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Three-Dimensional Doppler Images of the Disklike and Streamlike States of U Coronae Borealis
The three-dimensional (3D) Radioastronomical Approach to Dopplertomography has been used to study the Hα emission sources in UCoronae Borealis. These 3D tomograms provide greater resolution than theprojected two-dimensional version and highlight the jetlike gas flows inthe V z direction transverse to the orbital plane. In thispaper, the 3D tomograms are compared at two distinct epochs when U CrBwas in the disklike state (1993 data) and the streamlike state (1994data). Both states display a prominent emission source, thecircumprimary bulge, which is produced when the gas stream strikes thephotosphere of the mass gainer. This source is detected withinVz = ±150 km s–1, and demonstratesthat the bulge is not confined to the orbital plane although it achievesa maximum strength near Vz = 0 km s–1. Otheremission sources include the stream-star and stream-disk shocks and aLocalized Region (LR) where the circling disk material strikes theincoming gas stream. The LR has V z velocities of 200-500km s–1 in the disklike state. The disk emission is seenover a range of V z velocities, and there is evidence thatthe disk is inclined to the orbital plane or may have two arms. The gasstream flows along its predicted trajectory in the streamlike state, anda comparison with the disklike state suggests that the gas stream has ahigher density than the disk in both states of this binary.
| Spin-up and hot spots can drive mass out of a binary
Context: The observed distribution of orbital periods of Algols with aB-type primary at birth agrees fairly well with the prediction fromconservative theory. Conservative evolution fails, however, to producethe rather large fraction of Algols observed with a high mass-ratio,especially: q in [0.4-0.6]. Aims: In order to keep Algols for a longertime with a higher mass-ratio without disturbing the distribution oforbital periods too much, interacting binaries have to lose asignificant fraction of their total mass without losing much angularmomentum before or during Algolism. We propose a mechanism that meetsboth requirements. Methods: In the case of direct impact the gainerspins up: sometimes up to critical velocity. Equatorial material on thegainer is therefore less bound. A similar statement applies to materiallocated at the edge of an accretion disc. The incoming material moreovercreates a hot spot in the area of impact. The sum of the rotational andradiative energy of hot spot material depends on the mass-transfer-rate.The sum of both energies overcomes the binding energy at a well definedcritical value of the mass-transfer-rate. As long as the transfer-rateis smaller than this critical value RLOF happens conservatively. But assoon as the critical rate is exceeded the gainer will acquire no morethan the critical value and RLOF runs into a liberal era. Results:Low-mass binaries never achieve mass-transfer-rates larger than thecritical value. Intermediate-mass binaries evolve mainly conservativelybut mass will be blown away from the system during the short era ofrapid mass-transfer soon after the onset of RLOF. We have calculated theevolution of binaries with a 9 Mȯ primary and a 5.4Mȯ companion over a range of initial orbital periods,covering case-A RLOF. Mass-loss from the system is achieved duringdirect impact only. Conclusions: We find systems that show Algolism formore than ten million years. RLOF occurs almost always conservatively.Only during some 20 000 years the gainer is not capable of grasping allthe material that comes from the donor. The mass-ratio q in [0.4-0.6]which was hardly populated by conservative evolution now contains Algolsfor a significant fraction of their existence.Binary models are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/487/1129
| Spurious Eccentricities of Distorted Binary Components
I discuss the effect of physical distortion on the velocities of closebinary components and how we may use the resulting distortion ofvelocity curves to constrain some properties of binary systems, such asinclination and mass ratio. Precise new velocities for 5 Cetconvincingly detect these distortions with their theoretically predictedphase dependence. We can even use such distortions of velocity curves totest Lucy's theory of convective gravity darkening. The observeddistortions for TT Hya and 5 Cet require the contact components of thosesystems to be gravity darkened, probably somewhat more than predicted byLucy's theory, but clearly not as much as expected for a radiative star.These results imply there is no credible evidence for eccentric orbitsin binaries with contact components. I also present some speculativeanalyses of the observed properties of a binary encased in a nonrotatingcommon envelope, if such an object could actually exist, and discuss howthe limb darkening of some recently calculated model atmospheres forgiant stars may bias my results for velocity-curve distortions, as wellas other results from a wide range of analyses of binary stars.
| Revealing the Nature of Algol Disks through Optical and UV Spectroscopy, Synthetic Spectra, and Tomography of TT Hydrae
We have developed a systematic procedure to study the disks inAlgol-type binaries using spectroscopic analysis, synthetic spectra, andtomography. We analyzed 119 Hα spectra of TT Hya, an Algol-typeeclipsing interacting binary, collected from 1985 to 2001. The newradial velocities enabled us to derive reliable orbital elements,including a small nonzero eccentricity, and to improve the accuracy ofthe absolute dimensions of the system. High-resolution IUE spectra werealso analyzed to study the formation of the UV lines and continuum.Synthetic spectra of the iron curtain using our new SHELLSPEC programenabled us to derive a characteristic disk temperature of 7000 K. Wehave demonstrated that the UV emission lines seen during total primaryeclipse cannot originate from the accretion disk but most likely arisefrom a hotter disk-stream interaction region. The synthetic spectra ofthe stars, disk, and stream allowed us to derive a mass transfer rate>=2×10-10 Msolar yr-1. Dopplertomography of the observed Hα profiles revealed a distinctaccretion disk. The difference spectra produced by subtracting thesynthetic spectra of the stars resulted in an image of the disk, whichvirtually disappeared once the composite synthetic spectra of the starsand disk were used to calculate the difference spectra. An intensityenhancement of the resulting tomogram revealed images of the gas streamand an emission arc. We successfully modeled the gas stream usingSHELLSPEC and associated the emission arc with an asymmetry in theaccretion disk.
| Theoretical study of partial frequency redistribution function in irradiated, moving atmospheres of close binary components
We have studied the effects of partial frequency redistribution functionwith angle-averaged RII-A in irradiated and movingatmospheres of close binary components. We have considered theatmospheric extension of the primary component to be twice the radius ofthe primary component in a close binary system. We have considered twocases: (i) when the atmosphere is at rest and (ii) when the atmosphereis moving. In both the cases, we have computed the line profiles alongthe line of sight for a given optical depth. The irradiation from thesecondary component is assumed to be one, five and 10 times theself-radiation. The line fluxes in the line of sight are calculated byusing the total source functions due to self-radiation of the primarycomponent and due to the irradiation from the secondary component. Wehave noted double-peaked emission lines in the case of a static mediumand a reduction of emission peaks in the case of velocity field.
| A catalogue of close binaries located in the δ Scuti region of the Cepheid instability strip
A catalogue of close eclipsing binary systems (detached andsemidetached) with at least one of the components located in the δScuti region of the Cepheid instability strip is presented. Thepositions of the stars in the instability strip are determined by theiraccurate temperatures and luminosities. Observationally detectedbinaries (20 semidetached, four detached and one unclassified) withoscillating components were included in the catalogue as a separatetable. The primaries of the oscillating Algols tend to be located nearthe blue edge of the instability strip. Using reliable luminosities andtemperatures determined by recent photometric and spectroscopic studies,we have found that at least one or two components of 71 detached and 90semidetached systems are located in the δ Scuti region of theCepheid instability strip. In addition, 36 detached or semidetachedsystems discovered by the Hipparcos satellite were also given as aseparate list. One of their components is seen in the δ Scutiregion, according to their spectral type or B - V colours. They arepotential candidate binaries with the δ Scuti-type pulsatingcomponents which need further photometric and spectroscopic studies inbetter precision. This catalogue covers information and literaturereferences for 25 known and 197 candidate binaries with pulsatingcomponents.
| Are the W Ursae Majoris-type systems EK Comae Berenices and UX Eridani surrounded by circumstellar matter?
The variations of the orbital periods of two nearly neglected W UMa-typeeclipsing binaries, EK Comae Berenices and UX Eridani, are presentedthrough a detailed analysis of the O C diagrams. It is found that theorbital period of EK Com is decreasing and the period of UX Eridani isincreasing, and several sudden jumps have occurred in the orbitalperiods of both binaries. We analyze the mechanism(s), which mightunderlie the changes of the orbital periods of both systems, and obtainsome new results. The long-term decrease of the orbital period of EKComae Berenices might be caused by the decrease of the orbital angularmomentum due to a magnetic stellar wind (MSW) or by mass transfer fromthe more massive to the less massive component. The secular increase inthe orbital period of UX Eridani might be caused by mass transfer fromthe less massive to the more massive star. The possible mechanisms,which underlie the sudden changes in the orbital periods of the closebinary systems are as the followings: (1) the variations of thestructure due to the variation of the magnetic field; (2) the rapid massexchange between the close binaries and their circumstellar matter.Finally, the evolutionary status of the systems EK Comae Berenices andUX Eridani is discussed.
| 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.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Why Are the Secondary Stars in Polars So Normal?
We have used NIRSPEC on Keck II to obtain K-band spectroscopy of severalmagnetic cataclysmic variables. These data reveal that the secondarystars in these binary systems have spectra that are consistent withnormal, late-type dwarfs in both their atomic and molecular linestrengths, as well as in the slopes of their continua. This result is instark contrast to the infrared spectra of their nonmagnetic cousins,nearly all of which show peculiar abundances, especially of CNO speciesand their isotopes. It appears that the evolutionary path taken by thesecondary stars in magnetic systems differs from that for thenonmagnetic systems. We discuss the implications of this result.
| 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.
| A Study of Synthetic and Observed Hα Spectra of TT Hydrae
The formation and properties of accretion disks and circumstellarmaterial in Algol-type systems are not very well understood. In order tostudy the underlying physics of these structures, we have calculatedsynthetic Hα spectra of TT Hya, which is an Algol-type eclipsingbinary with an accretion disk. Both the primary and secondary stars wereconsidered in the calculations, as well as a disk surrounding theprimary. The Roche model for the secondary star was assumed. Thesynthetic spectra cover all the phases, including primary eclipse, andare compared with the observed spectra. The influence of various effectsand free parameters of the disk on the emerging spectrum was studied.This enabled us to put some constraints on the geometry, temperature,density, and velocity fields within the disk. Differences found betweenthe observed and synthetic spectra unravel the existence of a gasstream, as well as a hotter disk-gas interaction region. An additionalcooler circumstellar region between the C1 and C2 Roche surfaces issuggested to account for various observed effects. A new computer codecalled SHELLSPEC was created for this purpose and is briefly describedin this work as well. It is designed to solve simple radiative transferalong the line of sight in three-dimensional moving media. The scatteredlight from a central object is taken into account assuming an opticallythin environment. Output intensities are then integrated through thetwo-dimensional projection surface of a three-dimensional object. Theassumptions of the code include LTE and optional known state quantitiesand velocity fields in three dimensions.
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
| Addressing confusion in double star nomenclature: The Washington Multiplicity Catalog
Advances in instrumentation and reduction methods are blurring thehistorical distinctions between various classes of double stars. Oneresult of this is increasing confusion in double star nomenclature, asthe conventions followed by different observers are sometimesincompatible. The Washington Multiplicity Catalog is presented as ameans of developing a single nomenclature scheme for all types ofdoubles, as well as a comprehensive database for all duplicityinformation.
| Mass and Angular Momentum Transfer in the Massive Algol Binary RY Persei
We present an investigation of the Hα emission-line variationsobserved in the massive Algol binary RY Per. We give new radial velocitydata for the secondary based on our optical spectra and for the primarybased on high-dispersion UV spectra. We present revised orbital elementsand an estimate of the primary's projected rotational velocity (whichindicates that the primary is rotating 7 times faster than thesynchronous rate). We use a Doppler tomography algorithm to reconstructthe individual primary and secondary spectra in the region of Hα,and we subtract the latter from each of our observations to obtainprofiles of the primary and its disk alone. Our Hα observations ofRY Per show that the mass-gaining primary is surrounded by a persistentbut time-variable accretion disk. The profile that is observed outsideeclipse has weak double-peaked emission flanking a deep centralabsorption, and we find that these properties can be reproduced by adisk model that includes the absorption of photospheric light by theband of the disk seen in projection against the face of the star. Wedeveloped a new method to reconstruct the disk surface densitydistribution from the ensemble of Hα profiles observed around theorbit, and this method accounts for the effects of disk occultation bythe stellar components, the obscuration of the primary by the disk, andflux contributions from optically thick disk elements. The resultingsurface density distribution is elongated along the axis joining thestars in the same way as seen in hydrodynamical simulations of gas flowsthat strike the mass gainer near the trailing edge of the star. Thistype of gas stream configuration is optimal for the transfer of angularmomentum, and we show that rapid rotation is found in other Algolsystems that have passed through a similar stage.
| Up-to-Date Linear Elements of Eclipsing Binaries
About 1800 O-C diagrams of eclipsing binaries were analyzed and up-todate linear elements were computed. The regularly updated ephemerides(as a continuation of SAC) are available only in electronic form at theInternet address: http://www.as.ap.krakow.pl/ephem/.
| 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.
| Eclipse mapping of the hot circumstellar plasma in Algol binaries
Phase-resolved FUV observations of three Algol-type interacting binaries(V356 Sgr, TT Hya, and RY Per) have been made during totality with theFar Ultraviolet Spectroscopic Explorer to map the location of the hotcircumstellar plasma that produces emission lines of O VI, Si III,IV SIV, C III, and N II. Since O VI shows very little variation in profile,strength, and velocity as the disk of the secondary occults the lineformation region, we conclude that the emission originates in materialthat has a substantial flow perpendicular to the orbital plane (perhapsa bipolar jet). The behavior of the emission lines from themoderate-ionization species suggests that the plasma producing theseemission features has a large equatorial component.
| 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.
| 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
| 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.
| A spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
| 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
| 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.
| 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.
| 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.
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| Csillagkép: | Északi Vízikígyó |
| Rektaszcenzió: | 11h13m12.50s |
| Deklináció: | -26°27'54.3" |
| Vizuális fényesség: | 7.308 |
| Távolság: | 153.846 parszek |
| RA sajátmozgás: | -18.8 |
| Dec sajátmozgás: | 9.9 |
| B-T magnitude: | 7.472 |
| V-T magnitude: | 7.322 |
Katalógusok és elnevezések:
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