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Studies of the Diffuse Interstellar Bands. IV. The Nearly Perfect Correlation Between ??6196.0 and 6613.6
In a sample of 114 diffuse cloud sightlines spanning a wide range ofinterstellar environments, we find the equivalent widths of the diffuseinterstellar bands (DIBs) ?6196.0 and ?6613.6 to beextremely well correlated, with a correlation coefficient of 0.986. Amaximum likelihood functional relationship analysis shows that theobservations are consistent with a perfect correlation if theobservational errors, which are dominated by continuum placement andother systematics such as interfering lines, have been underestimated bya factor of 2. The quality of this correlation far exceeds otherpreviously studied correlations, such as that between the ?5780.5DIB and either the color excess or the atomic hydrogen column density.The unusually tight correlation between these two DIBs would seem tosuggest that they might represent the first pair of DIBs known to be dueto the same molecular carrier. However, further theoretical work will berequired to determine whether the different linewidths and band shapesof these two DIBs can be consistent with a common carrier. If the twoDIBs do not in fact share the same molecular carrier, their two carriersmust be chemically very closely related.
| 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).
| The Extension of the Transition Temperature Plasma into the Lower Galactic Halo
Column densities for H I, Al III, Si IV, C IV, and O VI toward 109 starsand 30 extragalactic objects have been assembled to study the extensionsof these species away from the Galactic plane into the Galactic halo. HI and Al III mostly trace the warm neutral and warm ionized medium,respectively, while Si IV, C IV, and O VI trace a combination of warmphotoionized and collisionally ionized plasmas. The much larger objectsample compared to previous studies allows us to consider and correctfor the effects of the sample bias that has affected earlier but smallersurveys of the gas distributions. We find that Si IV and C IV havesimilar exponential scale heights of 3.2(+1.0, -0.6) and 3.6(+1.0,-0.8) kpc. The scale height of O VI is marginally smaller with h =2.6 ± 0.6 kpc. The transition temperature gas is ~3 times moreextended than the warm ionized medium traced by Al III with h =0.90(+0.62, -0.33) kpc and ~12 times more extended than the warmneutral medium traced by H I with h = 0.24 ± 0.06 kpc. There is afactor of 2 decrease in the dispersion of the log of the column densityratios for transition temperature gas for lines of sight in the Galacticdisk compared to extragalactic lines of sight through the entire halo.The observations are compared to the predictions of the various modelsfor the production of the transition temperature gas in the halo. Theappendix presents a revision to the electron scale height of Gaensler etal.'s 2008 study based on electron dispersion measures.
| 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.
| Ultraviolet Survey of CO and H2 in Diffuse Molecular Clouds: The Reflection of Two Photochemistry Regimes in Abundance Relationships
We carried out a comprehensive far-UV survey of 12CO andH2 column densities along diffuse molecular Galactic sightlines. This sample includes new measurements of CO from HST spectraalong 62 sight lines and new measurements of H2 from FUSEdata along 58 sight lines. In addition, high-resolution optical datawere obtained at the McDonald and European Southern Observatories,yielding new abundances for CH, CH+, and CN along 42 sightlines to aid in interpreting the CO results. These new sight lines wereselected according to detectable amounts of CO in their spectra andprovide information on both lower density (<=100 cm-3) andhigher density diffuse clouds. A plot of logN(CO) versuslogN(H2) shows that two power-law relationships are neededfor a good fit of the entire sample, with a break located atlogN(CO,cm-2)=14.1 and logN(H2)=20.4,corresponding to a change in production route for CO in higher densitygas. Similar logarithmic plots among all five diatomic molecules revealadditional examples of dual slopes in the cases of CO versus CH (breakat logN=14.1, 13.0), CH+ versus H2 (13.1, 20.3),and CH+ versus CO (13.2, 14.1). We employ both analytical andnumerical chemical schemes in order to derive details of the molecularenvironments. In the denser gas, where C2 and CN moleculesalso reside, reactions involving C+ and OH are the dominantfactor leading to CO formation via equilibrium chemistry. In thelow-density gas, where equilibrium chemistry studies have failed toreproduce the abundance of CH+, our numerical analysis showsthat nonequilibrium chemistry must be employed for correctly predictingthe abundances of both CH+ and CO.
| Search for OB stars running away from young star clusters. I. NGC 6611
N-body simulations have shown that the dynamical decay of the young (~1Myr) Orion Nebula cluster could be responsible for the loss of at leasthalf of its initial content of OB stars. This result suggests that otheryoung stellar systems could also lose a significant fraction of theirmassive stars at the very beginning of their evolution. To confirm thisexpectation, we used the Mid-Infrared Galactic Plane Survey (completedby the Midcourse Space Experiment satellite) to search for bow shocksaround a number of young (?several Myr) clusters and OBassociations. We discovered dozens of bow shocks generated by OB starsrunning away from these stellar systems, supporting the idea ofsignificant dynamical loss of OB stars. In this paper, we report thediscovery of three bow shocks produced by O-type stars ejected from theopen cluster NGC 6611 (M16). One of the bow shocks is associated withthe O9.5Iab star HD165319, which was suggested to be one of “thebest examples for isolated Galactic high-mass star formation” (deWit et al. 2005, A&A, 437, 247). Possible implications of ourresults for the origin of field OB stars are discussed.
| On the origin of field O-type stars
Aims. We aim to identify the origins of field O-stars in the nearest 2to 3 kpc around the Sun using the best presently available kinematicdata on O-stars and on young open clusters. We investigate the questionof whether the present-day data are consistent with the assumption thatO-stars have formed in groups (clusters, associations), or in isolation. Methods: We apply the epicycle theory to back-trace the orbits ofO-type stars and of candidate parent open clusters. Results: From the370 O-stars in the “Galactic O star catalog v 2.0” (GOSV2)we have investigated 93 stars classified as field, and found the originfor 73 of them in 48 open clusters younger than 30 Myr. Only for 32stars or about 9% of all O-stars from this catalogue is the question oftheir origin in groups not solved; some of them may have originated inisolation or may have disintegrated the group in which they formed.Fifty percent of the young open clusters (age < 30 Myr) in the“Catalogue of Open Cluster Data” (COCD) have O-stars asmembers, or have ejected at least one O-star in the first 10 Myr oftheir life, or both. During this period the average mass loss from openclusters by ejecting O-stars is found to be 3 to 5 M_ȯ per Myr. Weprove that ζ Pup had its origin in the open cluster Trumpler 10which it left about 2.5 Myr ago, and that its present-day distance is300 pc (compared to 440 pc before). The revised distance implies asignificant revision of the stellar parameters (a radius of 14 R_ȯ,a mass of 22.5 M_ȯ, and a luminosity of log L/L_ȯ of 5.74)i.e., ζ Pup is closer, less massive, and less luminous thanpreviously thought. Our findings provide independent estimates of thepresent-day distances and absolute magnitudes of field O-stars.
| Adaptive Optics Photometry and Astrometry of Binary Stars. III. a Faint Companion Search of O-Star Systems
We present the results of an adaptive optics survey for faint companionsamong Galactic O-type star systems (with V lsim 8) using the AdvancedElectro-Optical System (AEOS) 3.6 m telescope on Haleakala. We surveyedthese O-star systems in the I-band, typically being able to detect acompanion with a magnitude difference of utrimI lsim 6 in theprojected separation range 0farcs5 < ρ < 1farcs0, andutrimI lsim 9.5 in the range 1farcs0 < ρ < 5farcs0.In the course of the survey, we discovered 40 new companions among 31 ofthe 116 objects examined and made astrometric and differential magnitudemeasurements of 24 additional known pairs, several of them beingconfirmation detections. We present new astrometric orbits for twobinaries, BU 1032AB (WDS 05387–0236 σ Ori AB) and SEE 322(WDS 17158–3344 HD 155889AB). We lack magnitude differences forother filter bands, so it is difficult to determine physical fromline-of-sight companions, but we present empirical arguments for thelimiting magnitude difference where field contamination is significant.Based on observations made at the Maui Space Surveillance Systemoperated by Detachment 15 of the US Air Force Research Laboratory'sDirected Energy Directorate.
| The Far Ultraviolet Spectroscopic Explorer Survey of O VI Absorption in the Disk of the Milky Way
To probe the distribution and physical characteristics of interstellargas at temperatures T~3×105 K in the disk of the MilkyWay, we have used the Far Ultraviolet Spectroscopic Explorer (FUSE) toobserve absorption lines of O VI λ1032 toward 148 early-typestars situated at distances >1 kpc. After subtracting off a mildexcess of O VI arising from the Local Bubble, combining our new resultswith earlier surveys of O VI, and eliminating stars that showconspicuous localized X-ray emission, we find an average O VI midplanedensity n0=1.3×10-8 cm-3. Thedensity decreases away from the plane of the Galaxy in a way that isconsistent with an exponential scale height of 3.2 kpc at negativelatitudes or 4.6 kpc at positive latitudes. Average volume densities ofO VI along different sight lines exhibit a dispersion of about 0.26 dex,irrespective of the distances to the target stars. This indicates that OVI does not arise in randomly situated clouds of a fixed size anddensity, but instead is distributed in regions that have a very broadrange of column densities, with the more strongly absorbing cloudshaving a lower space density. Line widths and centroid velocities aremuch larger than those expected from differential Galactic rotation, butthey are nevertheless correlated with distance and N(O VI), whichreinforces our picture of a diverse population of hot plasma regionsthat are ubiquitous over the entire Galactic disk. The velocity extremesof the O VI profiles show a loose correlation with those of very stronglines of less ionized species, supporting a picture of a turbulent,multiphase medium churned by shock-heated gas from multiple supernovaexplosions.
| Automated classification of ELODIE stellar spectral library using probabilistic artificial neural networks
A Probabilistic Neural Network model has been used for automatedclassification of ELODIE stellar spectral library consisting of about2000 spectra into 158 known spectro-luminosity classes. The full spectrawith 561 flux bins and a PCA reduced set of 57, 26 and 16 componentshave been used for the training and test sessions. The results show aspectral type classification accuracy of 3.2 sub-spectral type andluminosity class accuracy of 2.7 for the full spectra and an accuracy of3.1 and 2.6 respectively with the PCA set. This technique will be usefulfor future upcoming large databases and their rapid classification.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| 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.
| 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.
| 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.
| 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.
| 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.
| The Effective Temperatures of Mid-O Stars
We derived photospheric parameters, mass-loss rates, and wind velocitiesof Galactic O6-O7 stars by analyzing high-resolution spectra in thefar-UV and UV ranges with line-blanketed, hydrodynamic, non-LTEspherical models. We combined spectra from the Far UltravioletSpectroscopic Explorer (FUSE) in the range 905-1187 Å andInternational Ultraviolet Explorer (IUE) archival spectra (1150-3250Å) and used the WM-BASIC code of Pauldrach et al. to compute modelspectra. Lines in the FUSE range include high ionization stages (e.g., OVI) and lower abundance non-CNO elements (e.g., P V). Analyzed inaddition to the N IV, N V, Si IV, and C IV lines in the IUE range, thesefeatures play a crucial role in uniquely constraining the stellarparameters, assessing the presence of shocks in the wind, andquantifying the effects of the resulting soft X-rays on the windionization. The effective temperatures derived from the consistentanalysis of the far-UV and UV spectra are significantly (~6000 K or 15%on average, or between 4000 and 8000 K) lower than most valuespreviously derived for some of our targets and lower than typical valuesassigned to their spectral types from different compilations. Thisresult has great implications for our understanding of the evolution ofmassive stars and the characterization of young stellar populations, aswell as for energy balance calculations of H II regions. Based onobservations with the NASA-CNES-CSA Far Ultraviolet SpectroscopicExplorer, which is operated by The Johns Hopkins University under NASAcontract NAS5-32985, and on IUE observations from the MAST and INESarchives.
| An Atlas of Galactic OB Spectra Observed with the Far Ultraviolet Spectroscopic Explorer
An atlas of far-ultraviolet spectra of 45 Galactic OB stars observedwith the Far Ultraviolet Spectroscopic Explorer is presented. The atlascovers the wavelength region between 912 and 1185 Å with aneffective spectral resolution of 0.12 Å. Systematic trends in themorphology and strength of stellar features are discussed. Particularattention is drawn to the variations of the C III λ1176, S IVλλ1063, 1073, and P V λλ1118, 1128 lineprofiles as a function of temperature and luminosity class; and the lackof a luminosity dependence associated with O VI λλ1032,1038. Numerous interstellar lines are also identified. Based onobservations made with the NASA-CNES-CSA Far Ultraviolet SpectroscopicExplorer. FUSE is operated for NASA by the Johns Hopkins Universityunder NASA contract NAS5-32985.
| IUE Absorption-Line Observations of the Moderately and Highly Ionized Interstellar Medium toward 164 Early-Type Stars
We present measurements of Galactic interstellar Al III, Si IV, and C IVabsorption recorded in high-resolution archival ultraviolet spectra of164 hot early-type stars observed by the International UltravioletExplorer (IUE) satellite. The objects studied were drawn from the listof hot stars scheduled to be observed with the Far UltravioletSpectroscopic Explorer (FUSE) satellite as part of observing programsdesigned to investigate absorption by O VI in the Galactic disk andhalo. Multiple IUE echelle-mode integrations have been combined toproduce a single ultraviolet (1150-1900 Å) spectrum of each starwith a spectral resolution of ~25 km s-1 (FWHM). Selectedabsorption-line profiles are presented for each star along with plots ofthe apparent column density per unit velocity for each line of the AlIII, Si IV, and C IV doublets. We report absorption-line equivalentwidths, absorption velocities, and integrated column densities based onthe apparent optical depth method of examining interstellar absorptionlines. We also determine column densities and Doppler parameters fromsingle-component curve-of-growth analyses. The scientific analysis ofthese observations will be undertaken after the FUSE satellite producessimilar measurements for absorption by interstellar O IV, Fe III, S III,and other ions. Based on archival data from observations obtained withthe International Ultraviolet Explorer (IUE) satellite sponsored byNASA, SERC, and ESA.
| Tomographic Separation of Composite Spectra. VII. The Physical Properties of the Massive Triple System HD 135240 (δ Circini)
We present the results of a radial velocity study of the massive,double-lined, O binary HD 135240 based primarily on UV spectroscopy fromthe International Ultraviolet Explorer. Cross-correlation methodsindicate the presence of a third stationary spectral line componentwhich indicates that the system is a triple consisting of a central 3.9day close binary with a distant companion. We measured radial velocitiesfrom the cross-correlation functions after removal of the thirdcomponent, and we combined these with velocities obtained from Hαspectroscopy to reassess the orbital elements. We applied a Dopplertomography algorithm to reconstruct the individual UV spectra of allthree stars, and we determine spectral classifications of O7 III-V, O9.5V, and B0.5 V for the primary, secondary, and tertiary, respectively,using UV criteria defined by Penny, Gies, & Bagnuolo. We comparethese reconstructed spectra to standard single-star spectra to find theUV flux ratios of the components(F2/F1=0.239+/-0.022, andF3/F1=0.179+/-0.021). Hipparcos photometry revealsthat the central pair is an eclipsing binary, and we present the firstmodel fit of the light curve from which we derive an orbitalinclination, i=74deg+/-3deg. This analysisindicates that neither star is currently experiencing Roche lobeoverflow. We place the individual components in the theoretical H-Rdiagram, and we show that the masses derived from the combinedspectroscopic and photometric analysis(Mp/Msolar=21.6+/-2.0 andMs/Msolar=12.4+/-1.0) are significantly lower thanthose computed from evolutionary tracks for single stars.
| The Serpens OB2 Association and Its Thermal ``Chimney''
UBVRI photometry and MK spectral types have been obtained for a nearlycomplete sample of the massive star population of the Serpens OB2association. This relatively neglected association is found to containover 100 OB stars at a distance of 1.9+/-0.3 kpc and with a common ageof 5+/-1 Myr. These stars illuminate the large H II region S54, and aredirectly connected to the unusual thermal ``chimney'' detected byMüller et al. Evidence is given of continuing star formation withinthe association, and the relationship between the association stars andthe chimney is discussed.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| 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
| 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.
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Datos observacionales y astrométricos
| Constelación: | Serpiente |
| Ascensión Recta: | 17h26m17.33s |
| Declinación: | -10°59'34.8" |
| Magnitud Aparente: | 7.799 |
| Distancia: | 362.319 parsecs |
| Movimiento Propio en Ascensión Recta: | -11.5 |
| Movimiento Propio en Declinación: | 0.1 |
| B-T magnitude: | 7.94 |
| V-T magnitude: | 7.811 |
Catálogos y designaciones:
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