내용
사진
사진 업로드
DSS Images Other Images
관련 글
B.R.N.O. Contributions #34
Not Available
| A spectroscopic study of the Algol-type binaries S Equulei and KO Aquilae: absolute parameters and mass transfer
We present and analyse high-resolution optical spectra of two Algolbinaries, namely S Equ and KO Aql, obtained with the echellespectrograph at Catania Astrophysical Observatory. New accurate radialvelocities (RVs) for the hotter primary components are obtained. Thanksto the cross-correlation procedure, we were able to measure, for thefirst time to our knowledge, RVs also for the cool secondary componentsof S Equ and KO Aql. By combining the parameters obtained from thesolution of the RV curves with those obtained from the light-curveanalysis, reliable absolute parameters of the systems have been derived.The rotational velocity of the hotter components of S Equ and KO Aql hasbeen measured and it is found that the gainers of both systems rotateabout 30 per cent faster than synchronously. This is likely due to masstransfer across the Lagrangian L1 point from the cooler tothe hotter component. The lower luminosity of the mass-gainingcomponents of these systems compared to normal main-sequence stars ofthe same mass can also be an effect of the mass transfer. The Hαprofiles were analysed with the `synthesis and subtraction' techniqueand reveal clear evidence of mass transfer and accretion structures. Inboth systems, especially before the primary eclipses and afterwards, weclearly observed extra absorption lines. From the integrated absorptionand the RV variations of these features, we found that the massaccretion is very dense around the impact region of the hottercomponents. A double-peaked emission in the spectra of S Equ was seenoutside the eclipses. One of these peaks is likely originated in aregion between the centre of mass and the cooler component, which isoccupied by the flowing matter. Furthermore, the Hα differencespectra of S Equ and KO Aql also display emission features, which shouldbe arising from the magnetic activity of the cooler components.Based on observations collected at the Catania Astrophysical Observatory(Italy).E-mail: fsoydugan@comu.edu.tr
| Third-Body Parameters from Whole Light and Velocity Curves
Eclipsing binaries can improve multiple system statistics via thelight-time effect and radial velocity shifts. Here an algorithm operateson data of mixed type to exploit these opportunities. Main reasons forenhanced reliability are that (1) combined light and velocity curvesgive better timewise coverage than either type alone, (2) properlyweighted solutions impersonally balance light and velocity information,and (3) the entire theory is within the computer model, so observationsare used directly without corrections. A brief history of mixedwhole-curve solutions is given and the relative importance of light-timeand radial velocity input for third-body parameters is discussed andquantified. Period sifting by power spectral analysis is essentiallyindispensable in preliminary work. Applications are to the Algol-typesystem DM Persei and the detached system VV Orionis. An assumption ofcoplanarity for DM Per's inner and outer orbits is tested and quantifiedby dynamical experiments. Derived third-body parameters for DM Per aremainly reasonable and self-consistent. For comparison with whole-curveresults, we also investigated DM Per's ephemeris in terms of eclipsetimings and found whole-curve solutions to give smaller standard errorsin reference epoch (T0), binary orbit period (P), and dP/dt,over a similar baseline in time. An astonishing outcome is lack ofevidence that can pass reasonable validity tests for VV Ori'swell-accepted third star with P~120 days. Estimates of third light doindicate a third star, but the correct period cannot now be established,so the star cannot be identified as the one heretofore recognized fromradial velocity evidence. The much cited 120 day period appears to be anartifact of the window function for VV Ori's historical velocityobservations.
| 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.
| Modeling of PMS Ae/Fe stars using UV spectra
Context: .Spectral classification of AeFe stars, based on visualobservations, may lead to ambiguous conclusions. Aims: . We aimto reduce these ambiguities by using UV spectra for the classificationof these stars, because the rise of the continuum in the UV is highlysensitive to the stellar spectral type of A/F-type stars. Methods: . We analyse the low-resolution UV spectra in terms of a3-component model, that consists of spectra of a central star, of anoptically-thick accretion disc, and of a boundary-layer between the discand star. The disc-component was calculated as a juxtaposition of Planckspectra, while the 2 other components were simulated by thelow-resolution UV spectra of well-classified standard stars (taken fromthe IUE spectral atlases). The hot boundary-layer shows strongsimilarities to the spectra of late-B type supergiants (see Appendix A). Results: . We modeled the low-resolution UV spectra of 37 AeFestars. Each spectral match provides 8 model parameters: spectral typeand luminosity-class of photosphere and boundary-layer, temperature andwidth of the boundary-layer, disc-inclination and circumstellarextinction. From the results of these analyses, combined with availabletheoretical PMS evolutionary tracks, we could estimate their masses andages and derive their mass-accretion rates. For a number of analysed PMSstars we calculated the corresponding SEDs and compared these with theobserved SEDs. Conclusions: . All stars (except βPic) showindications of accretion, that affect the resulting spectral type of thestellar photosphere. Formerly this led to ambiguities in classificatonof PMS stars as the boundary-layer was not taken into consideration. Wegive evidence for an increase of the mass-accretion rate with stellarmass and for a decreases of this rate with stellar age.
| An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium
We present a survey of diffuse O VI emission in the interstellar medium(ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).Spanning 5.5 yr of FUSE observations, from launch through 2004 December,our data set consists of 2925 exposures along 183 sight lines, includingall of those with previously published O VI detections. The data wereprocessed using an implementation of CalFUSE version 3.1 modified tooptimize the signal-to-noise ratio and velocity scale of spectra from anaperture-filling source. Of our 183 sight lines, 73 show O VIλ1032 emission, 29 at >3 σ significance. Six of the 3σ features have velocities |vLSR|>120 kms-1, while the others have |vLSR|<=50 kms-1. Measured intensities range from 1800 to 9100 LU (lineunit; 1 photon cm-2 s-1 sr-1), with amedian of 3300 LU. Combining our results with published O VI absorptiondata, we find that an O VI-bearing interface in the local ISM yields anelectron density ne=0.2-0.3 cm-3 and a path lengthof 0.1 pc, while O VI-emitting regions associated with high-velocityclouds in the Galactic halo have densities an order of magnitude lowerand path lengths 2 orders of magnitude longer. Although the O VIintensities along these sight lines are similar, the emission isproduced by gas with very different properties.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
| 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.
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderliche Sterne e.V.
Not Available
| Polarimetric Study of the Massive Interacting Binary W Serpentis: Discovery of High-Latitude Scattering Spot/Jet
We present multicolor (UBVRI) polarimetry and additional B-band CCDpolarimetry of the peculiar, strongly interacting binary W Ser, withgood coverage over the 14.16 day orbital period in the three observingseasons 2001-2003. An interesting finding is that the first harmonicdominates in polarization variations over the binary cycle in eachseason, indicating that the main contribution to the polarized flux iscoming from a localized region away from the orbital plane. We apply ournew model codes for electron scattering in circumstellar matter tointerpret the data and find that a ``spot or jet'' like region atlatitude φ~65deg has clearly the best signal-to-noiseratio (>30) among the detected scattering components. Significantshell and stream components are also found, but no disk is seen in thepolarized light. The upper limits for the total number of free electronsin an optically thin scattering disk are an order of magnitude lowerthan in the spherical shell around the primary star. A possible reasonis that the accretion disk is optically thick and has a clearly definedand visible pseudophotosphere. Multiple scattering and absorptioneffects in an optically thick regime reduce the polarization of theobserved light to small levels. Scattering from optically thin parts ofthe circumstellar matter, the shell, the stream, and the high-latitudespot/jet, possibly associated with optically thin polar regions of theaccretion disk, dominates in the observed polarization of W Ser.
| Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| Spectroscopic binaries with elliptical orbits
The radial velocity curves of many spectroscopic binaries (SBs) areperturbed by gas streams or proximity effects. For SBs with circularorbits, these perturbations can give rise to spurious orbitaleccentricities of high statistical significance. But tests to identifysuch anomalous orbits can be constructed since perturbed velocity curvesare in general no longer Keplerian. The derived tests are applied bothto synthetic and to observed velocity curves.
| Two- and Three-Dimensional Hydrodynamical Simulations of Mass Transfer in Semidetached Binaries with Explicit Radiative Cooling and Self-Absorption in Their Gaseous Envelopes
We have modeled the mass transfer in three Algol-type binaries usingtwo-and three-dimensional numerical hydrodynamical techniques. Radiativecooling and absorption in the envelopes surrounding the components ofthe close binaries are explicitly taken into account. The resultingenvelope temperatures are consistent with those observed. We derivedthese temperatures by considering the energy balance in the moving gas,including heating due to the numerical viscosity that is inherent to thesimulations and radiative cooling. The radiative cooling was calculatedassuming an optically thin plasma in a state of ionization balance.Taking into account both of these processes yielded temperatures of 400030 000 K in the disk around the accreting primary and in the commonenvelope surrounding the close binary. Our computations also indicatethat the envelope morphology is not sensitive to the radiative-coolingmodel used.
| The BAA Observers' Workshops: Observing eclipsing variables: a beginners' guide
The General Catalogue of Variable Stars (GCVS)1 lists many differentclasses of variable star. Some of these are well known and contain manymembers; others are more obscure and contain only a few examples.However, it is also possible to split variable stars into just two basiccategories: the intrinsic variables ? stars like Mira variables, Cepheidvariables, novae and supernovae ? in which the stars themselves arevarying in brightness, and the extrinsic variables, in which theindividual stars themselves do not actually vary, and prominent amongthese are the eclipsing variables.
| Semi-detached binaries as probes of the Local Group
Evolutionary and distance estimation issues for eclipsing binaries (EBs)are examined in the context of spin-off from gravitational lens surveysand the GAIA mission. The OGLE survey shows a major deficiency of normalAlgol type binaries in the Small Magellanic Cloud. Statistical analysiscoupled with further observing will be needed to decide if the Algolshortfall is an evolutionary effect connected with low metallicity or isonly apparent. Distances estimated for EBs are directly physical, withno need for calibration via nearby examples with known distances (EBdistance indicators are therefore not standard candles, contrary tocommon usage of the name). Only the best examples will be needed fordistances, given the enormous numbers of EBs expected from GAIA, so onecan be very selective. Accordingly the relative merits of detached (DB),semi-detached (SD), and overcontact (OC) EBs are discussed, withemphasis on under-recognized advantages of SDs and OCs. Included areconsiderations of orbital eccentricity, morphology, photometric massratios, observing efficiency, aliasing of radii, and practicality.
| The Impact of Space Experiments on our Knowledge of the Physics of the Universe
With the advent of space experiments it was demonstrated that cosmicsources emit energy practically across all the electromagnetic spectrumvia different physical processes. Several physical quantities givewitness to these processes which usually are not stationary; thosephysical observable quantities are then generally variable. Thereforesimultaneous multifrequency observations are strictly necessary in orderto understand the actual behaviour of cosmic sources. Space experimentshave opened practically all the electromagnetic windows on the Universe.A discussion of the most important results coming from multifrequencyphotonic astrophysics experiments will provide new inputs for theadvance of the knowledge of the physics, very often in its more extremeconditions. A multitude of high quality data across practically thewhole electromagnetic spectrum came at the scientific community'sdisposal a few years after the beginning of the Space Era. With thesedata we are attempting to explain the physics governing the Universeand, moreover, its origin, which has been and still is a matter of thegreatest curiosity for humanity. In this paper we will try to describethe last steps of the investigation born with the advent of spaceexperiments, to note upon the most important results and open problemsstill existing, and to comment upon the perspectives we can reasonablyexpect. Once the idea of this paper was well accepted by ourselves, wehad the problem of how to plan the exposition. Indeed, the exposition ofthe results can be made in different ways, following several points ofview, according to: - a division in diffuse and discrete sources; -different classes of cosmic sources; - different spectral ranges, whichimplies in turn a sub-classification in accordance with differenttechniques of observations; - different physical emission mechanisms ofelectromagnetic radiation; - different vehicles used for launching theexperiments (aircraft, balloons, rockets, satellites, observatories). Inorder to exhaustively present The Impact of Space Experiments on ourKnowledge of the Physics of the Universe it would then have beennecessary to write a kind of Encyclopaedia of the Astronomical SpaceResearch, which is not our desire. On the contrary, since our goal is toprovide an useful tool for the reader who has not specialized in spaceastrophysics and for the students, we decided to write this paper in theform of a review, the length of which can be still consideredreasonable, taking into account the complexity of the argumentsdiscussed. Because of the impossibility of realizing a complete pictureof the physics governing the Universe, we were obliged to select how toproceed, the subjects to be discussed the more or the less, or those tobe rejected. Because this work was born in the Ph.D. thesis of one of us(LSG) (Sabau-Graziati, 1990) we decided to follow the `astronomicaltradition' used there, namely: the spectral energy ranges. Although suchenergy ranges do not determine physical objects (even if in many casessuch ranges are used to define the sources as: radio, infrared, optical,ultraviolet, X-ray, γ-ray emitters), they do determine themethods of study, and from the technical point of view they define thetechnology employed in the relative experiments. However, since then wehave decided to avoid a deep description of the experiments, satellites,and observatories, simply to grant a preference to the physical results,rather than to technologies, however fundamental for obtaining thoseresults. The exposition, after an introduction (Section 1) and somecrucial results from space astronomy (Section 2), has been focussed intothree parts: the physics of the diffuse cosmic sources deduced fromspace experiments (Section 3), the physics of cosmic rays from ground-and space-based experiments (Section 4), and the physics of discretecosmic sources deduced from space experiments (Section 5). In this firstpart of the paper we have used the logic of describing the main resultsobtained in different energy ranges, which in turn characterize theexperiments on board space vehicles. Within each energy range we havediscussed the contributions to the knowledge of various kind of cosmicsources coming from different experiments. And this part is mainlyderived by the bulk of the introductory part of LSG's Ph.D. thesis. Inthe second part of the paper, starting from Section 6, we have preferredto discuss several classes of cosmic sources independently of the energyranges, mainly focussing the results from a multifrequency point ofview, making a preference for the knowledge of the physics governing thewhole class. This was decided also because of the multitude of new spaceexperiments launched in the last fifteen years, which would haverendered almost impossible a discussion of the results divided intoenergy ranges without weakening the construction of the entire puzzle.We do not pretend to cover every aspect of every subject consideredunder the heading of the physics of the universe. Instead a crosssection of essays on historical, modern, and philosophical topics areoffered and combined with personal views into tricks of the spaceastrophysics trade. The reader is, then, invited to accept this papereven though it obviously lacks completeness and the arguments discussedare certainly biased by a selection effect owed essentially to ourknowledge, and to it being of a reasonable length. Some parts of itcould seem, in certain sense, to belong to an older paper, in which the`news' is not reported. But this is owed to our own choice, just in fullaccord with the goals of the text: we want to present those resultswhich have, in our opinion, been really important, in the development ofthe science. These impacting results do not necessarily constitute thelast news. This text was formally closed just on the day of the launchof the INTEGRAL satellite: October 17, 2002. After that date onlyfinishing touches have been added.
| 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
| Two-Dimensional Hydrodynamical Modeling of Mass Transfer in Semidetached Binaries with Asynchronously Rotating Components
We have modeled the mass transfer in the three semidetached binaries UCep, RZ Sct, and V373 Cas taking into account radiative cooling bothimplicitly and explicitly. The systems have asynchronously rotatingcomponents and high mass-transfer rates of the order of 10-6 Mȯ/yr; they are undergoing various stages of their evolution. Anaccreting star rotates asynchronously if added angular momentum isredistributed over the entire star over a time that exceeds thesynchronization time. Calculations have indicated that, in the modelconsidered, mass transfer through the point L1 is unable todesynchronize the donor star. The formation of an accretion disk andouter envelope depends on the component-mass ratio of the binary. Ifthis ratio is of the order of unity, the flow makes a direct impact withthe atmosphere of the accreting star, resulting in the formation of asmall accretion disk and a relatively dense outer envelope. This is trueof the disks in U Cep and V373 Cas. When the component-mass ratiosubstantially exceeds unity (the case in RZ Sct), the flow forms alarge, dense accretion disk and less dense outer envelope. Taking intoaccount radiative cooling both implicitly and explicitly, we show that aseries of shocks forms in the envelopes of these systems.
| From the Heart of the Ghoul: C and N Abundances in the Corona of Algol B
Chandra Low Energy Transmission Grating Spectrograph observations ofAlgol have been used to determine the abundances of C and N in thesecondary star for the first time. In order to minimize errors arisingfrom an uncertain coronal differential emission measure as a function oftemperature, the analysis was performed relative to similar observationsof an adopted ``standard'' star, HR 1099. It is demonstrated that HR1099 and Algol are coronal twins in many respects and that their X-rayspectra are very similar in nearly all details, except for the observedstrengths of C and N lines. The H-like2p2P3/2,1/2-->1s2S1/2transitions of C and N in the coronae of Algol and HR 1099 demonstratethat the surface abundances of Algol B have been strongly modified by CNprocessing, as shown earlier by Schmitt & Ness. It is found that Nis enhanced in Algol B by a factor of 3 compared with HR 1099. No Clines are detected in the Algol spectrum, indicating a C depletionrelative to HR 1099 by a factor of 10 or more. These C and N abundancesindicate that Algol B must have lost at least half of its initial massand are consistent with predictions of evolutionary models that includenonconservative mass transfer and angular momentum loss through magneticactivity. Based on H-like and He-like transitions in O and Ne, it isestimated that Algol is slightly metal poor, by 0.2 dex in terms of thecoronal abundances of light elements relative to HR 1099, while the FeXVII2p53d1P1-->2p61S0transition indicates a very similar Fe abundance. In reviewing coronalabundance results for active stars in the literature and drawing on anearlier Chandra study of the coronal abundances of HR 1099, it isconcluded that Fe is very likely depleted in the coronae of both Algoland HR 1099 by 0.5 dex relative to their photospheric compositions, butthat Ne is enhanced by a similar magnitude. Light elements such as C, N,and O are likely depleted in both stars by of order 0.3 dex. Thesimilarities in these large-abundance anomalies in HR 1099 and Algol arenotable. Despite such compositional fractionation in these coronae, therelative C and N abundances in HR 1099, determined by comparing observedline strengths with theoretical C/N line ratios, are consistent withrecent solar values, indicating that differential fractionation betweenthese elements is not significant and that little or no dredge-up ofmaterial subjected to CN processing has occurred on the subgiantcomponent.
| 162-nd List of Minima Timings of Eclipsing Binaries by BBSAG Observers
Not Available
| Photoelectric Minimum Times of Some Eclipsing Binary Stars
We present 12 minimum times of 6 eclipsing binaries observed in theyears from 1996 to 1999.
| Ultraviolet Spectroscopic Analysis of Mass Flow in the Interacting Binary U Cephei
Twenty-nine far-ultraviolet and forty-seven near-ultraviolet highresolution International Ultraviolet Explorer (IUE) Satellite archivalspectra of the interacting Algol-type binary U Cephei ( B7 V + G8 III-IV) have been analyzed in order to determine the nature of the variablemass flow occurring in this system. Relatively good phase coverage wasobtained in 1989 with fourteen far-ultraviolet and fifteennear-ultraviolet spectra spread over 1.2 orbits. The effects of gasstreaming within and out of the system and of pseudophotospheric flow onthe primary star are clearly seen in the ultraviolet resonance lines ofSi IV (λ λ 1393, 1402 ), CIV (λ λ 1548,1550), Al II (λ 1670 ), Al III (λ λ 1854, 1862 ),Fe II (λ 2599 ), and Mg II (λ λ 2795, 2802 ). Amajor mass flow outburst occurred in 1986 and a weaker outburst appearsin some of the 1989 spectra. Light curves were constructed at a numberof ultraviolet wavelengths. These light curves show significantdepartures from those expected from quiescent eclipsing binaries. It maybe concluded that U Cep, and a number of other Algol-type binariesstudied elsewhere, show pseudophotospheric accretion phenomena, massexchange and systemic mass loss with occasional, variable, short-termincreases in activity.
| Problems in modeling evolutionary processes in close binaries
In modeling the evolutionary processes of interacting binaries, a numberof assumptions are invoked by many workers concerning the manner of themass flow between the two stars. This article reviews the validity ofthe four assumptions most commonly used, namely, assumptions concerning(A) the critical Roche equipotential surface (the so-called Roche lobe),(B) accretion of matter from one star to its companion, (C) mass lossfrom the binary system, and (D), which is related to the last two items,whether the mass flow in a binary system is conservative or not. A largenumber of workers in this field appear to assume that the critical Rocheequipotential surfaces (Roche lobes, in their lexicon) control the massflow with the Lagrangian 1 point acting like a nozzle, channeling arather well collimated jet of gas. Similarly, they also assume thataccretion `disks' are formed in this process and those `disks' haveproperties very similar to solid disks with well defined surfaces andwith precession, nutation etc. Finally, they assume, except in the mostextreme case of rapid mass flow, conservative mass flow in which allmass lost by one star is completely accreted by the companion. Thesecommonly invoked assumptions are critically examined from bothobservational data and relevant physics and are shown to be lackingrealistic justification. We show what the concept of Roche equipotentialsurfaces actually tells us, and examine the manners of actual mass flowobserved in selected binaries.
| 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.
| 149 Bedeckungssterne der BAV-Programme. Eine Analyse der Beobachtungstatigkeit seit den Angangen.
Not Available
| Das Brunner Punktesystem.
Not Available
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
Not Available
| Variation mechanisms in symbiotic nova V1329 Cygni
U,B,V light curves of symbiotic nova V1329 Cygni (=HBV 475) are modelledin terms of combined wind and chromospheric fluorescence, with eclipsesand shadowing of fluorescent regions, eccentric orbit effects, andconversion of far-ultraviolet energy into the optical bands.Observational evidence regarding fluorescent brightness variationmechanisms is provided by waveforms and amplitudes and their changesfrom bandpass to bandpass. The combined set of U,B,V variations cannotbe satisfied with a wind-only or chromosphere-only model. Contrary toarguments in the literature, chromospheric fluorescence can becomparable to wind fluorescence in brightness and can be far strongerthan photospheric emission from a red giant. We show why there is noconflict between the existence of strong chromospheric fluorescence andsymbiotic binary energetics, at least in this example. Ultraviolet andoptical radial velocities are also discussed and fitted. Some parts ofthe fluorescent binary model omitted from the original paper by Wilsonfor lack of space are given here. Fitting was done both subjectively andby differential corrections (least-squares criterion), thus providinginsight into the interplay of wind and chromospheric effects. The largebandpass-dependent waveform and amplitude changes are accounted for bydiffering relative amounts of wind and chromosphere fluorescence, withthe chromosphere relatively bright in U and the wind relatively brightin B and V. A strong test of the model is provided by the way theamplitude and waveform change together - larger amplitude must go withwider minima, as observed. The differential corrections solutions fitthe light curves rather well. Because they were done in JD rather thanin phase, the solutions were also able to find ephemeris parameters.Potentially interesting is an enormous period change ofdP/dt~-0.0020+/-0.0004 s.d. which, if confirmed, means that the ~955dperiod is dropping by 2d each cycle. Parameter results are tabulated,but our emphasis is on identification of variation mechanisms ratherthan specific numbers. Observational selection favours discovery ofperiodic fluorescent variation for arguments of periastron nearω=π/2 because wind and chromospheric fluorescence then combineto give maximum amplitude. The possibility of pre-outburst drops inbrightness being eclipses is examined. We urge spectroscopic observersto gather infrared radial velocities of the red giant and to search forsubtle evidence of eclipses of the hot object. Infrared light curvesalso would be helpful if reasonably large numbers of data points couldbe accumulated.
| Short-Period Light Variation of an Eclipsing Binary System: RZ Cassiopeiae
The eclipsing binary system RZ Cas is known to exhibit variation in itslight curves at the primary minimum, usually showing apartial-eclipse-type curve but sometimes indicating a flat minimum,which is evidence for a total eclipse. We observed RZ Cas not onlyduring the primary eclipse, but also during the out-of-eclipse phase,and we have found a short-period light variation with a frequency of62.20 cycles day-1 (period of 23.15 minutes), whose maximumamplitude is 0.02 mag. This short-period variation can modulate theshape of the light curve at the primary minimum effectively. Thebrightness-color relationship of the short-period variation suggests aδ Scuti type oscillation.
| 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
| UBV Photometry of the Massive Eclipsing Binary TT Aur
UBV observations of the massive binary system TT Aur were carried outmainly at the Turkish National Observatory (TUG). These observations,together with IUE spectra and times of eclipse minima collected from theliterature, were used to study the system parameters. Simultaneoussolution of the light curves by the Wilson-Devinney code allows asemi-detached configu-ration with a slightly larger Roche-lobe fillingsecondary. This picture is supported by other evidence. The shoulders ofthe primary minimum suggest some excess absorption, in keeping withcircumstellar material in the form of a disk-like structure around theprimary component. The deeper primary minimum in the U filter mayindicate a hotter region on the secondary-facing hemisphere of theprimary. The period variation of the system can also be related to thepossible existence of a third component in a circular orbit around thesystem. An alternative detached representation is also considered usingoptimal curve-fitting techniques. We appeal for further observations tohelp resolve some outstanding issues in this interesting massive binary.
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
