream-like and disk-like states,and provide direct evidence of active mass transfer within the Algols.This work produced the very first images of the gas stream for theentire class of interacting binaries, and demonstrated that the Algolsare far more active than formerly believed, with variability on timescales of weeks to months.
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
Not Available
| The Origin of Cyclic Period Changes in Close Binaries: The Case of the Algol Binary WW Cygni
Year- to decade-long cyclic orbital period changes have been observed inseveral classes of close binary systems, including Algol, W UrsaeMajoris, and RS Canum Venaticorum systems and the cataclysmic variables.The origin of these changes is unknown, but mass loss, apsidal motion,magnetic activity, and the presence of a third body have all beenproposed. In this paper, we use new CCD observations and thecentury-long historical record of the times of primary eclipse for WWCygni to explore the cause of these period changes. WW Cyg is an Algolbinary whose orbital period undergoes a 56 yr cyclic variation with anamplitude of ~0.02 days. We consider and reject the hypotheses of masstransfer, mass loss, apsidal motion, and the gravitational influence ofan unseen companion as the cause for these changes. A model proposed byApplegate, which invokes changes in the gravitational quadrupole momentof the convective and rotating secondary star, is the most likelyexplanation of this star's orbital period changes. This finding is basedon an examination of WW Cyg's residual O-C curve and an analysis of theperiod changes seen in 66 other Algols. Variations in the gravitationalquadrupole moment are also considered to be the most likely explanationfor the cyclic period changes observed in several different types ofbinary systems.
| Das Brunner Punktesystem.
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.
| Survey of Hα Mass Transfer Structures in Classical Algol-Type Binaries
Five years of Hα survey data for 37 ``classical'' Algol-typebinaries are presented. All these systems have primaries with a spectraltype of A or B, have a period of less than 5 days, and are visible inthe Northern Hemisphere. Data were collected with the 1.02 m reflectorat the US Naval Observatory, Flagstaff Station. The survey consists ofover 460 system spectra. Each system was observed at least once duringthe 5 years, with many systems observed several times over severalepochs. Difference profiles are calculated for most spectra by modelingand subtracting the spectrum of the photospheres of the stellarcomponents. We examined each spectrum for the presence of mass transfer,stream-star and stream-disk interaction, a disk or circumstellar bulge,and chromospheric emission. We present information on the prevalence ofmass transfer activity, disk presence, and system states associated withparticular mass transfer structures. We show that no currently publishedstudy, including this one, has enough data for a rigorous statisticalidentification of system states.
| 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.
| An observational study of Algol-type binaries
The primary purpose of this thesis is to obtain more accurate orbitalparameters for a number of Algol-type binaries. In this study, fivesystems were observed in two observing runs in 1994 (La Palma, 7 nights)and 1997 (Mexico, 4 nights). The 1994 run consisted of single slitobservations of U CrB, TU Mon and TX UMa. In 1997, U CrB was repeatedand RS Vul and GU Her were added to the target list; in this case, theobserving was carried out with an Echelle spectrograph. Data reductionwas done using FIGARO and IRAF for the 1994 and 1997 data sets,respectively. The radial velocity curves of these five systems wereanalysed to obtain accurate orbital parameters, in particular to try toobtain radial velocity semi-amplitudes, K1 and K2, for both components.For U CrB, a new pair of K1 and K2 was found which leads us to a muchmore sensible point in the evolutionary sequence of this system. For TXUMa and TU Mon only confirmation of their published K1 values could beachieved because of their low resolution spectra which did not enablethe other component to be resolved. For RS Vul, K1 was confirmed.Because of the inadequate phase coverage at one quadrature, the K2 valuecould not be improved, but a comparison was made with the latestpublished value. GU Her was defined to be a `cool algol' (i.e. bothcomponents are late type sub giants), and the K1 and K2 value of thesystem was found for the first time. Besides radial velocity studies,magnetic activity in Algol-type binaries and its relation to theirevolutionary sequences is also discussed. In this part of study someAlgol--type binaries are categorised into four Groups depending on theevolutionary stage of the system. We claim to find that there is aremarkable correlation between evolutionary status and X--ray activityin the mass losing star of the system. In addition to already observedand categorised systems a list of systems is presented as candidates forthis categorisation.
| Morphologies of Hα Accretion Regions in Algol Binaries
We have investigated a group of 18 Algol-type binaries to determine thegeneral morphologies and physical properties of the accretion regions inthese systems. The systems studied were V505 Sgr, RZ Cas, AI Dra, TVCas, TW Cas, delta Lib, RW Tau, TW Dra, beta Per, TX UMa, U Sge, S Equ,U CrB, RS Vul, SW Cyg, CX Dra, TT Hya, and AU Mon, in order ofincreasing orbital period P=1.18-11.11 days. In addition, the RSCVn-type binary HR 1099 (V711 Tau) was observed to illustrate theappearance of chromospheric Hα emission. Nearly 2200 time-resolvedHα spectra were collected from 1992 March to 1994 December withthe McMath-Pierce Solar Telescope at NSO and mostly with theCoudé Feed Telescope at KPNO. The spectra were obtained at phasesaround the entire orbit of each binary and were closely spaced to permitthe detection of transitions in the profiles. Moreover, the spectra wereobtained typically within three orbital cycles to reduce the influenceof secular variations. Difference profiles were calculated bysubtracting a composite theoretical photospheric spectrum from theobserved spectrum. The analysis of the Hα difference profilesdemonstrates that the accretion structures in Algol binaries have fourbasic morphological types: (1) double-peaked emission systems in whichthe accretion structure is a transient or classical accretion disk; (2)single-peaked emission systems in which the accreted gas was found alongthe trajectory of the gas stream and also between the two stars in anaccretion annulus; (3) alternating single- and double-peaked emissionsystems, which can change between a single-peaked and a double-peakedtype within an orbital cycle; and (4) weak spectrum systems in whichthere was little evidence of any accretion structure since thedifference spectra are weak at all phases. The first two types are thedominant morphologies. The first type can be interpreted physically as adisklike distribution, while the second is a gas stream-likedistribution. The most common type in short-period Algols with 2.7days6 days)were found to have slightly variable but permanent accretion disks atall epochs (i.e., CX Dra, TT Hya, and AU Mon), similar to those found incataclysmic variables. SW Cyg (P=4.57 days) was found to be anintermediate case between the shorter period systems with P<4.5 daysand the longer period group with P>6 days. Two systems, U Sge and UCrB, displayed alternating single- and double-peaked emission atdifferent epochs (Type 3), and changes from one type to another weredetected within a 12 hour time interval. Observations at multiple epochssuggest that four members of the single-peaked emission group, namely RWTau, TX UMa, S Equ, and RS Vul, may actually belong to the alternatinggroup. So, the complete group of alternating systems covers periods of2.7 days
| 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.
| Searching for old neutron stars with ROSAT. II. Soft X-ray sources in galactic dark clouds
This is the second in a series of three papers constraining the numberof detectable old neutron stars in the Galaxy. Here, I present thestatistical analysis of a sample of X-ray sources coincident with areasof dark clouds in the Galactic plane. I compare this sample with allsources in the ROSAT All-Sky Survey bright source catalog within 20(deg)of the Galactic plane. I present the results of an identificationprogram of a subset of sources that are compatible with a soft, thermalX-ray spectrum and an effective source temperature of less than 70eV.The three brightest sources in this sample form an intriguing subgroup.One of them is a previously identified candidate for an accretingneutron star. I identify the other two sources with hot white dwarfstars. I find no new accreting neutron star candidate in this sample.Based on this result, I derive an upper limit to the space density ofaccreting neutron stars in fields of Galactic dark clouds of ~ 2sr(-1)at a count rate >0.05s(-1) .
| Hydrodynamic Simulations of H alpha Emission in Algol-Type Binaries
Two-dimensional hydrodynamic simulations of mass transfer inshort-period Algol-type binaries were performed using the numerical codeVirginia Hydrodynamics 1. This code uses the piecewise parabolic methodwith a Lagrangian remap. Our version of the code also accounts forradiative cooling and collisional ionization and excitation processes.The purpose of performing the simulations was to study the H alphaemission from circumstellar gas in the Algols. Using observationalevidence from the literature to constrain the gas stream properties,hydrodynamic maps of the H alpha emissivity in the two systems beta Per(P = 2.87 days) and TT Hya (P = 6.95 days) were made in both Cartesianand velocity coordinates from the simulation data. The velocity mapswere then compared to Doppler tomograms constructed from observed Halpha line emission in these systems. Since the tomograms cannot bedirectly transformed to maps of emission in spatial coordinates, thesimulated Cartesian maps enabled us to interpret the dynamical processesthat produce the features observed in the Doppler tomograms. We findthat the simulations produce asymmetric accretion structures with manyfeatures similar to those found in the Doppler tomograms of Algolsystems.
| Radio emission from Algol-type binaries. I. Results of 1992-1993 VLA survey
In this paper we report on a 5 GHz survey of 26 Algol-type binaries. Sixsystems were detected. We combine the new results with previouslypublished data to derive some radio characteristics of Algols and tocompare them with those of other active binaries. The radio detectionrate of 30 %, a factor that is somewhat smaller compared to the case ofRSCVn-type, does not seem to be due to a reduced coronal activity. Infact, Algols share many similarities with the radio behavior of RS CVnsand the 5 GHz luminosity functions of both kind of systems look quitesimilar. Among the different possibilities, the high radio variabilityand distances, which, on average, are larger than those of RS CVns, seemto be the most reasonable explanation for the apparently reducedactivity at radio wavelengths.
| 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
| Chemical Evolution of Algols
Not Available
| Doppler Tomography and S-Wave Analysis of Circumstellar Gas in beta Persei
The Hα difference profiles of fl Per obtained from 1976 to 1977have been analyzed in several ways to study the gas flows in the binary.These difference profiles were obtained by removing the combined stellarphotospheric absorption contribution from the observed profiles toenhance the weak emission from circumstellar gas. The differenceprofiles display strong narrow single-peaked emission and broaderdouble-peaked emission. The line strengths peaked near phase 0.7 for theblueshifted emission and near phase 0.2 for the redshifted emission.These maxirna occur at phases where our line of sight would pass throughthe gas stream or an accretion region located between the stars. Theorbital variations of the radial velocities of the single- anddouble-peaked emission followed S-waves. The source of the single-peaked emission was found at velocities close to the L_{1 }point on theside of the secondary star in the direction of the gas streamtrajectory, as if associated with the gas stream. However, the source ofthe double-peaked emission was found at velocities almost halfwaybetween that of the stars, in the direction away from the gas stream.The double-peaked nature of these profiles imply that they arise from anaccretion region surrounding the primary star, with the most intense,concentrated part between the stars. Reconstructed Doppler images of thebinary from Doppler tomography are consistent with the S-wave analysisand show that there are several sources of emission (from strongest toweakest): a gas stream, a localized region, and an unstable asymmetricaccretion annulus. The gas stream extends from the L_{1 }point to theimpact site on the stellar surface, but it tapers sharply about halfwayalong its path as if blocked by material around the primary. Finally,the weakest source arose from the region around the secondary star, sochromospheric emission from the magnetically active subgiant secondaryhas been detected in the Doppler image.
| 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.
| Circumstellar Matter in Direct Impact Algol Systems
Not Available
| Doppler tomography of the gas stream in short-period Algol binaries
Doppler tomography of H alpha difference profiles of four short-periodAlgol-type binaries has revealed the gas stream due to Roche lobeoverflow and disklike structures around the mass gainer. The position ofthe gas stream in the Doppler tomogram closely follows the predictedfree fall path from the inner Lagrangian point in the rotating referenceframe. In U CrB, U Sge, RS Vul, and beta Per, the disklike structures inthe tomograms are asymmetric distributions of gas extending out toseveral times the synchronous rotation rate of the primary star. Thesetomograms display the first distinct 'images' of gas streams in theAlgols, and in the entire class of interacting binaries.
| Doppler Tomography of Accretion Regions in Algol Binaries
The technique of Doppler Tomography has been used to reconstruct imagesof the accretion regions in the short-period Algol-type binaries RS Vul,U Sge, U CrB, beta Per, S Equ, TX UMa and SW Cyg. Hα differenceprofiles of these systems show single and/or double-peaked emissionfeatures at most phases outside of primary eclipse, and absorptionfeatures throughout primary eclipse, except at mid-eclipse. A BackProjection Tomography code was used to generate the sources of Hαemission in the orbital plane of the binary. The tomograms show clearevidence of a gas flow along the predicted free-fall path of the gasstream as well as asymmetric disk-like structures both on and around themass gainer. Another source of Hα emission is associated with thecool magnetically active secondary. The gas stream source was strongestin U CrB while the disk emission was strongest in SW Cyg. Observationsof U Sge in June 1993 show evidence of a strong almost Keplerianaccretion disk, but in June 1994 the emission from this binary waspredominantly from the gas stream. The disk emission seen in the Algolsis reminiscent of that seen in the cataclysmic variables (e.g., U Gem).
| Rotation of close binary system components
The rotation of close binary system components is investigated. Theprincipal physical characteristics as well as the equatorial rotationaland the axial and orbital inclinations for 46 close binary systems weredetermined. It is found that the rotation axes of the individual starsin a pair cross the orbital plane under different angles. As a rule, therotation and orbital periods of a vast majority of the systemsinvestigated here do not coincide.
| The Chemical Composition of Algol Systems - Part Five - Confirmation of Carbon Deficiencies in the Primaries of Eight Systems
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993MNRAS.265..581T&db_key=AST
| 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.
| Catalogue of astrophysical parameters of binary systems
Not Available
| Chemical evolution of Algol-type stars - Mass-exchanging binary systems in cases AB and early B
Carbon and nitrogen abundances in the photospheres of Algol-typebinaries are examined using theoretical models of semidetached systems.It is found that only convection, thermohaline mixing, and circulationcaused by the accretion effect are important for binary systems in thesemidetached phase. There is no significant difference in the chemicalcomposition of components between case AB and early case B masstransfer. A real difference is found between systems which evolve frominitial mass ratios of 10/4 and 10/9. Neither stellar wind nor magneticstellar wind affect the chemical composition of the secondarycomponents. Analysis of the evolutionary status of the Algol-typebinaries revealed that about half of them have evolved from initial massratios of about 10/4.
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
