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Surface abundances of light elements for a large sample of early B-type stars - IV. The magnesium abundance in 52 stars - a test of metallicity
From high-resolution spectra a non-local thermodynamic equilibriumanalysis of the MgII 4481.2-Åfeature is implemented for 52 earlyand medium local B stars on the main sequence (MS). The influence of theneighbouring line AlIII 4479.9-Åis considered. The magnesiumabundance is determined; it is found that logɛ(Mg) = 7.67 +/-0.21 on average. It is shown that uncertainties in the microturbulentparameter Vt are the main source of errors inlogɛ(Mg). When using 36 stars with the most reliableVt values derived from OII and NII lines, we obtain the meanabundance logɛ(Mg) = 7.59 +/- 0.15. The latter value isprecisely confirmed for several hot B stars from an analysis of the MgII7877-Åweak line. The derived abundance logɛ(Mg) = 7.59 +/-0.15 is in excellent agreement with the solar magnesium abundancelogɛsolar (Mg) = 7.55 +/- 0.02, as well as with theproto-Sun abundance logɛps(Mg) = 7.62 +/- 0.02. Thus,it is confirmed that the Sun and the B-type MS stars in ourneighbourhood have the same metallicity.
| B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
| New runaway OB stars with HIPPARCOS
A Monte Carlo method for detection of runaway OB stars fromobservational data is proposed. 61 runaway OB star candidates have beendetected by an analysis of Hipparcos proper motions. The peculiartangential and total transverse velocities have been determined forthese stars. A list of the detected runaway star candidates ispresented. The evidence of a discrepancy between photometric andparallactic distances of runaway OB star candidates is presented.
| Surface abundances of light elements for a large sample of early B-type stars - III. An analysis of helium lines in spectra of 102 stars
Non-local thermodynamic equilibrium analysis of He I lines in spectraof 102 B stars is implemented in order to derive the helium abundanceHe/H, the microturbulent parameter Vt and the projectedrotation velocity v sini. A simultaneous determination of He/H andVt for the stars is effected by analysing equivalent widthsof the 4471- and 4922-Å lines primarily as indicators of He/H andthe 4713-, 5016-, 5876- and 6678-Å lines primarily as indicatorsof Vt. The rotation velocities v sini are found from profilesof the same lines. It is shown that, when Vt > 7 kms-1, the Vt(He I) values determined from He Ilines are systematically overestimated as compared with theVt(OII, NII) values derived from OII and NII lines. Thisdiscrepancy is especially appreciable for hot evolved B giants withVt(He I) = 16-23 km s-1 and may indicate a failureof classical model atmospheres to represent the strong He I lines forthese stars.Two programme stars, HR 1512 and 7651, are found to be helium-weakstars. The remaining 100 stars are divided into three groups accordingto their masses M. The microturbulent parameter Vt(He I) islow for all stars of group A (M= 4.1-6.9 Msolar) and for allstars with the relative ages t/tMS < 0.8 of group B (M=7.0-11.2 Msolar). Their Vt(He I) values are withinthe 0 to 5 km s-1 range, as a rule; the mean value isVt= 1.7 km s-1. Only evolved giants of group B,which are close to the termination of the main-sequence (MS)evolutionary phase (t/tMS > 0.8), show Vt(He I)up to 11 km s-1. The helium abundance He/H is correlated withthe relative age t/tMS in both groups; the averaged He/Henhancement during the MS phase is 26 per cent. For group C, containingthe most massive stars (M= 12.4-18.8 Msolar), theVt(He I) values display a correlation with t/tMS,varying from 4 to 23 km s-1. The He/H determination for hotevolved B giants of the group with Vt(He I) > 15 kms-1 depends on a choice between the Vt(He I) andVt(OII, NII) scales. The mean He/H enrichment by 67 per centduring the MS phase is found, if the abundances He/H are based on theVt(OII, NII) scale; however, two evolved giants withespecially high v sini, HR 7446 and 7993, show the He/H enhancement byabout a factor of 2.5. When using the same Vt scale, we founda trend of He/H with projected rotational velocities v sini a largedispersion for v sini > 150 km s-1 can result fromdifferences in masses M.A comparison with the stellar model computations with rotationallyinduced mixing shows that the observed helium enrichment during the MSphase can be explained by rotation with initial velocities 250-400 kms-1. The He/H distribution on M and v sini based on theVt(OII, NII) scale seems to be in better agreement with thetheory than one based on the Vt(He I) scale. The mean valueHe/H = 0.10 derived for stars in the zero age main sequence (ZAMS)vicinity can be adopted as the typical initial helium abundance forearly B stars in the solar neighbourhood.
| Interstellar Silicon Abundance
We present 34 measurements of silicon gas phase column densities in theinterstellar medium. We have used spectra containing the SiII 1808 Angline which were obtained with the Goddard High Resolution Spectrograph(GHRS) aboard the Hubble Space Telescope (HST). Extinction curveparameters are determined for analyzed lines of sight and relationbetween Si/H ratio and extinction parameters is discussed. We find theabundance of gas phase silicon in diffuse clouds to be lower than thesolar value by a factor of four.
| Radial velocities of early-type stars in the Perseus OB2 association
We present radial velocities for 29 B- and A-type stars in the field ofthe nearby association Perseus OB2. The velocities are derived fromspectra obtained with AURELIE, via cross correlation with radialvelocity standards matched as closely as possible in spectral type. Theresulting accuracy is ~ 2-3 km s-1. We use thesemeasurements, together with published values for a few other early-typestars, to study membership of the association. The mean radial velocity(and measured velocity dispersion) of Per OB2 is 23.5 +/- 3.9 kms-1, and lies ~ 15 km s-1 away from the meanvelocity of the local disk field stars. We identify a number ofinterlopers in the list of possible late-B- and A-type members which wasbased on Hipparcos parallaxes and proper motions, and discuss thecolour-magnitude diagram of the association.Based on observations made at the Observatoire de Haute-Provence (CNRS),France.
| Surface abundances of light elements for a large sample of early B-type stars - II. Basic parameters of 107 stars
Effective temperatures Teff, surface gravities logg andinterstellar extinctions AV are found for 107 B stars.Distances d of the stars, which are based on the derivedTeff, logg and AV values, show good agreement withthose obtained from the Hipparcos parallaxes. Comparing theTeff and logg values with evolutionary computations, we infermasses, radii, luminosities, ages and relative ages of the stars.Empirical relations between the Teff and logg parameters, onthe one hand, and the photometric indices Q, [c1] and β,on the other hand, are constructed; these relations give a fast methodfor the Teff and logg estimation of early and medium B stars.Inclusion of the infrared J, H and K colours into the Teff,logg and AV determination shows that (i) the Teffand logg parameters are altered only slightly; (ii) the AVvalue is rather sensitive to these colours, so an accuracy better than0.05mag in the JHK data is necessary for precise AVevaluation.
| 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.
| On the origin of the O and B-type stars with high velocities. II. Runaway stars and pulsars ejected from the nearby young stellar groups
We use milli-arcsecond accuracy astrometry (proper motions andparallaxes) from Hipparcos and from radio observations to retrace theorbits of 56 runaway stars and nine compact objects with distances lessthan 700 pc, to identify the parent stellar group. It is possible todeduce the specific formation scenario with near certainty for twocases. (i) We find that the runaway star zeta Ophiuchi and the pulsarPSR J1932+1059 originated about 1 Myr ago in a supernova explosion in abinary in the Upper Scorpius subgroup of the Sco OB2 association. Thepulsar received a kick velocity of ~ 350 km s-1 in thisevent, which dissociated the binary, and gave zeta Oph its large spacevelocity. (ii) Blaauw & Morgan and Gies & Bolton alreadypostulated a common origin for the runaway-pair AE Aur and mu Col,possibly involving the massive highly-eccentric binary iota Ori, basedon their equal and opposite velocities. We demonstrate that these threeobjects indeed occupied a very small volume ~ 2.5 Myr ago, and show thatthey were ejected from the nascent Trapezium cluster. We identify theparent group for two more pulsars: both likely originate in the ~ 50 Myrold association Per OB3, which contains the open cluster alpha Persei.At least 21 of the 56 runaway stars in our sample can be linked to thenearby associations and young open clusters. These include the classicalrunaways 53 Arietis (Ori OB1), xi Persei (Per OB2), and lambda Cephei(Cep OB3), and fifteen new identifications, amongst which a pair ofstars running away in opposite directions from the region containing thelambda Ori cluster. Other currently nearby runaways and pulsarsoriginated beyond 700 pc, where our knowledge of the parent groups isvery incomplete.
| Surface abundances of light elements for a large sample of early B-type stars - I. Spectral observations of 123 stars; measurements of hydrogen and helium lines; infrared photometry
High-resolution spectral observations of 123 B0-B5 stars in the mainsequence evolutionary phase were obtained at two observatories, namelythe McDonald Observatory (McDO) and the Crimean AstrophysicalObservatory (CrAO). Accurate equivalent widths W of two Balmer lines,Hβ and Hγ, and ten Hei lines were obtained for all the stars,as well as of the Heiiλ4686 line for the hottest ones. A carefulanalysis of the measured equivalent widths was performed. It is shownthat there is a very good agreement between the W values derived fromthe McDO and CrAO spectra for 14 common stars. A comparison withpublished data leads to the conclusion that the W values measuredearlier by some authors for strong Hei lines are very likely to beunderestimated. Infrared photometric observations in the J, H, and Kbands were performed for 70 programme stars. All these data will be usedin other papers: in particular for the Teff and loggdetermination and for the He, C, N and O abundance analyses.
| Interstellar Carbon Abundance
We present 10 new measurements of carbon gas phase column density in theinterstellar medium. We have used spectra made with the Goddard HighResolution Spectrograph aboard the Hubble Space Telescope containing theCII 1334.5 Ang and CII* 1335.7 Ang lines. The continuum reconstructionmethod has been used to obtain the carbon column density from theLorentzian damped lines. Extinction curve parameters are determined inselected directions and relation between C/H ratio and extinctionparameters is discussed. A correlation has been found between C/H andthe strength of the 2175 Ang bump. Unlike previous results, we noticethat C/H changes with fractional abundance of molecular hydrogen,f(H_2). The average value of C/H=3.55*10^{-4} for lines of sight withf(H_2)<1*10^{-3} is the same as solar photospheric abundance fromGrevese and Noels (1993) and may represent the real cosmic carbonabundance.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Continuous declination system set up by observations of photoelectric astrolabe Mark I In Irkutsk. The first results of international cooperation between CSAO and VS NIIFTRI
The Photoelectric Astrolabe Mark I (PHA I) has been revised with a newcombined prism which could work as an almucantar with zenith distance of45(deg) , to measure continuous declinations at the latitude of Irkutsk,Russia (phi = 52fdg2 ). The PHA I has been working at the astronomicalbase of VS NIIFTRI in Irkutsk since Nov. 1995 based on an internationalcooperation agreement of near 4 years for star catalogue and EOPmeasurements. The first observing program was ended in June 1997, givingcorrections in both right ascension and declination to 200 stars with noblind zone in declination determination, which most astrolabe cataloguesin the world usually would have. Appendix is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html.
| Long-term visual spectrophotometric behaviour of Be stars
The long-term spectrophotometric variations of 49 Be stars are studiedusing the U and V magnitudes of the UBV system, the total Balmerdiscontinuity D and the visible gradient Phi _rb. BCD spectrophotometricand photometric data in five different photometric systems, obtained inmost cases since 1950 and reduced to the BCD system, were used. The(U,D), (V,D), (Phi _rb,D) and (Phi _rb,V) correlations obtained differfrom star to star and they can be single or double-valued. They differclearly for Be phases or Be-shell phases. Be stars with small Vsin ishowing the ``spectrophotometric shell behaviour'': D > D_*, werefound. This finding implies either that strongly flattened models ofcircumstellar envelopes are in doubt for these stars, or that not all Bestars are rapid rotators. Comparison of observed variations with thosepredicted for model Be stars with spherical circumstellar envelopes ofvariable densities and dimensions implies that spectrophotometricpatterns of Be phases are due to circumstellar envelopes in low opacityregimes, while those of spectrophotometric shell phases are due tocircumstellar envelopes in high opacity regimes. In a given star, theenvelope regions responsible for the observed variations of D and Phi_rbin spectrophotometric shell phases seem to be smaller and denser thanthose producing the observed variations of these parameters inspectrophotometric Be phases. The high positive RV found in strong shellphases might favor the formation of compact circumstellar layers nearthe star. Figure 6 is only available in electronic form at CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| On Space Velocities of Binary Stars in Which One Component Has Experienced a Supernova Explosion
When one component of an evolved binary loses a significant fraction ofits initial mass in a symmetric supernova explosion but remains bound toits companion, the remnant binary recoils with a velocity that can becomparable to the orbital velocity of the supernova precursor. Thisvelocity is enough to explain the observed peculiar space velocitiesand/or distances from the Galactic plane of most X-ray binaries andbinary OB runaway stars. Some exceptions certainly occur, butuncertainties in estimates of velocities and distances, as well asmechanisms other than a popular asymmetric kick, may be responsible formost of the exceptions.
| Mesures de vitesses radiales. VIII. Accompagnement AU sol DU programme d'observation DU satellite HIPPARCOS
We publish 1879 radial velocities of stars distributed in 105 fields of4^{\circ} \times 4^{\circ}. We continue the PPO series \cite[(Fehrenbachet al. 1987;]{Feh87} \cite[Duflot et al. 1990, 1992 and 1995),]{Du90}using the Fehrenbach objective prism method. Table 1 only available inelectronic form at CDS via to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| ROSAT Survey Observations of the Monogem Ring
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...463..224P&db_key=AST
| A Search for Pulsar Companions to OB Runaway Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...461..357S&db_key=AST
| DO OB Runaway Stars Have Pulsar Companions?
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1220P&db_key=AST
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Dust emission as a quantitative probe of star-forming regions.
This article discusses thermal emission from interstellar dust as aquantitative probe of gas in star-forming regions, with particularemphasis on the interpretation of observations made at millimeter andsubmillimeter wavelengths. Expressions relating dust opacity to thecolumn density of hydrogen are derived. Examination of the uncertaintiesassociated with the observations and with intepretation shows thatbeam-averaged hydrogen column densities in these regions can bedetermined within factors of 5-20. The largest source of uncertaintylies in the conversion of derived dust opacities into gas columndensities. Within the wavelength range 100<λ<3000μm, wesuggest the relationshipN(H)/τ_dust_=~1.1x10^20lambda^2.0^cm^-2^ for dense dustclouds until the nature of the dust grains within these clouds becomesbetter known.
| The Geminga enigma - How many are there in the gamma-ray sky?
The distance to the high-energy gamma-ray source Geminga is discussed interms of recent optical, UV, EUV and X-ray observations, and itspotential birthplaces are reviewed. The distance limits derived placeconstraints on the pulsar beaming factor, f(gamma), and its efficiencyof turning rotational kinetic energy into gamma-rays, eta. Using similarconstraints on four other rotation-powered neutron stars derived fromCOS-B and EGRET data and the fact that 553 other known radio pulsarswere not detected in the COS-B survey, I define a region of thef(gamma)-eta plane which is consistent with the observations, and whichprovides a method for determining the number of additional pulsars wecan expect to find in the EGRET survey. A consideration of theunidentified COS-B point sources agrees with previous work suggestingthat they too are rotation-powered neutron stars. Independent of theiridentity, however, their numbers provide additional constraints on eta,f(gamma), and the gamma-ray pulsar population of the Galaxy.
| An IUE survey of interstellar H I LY alpha absorption. 1: Column densities
We measure Galactic interstellar neutral hydrogen column densities byanalyzing archival interstellar Ly alpha absorption line data toward 554B2 and hotter stars observed at high resolution with the IUE satellite.This study more than doubles the number of lines of sight with measuresof N(H I) based on Ly alpha. We have included the scattered lightbackground correction algorithm of Bianchi and Bohlin in our datareduction. We use the correlation between the Balmer discontinuity(c1) index and the stellar Ly alpha absorption in order toassess the effects of stellar Ly alpha contamination. Approximately 40%of the B stars with measured (c1) index, exhibit seriousstellar Ly alpha contamination. One table contains the derived values ofthe interstellar N(H I) for 393 stars with at most small amounts ofstellar contamination. Another lists the observed values of total N(H I)for 161 stars with suspected stellar Ly alpha contamination and/oruncertain stellar parameters.
| Improved Mean Positions and Proper Motions for the 995 FK4 Sup Stars not Included in the FK5 Extension
Not Available
| Far-ultraviolet stellar photometry - A field in Monoceros
FUV photometry of stars in a field in Monoceros in the wavelength rangefrom 1230 to 1600 A has been carried out using data from anelectrographic Schmidt camera carried on a sounding rocket. Ultravioletmagnitudes were extracted for 602 objects in the field. Fifty-eightpercent were tentatively identified with visible stars using the SIMBADdata base while another 25 percent are blends of objects too closetogether to separate with our resolution. Eleven of the UV objectscoincide with parts of the star clusters NGC 2169, NGC 2244, and NGC2264 in which individual stars cannot be resolved. As in previousstudies, the majority of the identified ultraviolet sources areidentified with early-stars. However, there are a significant number forwhich no such identification was possible, and we suggest that many ofthese are nearby white dwarfs.
| The measurement of precise radial velocities of early type stars
Methods are discussed which have made it possible to measure radialvelocities to within 1-3 km/s for O, B, and A spectral-type stars of allv sin i. The methods are based on the premise that neither the spectraltype nor the rotation velocity of a star need be well known prior to thevelocity measurement. This makes them particularly suitable for surveystudies or programs dealing with very heterogeneous samples of earlystars. Observations of early type members of the Pleiades and AlphaPersei open clusters at 3787 A shown that the radial-velocity zero pointused here for the early type stars is consistent with that for late-typestars to about 1 km/s for all spectral types and projected rotationvelocities.
| Absolute magnitudes of B emission line stars - Correlation between the luminosity excess and the effective temperature
A new determination of the visual absolute magnitude of Be stars iscarried out. For this, a new calibration of visual absolute magnitudesof B stars of luminosity classes, V, IV, and III is first obtained froma sample of 215 stars. The absolute luminosity excess in the visual isdetermined for a sample of 49 Be stars. It is found that this excess iscorrelated with the effective temperature of the underlying stars. Awell defined correlation between this excess and the emission in thefirst two Balmer lines is established. From these results, using asimple model of circumstellar envelope, it is inferred that the zones ofthe circumstellar envelope contributing to the emission in the continuumand in the lines have to be rather small. It is also deduced that theemission measure of the envelope is correlated with the temperature ofthe central star and that the irregular photometric variations of Bestars are an envelope-opacity phenomenon.
| Intrinsic Energy Distributions in Spectra of Early Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990MNRAS.246..408P&db_key=AST
| Third preliminary catalogue of stars observed with the photoelectric astrolabe of the Beijing Astronomical Observatory.
Not Available
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