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Публикации по объекту
Direct Measurement of the Ratio of Carbon Monoxide to Molecular Hydrogen in the Diffuse Interstellar Medium
We have used archival far-ultraviolet spectra from observations made byHST STIS and FUSE to determine the column densities and rotationalexcitation temperatures for carbon monoxide and molecular hydrogen,respectively, along 23 sight lines to Galactic O and B stars. Thereddening values range from E(B-V)=0.07 to 0.62, sampling the diffuse totranslucent interstellar medium (ISM). We find that the H2column densities range from 5×1018 to8×1020 cm-2 and the CO from upper limitsaround 2×1012 cm-2 to detections as high as1.4×1016 cm-2. CO increases with increasingH2, roughly following a power law of factor ~2. TheCO/H2 column density ratio is thus not constant, ranging from10-7 to 10-5, with a mean value of3×10-6. The sample segregates into ``diffuse'' and``translucent'' regimes, the former with molecular fraction <~0.25and AV/d<1 mag kpc-1. The mean CO/H2for these two regimes are 3.6×10-7 and9.3×10-6, respectively, significantly lower than thecanonical dark cloud value of 10-4. Six sight lines show theisotopic variant 13CO, and the isotopic ratio we observe(~50-70) is consistent with, if perhaps a little below, the average12C/13C for the ISM at large. The averageH2 rotational excitation temperature is 74+/-24 K, agreeingwell with previous studies, and the average CO temperature is 4.1 K,with some sight lines showing temperatures as high as 6.4 K. The higherexcitation CO is observed with higher column densities, consistent withthe effects of photon trapping in clouds with densities in the 20-100cm-3 range. We discuss the implications for the structure ofthe diffuse/translucent regimes of the ISM and the estimation ofmolecular mass in galaxies.
| On the Hipparcos parallaxes of O stars
We compare the absolute visual magnitude of the majority of bright Ostars in the sky as predicted from their spectral type with the absolutemagnitude calculated from their apparent magnitude and the Hipparcosparallax. We find that many stars appear to be much fainter thanexpected, up to five magnitudes. We find no evidence for a correlationbetween magnitude differences and the stellar rotational velocity assuggested for OB stars by Lamers et al. (1997, A&A, 325, L25), whosesmall sample of stars is partly included in ours. Instead, by means of asimulation we show how these differences arise naturally from the largedistances at which O stars are located, and the level of precision ofthe parallax measurements achieved by Hipparcos. Straightforwardlyderiving a distance from the Hipparcos parallax yields reliable resultsfor one or two O stars only. We discuss several types of bias reportedin the literature in connection with parallax samples (Lutz-Kelker,Malmquist) and investigate how they affect the O star sample. Inaddition, we test three absolute magnitude calibrations from theliterature (Schmidt-Kaler et al. 1982, Landolt-Börnstein; Howarth& Prinja 1989, ApJS, 69, 527; Vacca et al. 1996, ApJ, 460, 914) andfind that they are consistent with the Hipparcos measurements. AlthoughO stars conform nicely to the simulation, we notice that some B stars inthe sample of \citeauthor{La97} have a magnitude difference larger thanexpected.
| A Galactic O Star Catalog
We have produced a catalog of 378 Galactic O stars with accuratespectral classifications that is complete for V<8 but includes manyfainter stars. The catalog provides cross-identifications with othersources; coordinates (obtained in most cases from Tycho-2 data);astrometric distances for 24 of the nearest stars; optical (Tycho-2,Johnson, and Strömgren) and NIR photometry; group membership,runaway character, and multiplicity information; and a Web-based versionwith links to on-line services.
| The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| Lyman Continuum Extinction by Dust in H II Regions of Galaxies
We examine Lyman continuum extinction (LCE) in H II regions by comparinginfrared fluxes of 49 H II regions in the Galaxy, M31, M33, and theLarge Megellanic Cloud with estimated production rates of Lymancontinuum photons. A typical fraction of Lyman continuum photons thatcontribute to hydrogen ionization in the H II regions of three spiralgalaxies is <~50%. The fraction may become smaller as the metallicity(or dust-to-gas ratio) increases. We examine the LCE effect on estimatedstar formation rates of galaxies. The correction factor for the Galacticdust-to-gas ratio is 2-5.
| The origin of the runaway high-mass X-ray binary HD 153919/4U1700-37
Based on its Hipparcos proper motion, we propose that the high-massX-ray binary HD 153919/4U1700-37 originates in the OB association ScoOB1. At a distance of 1.9 kpc the space velocity of 4U1700-37 withrespect to Sco OB1 is 75 km s-1. This runaway velocityindicates that the progenitor of the compact X-ray source lost about 7Msun during the (assumed symmetric) supernova explosion. Thesystem's kinematical age is about 2 +/- 0.5 million years which marksthe date of the supernova explosion forming the compact object. Thepresent age of Sco OB1 is la 8 Myr; its suggested core, NGC 6231, seemsto be somewhat younger ( ~ 5 Myr). If HD 153919/4U1700-37 was born as amember of Sco OB1, this implies that the initially most massive star inthe system terminated its evolution within la 6 million years,corresponding to an initial mass ga 30 Msun. With theseparameters the evolution of the binary system can be constrained. Basedon data obtained with ESA's astrometric satellite Hipparcos.
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 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/Abstract.html
| Five-colour photometry of OB-stars in the Southern Hemisphere
Observations of OB-stars, made in 1959 and 1960 at the Leiden SouthernStation near Hartebeespoortdam, South Africa, with the VBLUW photometerattached to the 90 cm light-collector, are given in this paper. They arecompared with photometry obtained by \cite[Graham (1968),]{gra68}\cite[Walraven & Walraven (1977),]{wal77} \cite[Lub & Pel(1977)]{lub77} and \cite[Van Genderen et al. (1984).]{gen84} Formulaefor the transformation of the present observations to those of\cite[Walraven & Walraven (1977)]{wal77} and \cite[Lub & Pel(1977)]{lub77} are given. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| Bright prospects: Comparing the H-alpha survey with large-scale radio continuum emission
Prospects for comparisons between the AAO/UKST H-alpha survey andlarge-scale radio continuum emission are considered, with particularreference to the recently completed Parkes 2.4-GHz survey of thesouthern Galactic Plane. Both these surveys have a high sensitivity tothermal emission, and comparisons between the Parkes work and previousH-alpha surveys show many objects in common. Possibilities for newdetections include: a number of new supernova remnants; the faintextensions and envelopes surrounding `classical' HII complexes, andother faint regions of thermal emission; several active HII complexes,including an outflow of ionized gas from IC 4628 and a number ofbi-polar `plumes' of low-density, thermal material apparently associatedwith HII complexes on the Carina spiral arm.
| 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.
| ICCD speckle observations of binary stars. XIX - an astrometric/spectroscopic survey of O stars
We present the results of a speckle interferometric survey made with theCHARA speckle camera and 4 m class telescopes of Galactic O-type starswith V less than 8. We can detect with the speckle camera binaries inthe angular separation range 0.035-1.5 arcsec with delta M less than 3,and we have discovered 15 binaries among 227 O-type systems. We combinedour results on visual binaries with measurements of wider pairs from theWashington Double Star Catalog and fainter pairs from the HipparcosCatalog, and we made a literature survey of the spectroscopic binariesamong the sample. We then investigated the overall binary frequency ofthe sample and the orbital characteristics of the known binaries.Binaries are common among O stars in clusters and associations but lessso among field and especially runaway stars. There are many triplesystems among the speckle binaries, and we discuss their possible rolein the ejection of stars from clusters. The period distribution of thebinaries is bimodal in log P, but we suggest that binaries with periodsof years and decades may eventually be found to fill the gap. The massratio distribution of the visual binaries increases toward lower massratios, but low mass ratio companions are rare among close,spectroscopic binaries. We present distributions of the eccentricity andlongitude of periastron for spectroscopic binaries with ellipticalorbits, and we find strong evidence of a bias in the longitude ofperiastron distribution.
| Cross-correlation characteristics of OB stars from IUE spectroscopy
We present a catalogue of homogeneous measures of the linewidthparameter, v_esin i, for 373 O-type stars and early B supergiants(including the separate components of 25 binary and three triplesystems), produced by cross-correlating high-resolution,short-wavelength IUE spectra against a `template' spectrum of tauSco. Wealso tabulate terminal velocities. There are no O supergiants in oursample with v_esin i<65 km s^-1, and only one supergiant earlier thanB5 has v_esin i<50 km s^-1, confirming that an important linebroadening mechanism in addition to rotation must be present in theseobjects. A calibration of the area under the cross-correlation peakagainst spectral type is used to obtain estimates of continuum intensityratios of the components in 28 spectroscopically binary or multiplesystems. At least seven SB2 systems show evidence for the `Struve-Sahadeeffect', a systematic variation in relative line strength as a functionof orbital phase. The stellar wind profiles of the most rapid rotator inour sample, the O9III:n* star HD 191423 (v_esin i=436km s^-1), show itto have a `wind-compressed disc' similar to that of HD 93521; this starand other rapid rotators are good candidates for studies of non-radialpulsation.
| Projected Rotational Velocities of O-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...463..737P&db_key=AST
| Absorption Line Profile Variations among the O Stars. I. The Incidence of Variability
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..103..475F&db_key=AST
| Two-dimensional Ultraviolet Spectral Typing of O-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...460..906P&db_key=AST
| 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.
| A spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| 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.
| Synthetic UV Lines of Si IV, C IV, and He II from a Population of Massive Stars in Starburst Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...418..749R&db_key=AST
| A study of SCO 0B1 and NGC 6231. II - A new analysis
A new analysis of the Sco 0B1 association, and the two open clusters NGC6231 and Tr 24 was undertaken, making use of the extensive amount ofpublished data for this region of the southern sky. The averageinterstellar reddening, due mostly to foreground particulate matter, isE(b - y) = 0.326 mag or E(B - V) = 0.44 mag, with a pronouncednorth-to-south variation across the association. The distance moduli ofthe three aggregates are indistinguishable from one another; their meandistance from the sun is 2.0 kpc. A logarithmic age of 6.9 +/- 0.2 yearswas derived for the systems. Photometric criteria were used to assigndifferent degrees of membership to the B-type stars. Potential variablestar candidates were noted. Contrary to previous suggestions, NGC 6231retains its role as the nucleus of Sco 0B1 and, finally, the physicalreality of Tr 24 itself is questioned and briefly discussed.
| Photospheric Absorption Lines in the Ultraviolet Spectra of O-Stars and B-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990MNRAS.246..392P&db_key=AST
| Terminal velocities for a large sample of O stars, B supergiants, and Wolf-Rayet stars
It is argued that easily measured, reliable estimates of terminalvelocities for early-type stars are provided by the central velocityasymptotically approached by narrow absorption features and by theviolet limit of zero residual intensity in saturated P Cygni profiles.These estimators are used to determine terminal velocities, v(infinity),for 181 O stars, 70 early B supergiants, and 35 Wolf-Rayet stars. For OBstars, the values are typically 15-20 percent smaller than the extremeviolet edge velocities, v(edge), while for WR stars v(infinity) = 0.76v(edge) on average. New mass-loss rates for WR stars which are thermalradio emitters are given, taking into account the new terminalvelocities and recent revisions to estimates of distances and to themean nuclear mass per electron. The relationships between v(infinity),the surface escape velocities, and effective temperatures are examined.
| The upper main sequence of OB associations. II - The single-lined O stars: Spectral classification of northern stars and lines of C and N
The properties of the stars close to the upper main sequence of OBassociations are studied in order to provide constraints on the theoryof evolution of massive stars. The spectral classification of northernsingle-lined O stars, most of them belonging to the associations CygOB1, Per OB1 and Cas OB6, is presented. The classification is performedaccording to Conti's classification scheme for O stars, amended byMathys (1988). The behavior of the C and N lines of the stars isstudied, in order to determine whether CNO-processed material is visibleat their surface. Three new ON stars have been discovered: BD + 36 deg4063 (O9.71), HD 13268 (O8V), and HD 110360 (O7V).
| The spectral energy distribution of early-type stars. II - The extinction law towards O-type stars
Photometric measurements through different pass-bands are used todetermine the color-excess E(B-V) for O-type stars in the UV and IRspectral regions. The results are used to examine the extinctioncharacter of the stars. It is found that, in the UV, each O-type starhas its own extinction character. In general, the visual and NIRextinction in the direction of O-type stars are normal.
| The List of the Pairs of Stars with Different Light Absorptions in the Circumstellar Environments
Not Available
| The stellar winds of 203 Galactic O stars - A quantitative ultraviolet survey
Measurements of the resonance lines of C IV, N V, and Si IV in a sampleof 203 O stars observed using IUE in a high-resolution mode arepresented. The data are discussed using a consistent set of radius,luminosity, and mass estimates. The ratio of the maximum observedvelocity and the terminal (farfield) velocity is found to average at 3.0for 131 stars with strong or saturated lines, and at 2.6 for all stars.An expression is given which is the best available predictor of O starmass loss rates, giving an accuracy better than a factor of twoirrespective of luminosity class. The ionization fractions C(3+)/C andN(4+)/N are found to be independent of stellar effective temperature,but increase by a factor of about two from main sequence stars tosupergiants. Two new possible ON stars are identified, and enhancedsurface nitrogen abundance is confimed in ON stars. Discrete narrowabsorption features are found to be virtually universal characteristicof O star P Cygni profiles.
| Mass loss from stars : the universal formula for mass loss rate
Not Available
| The upper main sequence of OB associations. I - Spectral types and lines of C and N of southern single-lined O stars
The single-line O stars belonging to the southern associations Vel OB1,Car OB1, Cen OB1, and Sco OB1 are studied. Their spectral type isderived in Conti's classification scheme for O stars, amended to includethe O9.7 subtype and to deal with fairly high S/N CCD spectra. Thebehavior of the C and N lines of these stars is studied in order todetermine whether CNO-processed material is visible at their surface.
| Young stellar-gas complexes in the Galaxy
It is found that about 90 percent of OB-associations and o-b2 clusterssituated within 3 kpc of the sun can be united into complexes withdiameters of 150-700 pc. Almost all of these clusters contain giantmolecular clouds with a mass greater than about 100,000 solar masses. Anumber of complexes are associated with giant H I clouds; a few of thesmall complexes are situated in the HI caverns. The concentration ofOB-associations and young clusters in star complexes attests to theircommon origin in the supergiant gaseous clouds.
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