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New Times of Minima of Some Eclipsing Binary Stars
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| V839 Oph - 60 Years after Its Discovery
The first part of this contribution contains a brief review ofobservational history and recent knowledge of the eclipsing binary V839Oph. The second part concerns changes in orbital period of this star. Inthe third part devoted to light curve peculiarities some visual lightcurves of V839 Oph are compared with a light curve of classic nova V1500Cyg.
| Orbital period investigations of two short-period early-type overcontact binaries BH Cen and V701 Sco in two extremely young galactic clusters IC 2944 and NGC 6383
Both V701 Sco and BH Cen are two early-type short-period overcontactsystems (P = 0.d762 and P = 0.d792, respectively).V701 Sco is a member of the young galactic cluster NGC 6383, while BHCen is a component of a younger galactic cluster IC 2944 where starformation is in process. They provide good opportunity to understand theformation and evolution of binary stars. In the present paper, orbitalperiod changes of the two binaries are investigated. It is discoveredthat the orbital period of BH Cen shows a long-term increase with a rateof dP/dt = +1.70(±0.39) × 10‑7 days/yearwhile it undergoes a cyclic oscillation with a period of 44.6 years andan amplitude of A3 = 0.d0216. For V701 Sco, itsO-C curve reveals a periodic change with a period of 41.2 years andamplitude of A3 = 0.d0158. The mass ratio of BHCen is 0.84, but V701 Sco contains twin B1-1.5V type stars with a massratio of unit. The continuous period increase of BH Cen is caused by themass transfer from the less massive component to the more massive one ata rate of dM2/dt = 3.5 × 10‑6days/year. The cyclic period changes of both systems can be plausiblyexplained as the results of light-travel time effects suggesting thatthey are triple systems. The astrophysical parameters of the unseentertiary components in the two systems have been determined. We thinkthat the invisible tertiary components in both binaries played animportant role in the formations and evolutions of the overcontactconfigurations by bringing angular momentum out from the centralsystems. For BH Cen, this process created the initial short period andwill support its evolution into an overcontact configuration via a CaseA mass transfer within the life time of the extremely young cluster IC2944. For V701 Sco, two identical zero-age main-sequence components inan overcontact configuration suggest that it may have been formed byfission, possibly by the fission of the third body. The fact that nolong-term continuous period variations were found for V701 Sco maysuggest that an overcontact binary with the mass ratio of unity can bein an equilibrium revealing that the original configuration of thebinary was overcontact as is its present state. It has been reportedthat faint stars in the two extremely young clusters are relativelyscare. From the present study, it is shown that faint stars in youngclusters are usually formed as companions of OB stars (includingbinaries). It is very difficult to detect them because of their lowluminosity when compared with the more luminous OB stars.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Die 37. Tagung in BRNO.
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| Contact Binaries with Additional Components. II. A Spectroscopic Search for Faint Tertiaries
It is unclear how very close binary stars form, given that during thepre-main-sequence phase the component stars would have been inside eachother. One hypothesis is that they formed farther apart but were broughtin closer after formation by gravitational interaction with a thirdmember of the system. If so, all close binaries should be members oftriple (or higher order) systems. As a test of this prediction, wepresent a search for the signature of third components in archivalspectra of close binaries. In our sample of 75 objects, 23 show evidencefor the presence of a third component, down to a detection limit oftertiary flux contributions of about 0.8% at 5200 Å (consideringonly contact and semidetached binaries, we find 20 out of 66). In ahomogeneous subset of 59 contact binaries, we are fairly confident thatthe 15 tertiaries we have detected are all tertiaries present with massratios 0.28<~M3/M12<~0.75 and implied outerperiods P<~106 days. We find that if the frequency oftertiaries were the same as that of binary companions to solar-typestars, one would expect to detect about 12 tertiaries. In contrast, ifall contact binaries were in triple systems, one would expect about 20.Thus, our results are not conclusive but are sufficiently suggestive towarrant further studies.
| Deep, Low Mass Ratio Overcontact Binary Systems. VI. AH Cancri in the Old Open Cluster M67
CCD photometric light curves in the B and V bands obtained in 2001 andin the V band obtained in 2002 of AH Cnc in the old open cluster M67 arepresented. It is shown that AH Cnc is a total-eclipsing binary and itslight curves correspond to a typical A type according to Binnendijk'sclassification. The variations of the light curve around the primaryminimum and second maximum were found. Our nine epochs of light minimummonitored from 2001 to 2005, including others collected from theliterature, were used to create the first study of the period changes ofthe binary system. A cyclic oscillation with a period of 36.5 yr and anamplitude of 0.0237 days was discovered to be superposed on a continuousperiod increase (dP/dt=3.99×10-7 days yr-1).Weak evidence indicates that there exists another small-amplitude periodoscillation (A4=0.0035 days, P4=7.75 yr). Thesymmetric light curves in the B and V bands obtained in 2001 wereanalyzed with the 2003 version of the Wilson-Devinney code. It isconfirmed that AH Cnc is a deep overcontact binary system with a highdegree of overcontact f=58.5%+/-4.5% and a low mass ratio ofq=0.1682+/-0.0012. The existence of the third light and the cyclicperiod oscillation both may suggest that AH Cnc is a triple systemcontaining an unseen third body. The tertiary component may have playedan important role in the origin of the overcontact binary star byremoving angular momentum from the central system, which would cause itto have a short initial orbital period and thus evolve into anovercontact configuration by angular momentum loss. The long-term periodincrease can be interpreted as a mass transfer from the less massivecomponent to the more massive one. As the orbital period increases, thedecrease of the mass ratio will cause it finally to evolve into a singlerapid-rotating star when the system meets the more familiar criterionthat the orbital angular momentum be less than 3 times the total spinangular momentum. Therefore, AH Cnc may be a progenitor of the bluestraggler stars in M67.
| 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.
| 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.
| An Orbital Period Study of the W UMa-Type Binary RZ Comae Berenicis
New photoelectric and CCD photometry observations of a short-period WUMa-type binary system, RZ Com, are presented. The light curves ofBroglia (1960, Contr. Milano-Merate, 165) were symmetric in V band,while the present light curve shows a typical O'Connell effect, withMaximum I brighter than Maximum II by 0.015mag. It is found that thelight curve of the binary star has changed from W-subtype to A-subtypeaccording to Binnendijk's classification. This variation may be causedby the activity of dark spot on the primary component. Combining fournewly determined times of the light minimum with others published in theliterature, the orbital period change of the system was investigated. Asmall-amplitude oscillation (A = 0.0058 d), with a period of 44.8yr hasbeen discovered to be superimposed on a long-term period increase with arate of dP/dt = +4.12 × 10-8 d yr-1. Theperiod oscillation can be explained either by the light-time effect viathe presence of an unseen third body or by magnetic-activity cycles ofthe components. The mass ratio of RZ Com is q = 0.43. The secular periodvariation is in agreement with the conclusions of Qian (2001, MNRAS,328, 914; 2003, MNRAS, 342, 1260). This indicates that it is on theTRO-controlled stage of the evolutionary scheme proposed by Qian.
| Kinematics of W Ursae Majoris type binaries and evidence of the two types of formation
We study the kinematics of 129 W UMa binaries and we discuss itsimplications on the contact binary evolution. The sample is found to beheterogeneous in the velocity space. That is, kinematically younger andolder contact binaries exist in the sample. A kinematically young (0.5Gyr) subsample (moving group) is formed by selecting the systems thatsatisfy the kinematical criteria of moving groups. After removing thepossible moving group members and the systems that are known to bemembers of open clusters, the rest of the sample is called the fieldcontact binary (FCB) group. The FCB group is further divided into fourgroups according to the orbital period ranges. Then, a correlation isfound in the sense that shorter-period less-massive systems have largervelocity dispersions than the longer-period more-massive systems.Dispersions in the velocity space indicate a 5.47-Gyr kinematical agefor the FCB group. Compared with the field chromospherically activebinaries (CABs), presumably detached binary progenitors of the contactsystems, the FCB group appears to be 1.61 Gyr older. Assuming anequilibrium in the formation and destruction of CAB and W UMa systems inthe Galaxy, this age difference is treated as an empirically deducedlifetime of the contact stage. Because the kinematical ages (3.21, 3.51,7.14 and 8.89 Gyr) of the four subgroups of the FCB group are muchlonger than the 1.61-Gyr lifetime of the contact stage, the pre-contactstages of the FCB group must dominantly be producing the largedispersions. The kinematically young (0.5 Gyr) moving group covers thesame total mass, period and spectral ranges as the FCB group. However,the very young age of this group does not leave enough room forpre-contact stages, and thus it is most likely that these systems wereformed in the beginning of the main sequence or during thepre-main-sequence contraction phase, either by a fission process or mostprobably by fast spiralling in of two components in a common envelope.
| Improved astrophysical parameters for the overcontact binary FG Hydrae
Photometric data on FG Hya obtained in 2002 and 2004 are presented.Three data sets show the exchange between A-type, W-type and thevariable O'Connell effects. The photometric mass ratio (q= 0.1115 +/-0.0003) derived from B and V light curves is almost the same as thespectroscopic mass ratio (qsp= 0.112 +/- 0.004). The newphotometric solutions reveal that FG Hya is a deep overcontact binarysystem (f= 85.6 +/- 1.8 per cent) with a spotted massive component. Aperiod investigation, based on all available photoelectric or CCD timesof light minimum, shows that the O-C curve of FG Hya can be explained asa combination of a secular period decrease and a cyclic variation with aperiod of 36.4yr and an amplitude of 0.0289 d. By comparing thevariation of the depth of the primary minimum with the change of thecyclic period, it is discovered that both of them may vary with the samecycle length of 36.4yr and in the same phase. The variation of the lightcurve, the spotted primary component and the connection between thecyclic period change and the depth of the primary minimum, all maysuggest that the G0-type component displays solar-type magnetic activitywith a 36.4-yr cycle length. The long-time period decrease isinterpreted by mass transfer from the more massive component to the lessmassive one or/and angular momentum loss due to mass outflow from theouter Lagrangian point.
| New Times of Minima of Some Eclipsing Binary Stars
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| Photoelectric Minima of Some Eclipsing Binary Stars
We present 70 minima times of 35 eclipsing binaries.
| Photoelectric Minima of Some Eclipsing Binary Stars
We present 24 minima times of 18 eclipsing binaries.
| Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| GR Virginis: A Deep Overcontact Binary
Orbital period variations of the low-mass ratio (q=0.122) overcontactbinary system, GR Vir, were investigated by using two new CCD times ofminimum light and other photoelectric data compiled from literatures. Itis found that the O-C residuals of GR Vir show a cyclic variation with aperiod of 19.3 yr and an amplitude of 0.0140 days while they areundergoing a long-term decrease (dP/dt=-4.32×10-7 daysyr-1). Meanwhile, the 1988 photoelectric observations fromCereda et al. were analyzed using the Wilson-Devinney method. Like somelow-mass ratio overcontact binary stars (e.g., AW UMa), GR Vir is anA-type overcontact binary with a high degree of overcontact (f=78.6%).By combining the spectroscopic solutions with the photometric elements,the absolute parameters of the system are determined as follows:M1=1.36Msolar,M2=0.17Msolar, a=2.40Rsolar,R1=1.42Rsolar,R2=0.61Rsolar,L1=2.87Lsolar, andL2=0.48Lsolar. The long-term period decrease isinterpreted as the result of mass transfer from the more massivecomponent to the less massive one in combination with the angularmomentum loss due to mass outflow from the L2 point. Theconditions in GR Vir resemble those in AW UMa. Both systems show a highdegree of overcontact, low mass ratios, and secular shrinking of theirorbits. As their orbital periods decrease, the shrinking of the innerand outer critical Roche lobes will cause the common convective envelopeto become deeper, until finally the formation of single, rapid-rotationstars is inevitable. The period oscillation may by caused either by thepresence of an unseen tertiary component (e.g., a white dwarf) or bymagnetic activity on the part of the primary component.
| On the properties of contact binary stars
We have compiled a catalogue of light curve solutions of contact binarystars. It contains the results of 159 light curve solutions. Theproperties of contact binary stars were studied using the cataloguedata. As is well known since Lucy's (\cite{Lucy68a},b) and Mochnacki's(\cite{Mochnacki81}) studies, primary components transfer their ownenergy to the secondary star via the common envelope around the twostars. This transfer was parameterized by a transfer parameter (ratio ofthe observed and intrinsic luminosities of the primary star). We provethat this transfer parameter is a simple function of the mass andluminosity ratios. We introduced a new type of contact binary stars: Hsubtype systems which have a large mass ratio (q>0.72). These systemsshow behaviour in the luminosity ratio- transfer parameter diagram thatis very different from that of other systems and according to ourresults the energy transfer rate is less efficient in them than in othertypes of contact binary stars. We also show that different types ofcontact binaries have well defined locations on the mass ratio -luminosity ratio diagram. Several contact binary systems do not followLucy's relation (L2/L1 =(M2/M1)0.92). No strict mass ratio -luminosity ratio relation of contact binary stars exists.Tables 2 and 3 are available in electronic form athttp://www.edpsciences.org
| Period Changes of Two W UMa-Type Contact Binaries: RW Comae Berenices and CC Comae Berenices
From the present times of minimum light and those collected from theliterature, changes in the orbital period of the two W UMa-type contactbinaries RW Com and CC Com are analyzed. The results reveal that theperiod changes of these two systems show the same natures, with ashort-term oscillation superposed on the secular decrease. For RW Com,its period shows a secular decrease at a rate ofdP/dt=0.43×10-7 days yr-1. An oscillationwith a periodicity of 13.7 yr and an amplitude ofΔP=5.4×10-7 days is superposed on the seculardecrease. For CC Com, its period shows a secular decrease at a rate ofdP/dt=0.40×10-7 days yr-1. An oscillationwith a periodicity of 16.1 yr and an amplitude ofΔP=2.8×10-7 days is superposed on the seculardecrease. The period secular decreases of the two systems may beexplained by a mass-transfer rate of dm/dt=0.29×10-7Msolar yr-1 for RW Com anddm/dt=0.52×10-7 Msolar yr-1 forCC Com. The period short-term oscillations of the two systems may beexplained by the magnetic activity cycle model given by Applegate, andthe parameters for the magnetic activity cycle model are presented.
| Photoelectric Minima of Some Eclipsing Binary Stars
We present 48 minima times of 10 eclipsing binaries.
| Catalogue of the field contact binary stars
A catalogue of 361 galactic contact binaries is presented. Listedcontact binaries are divided into five groups according to the type andquality of the available observations and parameters. For all systemsthe ephemeris for the primary minimum, minimum and maximum visualbrightness and equatorial coordinates are given. If available,photometric elements, (m1+m2)sin3i,spectral type, parallax and magnitude of the O'Connell effect are alsogiven. Photometric data for several systems are augmented by newobservations. The quality of the available data is assessed and systemsrequiring modern light-curve solutions are selected. Selectedstatistical properties of the collected data are discussed.
| Photometric study of the over-contact binary star GSC 3822-1056
Here we present the first Johnson-Cousins VRC light curves ofthe over-contact binary star GSC 3822-1056. A periodstudy and the light curve solution are also given. An extremely highrate of period increase (+11.6 s/century) was found. The origin of thisperiod change can be: (i) partly covered light-time effect due to theorbital motion around the mass center of a possible third body; (ii)mass transfer between the components.The light curve was solved using the 1998 Wilson-Devinney Code. Weexamined the light curve with and without third light. Both solutionsyielded a contact configuration with high temperature difference betweenthe components. Despite the high degree of the contact (f=0.57), thetemperature difference between the components DeltaT=Tprimary-Tsecondary=1045 K.The high mass ratio of the system and its other unusual propertiessuggest that GSC 3822-1056 may be a recently formedcontact binary.Observations were made by the 80 cm ``IAC80'' telescope at Observatoriodel Teide in Tenerife, Spain, operated by Instituto de Astrofisica deCanarias.Tables 2a-c are only 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/403/637
| A period investigation of the overcontact binary system V417 Aquilae
A detailed orbital period investigation of the short-period (P=0fd 37)W UMa type star, V417 Aql, is presented based on the analysis of its O-Cdata. It is shown that the period change of the binary system iscontinuous. A periodic variation, with a period of 42.4 years and anamplitude of 0fd 0130, is found superimposed on a long-term perioddecrease (dP/dt=-5.50x10-8 days/year). The period oscillationcan be explained either by the light-time effect via the presence of anunseen third body or by magnetic activity cycles of the components. V417Aql is a W-type overcontact binary system with a low mass ratio ofq=0.36. The long-term period variation is in agreement with theconclusion of Qian (\cite{Qian01}b) that a low-mass ratio W-type systemusually shows a secular period decrease. This suggests that V417 Aql ison the AML-controlled stage of the evolutionary scheme proposed by Qian(\cite{Qian01}b). Meanwhile, the light-curve paradox encountered by TROtheory is discussed.
| New Elements of the contact binary V839 Ophiuchi
Not Available
| CCD Minima of selected binary stars in 2001
We present CCD minima observations of 13 eclipsing binaries.
| Period Studies of Some Neglected Close Binaries: EP Andromedae, V724 Aquilae, SS Comae, AM Eridani, FZ Orionis, BY Pegasi, EQ Tauri, and NO Vulpeculae
Orbital period changes of eight neglected short-period close binaries,EP And, V724 Aql, SS Com, AM Eri, FZ Ori, BY Peg, EQ Tau, and NO Vul,are presented based on the analysis of their O-C observations. It isfound that the periods of BY Peg and EQ Tau are decreasing at rates ofdP/dt=-1.67×10-7 and -1.72×10-7 dayyr-1, respectively, while the orbital periods of SS Com andAM Eri show secular increase at rates ofdP/dt=+5.91×10-7 and +4.39×10-7 dayyr-1. Weak evidence also indicates that the orbital period ofEP And is increasing. For FZ Ori, the decrease rate of orbital period isrevised. For the other two systems, V724 Aql and NO Vul, their O-C curvecan be described by a sudden period decrease or a continuous perioddecrease; further investigation is needed. The period changes of theeight systems can be explained by mass transfer between the twocomponents and/or mass and angular momentum loss from these binaries. Astrong mass-radius relation for observed contact binaries is formedbased on the parameters given by Maceroni & Van't Veer. It is shownthat the parameters of SS Com and EQ Tau given by Brancewicz &Dworak do not agree with the mass-radius relation. This may suggest thatthe two systems are not yet in contact. In order to understand thephysical properties of these binaries, complete photoelectric or CCDlight curves and radial velocity observations are needed.
| V842 Her: a W UMa Star with Constant Period
Times of minima of V842 Herculis were collected from the literature andtwo new moments of minima are published. A period determination wascarried out based on these minima and constant period was suspected(between 2490000-2520000). We commend the observation of V842 Herculis.
| UBV Photometry of the W UMa Star V839 Ophiuchi
Not Available
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
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