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Contact Binaries with Additional Components. III. A Search Using Adaptive Optics
We present results of the Canada-France-Hawaii Telescope adaptive optics(AO) search for companions of a homogeneous group of contact binarystars, as a contribution to our attempts to prove the hypothesis thatthese binaries require a third star to become as close as observed. Inaddition to directly discovering companions at separations of>=1″, we introduced a new method of AO image analysis utilizingdistortions of the AO diffraction ring pattern at separations of0.07″-1″. Very close companions, with separations in thelatter range, were discovered in the systems HV Aqr, OO Aql, CK Boo, XYLeo, BE Scl, and RZ Tau. More distant companions were detected in V402Aur, AO Cam, and V2082 Cyg. Our results provide a contribution to themounting evidence that the presence of close companions is a very commonphenomenon for very close binaries with orbital periods <1 day.Based on observations obtained at the Canada-France-Hawaii Telescope,which is operated by the National Research Council of Canada, theInstitut National des Sciences de l'Univers of the Centre National de laRecherche Scientifique of France, and the University of Hawaii.
| B.R.N.O. Contributions #34
Not Available
| New Times of Minima of Some Eclipsing Binary Stars
Not Available
| Orbital Period Changes for the Weak-Contact Binary TY Bootis
We present a detailed period analysis of TY Bootis, based on allavailable light minimum times covering about 80 years. We discoveredthat there exists a cyclic variation overlaying a secular perioddecrease from the distorted (O-C) diagram. A long-term decrease with asinusoidal oscillation (i.e., eq. [2]) or with a light-time effect(i.e., eq. [3]) may be reasonable due to the smaller difference betweentheir sum of residuals. The sinusoidal change with a period of 59.7 yrfor equation (2) can be attributed to either a light-time effect orcyclic magnetic activity of both components. For the assumed third body,the period and eccentricity of the light-time orbit areP3=58.6 yr and e'=0.1744, respectively. If theexistence of an additional unseen body is true, this binary may be atertiary system. The long-term orbital period decrease suggests that TYBoo is undergoing a mass transfer from the primary component to thesecondary component at a rate of dm/dt=-3.15×10-8Msolar yr-1 for equation (2) ordm/dt=-2.90×10-8 Msolar yr-1 forequation (3). As its mass transfers, accompanied by angular momentumloss due to mass outflow L2, this binary will evolve into adeep contact configuration.
| Eclipsed X-ray flares in binary stars: geometrical constraints on the flare's location and size
Aims: The observation of eclipses during X-ray flares taking place inactive cool stars binaries allows us to calculate the position and sizeof the flares. This information cannot be derived by analyzing the decayof the flares, a frequently used approach in the literature thatrequires the assumption of a physical model. We make use of theeclipsing light curve to constrain the set of possible solutions, fromthe geometrical point of view, in two flares of Algol, and one flare inVW Cep. Methods: We make use of a technique developed with the systemSV Cam (i˜ 90°) and generalize it to binary systems witharbitrary inclination. The method simulates all possible geometricalsituations that can produce the times of the four contacts of theeclipse. As an approximation we assume that the emitting region has aspherical shape that remains unchanged during the eclipse. We show,however, that this is a good approximation for the problem. Results:The solutions observed indicate that in two of the three cases the flarecannot be polar (|θ| < 55°) and in a third one the flarecan be placed either near the pole or at other latitudes. The emittingregions must have a small size (0.002-0.5 R*), but ifinterpreted as the apex of coronal loops, their length could actually beup to 3.1 R* for one of the Algol flares. These measurementsimply a lower limit to the electron density in the emitting regionbetween log ne (cm-3) 10.4 and 14.0, and amagnetic field between 70 and 3500 G. Similar results are found if theemitting region is assumed to be loop-shaped.Figures 8-12 and 15-18 are only available in electronic form viahttp://www.aanda.org
| Physical parameters and multiplicity of five southern close eclipsing binaries
Aims.We detected tertiary components of close binaries from spectroscopyand light curve modelling, investigated the light-travel time effect andthe possibility of magnetic activity cycles, measured mass ratios forunstudied systems, and derived absolute parameters. Methods: We carriedout new photometric and spectroscopic observations of five bright (< 10.5 mag) close eclipsing binaries, predominantly in thesouthern skies. We obtained full Johnson BV light curves, which weremodelled with the Wilson-Devinney code. Radial velocities were measuredwith the cross-correlation method using IAU radial velocity standards asspectral templates. Period changes were studied with the O-C method,utilising published epochs of minimum light (XY Leo) and ASAS photometry(VZ Lib). Results: For three objects (DX Tuc, QY Hya, V870 Ara),absolute parameters have been determined for the first time. Wespectroscopically detected the tertiary components in XY Leo and VZ Liband discovered one in QY Hya. For XY Leo we updated the light-timeeffect parameters and detected a secondary periodicity of about 5100 din the O-C diagram that may hint at the existence of short-periodmagnetic cycles. A combination of recent photometric data shows that theorbital period of the tertiary star in VZ Lib is likely to be over 1500d. QY Hya is a semi-detached X-ray active binary in a triple system withK and M-type components, while V870 Ara is a contact binary with thethird smallest spectroscopic mass ratio for a W UMa star to date (q =0.082 ± 0.030). Being close to the theoretical minimum forcontact binaries, this small mass ratio suggests that V870 Ara has thepotential of constraining evolutionary scenarios of binary mergers. Theinferred distances to these systems are compatible with the Hipparcosparallaxes.Based on observations made at the Siding Spring Observatory, Australia.Light curves and radial velocity data are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/465/943
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Doppler imaging of stellar surface structure. XXIII. The ellipsoidal K giant binary ζ Andromedae
Aims.We present the first Doppler images of the bright RS CVn-typebinary ζ And. The star is a magnetically active K1 giant with itsrotation synchronized to the 17.8-day orbital period. Our revisedlithium abundance of log n=1.2 places ζ And in the vicinity ofLi-rich RGB stars but it is nevertheless a Li-normal chromosphericallyactive binary star. The star seems to undergo its first standarddredge-up dilution. Methods: Four consecutive Doppler images wereobtained from a continuous 67-night observing run at NSO-McMath in1996/97. An additional single image was obtained from a continuous19-night run at KPNO in 1997/98. These unique data allow to compute asmall time series of the evolution of the star's surface structure. Allline-profile inversions are done with a modified TempMap version thattakes into account the non-spherical shape of the star. Representativetest reconstructions are performed and demonstrate the code'sreliability and robustness. Results: High and low-latitude spotactivity was recovered together with an asymmetric polar cap-likefeature. The latter dominated the first half of the two-month timeseries in 1996/97. The second half showed mostly medium-to-high latitudeactivity and only a fainter polar spot. The coolest areas were restoredwith a temperature contrast of about 1000±200 K. Some weakerfeatures at equatorial latitudes were also recovered but these could bepartially spurious and appear blurred due to imperfect phase coverage.We use our line profiles to reconstruct an average non-sphericity ofR_pole/R_point=0.96 which would, if not taken into account, mimic atemperature difference pole-to-equator of ≈220 K, especially at thephases of quadrature. Finally, we apply two different methods forrestoring surface differential rotation and found a weak solar-typerotation law with a shear ΔΩ≈0.95°/day(α=ΔΩ/Ω_eq=+0.049±0.003), i.e. roughly afactor of four weaker at a rotation rate roughly 1.5 times faster thanthe Sun's.Figures A.1-A.3 and Table A.1 are only available in electronic form athttp://www.aanda.org
| New Times of Minima of Eclipsing Binary Systems
We present 82 photoelectric minima observations of 34 eclipsingbinaries.
| Combining astrometry with the light-time effect: The case of VW Cep, ζ Phe and HT Vir
Three eclipsing binary systems with astrometric orbit have been studied.For a detailed analysis two circular-orbit binaries (VW Cep and HT Vir)and one binary with an eccentric orbit (ζ Phe) have been chosen.Merging together astrometry and the analysis of the times of minima, oneis able to describe the orbit of such a system completely. The O-Cdiagrams and the astrometric orbits of the third bodies were analysedsimultaneously for these three systems by the least-squares method. Theintroduced algorithm is useful and powerful, but also time consuming,due to many parameters which one is trying to derive. The new orbits forthe third bodies in these systems were found with periods 30, 221, and261 yr, and eccentricities 0.63, 0.37, and 0.64 for VW Cep, ζ Phe,and HT Vir, respectively. Also an independent approach to compute thedistances to these systems was used. The use of this algorithm to VW Cepgave the distance d=(27.90 ± 0.29) pc, which is in excellentagreement with the previous Hipparcos result.Based on observations secured at the South Africa AstronomicalObservatory, Sutherland, South Africa.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| A Methodology for the Description of Multiple Stellar Systems with Spectroscopic Subcomponents
We propose a methodology for analyzing triple stellar systems thatinclude a visual double star wherein one of the components is a single-or double-lined spectroscopic binary. By using this methodology, we cancalculate the most probable values of the spectroscopic binary'sinclination, the angular separation between its components, and itsstellar masses, and we can even estimate the spectral types. For a few WUMa-type eclipsing binaries, stellar radii are also determined.Moreover, we present new formulae for calculating stellar massesdepending on spectral type. In this way we have studied 61 triplesystems, five of them W UMa-type eclipsing binaries with low-masssubcomponents. In addition, we study nine quadruple systems, applyingthe same methodology and considering them twice as a triple system. Withthe aim of having more accurate orbital elements, we have takenadvantage of the occasion to calculate and improve orbits. In this waywe have used a new speckle measurement to improve the orbital elementsfor the binary Hu 506 AB. Also, new visual orbits are calculated for thebinaries BAG 10 Aa and LAB 6 Aa. Finally, we give a list of fivespectroscopic binaries with more than 0.1" for the maximum angularseparation; these should be easily observable as visual binaries bymeans of interferometric techniques.
| X-Ray Spectroscopy of the Contact Binary VW Cephei
Short-period binaries represent extreme cases in the generation ofstellar coronae via a rotational dynamo. Such stars are important forprobing the origin and nature of coronae in the regimes of rapidrotation and activity saturation. VW Cep (P=0.28 days) is a relativelybright, partially eclipsing, very active object. Light curves made fromChandra HETGS data show flaring and rotational modulation but noeclipses. Velocity modulation of emission lines indicates that onecomponent dominates the X-ray emission. The emission measure is highlystructured, having three peaks. Helium-like triplet lines give electrondensities of about (3-18)×1010 cm-3. Weconclude that the corona is predominantly on the polar regions of theprimary star and is compact.
| Are the W Ursae Majoris-type systems EK Comae Berenices and UX Eridani surrounded by circumstellar matter?
The variations of the orbital periods of two nearly neglected W UMa-typeeclipsing binaries, EK Comae Berenices and UX Eridani, are presentedthrough a detailed analysis of the O C diagrams. It is found that theorbital period of EK Com is decreasing and the period of UX Eridani isincreasing, and several sudden jumps have occurred in the orbitalperiods of both binaries. We analyze the mechanism(s), which mightunderlie the changes of the orbital periods of both systems, and obtainsome new results. The long-term decrease of the orbital period of EKComae Berenices might be caused by the decrease of the orbital angularmomentum due to a magnetic stellar wind (MSW) or by mass transfer fromthe more massive to the less massive component. The secular increase inthe orbital period of UX Eridani might be caused by mass transfer fromthe less massive to the more massive star. The possible mechanisms,which underlie the sudden changes in the orbital periods of the closebinary systems are as the followings: (1) the variations of thestructure due to the variation of the magnetic field; (2) the rapid massexchange between the close binaries and their circumstellar matter.Finally, the evolutionary status of the systems EK Comae Berenices andUX Eridani is discussed.
| Variation in the orbital period of W UMa-type contact systems
The secular variation in the orbital period Porb is studiedas a function of the mass ratio q of the components in a sample of 73contact systems of class W UMa constructed from a survey of current(1991–2003) published photometric and spectroscopic data. Almostall the W UMa-systems (>93% of this sample) are found to have avariation in their orbital periods Porb which alternates insign independently of their division into A-and Wsubclasses. Astatistical study of this sample in terms of the observedcharacteristics dPorb/dt and q showed that on the average thenumbers of increases (35 systems) and decreases (33 systems) in theperiods are the same, which indicates the existence of flows directedalternately from one component to the other and illustrates the cyclicalcharacter of the thermal oscillations. An analysis of the behavior ofdPorb/dt as a function of the mass interval of the primarycomponent yields a more accurate value for the mass ratio, q ≈ 0.4÷ 0.45 at which contact binaries are separated into A-andW-subclasses. No correlations were observed between the fill-out factorfor the outer contact configuration, the total mass of the contactsystem, and the mass ratio of the components, on one hand, and the signof the secular variation in the period. The physical properties andevolutionary features of these systems are discussed.
| Contact Binaries with Additional Components. I. The Extant Data
We have attempted to establish observational evidence for the presenceof distant companions that may have acquired and/or absorbed angularmomentum during the evolution of multiple systems, thus facilitating orenabling the formation of contact binaries. In this preliminaryinvestigation we use several techniques (some of themdistance-independent) and mostly disregard the detection biases ofindividual techniques in an attempt to establish a lower limit to thefrequency of triple systems. While the whole sample of 151 contactbinary stars brighter than Vmax=10 mag gives a firm lowerlimit of 42%+/-5%, the corresponding number for the much better observednorthern-sky subsample is 59%+/-8%. These estimates indicate that mostcontact binary stars exist in multiple systems.
| Luminosity function of contact binaries based on the All Sky Automated Survey (ASAS)
The luminosity function for contact binary stars of the W UMa type isevaluated on the basis of the All Sky Automated Survey (ASAS)photometric project covering all stars south of δ=+ 28° withina magnitude range 8 < V < 13. Lack of colour indices enforced alimitation to 3374 systems with P < 0.562 d (i.e. 73 per cent of allsystems with P < 1 d) where a simplified MV(logP)calibration could be used. The spatial density relative to themain-sequence FGK stars of 0.2 per cent, as established previously fromthe Hipparcos sample to V= 7.5, is confirmed. While the numbers ofcontact binaries in the ASAS are large and thus the statisticaluncertainties small, derivation of the luminosity function required acorrection for missed systems with small amplitudes and with orbitalperiods longer than 0.562 d; the correction, by a factor of 3, carriesan uncertainty of about 30 per cent.
| A Comparative Study of Flaring Loops in Active Stars
Dynamo activity in stars of different types is expected to generatemagnetic fields with different characteristics. As a result, adifferential study of the characteristics of magnetic loops in a broadsample of stars may yield information about dynamo systematics. In theabsence of direct imaging, certain physical parameters of a stellarmagnetic loop can be extracted if a flare occurs in that loop. In thispaper we employ a simple nonhydrodynamic approach introduced by Haisch,to analyze a homogeneous sample of all of the flares we could identifyin the EUVE DS database: a total of 134 flares that occurred on 44 starsranging in spectral type from F to M and in luminosity class from V toIII. All of the flare light curves that have been used in the presentstudy were obtained by a single instrument (EUVE DS). For each flare, wehave applied Haisch's simplified approach (HSA) in order to determineloop length, temperature, electron density, and magnetic field. For eachof our target stars, a literature survey has been performed to determinequantitatively the extent to which our results are consistent withindependent studies. The results obtained by HSA are found to be wellsupported by results obtained by other methods. Our survey suggeststhat, on the main sequence, short loops (with lengths<=0.5R*) may be found in stars of all classes, while thelargest loops (with lengths up to 2R*) appear to be confinedto M dwarfs. Based on EUVE data, the transition from small to largeloops on the main sequence appears to occur between spectral types K2and M0. We discuss the implications of this result for dynamo theories.
| New CCD Times of Minima of Eclipsing Binary Systems
We present a total of 208 CCD timings for 103 eclipsing binaries.
| New Times of Minima of Eclipsing Binary Systems and of Maximum of SXPHE Type Stars
We present 64 photoelectric minima observations of 31 eclipsingbinaries. We also report three new times of maxima of three SXPHE typepulsating stars.
| BO Canum Venaticorum and SS Comae Berenices: A Photometric Study of AW UMa-Type Binaries
BO CVn and SS Com are two short-period W UMa-type binary stars withspectral types earlier than F5. In the present paper new CCD photometriclight curves in B, V, and R bands of BO CVn and the first complete lightcurve in V band of SS Com are presented. The light curves of the twobinaries are symmetric, and no variations of the light curves were foundfor both systems that are quite unlike those of cooler overcontactbinaries. These observational properties may suggest weak photosphericdark spot activity in the two systems during the observational timeintervals. Photometric solutions of the two W UMa-type binaries werederived by using the 2003 version of the Wilson-Devinney (W-D) method.The new solutions suggest that they are overcontact binary stars withdegrees of overcontact of f=40.6% for BO CVn and f=49.6% for SS Com. Ournew times of light minimum confirmed the long-time period increases ofthe two systems, and the rates of continuous period increase wererevised. The long-time period increases, the orbital periods, thedegrees of overcontact, and the mass ratios all suggest that they are onan evolutionary stage of mass transfer from the less massive componentto the more massive one, and SS Com will reach the present evolutionarystate of BO CVn. The slow evolution toward extreme mass ratio will causethem finally to coalesce to single stars. Therefore, both of them are AWUMa-type near-coalescent overcontact binary systems.
| Photospheric and chromospheric active regions on three single-lined RS CVn binaries
A monitoring of three active RS CVn binaries has been performed withmedium resolution spectroscopy with the aim of investigating thebehavior of chromospheric and photospheric inhomogeneities. Surfacetemperature, as recovered from line-depth ratios (LDRs), allowed us tomap the photospheric spots, while the Hα emission has been used asan indicator of chromospheric inhomogeneities. We have found that therotational modulation of the Hα emission is always in anti-phasewith the temperature wave, i.e. at the time of our observations activeregions at chromospheric and photospheric levels are closely spatiallyassociated in these active stars. The residual Hα profiles,obtained as the difference between the observed spectra and non-activetemplates, are well reproduced by a two Gaussian fitting. The broademission component, responsible for the wide emission wings in near allthe spectra, is often blue-shifted with respect to the center of thestellar disk. The narrow Hα emission displays a phase-dependentvariation in all stars and is anti-correlated with the photosphericdiagnostics, while the broad one displays no or little rotationalmodulation. We suggest that the broad emission component is mainlyrelated to physical phenomena, like micro-flaring or strongchromospheric velocity fields, occurring all over the star disk, whilethe central narrow emission is more affected by chromospheric plages. Wehave also detected a modulation of the intensity of the He I D3 linewith the star rotation, suggesting surface features also in the upperchromosphere of these stars.
| 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.
| A compact flare eclipsed in the corona of SV Camelopardalis
The eclipsing active binary SV Cam (G0V/K6V, Porb=0.593071 d)was observed with XMM-Newton during two campaigns in 2001 and 2003. Noeclipses in the quiescent emission are clearly identified, but a flarewas eclipsed during the 2001 campaign, allowing us to stronglyconstrain, from purely geometrical considerations, the position and sizeof the event: the flare is compact and it is formed at a latitude below65°. The size, temperature and Emission Measure of the flare implyan electron density of log ne (cm-3)10.6{-}13.3 and a magnetic field of 65-1400 G in order to confine theplasma, consistent with the measurements that are obtained fromdensity-sensitive line ratios in other similar active stars. Averageemission seems to come from either extended or polar regions because oflack of eclipses. The Emission Measure Distribution, coronal abundancesand characteristics of variability are very similar to other activestars such as AB Dor (K1V).
| Bericht uber die 3. Veraenderlichen-Beobachtungswoche in Kirchheim.
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| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderliche Sterne e.V.
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| New Minima of Selected Eclipsing Close Binaries
We present 180 CCD and photoelectric times of minima of selected closeeclipsing binaries.
| New Times of Minima of Some Eclipsing Binary Stars
Not Available
| The first CCD photometric study of the neglected W UMa-type binary PP Lacertae
The first complete charge couple device (CCD) photometric light curve inV band of the neglected W UMa-type binary star, PP Lacertae, ispresented. It is shown that the system is a complete eclipsing binaryand belongs to W type according to Binnendijk’s classificationwhere the occultation minimum is much deep than the transit one. Thelight curve is symmetric and no day-to-day variation of the light curvewas found. These properties enable good chance to determine photometricparameters of the binary system. Photometric solutions based on thecomplete light curve were derived with the 2003 version of the W D code.It is suggested that PP Lacertae is a W-type overcontact binary systemwith a mass ratio of q = 2.3000(±0.0044) and a median degree ofovercontact of f = 23.9%(±1.1%). The temperature of the lessmassive component is about 260 K higher than that of the more massiveone. Our four CCD times of light minimum, including others collectedfrom the literature, have been used for the period study. It is foundthat the period showed a small-amplitude cyclic oscillation with aperiod of 19.7 years and an amplitude of 0.d0058, which canbe explained as the light-time effect of an unseen third body.
| Indirect evidence for short period magnetic cycles in W UMa stars. Period analysis of five overcontact systems.
Complex period variations of five W UMa type binaries (ABAnd, OO Aql, DK Cyg,V566 Oph, U Peg) were investigatedby analyzing their O-C diagrams, and several common features were found.Four of the five systems show secular period variations at a constantrate on the order of |dot{P}sec/P|10-7yr-1. In the case of AB And, OOAql, and U Peg a high-amplitude, nearlyone-century long quasi-sinusoidal pattern was also found. It might beexplained as light-time effect, or by some magnetic phenomena, althoughthe mathematical, and consequently the physical, parameters of thesefits are very problematic, as the obtained periods are very close to thelength of the total data range. The most interesting feature of thestudied O-C diagrams is a low amplitude ( 2-4×10-3 d)modulation with a period around 18-20 yr in four of the five cases. Thisphenomenon might be indirect evidence of some magnetic cycle inlate-type overcontact binaries as an analog to the observed activitycycles in RS CVn systems.
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