Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
The Algol System XX Cephei
We present new five-color photometric and spectroscopic observations ofthe Algol system XX Cephei (V=9.13, P=2.3 days). This system is known tohave a variable period. From analysis of both the period variations andthe light curve we found no support for apsidal motion. However, thereis a possible light-time effect. The period changes could also beepisodic. Our spectroscopic analysis yielded a classification of A4. Wefound no evidence of features attributable to the cooler component or ofactive mass transfer. Our photometric solution, using theWilson-Devinney modeling program, showed the system to be an Algolconfiguration with a mass ratio of 0.17. We determined the masses andradii, in solar units, to be M1=1.92, M2=0.33,R1=2.07, and R2=2.32, and the temperatures to beT1=8500 K and T2=4555 K. From the parallax givenin the Hipparcos catalog, neglecting reddening, absolute magnitudes ofMV=1.73 and 4.43 were determined for the primary andsecondary components, respectively.
| 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.
| B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
| Semi-detached binaries as probes of the Local Group
Evolutionary and distance estimation issues for eclipsing binaries (EBs)are examined in the context of spin-off from gravitational lens surveysand the GAIA mission. The OGLE survey shows a major deficiency of normalAlgol type binaries in the Small Magellanic Cloud. Statistical analysiscoupled with further observing will be needed to decide if the Algolshortfall is an evolutionary effect connected with low metallicity or isonly apparent. Distances estimated for EBs are directly physical, withno need for calibration via nearby examples with known distances (EBdistance indicators are therefore not standard candles, contrary tocommon usage of the name). Only the best examples will be needed fordistances, given the enormous numbers of EBs expected from GAIA, so onecan be very selective. Accordingly the relative merits of detached (DB),semi-detached (SD), and overcontact (OC) EBs are discussed, withemphasis on under-recognized advantages of SDs and OCs. Included areconsiderations of orbital eccentricity, morphology, photometric massratios, observing efficiency, aliasing of radii, and practicality.
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
Not Available
| 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
| NP Pavonis : Differential Corrections Analysis of the UBV Observations
The first photoelectric analysis of the NPbinary system based on U, B,and V light curves and modeled using the Wilson & Devinney approach,is presented. The light curves are defined by 3861 individualobservations. The components and the orbit appears to be in generalstable. The primary, more massive, more luminous is the greatercomponent, eclipsed at primary minimum and is detached from its Rochelobe (94%). The secondary nearly fills its Roche lobe (99%) and has atemperature difference of Delta = - 1330^oK. The absolute elements wereobtained supposing that the primary follows the mass-luminosityrelation.
| Evolution of Wolf-Rayet Stars in Binary Systems: An Analysis of the Mass and Orbital-Eccentricity Distributions
We have undertaken a statistical study of the component mass ratios andthe orbital eccentricities of WR + O close binary, detachedmain-sequence (DMS), contact early-type (CE), and semidetached (SD)systems. A comparison of the characteristics of WR + O systems and ofDMS, CE, and SD systems has enabled us to draw certain conclusions aboutthe evolutionary paths of WR + O binaries and to demonstrate that up to90% of all known WR + O binaries formed as a result of mass transfer inmassive close O + O binary systems. Since there is a clear correlationbetween the component masses in SD systems with subgiants, the absenceof an anticorrelation between the masses of the WR stars and O stars inWR + O binaries cannot be considered evidence against the formation ofWR + O binaries via mass transfer. The spectroscopic transitionalorbital period P tr sp corresponding to the transition from nearlycircular orbits (e sp<0.1) to elliptical orbits (e sp≥0.1) is14d for WR + O systems and 2d 3d for OB + OB systems. Theperiod range in which all WR + O orbits are circular &$(1mathop dlimits_. 6 ≤slant P ≤slant 14(d) ); is close to the range for SD systems with subgiants, &0mathop dlimits_. 7 ≤slant P ≤slant 15(d); . The large difference between the P tr sp values for WR + O and OB +OB systems suggests that a mechanism of orbit circularization additionalto that for OB + OB systems at the DMS stage (tidal dissipation of theorbital energy due to radiative damping of the dynamical tides) acts inWR + O binaries. It is natural to suggest mass transfer in the parent O+ O binaries as this supplementary orbit-circularization mechanism.Since the transitional period between circular and elliptical orbits forclose binaries with convective envelopes and ages of 5×109 yearsis &P_{tr} = 12mathop dlimits_. 4$; , the orbits of most known SD systems with subgiants had enough timeto circularize during the DMS stage, prior to the mass transfer. Thus,for most SD systems, mass transfer plays a secondary role incircularization of their orbits. In many cases, the initial orbitaleccentricities of the O + O binary progenitors of WR + O systems arepreserved, due to the low viscosity of the O-star envelopes and theshort timescale for their nuclear evolution until the primary O starfills its Roche lobe and the mass transfer begins. The mass transfer inthe parent O + O systems is short-lived, and the number of orbitalcycles during the early mass-transfer stage is relatively low (lowerthan for the progenitors of SD systems by three or four orders ofmagnitude). The continued transfer of mass from the less massive to themore massive star after the component masses have become equal leads tothe formation of a WR + O system, and the orbit's residual eccentricityincreases to the observed value. The increase of the orbitaleccentricity is also facilitated by variable radial mass loss via thewind from the WR star in the WR + O system during its motion in theelliptical orbit. The result is that WR + O binaries can haveconsiderable orbital eccentricities, despite their intense masstransfer. For this reason, the presence of appreciable eccentricitiesamong WR + O binaries with large orbital periods cannot be consideredfirm evidence against mass transfer in the parent O + O binary systems.Only for the WR + O binaries with the longest orbital periods (4 of 35known systems, or 11 %) can the evolution of the parent O + O binariesoccur without filling of the Roche lobe by the primary O star, beinggoverned by radial outflow in the form of the stellar wind and possiblyby the LBV phenomenon, as in the case of HD 5980.
| 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.
| VLA Radio Positions of Stars: 1978-1995
VLA astrometric positions of the radio emission from 52 stars arereported, from observations obtained between 1978 and 1995. Thepositions of these stars have been obtained and reduced in a uniformmanner. Based on our measurements, the offset of the optical (Hipparcos)frame from the radio reference frame is in agreement with the Hipparcosextragalactic link results, within their mean errors. Comparison of theVLA measurements with the Hipparcos optical positions confirms earlierestimates of the accuracy of these positions as 30 mas. Long-termmeasurements of UX Ari have improved its proper motion.
| Orbital period study of the Algol-type eclipsing binary system TW Draconis
The century-long times of light minimum of the Algol-type eclipsingbinary star, TW Dra (BD/+64°1077, SpA5V+K2III), are investigated byconsidering a new pattern of period change. Two sudden period increasesand two successive period decreases are discovered to superimpose on arapid secular increase (dP/dt=+4.43×10-6days/year). Thesecular increase may be caused by a dynamical mass transfer from thesecondary to the primary component(dm/dt=6.81×10-7Msolar/year) that is inagreement with the semi-detached configuration of the system and withthe existence of a hot spot and a gaseous stream in the binary system.The irregular period jumps superimposed on the secular increase can beexplained by the structure variation of the K2-type giant viainstabilities of the outer convective layer or via magnetic activitycycles.
| 149 Bedeckungssterne der BAV-Programme. Eine Analyse der Beobachtungstatigkeit seit den Angangen.
Not Available
| Das Brunner Punktesystem.
Not Available
| 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.
| Photometric Solutions for Semidetached Eclipsing Binaries: Selection of Distance Indicators in the Small Magellanic Cloud
Estimation of distances to nearby galaxies by the use of eclipsingbinaries as standard candles has recently become feasible because of newlarge-scale instruments and the discovery of thousands of eclipsingbinaries as spin-off from Galactic microlensing surveys. Publishedmeasurements of distances to detached eclipsing binaries in the LargeMagellanic Cloud combine stellar surface areas (in absolute units)determined from photometric light and radial velocity curves withsurface brightnesses from model atmospheres and observed spectra. Themethod does not require the stars to be normal or undistorted and is notlimited in its applicability to the well-detached systems that havetraditionally been considered. We discuss the potential usefulness ofsemidetached vis à vis detached eclipsing binaries for distancedetermination and examine and quantify criteria for their selection fromlarge catalogs. Following our earlier paper on detached binaries in theSmall Magellanic Cloud (SMC), we carry out semidetached light-curvesolutions for SMC binaries discovered by the OGLE collaboration,identify candidates for SMC distance estimation that can be targets offuture high-quality observations, and tabulate results of OGLElight-curve solutions. We point out that semidetached binaries haveimportant advantages over well-detached systems as standard candles,although this idea runs counter to the usual view that the latter areoptimal distance indicators. Potential advantages are that (1)light-curve solutions can be strengthened by exploiting lobe-fillingconfigurations, (2) only single-lined spectra may be needed for radialvelocities because the mass ratio can be determined from photometry inthe case of complete eclipses, and (3) nearly all semidetached binarieshave sensibly circular orbits, which is not true for detached binaries.We carry out simulations with synthetic data to see if semidetachedbinaries can be reliably identified and to quantify the accuracy ofsolutions. The simulations were done for detached as well assemidetached binaries so as to constitute a proper controlled study. Thesimulations demonstrate two additional advantages for semidetacheddistance determination candidates; (4) the well-known difficulty indistinguishing solutions with interchanged radii (aliasing) is much lesssevere for semidetached than for detached binaries and (5) the conditionof complete eclipse (which removes a near degeneracy between inclinationand the ratio of the radii) is identified with improved reliability. Inmany cases we find that parameters are accurately determined (e.g.,relative errors in radii smaller than 10%) and that detached andsemidetached systems can be distinguished. We select 36 candidatesemidetached systems (although seven of these are doubtful because oflarge mass ratios or periods) from the OGLE SMC eclipsing binarycatalog. We expected that most semidetached candidates would have lightcurves similar to those of common Algol binaries, but that turned outnot to be the case, and we note that fully Algol-like light curves arenearly absent in the OGLE sample. We discuss possible explanations forthe near absence of obvious Algols in OGLE, including whether theirpaucity is real or apparent.
| 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.
| Optical positions of 55 radio stars from astrolabe observations from the Yunnan Observatory
The observations by the photoelectric astrolabe at Yunnan Observatoryrelative to the Hipparcos Catalogue and the optical positions of 55radio stars were obtained from observations between 1991 and 2000. Theyall resulted from processing the photon counts obtained by means of theastrolabe after the automation of the instrument. There are 46 stars incommon with the Hipparcos Catalogue. Tables \ref{t1} and \ref{t2} arealso available in electronic form at the CDS via anonymous ftpcdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/383/1062.
| U Cep - visuell, elektronisch und nach Literaturrecherche.
Not Available
| 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.
| 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
| 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.
| Is asynchronism in semidetached binary systems real?
We analyze statistical relationships between the parameters ofAlgol-type binaries with asynchronous rotation of the primary componentsand provide observational evidence for denser, more extended gaseousenvelopes in the eclipsing systems of this group. We conclude thatasynchronism of the primary components in such systems is not real. Thelines that are used to determine the rotational velocities of thesecomponents originate mostly in the part of the atmosphere which acquiresan additional angular momentum during the interaction with the gasstream and produces a transient accretion disk near the equatorialplane.
| 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.
| 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.
| Optical Positions of 44 Radio Stars from Astrolabe Observations
The observations made with the photoelectric astrolabe at YunnanObservatory since 1986 have been reprocessed in the Hipparcos Catalogue,and the optical positions of 44 radio stars obtained. These are all thestars in common with the Hipparcos Catalogue.
| Apsidal Motion in Double Stars. I. Catalog
A catalog of 128 double stars with measured periods of apsidal motion iscompiled. Besides the apsidal periods, the orbital elements of binariesand physical parameters of components (masses, radii, effectivetemperatures, surface gravities) are given. The agreement of the apsidalperiods found by various authors is discussed.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Nyíl |
| Rektaszcenzió: | 19h18m48.50s |
| Deklináció: | +19°36'38.0" |
| Vizuális fényesség: | 6.58 |
| Távolság: | 310.559 parszek |
| RA sajátmozgás: | 0.1 |
| Dec sajátmozgás: | 1 |
| B-T magnitude: | 6.499 |
| V-T magnitude: | 6.498 |
Katalógusok és elnevezések:
|
