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Composition of the Interstellar Medium
We present an analysis of the FeII, GeII, MgI, MgII, SI, SII, SiII andZnII interstellar lines for 63 stars. Column density of MgII, SII, SiIIand ZnII is well correlated with distance. However, the column density-- distance relation should be used with care for the estimation of thedistance to OB stars. For stars with large f(H_2) this relation can leadto a large overestimation of the distance. The column densities of MgII,SiII and GeII (our largest samples of data) normalized to their totalhydrogen column densities decrease with interstellar reddening E(B-V) asexpected for elements that are incorporated into dust grains. The GeIIabundance (GeII/H) is lower in dense molecular clouds. The abundances ofall analyzed elements are generally lower than their Solar Systemvalues.
| The Origins and Evolutionary Status of B Stars Found Far from the Galactic Plane. I. Composition and Spectral Features
The existence of faint blue stars far above the Galactic plane that havespectra that are similar to nearby Population I B stars presents severalinteresting questions. Among them are the following: Can a Population IB star travel from the disk to a position many kiloparsecs above theplane in a relatively short main-sequence lifetime? Is it possible thatsingle massive star formation is occurring far from the Galactic plane?Are these objects something else masquerading as main-sequence B stars?This paper (the first of two) analyzes the abundances of a sample ofthese stars and reveals several that are chemically similar to nearbyPopulation I B stars, whereas others clearly have abundance patternsmore like those expected in blue horizontal-branch (BHB) orpost-asymptotic giant branch stars. Several of those with old evolvedstar abundances also have interesting features of note in their spectra.We also consider why this sample does not have any classical Be starsand identify at least two nearby solar-metallicity BHB stars.Based on observations made at the 2.1 m Otto Struve Telescope ofMcDonald Observatory operated by the University of Texas at Austin.
| Large-scale wind structures in OB supergiants: a search for rotationally modulated Hα variability
We present the results of a long-term monitoring campaign of theHα line in a sample of bright OB supergiants (O7.5-B9) which aimsat detecting rotationally modulated changes potentially related to theexistence of large-scale wind structures. A total of 22 objects weremonitored during 36 nights spread over six months in 2001-2002.Coordinated broad-band photometric observations were also obtained forsome targets. Conspicuous evidence for variability in Hα is foundfor the stars displaying a feature contaminated by wind emission. Mostchanges take place on a daily time-scale, although hourly variations arealso occasionally detected. Convincing evidence for a cyclical patternof variability in Hα has been found in two stars: HD 14134 and HD42087. Periodic signals are also detected in other stars, butindependent confirmation is required. Rotational modulation is suggestedfrom the similarity between the observed recurrence time-scales (in therange 13-25 d) and estimated periods of stellar rotation. We callattention to the atypical case of HD 14134, which exhibits a clear12.8-d periodicity, both in the photometric and in the spectroscopicdata sets. This places this object among a handful of early-type starswhere one may observe a clear link between extended wind structures andphotospheric disturbances. Further modelling may test the hypothesisthat azimuthally-extended wind streams are responsible for the patternsof spectral variability in our target stars.
| Interstellar Silicon Abundance
We present 34 measurements of silicon gas phase column densities in theinterstellar medium. We have used spectra containing the SiII 1808 Angline which were obtained with the Goddard High Resolution Spectrograph(GHRS) aboard the Hubble Space Telescope (HST). Extinction curveparameters are determined for analyzed lines of sight and relationbetween Si/H ratio and extinction parameters is discussed. We find theabundance of gas phase silicon in diffuse clouds to be lower than thesolar value by a factor of four.
| Highly Ionized Gas in the Galactic Halo: A FUSE Survey of O VI Absorption toward 22 Halo Stars
Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of 22 Galactichalo stars are studied to determine the amount of O VI in the Galactichalo between ~0.3 and ~10 kpc from the Galactic midplane. Strong O VIλ1031.93 absorption was detected toward 21 stars, and a reliable3 σ upper limit was obtained toward HD 97991. The weaker member ofthe O VI doublet at 1037.62 Å could be studied toward only sixstars because of stellar and interstellar blending problems. Themeasured logarithmic total column densities vary from 13.65 to 14.57with =14.17+/-0.28 (1 σ). The observed columns arereasonably consistent with a patchy exponential O VI distribution with amidplane density of 1.7×10-8 cm-3 and scaleheight between 2.3 and 4 kpc. We do not see clear signs of stronghigh-velocity components in O VI absorption along the Galactic sightlines, which indicates the general absence of high-velocity O VI within2-5 kpc of the Galactic midplane. This result is in marked contrast tothe findings of Sembach et al., who reported high-velocity O VIabsorption toward ~60% of the complete halo sight lines observed byFUSE. The line centroid velocities of the O VI absorption do not reflectGalactic rotation well. The O VI velocity dispersions range from 33 to78 km s-1, with an average of =45+/-11 kms-1 (1 σ). These values are much higher than the valueof ~18 km s-1 expected from thermal broadening for gas atT~3×105 K, the temperature at which O VI is expected toreach its peak abundance in collisional ionization equilibrium.Turbulence, inflow, and outflow must have an effect on the shape of theO VI profiles. Kinematical comparisons of O VI with Ar I reveal thateight of 21 sight lines are closely aligned in LSR velocity(|ΔVLSR|<=5 km s-1), while nine of 21exhibit significant velocity differences(|ΔVLSR|>=15 km s-1). This dual behaviormay indicate the presence of two different types of O VI-bearingenvironments toward the Galactic sight lines. The correlation betweenthe H I and O VI intermediate-velocity absorption is poor. We couldidentify the known H I intermediate-velocity components in the Ar Iabsorption but not in the O VI absorption in most cases. Comparison of OVI with other highly ionized species suggests that the high ions areproduced primarily by cooling hot gas in the Galactic fountain flow andthat turbulent mixing also has a significant contribution. The role ofturbulent mixing varies from negligible to dominant. It is mostimportant toward sight lines that sample supernova remnants like Loops Iand IV. The average N(C IV)/N(O VI) ratios for the nearby halo (thiswork) and complete halo (Savage et al.) are similar (~0.6), but thedispersion is larger in the sample of nearby halo sight lines. We areable to show that the O VI enhancement toward the Galactic center regionthat was observed in the FUSE survey of complete halo sight lines(Savage et al.) is likely associated with processes occurring near theGalactic center by comparing the observations toward the nearby HD177566 sight line to those toward extragalactic targets.
| Origins of the Highly Ionized Gas along the Line of Sight toward HD 116852
We present Hubble Space Telescope Imaging Spectrograph (HST/STIS) andFar Ultraviolet Spectroscopic Explorer (FUSE) observations of high ioninterstellar ultraviolet absorption along the sight line to HD 116852.At a distance of 4.8 kpc, HD 116852 is an O9 III star lying in the lowGalactic halo, -1.3 kpc from the plane of the Galaxy in the directionl=304.9d, b=-16.1d. The sight line passes underneath theSagittarius-Carina and the Norma-Centaurus spiral arms. The STIS E140Hgrating observations provide high-resolution (FWHM~2.7kms-1)spectra of the resonance doublets of Si IV, C IV, and N V. These dataare complemented by medium-resolution (FWHM~20kms-1) FUSEspectra of O VI. The integrated logarithmic column densities are logN(SiIV)=13.60+/-0.02, logN(C IV)=14.08+/-0.03, logN(NV)=13.34+0.05-0.06, and logN(O VI)=14.28+/-0.01.We find evidence for three distinct types of highly ionized gas presentin the data. First, two narrow absorption components are resolved in theSi IV and C IV profiles, at approximate LSR velocities of -36 and -10 kms-1 . These narrow components appear to be produced in gasassociated with the Norma and Sagittarius spiral arms, at approximatez-distances of -1.0 and -0.5 kpc, respectively. The temperature of thegas in these narrow components, as implied by their b-values, suggeststhat the gas is photoionized. The ratio of C IV to Si IV in these narrowcomponents is low compared to the Galactic average. Second, we detect anintermediate-width component in C IV and Si IV, at 17 km s-1,which we propose could arise at the conductive interface at the boundarybetween a low column density neutral or weakly ionized cloud and thesurrounding hot medium. Finally, a broad collisionally ionized componentof gas responsible for producing the smooth N V and O VI profiles isobserved; such absorption is also present to a lesser degree in theprofiles of Si IV and C IV. The broad O VI absorption is observed at avelocity displaced from the broad C IV component by almost 20 kms-1, an amount large enough to suggest that the two ions maynot coexist in the same physical location. If these two ions do existtogether, then the ratio N(C IV)/N(O VI) is too low to be consistentwith turbulent mixing layer models, but could be explained by radiativecooling or conductive heating models. Combining our results with highresolution observations of four other sight lines from the literature,we find an average C IV component frequency of1.0+/-0.25kpc-1.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| Far Ultraviolet Spectroscopic Explorer Observations of O VI Overlying the Scutum Supershell
We present Far Ultraviolet Spectroscopic Explorer observations of the B0III star HD 177989 (l=17.8d, b=-11.9d, d=4.9 kpc). This line of sightpasses through the high-latitude outflow from the Scutum supershell (GS018-04+44), a structure that lies at a kinematic distance of ~3.5 kpcand spans ~5° in diameter. The O VI λ1031.93 line is comparedwith Space Telescope Imaging Spectrograph (STIS) observations of Si IV,C IV, and N V to examine the ionizing mechanisms responsible forproducing the high ion absorption, as well as to study the processes bywhich gas is expelled into the halo. The O VI profile spans a similarvelocity range as the other highly ionized atoms, from -70 to +80 kms-1. Component fits reveal very broad absorption at thekinematic velocity of the Scutum shell, which differs from the narrow SiIV, C IV, and N V components, suggesting that these other species occupya more confined region. It is possible that the O VI is present in hotgas from the shell interior that is diffusing into the high-latituderegion above it. The column densities in the Scutum supershell componentare N(SiIV)=(3.59+/-0.09)×1013,N(CIV)=(1.78+/-0.04)×1014,N(NV)=(8.89+/-0.79)×1012, and N(OVI)=(7.76+/-0.75)×1013 cm-2. The correspondingcolumn density ratios of N(CIV)/N(SiIV)=4.96+/-0.17,N(CIV)/N(NV)=20.0+/-1.8, and N(CIV)/N(OVI)=2.29+/-0.23 show that whilethe C IV and Si IV columns are amplified in this region, the enhancementis not reflected in N V or O VI. We suggest that such ionic ratios andcolumn densities could be produced by ~150-200 turbulent mixing layerslying in a fragmented medium above the polar cap of the superbubble. Wenote through a sight-line comparison that although these absorptioncharacteristics are similar to those near the center of Radio Loops Iand IV, they differ considerably from those near the edges of the loops.It is apparent that the traits of high ion absorption in a supershell,as well as the ionizing mechanisms responsible, can vary among sightlines through the shell.
| STIS and GHRS Observations of Warm and Hot Gas Overlying the Scutum Supershell (GS 018-04+44)
We present Space Telescope Imaging Spectrograph (STIS) and Goddard HighResolution Spectrograph (GHRS) observations of interstellar UVabsorption toward HD 177989, a B0 III star at 4.9 kpc in the directionl=17.8d, b=-11.9d. The line of sight passes through the high-latitudeejecta of the Scutum supershell (GS 018-06+44), which is ~5° indiameter extending ~7° below the Galactic plane at a kinematicdistance of ~3.5 kpc in the Scutum spiral arm. The observations with theSTIS E140H and GHRS echelle B gratings provide far- and middle-UVspectra at resolutions (FWHM) of ~3 km s-1 and asignal-to-noise ratio (S/N) of ~20:1 to 50:1. The observations revealstrong and broad absorption in the lines of Si IV and C IV centered onLSR velocities of +18 and +42 km s-1 and weaker absorptionfrom these ions near -50 and -13 km s-1. Weak absorption by NV extends over the full velocity range traced by Si IV and C IV. The +18km s-1 high-ionization absorption likely occurs in gas ~400pc below the Sagittarius spiral arm, while the extremely strong +42 kms-1 absorption occurs in highly ionized gas in the Scutumsupershell at a distance of ~700 pc below the Galactic plane. Theproperties of the highly ionized gas associated with the Scutumsupershell are similar to the gas found in radio loops I and IV; in bothcases there is a strong enhancement in the column density of C IVwithout a corresponding increase in the column density of N V, whichcauses N(C IV)/N(N V) to be among the largest measured in theinterstellar medium. The low-ionization absorption lines of N I, S II,Si II, and Fe II produce narrow absorption features at +37, +40 kms-1 and +55, +60 km s-1. The strength andkinematic properties of these absorption features bear no resemblance tothose expected for the high-latitude neutral cloud seen in the H I 21 cmline. This may be due to the relatively low angular resolution (FWHM~21') of the 21 cm observations. The kinematic relationships among thehigh-ionization and low-ionization absorption lines observed in the UVsuggest a related origin in a hot-warm gas interface region. We arepossibly seeing the warm gas in the swept-up shell surrounding a regionwhere hot gas is being vented into the halo. In the warm gas, N(N I)/N(SII) ~0.01 solar, which implies a similar value forN(H0)/[N(H0)+N(H+)]. The warm neutraland ionized gas in the matter overlying the Scutum supershell has valuesof Si /S and Fe /S roughly similar to those found in the warm neutralmedium of the Galactic disk in the vicinity of the Sun. While there hasbeen grain processing in the ejecta of the Scutum supershell, theprocessing has not been complete. Based on observations of interstellarC IV and Si IV at high S/N and high resolution toward four very distantstars, we determine that highly ionized gas absorption components occurat a frequency of ~1 component kpc-1. The strongestcomponents are associated with lines of sight that pass over or underspiral arms or that pass though Galactic supershells. Based onobservations obtained with the Space Telescope Imaging Spectrograph andthe Goddard High Resolution Spectrograph on the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555.
| Observational Evidence of Supershell Blowout in GS 018-04+44: The Scutum Supershell
Emission in the H I 21 cm line has been mapped for a region of theGalaxy that includes two known supershells, GS 018-04+44 and GS034-06+65. We focus on the GS 018-04+44, hereafter referred to as theScutum Supershell, which is an elongated shell about 5 deg in diameterextending to -7 deg below the Galactic plane. The Scutum shell lies at akinematic distance of ~3300 pc, implying a shell diameter of ~290 pcwith a vertical extension of ~400 pc away from the Galactic plane. TheScutum shell contains 6.2x105 Msolar swept intothe walls. We observe that the top of the shell is missing, and asubstantial column of H I rises from the shell walls tob=-11deg, culminating in a large cloud of neutral hydrogen,3.74x104 Msolar, located ~630 pc from the plane.ROSAT data show X-ray emission that closely anticorrelates with the 21cm emission. This emission probably originates from hot gas within theScutum Supershell. After approximately correcting for the foregroundabsorption, we find that the 1.5 keV X-rays peak at the base of theshell, the 0.75 keV emission peaks in the interior and at the top of theshell, and the 0.25 keV emission extends to high latitudes above theshell. The X-ray luminosity is roughly ~5x1036 ergss-1. The Wisconsin Hα Mapper (WHAM) survey shows thepresence of Hα emission that exhibits a morphology similar to thatof the H I. Spectra indicate the presence of ionized hydrogen atvelocities similar to the H I, placing ionized material at the samekinematic distance as the neutral material. IRAS images in the 60 and100 μm wavebands reveal the presence of dust correlated with theneutral hydrogen. Infrared surface brightness indicates an excess in the100 μm emission, which could indicate a molecular hydrogen componentwith a column density of 2.4x1021 cm-2 in thedensest regions of the high-latitude cloud of neutral hydrogen. IUEultraviolet high dispersion spectra of HD 177989 (l=17.89d, b=-11.88d)and HD 175754 (l=16.40d, b=-9.92d) reveal the presence of very strongabsorption by highly ionized gas at a velocity that associates theabsorption with the ejecta of the Scutum Supershell. In the case of HD177989, the high ion column density ratios suggest an origin in aturbulent mixing layer where hot and cool gases mix in the presence ofshear flows. The Hα and X-ray emission suggest that a multitude ofenergetic phenomena exist in this region, providing the necessaryionizing radiation. Indeed, there are multiple supernova remnants, H IIregions, and hot stars, which could all contribute sizeable amounts ofenergy and ionizing radiation. The combination of these data setsindicates observational evidence of a ``blowout'' phenomena whereby hotmaterial produced within the Scutum Supershell has blown through the topof the shell and been pushed to high latitude. Based on observationsfrom the Green Bank 43m radio telescope, the ROSAT All-Sky Survey, theWHAM All-Sky Survey, IRAS, and IUE.
| Interstellar Carbon Abundance
We present 10 new measurements of carbon gas phase column density in theinterstellar medium. We have used spectra made with the Goddard HighResolution Spectrograph aboard the Hubble Space Telescope containing theCII 1334.5 Ang and CII* 1335.7 Ang lines. The continuum reconstructionmethod has been used to obtain the carbon column density from theLorentzian damped lines. Extinction curve parameters are determined inselected directions and relation between C/H ratio and extinctionparameters is discussed. A correlation has been found between C/H andthe strength of the 2175 Ang bump. Unlike previous results, we noticethat C/H changes with fractional abundance of molecular hydrogen,f(H_2). The average value of C/H=3.55*10^{-4} for lines of sight withf(H_2)<1*10^{-3} is the same as solar photospheric abundance fromGrevese and Noels (1993) and may represent the real cosmic carbonabundance.
| 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
| Echelle Spectroscopy of Interstellar Absorption toward MU Columbae with the Goddard High Resolution Spectrograph
Goddard High Resolution Spectrograph echelle-mode observations of theinterstellar absorption lines of Mg II, Si IV, C IV, and N V toward muColumbae (HD 38666) are presented. The observations have a spectralresolution of 3.5 km s^-1 and signal-to-noise ratios (S/Ns) of 20-200.The mu Col sight line (l=237.3d, b=-27.1d, d=0.40 kpc, z=-0.18 kpc)extends though the Local Bubble and the warm neutral, warm ionized, andhot ionized phases of the interstellar medium (ISM). The high-ionizationcolumn densities toward mu Col are log N(Si IV)=12.16+/-0.05, log N(CIV)=12.88+/-0.02, and logN(N V)=11.8-12.3. Profile fits to Copernicussatellite measures of O VI absorption toward mu Col yield log N(OVI)=13.82+/-0.01 and b=38.7 km s^-1. This implies N(C IV)/N(OVI)=0.11+/-0.01, which is typical of the values found for the hot ISM ofthe Galactic disk. The O VI profile is twice as broad as the C IV and NV profiles, even though these species have roughly similar averagevelocities. Some of the C IV, N V, and O VI absorption toward mu Col mayoccur at the interface of the Local Cloud and Local Bubble, althoughadditional contributions to these ions probably also occur in moredistant gas along the sight line. A substantial part of the Si IVabsorption likely arises in warm photoionized gas in an H II regionsurrounding mu Col. The profile width differences among thehigh-ionization lines of C IV, N V, and O VI could be produced if theline of sight passes through a highly evolved supernova remnant. Theobservations for mu Col and for other stars observed at high resolutionwith the GHRS reveal that multiple gas types (warm and hot) contributeto the absorption by the highly ionized atoms along both nearby anddistant sight lines. Disentangling the relative contributions from thedifferent gas types requires high-resolution and high-S/N observations.The Mg II observations, combined with a solar Mg reference abundance,imply that the Mg depletion toward mu Col is -0.31 dex. As observed forother sight lines through the warm neutral medium, the gas-phaseobservations of Mg, when combined with results for Fe and Si, suggestthat Mg and Fe are more deficient from the gas phase than one wouldexpect if these elements are only contained in silicate dust grains.
| The interstellar clouds of ADAMS and Blaauw revisited: an HI absorption study - II.
Not Available
| The interstellar clouds of ADAMS and Blaauw revisited: an HI absorption study - I.
Not Available
| The Edinburgh-Cape Blue Object Survey - II. Zone 1 - the North Galactic CAP
Results for Zone 1 of the Edinburgh-Cape (EC) Blue Object Survey arepresented. This zone covers that part of the North Galactic Cap morethan ~30 deg from the Galactic plane and south of about -12^ deg_.3declination (although a few fields north of this declination areincluded). The zone effectively complements the Palomar-Green Survey inthe North Galactic Cap, although the EC Survey should be more completeto a fainter limit (B=16.5 mag) and to somewhat redder stars (U-B bluerthan about -0.4). Zone 1 covers approximately 1560 deg^2 and contains675 blue objects for which we list equatorial coordinates accurate to ~1arcsec, UBV photoelectric photometry, and spectral types determined frommoderate-dispersion (100 A mm^-1) spectrograms.
| 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
| 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.
| Cross-correlation characteristics of OB stars from IUE spectroscopy
We present a catalogue of homogeneous measures of the linewidthparameter, v_esin i, for 373 O-type stars and early B supergiants(including the separate components of 25 binary and three triplesystems), produced by cross-correlating high-resolution,short-wavelength IUE spectra against a `template' spectrum of tauSco. Wealso tabulate terminal velocities. There are no O supergiants in oursample with v_esin i<65 km s^-1, and only one supergiant earlier thanB5 has v_esin i<50 km s^-1, confirming that an important linebroadening mechanism in addition to rotation must be present in theseobjects. A calibration of the area under the cross-correlation peakagainst spectral type is used to obtain estimates of continuum intensityratios of the components in 28 spectroscopically binary or multiplesystems. At least seven SB2 systems show evidence for the `Struve-Sahadeeffect', a systematic variation in relative line strength as a functionof orbital phase. The stellar wind profiles of the most rapid rotator inour sample, the O9III:n* star HD 191423 (v_esin i=436km s^-1), show itto have a `wind-compressed disc' similar to that of HD 93521; this starand other rapid rotators are good candidates for studies of non-radialpulsation.
| Coronal Gas in the Halo. II. ORFEUS Observations of Galactic Halo Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...465..296H&db_key=AST
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Apparently normal, high-latitude B stars from the Edinburgh-Cape survey - II
Low-dispersion spectrograms and UBV photometry are used to carry out asimple analysis of a second sample of apparently normal, high galacticlatitude B stars detected in the Edinburgh-Cape faint blue objectsurvey. The sample is bigger than that in Paper I and contains morefaint stars. Of the 30 stars, eight are classified as `weak-line' starsand appear very similar to stars in the blue horizontal branch ofglobular clusters. A further eight stars are sdB stars (including twopossible binaries), and 11 stars appear to be normal B stars. Nine ofthese have distances from the Galactic plane in the approximate range1<=z<=4 kpc, and two are probably much moredistant. These results, and those of Paper I, indicate that B stars atlarge distances from the Galactic plane (z<~5kpc) must be very rare. Three stars do not fall into obvious categories;two of them are helium-rich and all may be hot subdwarfs.
| Properties of the highly ionized disk and halo gas toward two distant high-latitude stars
Goddard High Resolution Spectrograph (GHRS) intermediate -resolutionobservations of S III, Si III, Al III, Si IV, C IV, and N V absorptionalong the sight lines to HD 18100 (l = 217.9 deg, b = -62.7, d = 3.1kpc, z = -2.8 kpc) and HD 100340 (l = 258.9 deg, b = +61.2 deg, d = 5.3kpc, z = 4.6 kpc) are presented. These small science aperture spectrahave resolutions ranging from 11 to 20 km/s full width at half maximum(FWHM) and S/N from 30 to 65 per diode substep. Strong absorption bymoderately and highly ionized gas is seen in each direction. Theabsorption in the direction of the south Galactic polar region (HD18100) is kinematically simple, while the absorption in the direction ofnorth Galactic polar region (HD 100304) is kinematically complex. Ineach case the absorption by the highly ionized gas lies within thevelocity range of absorption by neutral and weakly ionized gas. Alongeach sight line, the velocity dispersion determined from the unsaturatedabsorption lines increases with the energy required to create each ion.The logarithmic column densities for Al III, Si IV, C IV, and N V arelog N(atoms/sq cm = 12.71, 13.10, 13.58, and 12.75 toward HD 18100 andlog N = 12.88, 13.31, 13.83, and 13.04 toward HD 100340. Average ionicratios among these species are very similar along the two sight lines.Differences in profile shape between the absorption for AL II, Si IV, CIV, and N V provide additional support for the claim of Savage, Sembach,& Cardelli (1994) that there exists two types of highly ionized gasin the interstellar medium. One type of highly ionized gas isresponsible for the structured Si IV absorption and part of the C IVabsorption. In this gas N(C IV)/N(Si IV) approximately 3.0 and N(CIV)/N(N V) greater than 6. The absorption by this gas seems to beassociated with some type of self-regulating interface or mixing layerbetween the warm and hot interstellar medium. The other type of highlyionized gas is responsible for most of the N V absorption, part of the CIV absorption, and has very little associated Si IV absorption. In thisgas N(C IV)/N(N V) is approximately 1 to 3. This gas is hot (T greaterthan 2 x 105 K) and may be tracing the cooling gas ofsupernova (SN) bubbles or a Galactic fountain. The relative mixture ofthese two types of highly ionized gas varies from one sight line to thenext. The two sight lines in this study sample halo gas in the solarneighborhood and have a smaller percentage of the more highly ionizedgas than inner Galaxy sight lines.
| Abundance analysis of the hot post-AGB star Barnard 29.
We present a model atmosphere analysis for the relatively bright (V~13)globular cluster post-AGB star, Barnard 29, using IUE and highresolution (0.06A FWHM) optical spectra. The derived atmosphericparameters are T_eff_=20000+/-1000K and logg=3.0+/-0.1dex, which imply acurrent mass of ~0.55Msun_. The chemical composition providesimportant constraints on the post-AGB evolutionary stage. We find anoverall metal deficiency of 1.46+/-0.11dex, which is compatible with themean [Fe/H] obtained from previous M13 studies. The most interestingfeature is the severe carbon deficiency of more than 2.0dex which hasalso been observed in a number of high latitude B-type low gravitystars. Hence the present results supports the recent classification ofthese objects as hot post-AGB stars. Relative to the overallmetallicity, the observed carbon deficiency of Barnard 29 coupled with asignificant nitrogen overabundance indicates that this star has left theAGB before the third dredge-up has occurred. The implications for AGBand post-AGB evolution are briefly discussed.
| An IUE survey of interstellar H I LY alpha absorption. 1: Column densities
We measure Galactic interstellar neutral hydrogen column densities byanalyzing archival interstellar Ly alpha absorption line data toward 554B2 and hotter stars observed at high resolution with the IUE satellite.This study more than doubles the number of lines of sight with measuresof N(H I) based on Ly alpha. We have included the scattered lightbackground correction algorithm of Bianchi and Bohlin in our datareduction. We use the correlation between the Balmer discontinuity(c1) index and the stellar Ly alpha absorption in order toassess the effects of stellar Ly alpha contamination. Approximately 40%of the B stars with measured (c1) index, exhibit seriousstellar Ly alpha contamination. One table contains the derived values ofthe interstellar N(H I) for 393 stars with at most small amounts ofstellar contamination. Another lists the observed values of total N(H I)for 161 stars with suspected stellar Ly alpha contamination and/oruncertain stellar parameters.
| IUE observations of highly ionized gas toward distant stars in the Milky Way
Combined high-dispersion IUE spectra of interstellar Si IV, C IV, and NV absorption along distant sight lines toward early-type stars in theGalactic disk and low halo are discussed. The highly ionized specieshave complex profiles and exhibit stronger absorption toward distantlow-latitude stars than toward high-latitude stars. Absorption alonglow-latitude directions is often broadened substantially by Galacticrotation. Along these sight lines the Si IV, C IV, and N V profiles aremore similar in shape to each other than to those of Al III, which is atracer of photoionized interstellar gas. The observed column densityratios of the high ions are similar in widely different regions withinthe Galaxy. The similarities in the high ion profile shapes alongindividual sight lines and integrated column density ratios alongdifferent sight lines suggest a common origin for these species incollisionally ionized gas associated with a global process such as aGalactic fountain.
| A high-resolution optical and radio study of Milky Way halo gas
Optical interstellar absorption lines of Ti II and Ca II and the 21 cmemission line of H I were observed at high-resolution (6 and 1 km/s,respectively) and high detection sensitivity along 25 lines of sight inthe Galactic halo. The sample includes 16 distant halo stars matchedwith one or more nearly aligned foreground stars as well as local starsalong five extragalactic sight lines. The data show substantialinterstellar material, at both low and intermediate velocities, between250 and 1000 pc beyond the Galactic plane. As much as one-third of thetotal gas observed in Ca II absorption may be beyond 1 kpc, and thegaseous Ti II may lie in an even thicker layer. The directly determinedgaseous Ti abundance above the Galactic plane exceeds that in the disk,on the average, by a factor of 4 to 6 and, for individual cloudcomponents, is further enhanced at higher LSR velocity. Thirty threediscrete high-latitude clouds are detected in Ca II absorption, and 17discrete clouds, including three high-velocity clouds, are identified inH I emission. The kinematics of the high-latitude gas observed in Ti IIand Ca II absorption is characterized by significant peculiar velocitieswith respect to a model corotating halo.
| Infrared Observations of Possible Hot Post-Asymptotic Giant Branch Stars
Abstract image available at:http://adsabs.harvard.edu/abs/1993A&A...272..243C
| Observations of highly ionized gas in the Galactic halo
A sample of high-quality sight lines is studied by means of IUE spectrato study the formation of Si IV, C IV, and N V in the Galaxy andconstrain the mechanisms of halo gas formation. High-dispersion IUEspectra are taken for 12 objects to give combined spectra for studyingthe halo gas along the sight lines. N V absorption is reported in 10 ofthe sightlines suggesting that hot collisionally ionized gas dominatesthe Galactic halo. Analyses are conducted to derive the Doppler-spreadparameters of the Si IV, C IV, and N V components that are theorized todominate the collisionally ionized gas. The observed column-densityratios of the high ions are given and shown to be generally constantthroughout the Galaxy with no variation according to the distance of theabsorbing gas from the Galactic plane. Existing photoionization andcollisional models cannot simultaneously predict the column densitiesand ratios of Si IV, C IV, and N V. It is concluded that theimplementation of self-ionization and other mechanisms could make themodels more effective.
| Ultraviolet and radio observations of Milky Way halo gas
Interstellar-absorption-line and 21-cm emission-line data for sightlines to 56 stars are combined in order to study the kinematics andspatial distribution of the gas that is at great distances from theGalactic plane. Measurements of the interstellar velocities and H Icolumn densities from the 21-cm emission and Ly-alpha absorption areincluded. The problem of contamination of the interstellar Ly-alphaabsorption line by stellar Ly-alpha absorption is analyzed, and thisinformation is used to reevaluate the vertical distribution of H I. Anew method for determining lower limits on the vertical distribution ofgas by including information on the velocity structure in the gas ispresented. The data for individual sight lines are discussed.
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | בתולה |
| התרוממות ימנית: | 13h44m31.31s |
| סירוב: | -17°56'13.2" |
| גודל גלוי: | 7.507 |
| מרחק: | 1298.701 פארסק |
| תנועה נכונה: | -13 |
| תנועה נכונה: | 3 |
| B-T magnitude: | 7.405 |
| V-T magnitude: | 7.499 |
קטלוגים וכינוים:
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