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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.
| 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.
| 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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| 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.
| CK Bootis: a W UMa system with a small mass ratio
We present an analysis of BVR light curves of an eclipsing binary {CKBootis}, a system with a very small mass ratio. The light curves appearto exhibit a typical O'Connell effect. The light curves are analyzed bymeans of the latest version of the WD program. The asymmetry of thelight curves is explained by a cool star spot model. The simultaneousBVR synthetic light curve analysis gives a tiny mass ratio of 0.12, anextremely large fill-out factor of 0.65, and a very small differencebetween the component temperatures of 90 K. The absolute parameters ofthe system were also derived by combining the photometric solutions withthe radial velocity data. The mass of the secondary is very low (0.15M_ȯ) and it continues losing mass. Thirty seven new times ofminimum are reported. It is found that the orbital period of the systemhas a quasi periodic variation, superimposed on a period increase. Thelong-term period increase rate is deduced to be dP/dt = 3.54 x10-7 d yr-1, which can be interpreted as being dueto mass transfer from the less massive star to the more massivecomponent.
| 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.
| New Times of Minima of Eclipsing Binary Systems
Not Available
| CCD Times of Minima of Some Eclipsing Binaries in 2002
We present CCD observations of minima of 11 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.
| The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| 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.
| Period variation and spot model for the W UMa type binary TY UMa
We present the full VRI light curves and the times of minima of TY UMato provide a complete photometric solution and a long-term trend ofperiod variation. The light curves show a high degree of asymmetry (theO'Connell effect). The maxima at 0.25 phase (Max I) are 0.021, 0.015,and 0.020mag fainter than those at 0.75 phase (Max II) in V , R , and I, respectively. The period of TY UMa has varied in a sinusoidal way,superimposed on the long-term upward parabolic variation. The secularlyincreasing rate of the period is deduced as 1.83s per century (Pdot /P=5.788×10-10 dd-1 ) . The period ofsinusoidal variation is about 57.4yr. The spot model has been applied tofit the asymmetric light curves of TY UMa, to explain light variations.By changing only the spot parameters, the model light curves can fit theobserved light curves for three epochs. This indicates that thevariation of the spot location and size is the main reason for changingthe shape of light curves, including two different maxima and theinterchanging depths of occultation and transit minima.
| CCD Times of Minima of Faint Eclipsing Binaries in 2000
196 CCD minima observations of 122 eclipsing binaries made by the authorin 2000 are presented. The observed stars were chosen from the catalogueBRKA of observing programme of BRNO-Variable Star Section of CAS.
| Observational evidence and analysis of the coupling between the dynamical and the thermodynamic processes for close binaries.
Analytical methods of the orbital period, the types of its variations,the mechanisms causing the changes in the orbital period, and problemsand progresses in the orbital period study are introduced. Theproperties of the variations in te orbital period and in the lightcurve, and the connections between the changes of the orbital period andthe light curve in different types of close binaries are also reviewed.The changes of the orbital period, the variations of the light curve andtheir connections in some sample stars are studied. The statisticalrelation of the parameters in contact binaries is also investigated.
| 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.
| A possible relation between the period change and the mass ratio for W-type contact binaries
Orbital period changes of eight W-type contact binaries (TY Boo, BH Cas,AD Cnc, TX Cnc, RZ Com, LS Del, BB Peg and AA UMa) are presented basedon the analysis of their O-C curves. It is found that the periods of thefive systems TY Boo, TX Cnc, RZ Com, LS Del and AA UMa show secularincrease. For BB Peg, its period increase rate has been revised. For ADCnc, weak evidence also shows that its orbital period is increasing. Forthe remaining BH Cas, the three times of light minimum given by Agerer& Hubscher indicate that, recently, its period has been increasing.However, the properties of the period need further study. The massratios of all the systems are larger than 0.4. The period increases ofthe systems may suggest that the W-type W UMa stars with high mass ratio(q>0.4) usually show their period increase. In order to check thisconclusion, secular period changes of 30 W-type contact binaries havebeen collected from the literature. It is found that systems showingperiod increase usually have a higher mass ratio (q>0.4), and theperiods of low-mass ratio systems (q<0.4) are varying in a seculardecrease. This strongly suggests that a relation between the orbitalperiod variation and the mass ratio for W-type contact binaries mayexist. If the secular period change is caused by conservative masstransfer between the components, this relation may suggest that theevolution of the W-type systems is oscillation around a critical massratio (q~0.4). However this is highly speculative. On the other hand,the relation may be potentially strong observational evidence forRahunen's conclusion that angular momentum loss (AML) may enable thecomponents of a contact binary to remain in good contact throughout thethermal relaxation oscillation (TRO) cycle. This connection could beexplained by the combination of the TRO and the variable AML via thechange of depth of contact, which needs further studies observationallyand theoretically.
| ROSAT all-sky survey of W Ursae Majoris stars and the problem of supersaturation
From ROSAT all-sky survey (RASS) data we obtained X-ray fluxes for 57 WUMa type contact systems. In our sample we detected three stars whichare the shortest period main sequence binaries ever found as X-raysources. For stars with (B-V)_0 < 0.6 the normalized X-ray fluxdecreases with a decreasing color index but for (B-V)_0 > 0.6 aplateau is reached, similar to the saturation level observed for single,rapidly rotating stars. The X-ray flux of W UMa stars is about 4-5 timesweaker than that of the fastest rotating single stars. Because earlytype, low activity variables have longer periods, an apparentperiod-activity relation is seen among our stars, while cool stars with(B-V)_0 > 0.6 and rotation periods between 0.23 and 0.45 days do notshow any such relation. The lower X-ray emission of the single, ultrafast rotators (UFRs) and W UMa stars is interpreted as the result of adecreased coronal filling factor. The physical mechanisms responsiblefor the decreased surface coverage differs for UFRs and W UMa systems.For UFRs we propose strong polar updrafts within a convection zone,driven by nonuniform heating from below. The updrafts should beaccompanied by large scale poleward flows near the bottom of theconvective layer and equatorward flows in the surface layers. The flowsdrag dynamo generated fields toward the poles and create a field-freeequatorial region with a width depending on the stellar rotation rate.For W UMa stars we propose that a large scale horizontal flow embracingboth stars will prevent the magnetic field from producing long-livedstructures filled with hot X-ray emitting plasma. The decreased activityof the fastest rotating UFRs increases the angular momentum loss timescale of stars in a supersaturated state. Thus the existence of a periodcutoff and a limiting mass of W UMa stars can be naturally explained.
| Photoelectric Minima of Selected Eclipsing Binaries
Not Available
| Radial Velocity Studies of Close Binary Stars. II.
Radial velocity measurements and simple sine-curve fits to the orbitalvelocity variations are presented for the second set of 10 contactbinary systems. Eight systems are of the A type: AH Aur, CK Boo, DK Cyg,UZ Leo, XZ Leo, V839 Oph, GR Vir, and NN Vir; V842 Her is the only Wtype, while SV Equ appears to be a semidetached system seen at a loworbital inclination rather than a contact binary. Several of the studiedsystems are prime candidates for complete light and radial velocitysynthesis solutions.
| Absolute Magnitude Calibration for the W UMa-Type Systems Based on HIPPARCOS Data
Hipparcos parallax data for 40 contact binary stars of the W UMa-type(with epsilon M_V < 0.5) are used to derive a new, (B-V)-basedabsolute-magnitude calibration of the form M_V = M_V(log P,B-V). Thecalibration covers the ranges 0.26 < (B-V)_0 < 1.14, 0.24 < P< 1.15 day, and 1.4 < M_V < 6.1; it is based on a solutionweighted by relative errors in the parallaxes (2.7% to 24%). Previouscalibrations have not been based on such a wide period and color space,and while they have been able to predict M_V with sufficient accuracyfor systems closely following the well-known period-color relation, thenew calibration should be able to give also good predictions for moreexotic ``outlying'' contact binary systems. The main limitations of thiscalibration are the inadequate quality of the ground-based photometricdata, and the restriction to the (B-V) index, which is more sensitive tometallicity effects than the (V-I) index; metallicities are, however,basically unknown for the local W UMa-type systems. (SECTION: Stars)
| Photoelectric Minima of Some Eclipsing Binaries
Not Available
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