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CoRoT photometry and high-resolution spectroscopy of the interacting eclipsing binary AU Monocerotis
Analyses of very accurate CoRoT space photometry, past Johnson Vphotoelectric photometry and high-resolution echelle spectra led to thedetermination of improved and consistent fundamental stellar propertiesof both components of AU Monocerotis. We derived new, accurateephemerides for both the orbital motion (with a period of ) and thelong-term, overall brightness variation (with a period of ) of thisstrongly interacting Be + G semi-detached binary. It is shown that thislong-term variation must be due to attenuation of the total light bysome variable circumbinary material. We derived the binary mass ratioMG/MB = 0.17 +/- 0.03 based on the assumption thatthe G-type secondary fills its Roche lobe and rotates synchronously.Using this value of the mass ratio as well as the radial velocities ofthe G-star, we obtained a consistent light curve model and improvedestimates of the stellar masses, radii, luminosities and effectivetemperatures. We demonstrate that the observed lines of the B-typeprimary may not be of photospheric origin. We also discover rapid andperiodic light changes visible in the high-quality residual CoRoT lightcurves. AU Mon is put into perspective by a comparison with knownbinaries exhibiting long-term cyclic light changes.Based on photometry collected by the CoRoT space mission as well asspectroscopy obtained with the FEROS spectrograph attached to the 2.2-mtelescope at European Southern Observatory (ESO), La Silla, Chile, underthe ESO Large Programme LP178.D-0361, and with the SOPHIE spectrographof the Observatoire de Haute-Provence (France). The CoRoT space missionwas developed and is operated by the French space agency CNES, with theparticipation of ESA's RSSD and Science Programmes, Austria, Belgium,Brazil, Germany and Spain. Based on observations collected at the CentroAstronómico Hispano Alemán (CAHA) at Calar Alto, operatedjointly by the Max-Planck-Institut für Astronomie and the Institutode Astrofísica de Andalucía (CSIC).E-mail: maarten.desmet@ster.kuleuven.be
| Masses and luminosities of O- and B-type stars and red supergiants
Massive stars are of interest as progenitors of supernovae, i.e.neutron stars and black holes, which can be sources of gravitationalwaves. Recent population synthesis models can predict neutron star andgravitational wave observations but deal with a fixed supernova rate oran assumed initial mass function for the population of massive stars. Here we investigate those massive stars, which are supernovaprogenitors, i.e. with O- and early B-type stars, and also allsupergiants within 3 kpc. We restrict our sample to those massive starsdetected both in 2MASS and observed by Hipparcos, i.e. only those starswith parallax and precise photometry. To determine the luminositieswe calculated the extinctions from published multi-colour photometry,spectral types, luminosity class, all corrected for multiplicity andrecently revised Hipparcos distances. We use luminosities andtemperatures to estimate the masses and ages of these stars usingdifferent models from different authors. Having estimated theluminosities of all our stars within 3 kpc, in particular for all O- andearly B-type stars, we have determined the median and mean luminositiesfor all spectral types for luminosity classes I, III, and V. Ourluminosity values for supergiants deviate from earlier results: Previouswork generally overestimates distances and luminosities compared to ourdata, this is likely due to Hipparcos parallaxes (generally moreaccurate and larger than previous ground-based data) and the fact thatmany massive stars have recently been resolved into multiples of lowermasses and luminosities. From luminosities and effective temperatureswe derived masses and ages using mass tracks and isochrones fromdifferent authors. From masses and ages we estimated lifetimes andderived a lower limit for the supernova rate of ?20 events/Myraveraged over the next 10 Myr within 600 pc from the sun. These data arethen used to search for areas in the sky with higher likelihood for asupernova or gravitational wave event (like OB associations).
| A period study and light-curve synthesis for the Algol-type semidetached binary XXCephei
We obtained CCD photometric observations of the Algol-type semidetachedbinary XXCephei (XXCep) during 15 nights from 2002 September 17 to 2003February 2, and also on 2005 January 21. Except for those data taken onthe last night of the concentrated observing season, the 3881measurements were obtained over an interval of only 106 nights. Fromthese data, four new times of minimum light were calculated. The (O- C)diagram formed from all available timings, and thus the orbital periodof the system, can be partly represented as a beat effect between twocyclical variations with different periods (yr, yr) and amplitudes(K1=0.015d, K2=0.103d), respectively. Bothphysical and non-physical interpretations of these cycles wereinvestigated. The long-term sinusoidal variation is too long formagnetic cycling in solar-type single and close binary stars. Inaddition, we have studied the effect of a possible secular periodvariation. By analysing the residuals from our Wilson-Devinney (WD)binary model, we found small light variations with a period of 5.99dwith amplitudes growing toward longer wavelengths. We think that theseoscillations may be produced by instabilities at the systemicL1 point (also occupied by the point of the cool star) andthat these instabilities are, in turn, caused by non-uniform andsporadic convection. There is also a short-period oscillation of about45min in the WD light residuals that is attributed to accretion on tothe mass-gaining primary component from a feeble gas stream originatingon the cool donor star.
| Accretion discs with strong toroidal magnetic fields
Simulations and analytic arguments suggest that the turbulence driven bymagnetorotational instability (MRI) in accretion discs can amplify thetoroidal (azimuthal) component of the magnetic field to a point at whichmagnetic pressure exceeds the combined gas + radiation pressure in thedisc. Arguing from the recent analysis by Pessah & Psaltis, andother MRI results in the literature, we conjecture that the limitingfield strength for a thin disc is such that the Alfvén speedroughly equals the geometric mean of the Keplerian speed and the speedof sound in gas. We examine the properties of such magneticallydominated discs, and show that they resolve a number of outstandingproblems in accretion disc theory. The discs would be thicker thanstandard (Shakura-Sunyaev) discs at the same radius and accretion rate,and would tend to have higher colour temperatures. If they transportangular momentum according to an ? prescription, they would bestable against the thermal and viscous instabilities that are found instandard disc models. In discs fuelling active galactic nuclei, magneticpressure support could also alleviate the restriction on accretion rateimposed by disc self-gravity.
| Indirect imaging of an accretion disk rim in the long-period interacting binary W Crucis
Context: .Light curves of the long-period Algols are known for theircomplex shape (asymmetry in the eclipse, light variations outside theeclipse, changes from cycle-to-cycle), but their interpretation is notpossible in the standard model of binary stars. Aims: . Wedetermined that complex structures present in these active Algol systemscould be studied with the eclipse-mapping method that was successfullyapplied to the new 7-color photometric observations in the Geneva systemof W Cru, belonging to the isolated group of these active Algols.Methods: . Several cycles of this long-period (198.5 days) eclipsingbinary were covered by observations. We used a modified Rutten'sapproach to the eclipse-mapping. The optimization of the system'sparameters and the recovery of the disk intensity distribution areperformed using a genetic algorithm (GA). Results: .The finding ofa primary (hot) component is hidden in thick accretion disk confirmsprevious solutions. The mass of the primary component, M1 =8.2 Mȯ, indicates that it is a mid-B type star. Themass-losing component fills its critical lobe, which, for the system'sparameters, means it is a G-type supergiant with a mass M2 =1.6 Mȯ. The disk is very extended geometrically, and itsouter radius is about 80% of the primary's critical lobe. Areconstructed image reveals the rather clumpy and nonuniform brightnessdistribution of an accretion disk rim in this system that is seen almostedge-on. This clumpiness accounts for light curve distortions andasymmetries, as well as for secular changes.
| Analysis of Van Houten's Estimates of Variable Stars From Photographic Plates
Huge amount of observations from photogrphic plates made by C. J. vanHouten remained unprocessed and unpublished after his death. The datawere obtained during the first half of the 20th century. All of thestars are situated on the southern hemisphere a most of them areeclipsing binaries. These times of minima can do a great job for O-Canalysis of these objects. The aim of this paper is to introduce thisproject.
| 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.
| 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.
| 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/.
| 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.
| Accretion disk in the binary system V367 Cygni
New photoelectric observations of the interacting binary V367 Cyg weremade during two consecutive seasons, 1996 and 1997, using thetwo-channel photometer at Mt. Suhora Observatory. The BVRI light curvesare analyzed and system parameters are derived for two alternativemodels: with and without an accretion disk. A contact configuration isobtained for the no-disk model. The semidetached model, with a diskaround the invisible component gives a better fit and, in addition,explains most of the observed features of V367 Cyg. The disk in V367 Cyghas a radius of about R_d=23 Rsun, almost completely fillingthe secondary component's Roche lobe. Mass is transferred from the lessmassive (3.3 Msun) to the more massive (4.0 Msun)star at a high rate of 5-7 10-5 Msun/yr. Theoriginal observations are 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/368/932
| 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.
| The use of the NextGen model atmospheres for cool giants in a light curve synthesis code
We have written a light curve synthesis code that makes direct use ofmodel atmosphere specific intensities, in particular the NextGen modelatmosphere grid for cool giants (Teff<= 6800 K and log(g)<= 3.5, Hauschildt et al. \cite{hauschildt99}). We point out thatthese models (computed using spherical geometry) predict a limbdarkening behaviour that deviates significantly from a simple linear ortwo-parameter law (there is less intensity at the limb of the star). Thepresence of a significantly nonlinear limb darkening law has two mainconsequences. First, the ellipsoidal light curve computed for a tidallydistorted giant using the NextGen intensities is in general differentfrom the light curve computed using the same geometry but with the blackbody approximation and a one- or two-parameter limb darkening law. Inmost cases the light curves computed with the NextGen intensities havedeeper minima than their black body counterparts. Thus the light curvesolutions for binaries with a giant component obtained with models withnear linear limb darkening (either black body or plane-parallel modelatmosphere intensities) are biased. Observations over a wide wavelengthrange (i.e. both the optical and infrared) are particularly useful indiscriminating between models with nearly linear limb darkening and theNextGen models. Second, we show that rotational broadening kernels forRoche lobe filling (or nearly filling) giants can be significantlydifferent from analytic kernels due to a combination of the nonsphericalshape of the star and the radical departure from a simple limb darkeninglaw. As a result, geometrical information inferred from Vrotsin i measurements of cool giants in binary systems are likewise biased.
| From OAO2 to HST. A quarter of a century of ultraviolet astronomy.
Not Available
| On Light Curves Modeling of Low Inclination Binary Systems with Accretion Disks
Computer generated light curves of a low inclination, semidetachedbinary system containing an accretion disk, were analyzed with theWilson-Devinney code (which does not account for the disk effects), tosearch for the best solution. The following inclinations wereconsidered: 77 arcdeg 4, 75 arcdeg 0 and 60 arcdeg 0 as well as threedifferent disk contributions to the total light: 2%, 15% and 30%. Forthe disk contribution being small (2%), the resulting configurationagreed with the input one. For higher disk light detached geometry wasderived. The parameters obtained from modeling greatly differ from theinput ones and the fits are quite good.
| Toward a model of the strongly interacting binary W Crucis with genetic algorithm.
Not Available
| Spectroscopic observations of the interacting binary BY Crucis.
We present multi-wavelength spectroscopic data of the 106 day periodinteracting binary BY Crucis (Daems et al., 1997A&A...317..823D).The system consist of an early F-type supergiant that fills its Rochelobe and a more massive companion, hidden in a thick accretion disc. Inthe far-UV spectra (from 1200Å to 1950Å), strong emissionlines of highly ionised elements are observed, superposed on acontinuum. Both components of the UV flux originate from the accretiondisc around the companion. In the UV range from 1950Å to3150Å the radiation of the F-type mass donor is dominant. In thevisual and the red range we focused our interest on the Balmer lines(Halpha_, Hbeta_ and Hdelta_), He I5876Å, Na I 5890-5896Å, and the forbidden line [O I]6300Å. We also obtained spectra in various other regions, rangingfrom 3900Å to 6700Å. Evidence of mass transfer is observedin the He I-line, the Na I-lines, Hbeta_ and some Fe-lines.The Halpha_-line shows no variability, and its double peakedprofile implies that it is formed in a circumbinary disc or envelope.The [O I] line confirms the presence of matter around the binary system.By analysing the line profile variability of He I, we construct atentative image of the gas flow in the accretion disc around the unseencompanion. The Balmer lines are used to probe the outer, cooler gas,flowing through the outer Lagrangian point into a circumstellar disc orenvelope.
| 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)
| The strongly constrained interacting binary BY Crucis.
We discuss spectroscopic and photometric observations (UV to IR) of BYCrucis, a new bright member of the interacting binaries of the WSerpentis class. The orbital period is 106.4days, and the mass functionamounts to 5.92Msun_. The primary is an early-F supergiantwhich fills its Roche lobe; the massive secondary is hidden inside athick accretion disk, which is probably the dominant light source in theultraviolet. The observed variations in the photometric lightcurves arecaused mainly by ellipsoidal variations. It is unlikely that an eclipseoccurs. A particularly interesting circumstance is that BY Cru is aprobable member of a visual multiple system which contains anotherevolved star. This circumstance enables us to estimate with someaccuracy the age of the interacting binary and the initial mass of theprimary. The history of this binary is then much more constrained thanfor the other W Serpentis stars. Also taking into account the fact thatthe binary has avoided Case C Roche lobe overflow, we determine upperand lower bounds for the initial and present masses of both components,and conclude that mass transfer has only been moderatelynon-conservative.
| W Crucis: an eclipsing binary system containing an accretion disk.
Recently published B and V light curves of W Cru have been analyzed bymeans of the light curve synthesis. A consistent model of the system canbe obtained if a thick accretion disk is introduced. The disk completelyobscures the more massive, mass accreting star, explaining the problemof its invisibility in the spectrum. In this model, the deeper minimumis the one caused by the eclipse of the mass losing star by the disk.Masses of the components were calculated to be M_1_=7.8Msun_,M_2_=1.25Msun_, the orbital separation A=299Rsun_,while the radius of the secondary R_2_=76Rsun_. The systemseems to be a product of the 'Case-C' mass transfer evolution.
| Colour excesses of F-G supergiants and Cepheids from Geneva photometry.
A reddening scale for F-G supergiants and Cepheids is presented.Supergiants with low reddenings or in clusters form the basis of thecalibration. In this sense, it is entirely empirical. The data have beenobtained in the Geneva photometric system. Comparisons with otherreddening scales show no disagreement. The only problem is with Fernie'sscale for Cepheids (1990), where a systematic trend exists. Its originis not clear. It is suggested to extend the number of supergiants withindependently obtained colour excesses in order to test the existence ofa possible luminosity dependence of the calibration. A period-colourrelation for Cepheids is deduced, on the basis of the present reddeningcorrections. It gives strong support for V473 Lyr being a secondovertone pulsator.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Amateur Astronomy in South Africa
Not Available
| On light curve modeling of high-inclination binary systems with accretion disks
V light curves were calculated using a model of a binary system, seen atinclination close to 90 degrees and containing an optically thickaccretion disk. Three such generated light curves, differing in the diskcontribution, were used to obtain the best solution with theWilson-Devinney code. Application of a model, which does not account forthe disk presence, produces a good fit to input data but leads tospurious values for the star parameters, particularly for the systemmass ratio. In case when the disk light is relatively low, modeling ofthe light curves of high inclination systems in which an optically thickaccretion disk completely obscures the accreting star, using a modelwhich does not account for the disk effects, results in contactconfiguration. We suggest that this may be the case for somelong-period, beta Lyr-type, binary systems.
| Longterm Photometry of Variables at ESO - Part Two - the Second Data Catalogue 1986-1990
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102...79S&db_key=AST
| W Cru - a Phase Diagram
Not Available
| The calibration of the Stromgren photometric system for A, F and early G supergiants. I - The observational data
An empirical calibration of the Stromgren uvby-beta photometric systemfor the A, F, and early G supergiants is being derived. This paperexplains the observational program and the photometric reductiontechniques used and presents a catalog of new Stromgren photometry forover 600 A, F, and G supergiants.
| Long-term photometry of variables at ESO. I - The first data catalogue (1982-1986)
This paper presents the catalog of photometric data in the Stromgrensystem obtained during the first four years (October 1982 - September1986) of the Long-Term Photometry of Variables (LTPV) program at ESO.The data are available in computer-readable form.
| Observational physics of a mirror world
The existence of mirror, or shadow, particles is necessary in physicsfor the restoration of the symmetry of right and left systemcoordinates. These particles have only gravitational, or perhaps,superweak, interactions with ordinary matter and their own mirrorinteractions. Study of these interactions is possible only inastronomical observations. A quantitative analysis is conducted of thewide range of effects which the gravitational influence of mirrorobjects has on ordinary matter. A broad program of search forastronomical effects of mirror matter is proposed which would beconducted on a stellar to galaxy supercluster scale.
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