Local interstellar medium kinematics towards the Southern Coalsack and Chamaeleon-Musca dark clouds
We present the results of a spectroscopic programme aiming toinvestigate the kinematics of the local interstellar medium componentstowards the Southern Coalsack and Chamaeleon-Musca dark clouds. Theanalysis is based upon high-resolution (R~ 60000) spectra of theinterstellar Na I D absorption lines towards 63 B-type stars (d<= 500pc) selected to cover these clouds and the connecting area defined bythe Galactic coordinates: 308°>=l>= 294° and-22°<=b<= 5°. The radial velocities, column densities,velocity dispersions, colour excess and photometric distances to thestars are used to understand the kinematics and distribution of theinterstellar cloud components. The analysis indicates that theinterstellar gas is distributed in two extended sheet-like structurespermeating the whole area, one at d<= 60 pc and another around120-150 pc from the Sun. The nearby feature is approaching the localstandard of rest with an average radial velocity of -7 kms-1, has low average column density logNNaI~ 11.2cm-2 and velocity dispersion b~ 5 km s-1. The moredistant feature has column densities between 12.3 <=logNNaI<= 13.2, average velocity dispersion b~ 2.5 kms-1 and seems associated with the dust sheet observed towardsthe Coalsack, Musca and Chamaeleon direction. Its velocity is centredaround 0 km s-1, but there is a trend for increasing from -3km s-1 near b= 1° to 3 km s-1 near b=-18°.The nearby low column density feature indicates a general outflow fromthe Sco-Cen association, in agreement with several independent lines ofdata in the general searched direction. The dust and gas feature around120-150 pc seem to be part of an extended large-scale feature of similarkinematic properties, supposedly identified with the interaction zone ofthe Local and Loop I Bubbles. Assuming that the interface and thering-like volume of dense neutral matter that would have been formedduring the collision of the two bubbles have similar properties, ourresults suggest that the interaction zone between the bubbles is twistedand folded.
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Ultraviolet Interstellar Linear Polarization. V. Analysis of the Final Data Set
Using recent measurements of ultraviolet interstellar polarization, wehave examined its relationship to ultraviolet extinction and topolarization and extinction measurements in the visible and infrared.The relationship between the relative amount of ultraviolet polarizationand the parameter lambda_max, determined using only visible data, isconfirmed and strengthened, for example, by a tight correlation betweenp(6 mum^-1)/p_max and lambda^-1_max. A good fit to the wavelengthdependence of the polarization from the infrared to the ultraviolet canbe achieved with a five-parameter function combining a power law in theinfrared and a Serkowski-like function in the ultraviolet. Thepolarization efficiency (ratio of polarization to extinction) is less inthe ultraviolet than in the visual, and the ratio of these efficienciesincreases systematically with lambda^-1_max. We relate these effects tosystematic changes in the underlying aligned grain size distribution.The polarization efficiency of the grains causing the 2175 Åextinction bump along most sight lines is so (unusually) small that nostatistically significant polarization feature is detectable in thatwavelength region. Only two of 28 sight lines show a definitepolarization feature. The environments of the two bump sight lines aresimilar but not unique, and the mechanism for producing the polarizationfeature along only these two sight lines is still not known.
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Polarimetric variability of the Herbig Be star HD 100546
High accuracy polarimetric observations made on three nights arereported for the Herbig Be star HD 100546 revealing changes both in thelinear and circular components. Continuous monitoring over windows ~ 2hrs reveal no variation or secular change in p at levels ~ 0.0002 butnight-to-night changes ~ 0.0010 are clearly recorded. The p(V)/p(B)ratio indicates an interstellar polarization component. Accounting forthis by consideration of field stars does not, however, provide anintrinsic value for this ratio that is explained by electron scatteringand it is concluded that the basic polarigenic mechanism is scatteringby dust within the circumstellar environment.
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A Search for Star Clusters from the HIPPARCOS Data
We present results of a search for nearby star clusters and associationsusing Hipparcos Catalogue data, restricting the sample to stars withparallaxes above 2 mas (d <~ 500 pc). Two new OB associations havebeen identified in the Carina-Vela and Cepheus-Cygnus-Lyra-Vulpecularegions. A very probable new open cluster has been discovered in Carina.The cluster, a Car, named after its brightest member, is young (60 Myr)and nearby (d = 132 pc). However, only seven bona fide members can bedrawn from the Hipparcos data. We report a detection of nine opencluster candidates in the distance range of 150 to 400 pc, and sixpossible associations almost all located within the Gould belt, althoughslightly older than the known nearby associations. In all cases, wepresent Yale theoretical isochrone fits to the color-magnitude diagrams,which indicate a moderate spread of ages between 60 to 200 Myr.Evidently, these young open cluster and association candidates arerelated to the overall distribution of young OB and A-type stars in thesolar neighborhood.
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Ultraviolet Interstellar Polarization of Galactic Starlight.I.Observations by the Wisconsin Ultraviolet Photo Polarimeter Experiment
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2726A&db_key=AST
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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.
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Ultraviolet interstellar linear polarization. 2: The wavelength dependence
We present new ultraviolet (UV) polarimetry of the well-studiedinterstellar line of sight toward HD 204827 obtained with the FaintObject Spectrograph on Hubble Space Telescope. HD 204827 is of greatinterest because the dust along this line of sight has extremely lowvalues of both lambdamax and RV. Its far-UVextinction is very large, reflecting its small RV value. Inaddition, we reexamine the entire sample of 14 interstellar lines ofsight for which there are now UV polarization data. We find that thepreviously suggested relationship between lambdamax and thewavelength dependence of the polarization in the UV is stronglysupported by the data for this larger sample including HD 204827. Sevenstars with lambdamax greater than or equal to 0.54 micronagree well with an extrapolation of the Serkowski relation into the UVwhile seven stars with lambdamax less than or equal to 0.53micron show polarization in excess of the Serkowski extrapolation(super-Serkowski). However, the division of the observed lines of sightinto Serkowski and super-Serkowski categories is artificial. In fact,the amount of polarization in the UV is correlated with a singleparameter, lambdamax. This may indicate that there is a meaninterstellar polarization law analogous to the mean interstellarextinction law of Cardelli, Calyton, & Mathis which is based onRV. The data are consistent with a linear relationshipbetween 1/lambdamax and rho(UV)/rhomax but moredata are needed to define the functional form. We suggest that theSerkowski and super-Serkowski designations be replaced by high and lowlambdamax which are more physically descriptive. At the sametime, we note that all seven super-Serkowski (low lambdamax)stars lie in a relatively small region of the sky between lII= 90 deg - 150 deg and b = -5 deg - 15 deg. These stars all lie in orbehind a spur of the local Orion spiral arm. Similarly, most of theSerkowski (high lambdamax stars lie in or near theScorpio-Centaurus OB Association. So lines of sight covering largerareas of the sky are needed to test the universality of thelambdamax/UV polarization relationship. The recent discoveryof warm dust near HD 197770 suggests the possibility that a mechanismother than the traditional alignment to the Galactic magnetic field maybe invoked to explain its 2175 A polarization bump.
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The size distribution of interstellar dust particles as determined from polarization: Spheroids
We have determined the size distribution of polarizing interstellar dustgrains based on electromagnetic scattering by spheroidal particles,extending our original work based on infinite cylinders. Shapes andalignment variants included the following: perfectly aligned oblateparticles with axial ratios 1.414:1, 2:1, 4:1, and 6:1, picket fenceprolate particles with axial ratios 2:1 and 4:1, and 2:1 prolateparticles with perfect spinning alignment. Our analysis is based on baresilicate grains. The size distributions found are qualitatively similarto those derived using infinite cylinders. When expressed ascontributions to the total mass, the distributions peak at mean sizeapproximately 0.2 microns and are skewed, with the relative rate ofdecrease to larger and smaller sizes depending on lambda max.Using infinite cylinders, the specific requirement of a reasonable fitin the infrared produces a substantial dip in the mass distribution atapproximately 0.4 microns, hinting at a bimodal mass distribution. Butthis dip is not present when oblate and prolate particles are used. Thisconfirms that the dip is related to the incorrect behavior of scatteringfor infinite cylinders in the long wavelength limit. Fitting HSTultraviolet polarization data beyond 6 microns -1 introducesan additional bump at the small size end (approximately 0.01 microns) ofthe distribution. This unusual feature can be traced to the sudden risein the imaginary part of the refractive index of 'astronomicalsilicate.' When a 'modified astronomical silicate' is used, the size ofthe additional bump is much reduced, if not absent. Based both on thesmoothness of the mass distribution and on the fit to the polarizationcurve, oblate shapes are preferred to prolate. Among the oblates, the6:1 oblate shape gives the most satisfactory result, simply because thewidth of the calculated polarization curve of single-sized 6:1 oblateparticles is the narrowest. Mass distributions from fitting extinctioncurves using aligned spheroids have been determined. They resembleclosely those based on spheres. Polarization to extinction ratios arelarge enough to match the maximum interstellar value for all axialratios and shapes studied, though the most spherical (1.4:1 oblate and2:1 spinning prolate) particles would have to be nearly perfectlyaligned. The birefringence and interstellar circular polarization in theultraviolet are predicted.
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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.
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Ultraviolet interstellar polarization observed with the Hubble Space Telescope
We have used the Faint Object Spectrograph of the Hubble Space Telescopeto observe interstellar linear polarization from 1300 to 3300 A in twostars with well-studied interstellar polarization at visible wavelenths.The wavelength dependence of linear polarization declines smoothly withdecreasing wavelength and is devoid of structure associated with theprominent 2175 A absorption bump in the interstellar extinction curve.The data for one star (HD 161056) are consistent with an extrapolationbased on the Serkowski formula of a fit to the ground-based polariztion;the other star (HD 7252) shows excess (super-Serkowski) polarizationrelative to the extrapolation. Out of a total of 10 stars now studied bymeans of spectropolarimetry in the satellite ultraviolet, includingeight obseved with the Wisconsin Ultraviolet Photopolarimeter, five(those of longest lambda max) show Serkowski behavior, andfour others show super-Serkowski behavior; only one (HD 197770) showsevidence for polarization associated with the 2175 A bump. These resultsplace important constraints on the nature of the bump feature.
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Empirical temperature calibrations for early-type stars
Three 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.
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The variation of interstellar extinction in the ultraviolet
One hundred and fifty-four reddened stars that are apparently normal inthe visible were selected from the S2/68 Ultraviolet Sky Survey. Theultraviolet data for 92 of these cannot be explained in terms of a fixedinterstellar extinction law. Between 1400 and 2740 A, the extinctioncurve for each star can be well represented by two parts; astraight-line scattering component and a Lorentzian 2200 A absorptionfeature. Independent variations are found in both parts and these cannotbe explained by photometric or spectral classification errors. Bothparts vary smoothly, implying that there is no fixed extinction law, andone star in three is found to depart from the mean law by more than 1mag at either 1500 or 2200 A. The two variations allow not only all 154stars to be explained but also anomalous stars reported by otherauthors. These are not special but merely situated towards the limits ofthe variations. A variation in the relative proportions of graphite andsilicate grains goes some way towards explaining the observations. Theprofile of the 2200 A feature is determined, the symmetrical shape isconfirmed, and the profile fits a Lorentzian very closely.
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A catalog of ultraviolet interstellar extinction excesses for 1415 stars
Ultraviolet interstellar extinction excesses are presented for 1415stars with spectral types B7 and earlier. The excesses with respect to Vare derived from Astronomical Netherlands Satellite (ANS) 5-channel UVphotometry at central wavelengths of approximately 1550, 1800, 2500, and3300 A. A measure of the excess extinction in the 2200-A extinction bumpis also given. The data are valuable for investigating the systematicsof peculiar interstellar extinction and for studying the character of UVinterstellar extinction in the general direction of stars for which theextinction-curve shape is unknown.
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The local system of early type stars - Spatial extent and kinematics
Published uvby and H-beta photometric data and proper motions arecompiled and analyzed to characterize the structure and kinematics ofthe bright early-type O-A0 stars in the solar vicinity, with a focus onthe Gould belt. The selection and calibration techniques are explained,and the data are presented in extensive tables and graphs and discussedin detail. The Gould belt stars of age less than 20 Myr are shown togive belt inclination 19 deg to the Galactic plane and node-lineorientation in the direction of Galactic rotation, while the symmetricaldistribution about the Galactic plane and kinematic properties (purecircular differential rotation) of the belt stars over 60 Myr oldresemble those of fainter nonbelt stars of all ages. The unresolveddiscrepancy between the expansion observed in the youngest nearby starsand the predictions of simple models of expansion from a point isattributed to the inhomogeneous distribution of interstellar matter.
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Search for Beta Cephei stars south of declination -20 deg. II - Photometric and spectrographic observations of early B giants and subgiants - Winter objects
Results of the second part of a program begun in 1975 (Jerzykiewicz andSterken, 1977) are presented. Out of 39 Beta Cephei candidates observedphotometrically, seven turned out to vary with the b ranges exceeding0.020 m, while 21 have been found constant to within 0.010 m or better.For the 56 comparison stars these numbers are 6 and 25, respectively.From spectrographic observations one of the candidates, HD 129557 = HR5488 (B2 III), iis found to be a Beta Cephei variable with a period of0.135 d and the 2 K amplitude of 18.4 km/s. A comparison of the resultsof this program with other recent photometric searches for Beta Cepheivariables shows good agreement in most cases. There are severaldiscrepant stars, however. These are discussed in some detail. Aconclusion emerges that in the low temperature extension of the BetaCephei region, if such an extension exists at all, on-and-off typepulsations occur.
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The fundamental physical parameters of main-sequence and near main-sequence B type stars as derived from uvby,beta photometry
From spectrophotometric measurements of hydrogen line intensities, uvbyphotometry and photoelectrically determined H-beta and H-gamma indicesof 75 B2-B6 main-sequence stars, effective temperature and surfacegravity are derived by using the model atmospheres computed by Kurucz(1974). Comparisons between the g values and the MK luminosityclassification show good agreement for the MK standard stars but ratherserious disagreement for the average stars in such a way that most ofthe stars classified in luminosity class V really belong to class IV.Using the evolutionary model sequences calculated by Hejlesen et al.(1972) the stellar mass, age and luminosity are determined from the uvbyand beta data through effective temperature and surface gravity. Thetheoretically derived luminosities are in excellent agreement with theluminosities derived by calibrations.
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Prediction of spectral classification from photometric observations - Application of the UVBY beta photometry and the MK spectra classification. II - General case
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&A....85...93M&db_key=AST
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Prediction of spectral classification from photometric observations-application to the UVBY beta photometry and the MK spectral classification. I - Prediction assuming a luminosity class
An algorithm based on multiple stepwise and isotonic regressions isdeveloped for the prediction of spectral classification from photometricdata. The prediction assumes a luminosity class with reference touvbybeta photometry and the MK spectral classification. The precisionattained is about 90 percent and 80 percent probability of being withinone spectral subtype respectively for luminosity groups I and V and forluminosity groups III and IV. A list of stars for which discrepanciesappear between photometry and spectral classification is given.
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Structure and age of the local association /Pleiades group/
Intermediate-band indices are used to derive luminosities for some 500early-type stars with well-determined proper motions and radialvelocities. Space motion vectors and galactic coordinates are computedfor the stars considered. It is found that the local association membersare mainly concentrated in the Sco-Cen region in the Southern Hemisphereand the Cas-Tau region in the north.
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Optical interstellar lines in southern supergiants.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975ApJ...197..117C&db_key=AST
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Wavelength dependence of interstellar polarization and ratio of total to selective extinction
A multichannel polarimeter-photometer which uses dichroic filters toseparate the (UBVR) spectral regions is described. The instrument wasused with a 24-inch rotatable tube telescope for polarimetricobservation of nearby stars. Polarization data for 364 nearby stars aretabulated, together with the wavelength dependence of linear andinterstellar polarization.
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Absolute luminosity calibration of Stroemgren's 'intermediate group'
A relation defining the luminosity index for Stroemgren's (1966)intermediate group (A0 to A3 stars) in terms of absolute magnitude iscalibrated using a method based on the principle of maximum likelihood.This relation is also calibrated for the case when the 'a' index iscorrected for reddening. For both relations, calculations are made ofthe magnitude dispersion, the mean velocity components and correspondingdispersion, and the precision of each parameter. The results are shownto be in fairly good agreement with Stroemgren's (1966) values, and arelation incorporating the corrected 'a' index is proposed formain-sequence stars. The absolute magnitudes obtained with a relation ofthe present type are compared with those derived from trigonometricparallaxes and with those obtained by Eggen (1972).
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New kinematical data for bright southern OB-stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....5..129L&db_key=AST
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Four-color and H-beta photometry for bright B-type stars in the southern hemisphere.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971AJ.....76..621C&db_key=AST
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MK Spectral Types for Bright Southern OB Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969ApJ...157..313H&db_key=AST
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Radial velocities of 200 southern B stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1965MNRAS.130..281B&db_key=AST
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A Survey of Southern Be Stars
Not Available
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