Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
Observations towards early-type stars in the ESO-POP Survey - II. Searches for intermediate- and high-velocity clouds
We present CaII K and TiII optical spectra of early-type stars takenmainly from the ultraviolet and visual echelle spectrograph (UVES)Paranal Observatory Project, plus HI 21-cm spectra, from the Vila-Elisaand Leiden-Dwingeloo Surveys, which are employed to obtain distances tointermediate- and high-velocity clouds (IHVCs). HI emission at avelocity of -117 kms-1 towards the sightline HD30677 () withcolumn density ~1.7 × 1019 cm-2 has nocorresponding CaII K absorption in the UVES spectrum, which has asignal-to-noise ratio (S/N) of 610 per resolution element. The star hasa spectroscopically determined distance of 2.7 kpc, and hence sets thisas a firm lower distance limit towards Anti-Centre cloud ACII. Towardsanother sightline (HD46185 with ), HI at a velocity of +122kms-1 and column density of 1.2 × 1019cm-2 is seen. The corresponding CaII K spectrum has a S/N of780, although no absorption is observed at the cloud velocity. Thissimilarly places a firm lower distance limit of 2.9 kpc towards thisparcel of gas that may be an intermediate-velocity (IV) cloud. The lackof IV CaII absorption towards HD196426 () at a S/N of 500 reinforces alower distance limit of ~700 pc towards this part of complex gp, wherethe HI column density is 1.1 × 1019 cm-2 andvelocity is +78 kms-1. Additionally, no IV CaII is seen inabsorption in the spectrum of HD19445, which is strong in HI with acolumn density of 8 × 1019 cm-2 at avelocity of ~ -42 kms-1, placing a firm althoughuninteresting lower distance limit of 39 pc to this part of IV South.Finally, no high-velocity CaII K absorption is seen towards HD115363 ()at a S/N of 410, placing a lower distance of ~3.2 kpc towards the HVCgas at velocity of ~ +224 kms-1 and HI column density of 5.2× 1019 cm-2. This gas is in the same regionof the sky as complex WE (Wakker 2001), but at higher velocities. Thenon-detection of CaII K absorption sets a lower distance of ~3.2 kpctowards the HVC, which is unsurprising if this feature is indeed relatedto the Magellanic System.
| Effects of Metallicity on the Rotational Velocities of Massive Stars
Recent theoretical predictions for low-metallicity massive stars predictthat these stars should have drastically reduced equatorial winds (massloss) while on the main sequence, and so should retain most of theirangular momentum. Observations of both the Be/(B+Be) ratio and theblue-to-red supergiant ratio appear to have a metallicity dependencethat may be caused by high rotational velocities. We have analyzed 39archival Hubble Space Telescope Imaging Spectrograph (STIS),high-resolution, ultraviolet spectra of O-type stars in the MagellanicClouds to determine their projected rotational velocities Vsini. Ourmethodology is based on a previous study of the projected rotationalvelocities of Galactic O-type stars using International UltravioletExplorer (IUE) short-wavelength prime (SWP) camera high-dispersionspectra, which resulted in a catalog of Vsini values for 177 O-typestars. Here we present complementary Vsini values for 21 LargeMagellanic Cloud and 22 Small Magellanic Cloud O-type stars based onSTIS and IUE UV spectroscopy. The distribution of Vsini values forO-type stars in the Magellanic Clouds is compared to that of GalacticO-type stars. Despite the theoretical predictions and indirectobservational evidence for high rotation, the O-type stars in theMagellanic Clouds do not appear to rotate faster than their Galacticcounterparts.
| New Runaway O-stars Based on Data from HIPPARCOS
12 new runaway O-stars are identified using an analysis of their propermotions based on data from HIPPARCOS. The peculiar tangential and totaltransverse velocities of these stars are determined. A list of theobserved runaway stars is given.
| 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.
| Inferring Physical Conditions in Interstellar Clouds of H2
We have developed a code that models the formation, destruction,radiative transfer, and vibrational/rotational excitation ofH2 in a detailed fashion. We discuss generally how suchcodes, together with Far Ultraviolet Spectrographic Explorer (FUSE)observations of H2 in diffuse and translucent lines of sight,may be used to infer various physical parameters. We illustrate theeffects of changes in the major physical parameters (UV radiation field,gas density, metallicity), and we point out the extent to which changesin one parameter may be mirrored by changes in another. We provide ananalytic formula for the molecular fraction, fH2,as a function of cloud column density, radiation fields, and grainformation rate of H2. Some diffuse and translucent lines ofsight may be concatenations of multiple distinct clouds viewed together.Such situations can give rise to observables that agree with the data,complicating the problem of uniquely identifying one set of physicalparameters with a line of sight. Finally, we illustrate the applicationof our code to an ensemble of data, such as our FUSE survey ofH2 in the Large and Small Magellanic Clouds, in order toconstrain the elevated UV radiation field intensity and reduced grainformation rate of H2 in those low-metallicity environments.
| Distances and Metallicities of High- and Intermediate-Velocity Clouds
A table is presented that summarizes published absorption linemeasurements for the high- and intermediate-velocity clouds (HVCs andIVCs). New values are derived for N(H I) in the direction of observedprobes, in order to arrive at reliable abundances and abundance limits(the H I data are described in Paper II). Distances to stellar probesare revisited and calculated consistently, in order to derive distancebrackets or limits for many of the clouds, taking care to properlyinterpret nondetections. The main conclusions are the following. (1)Absolute abundances have been measured using lines of S II, N I, and OI, with the following resulting values: ~0.1 solar for one HVC (complexC), ~0.3 solar for the Magellanic Stream, ~0.5 solar for a southern IVC,and ~solar for two northern IVCs (the IV Arch and LLIV Arch). Finally,approximate values in the range 0.5-2 solar are found for three moreIVCs. (2) Depletion patterns in IVCs are like those in warm disk or halogas. (3) Most distance limits are based on strong UV lines of C II, SiII, and Mg II, a few on Ca II. Distance limits for major HVCs aregreater than 5 kpc, while distance brackets for several IVCs are in therange 0.5-2 kpc. (4) Mass limits for major IVCs are0.5-8×105 Msolar, but for major HVCs theyare more than 106 Msolar. (5) The Ca II/H I ratiovaries by up to a factor 2-5 within a single cloud, somewhat morebetween clouds. (6) The Na I/H I ratio varies by a factor of more than10 within a cloud, and even more between clouds. Thus, Ca II can beuseful for determining both lower and upper distance limits, but Na Ionly yields upper limits.
| GHRS and ORFEUS II Observations of the Highly Ionized Interstellar Medium toward ESO 141-055
We present Goddard High Resolution Spectrograph (GHRS) and ORFEUS IImeasurements of Si IV, C IV, N V, and O VI absorption in theinterstellar medium of the Galactic disk and halo toward the nucleus ofthe Seyfert galaxy ESO 141-055. The high-ionization absorption isstrong, with line strengths consistent with the spectral signatureexpected for hot (T>~10^5 K) collisionally ionized gas in either a``Galactic fountain'' or an inhomogeneous medium containing a mixture ofconductive interfaces and turbulent mixing layers. The total O VI columndensity of ~10^15 cm^-2 suggests that the scale height of O VI is large(>~3 kpc) in this direction. Models of the C IV velocity distributionalong the sight line are consistent with a large scale height for thehighly ionized gas. Comparison of the high ion column densities withmeasurements for other sight lines indicates that the highly ionized gasdistribution is patchy. The amount of O VI perpendicular to the Galacticplane varies by at least a factor of ~4 among the complete halo sightlines thus far studied. In addition to the high ion absorption, lines oflow-ionization species are also present in the spectra. With thepossible exception of Ar I, which may have a lower than expectedabundance resulting from partial photoionization of gas along the sightline, the absorption strengths are typical of those expected for thewarm, neutral interstellar medium. The sight line intercepts a coldmolecular cloud with N(H_2)~10^19 cm^-2. The cloud has an identifiablecounterpart in IRAS 100 μm emission maps of this region of the sky.We detect a Lyα absorber associated with ESO 141-055 at z=0.03492.This study presents an enticing glimpse into the interstellar andintergalactic absorption patterns that will be observed at high spectralresolution by the Far Ultraviolet Spectroscopic Explorer.
| Highly Ionized High-Velocity Clouds: Intergalactic Gas in the Local Group or Distant Gas in the Galactic Halo?
In the course of our studies of the gaseous halo surrounding the MilkyWay, we have recently identified several high-velocity clouds (HVCs;V_LSR<-100 km s^-1) in the directions of Mrk 509 and PKS 2155-304that have unusual ionization properties. The clouds exhibit strong C IVabsorption with little or no detectable low ion (C II, Si II) absorptionor H I 21 cm emission down to very sensitive levels. As the closestknown analog to the outer diffuse halos of damped Lyalpha absorbers andthe low H I column density metal-line absorption systems seen in thespectra of high-redshift quasars, these ``C IV HVCs'' present uniqueopportunities for relating the conditions within the Milky Way halo andnearby intergalactic gas to the properties of galactic halos at higherredshift. In this paper we present new Goddard High ResolutionSpectrograph (GHRS) intermediate-resolution measurements of theabsorption lines within these C IV HVCs and study the ionizationproperties of the gas in detail. The present data represent the mostcomplete set of measurements available for studying the ionizationconditions within HVCs. The C IV HVCs have ionization propertiesconsistent with photoionization by extragalactic background radiation,although some contribution by collisional ionization within a hot plasmacannot be ruled out. The clouds are probably low density (n_H~10^-4cm^-3), large (greater than several kiloparsecs), and mostly ionized(n_H i/n_H~10^-3) regions located well beyond the neutral gas layer ofthe Galaxy. The presence of weak H I HVCs detected through their 21 cmemission near both sight lines indicates that the C IV HVCs trace theextended, ionized, low-density regions of the H I HVCs. Several lines ofevidence, including very low thermal pressures (P/k ~2 cm^-3 K), favor alocation for the C IV HVCs in the Local Group or very distant Galactichalo. If the clouds are intergalactic in nature, their metallicitiescould be [Z/H]~-1 or lower, but higher metallicities [Z/H]>-1 arefavored if the clouds are located in the distant Galactic halo since thecloud sizes scale inversely with metallicity. We provide a summary ofthe HVCs detected in absorption at intermediate resolution with the GHRSand the IUE satellite and find that C IV HVCs are detected along threeof 10 extragalactic sight lines down to a level of logN(C iv)~13.3 (3sigma).
| 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.
| Projected Rotational Velocities of O-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...463..737P&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.
| Discovery of Highly Ionized High-Velocity Clouds toward Markarian 509
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...451..616S&db_key=AST
| An Extension of the Case-Hamburg OB Star Surveys
We have extended the Case-Hamburg OB star surveys to b = +- 30 degreesfor l = +- 60 degres using the Curtis Schmidt telescope and 4 degreeobjective prism at the Cerro Tololo Inter-American Observatory. Acatalog of 234 OB stars and other objects with peculiar spectra ispresented along with finding charts for those objects too faint to beincluded on the BD or CD charts. (SECTION: Stars)
| Probing the galactic disk and halo. 2: Hot interstellar gas toward the inner galaxy star HD 156359
We present Goddard High Resolution Spectrograph intermediate-resolutionmeasurements of the 1233-1256 A spectral region of HD 156396, a halostar at l = 328.7 deg, b = -14.5 deg in the inner Galaxy with a line-ofsight distance of 11.1 kpc and a z-distance of -2.8 kpc. The data have aresolution of 18 km/s Full Width at Half Maximum (FWHM) and asignal-to-noise ratio of approximately 50:1. We detect interstellarlines of Mg II, S II, S II, Ge II, and N V and determine log N/(Mg II) =15.78 +0.25, -0.27, log N(Si II) greater than 13.70, log N(S II) greaterthan 15.76, log N(Ge II) = 12.20 +0.09,-0.11, and log N(N v) = 14.06 +/-0.02. Assuming solar reference abundances, the diffuse clouds containingMg, S, and Ge along the sight line have average logarithmic depletionsD(Mg) = -0.6 +/- 0.3 dex, D(S) greater than -0.2 dex, and D(Ge) = -0.2+/- 0.2 dex. The Mg and Ge depletions are approximately 2 times smallerthan is typical of diffuse clouds in the solar vicinity. Galacticrotational modeling of the N v profiles indicates that the highlyionized gas traced by this ion has a scale height of approximately 1 kpcif gas at large z-distances corotates with the underlying disk gas.Rotational modeling of the Si iv and C iv profiles measured by the IUEsatellite yields similar scale height estimates. The scale heightresults contrast with previous studies of highly ionized gas in theouter Milky Way that reveal a more extended gas distribtion with happroximately equals 3-4 kpc. We detect a high-velocity feature in N vand Si II vLSR approximately equals + 125 km/s) that isprobably created in an interface between warm and hot gas.
| 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.
| Gas kinematics and ionization along the extended sight line to HD 116852
We present Goddard High-Resolution Spectrograph intermediateobservations of the interstellar medium toward HD 116852, a low halostar at a distance of 4.8 kpc (z = -1.3 kpc) in the direction l = 304.deg 9, b = 16.deg 1. The small science aperture observations havesignal-to-noise ratios ranging from 30 to 90 and resolutions of 11 to 18km/s (FWHM). We confirm the optical MK classification of this starthrough an analysis of its ultraviolet photosperic and stellar windprofiles. We detect interstellar lines of Al III, Si IV, C IV, and N Vtogether with lines of C I, C I*, C I**, Si II, Ge II, P II, and Ni II.We convert the Mg II, P II, S II, Al III, Si IV, C IV, and N V profilesinto measure of apparent column density as a function of LSR velocity.Gas scale height, velocity dispersion, and differential Galacticrotation effects govern the profile shapes. A simple computer model ofthe expected sight line column density profiles for the low and high ionspecies indicates that the gas velocity dispersions and scale heightsincrease as the ionization level of the gas increases. We find scaleheigts H greater than or = 1 kpc for the high ions, which are comparableto the z-distance of the star, whereas we find H approximatley = 0.6 to0.7 kpc for A1 III and H approximatley 0.1 kpc for P II and Ge II. Anenhancement in the Al II profile near -15 km/s accounts forapproximately 25% of the A1 III column along the sight line and probablyarises within gas located approximately 500 pc below theSagittarius-Carina spiral arm link. Portions of the broad underlying A1III distribution are associated with the higher ionization lines,perhaps in conductive interfaces. The presence of N V and the columndensity ratios of Si IV, C IV, and N V favor the interpretation thatmuch of the high ion absorption is produced by collisional ionization ingas with T = 1-3 x 105 K. An enhancement near -35 km/s inboth the Si IV and C IV profiles may be due to an outflow from the Normaspiral arm at a z-distance of about -1 kpc. The smooth decrease of theN(C IV)/N(Si IV) ratio at negative velocities may be due to an ISMionization structure for hot gas that changes distance from the Galacticplane or to a two phase gas distribution in which the relativecontribution from each phase changes with distance from the Galacticplane.
| 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.
| Synthetic UV Lines of Si IV, C IV, and He II from a Population of Massive Stars in Starburst Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...418..749R&db_key=AST
| The Diffuse Ionized Interstellar Medium: Structures Resulting from Ionization by O Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...417..579M&db_key=AST
| 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.
| Optical studies of interstellar material in low density regions of the Galaxy. I - A survey of interstellar NA I and CA II absorption toward 57 distant stars
We present high-resolution spectra of the Na I D and Ca II K linestoward 57 late-O and early-B stars along extended (d greater than 1 kpc)low-density paths through the Milky Way disk and halo. The sight linespreferentially sample diffuse gas in the interstellar medium (ISM) alonginterarm, Galactic center, and high latitude directions. We measureequivalent widths, apparent column densities, and absorption componentstructure. The Ca II to Na I ratios presented as a function of velocityfor each sight line exhibit variations due to elemental depletion,ionization, and density enhancements. Absorption along high latitudesight lines is kinematically simpler than it is along interarm andGalactic center sight lines. Galactic rotation noticeably broadens theabsorption profiles of distant stars located in these latter directions.Along several sight lines, we see Ca II absorption at velocitiescorresponding to large distances (/z/ about 1 kpc) from the Galacticplane. The effects of differences in the Ca II and Na I scale heightsand nonzero velocity dispersions are readily apparent in the data. Briefnotes are given for several sight lines with interesting absorptionproperties.
| 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 interstellar absorption toward HD 156359, a halo star at 11 kiloparsecs in the direction L = 329 deg and B = -15 deg
Results based on high-quality multiple IUE high-dispersion spectra arepresented for the HD 156359 sight line in the direction l = 328.7 degand b = -14.5 deg. The UV stellar spectrum of HD 156359 is consistentwith an MK classification of O9.7 Ib-II. The high-ionization UVinterstellar absorption line in the star's UV spectrum are very broadwith negative velocity extensions. Comparison of apparent column densityprofiles Na(v) for lines within each doublet indicates that there is nosignificant unresolved saturated structure in the Si IV or N V profiles.Direct integration of the Na(v) profiles for Si IV, C IV, and N V overvelocities from -150 km/s to +40 km/s yields total column densities oflog N = 14.10, 14.77, and 14.09, respectively. The definite detection ofN V absorption lines with profile shapes similar to the Si IV and C IVprofiles favors a common origin for all three species.
| Photospheric Absorption Lines in the Ultraviolet Spectra of O-Stars and B-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990MNRAS.246..392P&db_key=AST
| Terminal velocities for a large sample of O stars, B supergiants, and Wolf-Rayet stars
It is argued that easily measured, reliable estimates of terminalvelocities for early-type stars are provided by the central velocityasymptotically approached by narrow absorption features and by theviolet limit of zero residual intensity in saturated P Cygni profiles.These estimators are used to determine terminal velocities, v(infinity),for 181 O stars, 70 early B supergiants, and 35 Wolf-Rayet stars. For OBstars, the values are typically 15-20 percent smaller than the extremeviolet edge velocities, v(edge), while for WR stars v(infinity) = 0.76v(edge) on average. New mass-loss rates for WR stars which are thermalradio emitters are given, taking into account the new terminalvelocities and recent revisions to estimates of distances and to themean nuclear mass per electron. The relationships between v(infinity),the surface escape velocities, and effective temperatures are examined.
| Ultraviolet Interstellar Absorption Toward HD 156359: A Halo Star at 11 kpc in the Direction 1 = 327° and b = -14°
Not Available
| The distribution of interstellar AL III away from the Galactic plane
IUE spectra are analyzed to study the density distribution ofinterstellar Al III away from the Galactic plane. In most cases, themeasured values of the relative line strengths are consistent with onlymodest levels of line saturation. Al III is found to have an exponentialscale height and 1 sigma errors of 1.02(+0.36, -0.24) kpc. For the sameset of 70 stars, the scale height and 1 sigma errors for H I are0.67(+0.21, -0.16) kpc. The Al III scale height is similar to the valueobtained for free electrons from pulsar dispersion measures. The ionizedgas traced by Al III is somewhat more extended than the neutral gastraced by H I but less extended than the very highly ionized gas tracedby Si IV, C IV, and N V.
| Stellar wind velocities and luminosities of O stars
Stellar wind velocities (v-edge not greater than v-infinity) for 110 Ostars are calculated. The spectral types in the sample range from O3through B0; all luminosity classes are represented. Stars from clustersand associations (extreme Population I) as well as field stars areconsidered. There is a weak evidence of higher v-edge for extremePopulation I stars with respect to field stars. A lower limit forstellar luminosity is also computed, and a fair positive correlationbetween this quantity and v-edge is found. Evidence is found of avariation of the ratio v-infinity/v-esc within the sample.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Sunak |
| Sað Açýklýk: | 17h21m18.73s |
| Yükselim: | -62°55'05.4" |
| Görünürdeki Parlaklýk: | 9.642 |
| özdevim Sað Açýklýk: | 1.2 |
| özdevim Yükselim: | -9.5 |
| B-T magnitude: | 9.432 |
| V-T magnitude: | 9.625 |
Kataloglar ve belirtme:
|
INHABITED SKY
