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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.
| 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.
| 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.
| 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 Heavy-Element Enrichment of Lyα Clouds in the Virgo Supercluster
Using high signal-to-noise ratio echelle spectra of 3C 273 obtained withthe Space Telescope Imaging Spectrograph (resolution of 7 kms-1 FWHM), we constrain the metallicities of two Lyαclouds in the vicinity of the Virgo Cluster. We detect C II, Si II, andSi III absorption lines in the Lyα absorber atzabs=0.00530. Previous observations with the Far UltravioletSpectroscopic Explorer have revealed Lyβ-Lyθ absorptionlines at the same redshift, thereby accurately constraining the H Icolumn density. We model the ionization of the gas and derive[C/H]=-1.2+0.3-0.2, [Si/C]=0.2+/-0.1, andlognH=-2.8+/-0.3. The model implies a small absorberthickness, ~70 pc, and thermal pressure p/k~40 cm-3 K. It ismost likely that the absorber is pressure confined by an external mediumbecause gravitational confinement would require a very high ratio ofdark matter to baryonic matter. Based on a sample of Milky Way sightlines in which carbon and silicon abundances have been reliably measuredin the same interstellar cloud (including new measurements presentedherein), we argue that it is unlikely that the overabundance of Sirelative to C is due to depletion onto dust grains. Instead, thisprobably indicates that the gas has been predominately enriched byejecta from Type II supernovae. Such enrichment is most plausiblyprovided by an unbound galactic wind, given the absence of knowngalaxies within a projected distance of 100 kpc and the presence ofgalaxies capable of driving a wind at larger distances (e.g., H I1225+01). Such processes have been invoked to explain the observedabundances in the hot, X-ray-emitting gas in Virgo. However, the sightline to 3C 273 is more than 10° away from the X-ray emission region.We also constrain the metallicity and physical conditions of the Virgoabsorber at zabs=0.00337 in the spectrum of 3C 273 based ondetections of O VI and H I and an upper limit on C IV. If this absorberis collisionally ionized, the OVI/CIV limit requiresT>~105.3 K in the O VI-bearing gas. For either collisionalionization or photoionization, we find that [O/H]>~-2.0 atzabs=0.00337. Based on observations with the NASA/ESA HubbleSpace Telescope, obtained at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS 5-26555.
| 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.
| Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars
We present the results of statistical analyses of a sample of 627 Bestars. The parameters of intrinsic polarization (p*),projected rotational velocity (v sin i), and near IR excesses have beeninvestigated. The values of p* have been estimated for a muchlarger and more representative sample of Be stars (~490 objects) thanpreviously. We have confirmed that most Be stars of early spectral typehave statistically larger values of polarization and IR excesses incomparison with the late spectral type stars. It is found that thedistributions of p* diverge considerably for the differentspectral subgroups. In contrast to late spectral types (B5-B9.5), thedistribution of p* for B0-B2 stars does not peak at the valuep*=0%. Statistically significant differences in the meanprojected rotational velocities (/line{vsin i}) are found for differentspectral subgroups of Be stars in the sense that late spectral typestars (V luminosity class) generally rotate faster than early types, inagreement with previously published results. This behaviour is, however,not obvious for the III-IV luminosity class stars. Nevertheless, thecalculated values of the ratio vt/vc of the truerotational velocity, vt, to the critical velocity forbreak-up, vc, is larger for late spectral type stars of allluminosity classes. Thus, late spectral type stars appear to rotatecloser to their break-up rotational velocity. The distribution of nearIR excesses for early spectral subgroups is bi-modal, the position ofthe second peak displaying a maximum value E(V-L)~ 1 . m 3for O-B1.5 stars, decreasing to E(V-L)~0. m8 for intermediatespectral types (B3-B5). It is shown that bi-modality disappears for latespectral types (B6-B9.5). No correlations were found betweenp* and near IR excesses and between E(V-L) and vsin i for thedifferent subgroups of Be stars. In contrast to near IR excesses, arelation between p* and far IR excesses at 12 mu m is clearlyseen. A clear relation between p* and vsin i (as well asbetween p* and /line{vsin i}/vc) is found by thefact that plots of these parameters are bounded by a ``triangular"distribution of p*: vsin i, with a decrease of p*towards very small and very large vsin i (and /line{vsini}/vc) values. The latter behaviour can be understood in thecontext of a larger oblateness of circumstellar disks for the stars witha rapid rotation. From the analysis of correlations between differentobservational parameters we conclude that circumstellar envelopes forthe majority of Be stars are optically thin disks with the range of thehalf-opening angle of 10degr
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| 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.
| A spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
| UBV photometry for southern OB stars
New UBV photometry of 1227 OB stars in the southern Milky Way ispresented. For 1113 of these stars, MK spectral types have been reportedpreviously in a comprehensive survey to B = 10.0 mag.
| Catalog of Luminous Stars in the Southern Coalsack Zone
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982RMxAA...5..183M&db_key=AST
| A Catalogue of Be-Stars
Not Available
| On the 4430 A interstellar band - A visual classification
A system of visual classification of the strength of the interstellarband 4430 A has been developed, based on spectra taken at spectralclassification dispersion. The intensity of the band was divided into 8main classes, defined by a group of selected standard stars. The systemwas applied to 1,111 southern OB stars contained in the catalog ofspectral types by Garrison, Hiltner, and Schild (1977). The mean errorin the classification was estimated to be plus or minus 1 class.Equivalent widths were measured for 100 stars; an excellent correlationwith the visual estimations was obtained. A calibration between thesetwo parameters is given.
| MK spectral classifications for southern OB stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977ApJS...35..111G&db_key=AST
| Observations of southern emission-line stars
A catalog of 1929 stars showing H-alpha emission on photographic platesis presented which covers the entire southern sky south of declination-25 deg to a red limiting magnitude of about 11.0. The catalog providesprevious designations of known emission-line stars equatorial (1900) andgalactic coordinates, visual and photographic magnitudes, H-alphaemission parameters, spectral types, and notes on unusual spectralfeatures. The objects listed include 16 M stars, 25 S stars, 37 carbonstars, 20 symbiotic stars, 40 confirmed or suspected T Tauri stars, 16novae, 14 planetary nebulae, 11 P Cygni stars, 9 Bep stars, 87 confirmedor suspected Wolf-Rayet stars, and 26 'peculiar' stars. Two new Tassociations are discovered, one in Lupus and one in Chamaeleon. Objectswith variations in continuum or H-alpha intensity are noted, and thedistribution by spectral type is analyzed. It is found that the skydistribution of these emission-line stars shows significantconcentrations in the region of the small Sagittarius cloud and in theCarina region.
| Spectral classification from infrared spectra of moderate dispersion.
Abstract image available at:http://adsabs.harvard.edu/abs/1974ApJ...189..463A
| A spectral survey of the southern Milky Way 1 : general description and catalogue 1 (l=306 -318 degrees).
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974A&AS...16..445S&db_key=AST
| H-alpha emission objects in two selected regions of the southern Milky Way (Cen & Nor).
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&A.....8..123V&db_key=AST
| Faint Halpha-emission objects in nebulosities surrounding the star m Cen.
Not Available
| Additional Stars whose Spectra have a Bright H α Line.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1950ApJ...112...72M&db_key=AST
| Catalogue and Bibliography of Stars of Classes B and a whose Spectra have Bright Hydrogen Lines
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1933ApJ....78...87M&db_key=AST
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