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The Massive Runaway Stars HD 14633 and HD 15137
We present results from a radial velocity study of two runaway O-typestars, HD 14633 (ON8.5 V) and HD 15137 [O9.5 III(n)]. We find that HD14633 is a single-lined spectroscopic binary with an orbital period of15.4083 days. The second target, HD 15137, is a radial velocity variableand a possible single-lined spectroscopic binary with a period close to1 month. Both binaries have large eccentricity, small semiamplitude, anda small mass function. We show the trajectories of the stars in the skybased on an integration of motion in the Galactic potential, and wesuggest that both stars were ejected from the vicinity of the opencluster NGC 654 in the Perseus spiral arm. The binary orbital parametersand runaway velocities are consistent with the idea that both thesestars were ejected by supernova explosions in binaries and that theyhost neutron star companions. We find that the time of flight sinceejection is longer than the predicted evolutionary timescales for thestars. This discrepancy may indicate that the stars have a lower massthan normally associated with their spectral classifications, that theywere rejuvenated by mass transfer prior to the supernova, or that theirlives have been extended through rapid rotation.Based in part on observations made at the Observatoire de Haute Provence(CNRS), France.
| The origin of massive O-type field stars: II. Field O stars as runaways
In two papers we try to confirm that all Galactic high-mass stars areformed in a cluster environment, by excluding that O-type stars found inthe Galactic field actually formed there. In de Wit et al. (2004) wepresented deep K-band imaging of 5 arcmin fields centred on 43 massiveO-type field stars that revealed that the large majority of theseobjects are single objects. In this contribution we explore thepossibility that the field O stars are dynamically ejected from youngclusters, by investigating their peculiar space velocity distribution,their distance from the Galactic plane, and their spatial vicinity toknown young stellar clusters. We (re-)identify 22 field O-type stars ascandidate runaway OB-stars. The statistics show that 4 ± 2% ofall O-type stars with V<8m can be considered as formedoutside a cluster environment. Most are spectroscopically singleobjects, some are visual binaries. The derived percentage for O-typestars that form isolated in the field based on our statistical analysesis in agreement with what is expected from calculations adopting auniversal cluster richness distribution with power index of β= 1.7,assuming that the cluster richness distribution is continuous down tothe smallest clusters containing one single star.
| 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.
| New Runaway O-stars Based on Data from HIPPARCOS
12 new runaway O-stars are identified using an analysis of their propermotions based on data from HIPPARCOS. The peculiar tangential and totaltransverse velocities of these stars are determined. A list of theobserved runaway stars is given.
| 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.
| The origin of massive O-type field stars. I. A search for clusters
We present a study aimed at clarifying the birthplace for 43 massiveO-type field stars. In this first paper we present the observationalpart: a search for stellar clusters near the target stars. We derivestellar density maps at two different resolving scales, viz. 0.25pc and 1.0 pc from NTT and TNG imaging and the 2MASS catalogue.These scales are typical for cluster sizes. The main result is that thelarge majority of the O-type field population are isolated stars: only12% (5 out of 43) of the O-type field stars is found to harbour asmall-scale stellar cluster. We review the literature and aim atcharacterizing the stellar field of each O-type field star with theemphasis on star formation and the presence of known young stellarclusters. An analysis of the result of this paper and a discussion ofthe O-type field population as products of a dynamical ejection event ispresented in an accompanying paper.Based on observations collected at the European Southern Observatory,Chile, and at the Italian Telescopio Nazionale Galileo (TNG) operated onthe island of La Palma by the Centro Galileo Galilei of the CNAA(Consorzio Nazionale per l'Astronomia e l'Astrofisica) at the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias.Table 2 and Figs. 4 to 17 are available in electronic form athttp://www.edpsciences.org
| A study of RV in Galactic O stars from the 2MASS catalogue
We present new measurements of the interstellar reddening parameterRV=AV/E(B-V) towards 185 O stars, using J, H,Ks photometry from the 2MASS project. The results arecombined with data from the literature of 95 stars where RVhas been derived with the same technique, 22 of which in common with ourpresent sample from the 2MASS project catalogue. The averageRV from these 258 O stars is of 3.19 +/- 0.50. All objectswhose RV departs from this value by more than 2 sigma havebeen recognized. Ten objects have RV higher than this valueand two lower. It is found that anomalous RV can scarcely beassociated with anomalies in the general interstellar medium, e.g. withdifferent behaviour in different spiral arms. They are clearly linked tolocal cloud effect. In the Cygnus region RV values follow thebehaviour of the general interstellar medium, while in the Carina arm,in spite of the relatively larger distance, local cloud effects prevail.An explanation for this is suggested. The relatively few stars of oursample whose Hipparcos parallaxes are reliable, are found to havedistances systematically smaller than the distances derived by thespectroscopic parallaxes. We argue that this effect is consistent withthe recently claimed discovery of grey extinction towards OB stars.This publication makes use of data products from the Two Micron All SkySurvey (2MASS), which is a joint project of the University ofMassachusetts and the Infrared Processing and Analysis Center/CaliforniaInstitute of Technology, funded by the National Aeronautics and SpaceAdministration and the National Science Foundation.Tables 1 and 2 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/410/905
| The Distribution of Thermal Pressures in the Interstellar Medium from a Survey of C I Fine-Structure Excitation
We used the Space Telescope Imaging Spectrograph (STIS) with itssmallest entrance aperture (0.03" wide slit) and highest resolutionechelle gratings (E140H and E230H) to record the interstellar absorptionfeatures for 10 different multiplets of neutral carbon at a resolvingpower of λ/Δλ=200,000 in the UV spectra of 21early-type stars. Our objective was to measure the amount of C I in eachof its three fine-structure levels of the ground electronic state, sothat we could determine the thermal pressures in the absorbing gas andhow much they vary in different regions. Our observations areprincipally along directions out to several kiloparsecs in the Galacticplane near longitudes l=120deg and 300°, with the moredistant stars penetrating nearby portions of the Perseus andSagittarius-Carina arms of the Galaxy. We devised a special analysistechnique to decipher the overlapping absorption features in thedifferent multiplets, each with different arrangements of the closelyspaced transitions. In order to derive internally consistent results forall multiplets, we found that we had to modify the relative transitionf-values in a way that made generally weak transitions stronger thanamounts indicated in the current literature. We compared our measuredrelative populations of the excited fine-structure levels to thoseexpected from equilibria calculated with collisional rate constants forvarious densities, temperatures, and compositions. The median thermalpressure for our entire sample was p/k=2240 cm-3 K, orslightly higher if the representative temperatures of the material aremuch above or below a most favorable temperature of 40 K for theexcitation of the first excited level at a given pressure. For gas thatis moving outside the range of radial velocities permitted bydifferential Galactic rotation between us and the targets, about 15% ofthe C I indicates a thermal pressure p/k>5000 cm-3 K. Forgas within the allowed velocities, this fraction is only 1.5%. Thiscontrast reveals a relationship between pressure enhancements and thekinematics of the gas. Regardless of velocity, we usually can registerthe presence of a very small proportion of the gas that seems to be atp/k>~105 cm-3 K. We interpret these ubiquitouswisps of high-pressure material to arise either from small-scale densityenhancements created by converging flows in a turbulent medium or fromwarm turbulent boundary layers on the surfaces of dense clouds movingthrough an intercloud medium. For turbulent compression, our C Iexcitations indicate that the barytropic indexγeff>~0.90 must apply if the unperturbed gas startsout with representative densities and temperatures n=10 cm-3and T=100 K. This value for γeff is larger than thatexpected for interstellar material that remains in thermal equilibriumafter it is compressed from the same initial n and T. However, ifregions of enhanced pressure reach a size smaller than ~0.01 pc, thedynamical time starts to become shorter than the cooling time, andγeff should start to approach the adiabatic valuecp/cv=5/3. Some of the excited C I may arise fromthe target stars' H II regions or by the effects of optical pumping fromthe submillimeter line radiation emitted by them. We argue that thesecontributions are small, and our comparisons of the velocities ofstrongly excited C I to those of excited Si II seem to support thisoutlook. For six stars in the survey, absorption features frominterstellar excited O I could be detected at velocities slightlyshifted from the persistent features of telluric origin. These O I* andO I** features were especially strong in the spectra of HD 93843 and HD210839, the same stars that show exceptionally large C I excitations. Inappendices of this paper, we present evidence that (1) the wavelengthresolving power of STIS in the E14OH mode is indeed about 200,000, and(2) the telluric O I* and O I** features exhibit some evidence formacroscopic motions, since their broadenings are in excess of thatexpected for thermal Doppler broadening at an exospheric temperatureT=1000 K. Based on observations with the NASA/ESA Hubble Space Telescopeobtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS 5-26555.
| Determination of R_V towards galactic O stars
We present new measurements of the interstellar reddening parameterRV=AV/E(B-V) towards 35 O stars. The results arecombined with measurements from the literature for 60 stars to study thebehaviour of RV with heliocentric distance. RV isthe single basic parameter which characterizes the interstellarextinction from the near-infrared to the far-UV spectral region. Theabsolute extinction AV, from which RV is derived,is best determined by optical and near-infrared photometry (Cardelli etal. \cite{r3}). We consider important the derivation of RVwith the same technique in the direction of as many as possible galacticO stars.
| 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.
| 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.
| 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
| The Diffuse Ionized Interstellar Medium: Structures Resulting from Ionization by O Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...417..579M&db_key=AST
| Photoelectric photometry of OB stars in the Vilnius system
Not Available
| Variability and theoretical upper limit of the mass loss rate in OB-stars
Solutions of the stellar wind equations for 70 O-type and 19 B-typeindividual stars are presented. The calculated mass loss rates M,terminal velocities v(infinity) and line profiles are compared with theobserved ones. It is shown that a theoretical upper limit of the massloss rate exists. Wind variability in connection with this critical massloss rate is discussed.
| Mass loss of early-type stars - A comparison of theory with observational data
A comparison of theoretical calculations of stellar wind dynamics withobservational data for 62 stars is carried out. A conclusion about thenonstationary regulation mechanisms of the mass loss rate is made on thebasis of obtained solutions.
| The stellar temperature scale for stars of spectral types from O8 to F6 and the standard deviation of the MK spectral classification
Empirical effective temperature of 211 early-type stars found in aprevious investigation (Kontizas and Theodossiou, 1980; Theodossiou,1985) are combined with the effective temperatures of 313 early-typestars from the literature. From these effective temperatures of a totalnumber of 524 early-type stars of spectral types from O8 to F6 a newstellar temperature scale is developed along with the standard deviationof the MK spectral classification.
| 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 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.
| Galactic interstellar abundance surveys with IUE. II - The equivalent widths and column densities
This paper continues a survey of interstellar densities, abundances, andcloud structure in the Galaxy, using the International UltravioletExplorer (IUE) satellite. Equivalent widths of 18 ultraviolet resonancetransitions are presented and column densities for Si II, Mn II, Fe II,S II, and Zn II toward 261 early-type stars are derived. Theseequivalent widths and column densities agree within the stated errors ofearlier Copernicus, BUSS, or IUE surveys of Mn II, Fe II, S II, and ZnII for 45 stars in common. The column densities are derived fromsingle-component curves of growth with a common b-value based on that ofFe II and Si II.
| IUE-IRAS studies of the infrared cirrus
The 60 and 100 micron cirrus emission around 256 lines of sight in theIRAS all-sky survey was measured, and the flux averages were used tostudy the distribution, variations, and correlations of the IRASinfrared cirrus fluxes with various interstellar parameters. It wasfound that the 60 and 100 micron fluxes correlate with the depletion ofSi and show a trend with the depletion of Fe for 51 lines of sighttoward the Galactic halo. No correlation was found with the abundancesof Si, Mn, Fe, S, or Zn or with abundance ratios for the full sample of256 stars. An abundance ratio of about 3 x 10 to the 7th by numberrelative to H was derived from 60 and 100 micron flux ratios and the Hcolumn along the line of sight; this ratio appears to decrease by afactor of 10 into the halo.
| Galactic interstellar abundance surveys with IUE. III - Silicon, manganese, iron, sulfur, and zinc
This paper continues a survey of intestellar densities, abundances, andcloud structure in the Galaxy using the IUE satellite. A statisticaldata set of 223 O3-B2.5 stars is constructed, including 53 stars in theGalactic halo. It is found that S II lines in B stars, of luminosityclasses IV and V, have possible contamination from stellar S II,particular for stars with v sin i less than 200 km/s. The meanlogarithmic depletions are -1.00, -1.19. -0.63, and -0.23 (Si, Mn,Fe,S,Zn). Depletions of Si, Mn, and Fe correlate with the mean hydrogendensity n-bar along the line of sight, with a turnover for n-bar greaterthan 1/cm. Sulfur depletions correlate with n-bar along the line ofsight. The slight Zn depletion correlation also appears to bestatistically insignificant. No correlation of depletion is found withthe physical density derived from H2 rotational states in 21 lines ofsight. Depletion variations in the disk are consistent with a Galacticabundance gradient or with enhanced mean depletions in the anticenterregion.
| The kinematical and binary properties of association and field O stars
A catalog of 195 Galactic O-type stars brighter than V = 8.0 mag hasbeen compiled to compare the velocity distribution and binary frequencyamong cluster and association, field, and runaway stars. Both the fieldstars and runaway stars have a larger dispersion in peculiar radialvelocity, a more positive mean peculiar radial velocity, and a widerz-distribution than stars found in clusters and associations, which isconsistent with the ejection of field and runaway stars from theirbirthplaces in associations. Visual binaries are common among stars inclusters and associations, but their incidence is a factor of 2 loweramong field stars, and they are absent in the runaway stars. Similarly,there is a deficiency of spectroscopic binaries among field stars, andespecially the runaway stars, relative to the numbers found in clustersand associations. Many of these properties can be understood in terms ofejection through close gravitational interactions with binary starsduring an early high number density epoch in the evolution of clusters.
| The improvement of the star positions of the Potsdam PZT catalog
Regular determinations of the right ascension and declination of starswith the aid of a photographic zenith tube (PZT) were begun in ageodetic-astronomical observatory of the German Democratic Republic in1972. Results obtained during the years 1972 and 1973 were used for afirst improvement of stellar positions listed in the Third Catalog(Katalog) of the 'Astronomische Gesellschaft' (Astronomical Society)AGK3. The corrections resulted in a distinct improvement of the accuracyof the positional values. However, the possibility could not be excludedthat the results were still affected by remaining errors with systematiccharacteristics. In order to eliminate the considered deficiencies, newstellar coordinate corrections were computed on the basis of aconsiderably larger data set. The new catalog containing the reviseddata has been called PZT 80, while the data obtained on the basis of thefirst observations are listed in PZT 74. The new catalog is presented inthe appendix.
| Kinematic properties of supergiants in the Perseus spiral arm
Analysis of the space motions of supergiants in the Perseus arm regionindicates that the stellar peculiar-velocity field has a large-scalenonuniformity probably resulting both from the presence of sizablegroups of young stars and from systematic motions in the arm aspredicted by density-wave theory. Proper motions are tabulated for 78stars.
| Four-color and H-beta photometry for O-A0 type stars in three regions near the galactic equator
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982A&AS...49..561W&db_key=AST
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| Görünürdeki Parlaklýk: | 7.884 |
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