Contents
Images
Upload your image
DSS Images Other Images
Related articles
StarCAT: A Catalog of Space Telescope Imaging Spectrograph Ultraviolet Echelle Spectra of Stars
StarCAT is a catalog of high resolution ultraviolet spectra of objectsclassified as "stars," recorded by Space Telescope Imaging Spectrograph(STIS) during its initial seven years of operations (1997-2004). StarCATis based on 3184 echelle observations of 545 distinct targets, with atotal exposure duration of 5.2 Ms. For many of the objects, broadultraviolet coverage has been achieved by splicing echellegrams taken intwo or more FUV (1150-1700 Å) and/or NUV (1600-3100 Å)settings. In cases of multiple pointings on conspicuously variablesources, spectra were separated into independent epochs. Otherwise,different epochs were combined to enhance the signal-to-noise ratio(S/N). A post-facto correction to the {\sf calstis} pipeline data setscompensated for subtle wavelength distortions identified in a previousstudy of the STIS calibration lamps. An internal "fluxing" procedureyielded coherent spectral energy distributions (SEDs) for objects withbroadly overlapping wavelength coverage. The best StarCAT materialachieves 300 m s-1 internal velocity precision;absolute accuracy at the 1 km s-1 level; photometricaccuracy of order 4%; and relative flux precision several times better(limited mainly by knowledge of SEDs of UV standard stars). WhileStarCAT represents a milestone in the large-scale post-processing ofSTIS echellegrams, a number of potential improvements in the underlying"final" pipeline are identified.
| 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.
| 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.
| The Variation of Magnesium Depletion with Line-of-Sight Conditions
In this paper we report on the gas-phase abundance of singly ionizedmagnesium (Mg II) in 44 lines of sight, using data from the Hubble SpaceTelescope (HST). We measure Mg II column densities by analyzing medium-and high-resolution archival Space Telescope Imaging Spectrograph (STIS)spectra of the 1240 Å doublet of Mg II. We find that Mg IIdepletion is correlated with many line-of-sight parameters [e.g.,f(H2), EB-V, EB-V/r, AV, andAV/r] in addition to the well-known correlation with. These parameters should be more directly relatedto dust content and thus have more physical significance with regard tothe depletion of elements such as magnesium. We examine the significanceof these additional correlations as compared to the known correlationbetween Mg II depletion and . While none of thecorrelations are better predictors of Mg II depletion than, some are statistically significant even assumingfixed . We discuss the ranges over which thesecorrelations are valid, their strength at fixed ,and physical interpretations.
| New Insights on Interstellar Gas-Phase Iron
In this paper we report on the gas-phase abundance of singly ionizediron (Fe II) for 51 lines of sight, using data from FUSE. Fe II columndensities are derived by measuring the equivalent widths of several UVabsorption lines and subsequently fitting those to a curve of growth.Our derivation of Fe II column densities and abundances creates thelargest sample of iron abundances in moderately to highly reddened linesof sight explored with FUSE, lines of sight that are on average morereddened than lines of sight in previous Copernicus studies. We presentthree major results. First, we observe the well-established correlationbetween iron depletion and and also find trendsbetween iron depletion and other line-of-sight parameters [e.g.,f(H2), EB-V, and AV], and we examinethe significance of these trends. Of note, a few of our lines of sightprobe larger densities than previously explored and we do not seesignificantly enhanced depletion effects. Second, we present twodetections of an extremely weak Fe II line at 1901.773 Å in thearchival STIS spectra of two lines of sight (HD 24534 and HD 93222). Wecompare these detections to the column densities derived through FUSEspectra and comment on the line's f-value and utility for future studiesof Fe II. Finally, we present strong anecdotal evidence that the Fe IIf-values derived empirically through FUSE data are more accurate thanprevious values that have been theoretically calculated, with theprobable exception of f1112.
| 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.
| The Abundance of Interstellar Fluorine and Its Implications
We report results from a survey of neutral fluorine (F I) in theinterstellar medium. Data from FUSE were used to analyze 26 lines ofsight lying in both the galactic disk and halo, including lines toWolf-Rayet stars and through known supernova remnants. The equivalentwidths of the fluorine resonance lines at 951.871 and 954.827 Åwere measured or assigned upper limits and combined with a nitrogencurve of growth to obtain F I column densities. These column densitieswere then used to calculate fluorine depletions. Comparisons are made tothe previous study of F I by Federman and coworkers and implications forF I formation and depletion are discussed.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| VLT/UVES spectroscopy of Wray 977, the hypergiant companion to the X-ray pulsar GX301-2
Model atmosphere fits to high-resolution optical spectra ofWray 977 confirm the B hypergiant classification ofthe massive companion to the X-ray pulsar GX301-2.The models give a radius of 62 Rȯ, an effectivetemperature of 18 100 K and a luminosity of 5 × 105Lȯ. These values are somewhat reduced compared to thestellar parameters of Wray 977 measured previously.The deduced mass-loss rate and terminal velocity of the stellar wind are10-5 Mȯ yr-1 and 305 kms-1, respectively. The interstellar Na I D absorptionindicates that Wray 977 is located behind the firstintersection with the Sagittarius-Carina spiral arm (1-2.5 kpc) andprobably belongs to the stellar population of the Norma spiral arm at adistance of 3-4 kpc. The luminosity derived from the model atmosphere isconsistent with this distance (3 kpc). The luminosity of the wind-fedX-ray pulsar (LX 1037 erg s-1) isin good accordance with the Bondi-Hoyle mass accretion rate. The spectraobtained with UVES on the Very Large Telescope (VLT) cover a full orbitof the system, including periastron passage, from which we derive theradial-velocity curve of the B hypergiant. The measured radial-velocityamplitude is 10 ± 3 km s-1 yielding a mass ratio q =M_X/M_opt = 0.046 ± 0.014. The absence of an X-ray eclipseresults in a lower limit to the mass of Wray 977 of39 Mȯ. An upper limit of 68 or 53 Mȯ isderived for the mass of Wray 977 adopting a maximumneutron star mass of 3.2 or 2.5 Mȯ, respectively. Thecorresponding lower limit to the system inclination is i > 44°,supporting the view that the dip in the X-ray lightcurve is due toabsorption by the dense stellar wind of Wray 977(Leahy 2002). The "spectroscopic" mass of Wray 977 is43 ± 10 Mȯ, consistent with the range in massderived from the binarity constraints. The mass of the neutron star is1.85 ± 0.6 Mȯ. Time series of spectral linesformed in the dense stellar wind (e.g. He I 5876 Å and H α)indicate the presence of a gas stream trailing the neutron star in itsorbit. The long-term behaviour of the H α equivalent widthexhibits strong variations in wind strength; the sampling of the data isinsufficient to conclude whether a relation exists between windmass-loss rate and pulsar spin period.
| 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 Abundance of Interstellar Fluorine
Despite the importance of measuring the interstellar fluorine abundanceonly three previous detection has been made due to the low relativeabundance of fluorine, the lack of lines outside the far-ultraviolet,and blending of the available transitions with lines of molecularhydrogen. The nucleosynthetic source(s) of fluorine are still a matterof debate, and the present day abundance of fluorine can potentiallyconstrain models for its production. Furthermore, due to its extremereactivity, measurement of the gas-phase interstellar fluorine abundanceis important for models of gas and grain chemistry.We report on the results of high S/N-ratio (50-100) FUSE observations ofthe interstellar absorption lines of neutral fluorine at 951 and 954Angstroms toward two distant Galactic stars (HD 103779 and HD 164816).The sightline toward HD 103779 lies near the edge of the North PolarSpur and Radio Loop 1. HD 164816 is associated with the Lagoon nebula (M8) at a distance of about 1.5 kpc, and also probes both distant andlocal gas. Modeling of both interstellar and stellar absorption lineshas been used to determine the abundance from the (blended) strongfluorine line at 954.83 Angstroms. We have also made a sensitive searchfor the weaker line at 951.87 Angstroms to provide a consistency checkfor our models, and have made a tentative detection toward HD 103779.While preliminary analysis of these data suggests that the observedfluorine gas-phase abundances (and hence inferred depletions) areroughly consistent with previous measures toward delta Sco (Copernicus)and two stars in Cep OB2 (FUSE), there may be a slight enhancement inthe gas-phase abundance toward HD 103779.This research was supported by NASA grant NAG5-13005.
| Anomalous dust-to-gas ratios in the Galaxy
Lines of sight with E(B-V)/N(HI) considerably smaller than the averagevalue for the solar neighbourhood have been selected from the catalogueof Diplas & Savage. In order to develop quantitative considerations,estimates of the molecular hydrogen column density were obtained usingthe relation of Savage et al. extended at E(B-V) > 0.4 with therecent data of Rachford et al. Contrary to the prevailing opinion in theliterature for sightlines with similar behaviour, we found that only 22per cent of our sample was characterized by both an average gas densitylarger than 1 cm-3 and a value of RV larger thanthat in the diffuse interstellar medium. By computing extinction models,we were able to fit the E(B-V)/N(HI) by changing the value ofRV only for some sightlines. For the remaining ones, aρd/ρH ratio different from the averageGalactic value must be invoked. The application of the Kramers-Kronigrelation to the observed extinction curves confirmed this possibility.Moreover, attempts to fit such curves with models having grain volumescorresponding to the standard ρd/ρH ratiofailed.We find a linear relation between ρd/ρHand E(B-V)/N(H) for our sightlines. The average Galactic value marks theseparation into two groups characterized by lower abundances of C and Sitrapped into the grains when E(B-V)/N(H) is smaller than the Galacticvalue, and by larger abundances when E(B-V)/N(H) is greater.
| 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
| 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.
| A New Measurement of the Average Far-Ultraviolet Extinction Curve
We have measured the extinction curve in the far-ultraviolet wavelengthregion of (900-1200 Å) using spectra obtained with the BerkeleyEUV/FUV spectrometer during the ORFEUS I and the ORFEUS II (Orbiting andRetrievable Far and Extreme Ultraviolet Spectrometer) missions in 1993and 1996. From the complete sample of early-type stars observed duringthese missions, we have selected pairs of stars with the same spectraltype but different reddenings to measure the differential FUVextinction. We model the effects of molecular hydrogen absorption andexclude affected regions of the spectrum to determine the extinctionfrom dust alone. We minimize errors from inaccuracies in the catalogedspectral types of the stars by making our own determinations of spectraltypes based on their IUE spectra. We find substantial scatter in thecurves of individual star pairs and present a detailed examination ofthe uncertainties and their effects on each extinction curve. We findthat, given the potentially large uncertainties inherent in using thepair method at FUV wavelengths, a careful analysis of measurementuncertainties is critical to assessing the true dust extinction. Wepresent a new measurement of the average far-ultraviolet extinctioncurve to the Lyman limit; our new measurement is consistent with anextrapolation of the standard extinction curve of Savage & Mathis.
| 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.
| 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.
| Strömgren and Hβ photometry of O and B type stars in star-forming regions. III. Carina Spiral Feature
Strömgren and Hβ photometry of O and B type stars, generallybrighter than 9.5 mag is reported for the field of the Carina SpiralFeature. The observations are based on the PPM catalogue identificationsand are designed to improve the completeness of the existing uvbybetadata for the bright early-type stars in the field. We present new uvbyphotometry for 283 stars and Hβ photometry for 225 of them. Theseobservations are part of an ongoing effort to study the structure ofselected star-forming regions in the Milky Way by means of uvbybetaphotometry. A comparison of the new data to other uvbybeta data sets forthis field is presented. Based on data from the Strömgren AutomaticTelescope of the Copenhagen University Observatory, La Silla. Tables 1and 2 are only available in electronic form at the CDS via anonymous ftpto 130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html
| The Puzzle of HD 104994 (WR 46)
Intense coordinated spectroscopic and photometric monitoring of thesuspected Wolf-Rayet binary WR 46 in 1999 reveals clear periodicvariations, P=0.329+/-0.013 days, in the radial velocities of theemission lines of highest ionization potential, O VI and N V, founddeepest in the Wolf-Rayet wind and thus least likely to be perturbed bya companion. These are accompanied by coherent variability in theprofiles of lines with lower ionization/excitation potential and in thecontinuum flux. Most probably originating from orbital motion of theWolf-Rayet component of the binary, this periodic radial velocity signaldisappears from time to time, thus creating a puzzle yet to be solved.We show that the entangled patterns of the line profile variability aremainly governed by transitions between high and low states of thesystem's continuum flux. Based in part on observations obtained at theEuropean Southern Observatory, La Silla, Chile (ESO program 62.H-0110).
| Magellanic Cloud-Type Interstellar Dust along Low-Density Sight Lines in the Galaxy
We have studied the UV extinction properties along 30 Galactic sightlines using data from the International Ultraviolet Explorer archivethat have never been previously examined. These distant (d>1 kpc)sight lines were selected to investigate the distribution and physicalconditions of gas located in low-density regions of the Galactic diskand halo. The average densities along these sight lines are extremelylow. It is likely that they are dominated by the warm intercloud mediumand have little contribution from the cold cloud medium. We find that asubsample of these sight lines has extinction curves with weak bumps andvery steep far-UV extinction reminiscent of the Magellanic Clouds. Thesesight lines all lie in the region bounded by325deg<=l<=0deg and-5deg>=b>=-11deg. The gas along these sightlines shows forbidden velocities, which may indicate that the dust hasbeen subject to shocks. This type of low-density sight line may mimicthe environments found in the Magellanic Clouds. Large values of N(CaII)/N(Na I) indicating low depletion are associated with steep far-UVextinction. A possible correlation exists between decreasing bumpstrength and increasing far-UV steepness for extinction curves in theGalaxy and the Magellanic Clouds.
| 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.
| Absorption by Highly Ionized Interstellar Gas Along Extragalactic and Galactic Sight Lines
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113.2158S&db_key=AST
| Red and infrared colours of B stars and the reddening law in the Galaxy
The red and infrared intrinsic colours of B stars are derived fromphotometric observations through the UBV(RI)_CJHK and Hβ filters of257 early-type stars. Those stars for which the UBV and Hβmeasurements match the published spectral class, and which show no othersigns of peculiarity, are used to determine the intrinsic photometriccolours of B stars in the red and infrared. From these intrinsic coloursthe interstellar reddening relationships for the red and infraredcolours are evaluated, and the results are compared with previousestimates of these quantities. The values of R, E(B-V) and the distanceare then determined for the individual stars. R is confirmed to be closeto 3.1 in most cases, but was found to be much larger in somedirections. The relationship between R and the location of a star in theGalaxy is investigated. Usually the abnormally reddened stars seemed tobe associated with known regions of star formation. The paper alsoidentifies seven likely variable stars and a number of stars withpossible dust shells.
| High-Resolution Ultraviolet Observations of the Highly Ionized Interstellar Gas toward Radio Loops I and IV
We present new Goddard High-Resolution Spectrograph (GHRS) echelleobservations of the high ionization lines of Si IV, C IV, and N V towardHD 119608, a halo star at d = 4.1 kpc behind the Loop I and IV supernovaremnants. Absorption along the path to HD 119608 makes it possible tostudy energetic processes that may result in the flow of gas into theGalactic halo. The data have a resolution (FWHM) of ~3.5 km s-1 and S/Nratios of 30:1--50:1. The integrated high ion column densities log N =13.57 +/- 0.02, 14.48 +/- 0.06, and 13.45 +/- 0.07 for Si IV, C IV, andN V, respectively, imply a factor of 2--4 enhancement in the amount ofhighly ionized gas compared to average sight lines through the Galacticdisk and halo. The integrated high ion column density ratios, N(CIV)/N(Si IV) = 8.1 +/- 1.1 and N(C IV)/N(N V) = 10.7 +/- 2.1, are alsoseveral times larger than normal. These high ion results suggest theabsorption is influenced by passage of the sight line through the centerof Loop IV. The HD 119608 C IV absorption profile has a bimodal velocitystructure indicative of an expanding shell; we tentatively derive anexpansion velocity of 16 km s-1 for Radio Loop IV. A detailed analysisof the high ion profile structure indicates that multiple types ofhighly ionized gas with a range of properties exist along this sightline. We also reexamine the high ionization properties of the QSO 3C 273sight line using new intermediate-resolution (FWHM ~ 20 km s-1) GHRSdata. We obtain log N = 14.49 +/- 0.03 and 13.87 +/- 0.06 for C IV and NV, respectively. The C IV column density, which is 0.12 dex smaller thanearlier estimates, leads to somewhat smaller ionic ratios thanpreviously determined. We find N(C IV)/N(Si IV) = 5.1 +/- 0.6 and N(CIV)/N(N V) = 4.2 +/- 0.6. However, as for HD 119608, the high ion columndensities toward 3C 273 are larger than normal by factors of 2--4. The3C 273 high ion absorption profiles are much broader than those seentoward HD 119608 and other sight lines near the center of Loop IV. Thelarger line widths may result because the sight line passes through theturbulent edge of Loop IV as well as the X-ray and radio continuumemission regions of the North Polar Spur. We have compiled a list of thehighest quality IUE and GHRS high ion measurements available forinterstellar sight lines through the disk and halo and find thefollowing median averaged results: N(C IV)/N(Si IV) = 3.8 +/- 1.9 andN(C IV)/N(N V) = 4.0 +/- 2.4. These ratios are lower than those foundfor four Loop IV sight lines. We suggest a model for the production ofhighly ionized gas in Loop IV in which the contributions from turbulentmixing layers and conductive interfaces/SNR bubbles to the total highion column densities are approximately equal. Much of the high ionabsorption toward HD 119608 and 3C 273 may occur within a highlyfragmented medium within the remnant or the outer cavity walls of theremnant.
| 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
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Crux |
| Right ascension: | 11h56m57.55s |
| Declination: | -63°14'56.7" |
| Apparent magnitude: | 7.217 |
| Distance: | 1010.101 parsecs |
| Proper motion RA: | -7.2 |
| Proper motion Dec: | 0.6 |
| B-T magnitude: | 7.179 |
| V-T magnitude: | 7.214 |
Catalogs and designations:
|
INHABITED SKY
