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New Times of Minima of Some Eclipsing Binary Stars
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| On the Period Variation of the W UMa-type Contact Binary V502 Ophiuchi
The variation in the orbital period of the W UMa type contact binaryV502 Oph is analyzed. The orbital period exhibits a wavelike variationwith a periodicity of 23.0 years and an amplitude of ΔP =1.24×10-6 days superimposed on secular decrease ofdP/dt = 1.68×10-7 day per year. The long-term decreasemay be accompanied by the contraction of the secondary at a rate of 83 mper year and a mass transfer rate from the primary to the secondary of4.28×10-8Modot per year. The short-termoscillation may be explained by the presence of a third component.Orbital elements of the third body and its possible mass are presented.
| 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.
| 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.
| W Ursae Majoris Contact Binary Variables as X-Ray Sources
We present cross-identification of archived ROSAT X-ray point sourceswith W UMa variable stars found in the All-Sky Automated Survey. A totalof 34 W UMa stars have been found associated with X-ray emission. Wecompute the distances of these W UMa systems and hence their X-rayluminosities. Our data support the ``supersaturation'' phenomenon seenin these fast rotators, namely that the faster a W UMa star rotates, theweaker its X-ray luminosity.
| 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.
| 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.
| 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.
| New Times of Minima of Eclipsing Binary Stars
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| 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.
| On the Period Variation of the Neglected W UMa-type Binary System V714 Monocerotis
Some new CCD times of the light minimum for a neglected W UMa-typebinary star, V714 Monocerotis, observed in 2002 and 2003, are presented.By considering the general trend of the O ‑ C variation, aplausible O ‑ C curve was formed and a mean linear ephemeris wasobtained. It was found that the period of the binary star shows acontinuous decrease with rate of dP/dt = ‑1.48 ×10-7 d yr-1. In order to understand theevolutionary state of the binary system, new photometric andspectroscopic observations and a careful investigation on those data arerequired.
| Minima of Eclipsing Binaries in the ASAS-2 Database
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| Radial Velocity Studies of Close Binary Stars. IX.
Radial velocity measurements and sine-curve fits to the orbital velocityvariations are presented for the eighth set of 10 close binary systems:AB And, V402 Aur, V445 Cep, V2082 Cyg, BX Dra, V918 Her, V502 Oph, V1363Ori, KP Peg, and V335 Peg. Half of the systems (V445 Cep, V2082 Cyg,V918 Her, V1363 Ori, and V335 Peg) were discovered photometrically bythe Hipparcos mission, and all systems are double-lined (SB2) contactbinaries. The broadening function method permitted improvement of theorbital elements for AB And and V502 Oph. The other systems have beenobserved for radial velocity variations for the first time; in thisgroup are five bright (V<7.5) binaries: V445 Cep, V2082 Cyg, V918Her, KP Peg, and V335 Peg. Several of the studied systems are primecandidates for combined light and radial velocity synthesis solutions.Based on the data obtained at the David Dunlap Observatory, Universityof Toronto.
| 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.
| 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.
| 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 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.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| A CCD Photometric Study of the Contact Binary V396 Monocerotis
Complete BV light curves of the W Ursae Majoris binary V396 Mon arepresented. The present CCD photometric observations reveal that thelight curves of the system are obviously asymmetric, with the primarymaximum brighter than the secondary maximum (the ``O'Connell effect'').The light curves are analyzed by means of the latest version of theWilson-Devinney code. The results show that V396 Mon is a W-subtype WUMa contact binary with a mass ratio of 0.402. The asymmetry of thelight curves is explained by a cool spot on the secondary component. Thenature of the overluminosity of the secondary of a W UMa-type system isanalyzed. It is shown that the overluminosity of the secondary isclearly related to the mass of the primary and that, for a W UMa system,the higher the mass of the primary, the greater the overluminosity ofthe secondary. In addition, the overluminosity of the secondary is alsorelated to its own density: the lower the density of the secondary, thegreater its overluminosity.
| 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.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| An IUE Atlas of Pre-Main-Sequence Stars. II. Far-Ultraviolet Accretion Diagnostics in T Tauri Stars
We use our ultraviolet (UV) atlas of pre-main-sequence stars constructedfrom all useful, short-wavelength, low-resolution spectra in theInternational Ultraviolet Explorer (IUE) satellite Final Archive toanalyze the short-wavelength UV properties of 49 T Tauri stars (TTSs).We compare the line and continuum fluxes in these TTSs with each otherand with previously published parameters of these systems, includingrotation rate, infrared excess, and mass accretion rate. Theshort-wavelength continuum in the classical TTSs (CTTSs) appears tooriginate in a ~10,000 K optically thick plasma, while in the naked TTSs(NTTSs-stars without dusty disks) the continuum appears to originate inthe stellar atmosphere. We show that all of the TTSs in our sample liein the regime of ``saturated'' magnetic activity due to their smallRossby numbers. However, while some of the TTSs show emission linesurface fluxes consistent with this saturation level, many CTTSs showsignificantly stronger emission than predicted by saturation. In thesestars, the emission line luminosity in the high ionization lines presentin the spectrum between 1200 and 2000 Å correlates well with themass accretion rate. Therefore, we conclude that the bulk of theshort-wavelength emission seen in CTTSs results from accretion relatedprocesses and not from dynamo-driven magnetic activity. Using CTTSs withknown mass accretion rates, we calibrate the relationship between M andLC IV to derive the mass accretion rate for some CTTSs whichfor various reasons have never had their mass accretion rates measured.Finally, several of the CTTSs show strong emission from molecularhydrogen. While emission from H2 cannot form in gas at atemperature of ~105 K, the strength of the molecular hydrogenemission is nevertheless well correlated with all the other emissionsdisplayed in the IUE short-wavelength bandpass. This suggests that theH2 emission is in fact fluorescent emission pumped by theemission (likely Lyα) from hotter gas.
| The All Sky Automated Survey. Catalog of about 3800 Variable Stars
Results of the first two years of observations using the All SkyAutomated Survey prototype camera are presented. More than 140000 starsin 50 Selected Fields covering 300 square degrees were monitored eachclear night in the I-band resulting in the ASAS Photometric I-bandCatalog containing over 5*10^7 individual measurements. Nightlymonitoring of over 100 standard stars confirms that most of our dataremains within sigma_I=0.03 mag of the standard I system. Search for thestars varying on the time scales longer than a day revealed about 3800variable stars (mostly irregular, pulsating and binaries) brighter than13 mag. Only 630 of them are known or suspected variables included inthe GCVS (Kholopov 1985). Among the stars brighter than I approx 7.5(which are saturated on our frames) we have found about 50 variables (12are in the GCVS, 6 others in the Hipparcos catalog). Because of thelarge volume of data we present here only selected tables and lightcurves, but the complete ASAS Catalog of Variable Stars (currentlydivided into Periodic and Miscellaneous sections) and all photometricdata are available on the Internethttp://www.astrouw.edu.pl/~gp/asas/asas.html orhttp://archive.princeton.edu/~asas/
| Detection of Tertiary Components in W Ursa Majoris Systems
Extensive spectroscopic observations with good phase coverage of a smallsample of W UMa systems were made at the David Dunlap Observatory. Thedata were found to be very sensitive to the presence of tertiarycompanions. All of the systems studied were found, or were previouslyknown, to contain companion stars or binaries, including two systems notpreviously proven to have companions: SW Lac and V502 Oph. We suggestthat the existence of tertiary components in W UMa systems is morewidespread than previously known.
| An observational approach for the determination of gravity darkening in contact binaries of W UMa type
A new method for the determination of the gravity darkening exponents inclose binaries of W UMa type is presented. The method is based onKopal's method of Fourier analysis of the light changes of eclipsingvariables in the Frequency Domain. In the analysis, the exponents forboth components of a W UMa system are assumed to be the same. First, themethod was successfully applied to two theoretical (test) light curves,belonging to two systems with radiative and convective envelopes,respectively. Then the method was applied to 36 W UMa systems for whichgeometric and photometric elements have been derived by the mostpowerful techniques. Systems showing large light curve anomalies wereexcluded from the analysis, since the effectiveness of the methoddepends strongly on the quality of the observations. Our results confirmthe previous results with the assumed, same geometrical parameters.Thederived values of the gravity darkening exponents are very close to thepredicted ones by the existing theory of radiative transfer orconvective equilibrium.
| 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)
| Interaction of Eclipsing Binaries with their Environment
The interaction of eclipsing binary star systems with the mass around(in the form of star, planet, envelope or disk) affects the orbitalperiod of these systems. Thus, the long-term orbital period changes ofeclipsing binaries which can be deduced by using the observed times ofeclipse minima provide a good tool in understanding the interaction ofeclipsing binaries with their environment. In the present contributionmany examples of the orbital period changes of different eclipsingbinaries are presented and interpreted in terms of the interaction withtheir environment.
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