Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| All-Sky Automated Survey eclipsing binaries with observed high period change rates
We present 31 bright eclipsing contact and semidetached binaries thatshowed high period change rates (HPCRs) in a 5-yr interval inobservations by the All-Sky Automated Survey. The time-scales of thesechanges range from only 50 up to 400 kyr. The orbital periods of 10binaries are increasing and of 21 are decreasing, and even a largerexcess is seen in contact binaries, where the numbers are 5 and 17,respectively. Period change has previously been noticed for only two ofthese binaries; our observations confirmed a secular period drift for SVCen and period oscillations for VY Cet. The spectroscopic quadruplesystem V1084 Sco shows both period change and brightness modulation.According to our results, the incidence of asymmetry in the brightnessat maximum light in the HPCR domain may be different from the incidencein the general population. All investigated binaries were selected froma sample of 1711 (1135 contact and 576 semidetached) that fulfilled allcriteria of data quality. We also introduce a `branch' test to check ifluminosity changes on part of the binary's photosphere have led to aspurious or poorly characterized period change detection.
| Precise Times of Minimum Light of Neglected Eclipsing Binaries
Not Available
| The Case for Third Bodies as the Cause of Period Changes in Selected Algol Systems
Many eclipsing binary star systems show long-term variations in theirorbital periods, evident in their O-C (observed minus calculated period)diagrams. With data from the Robotic Optical Transient Search Experiment(ROTSE-I) compiled in the SkyDOT database, New Mexico State University 1m data, and recent American Association of Variable Star Observers(AAVSO) data, we revisit Borkovits and Hegedüs's best-casecandidates for third-body effects in eclipsing binaries: AB And, TV Cas,XX Cep, and AK Her. We also examine the possibility of a third bodyorbiting Y Cam. Our new data support their suggestion that a third bodyis present in all systems except AK Her, as is revealed by thesinusoidal variations of the O-C residuals. Our new data suggest that athird body alone cannot explain the variations seen in the O-C residualsof AK Her. We also provide a table of 143 eclipsing binary systems thathave historical AAVSO O-C data with new values computed from the SkyDOTdatabase.
| Periodic Changes in O-C Diagrams
The article describes basic ideas and physical background of a magneticdynamo model of quasiperiodic changes in the O-C diagram of eclipsingbinaries.
| 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.
| Minima Kurt Locher 2004-2005
Minima observed 2004..2005 by Kurt Locher visually, not accepted by IBVSas part of BBSAG Bulletin.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| CCD Observations of Times of Minima of Eclipsing Binaries
120 minima timings are reported for 39 E. B. systems observed from 2002to 2005 with the Rigel telescope at Winer Observatory. The timings weredetermined using a folded light curve analysis of light curves derivedfrom CCD images. Typical timing uncertainties were 30-60 sec.
| HATNET Variability Survey in the High Stellar Density ``Kepler Field'' with Millimagnitude Image Subtraction Photometry
The Hungarian-made Automated Telescope Network (HATnet) is an ongoingproject to detect transiting extrasolar planets using small-aperture (11cm diameter) robotic telescopes. In this paper, we present the resultsfrom using image subtraction photometry to reduce a crowded stellarfield observed with one of the HATnet telescopes (HAT-5). This field waschosen to overlap with the planned Kepler mission. We obtained I-bandlight curves for 98,000 objects in a 67 square degree field of viewcentered at J2000 (α,δ) =(19h44m00s0, +37°32'00.0"), near theGalactic plane in the constellations Cygnus and Lyra. These observationsinclude 788 exposures of 5 minutes' length over 30 days. For thebrightest stars (I~8.0) we achieved a precision of 3.5 mmag, falling to0.1 mag at the faint end (I~14). From these light curves we identify1617 variable stars, of which 1439 are newly discovered. The fact thatnearly 90% of the variables were previously undetected furtherdemonstrates the vast number of variables yet to be discovered evenamong fairly bright stars in our Galaxy. We also discuss some of themost interesting cases. These include V1171 Cyg, a triple system withthe inner two stars in a P=1.462 day period eclipsing orbit and theouter star a P=4.86 day Cepheid; HD 227269, an eccentric eclipsingsystem with a P=4.86 day period that also shows P=2.907 day pulsations;WW Cyg, a well-studied eclipsing binary; V482 Cyg, an R Coronae Borealisstar; and V546 Cyg, a PV Telescopii variable. We also detect a number ofsmall-amplitude variables, in some cases with full amplitude as low as10 mmag.
| Cyclic Period Changes in the Algol WW Cygni
Year to decade-long cyclic period changes have been observed in manyclasses of close binaries. The Algol binary WW Cygni shows a cyclicchange in its orbital period with an amplitude of slightly more than0.02 days and a period of 56 years. A hypothetical third or fourth bodydoes not satisfactorily explain the observed variation in the orbitalperiod. The change in luminosity and color of the system at primaryeclipse minimum are in agreement with the model proposed by Applegatefor a magnetic cycle induced period change in WW Cygni. We havecommenced monitoring 9 close binaries for evidence of the luminosity andcolor changes consistent with the magnetic cycle hypothesis. δLibrae is suggested as a case suitable for observation with an opticalinterferometer to test the third body proposed for this Algol system.
| 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
| 162-nd List of Minima Timings of Eclipsing Binaries by BBSAG Observers
Not Available
| Archive of Photometric Plates Obtained at Cluj Astronomical Observatory
The archive of photometric plates obtained at the AstronomicalObservatory of Cluj in the period 1952-1974 is presented. The plateinventory is made within the framework of the Wide-Field Plate Databaseproject. The plates were taken in the regions around 110 variable stars(eclipsing variables and RR Lyrae-type stars), as well as in somecomparison stars regions.
| 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.
| 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 Search for Trojan Extrasolar Planets: Planets in V442 Cas and YZ Aql?
In this project we are exploring the light curves of eclipsing binariesfor the signature of planets that may exist at the L4 and L5 Lagrangepoints of the stellar system. While no binaries are known to exist thatstrictly satisfy the stellar mass ratio constraint for the restrictedthree-body problem, the general solution would allow a planet formed atthe L-point to remain there if there are no major perturbing bodies suchas an additional planet. We have coined such objects "Trojan planets."The advantage of this approach is that the phases of the planetaryeclipses are known. We picked systems with deep primary eclipses, tomaximize the amount of system light eclipsed by the planet when in frontof the hotter star. We also scanned the Finding List for Observers ofInteractive Binary Stars, for G dwarf systems ,but found only a few thatwere high inclination and detached. The target list includes QY Aql, YZAql, V442 Cas, SS Cet, S Cnc, VW Cyg, WW Cyg, RR Dra, RX Gem, RY Gem, VWHya, Y Leo, TV Mon, BN Sct, UW Vir, AC UMa, TX UMa, and GSC 1657. Wehave concentrated on V442 Cas and YZ Aql, based on initial results thatshow anomalies in the light curves near the phases where a Trojan planeteclipse is expected. We present results on these two, as well as initialresults for some of the other systems. We gratefully acknowledge thesupport of the National Science Foundation, through grants AST-9731062and AST-0089248. We also appreciate the support of the Fund forAstrophysical Research. Gregory Shelton and Brenda Corbin, at the U.S.naval Observatory Library, have been indispensable in providingreferences for these binary systems. This research has made use of theSimbad database, operated at CDS, Strasbourg, France
| Anomalous Limb Darkening in the Atmospheres of Components of Close Binary Systems with a Strong Reflection Effect
Not Available
| Orbital period modulation and quadrupole moment changes in magnetically active close binaries
We discuss the main characteristics of the orbital period modulation inclose binaries with late-type components. We focus on the variousphysical scenarios proposed to explain this phenomenon and, inparticular, Hall's (1989) suggestion that it may be connected withmagnetic activity. Starting from the work of Applegate (1992) and Lanzaet al. (1998a), we develop an integral approach to evaluate thegravitational quadrupole moment of an active star and its variations,which we consider to be an important driver of the observed orbitalperiod changes. The method applies the tensor virial theorem afterChandrasekhar (1961) and directly relates the variation of thequadrupole moment with the changes of kinetic and magnetic energy of thestellar hydromagnetic dynamo. Particular effort has been applied inminimizing the number of free parameters entering the problem. A sampleof 46 close binaries with period changes of alternate signs has beenstudied by our method. The amplitude of the quadrupole moment changeappears to decrease with increasing angular velocity, implying that thetime-variable part of the kinetic energy of rotation varies as delta{cal T}/{cal T} ~ Omega ({-0.93+/-) 0.10}, with a correlationcoefficient of 0.83. The length of the cycle of the orbital periodmodulation seems to be correlated with the angular velocity asPmod ~ Omega ({-0.36+/-) 0.10}, but with a smallercorrelation coefficient of 0.62. These results support the suggestionthat a distributed non-linear dynamo is at work in the convectiveenvelopes of very active stars and that it strongly affects thedifferential rotation. We also discuss the energy budget of the processresponsible for the quadrupole moment variation and find that, onaverage, only ~ 10% of the energy required to maintain the differentialrotation may be lost by dissipation in the turbulent convective envelopeduring a cycle of the orbital period change. The problems of themagnetic field geometry and stability and the relationship between thelength of the activity cycle, as determined by the change of the area ofthe starspots and the orbital period modulation, respectively, are alsoaddressed.
| 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.
| Eclipse Timing Observations of Three Close Binaries
High precision timing observations of eclipse minima are given for theclose eclipsing binaries T LMi, EQ Tau, and WW Cyg.
| Chemical Evolution of Algols
Not Available
| 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.
| Effects of Gravitational Microlensing of Binary and Multiple Stars
Not Available
| Color Change Caused by Microlensing of Binary and Multiple Stars
Not Available
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Quantitative spectral types for 19 Algol secondaries
Time-resolved spectra of 19 short-period Algol-type binary star systemsobtained during total eclipse are used to derive the temperaturespectral class of the mass-losing secondary component. The spectralclassifications employed a quantitative comparison of the strengths ofabsorption features in stars of known spectral class with those of theprogram stars. The luminosity spectral class can not be determined fromthese data, so both main-sequence and giant stars were used for thecomparison. Our spectral types are compared with published types andfound to be generally in good agreement, unless the published types arederived from the light curves. The photometrically determined types aresystematically later than our directly determined types. This effect isshown also to exist in catalogs of Algol parameters.
| 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.
|
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: | Cygnus |
| Ascensió Recta: | 20h04m02.71s |
| Declinació: | +41°35'16.4" |
| Magnitud Aparent: | 10.097 |
| Moviment propi RA: | -0.7 |
| Moviment propi Dec: | -7.1 |
| B-T magnitude: | 10.187 |
| V-T magnitude: | 10.105 |
Catàlegs i designacions:
|
