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Computed Hβ indices from ATLAS9 model atmospheres
Aims.Grids of Hβ indices based on updated (new-ODF) ATLAS9 modelatmospheres were computed for solar and scaled solar metallicities[+0.5], [+0.2], [0.0], [ -0.5] , [ -1.0] , [ -1.5] , [ -2.0] , [ -2.5]and for α enhanced compositions [+0.5a], [0.0a], [ -0.5a] , [-1.0a] , [ -1.5a] , [ -2.0a] , [ -2.5a] , and [ -4.0a] . Methods:.Indices for T_eff > 5000 K were computed with the same methods asdescribed by Lester et al. (1986, LGK86) except for a differentnormalization of the computed natural system to the standard system.LGK86 used special ODFs to compute the fluxes. For T_eff ≤ 5000 K wecomputed the fluxes using the synthetic spectrum method. In order toassess the accuracy of the computed indices comparisons were made withthe indices computed by Smalley & Dworetsky (1995, A&A, 293,446, MD95) and with the empirical relations T_eff-Hβ given byAlonso et al. (1996, A&A, 313, 873) for several metallicities.Furthermore, for cool stars, temperatures inferred from the computedindices were compared with those of the fundamental stars listed byMD95. The same kind of comparison was made between gravities for B-typestars. Results: .The temperatures from the computed indices are ingood agreement, within the error limits, with the literature values for4750 K ≤ T_eff ≤ 8000 K, while the gravities agree for T_eff> 9000 K. The computed Hβ indices for the Sun and for Procyonare very close to the observed values. The comparison between theobserved and computed Hβ indices as function of the observedHβ has shown a very small trend which almost completely disappearswhen only stars hotter than 10 000 K are considered. The trend due tothe cool stars is probably related with the low accuracy of thefundamental T_eff which are affected by large errors for most of thestars.
| Evolution of interacting binaries with a B type primary at birth
We revisited the analytical expression for the mass ratio distributionfor non-evolved binaries with a B type primary. Selection effectsgoverning the observations were taken into account in order to comparetheory with observations. Theory was optimized so as to fit best withthe observed q-distribution of SB1s and SB2s. The accuracy of thistheoretical mass ratio distribution function is severely hindered by theuncertainties on the observations. We present a library of evolutionarycomputations for binaries with a B type primary at birth. Some liberalcomputations including loss of mass and angular momentum during binaryevolution are added to an extensive grid of conservative calculations.Our computations are compared statistically to the observeddistributions of orbital periods and mass ratios of Algols. ConservativeRoche Lobe Over Flow (RLOF) reproduces the observed distribution oforbital periods but fails to explain the observed mass ratios in therange q in [0.4-1]. In order to obtain a better fit the binaries have tolose a significant amount of matter, without losing much angularmomentum.
| 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.
| Observed Orbital Eccentricities
For 391 spectroscopic and visual binaries with known orbital elementsand having B0-F0 IV or V primaries, we collected the derivedeccentricities. As has been found by others, those binaries with periodsof a few days have been circularized. However, those with periods up toabout 1000 or more days show reduced eccentricities that asymptoticallyapproach a mean value of 0.5 for the longest periods. For those binarieswith periods greater than 1000 days their distribution of eccentricitiesis flat from 0 to nearly 1, indicating that in the formation of binariesthere is no preferential eccentricity. The binaries with intermediateperiods (10-100 days) lack highly eccentric orbits.
| Close binary stars in ob-association regions i. preliminary investigation
We performed a sample of O- and B-eclipsing binary stars inOB-association regions and obtained the preliminary list of 147 binariesin 45 OB-association regions. We tried to elucidate the question whether(or not) the close binaries belong to corresponding OB-associations,from the commonness of their proper motions, radial velocities anddistances. Based on the completeness of the data,the binaries aredevided into three groups and the scheme for calculation of degree ofbelonging of stars to OB-associations is developed. Necessary data arenot available for nine systems and they are given in a specific table.For 12 cases, the binaries project onto the regions of two associations.We show that 33 (22.3%) close binary stars are members, 65 (43.9%) areprobable members and 39 (26.4%) are less probable members of theOB-associations. We find that 11 binaries belong to the Galaxybackground. The comparison of the distributions of orbital periods forthe binaries in OB-associations and for O-, B-binaries of the Galaxybackground shows their considerable differences in the vicinity of thetwo-day period.
| Tidal Effects in Binaries of Various Periods
We found in the published literature the rotational velocities for 162B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V orIV, that are in spectroscopic or visual binaries with known orbitalelements. The data show that stars in binaries with periods of less thanabout 4 days have synchronized rotational and orbital motions. Stars inbinaries with periods of more than about 500 days have the samerotational velocities as single stars. However, the primaries inbinaries with periods of between 4 and 500 days have substantiallysmaller rotational velocities than single stars, implying that they havelost one-third to two-thirds of their angular momentum, presumablybecause of tidal interactions. The angular momentum losses increase withdecreasing binary separations or periods and increase with increasingage or decreasing mass.
| HD 153720 - A SB2 system with twin metallic-line components
We report the results of abundance determinations for the components ofthe SB2 star HD 153720 from high resolution (R=60 000) echelle highsignal-to-noise spectra of the wavelength region 3595-10 260 Åtaken with the 2.7 m telescope of the McDonald Observatory We found thevalues of the atmospheric parameters of the primary to be effectivetemperature Teff = 7425 K and surface gravity log g,= 4.0cgs, and of the secondary to be Teff = 7125 K and log g,= 3.9cgs. The microturbulent velocity is vmicro= 2.7 kms-1 for both components, and the projected rotationalvelocity is v sin i ,= 15 km s-1 also for both components.The abundances of about 20 elements were determined with the method ofspectrum synthesis. The components of HD 153720 are metallic-linestars. Possible inconsistencies between old and new measurements ofradial velocities may be explained by the existence of third body inthis system. A review of recent high resolution spectral observations ofeight A4-F1 binaries shows that only one of these systems can beclassified as normal.Based on observations obtained at the 2.7-m telescope of the McDonaldObservatory.The data are only available in electronic form athttp://www.edpsciences.org
| A new light-time effect study of AR Aurigae
A period study of the young binary AR Aur based on the extensive seriesof published photoelectric/ccd minima times indicates the cyclic (O-C)variation for the system. This continuous oscillatory variation coversalmost three cycles, about 6000 orbital periods, by the presentobservational data. It can be attributed to the light-time effect due toa third body with a period of 23.68±0.17 years in the system. Theanalysis yields a light-time semi-amplitude of 0.0084±0.0002 day andan orbital eccentricity of 0.20±0.04. Adopting the total mass of ARAur, the mass of the third body assumed in the co-planar orbit with thebinary is M3=0.54±0.03 Mȯ and thesemimajor axis of its orbit is a3 = 13.0 ± 0.2 AU.
| Abundance analysis of late B stars. Evidence for diffusion and against weak stellar winds
Based on high S/N spectra obtained at La Silla, Chile, and the SpecialAstrophysical Observatory, Russia, the abundances of He, C, O, Ne, Mg,Si, Ca, Fe, Sr, and Ba in 27 optically bright B5-B9 main-sequence starswere determined. NLTE effects were taken into account. A variety ofabundance patterns is present in late B stars. Accurate surfaceabundances of the diffusion indicators O, Mg, Ca, Sr and Ba suggest thatelement stratification due to diffusion is common in the program stars.Models of stellar atmospheres which include meridional mixing canexplain the observed anomalies. Although the program stars representonly a volume-limited sample of the solar neighbourhood this result isimportant for the cosmochemical evolution of the Galaxy: the surfaceabundances of the stars investigated do not necessarily reflect thechemical composition of the interstellar cloud they originated from.Furthermore, five program stars show narrow absorption lines in Ca II Kwhich can be attributed to circumstellar gas. Neon serves as a traceelement for the occurrence of weak stellar winds. Neon overabundances ofsome stars derived under the assumption of LTE suggest that such windshave been detected. In sharp contrast, the more realistic treatment ofNLTE leads to solar neon abundances and thus reveals that weak stellarwinds are absent in the program stars.Based on observations collected at the European Southern Observatory, LaSilla, Chile and at the Special Astrophysical Observatory, NizhnijArkhyz, Russia.
| HD 191110 a SB2 system with HgMn and Hg components. Orbital elements and abundance analysis
In this paper we present the first quantitative abundance analysis ofthe SB2 system with HgMn and Hg components HD 191110. Time-resolved(R=14 000) spectroscopic observations of this system have been obtainedduring September and October 2002 at the Catania AstrophysicalObservatory. Combining these observations with spectra (R = 50 000-110000) taken from the CFHT archive, we refined the orbital period of thissystem (P=9.34661 +/- 0.00002 d) and then we recalculated thefundamental parameters characterizing its orbit. From the fit of theHbeta profiles, obtained at different orbital phases, wedetermined the effective temperatures and surface gravities of eachcomponent and the light ratio: TeffA=11 000 K, loggA=3.60, TeffB= 10 700 K, loggB=3.90, LA/LB=1.20. Regarding thechemical composition, both components have solar abundances of sulfur,titanium and iron; magnesium and silicon are slightly underabundant;platinum and yttrium are overabundant. Manganese lines have beendetected only in the spectrum of the primary. As to rare-earths, twolines of NdIII have been identified in the secondary's spectrum. Otherlines we identified in our spectra belong to PII, CrII, NiII, SrII, ZrIIand AuII. We also discuss the isotopic structure of the HgII lambda3983.9 Å line.
| Coordinates and Identifications of Harvard Variables
Coordinates and identifications are presented for 726 Harvard Variablestars and suspected variables, discovered or studied by D. Hoffleit andannounced in Harvard Bulletins 874, 884, 887, 901, and 902; plus 141others, previously known, lying in the same fields.
| Das Brunner Punktesystem.
Not Available
| Studies of Intermediate-Mass Stellar Models Using Eclipsing Binaries
Evolutionary computations for intermediate-mass stars are analyzed usingobserved parameters for eclipsing SB2 binaries and theoreticalparameters based on evolutionary tracks. Modern observations cannot beused to distinguish between models with and without convectiveovershooting for stars in the vicinity of the main sequence.Statistically significant discrepancies between the observed andcomputed stellar parameters are associated with systematic errors inphotometric effective temperatures. After taking into account systematiceffects, the theoretical computations fit the observational datauniformly well throughout the entire mass interval studied. Empiricaland semiempirical (i.e., reduced to the ZAMS and with solar elementalabundances) formulas for the mass-luminosity, mass-effectivetemperature, and mass-radius relations are proposed.
| The Variability of the Hg II λ3984 Line of the Mercury-Manganese Star α Andromedae
The variability of the Hg II λ3984 line in the primary of thebinary star α And was discovered through the examination ofhigh-dispersion spectra with signal-to-noise ratios greater than 500.This first definitively identified spectrum variation in anymercury-manganese star is not due to the orbital motion of thecompanion. Rather, the variation is produced by the combination of the2.38236 day period of rotation of the primary that we determined and anonuniform surface distribution of mercury that is concentrated in itsequatorial region. If the surface mercury distribution exhibitslong-term stability, then it is likely that a weak magnetic fieldoperates in its atmosphere, but if changes are observed in the lineprofile over a period of a few years, then these would constitute directevidence for diffusion.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| Detached double-lined eclipsing binaries as critical tests of stellar evolution. Age and metallicity determinations from the HR diagram
Detached, double-lined spectroscopic binaries that are also eclipsingprovide the most accurate determinations of stellar mass, radius,temperature and distance-independent luminosity for each of theirindividual components, and hence constitute a stringent test ofsingle-star stellar evolution theory. We compile a large sample of 60non-interacting, well-detached systems mostly with typical errorssmaller than 2% for mass and radius and smaller than 5% for effectivetemperature, and compare them with the properties predicted by stellarevolutionary tracks from a minimization method. To assess the systematicerrors introduced by a given set of tracks, we compare the resultsobtained using three widely-used independent sets of tracks, computedwith different physical ingredients (the Geneva, Padova and Granadamodels). We also test the hypothesis that the components of thesesystems are coeval and have the same metallicity, and compare thederived ages and metallicities with the ones obtained by fitting asingle isochrone to the system. Overall, there is a good agreement amongthe different determinations, and we provide a comprehensive discussionon the sub-sample of systems which either present problems or haveestimated metallicities. Although within the errors the published trackscan fit most of the systems, a large degeneracy between age andmetallicity remains. The power of the test is thus limited because themetallicities of most of the systems are unknown. The full version ofTable 6 is only available in the electronic form athttp://www.edpsciences.org
| 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.
| Age and Metallicity Estimates for Moderate-Mass Stars in Eclipsing Binaries
We estimate the ages and metallicities for the components of 43 binarysystems using a compilation of accurate observational data on eclipsingbinaries for which lines of both components are visible in theirspectra, together with two independent modern sets of stellar evolutionmodels computed for a wide range of masses and chemical abundances. Theuncertainties of the resulting values are computed, and their stabilityis demonstrated. The ages and metallicity are compared with thosederived in other studies using different methods, as well as withindependent estimates from photometric observations and observations ofclusters. These comparisons con firm the reliability of our ageestimates. The resulting metallicities depend significantly on thechoice of theoretical model. Comparison with independent estimatesfavors the estimates based on the evolutionary tracks of the Genevagroup.
| Surface Brightness--Color Relation for Eclipsing Binaries with ubvy Photometry
The relation between visual surface brightness and (b-y)_0 color indexis constructed for eclipsing binaries with Hipparcos parallaxes andphotometry in the Stromgren four-color ubvy system. The relation isconsistent with the Popper relation derived for stars with angulardiameters obtained mainly from interferometry or from the lunaroccultation method. It is shown that the Lutz-Kelker correction tomagnitudes is in this case negligible.
| 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
| On the Variability of Late B III-V Stars
We investigate the Hipparcos Satellite photometry of luminosity classIII-V B6-B9 stars. Most are relatively non-variable. Candidates forwhich further study is desirable are identified.
| Comparison of Parallaxes from Eclipsing Binaries Method with Hipparcos Parallaxes
The parallaxes determined by Lacy (1979) by means of eclipsing binariesmethod are compared with the Hipparcos parallaxes for 19 systems. Theresidual scatter of the distance moduli inferred from eclipsing binariesmethod - after allowing for known errors as given by Lacy and Hipparcos- is equal to 0.18 mag. It decreases to 0.08 mag when obviously notfitting semi-detached systems and systems with chromospheric activity ofcomponents are removed from the sample.
| Atmospheric chemical composition of the "twin" components of equal mass in the CP SB2 system 66 Eri
We determine the atmospheric chemical composition of the components ofthe CP SB2 system 66 Eri with approximately equal masses (M_A / M_B =0.97) by using two CCD echelle spectra of the star. These spectra havebeen taken with the 1-m telescope at Special Astrophysical Observatorywith a spectral resolution of 36 000 and a signal-to-noise ratio no lessthan 100 in the wavelength range 4385-6695 A. The model-atmosphereparameters for the components are estimated by analyzing all availablephotometric and spectrophotometric data and the equivalent widths ofiron lines. For components A and B, we have obtained Teff_A =11 100 K, Teff_B = 10 900 K, lg(g_A) = 4.25, lg(g_B)= 4.25,Vturb_A = 0.9 km/s, Vturb_B = 0.7 km/s, and vsin(i_{A,B}) = 17 km/s. The derived projected rotational velocities ofthe components, together with the HIPPARCOS parallax and photometricobservations, show that their rotation may be synchronized with theorbital period. The star exhibits a considerable infrared excess atwavelengths longer than 25 micrometers. The synthetic-spectrum andmodel-atmosphere methods are used to determine the atmosphericabundances of 26 chemical elements in component B and 15 chemicalelements in component A. The components differ markedly in chemicalcomposition. The peculiar component B exhibits no chemical anomaliesthat are typical of the Hg-Mn group, such as an underabundance of He andAl and an enhancement of P and Ga, but shows large heavy-elementoverabundances reaching 4-5 dex. The atmosphere of component A alsoexhibits moderate overabundances of Mn and Ba, but no lines of otherheavy elements have been found in its spectrum. However, an estimate ofthe upper limit on their abundances does no rule out small heavy-elementoverabundances in the atmosphere of component A either. 66 Eri is thefirst and the only close SB2 system with CP non-Hg-Mn components studiedto date.
| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| Metallicity-dependent effective temperature determination for eclipsing binaries from synthetic UVBY Strömgren photometry
Strömgren synthetic photometry from an empirically calibrated gridof stellar atmosphere models has been used to derive the effectivetemperature of each component of double lined spectroscopic (SB2)eclipsing binaries. For this purpose, we have selected a sub-sample of20 SB2s for which (b-y), m_1, and c_1 individual indices are available.This new determination of effective temperature has been performed in ahomogeneous way for all these stars. As the effective temperaturedetermination is related to the assumed metallicity, we exploresimultaneous solutions in the ({{T_eff}},{[Fe/H]})-plane and present ourresults as confidence regions computed to match the observed values ofsurface gravity, (b-y), m_1, and c_1, taking into account interstellarreddening. These confidence regions show that previous estimates of{{T_eff}} are often too optimistic, and that {[Fe/H]} should not beneglected in such determinations. Comparisons with Ribas et al. (1998)using Hipparcos parallaxes are also presented for 8 binaries of ourworking sample, showing good agreement with the most reliableparallaxes. This point gives a significant weight to the validity of theBaSeL models for synthetic photometry applications.
| Chemical composition of the CP Hg-Mn components of approximately equal mass in the SB2 system 46 Draconis.
Not Available
| Elemental abundance analyses with DAO spectrograms - XVIII. The double-lined spectroscopic binary 46 Draconis
We present a study of the double-lined spectroscopic binary star 46Draconis (46 Dra). The variations of the gamma-velocity indicate thepresence of a third star which revolves around the mutual centre-of-massof the close binary system with a period of 33.6 yr. Perhaps this thirdstar is responsible for the observed X-ray radiation of 46 Dra. With atemperature difference of only 600 K, both components of the closebinary are mercury-manganese stars. This system demonstrates thechemical evolution of two apparently metal-rich objects with the sameinitial composition, but with slightly different masses and resultingeffective temperatures. Significant abundance differences are found forHe, Al, S, Sc, Mn, Sr, Ga, Xe and Pt. These provide tests for thetheories which purport to explain the anomalies.
| Abundance analysis of SB2 binary stars with HgMn primaries
We present a short review of the abundances in the atmospheres of SB2systems with Mercury-Manganese (HgMn) primaries. Up to now a carefulstudy has been made for both components of 8 out of 17 known SB2binaries with orbital periods shorter than 100 days and mass ratioranging from 1.08 to 2.2. For all eight systems we observe a lower Mnabundance in the secondary's atmospheres than in the primary's.Significant difference in the abundances is also found for some peculiarelements such as Ga, Xe, Pt. All secondary stars with effectivetemperatures less than 10 000 K show abundance characteristics typicalof the metallic-line stars.
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