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 Musca - the heavenly fly.Not Available Radial velocity measurements of B stars in the Scorpius-Centaurus associationWe derive single-epoch radial velocities for a sample of 56 B-type starsmembers of the subgroups Upper Scorpius, Upper Centaurus Lupus and LowerCentaurus Crux of the nearby Sco-Cen OB association. The radial velocitymeasurements were obtained by means of high-resolution echelle spectravia analysis of individual lines. The internal accuracy obtained in themeasurements is estimated to be typically 2-3 km s-1, butdepends on the projected rotational velocity of the target. Radialvelocity measurements taken for 2-3 epochs for the targets HD 120307, HD142990 and HD 139365 are variable and confirm that they arespectroscopic binaries, as previously identified in the literature.Spectral lines from two stellar components are resolved in the observedspectra of target stars HD 133242, HD 133955 and HD 143018, identifyingthem as spectroscopic binaries. A 3-5 μ m VLT spectroscopic survey of embedded young low mass stars I. Structure of the CO iceMedium resolution (lambda /Delta lambda = 5000-10 000) VLT-ISAACM-band spectra are presented of 39 young stellar objects in nearbylow-mass star forming clouds showing the 4.67 μm stretching vibrationmode of solid CO. By taking advantage of the unprecedentedly largesample, high S/N ratio and high spectral resolution, similarities in theice profiles from source to source are identified. It is found thatexcellent fits to all the spectra can be obtained using aphenomenological decomposition of the CO stretching vibration profile at4.67 μm into 3 components, centered on 2143.7 cm-1, 2139.9cm-1 and 2136.5 cm-1 with fixed widths of 3.0, 3.5and 10.6 cm-1, respectively. All observed interstellar COprofiles can thus be uniquely described by a model depending on only 3linear fit parameters, indicating that a maximum of 3 specific molecularenvironments of solid CO exist under astrophysical conditions. A simplephysical model of the CO ice is presented, which shows that the 2139.9cm-1 component is indistinguishable from pure CO ice. It isconcluded, that in the majority of the observed lines of sight, 60-90%of the CO is in a nearly pure form. In the same model the 2143.7cm-1 component can possibly be explained by the longitudinaloptical (LO) component of the vibrational transition in pure crystallineCO ice which appears when the background source is linearly polarised.The model therefore predicts the polarisation fraction at 4.67 μm,which can be confirmed by imaging polarimetry. The 2152 cm-1feature characteristic of CO on or in an unprocessed water matrix is notdetected toward any source and stringent upper limits are given. Whenthis is taken into account, the 2136.5 cm-1 component is notconsistent with the available water-rich laboratory mixtures and wesuggest that the carrier is not yet fully understood. A shallowabsorption band centered between 2165 cm-1 and 2180cm-1 is detected towards 30 sources. For low-mass stars, thisband is correlated with the CO component at 2136.5 cm-1,suggesting the presence of a carrier different from XCN at 2175cm-1. Furthermore the absorption band from solid13CO at 2092 cm-1 is detected towards IRS 51 inthe rho Ophiuchi cloud complex and an isotopic ratio of12CO/13CO=68+/-10 is derived. It is shown that allthe observed solid 12CO profiles, along with the solid13CO profile, are consistent with grains with an irregularlyshaped CO ice mantle simulated by a Continuous Distribution ofEllipsoids (CDE), but inconsistent with the commonly used models ofspherical grains in the Rayleigh limit.Based on observations obtained at the European Southern Observatory,Paranal, Chile, within the observing programs 164.I-0605 and 69.C-0441.ISO is an ESA project with instruments funded by ESA Member States(especially the PI countries: France, Germany, The Netherlands and theUK) and with the participation of ISAS and NASA.Table \ref{SourceList} and Appendices A and B are only available inelectronic form at http://www.edpsciences.org Formation scenarios for the young stellar associations between galactic longitudes l = 280degr - 360degrWe investigate the spatial distribution, the space velocities and agedistribution of the pre-main sequence (PMS) stars belonging toOphiuchus, Lupus and Chamaeleon star-forming regions (SFRs), and of theyoung early-type star members of the Scorpius-Centaurus OB association.These young stellar associations extend over the galactic longituderange from 280degr to 360degr , and are at a distance interval ofaround 100 and 200 pc. This study is based on a compilation ofdistances, proper motions and radial velocities from the literature forthe kinematic properties, and of basic stellar data for the constructionof Hertzsprung-Russel diagrams. Although there was no well-known OBassociation in Chamaeleon, the distances and the proper motions of agroup of 21 B- and A-type stars, taken from the Hipparcos Catalogue,lead us to propose that they form a young association. We show that theyoung early-type stars of the OB associations and the PMS stars of theSFRs follow a similar spatial distribution, i.e., there is no separationbetween the low and the high-mass young stars. We find no difference inthe kinematics nor in the ages of these two populations studied.Considering not only the stars selected by kinematic criteria but thewhole sample of young early-type stars, the scattering of their propermotions is similar to that of the PMS stars and all the young starsexhibit a common direction of motion. The space velocities of theHipparcos PMS stars of each SFR are compatible with the mean values ofthe OB associations. The PMS stars in each SFR span a wide range of ages(from 1 to 20 Myr). The ages of the OB subgroups are 8-10 Myr for UpperScorpius (US), and 16-20 Myr for Upper Centaurus Lupus (UCL) and forLower Centaurus Crux (LCC). Thus, our results do not confirm that UCL isolder than the LCC association. Based on these results and theuncertainties associated with the age determination, we cannot say thatthere is indeed a difference in the age of the two populations. Weanalyze the different scenarios for the triggering of large-scalestar-formation that have been proposed up to now, and argue that mostprobably we are observing a spiral arm that passes close to the Sun. Thealignment of young stars and molecular clouds and the average velocityof the stars in the opposite direction to the Galactic rotation agreewith the expected behavior of star formation in nearby spiral arms.Tables 1 to 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/913 Kinematics of Hipparcos Visual Binaries. II. Stars with Ground-Based Orbital SolutionsThis paper continues kinematical investigations of the Hipparcos visualbinaries with known orbits. A sample, consisting of 804 binary systemswith orbital elements determined from ground-based observations, isselected. The mean relative error of their parallaxes is about 12% andthe mean relative error of proper motions is about 4%. However, even 41%of the sample stars lack radial velocity measurements. The computedGalactic velocity components and other kinematical parameters are usedto divide the stars with known radial velocities into kinematical agegroups. The majority (92%) of binaries from the sample are thin diskstars, 7.6% have thick disk kinematics and only two binaries have halokinematics. Among them, the long-period variable Mira Ceti has a verydiscordant {Hipparcos} and ground-based parallax values. From the wholesample, 60 stars are ascribed to the thick disk and halo population.There is an urgent need to increase the number of the identified halobinaries with known orbits and substantially improve the situation withradial velocity data for stars with known orbits. The mass ratio distribution of B-type visual binaries in the Sco OB2 associationA sample of 115 B-type stars in the Sco OB2 association is examined forexistence of visual companions in the J and K_s bands, using the ADONISnear-infrared adaptive optics system and coronograph. Practically allthe components in the separation range 0farcs3 -6farcs4 (45-900 AU) andmagnitudes down to K = 16 were detected. The K and J - K photometry ofthe primaries and differential photometry and astrometry of the 96secondaries are presented. Ten secondaries are new physical components,as inferred from the photometric and statistical criteria, while therest of the newly detected objects are faint background stars. After asmall correction for detection incompleteness and a conversion of thefluxes into masses, an unbiased distribution of the components massratio q was derived. The power law f(q)~ q-0.5 fits theobservations well, whereas a q-1.8 distribution, whichcorresponds to a random pairing of stars, is rejected. The companionstar fraction is 0.20+/-0.04 per decade of separation which iscomparable to the highest measured binary fraction among low-mass PMSstars and ~ 1.6 times higher than the binary fraction of low-mass dwarfsin the solar neighborhood and in open clusters in the same separationrange. Based on observations collected at the European SouthernObservatory, La Silla, Chile (ESO programme 65.H-0179). Tables 1, 3 andthe full version of Table 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/382/92 Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associationsRadial motions of stars in nearby moving clusters are determined fromaccurate proper motions and trigonometric parallaxes, without any use ofspectroscopy. Assuming that cluster members share the same velocityvector (apart from a random dispersion), we apply a maximum-likelihoodmethod on astrometric data from Hipparcos to compute radial and spacevelocities (and their dispersions) in the Ursa Major, Hyades, ComaBerenices, Pleiades, and Praesepe clusters, and for theScorpius-Centaurus, alpha Persei, and HIP 98321'' associations. Theradial motion of the Hyades cluster is determined to within 0.4 kms-1 (standard error), and that of its individual stars towithin 0.6 km s-1. For other clusters, Hipparcos data yieldastrometric radial velocities with typical accuracies of a few kms-1. A comparison of these astrometric values withspectroscopic radial velocities in the literature shows a good generalagreement and, in the case of the best-determined Hyades cluster, alsopermits searches for subtle astrophysical differences, such as evidencefor enhanced convective blueshifts of F-dwarf spectra, and decreasedgravitational redshifts in giants. Similar comparisons for the ScorpiusOB2 complex indicate some expansion of its associations, albeit slowerthan expected from their ages. As a by-product from the radial-velocitysolutions, kinematically improved parallaxes for individual stars areobtained, enabling Hertzsprung-Russell diagrams with unprecedentedaccuracy in luminosity. For the Hyades (parallax accuracy 0.3 mas), itsmain sequence resembles a thin line, possibly with wiggles in it.Although this main sequence has underpopulated regions at certaincolours (previously suggested to be Böhm-Vitense gaps''), suchare not visible for other clusters, and are probably spurious. Futurespace astrometry missions carry a great potential for absoluteradial-velocity determinations, insensitive to the complexities ofstellar spectra. Based on observations by the ESA Hipparcos satellite.Extended versions of Tables \ref{tab1} and \ref{tab2} are available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.125.8) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/446 Binary Star Observations in Selected Instants of Good SeeingVideo recordings of images of binary stars at the focus of a 0.36mtelescope have been used to select images recorded in instants of goodseeing. The selected images have been analysed to give separations andposition angles for the binary systems which are in good agreement withvalues predicted from previous observations. In these exploratoryobservations it has been shown that separations of 0.9 arcseconds can bemeasured with an accuracy of ~2% and position angles to ~1-2 degreeswhen the average seeing was ~1.3 arcseconds. These observationsdemonstrated that the diffraction limit of the telescope could bereached when the seeing was a factor of 2-3 greater than it. A binarywith three magnitudes difference in the brightness of its components hasbeen measured with comparable accuracy although difficulties areanticipated for binaries with components closer than ~2 arcseconds withthis magnitude difference. The limiting magnitude is determined by theneed to limit exposure times of individual frames to be comparable withor less than the atmospheric coherence time. The standard theory of extinction and the spectrum of stars with very little reddeningThis paper examines the relationship between spectra of stars of samespectral type with extremely low reddenings. According to the standardtheory, the relationship between the spectrum of stars with samespectral type and small, but different reddenings should be different inthe optical and in the UV. This difference is not observed: the ratio ofthe spectra of two stars in directions where the reddening is largeenough to be detected and low enough not to give a noticeable2200Å bump is an exponential of /1/λ from the near-infraredto the far-UV. This result is in conformity with the ideas introduced inpreceding papers: the exponential optical extinction extends to the UV,and the spectrum of stars with enough reddening is contaminated by lightscattered at close angular distance from the stars. An application willbe the determination of the spectrum of a non-reddened star from thespectrum of a star of same spectral type with little reddening. Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statisticsThe 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 origin of the O and B-type stars with high velocities. II. Runaway stars and pulsars ejected from the nearby young stellar groupsWe 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. Two-colour photometry for 9473 components of close Hipparcos double and multiple starsUsing observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite. A HIPPARCOS Census of the Nearby OB AssociationsA 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 unboundmoving 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. Properties of He-rich stars. II. CNO abundances and projected rotational velocitiesWe present an abundance analysis of light elements in the most massivechemically peculiar (CP) stars, He-rich stars. The analysis is based onboth low and high-resolution observations collected at ESO, La Silla,Chile in the optical region and includes 6 standard and 21 He-richstars. Light element abundances display a diverse pattern fromunder-solar up to above-solar values. Carbon is found underabundant inthe hottest He-rich stars and normal in the coolest ones, according tothe LTE model predictions. The distribution of projected rotationalvelocities shows a significant excess of slow rotators, no He-rich starshaving vsin i > 130 km s(-1) . Based on observations collected at theEuropean Southern Observatory, La Silla, Chile (programmes 7-043 and7-010 of periods 49 and 50 resp.) Light element abundances in He-rich starsWe present an abundance analysis of light elements in He-rich stars. Theanalysis is based on both low and high resolution observations collectedat ESO, La Silla, Chile in the optical region and includes 6 standardsand 21 He-rich stars. Light-element abundances display a diversepattern: they range from under-solar up to above-solar values. ROSAT PSPC Observations of 27 Near--Main-Sequence B StarsIn this paper, we report on ROSAT Position Sensitive ProportionalCounter (PSPC) observations of 27 near--main-sequence B stars made withunprecedented sensitivity. Contrary to the results of previous surveys,it is found that 75% of the sample stars are X-ray sources, albeit mostat modest levels. The X-ray luminosities of the program stars range from5.6 x 1027 up to 2.2 x 1032 ergs s-1. We find that LX/LBol decreasesabruptly beyond about B0 and stabilizes at LX/LBol ~ 10-8.5 by about B2,with seven nondetections at B2 and later. For the B0 and B1 stars, ourmodeling suggests that wind attenuation of the X-ray photons issignificant, so that the emitted X-ray luminosity, corrected for thisattenuation, actually exceeds 10-7LBol in some cases. Presumably, thissituation is even more severe for O stars; thus, the well-known LX/LBol~ 10-7 law simply may be an artifact of the neglect of wind attenuation.The ROSAT PSPC observations of most of the B stars are very soft, withthe notable exception of tau Sco (B0 V). The wind emission measurefilling factors that we find for the very early B stars are rather large(roughly 0.1--1). This could be brought into line with theoreticalcalculations of the line-force instability, wind-shock mechanism if themass-loss rates of these stars are a few times higher than theorycurrently predicts. However, the X-rays from stars later than B2 requirefilling factors greater than unity and thus cannot be produced by anyradiation-driven wind-shock mechanism because there is simply not enoughwind material to produce the observed X-rays. It is possible that mid-to late-B stars represent some kind of transition to, or hybrid of, windand coronal X-ray mechanisms. Properties of He-rich stars. I. Their evolutionary state and helium abundance.A determination of the surface gravity and an abundance analysis ofhelium in a sample of 17 He-rich and 5 normal, reference stars ispresented. These results are derived from low resolution CCD spectra,but each star was measured at least 6 times in order to obtain asignificant average spectrum for the spectroscopic variables. The heliumabundances derived from the models used are very close to 0.1 fornormal, reference stars and are larger for the others, clearlyindicating the He-rich phenomenon in them. NLTE effects, errors on themicroturbulence value or on the surface gravity do not influence theestimated helium abundances. Nevertheless, synthesized Geneva coloursare affected by the He-rich peculiarity, especially the [U-B] indexwhich systematically changes by -0.025 mag per 0.1 of He abundance forthe coolest stars in the sample. We cannot confirm the correlationbetween the evolutionary state and the helium abundance reportedpreviously (Zboril et al. 1994, International Conference on CP andMagnetic Stars.", Tatranska Lomnica, eds. J. Zverko and J. Ziznovsky, p.105), although we used a more reliable technique of log(g)determination. All He-rich objects lie within the main sequence: theirsurface gravities are all inside the range 4.1 High S/N Echelle spectroscopy in young stellar groups. II. Rotational velocities of early-type stars in SCO OB2.We investigate the rotational velocities of early-type stars in the ScoOB2 association. We measure v.sin(i) for 156 established and probablemembers of the association. The measurements are performed with threedifferent techniques, which are in increasing order of expectedv.sin(i): 1) converting the widths of spectral lines directly tov.sin(i), 2) comparing artificially broadened spectra of low v.sin(i)stars to the target spectrum, 3) comparing the HeI λ4026 lineprofile to theoretical models. The sample is extended with literaturedata for 47 established members of Sco OB2. Analysis of the v.sin(i)distributions shows that there are no significant differences betweenthe subgroups of Sco OB2. We find that members of the binary populationof Sco OB2 on the whole rotate more slowly than the single stars. Inaddition, we find that the B7-B9 single star members rotatesignificantly faster than their B0-B6 counterparts. We test varioushypotheses for the distribution of v.sin(i) in the association. Theresults show that we cannot clearly exclude any form of randomdistribution of the direction and/or magnitude of the intrinsicrotational velocity vector. We also investigate the effects of rotationon colours in the Walraven photometric system. We show that positions ofB7-B9 single dwarfs above the main sequence are a consequence ofrotation. This establishes the influence of rotation on the Walravencolours, due primarily to surface gravity effects. The Pulkovo Spectrophotometric Catalog of Bright Stars in the Range from 320 TO 1080 NMA spectrophotometric catalog is presented, combining results of numerousobservations made by Pulkovo astronomers at different observing sites.The catalog consists of three parts: the first contains the data for 602stars in the spectral range of 320--735 nm with a resolution of 5 nm,the second one contains 285 stars in the spectral range of 500--1080 nmwith a resolution of 10 nm and the third one contains 278 stars combinedfrom the preceding catalogs in the spectral range of 320--1080 nm with aresolution of 10 nm. The data are presented in absolute energy unitsW/m(2) m, with a step of 2.5 nm and with an accuracy not lower than1.5--2.0%. 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. The determination of T_eff_ of B, A and F main sequence stars from the continuum between 3200 A and 3600 A.A method of determination of the effective temperature of B, A and Fmain sequence stars is proposed, using the slope of the continuumbetween 3200A and 3600A. The effective temperature calibration is basedon a sample of stars with energy distributions known from UV to the red.We have determined the Balmer jump and the effective temperatures for235 main sequence stars. The temperatures found have been compared withthose derived by Underhill et al. (1979), Kontizas & Theodossiou(1980), Theodossiou (1985), Morossi & Malagnini (1985). Thecomparison showed good agreement for most of the stars in common. On theother hand, the temperatures derived from the reddening-free colourfactor QUV, from the colour index (m1965-V) and from (B-V), given inGulati et al. (1989), are systematically lower than our temperatures,however the differences are within one-sigma error. The distribution of interstellar dust in the solar neighborhoodWe surveyed the IRAS data base at the positions of the 1808 O6-B9.5stars in The Bright Star Catalog for extended objects with excessemission at 60 microns, indicating the presence of interstellar dust atthe location of the star. Within 400 pc the filling factor of theinterstellar medium, for dust clouds with a density greater than 0.5/cucm is 14.6 + or - 2.4%. Above a density of 1.0/cu cm, the densitydistribution function appears to follow a power law index - 1.25. Whenthe dust clouds are mapped onto the galactic plane, the sun appears tobe located in a low-density region of the interstellar medium of widthabout 60 pc extending at least 500 pc in the direction of longitudes 80deg - 260 deg, a feature we call the 'local trough'. ICCD speckle observations of binary stars. VIII - Measurements during 1989-1991 from the Cerro Tololo 4 M telescopeOne-thousand eighty-eight observations of 947 binary star systems,observed by means of speckle interferometry with the 4 m telescope onCerro Tololo, are presented. These measurements, made during the period1989-1991, comprise the second installment of results stemming from theexpansion of our speckle program to the southern hemisphere. SAO stars with infrared excess in the IRAS Point Source CatalogWe have undertaken a search for SAO stars with infrared excess in theIRAS Point Source Catalog. In contrast to previous searches, the entireIRAS (12)-(25)-(60) color-color diagram was used. This selection yieldeda sample of 462 stars, of which a significant number are stars withcircumstellar material. The stars selected can be identified aspre-main-sequence stars, Be stars, protoplanetary systems, post-AGBstars, etc. A number of objects are (visual) binary stars.Characteristic temperatures and IR excesses are calculated and theirrelations to spectral type are investigated. Walraven photometry of nearby southern OB associationsHomogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included. Catalogue of i and w/w crit values for rotating early type starsNot Available The volume filling factor of the infrared cirrus IS 0.2The filling factor of the infrared cirrus in which luminous stars areembedded is estimated. The stars are assumed to be randomly situatedwith respect to the cirrus. A direct ratio of the number of stars withassociated cirrus emission to those which in principle could be detectedindicates that the cirrus filling factor is roughly 0.2. Empirical temperature calibrations for early-type starsThree temperature calibrations of suitable photometric quantities havebeen derived for O and B stars. A sample of 120 stars with reliableT(eff.) determinations has been used for establishing each calibration.The different calibrations have been critically discussed and compared.Temperature determinations for 1009 program stars have been obtainedwith an accuracy of the order of 10 percent. Stellar integrated fluxes in the wavelength range 380 NM - 900 NM derived from Johnson 13-colour photometryPetford et al. (1988) have reported measured integrated fluxes for 216stars with a wide spread of spectral type and luminosity, and mentionedthat a cubic-spline integration over the relevant Johnson 13-colormagnitudes, converted to fluxes using Johnson's calibration, is inexcellent agreement with those measurements. In this paper a list of thefluxes derived in this way, corrected for a small dependence on B-V, isgiven for all the 1215 stars in Johnson's 1975 catalog with completeentries.
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