Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
Properties and nature of Be stars. 24. Better data and model for the Be+F binary V360 Lacertae
Aims.We include existing photometric and spectroscopic material with newobservations in a detailed study of the Be+F binary V360Lac. Methods: .We used the programs FOTEL and KOREL toderive an improved linear ephemeris and to disentangle the line profilesof both binary components and telluric lines. The BINSYN software suite(described in the paper) is used to calculate synthetic light curves andspectra to fit the {UBV} photometry, an {IUE} spectrum, blue and redground-based spectra, and observed radial-velocity curves.Results: .The observations provide evidence of circumstellar matter inthe system. The system model shows that the Be primary star iscritically rotating, and that the synchronously rotating secondary starfills its Roche lobe. The primary star has a mass of7.45ȯ. Radial-velocity observations establish a massratio of 0.163. Light curve synthesis demonstrates that the observedlight curves are controlled largely by tidal distortion and irradiationof the massive primary by the less massive secondary. Synthetic spectrafit both blue and red observed spectra with the exception of spectrallines affected by circumstellar matter in the system. The syntheticspectra allow for gravity darkening and are consistent with criticalrotation of the primary. Synthetic spectrum fits to a dereddened {IUE}spectrum produce a calculated system distance of 512 pc. This distanceis 2σ beyond the Hipparcos distance.
| On the evolutionary status of Be stars. I. Field Be stars near the Sun
A sample of 97 galactic field Be stars were studied by taking intoaccount the effects induced by the fast rotation on their fundamentalparameters. All program stars were observed in the BCDspectrophotometric system in order to minimize the perturbationsproduced by the circumstellar environment on the spectral photosphericsignatures. This is one of the first attempts at determining stellarmasses and ages by simultaneously using model atmospheres andevolutionary tracks, both calculated for rotating objects. The stellarages (τ) normalized to the respective inferred time that eachrotating star can spend in the main sequence phase (τ_MS) reveal amass-dependent trend. This trend shows that: a) there are Be starsspread over the whole interval 0 τ/τ_MS 1 of themain sequence evolutionary phase; b) the distribution of points in the(τ/τMS,M/Mȯ) diagram indicates thatin massive stars (M 12~Mȯ) the Be phenomenon ispresent at smaller τ/τ_MS age ratios than for less massive stars(M 12~Mȯ). This distribution can be due to: i)higher mass-loss rates in massive objets, which can act to reduce thesurface fast rotation; ii) circulation time scales to transport angularmomentum from the core to the surface, which are longer the lower thestellar mass.
| 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.
| 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
| Autocorrelation Analysis of Hipparcos Photometry of Short-Period Be Stars
We have used Hipparcos epoch photometry and a form of autocorrelationanalysis to investigate the amplitude and timescale of the short-periodvariability of 82 Be stars, including 46 Be stars that were analyzed byHubert & Floquet using Fourier and CLEAN analysis and 36 other Bestars that were suspected of short-period variability. Our method hasgiven useful information for about 84% of these stars; for the rest, thetime distribution of the Hipparcos epoch photometry limits thecapability of our technique.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| Polarization variability in the interacting Be binary CX Draconis
We present new UBVRI polarization measurements of the interacting Bebinary CX Dra. On time scale of several weeks polarization variationsclearly correlate with the binary orbital motion. Long term changes inpolarization are seen in the course of several months. Analysis of theperiodic component of polarization gives orbital inclination i =~ 73degrwhich is substantially higher than values previously reported in theliterature (55degr ). Our two datasets obtained about 9 months apartreveal significant changes in the distribution of the scatteringmaterial of the circumbinary envelope.
| 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
| Search for duplicity in periodic variable Be stars
Four Be stars, HR 1960, HR 2968,HR 3237 and HR 3642, selectedaccording to their periodic variations in HIPPARCOS and GENEVAphotometries, were monitored from 1998 until 2001 with the CORALIEspectrograph. Among these stars, two are new spectroscopic binaries andone is a new lambda Eri short period variable. HR 1960 is a lowamplitude (K = 3.4 km s-1) SB1 with a period of 395.48 d inagreement with the photometric prediction. HR 3237 is a short period SB1(P = 5.1526 d). HR 3642 presents some interesting variations inphotometry and spectroscopy: indeed, a mid- and a short-term variationis present with periods of 137.99 d (Hp magnitude) and 1.13028 d (radialvelocity) respectively. The short-term variation, characteristic of thelambda Eri stars, probably implies non-radial pulsations orinhomogeneities in the corotating disc. The last star, HR 2968, is anexcellent photometric binary candidate, but no spectroscopic obviousnessof a companion has been found. Based on observations collected at theSwiss 40 cm, 70 cm and 120 cm telescopes at the European SouthernObservatory (La Silla, Chile) and on data from the ESA HIPPARCOSsatellite. The photometric and radial velocity data are only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/385/488 Table 3 is onlyavailable in electronic form at http://www.edpsciences.org
| Photometric Monitoring of Bright Be Stars. IV. 1996-1999
We report long-term UBV observations of 15 bright, active Be stars,namely: X Persei, EW Canis Majoris, θ Coronae Borealis, 4 (V839)Herculis, 88 (V744) Herculis, 66 (V2048) Ophiuchi, NW Serpentis, CXDraconis, 12 (V395) Vulpeculae, 28 (V1624) Cygni, QR Vulpeculae, 59(V832) Cygni, EW Lacertae, ο Andromedae, and KX Andromedae. Theobservations were made in 1996-1999 through the Automatic PhotometricTelescope Service in Arizona and through the American Association ofVariable Star Observers (AAVSO) photoelectric photometry program andhave been added to a database extending back 20 years. We describe thestars' recent behavior and also comment on the long-term behavior ofsome of them. They vary photometrically on timescales ranging from abouta day to many years.
| Ultraviolet Spectrophotometry of Variable Early-Type Be and B Stars Derived from High-Resolution IUE Data
High-dispersion IUE data encode significant information about aggregateline absorptions that cannot be conveniently extracted from individualstellar spectra. Here we apply a new technique in which fluxes from eachechelle order of a short-wavelength IUE spectrum are binned together toconstruct low-resolution spectra of a rapidly varying B or Be star. Thedivision of binned spectra obtained during a ``bright-star'' phase byspectra from a ``faint-star'' phase leads to a ratioed spectrum thatcontains information about the mechanism responsible for a star'svariability. The most likely candidate mechanisms are either theperiodic or episodic occultations of the star by ejected matter or achange in photospheric structure, e.g., from pulsation. We model thevariations caused by these mechanism by means of model atmosphere andabsorbing-slab codes. Line absorptions strength changes are rathersensitive to physical conditions in circumstellar shells and ``clouds''at temperatures of 8000-13,000 K, which is the regime expected forcircumstellar structures of early B stars. To demonstrate proofs of thisconcept, we construct spectral ratios for circumstellar structuresassociated with flux variability in various Be stars: (1) Vela X-1 has abow-shock wind trailing its neutron star companion; at successive phasesand hence in different sectors, the wind exhibits spectrophotometricsignatures of a 13,000 or 26,000 K medium; (2) 88 Her undergoes episodic``outbursts'' during which its UV flux fades, followed a year later by adimming at visible wavelengths as well; the ratioed spectrum indicatesthe ``phase lag'' is a result of a nearly gray opacity that dominatesall wavelengths as the shell expands from the star and cools, permittingthe absorptions in the visible to ``catch up'' to those in the UV; and(3) ζ Tau and 60 Cyg exhibit periodic spectrum and flux changes,which match model absorptions for occulting clouds but are actually mosteasily seen from selective variations of various resonance lines. Inaddition, ratioed UV spectra of radial and large-amplitude nonradialpulsating stars show unique spectrophotometric signatures, which can besimulated with model atmospheres. An analysis of ratioed spectraobtained for a representative sample of 18 classical Be stars known tohave rapid periodic flux variations indicates that 13 of them haveratioed spectra that are relatively featureless or have signatures ofpulsation. Ratioed spectra of three others in the sample exhibitsignatures that are consistent with the presence of corotating clouds.
| A Search for High-Velocity Be Stars
We present an analysis of the kinematics of Be stars based uponHipparcos proper motions and published radial velocities. We findapproximately 23 of the 344 stars in our sample have peculiar spacemotions greater than 40 km s-1 and up to 102 kms-1. We argue that these high-velocity stars are the resultof either a supernova that disrupted a binary or ejection by closeencounters of binaries in young clusters. Be stars spun up by binarymass transfer will appear as high-velocity objects if there wassignificant mass loss during the supernova explosion of the initiallymore massive star, but the generally moderate peculiar velocities of BeX-ray binaries indicate that the progenitors lose most of their massprior to the supernova (in accordance with model predictions). Binaryformation models for Be stars predict that most systems bypass thesupernova stage (and do not receive runaway velocities) to createultimately Be+white dwarf binaries. The fraction of Be stars spun up bybinary mass transfer remains unknown, since the post-mass transfercompanions are difficult to detect.
| 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.
| High and intermediate-resolution spectroscopy of Be stars 4481 lines
We present an atlas of Hγ , He i lambda 4471 and Mg ii lambda 4481line profiles obtained in a 10 year observation period of 116 Be stars,which enabled many of them to be observed at quite different emissionepochs. From the best fit of the observed He i lambda 4471 line profileswith non-LTE, uniform (Teff,log g) and full limb-darkenedmodel line profiles, we determined the V sin i of the program stars. Toaccount, to some degree, for the line formation peculiarities related tothe rapid rotation-induced non-uniform distributions of temperature andgravity on the stellar surface, the fit was achieved by considering(Teff,log g) as free parameters. This method produced V sin iestimations that correlate with the rotational velocities determined bySlettebak (1982) within a dispersion sigma <= 30 km s-1and without any systematic deviation. They can be considered as given inthe new Slettebak's et al. (1975) system. Only 13 program stars havediscrepant V sin i values. In some objects, this discrepancy could beattributed to binary effects. Using the newly determined V sin iparameters, we found that the ratio of true rotational velocitiesV/Vc of the program Be stars has a very low dispersion aroundthe mean value. Assuming then that all the stars are rigid rotators withthe same ratio V(/lineω)/Vc, we looked for the value of/line ω that better represents the distribution of V sini/Vc for randomly oriented rotational axes. We obtained/lineω = 0.795. This value enabled us to determine the probableinclination angle of the stellar rotation axis of the program stars. Inthe observed line profiles of Hγ , He i lambda 4471, Mg ii lambda4481 and Fe ii lambda 4351 we measured several parameters related to theabsorption and/or emission components, such as: equivalent width,residual emission and/or absorption intensity, FWHM, emission peakseparations, etc. The parameters related to the Hγ line emissionprofiles were used to investigate the structure of the nearbyenvironment of the central star. From the characteristics of thecorrelations between these quantities and the inferred inclinationangle, we concluded that in most of cases the Hγ line emissionforming regions may not be strongly flattened. Using a simplerepresentation of the radiation flux emitted by the star+envelopesystem, we derived first order estimates of physical parameterscharacterizing the Hγ line emission formation region. Thus, weobtained that the total extent of the Hγ region is Rf=~ 2.5 +/- 1.0 R* and that the density distribution in theselayers can be mimicked with a power law rho ~ R-alpha , wherealpha =2.5+2.2-0.6. The same approach enabled usto estimate the optical depth of the Hγ line emission formationregion. From its dependence with the aspect angle, we concluded thatthese regions are caracterized by a modest flattening and that the rho(equator)/rho (pole) density contrast of the circumstellar envelope nearthe star should be two orders of magnitude lower than predicted bymodels based on a priori disc-shaped circumstellar envelopes. We foundthat the separation between the emission peaks, Deltap, andthe full width at half maximum, Delta 1/2, of the Hγline emission are not only sensitive to kinematic effects, but to lineoptical depth as well. This finding agrees with previous theoreticalpredictions and confirms that Huang's (1972) relation overestimates theextent of the Hγ line emission formation region. Data obtained atCASLEO operated under agreement between the CONICET and the NationalUniversities of La Plata, Córdoba and San Juan, Argentina, at ESOLa Silla, Chile and at OHP, France.}\fnmsep\thanks{Tables 2 to 7 andFigs. 1 and 2 are only available in full in electronic form at CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/378/861}} \subtitle{Anatlas of Hγ , He {\fontsize {10pt}{12pt}\selectfont I} 4471 and Mg{\fontsize {10pt}{12pt}\selectfont II
| Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars
We present the results of statistical analyses of a sample of 627 Bestars. The parameters of intrinsic polarization (p*),projected rotational velocity (v sin i), and near IR excesses have beeninvestigated. The values of p* have been estimated for a muchlarger and more representative sample of Be stars (~490 objects) thanpreviously. We have confirmed that most Be stars of early spectral typehave statistically larger values of polarization and IR excesses incomparison with the late spectral type stars. It is found that thedistributions of p* diverge considerably for the differentspectral subgroups. In contrast to late spectral types (B5-B9.5), thedistribution of p* for B0-B2 stars does not peak at the valuep*=0%. Statistically significant differences in the meanprojected rotational velocities (/line{vsin i}) are found for differentspectral subgroups of Be stars in the sense that late spectral typestars (V luminosity class) generally rotate faster than early types, inagreement with previously published results. This behaviour is, however,not obvious for the III-IV luminosity class stars. Nevertheless, thecalculated values of the ratio vt/vc of the truerotational velocity, vt, to the critical velocity forbreak-up, vc, is larger for late spectral type stars of allluminosity classes. Thus, late spectral type stars appear to rotatecloser to their break-up rotational velocity. The distribution of nearIR excesses for early spectral subgroups is bi-modal, the position ofthe second peak displaying a maximum value E(V-L)~ 1 . m 3for O-B1.5 stars, decreasing to E(V-L)~0. m8 for intermediatespectral types (B3-B5). It is shown that bi-modality disappears for latespectral types (B6-B9.5). No correlations were found betweenp* and near IR excesses and between E(V-L) and vsin i for thedifferent subgroups of Be stars. In contrast to near IR excesses, arelation between p* and far IR excesses at 12 mu m is clearlyseen. A clear relation between p* and vsin i (as well asbetween p* and /line{vsin i}/vc) is found by thefact that plots of these parameters are bounded by a ``triangular"distribution of p*: vsin i, with a decrease of p*towards very small and very large vsin i (and /line{vsini}/vc) values. The latter behaviour can be understood in thecontext of a larger oblateness of circumstellar disks for the stars witha rapid rotation. From the analysis of correlations between differentobservational parameters we conclude that circumstellar envelopes forthe majority of Be stars are optically thin disks with the range of thehalf-opening angle of 10degr
| 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
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| On the Variability of O4-B5 Luminosity Class III-V Stars
We investigate the Hipparcos Satellite photometry of O4-B5 luminosityclass III-V stars. Some for which further study is desirable areidentified. These stars in general are more variable than cooler stars
| 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.
| 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
| 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.
| The photometric variability of the Be star NW Serpentis
{NW Ser} is a bright (V = 6.1 - 6.2) active Be star which is known tovary photometrically on a time scale of hours to days. Using bothHipparcos and ground-based photometry, and using light curve,autocorrelation, power spectrum analysis and phase dispersionminimalization techniques, we have concluded that the period is close to0.46d - a period typical of stars of this type, and in good agreementwith the value of 0.488d, recently determined by Hubert & Floquetfrom Hipparcos data. It is possible that the period is near twice thisvalue, but the evidence is not strong. We also find a period of about5d. from both the ground-based and Hipparcos data.
| 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.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Photometric Monitoring of Bright Be Stars. III. 1988-89 and 1992-95
We report long-term photometric (BV) observations of 23 bright, activeBe stars made in 1988 and 1989 and 1992 and 1995 with the 0.4m telescopeat the University of Toronto. Cumulative light curves, includingobservations made earlier at the University of Toronto, and with theAutomatic Photometric Telescope Service in Arizona, are presented forseveral of the stars. Many of the stars show cyclic variations of up to0.2 in V and B on time scales of a few years, as well as variations ontime scales of about a day. (SECTION: Stars)
| Astrophysics in 1996
The loudest astronomical headlines of the year came from both very near(planets orbiting stars in the solar neighborhood) and very far(galaxies and parts of galaxies at redshifts of 1 to 3 and more). Weexplore these and other happenings in our Solar System (Galileo atJupiter, Comet Hyakutake), Milky Way (the bursting pulsar, spottedstars), Local Group (masers, MACHOs, and more), and Universe(gravitational lensing, an assortment of extrema). (SECTION: InvitedReview Paper)
| ICCD Speckle Observations of Binary Stars.XVIII.An Investigation of Be =
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.2112M&db_key=AST
| Systematic Errors in the FK5 Catalog as Derived from CCD Observations in the Extragalactic Reference Frame.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..850S&db_key=AST
| UBV photometry of Be stars at Hvar: 1972--1990
A summary of results of the systematic UBV photoelectric monitoring ofbright northern Be stars carried out at the Hvar Observatory between1972 and 1990 is presented. Altogether, 76 Be stars of all luminosityclasses were observed and 13,848 UBV measurements secured.Simultaneously, 9,648 UBV measurements of 48 check stars (most of themof early spectral types) were obtained. A careful transformation of allobservations into the standard Johnson system allowed detection andmonitoring of even very mild long-term light and colour variations ofthese objects. Almost all early-type Be stars in the sample turned outto be variable. For several stars phase-locked light variations relatedto their binary nature were established. Sudden brightenings, on a timescale of a few days, were detected for o Cas and QR Vul. Tables 2 and 3are only available in electronic form at CDS via ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Dragone |
| Ascensione retta: | 18h46m43.10s |
| Declinazione: | +52°59'17.0" |
| Magnitudine apparente: | 5.88 |
| Distanza: | 666.667 parsec |
| Moto proprio RA: | 9.8 |
| Moto proprio Dec: | -5.1 |
| B-T magnitude: | 5.77 |
| V-T magnitude: | 5.867 |
Cataloghi e designazioni:
|
