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A newly discovered active contact binary in the field of NGC 1348
We present a CCD photometry study of a newly discovered active eclipsingbinary in the field of open cluster NGC 1348 based on the firsttime-series photometric observation. From the minimum times, wedetermined an orbital period of P = 0.691363 d. Among our datasets, theBV (RI)c light curves obtained in November 2008 were analyzedusing the Wilson-Devinney light curve modeling technique. Because of theuncertainty of the membership of this binary in open cluster NGC 1348,we have analyzed the photometric data in two cases with differentprimary effective temperatures: Case A (T1 = 7750 K) and CaseB (T1 = 5250 K). Our analyses reveal that, for Case A, it isa deep (f > 70%), very low mass ratio (q ⋍ 0.096) binarysystem, indicating that it is now in the late evolution stage of acontact binary; while for Case B, it is a red system withextraordinarily long orbital period with respect to the period-colorrelation for normal contact binaries, which suggests that this binaryhas evolved off the main sequence. The well known O'Connell effect(e.g., ΔB ⋍ 0.03 mag) was found in the dataset obtained inNovember 2008, which could be due to the existence of starspots on thecomponents, therefore the corresponding spot properties (for Case A: hotspot; for Case B: dark spot) were determined using the Wilson-Devinneycode. With the purpose of analyzing the dark spot activity for Case B,we compared the light curves derived in different observing runs, andfound that a slight change appeared from November to December, 2008,which indicates the evolution of spot activity on at least one componentover a time scale of about one month.
| Marginally low mass ratio close binary system V1191 Cyg
The light and radial velocity curves of V1191 Cyg are solvedsimultaneously. The orbital and physical parameters of thesystem are determined. New observations indicate a very highmass transfer rate between the components. New observations showthat the depths of the minima of the light curve have been interchanged.
| UBVRc Ic Analysis of the Recently Discovered Totally Eclipsing Extreme Mass Ratio Binary V1853 Orionis, and a Statistical Look at 25 Other Extreme Mass Ratio Solar-type Contact Binaries
We present precision CCD light curves, a period study, photometricallyderived standard magnitudes, and a five-color simultaneous Wilson codesolution of the totally eclipsing, yet shallow amplitude (Av~ 0.4 mag) eclipsing, binary V1853 Orionis. It is determined to be anextreme mass ratio, q = 0.20, W-type W UMa overcontact binary. From ourstandard star observations, we find that the variable is a late-type Fspectral-type dwarf, with a secondary component of about 0.24 solarmasses (stellar type M5V). Its long eclipse duration (41 minutes) ascompared to its period, 0.383 days, attests to the small relative sizeof the secondary. Furthermore, it has reached a Roche lobe fill-out of~50% of its outer critical lobe as it approaches its final stages ofbinary star evolution, that of a fast spinning single star. Finally, asummary of about 25 extreme mass ratio solar-type binaries is given.
| Random forest automated supervised classification of Hipparcos periodic variable stars
We present an evaluation of the performance of an automatedclassification of the Hipparcos periodic variable stars into 26 types.The sub-sample with the most reliable variability types available in theliterature is used to train supervised algorithms to characterize thetype dependencies on a number of attributes. The most useful attributesevaluated with the random forest methodology include, in decreasingorder of importance, the period, the amplitude, the V-I colour index,the absolute magnitude, the residual around the folded light-curvemodel, the magnitude distribution skewness and the amplitude of thesecond harmonic of the Fourier series model relative to that of thefundamental frequency. Random forests and a multi-stage scheme involvingBayesian network and Gaussian mixture methods lead to statisticallyequivalent results. In standard 10-fold cross-validation (CV)experiments, the rate of correct classification is between 90 and 100per cent, depending on the variability type. The main mis-classificationcases, up to a rate of about 10 per cent, arise due to confusion betweenSPB and ACV blue variables and between eclipsing binaries, ellipsoidalvariables and other variability types. Our training set and thepredicted types for the other Hipparcos periodic stars are availableonline.
| On the minimum mass ratio of W UMa binaries
Using Eggleton's stellar evolution code, we study the minimum mass ratio(qmin) of W Ursae Majoris (W UMa) binaries that havedifferent primary masses. It is found that the minimum mass ratio of WUMa binaries decreases with increasing mass of the primary if theprimary's mass is less than about 1.3Msolar, while above thismass the ratio is roughly constant. By comparing the theoretical minimummass ratio with observational data, it is found that the existence oflow-q systems can be explained by the different structure of primarieswith different masses. This suggests that the dimensionless gyrationradius (k21) and thus the structure of the primaryis very important in determining the minimum mass ratio. In addition, weinvestigate the mass loss during the merging process of W UMa systemsand calculate the rotation velocities of the single stars formed bymergers of W UMa binaries due to tidal instability. It is found that inthe case of conservation of mass and angular momentum, the merged singlestars rotate with an equatorial velocity of about~588-819kms-1, which is much larger than their break-upvelocities (vb). This suggests that the merged stars shouldextend to a very large radius (~3.7-5.3 times the radii of theprimaries) or else W UMa systems should lose a large amount of mass(~21-33 per cent of the total mass) during the merging process. If theeffect of magnetic braking is considered, the mass loss decreases to~12-18 per cent of the total mass. This implies that significant angularmomentum and mass might be lost from W UMa systems in the course of themerging process, and this kind of mass and angular momentum loss mightbe driven by the release of orbital energy of the secondaries, similarlyto common-envelope evolution.
| The Minimum Mass Ratio for Contact Close Binary Systems of W Ursae Majoris-type
Extreme mass ratio close binaries of W UMa-type represent an interestingclass of objects in which ˜1M main-sequence star is in contactwith a significantly less massive companion (M˜0.1M). Earliertheoretical investigations of these systems found that there is aminimum mass ratio q=M/M≈0.085-0.095 (obtained for n=3polytrope-fully radiative primary) above which these systems are stable.If the mass ratio is lower than minimum, a tidal instability develops(Darwin's instability). This instability, which is secular, growing on aviscous dissipation timescale, eventually forces the stars to merge intoa single, rapidly rotating object (such as FK Com-type stars or bluestragglers), implying that such systems would not be observed. Thereappear to be, however, some W UMa-type binaries with empiricallyobtained q values below the theoretical limit for stability. The aim ofthis dissertation was to try to resolve the discrepancy between theoryand observations by considering rotating polytropes. Other candidatesystems for stellar mergers such as AM CVn-type stars have also beendiscussed in the dissertation.
| Possible solution to the problem of the extreme mass ratio W UMa-type binaries
When the total angular momentum of a binary system is at a critical(minimum) value, a tidal instability occurs (Darwin's instability),eventually forcing the stars to merge into a single, rapidly rotatingobject. The instability sets in at some critical separation which in thecase of contact binaries corresponds to a minimum mass ratio dependingon dimensionless gyration radius k1. If one considers n = 3polytrope (fully radiative primary with Γ1 = 4/3),k21 = 0.075 and qmin ~ 0.085-0.095.There appears to be, however, some W UMa-type binaries with q valuesvery close, if not below these theoretical limits, implying that primaryin these systems is probably more centrally condensed. We try to solvethe discrepancy between theory and observations by considering rotatingpolytropes. We show by deriving and solving a modified Lane-Emdenequation for n = 3 polytrope that including the effects of rotation doesincrease the central concentration and could reduce qmin toas low as 0.070-0.074, more consistent with the observed population.
| B.R.N.O. Times of minima
Not Available
| Angular momentum and mass evolution of contact binaries
Various scenarios of contact binary evolution have been proposed in thepast, giving hints of (sometimes contradictory) evolutionary sequencesconnecting A- and W-type systems. As the components of close detachedbinaries approach each other and contact binaries are formed, followingevolutionary paths transforms them into systems of two categories:A-type and W-type. The systems evolve in a similar way but underslightly different circumstances. The mass/energy transfer rate isdifferent, leading to quite different evolutionary results. Analternative scenario of evolution in contact is presented and discussed,based on the observational data of over one hundred low-temperaturecontact binaries. It results from the observed correlations amongcontact binary physical and orbital parameters. Theoretical tracks arecomputed assuming angular momentum loss from a system via stellar wind,accompanied by mass transfer from an advanced evolutionary secondary tothe main-sequence primary. A good agreement is seen between the tracksand the observed graphs. Independently of details of the evolution incontact and a relation between A- and W-type systems, the ultimate fateof contact binaries involves the coalescence of both components into asingle fast rotating star.
| The evolutionary status of W Ursae Majoris-type systems
Well-determined physical parameters of 130 W Ursae Majoris (W UMa)systems were collected from the literature. Based on these data, theevolutionary status and dynamical evolution of W UMa systems areinvestigated. It is found that there is no evolutionary differencebetween W- and A-type systems in the M-J diagram, which is consistentwith the results derived from the analysis of observed spectral type andof M-R and M-L diagrams of W UMa systems. M-R and M-L diagrams of W- andA-type systems indicate that a large amount of energy should betransferred from the more massive to the less massive component, so thatthey are not in thermal equilibrium and undergo thermal relaxationoscillation. Moreover, the distribution of angular momentum, togetherwith the distribution of the mass ratio, suggests that the mass ratio ofthe observed W UMa systems decreases with decreasing total mass. Thiscould be the result of the dynamical evolution of W UMa systems, whichsuffer angular momentum loss and mass loss as a result of the magneticstellar wind. Consequently, the tidal instability forces these systemstowards lower q values and finally to rapidly rotating single stars.
| The minimum mass ratio of W UMa-type binary systems
When the total angular momentum of a binary system Jtot =Jorb + Jspin is at a certain critical (minimum)value, a tidal instability occurs which eventually forces the stars tomerge into a single, rapidly rotating object. The instability occurswhen Jorb = 3Jspin, which in the case of contactbinaries corresponds to a minimum mass ratio qmin ~0.071-0.078. The minimum mass ratio is obtained under the assumptionthat stellar radii are fixed and independent. This is not the case withcontact binaries where, according to the Roche model, we haveR2 = R2(R1, a, q). By finding a newcriterion for contact binaries, which arises from dJtot = 0,and assuming k21 ≠ k22for the component's dimensionless gyration radii, a theoretical lowerlimit qmin = 0.094-0.109 for overcontact degree f = 0-1 isobtained.
| Masses and angular momenta of contact binary stars
Results are presented on component masses and system angular momenta forover 100 low-temperature contact binaries. It is found that thesecondary components in close binary systems are very similar in mass.Our observational evidence strongly supports the argument that theevolutionary process goes from near-contact binaries to A-type contactbinaries, without any need of mass loss from the system. Furthermore,the evolutionary direction of A-type into W-type systems with asimultaneous mass and angular momentum loss is also discussed. Theopposite direction of evolution seems to be unlikely, since it requiresan increase of the total mass and the angular momentum of the system.
| Physical Parameters of Components in Close Binary Systems: VI
New high-quality CCD photometric light curves for the W UMa-type systemsV410 Aur, CK Boo, FP Boo, V921 Her, ET Leo, XZ Leo, V839 Oph, V2357 Oph,AQ Psc and VY Sex are presented. The new multicolor light curves,combined with the spectroscopic data recently obtained at David DunlapObservatory, are analyzed with the Wilson-Devinney code to yield thephysical parameters (masses, radii and luminosities) of the components. Our models for all ten systems resulted in a contact configuration. Fourbinaries (V921 Her, XZ Leo, V2357 Oph and VY Sex) have low, while two(V410 Aur and CK Boo) have high fill-out factors. FP Boo, ET Leo, V839Oph and AQ Psc have medium values of the fill-out factor. Three of thesystems (FP Boo, V921 Her and XZ Leo) have very bright primaries as aresult of their high temperatures and large radii.
| 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.
| CCD Times of Minima of Several Eclipsing Binaries
54 CCD minima timings of 28 eclipsing binaries made mainly by the authorare presented.
| Radial Velocity Studies of Close Binary Stars. X.
Radial velocity measurements and sine-curve fits to orbital velocityvariations are presented for the ninth set of 10 close binary systems:V395 And, HS Aqr, V449 Aur, FP Boo, SW Lac, KS Peg, IW Per, V592 Per, TUUMi, and FO Vir. The first three are very close, possibly detached,early-type binaries, and all three require further investigation.Particularly interesting is V395 And, whose spectral type is as early asB7/8 for a 0.685 day orbit binary. KS Peg and IW Per are single-linebinaries, with the former probably hosting a very low mass star. We havedetected a low-mass secondary in an important semidetached system, FOVir, at q=0.125+/-0.005. The contact binary FP Boo is also a very smallmass ratio system, q=0.106+/-0.005. The other contact binaries in thisgroup are V592 Per, TU UMi, and the well-known SW Lac. V592 Per and TUUMi have bright tertiary companions; for these binaries, and for V395And, we used a novel technique of arranging the broadening functionsinto a two-dimensional image in phase. The case of TU UMi turned out tobe intractable even using this approach, and we have not been able toderive a firm radial velocity orbit for this binary. Three systems ofthis group were observed spectroscopically before: HS Aqr, SW Lac, andKS Peg.Based on the data obtained at the David Dunlap Observatory, Universityof Toronto.
| 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/.
| Key parameters of W UMa-type contact binaries discovered by HIPPARCOS
A sample of W UMa-type binaries which were discovered by the HIPPARCOSsatellite was constructed with the aid of well defined selectioncriteria described in this work. The selection process showed up thatseveral systems of which the variability types have been assigned as EBin HIPPARCOS catalogue are genuine contact binaries of W UMa-type. Thelight curves of the 64 selected systems based on HIPPARCOS photometrywere analyzed with the aid of light curve synthesis method by Rucinskiand their geometric elements (namely mass ratio q, degree of contact f,and orbital inclination i) were determined. The solutions were obtainedfor the first time for many of the systems in the sample and would be agood source for their future light curve analyses based on more precisefollow-up observations.Based on observations made with the ESA HIPPARCOSastrometry satellite.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
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