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Atomic and Molecular Carbon as a Tracer of Translucent Clouds
Using archival, high-resolution far-ultraviolet Hubble SpaceTelescope/Space Telescope Imaging Spectrograph spectra of 34 Galactic Oand B stars, we measure C I column densities and compare them withmeasurements from the literature of CO and H2 with regard tounderstanding the presence of translucent clouds along the line ofsight. We find that the CO/H2 and CO/C I ratios provide gooddiscriminators for the presence of translucent material, and bothincrease as a function of molecular fraction, fN =2N(H2)/N(H). We suggest that sightlines with values belowCO/H2 ?10-6 and CO/C I ?1 containmostly diffuse molecular clouds, while those with values above sampleclouds in the transition region between diffuse and dark. Thesediscriminating values are also consistent with the change in slope ofthe CO versus H2 correlation near the column density at whichCO shielding becomes important, as evidenced by the change inphotochemistry regime studied by Sheffer et al. Based on the lack ofcorrelation of the presence of translucent material with traditionalmeasures of extinction, we recommend defining "translucent clouds" basedon the molecular content rather than line-of-sight extinctionproperties.
| FUSE Measurements of Far-Ultraviolet Extinction. III. The Dependence on R(V) and Discrete Feature Limits from 75 Galactic Sightlines
We present a sample of 75 extinction curves derived from Far UltravioletSpectroscopic Explorer (FUSE) far-ultraviolet spectra supplemented byexisting International Ultraviolet Explorer (IUE) spectra. Theextinction curves were created using the standard pair method based on anew set of dereddened FUSE+IUE comparison stars. Molecular hydrogenabsorption features were removed using individualized H2models for each sightline. The general shape of the FUSE extinction (8.4μm-1 < λ-1 < 11μm-1) was found to be broadly consistent withextrapolations from the IUE extinction (3.3 μm-1< λ-1 < 8.6 μm-1)curve. Significant differences were seen in the strength of the far-UVrise and the width of the 2175 Å bump. All the FUSE+IUE extinctioncurves had positive far-UV slopes giving no indication that the far-UVrise was turning over at the shortest wavelengths. The dependence ofA(λ)/A(V) versus R(V)-1 in the far-UV using thesightlines in our sample was found to be stronger than tentativelyindicated by previous work. We present an updated R(V)-dependentrelationship for the full UV wavelength range (3.3μm-1 <= λ-1 <= 11μm-1). Finally, we searched for discrete absorptionfeatures in the far-ultraviolet. We found a 3σ upper limit of~0.12A(V) on features with a resolution of 250 (~4 Å width) and3σ upper limits of ~0.15A(V) for λ-1 <9.6 μm-1 and ~0.68A(V) forλ-1>9.6 μm-1 on featureswith a resolution of 104 (~0.1 Å width).
| A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
A study of gas-phase element abundances reported in the literature for17 different elements sampled over 243 sight lines in the local part ofour Galaxy reveals that the depletions into solid form (dust grains) areextremely well characterized by trends that employ only three kinds ofparameters. One is an index that describes the overall level ofdepletion applicable to the gas in any particular sight line, and theother two represent linear coefficients that describe how to derive eachelement's depletion from this sight-line parameter. The information fromthis study reveals the relative proportions of different elements thatare incorporated into dust at different stages of grain growth. Anextremely simple scheme is proposed for deriving the dust contents andmetallicities of absorption-line systems that are seen in the spectra ofdistant quasars or the optical afterglows of gamma-ray bursts. Contraryto presently accepted thinking, the elements sulfur and krypton appearto show measurable changes in their depletions as the general levels ofdepletions of other elements increase, although more data are needed toascertain whether or not these findings are truly compelling. Nitrogenappears to show no such increase. The incorporation of oxygen into solidform in the densest gas regions far exceeds the amounts that can takethe form of silicates or metallic oxides; this conclusion is based ondifferential measurements of depletion and thus is unaffected byuncertainties in the solar abundance reference scale.Based in large part on published observations from (1) the NASA/ESAHubble Space Telescope obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555, (2) theFar Ultraviolet Spectroscopic Explorer (FUSE) mission operated by JohnsHopkins University, supported by NASA contract NAS5-32985, and (3) TheCopernicus satellite, supported by NASA grant NAGW-77 to PrincetonUniversity.
| A FUSE Survey of the Rotation Rates of Very Massive Stars in the Small and Large Magellanic Clouds
We present projected rotational velocity values for 97 Galactic, 55 SMC,and 106 LMC O-B type stars from archival FUSE observations. The evolvedand unevolved samples from each environment are compared through theKolmogorov-Smirnov test to determine if the distribution of equatorialrotational velocities is metallicity dependent for these massiveobjects. Stellar interior models predict that massive stars with SMCmetallicity will have significantly reduced angular momentum loss on themain sequence compared to their Galactic counterparts. Our results findsome support for this prediction but also show that even at Galacticmetallicity, evolved and unevolved massive stars have fairly similarfractions of stars with large Vsin i values. Macroturbulent broadeningthat is present in the spectral features of Galactic evolved massivestars is lower in the LMC and SMC samples. This suggests the processesthat lead to macroturbulence are dependent upon metallicity.
| A New FUSE Survey of Interstellar HD
We have used archival FUSE data to complete a survey of interstellar HDin 41 lines of sight with a wide range of extinctions. This follow-up toan earlier survey was made to further assess the utility of HD as acosmological probe; to analyze the HD formation process; and to see whattrends with other interstellar properties were present in the data. Weemployed the curve-of-growth method, supported by line profile fitting,to derive accurate column densities of HD. We find that theN(HD)/2N(H2) ratio is substantially lower than the atomic D/Hratio and conclude that the molecular ratio has no bearing on cosmology,because local processes are responsible for the formation of HD. Basedon correlations with E(B-V), H2, CO, and iron depletion, wefind that HD is formed in the densest portion of the clouds; the slopeof the logN(HD)/logN(H2) correlation is greater than 1.0,caused by the destruction rate of HD declining more slowly than that ofH2; and, as a sidelight, that the depletions are densitydependent.
| An Analysis of the Shapes of Interstellar Extinction Curves. V. The IR-through-UV Curve Morphology
We study the IR-through-UV interstellar extinction curves towards 328Galactic B and late-O stars. We use a new technique which employsstellar atmosphere models in lieu of unreddened "standard" stars. Thistechnique is capable of virtually eliminating spectral mismatch errorsin the curves. It also allows a quantitative assessment of the errorsand enables a rigorous testing of the significance of relationshipsbetween various curve parameters, regardless of whether theiruncertainties are correlated. Analysis of the curves gives the followingresults: (1) In accord with our previous findings, the central positionof the 2175 A extinction bump is mildly variable, its width is highlyvariable, and the two variations are unrelated. (2) Strong correlationsare found among some extinction properties within the UV region, andwithin the IR region. (3) With the exception of a few curves withextreme (i.e., large) values of R(V), the UV and IR portions of Galacticextinction curves are not correlated with each other. (4) The largesightline-to-sightline variation seen in our sample implies that anyaverage Galactic extinction curve will always reflect the biases of itsparent sample. (5) The use of an average curve to deredden a spectralenergy distribution (SED) will result in significant errors, and arealistic error budget for the dereddened SED must include the observedvariance of Galactic curves. While the observed largesightline-to-sightline variations, and the lack of correlation among thevarious features of the curves, make it difficult to meaningfullycharacterize average extinction properties, they demonstrate thatextinction curves respond sensitively to local conditions. Thus, eachcurve contains potentially unique information about the grains along itssightline.
| 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.
| Variations in the D/H Ratio of Extended Sight Lines from Far Ultraviolet Spectroscopic Explorer Observations
We use new FUSE data to determine the column densities of interstellar DI, N I, O I, Fe II, and H2 along the HD 41161 and HD 53975sight lines. Together with N(H I) from the literature, we derive D/H,N/H, and O/H ratios. These sight lines have logN(H I)>21.00 and probegas up to ~1300 pc, allowing us to determine the gas-phase D/H ratio ina hydrogen column density range, logN(H)>20.70, where the only fivemeasurements available in the literature yield a weighted average ofD/H=(0.86+/-0.08)×10-5. We findD/H=(2.14+0.51-0.43)×10-5 alongthe HD 41161 sight line. This ratio is ~3 σ higher than theweighted mean D/H ratio quoted above, while the D/H ratio for the HD53975 line of sight,D/H=(1.02+0.23-0.20)×10-5, agreeswithin the 1 σ uncertainties. Our D/H measurement along the HD41161 sight line presents the first evidence of variations of D/H athigh N(H). Our result seems to indicate either that the long sight linesthat, according to the deuterium depletion model, are dominated by coldundisturbed gas where deuterium would be depleted onto carbonaceousgrains occur at higher N(H) than previously thought, or that theclumping of low D/H values in the literature for the long sight lineshas another explanation. Both of the O/H ratios derived here,(9.12+2.15-1.83)×10-4 and(5.37+1.35-1.14)×10-4 (for HD41161 and HD 53975, respectively), are higher than what has been foundby other authors. Finally, we derive(N/H)×105=8.32+2.09-1.76 and5.07+1.45-1.21, and(D/O)×102=2.29+0.40-0.35 and1.91+0.51-0.43, for HD 41161 and HD 53975,respectively. In addition, the relatively high signal-to-noise ratio ofthe HD 41161 data allows us to place constraints on the f-values of someneutral chlorine transitions present in the FUSE bandpass for which onlytheoretical values are available.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by the Johns HopkinsUniversity under NASA contract NAS5-32985.
| The Homogeneity of Interstellar Elemental Abundances in the Galactic Disk
We present interstellar elemental abundance measurements derived fromSpace Telescope Imaging Spectrograph echelle observations of 47 sightlines extending up to 6.5 kpc through the Galactic disk. These pathsprobe a variety of interstellar environments, covering ranges of nearly4 orders of magnitude in molecular hydrogen fraction f(H2)and more than 2 in mean hydrogen sight-line density. Coupling the current data with Goddard HighResolution Spectrograph data from 17 additional sight lines and thecorresponding Far Ultraviolet Spectroscopic Explorer and Copernicusobservations of H2 absorption features, we explore magnesium,phosphorus, manganese, nickel, copper, and germanium gas-phase abundancevariations as a function of : density-dependentdepletion is noted for each element, consistent with a smooth transitionbetween two abundance plateaus identified with warm and cold neutralinterstellar medium depletion levels. The observed scatter with respectto an analytic description of these transitions implies that totalelemental abundances are homogeneous on length scales of hundreds ofparsecs, to the limits of abundance measurement uncertainty. Theprobable upper limit we determine for intrinsic variability at any is 0.04 dex, aside from an apparent 0.10 dexdeficit in copper (and oxygen) abundances within 800 pc of the Sun.Magnesium dust abundances are shown to scale with the amount of siliconin dust, and in combination with a similar relationship between iron andsilicon, these data appear to favor the young F and G star values ofSofia & Meyer as an elemental abundance standard for the Galaxy.Based on observations with the NASA/ESA.
| FUSE Determination of a Low Deuterium Abundance along an Extended Sight Line in the Galactic Disk
We present a study of the deuterium abundance along the extended sightline toward HD 90087 with the Far Ultraviolet Spectroscopic Explorer(FUSE). HD 90087 is a O9.5 III star located in the Galactic disk at adistance of ~2.7 kpc away from the Sun. Both in terms of distance andcolumn densities, HD 90087 has the longest and densest sight lineobserved in the Galactic disk for which a deuterium abundance has beenmeasured from ultraviolet absorption lines so far. Because manyinterstellar clouds are probed along this sight line, possiblevariations in the properties of individual clouds should be averagedout. This would yield a deuterium abundance that is characteristic ofthe interstellar medium on scales larger than the Local Bubble. The FUSEspectra of HD 90087 show numerous blended interstellar and stellarfeatures. We have measured interstellar column densities of neutralatoms, ions, and molecules by simultaneously fitting the interstellarabsorption lines detected in the different FUSE channels. As far aspossible, saturated lines were excluded from the fits in order tominimize possible systematic errors. IUE (International UltravioletExplorer) archival data are also used to measure neutral hydrogen. Wereport D/O=(1.7+/-0.7)×10-2 andD/H=(9.8+/-3.8)×10-6 (2 σ). Our new resultsconfirm that the gas-phase deuterium abundance in the distantinterstellar medium is significantly lower than the one measured withinthe Local Bubble. We supplement our study with a revision of the oxygenabundance toward Feige 110, a moderately distant (~200 pc) sdOB star,located ~150 pc below the Galactic plane. Excluding saturated lines fromthe fits of the FUSE spectra is critical; this led us to derive an O Icolumn density about 2 times larger than the one previously reported forFeige 110. The corresponding updated D/O ratio on this sight line isD/O=(2.6+/-1.0)×10-2 (2 σ), which is lower thanthe one measured within the Local Bubble. The data set available nowoutside the Local Bubble, which is based primarily on FUSE measurements,shows a contrast between the constancy of D/O and the variability ofD/H. As oxygen is considered to be a good proxy for hydrogen within theinterstellar medium, this discrepancy is puzzling.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| The Homogeneity of Interstellar Oxygen in the Galactic Disk
We present an analysis of high-resolution Hubble Space Telescope (HST)Space Telescope Imaging Spectrograph (STIS) observations of O Iλ1356 and H I Lyα absorption in 36 sight lines that probe avariety of Galactic disk environments and include paths that range overnearly 4 orders of magnitude in f(H2), over 2 orders ofmagnitude in , and that extend up to 6.5 kpc inlength. Since the majority of these sight lines have also been observedby the Far Ultraviolet Spectroscopic Explorer (FUSE), we have undertakenthe study of gas-phase O/H abundance ratio homogeneity using the currentsample and previously published Goddard High Resolution Spectrograph(GHRS) results. Two distinct trends are identified in the 56 sight linesample: an apparent decrease in gas-phase oxygen abundance withincreasing mean sight-line density () and a gapbetween the mean O/H ratio for sight lines shorter and longer than about800 pc. The first effect is a smooth transition between two depletionlevels associated with large mean density intervals; it is centered near=1.5cm-3 and is similar to trendsevident in gas-phase abundances of other elements. Paths less dense thanthe central value exhibit a mean O/H ratio of log10(O/H)=-3.41+/-0.01 (or 390+/-10ppm), which is consistent with averages determined for several longlow-density paths observed by STIS (André et al. 2003) and shortlow-density paths observed by FUSE (Moos et al. 2002). Sight lines ofhigher mean density exhibit an average O/H value of log10(O/H)=-3.55+/-0.02 (284+/-12ppm). The data points for low- paths are scatteredmore widely than those for denser sight lines, because O/H ratios forsuch paths shorter than 800 pc are generally about 0.10 dex lower thanthe values for longer ones. Scenarios that would be consistent withthese results include a recent infall of metal-poor gas onto the localGalactic disk and an interstellar environment toward Orion that isconducive to reducing the apparent gas-phase oxygen abundance.Based on observations with the NASA/ESA Hubble Space Telescope (HST) andthe NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer (FUSE). HSTspectra were obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS5-26555 FUSE is operated for NASA by theJohns Hopkins University under NASA contract NAS5-32985.
| 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 Carina Spiral Feature: Strömgren-Hβ photometry approach. I. The photometric data-base
A data-base collating all uvbybeta photometry available at present forO-B9 stars brighter than 10th visual magnitude in the field of theCarina Spiral Feature is presented. The completeness and homogeneity ofthe data-base are discussed.Based on CDS data.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/410/523
| Oxygen Gas-Phase Abundance Revisited
We present new measurements of the interstellar gas-phase oxygenabundance along the sight lines toward 19 early-type Galactic stars atan average distance of 2.6 kpc. We derive O I column densities fromHubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS)observations of the weak 1355 Å intersystem transition. We derivetotal hydrogen column densities [N(HI)+2N(H2)] using HST/STISobservations of Lyα and Far Ultraviolet Spectroscopic Explorer(FUSE) observations of molecular hydrogen. The molecular hydrogencontent of these sight lines ranges fromf(H2)=2N(H2)/[N(HI)+2N(H2)]=0.03 to0.47. The average of6.3×1021 cm-2 mag-1 with astandard deviation of 15% is consistent with previous surveys. The meanoxygen abundance along these sight lines, which probe a wide range ofGalactic environments in the distant interstellar medium, is106 (O/H)gas=408+/-13 (1 σ in the mean). Wesee no evidence for decreasing gas-phase oxygen abundance withincreasing molecular hydrogen fraction, and the relative constancy of(O/H)gas suggests that the component of dust containing theoxygen is not readily destroyed. We estimate that, if 60% of the dustgrains are resilient against destruction by shocks, the distantinterstellar total oxygen abundance can be reconciliated with the solarvalue derived from the most recent measurements of 106(O/H)gassolar=517+/-58 (1 σ). We note thatthe smaller oxygen abundances derived for the interstellar gas within500 pc or from nearby B star surveys are consistent with a localelemental deficit.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| Synthetic High-Resolution Line Spectra of Star-forming Galaxies below 1200 Å
We have generated a set of far-ultraviolet stellar libraries usingspectra of OB and Wolf-Rayet stars in the Galaxy and the Large and SmallMagellanic Cloud. The spectra were collected with the Far UltravioletSpectroscopic Explorer and cover a wavelength range from 1003.1 to1182.7 Å at a resolution of 0.127 Å. The libraries extendfrom the earliest O to late-O and early-B stars for the Magellanic Cloudand Galactic libraries, respectively. Attention is paid to the complexblending of stellar and interstellar lines, which can be significant,especially in models using Galactic stars. The most severe contaminationis due to molecular hydrogen. Using a simple model for the H2line strength, we were able to remove the molecular hydrogen lines in asubset of Magellanic Cloud stars. Variations of the photospheric andwind features of C III λ1176, O VI λλ1032, 1038, PV λλ1118, 1128, and S IV λλ1063, 1073, 1074are discussed as a function of temperature and luminosity class. Thespectral libraries were implemented into the LavalSB and Starburst99packages and used to compute a standard set of synthetic spectra ofstar-forming galaxies. Representative spectra are presented for variousinitial mass functions and star formation histories. The valid parameterspace is confined to the youngest ages of less than ~=10 Myr for aninstantaneous burst, prior to the age when incompleteness of spectraltypes in the libraries sets in. For a continuous burst at solarmetallicity, the parameter space is not limited. The suite of models isuseful for interpreting the rest-frame far-ultraviolet in local andhigh-redshift galaxies. Based on observations made with theNASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE is operatedfor NASA by the Johns Hopkins University under NASA contract NAS5-32985.
| Optical spectroscopy of X-Mega targets - IV. CPD - 59°2636: a new O-type multiple system in the Carina Nebula
High-resolution optical spectroscopy of CPD - 59°2636, one of theO-type stars in the open cluster Trumpler 16 in the Carina Nebula,reveals this object to be a multiple system displaying triple lineswhich we label as components A, B and C of spectral types O7 V, O8 V andO9 V, respectively. From our radial velocity measurements we find thatthe components A and B form a close binary with a period of 3.6284 d,and we obtain the first circular radial velocity orbit for this systemwith semi-amplitudes of 184 and 192 km s-1, leading tominimum masses of 10.1 and 9.7 Msolar. We find that thecomponent C is a single lined binary with a period of 5.034 d andsemi-amplitude of 48 km s-1. We also analyse the X-rayradiation from CPD - 59°2636, finding neither appreciableoverluminosity nor phase-related X-ray flux variations.
| Research Note The evolutionary status of the early-type binary HD 115071
An analysis of the Hipparcos photometry of HD 115071 shows that it is anellipsoidal variable with a period of 2.73126 days, twice that suggestedpreviously. Modelling the light curve combined with the available radialvelocities suggests that the more massive, hotter component is smallerand less luminous than the cooler component, which is probably fillingits Roche lobe. The likely age of the system indicates that it is a MS +MS blue straggler, created by Case A mass exchange.
| A Search for Interstellar Bubbles surrounding Massive Stars in Perseus OB1
We have examined the interstellar medium in the vicinity of massivestars belonging to the Per OB1 association based on neutral hydrogen 21cm observations obtained with the 100 m radio telescope at Effelsberg(HPBW=8.4′) and complementary data from the Leiden-Dwingeloo H ISurvey (HPBW=36'). The higher angular resolution H I observationsallowed us to discover probable wind-blown bubbles related to fourmassive stars in the association, namely, HD 14442 [O5n(f)p], HD 14947[O5If+], HD 13022 [O9.5II-III((n))], and HD 13338 [O9.5V], while thedetection of a wind-blown bubble associated with HD 16691 [O5If+] isless conclusive. A clear H I shell coincident in position with two B1IIIstars (HD 15233 and Hilt 311) was also detected. Some of these featuresalso have infrared and/or molecular counterparts. The energetics of thestructures related to each massive star is analyzed. The new H Iinterstellar bubbles appear to be similar to the ones found surroundingWolf-Rayet stars and other Of stars. The large-scale maps obtained usingthe lower angular resolution H I data show that most of the early-typestars belonging to Per OB1 are placed in a region of low H I emission.The association could have blown a H I shell of about 350×550 pcin size. This large H I shell has an infrared counterpart.
| 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
| On the Correlation between CO Absorption and Far-Ultraviolet Nonlinear Extinction toward Galactic OB Stars
A sample of 59 sight lines to reddened Galactic OB stars was examinedfor correlations of the strength of the CO Fourth Positive(A1Π-X1Σ+) absorption bandsystem with the ultraviolet interstellar extinction curve parameters. Weused archival high-dispersion NEWSIPS IUE spectra to measure the COabsorption for comparison with parametric fits of the extinction curvesfrom the literature. A strong correlation with the nonlinear far-UVcurvature term was found with greater absorption, normalized to E(B-V),being associated with more curvature. A weaker trend with the linearextinction term was also found. Mechanisms for enhancing CO in dustenvironments exhibiting high nonlinear curvature are discussed.
| Tomographic Separation of Composite Spectra. VI. The Physical Properties of the Massive Close Binary HD 152248
We present the results of a Doppler tomographic reconstruction of the UVspectra of the double-lined O binary HD 152248 based on observationsmade with IUE. We used cross-correlation methods to obtain radialvelocities, confirm the orbital elements, estimate the UV flux ratio,and determine projected rotational velocities. The individual componentspectra are classified as O7 I+O7 I using UV criteria defined by Penny,Gies, & Bagnuolo. We present a model fit of the eclipsing lightcurve from which we derive an orbital inclination, i=72^deg+/-3^deg.This analysis indicates that neither star is currently experiencingRoche lobe overflow. We place the individual components in thetheoretical H-R diagram and show that the individual masses(M_p/M_solar=24.2+/-2.0 M_s/M_solar=25.8+/-2.0) derived from thecombined spectroscopic and photometric analysis are significantly lowerthan those computed from evolutionary tracks for single stars.
| Possible wind blown bubbles associated with five Of stars
Four fields of ~ 5(deg) x 4(deg) have been surveyed using the Hi -21 cmline (hpbw = 0 fdg 5) in searching for Hi interstellar bubbles in theenvirons of several Of stars. The analysis of the data disclosed fourbubble candidates, three with almost complete envelopes. Theirdimensions are ~ 40 pc and their expansion velocities around 10 km s(-1). For each structure swept-up masses (1000 to 8800 Msun),original ambient gas densities ( <~ 0.6 cm(-3) ), dynamical ages ( ~2 Myr) and kinetic energies (<~ 2 x 10(49) erg) were derived. Theorigin of the Hi shells is discussed, taking into account theirkinematics, energy, age and the emission at other wavelengths. As in thecase of several WR Hi shells, the O strong stellar winds would be themain agents blowing the Hi bubbles.
| 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.
| Spectroscopic bianry orbits from ultraviolet radial velocities. Paper 26: HD 165052
Not Available
| Three massive binaries and the Struve-Sahade effect
Not Available
| A Radial Velocity Database for Stephenson-Sanduleak Southern Luminous Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113..823R&db_key=AST
| 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.
| A Spectral Atlas of Hot, Luminous Stars at 2 Microns
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..107..281H&db_key=AST
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| קבוצת-כוכבים: | שדרית |
| התרוממות ימנית: | 10h34m46.63s |
| סירוב: | -58°09'22.0" |
| גודל גלוי: | 8.151 |
| מרחק: | 4000 פארסק |
| תנועה נכונה: | -5.9 |
| תנועה נכונה: | 5.6 |
| B-T magnitude: | 8.059 |
| V-T magnitude: | 8.144 |
קטלוגים וכינוים:
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INHABITED SKY
