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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.
| Atlas and Catalog of Dark Clouds Based on Digitized Sky Survey I
We present a quantitative atlas and catalog of dark clouds derived byusing the optical database ``Digitized Sky Survey I''. Applying atraditional star-count technique to 1043 plates contained in thedatabase, we produced an AV map covering the entire region inthe galactic latitude range |b| ≤ 40°. The map was drawn at twodifferent angular resolutions of 6' and 18', and is shown in detail in aseries of figures in this paper. Based on the AV map, weidentified 2448 dark clouds and 2841 clumps located inside them. Somephysical parameters, such as the position, extent, and opticalextinction, were measured for each of the clouds and clumps. We alsosearched for counterparts among already known dark clouds in theliterature. The catalog of dark clouds presented in this paper lists thecloud parameters as well as the counterparts.
| Determining the Physical Properties of the B Stars. II. Calibration of Synthetic Photometry
We present a new calibration of optical (UBV, Strömgren uvbyβ,and Geneva) and near-IR (Johnson RIJHK and Two Micron All Sky Survey)photometry for B and early A stars derived from Kurucz ATLAS9 modelatmospheres. Our sample of stars consists of 45 normal nearby B andearly A stars that have high-quality, low-resolution IUE spectra andaccurate Hipparcos parallaxes. The calibration is unique because itrelies only on the UV spectral energy distributions, the absolute fluxcalibration of the V filter, and the Hipparcos distances to determinethe appropriate model atmospheres for the program stars. These modelsare then used to calibrate the synthetic photometry. We compare ourresults with previous well-accepted results and provide a thoroughdiscussion of the random errors and systematic effects affecting thecalibration. In particular, we demonstrate the influence of vsini onsurface gravities derived from fitting model atmospheres. Finally, wediscuss some of our intended applications of this new calibration.
| The latitude and epoch for the formation of the southern Greek constellations
Not Available
| The mass ratio distribution of B-type visual binaries in the Sco OB2 association
A 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
| 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
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| The Chemical Evolution of the Globular Cluster ω Centauri (NGC 5139)
We present abundances for 22 chemical elements in 10 red giant membersof the massive Galactic globular cluster ω Centauri. The spectraare of relatively high spectral resolution and signal-to-noise. Usingthese abundances plus published literature values, abundance trends aredefined as a function of the standard metallicity indicator iron. Thelowest metallicity stars in ω Cen have [Fe/H]~-1.8, and theinitial abundance distribution in the cluster is established at thismetallicity. The stars in the cluster span a range of [Fe/H]~-1.8 to-0.8. At the lowest metallicity, the heavy-element abundance is found tobe well characterized by a scaled solar system r-process distribution,as found in other stellar populations at this metallicity. As ironincreases, the s-process heavy-element abundances increase dramatically.Comparisons of the s-process increases with recent stellar models findsthat s-process nucleosynthesis in 1.5-3 Msolar asymptoticgiant branch stars (AGB) fits well the heavy-element abundancedistributions. In these low-mass AGB stars, the dominant neutron sourceis 13C(α,n)16O. A comparison of the Rb/Zrabundance ratios in ω Cen finds that these ratios are consistentwith the 13C source. The reason ω Cen displays such alarge s-process component is possibly due to the fact that in such arelatively low-mass stellar system, AGB ejecta, because of their lowvelocity winds, are more efficiently retained in the cluster relative tothe much faster moving Type II supernova ejecta. Significant s-processenrichment relative to Fe, from the lower mass AGB stars, would requirethat the cluster was active in star formation for quite a long intervalof time, of the order of 2-3 Gyr. The AGB ejecta were mixed with theretained fraction of Type II supernova ejecta and with the residual gasof initial composition. The analysis of α-rich elements shows thatno significant amounts of Type Ia supernova debris were retained by thecluster. In this context, interpretation of the low and constantobserved [Cu/Fe]~-0.6 (derived here for the first time in this cluster)finds a plausible interpretation.
| 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.
| ROSAT PSPC Observations of 27 Near--Main-Sequence B Stars
In 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.
| 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 NM
A 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%.
| Time-dependent Ionization of H and He in the Local Interstellar Medium
We present time-dependent ionization calculations in an attempt toexplain the recent high He ionization fractions deduced from EUVEobservations for gas in the local interstellar medium (LISM), especiallyin the Local Cloud in which the Sun is embedded. The observed high Heionization fractions and low upper limits for the local EUV ionizingradiation field for He imply nonequilibrium ionization for this element.In this paper, we explore what effects a recent supernova explosion,possibly linked to the origin of the nearby Loop I supernova remnant,might have on the observed ionization of both H and He in the LISM Weinclude contributions from the local EUV radiation field, collisionalionization, radiative and dielectronic recombination, and chargeexchange in our time-dependent code. Our results indicate that theobserved He and H ionization likely denote gas in a nonequilibrium ionicrecombination phase. These calculations clearly show that a UV flashassociated with a supernova would produce only trace H and He ionizationin the Local Cloud unless the ambient interstellar gas were within 20 pcof the explosion. More likely, time-dependent ionization at the Sunwould be due to the resulting shocks produced by this event. If shocksare responsible for the observed He ionization, between 2 and 3.4million yr have elapsed since the start of the H and He recombinationphase. We find that the local EUV radiation from discrete stellarsources and the surrounding 106 K hot plasma still can have significanteffects on the ionization of H and He, respectively, in the Local Cloud.More importantly, our time-dependent calculations can reproduce the Hand He ionization fractions observed from EUVE The He ionizationfraction seems to be a very sensitive diagnostic for time-dependentionization in the LISM. However, further observations and additionalconstraints are necessary before deducing a unique history for the LISM.
| The Distribution of Dust Clouds in the Interstellar Medium
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...457..764D&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.
| 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.
| Decoupled line driven outflow around B and Be stars.
The semi-analytic model of Bjorkman & Cassinelli for the equatorial`discs' around Be stars is re-examined and shown to be capable ofproducing higher equator-to-pole density contrasts when the effects ofthe dynamical decoupling of the stellar radiation field from theoutflowing gas are incorporated. The enhancement, as measured by thenormal component of the momentum fed into the disc, is in the region ofa factor of 2. Inclusion of the effect also lowers the threshold stellarrotation rate for the formation of a wind-compressed disc fromv_rot_/v_crit_=~0.4 to 0.25. Two physical mechanisms that may give riseto this decoupling, which are most effective in B star winds, arepresented and their relative merits compared. This comparison isperformed with reference to available UV and X-ray observations.Ion-stripping (Springmann & Pauldrach 1992) could be the cause ofthe low observed maximum outflow velocities, but it cannotsimultaneously explain the ubiquitous high-temperature (>10^6^K)X-ray emission. Shock disruption of the wind ionization balance (Castor1987) may also terminate the outward radiative acceleration in the windsof B stars. This effect suggests a simple method for setting an upperlimit to the X-ray emission from weak shock-disrupted winds whichcompares reasonably favourably with X-ray luminosities derived fromROSAT data.
| The students' observatory 1935-43 : when Aller measured radial velocities and Popper interpreted stellar spectra, with brief updates on the significance of DQ Her, SN 1937C, alpha Cygni, RY Scuti and the rotation of M 33.
Not Available
| The local distribution of NA I interstellar gas
We present high-resolution absorption measurements (lambda/Delta lambdaapproximately 75,000) of the interstellar Na I D lines at 5890 A toward80 southern hemisphere early-type stars located in the localinterstellar medium (LISM). Combining these results with other sodiummeasurements taken from the literature, we produce galactic maps of thedistribution of neutral sodium column density for a total of 293 starsgenerally lying within approximately 250 pc of the Sun. These mapsreveal the approximate shape of the mid-plane contours of the rarefiedregion of interstellar space termed the Local Bubble. Its shape is seenas highly asymmetric, with a radius ranging from 30 to 300 pc, and withan average radius of 60 pc. Similar plots of the Galactic mid-planedistribution of sources emitting extreme ultraviolet radiation show thatthey also trace out similar contours of the Local Bubble derived from NaI absorption measurements. We conclude that the Local Bubble absorptioninterface can be represented by a hydrogen column density,NuETA = 2 x 1019 cm-2, which explainsboth the local distribution of Na I absorption and the observed galacticdistribution of extreme ultraviolet sources. The derived mid-planecontours of the Bubble generally reproduce the large-scale featurescarved out in the interstellar medium by several nearby galactic shellstructures.
| Rotation of close binary system components
The rotation of close binary system components is investigated. Theprincipal physical characteristics as well as the equatorial rotationaland the axial and orbital inclinations for 46 close binary systems weredetermined. It is found that the rotation axes of the individual starsin a pair cross the orbital plane under different angles. As a rule, therotation and orbital periods of a vast majority of the systemsinvestigated here do not coincide.
| Second astrolabe catalogue of Santiago.
Positions for 350 FK5 and 164 FK5 Extension stars as determined with theDanjon astrolabe of Santiago and differences astrolabe-catalogue aregiven for Equinox J2000.0 and for the mean observation epoch of eachstar. The average mean error in alpha is +/-0.005s and +/-0.07" indelta. The mean epoch of observation of the catalogue is J1979.96.
| The Zn^+^/Na^0^ interstellar ratio
We study the behaviour of the interstellar R_n_=n(Zn^+^)/n(Na^0^) ratioin ionization equilibrium conditions. The ratio is very sensitive tovariations of the physical state of the gas and is only marginallyaffected by variations of interstellar depletion. We find logR_n_ {in}[=~-2,=~0] dex in cold molecular clouds, logR_n_ {in} about [0,+1] dexin cold atomic gas, and logR_n_ {in} about [+1,+3] dex in warm gas. Wecompare the theoretical R_n_ ratio with the column-density ratioR_N_=N(ZnII)/N(NaI) measured in a sample of 48 interstellar lines ofsight. The comparison supports the validity of the assumption ofionization equilibrium and indicates that R_N_ is a good indicator ofthe physical state of the gas. The few deviations from ionizationequilibrium that we find are all located in the general direction ofβ CMa, where studies of the local ISM revealed the presence of anextended (=~ 2x10^2^ pc) tunnel of hot gas. Finally, we report theresults of a correlation analysis logR_N_-logN(NaI) and logR_N_-logN(H).The correlations that we derive imply the presence of a mechanismlinking the physical state of interstellar clouds to their columndensity. A practical consequence of the correlation with N(NaI) is thata NaI measurement alone is sufficient to estimate the physical state ofthe gas in many situations of interest.
| High-resolution CA II observations of the local interstellar medium
High-resolution absorption measurements of the interstellar Ca II K lineobserved toward 46 early-type stars in the local ISM (LISM) arepresented. Ca II was detected in 36 of the 46 stars with 82 individualcloud components identified. Ca II was detected to most of the starscloser than 50 pc, except in the region of the Galactic quadrant l =180-270 degrees which also contains the empty line of sight to B CMa at220 pc. The mean local standard of rest velocity of the 82 Ca IIcomponents implies that the LISM clouds are associated with the motionof the solar neighborhood and not the sun. If the present data arecombined with other nearby Ca II component velocities taken from theliterature, then a cloud centered approximately at l = 90 deg, b = -40deg moving coherently with the local interstellar wind vector issupported at a significance level of 99 percent. The Ca II data havebeen combined with Na I data for the same stars to produce a N(NaI)/N(Ca II) ratio for each identified absorption feature. This ratioplotted against the local standard of rest velocities of the cloudsshows that the Routly-Spitzer effect exists down to +/- 10 km/s, whichsupports grain desorption/destruction models that are efficient atreturning calcium to the gas phase at these low velocities.
| Corrections to the right ascension to be applied to the apparent places of 1217 stars given in "The Chinese Astronomical Almanach" for the year 1984 to 1992.
Not Available
| The velocity structure of the interstellar gas towards stars in the globular cluster Omega Centauri
High-resolution spectra of Na I interstellar lines are presented for 16stars in the globular cluster Omega Cen and for a closer star (HD116226) approximately 1 deg from the cluster. Toward the cluster starsthere are four identified groups of components at the approximatevelocities V(LSR) = -3, -15, -34 and -42 km/s. There is variation in thedetailed velocity structure of the gas across the face of the cluster onan angular scale not greater than 1 arcmin, especially in the highervelocity components. From the present data and from interstellar gassurveys toward nearby stars, it appears that the bulk of the gas towardthe distant cluster stars lies beyond the large expanding Sco-Cen shelland the flow of local interstellar material discussed by Crutcher(1984). The origin of the observed absorption features remainsuncertain. However, it is suggested that the components having low LSRradial velocities are produced by gas associated with the local ridge ofmolecular clouds mapped by Dame et al.(1987), and that the highervelocity components arise in the outlying gas in the Carina spiral arm.
| A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
| The low filling factor of dust in the Galaxy
The neighborhood of 745 luminous stars in the IRAS Skyflux plates wasexamined for the presence of dust heated by the nearby star. One-hundredtwenty-three dust clouds were found around only 106 of the stars with avolume filling factor of 0.006 and an intercloud separation of 46 pc.Nowhere was a region found where the dust is smoothly distributedthrough the volume of space heated by the star; hence an upper limit of0.06/cu cm is placed on the equivalent gas density in the intercloudregions. Due to the lack of IR emission near the star, it is found thatless than 1 percent of the stellar luminosity is reprocessed within 10pc of the star. The clouds have an average density of 0.22/cu cm and aradius of 1.9 pc, albeit with wide variations in their properties. Twodifferent scale heights of 140 and 540 pc were found for the number ofclouds around different groups of stars, which are interpreted asevidence for different distributions of dust in and out of the Galacticdisk.
| Highly ionized gas in the GUM nebula and elsewhere - A comparison of IUE and Copernicus satellite results
The data from six high-dispersion IUE echelle spectra are averaged inorder to obtain an interstellar absorption line spectrum with an S/N ofabout 30 and a resolution of about 25 km/s. The interstellar lines of CIV and Si IV are very strong and broad and N V is detected. The profilesfor these species and Al III are compared to the Copernicus satelliteprofiles for O VI. The high ionization lines toward HD 64760 are muchstronger and broader than those recorded toward Zeta Pup and Gamma super2 Vel, the two exciting stars of the Gum nebula. The profiles for Al IIIand Si IV are similar and considerably narrower than the O VI profile.An origin in photoionized Gum nebula gas is suggested as the most likelyexplanation for Al III and Si IV. The C IV profile has a high positivevelocity wing extending to approximately +80 km/s, which is similar inappearance to the positive velocity portion of the O VI profile. It isinferred that a substantial part of the observed C IV has an origin inthe collisionally ionized gas most likely rsponsible for the O VI.
| Santiago Fundamental Catalogue - A catalogue of 1105 FK5 stars (equinox J2000.0)
The positions in right ascension and declination of 1105 FK5 stars,observed with a Meridian Circle during the period 1979 to 1991, aregiven. The average mean square error of a position, for the wholecatalog, is +/- 0.009 s in right ascension and +/- 0.10 arcsec indeclination. The mean epoch of the catalog is 1983.148.
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