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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.
| Three-dimensional Doppler Tomogram of Gas Flows in the Algol-Type Binary U Coronae Borealis
The reconstruction of three-dimensional (3D) Doppler tomograms based onobservational data has been accomplished for the first time. Thedistribution of the Hα emission intensityI(Vx,Vy,Vz) of the interacting Algolbinary system U Coronae Borealis has been restored in 3D velocity spacewith resolutions of 30 km s-1 in Vx andVy and 110 km s-1 in Vz. Thereconstruction was based on 47 Hα spectra from 1994 by applyingthe developed radioastronomical approach (RA) to few-projectionstomography. The comparison between the previous 2D and our 3D Dopplertomograms shows similarities with the main structural features of thegas flows in the orbital plane. Specifically, the gas stream along theballistic trajectory and equatorial emission centered on the primarystar are displayed on the 3D Doppler tomogram as distinct emissionsources. A high-velocity stream (Vz~200 km s-1)with strong emission intensity has also been discovered moving in thedirection across the orbital plane of the system.
| Evolution of interacting binaries with a B type primary at birth
We revisited the analytical expression for the mass ratio distributionfor non-evolved binaries with a B type primary. Selection effectsgoverning the observations were taken into account in order to comparetheory with observations. Theory was optimized so as to fit best withthe observed q-distribution of SB1s and SB2s. The accuracy of thistheoretical mass ratio distribution function is severely hindered by theuncertainties on the observations. We present a library of evolutionarycomputations for binaries with a B type primary at birth. Some liberalcomputations including loss of mass and angular momentum during binaryevolution are added to an extensive grid of conservative calculations.Our computations are compared statistically to the observeddistributions of orbital periods and mass ratios of Algols. ConservativeRoche Lobe Over Flow (RLOF) reproduces the observed distribution oforbital periods but fails to explain the observed mass ratios in therange q in [0.4-1]. In order to obtain a better fit the binaries have tolose a significant amount of matter, without losing much angularmomentum.
| 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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
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| 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.
| A photometric-spectroscopic analysis and the evolutionary status of the Algol-type binary U Coronae Borealis
The prime purposes of this study are to obtain reliable orbitalparameters for the Algol-type binary U Coronae Borealis (U CrB) and toexplain the evolutionary status of this system. All observations of theprimary star's radial velocity are consistent with the valueK1= 58.6 +/- 2.0 km s-1. Measurements of theradial velocity of the secondary component give K2=185.2+/-5.0 km s-1. Using the photometrically determined inclinationof 78.7 +/- 0.3, the masses of the two stars are therefore deduced to be4.74 +/- 0.28 and 1.46 +/- 0.06 Msolar for the primary andsecondary components, respectively. Using all available observations, wediscuss the origin and evolution of the close binary system U CrB. Wederive the restrictions concerning masses and period from a generalnetwork of calculations of medium mass close binary evolution. Detailedmodels are calculated within the derived ranges, giving the most likelyinitial system parameters as and Pi= 1.4 d. It turns out thatthe interactive evolution up to the present stage has beennon-conservative. During its evolution, U CrB has lost about 14 per centof its initial total mass (ΔM~ 1 Msolar) and around 18per cent of its initial total angular momentum. We also examine thepossibility of probing dynamo action in the mass-losing component of UCrB. We point out that, in order to maintain the evolution of U CrB inits later stages, which is presumably driven by stellar `magneticbraking', an efficient mechanism for producing large-scale surfacemagnetic fields in the donor star is required. We suggest that observedX-ray activity in U CrB may be a good indicator of its evolutionarystatus and the internal structure of the mass-losing component.
| Beobachtungsegebnisse Bundesdeutsche Arbeitsgemainschaft fur Veranderliche Sterne e.V.
Not Available
| The WARPS Survey. VI. Galaxy Cluster and Source Identifications from Phase I
We present in catalog form the optical identifications for objects fromthe first phase of the Wide Angle ROSAT Pointed Survey (WARPS). WARPS isa serendipitous survey of relatively deep, pointed ROSAT observationsfor clusters of galaxies. The X-ray source detection algorithm used byWARPS is Voronoi Tessellation and Percolation (VTP), a technique whichis equally sensitive to point sources and extended sources of lowsurface brightness. WARPS-I is based on the central regions of 86 ROSATPSPC fields, covering an area of 16.2 square degrees. We describe herethe X-ray source screening and optical identification process forWARPS-I, which yielded 34 clusters at 0.06
| Hα spectroscopy and BV photometry of RT Lacertae
Contemporaneous spectroscopic and photometric B V observations of the RSCVn type eclipsing binary RT Lacertae were performedin summer 2000. The photometric observations were obtained at the EgeUniversity Observatory, while the spectroscopic ones were carried out atCatania Astrophysical Observatory in the spectral range 5860-6700Å. We obtained a high quality radial velocity curve of the systemthat allowed us to give more accurate values of the orbital parameters.A steady decrease of the barycentric velocity from 1920 to 2000 has beenpointed out and has been discussed in the context of a third bodyhypothesis. Through the subtraction of a ``synthetic'' spectrum, builtup with spectra of inactive standard stars, we detected Hα excessemission which fills in the photospheric absorption profiles of bothcomponents. With the exception of a few spectra, taken close to theeclipses, in which some extra absorption or a faint double-peaked broademission appears, there is no further evidence of circumstellar matterin this system, as suggested in previous works. The hotter and moremassive star appears also as the more active at a chromospheric level,since it has a Hα flux about ten times greater than the companion,on average. Rotational modulation of the Hα emission has beendetected in both stars. The hemisphere of the more massive star facingthe observer at phase 0fp75 appears brighter (in Hα ) than thatseen at phase 0fp25 , while for the less massive G9 IV star the maximumHα emission is seen around phase 0fp0-0fp1 . From the analysis ofthe contemporaneous light curve (Lanza et al. \cite{Lanza2001}), themore massive G5 IV star results to be more active than the companion ata photospheric level, in agreement with the chromospheric behaviourobserved in Hα . In addition, the starspots of the G5 IV star aremainly located in the Hα brighter hemisphere, suggesting a closespatial association of spots and plages in this star. The G9 IV stardisplays instead the maximum Hα emission at the phase of maximumvisibility of the smaller spotted area found from the light-curveanalysis. The minimum Hα emission occurs when the more heavilyspotted region is visible. Based on observations collected at CataniaAstrophysical Observatory, Italy, and at Ege University Observatory,Turkey. Table 1 only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/388/298
| 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.
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| Das Brunner Punktesystem.
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| 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.
| A Complete Survey of Case A Binary Evolution with Comparison to Observed Algol-type Systems
We undertake a comparison of observed Algol-type binaries with a libraryof computed Case A binary evolution tracks. The library consists of 5500binary tracks with various values of initial primary massM10, mass ratio q0, and period P0,designed to sample the phase-space of Case A binaries in the range-0.10<=logM10<=1.7. Each binary is evolved using astandard code with the assumption that both total mass and orbitalangular momentum are conserved. This code follows the evolution of bothstars to the point where contact or reverse mass transfer occurs. Theresulting binary tracks show a rich variety of behavior that we sortinto several subclasses of case A and case B. We present the results ofthis classification, the final mass ratio, and the fraction of timespent in Roche Lobe overflow for each binary system. The conservativeassumption under which we created this library is expected to hold for abroad range of binaries, where both components have spectra in the rangeG0 to B1 and luminosity classes III to V. We gather a list of relativelywell-determined, observed hot Algol-type binaries meeting thiscriterion, as well as a list of cooler Algol-type binaries, for which weexpect significant dynamo-driven mass loss and angular momentum loss. Wefit each observed binary to our library of tracks using aχ2-minimizing procedure. We find that the hot Algolsdisplay overall acceptable χ2, confirming theconservative assumption, while the cool Algols show much less acceptableχ2, suggesting the need for more free parameters, such asmass and angular momentum loss.
| 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
| New labour on Algols: conservative or liberal?
I consider three topics related to the influence of magnetic braking,combined with tidal friction, on the orbital evolution of CVs. Firstly,I attempt to show that properties of Algols are roughly consistent withthe view that angular momentum loss (AML) takes place in systems withcool (G/K) components, but not in systems with hot (B/A) components.This is what one might expect if the AML requires an active dynamo asseen in the Sun and other cool stars. The timescale required is roughlyof the order of what might be expected by magnetic braking. Someenhanced mass loss (ML), presumably by stellar wind, also seems to benecessary in the more evolved Algol systems. Secondly, I urge thattheorists adopt a recipe for magnetic braking that is more on the linesof Stȩpień (1995) than of Skumanich (1972). Thirdly, Iargue that `interrupted magnetic braking', a mechanism often invoked toexplain the upper edge of the period gap in CVs, is not in accord withobserved properties of late M dwarfs and brown dwarfs, and that someother mechanism should be sought.
| A Multiwavelength Study of Spectral Variations in the CX Draconis Binary
An extensive collection of spectroscopic observations of the interactingbinary CX Dra spanning a 23 year interval have been analyzed. This studyincludes a refinement of the orbital solution of CX Dra; equivalentwidth measurements that show short-, medium-, and long-term behavior ofthe difference profiles; a calculation of the Balmer decrement; velocitymaps based on the velocity curves of the Hα and He I differenceemission peaks; trailed spectrograms of the Hα, Hβ, He I, andSi II lines; and Doppler tomograms at these four wavelengths. The mainconclusions are: 1. The circumstellar environment in the system changesin cycles of hundreds of days. The length of the cycles is variable.These cycles may be part of a ``super'' 4000 day cycle. 2. Theequivalent widths of the difference Hα and He I λ6678 linesare modulated with the orbital period of 6.696 days. The correspondingphase diagrams indicate a great deal of scatter, but the modulation isquite conspicuous when long data strings are used. The pattern of thephase diagram suggests a permanent presence of the emission in Hα,He I λ6678, and Si II λ6371 lines. 3. The radialvelocities of the Hα emission peak follow an S-wave. The resultingvelocity map shows that the source of the single-peaked emission liesclose to the L1 point, roughly between the primary and L1 point. 4.Doppler tomograms constructed for Hα observed and differenceprofiles show that the emission comes from a region of low velocity, agas stream, and an accretion disk. The Hβ emission arises from aregion that is cospatial with the Hα source. The Doppler tomogramsfor He I λ6678 and Si II λ6371 lines suggest that emissionin this gas also originates from a locus of a disk around the primarystar. 5. The model based on the equivalent widths of the differenceprofiles, the trailed spectrograms, and Doppler tomograms of theHα, He I λ6678, Si II λ6371, and Hβ linessuggests that the main source of the Hα emission is about halfwaybetween the stars at a distance of 0.49a from the primary star, and thatthe He I and Si II emission sources arise from an accretion diskcentered on the primary star.
| 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.
| Hα Spectroscopy of RW Monocerotis
Five years of sparse full-orbit Hα spectroscopy are presented forthe short-period Algol RW Monocerotis. A spectroscopic mass ratio isderived that confirms the published photometric mass ratio. Of the twopublished rotation rates of the primary star, 66 and 260 kms-1, the slower best fits our observations. Hα emissionwas not seen during any of five eclipses, indicating that the secondaryis notstrongly chromospherically active. At every epoch an emissionfeature between the two stars was found, confirming that there iscontinuous mass transfer. However, an accompanying accretion disk wasseen in only two of six observing runs, using out-of-eclipsespectroscopy. Comparing with models, we show how a single out-of-eclipseHα observation can provide information on the mass transferpresence at that epoch. Finally, we see redshifted absorption justbefore and after primary eclipse, consistent with the location andvelocity of a mass transfer stream. However, the Hα absorptionequivalent width (with respect to the out-of-eclipse continuum) fallsproportionally with the primary's visibility between first and secondcontact. This indicates that the stream is projected against the entireface of the primary, a much larger area than predicted by theory.
| 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
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| Analysis of the Si IV Ultraviolet Spectra of U Sagittae
Archival IUE spectra of U Sge have been used to study hot (~10^5 K)circumstellar gas in this system. The observed spectra contain severalUV resonance lines, of which the Si IV lines (lambdalambda1394 and 1405)are the strongest. These lines are observed in absorption, so we mustremove the photospheric absorption line contribution to the spectra inorder to see the emission produced by the circumstellar gas. We havedeveloped a robust method for creating such difference spectra from IUEdata. In the observed spectra we see a variation in the line profilesand line centers with an orbital phase suggesting the presence ofcircumstellar gas. The residual emission seen in the difference spectrais strongest between phases phi=0.3 and phi=0.7, with a strength of upto 0.2 of the continuum flux. This is confirmed by the presence of anemission region visible in the Doppler tomogram of the lambda1394 line.This is consistent with the location of an Hα ``absorption zone''seen in tomograms of U Sge and U CrB, and with theoretical predictionsof a high temperature accretion region.
| 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.
| ORFEUS-SPAS II Observations of Algol-type Interacting Binaries
The first results from ORFEUS-SPAS II observations of five Algol-typebinary systems obtained during the shuttle mission STS-80 in 1996November/December are reported. Single spectra covering 900-1220 A of AUMon, Z Vul, U CrB, and TX UMa were acquired with the Berkeleyspectrograph. TT Hya was observed at three phases (0.19, 0.63, and 0.95)to study mass flow and to investigate asymmetry in the circumstellarmaterial in the system. O VI was not detected in any of the binaries,which allows us to place an upper limit on Tion in the high-temperatureplasma seen in Algol-type binaries. Circumstellar material, presumablyassociated with the accretion disk, was detected in Fe III (UV1) in AUMon. We estimate a particle density in the range 108-109 cm-3 for theregion of the disk sampled during the observations. Evidence for massinfall was found in the phase 0.95 spectrum of TT Hya. From theadditional (redshifted) absorption in N II (1085 A) and N I (1135 A), wefind evidence for superionization in this plasma and estimate a lowerlimit of 10-12 Msolar yr-1 for the current infall rate.
| 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.
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