We have conducted a systematic survey for intervening OVI absorbers in available echelle spectra of 16 QSOs at z_QSO = 0.17-0.57. These spectra were obtained using HST/STIS with the E140M grating. Our search uncovered a total of 27 foreground OVI absorbers with rest-frame absorption equivalent width W_r(1031) > 25mA. Ten of these QSOs exhibit strong OVI absorbers in their vicinity. Our OVI survey does not require the known presence of Lya, and the echelle resolution allows us to identify the OVI absorption doublet based on their common line centroid and known flux ratio. We estimate the total redshift survey path, Δz, using a series of Monte-Carlo simulations, and find that Δz=1.66, 2.18, and 2.42 for absorbers of strength W_r = 30, 50 and 80mA, respectively, leading to a number density of dN(W > 50mA)/dz = 6.7 +/- 1.7 and dN(W > 30mA)/dz = 10.4 +/- 2.2. In contrast, we also measure dN/dz = 27 +/- 9 for OVI absorbers of W_r > 50mA at |Δv|< 5000 kms from the background QSOs. Using the random sample of OVI absorbers with well characterized survey completeness, we estimate a mean cosmological mass density of the OVI gas Ω(OVI)h = 1.7 +/- 0.3 x 10^-7. In addition, we show that <5% of OVI absorbers originate in underdense regions that do not show a significant trace of HI. Furthermore, we show that the neutral gas column N(HI) associated with these OVI absorbers spans nearly five orders of magnitude, and show moderate correlation with N(OVI). Finally, while the number density of OVI absorbers varies substantially from one sightline to another, it also appears to be inversely correlated with the number density of HI absorbers along individual lines of sight.
We present far-ultraviolet spectra of the Seyfert2 galaxy Mrk533 obtained with FUSE. These spectra show narrow asymmetrical OVI 1032,1038 emission lines with stronger wings shortward of the peak wavelength, but the degree of asymmetry of these wings in velocity is much lower than that of the wings of the lines of lower ionization. In the combined OVI profile there are marginal indications of local absorptions in the outflow. The CIII 977 line is seen weakly with a similar profile, but with very low signal to noise. These FUV spectra are among the first for a Seyfert of type2, i.e., a purported…
We use FUSE and STIS spectra to study intergalactic absorption towards the quasar PG1259+593 (z=0.478). We identify 135 intergalactic absorption lines with equivalent widths >10mA, tracing 78 absorption components in 72 Ly alpha/beta absorption-line systems. We concentrate on the distribution and physical properties of the WHIM as sampled by OVI and intrinsically broad Ly alpha lines. The number of intervening OVI absorbers for equivalent widths W>24 mA is 3-6 over an unobscured redshift path of dz=0.368. This implies a number density of OVI systems, dN/dz, of ~8-16 along this sight line. This…
We present a complete catalogue of 27 O VI absorbers at low redshift (0.12 < z < 0.5) from a blind survey of 16 QSO echelle spectra in the HST/STIS data archive. These absorbers are identified based only upon matching line profiles and the expected doublet ratio between the λλ1031, 1037 transitions. Subsequent searches are carried out to identify their associated transitions. Here we present all relevant absorption properties. By considering absorption components of different species which are well-aligned in velocity-space, we derive gas temperatures and non-thermal broadening values, b_{nt}.…
We present FUSE and STIS observations of the IGM toward PG 0953+415 (z_em = 0.239). An O VI system at z = 0.06807 is detected in H I Lya, Lyb, Lyg, O VI N V, C IV, and C III. The observations are modeled as a low density intervening gas with a metallicity of 0.4 (+0.6, -0.2) times solar in photoionization equilibrium with the ionizing extragalactic radiation. The best fit is achieved with an ionization parameter, logU = -1.35, which implies nH ~ 10-5 cm-3 and a path length of ~ 80 kpc through the absorbing gas. H I Lya absorption at z = 0.14232 spans a velocity range of 410 km s-1 with the str…
Recent FUSE and STIS observations of OVI absorption at low redshift along the sightline to distant quasars have been interpreted as the signature of a warm-hot diffuse component of the intergalactic medium (IGM). In these proceedings we show that the predicted numbers of such absorbers in numerical simulations agree with the observed characteristics, lending support to this idea. We find that collisionally ionized lines tend to be stronger and wider, while photo-ionized absorbers are weaker and narrower. We also find that a comparison of the predicted distribution of line widths to that observ…
Recent STIS and FUSE observations have detected OVI absorption lines at low redshift that are not clearly associated with any galactic system. In this paper, we argue that these lines are due to metal enriched hot gas in the intergalactic medium. Using numerical simulations of a cosmological-constant dominated cosmology, combined with reasonable assumptions about the metallicity distribution, we show that the number density and internal characteristics of these lines are correctly predicted. We find that the OVI is primarily produced by collisional ionization from gas at a few times 10^5 K for…
To gain insight into four highly ionized high-velocity clouds (HVCs) discovered by Sembach et al. (1999), we have analyzed data from the Hubble Space Telescope (HST) and Far Ultraviolet Spectroscopic Explorer (FUSE) for the PKS 2155-304 and Mrk 509 sight lines. We measure strong absorption in OVI and column densities of multiple ionization stages of silicon (SiII/III/IV) and carbon (CII/III/IV). We interpret this ionization pattern as a multiphase medium that contains both collisionally ionized and photoionized gas. Toward PKS 2155-304, for HVCs at -140 and -270 km/s, respectively, we measure …
We report the results of an extensive FUSE study of high velocity OVI absorption along 102 complete sight lines through the Galactic halo. The high velocity OVI traces a variety of phenomena, including tidal interactions with the Magellanic Clouds, accretion of gas, outflow from the Galactic disk, warm/hot gas interactions in a highly extended Galactic corona, and intergalactic gas in the Local Group. We identify 85 high velocity OVI features at velocities of -500 < v(LSR) < +500 km/s along 59 of the 102 sight lines. Approximately 60% of the sky (and perhaps as much as 85%) is covered by high …
We present the first observations of a Herbig Ae star with a circumstellar disk by the Far Ultraviolet Spectroscopic Explorer (FUSE), as well as a simultaneous observation of the star obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS). The spectra of AB Aurigae show emission and absorption features arising from gasses that have a wide range in temperature, from hot OVI emission to cold molecular hydrogen and CO absorption. Emissions from the highly ionized species OVI and CIII present in the FUSE spectrum are redshifted, while absorption features arising from …
We investigate the existence of a metal-rich OVI population in 10 high spectral resolution quasar spectra and define observational criteria for this class of absorbers. The low temperatures of nearly half of all OVI absorbers (redshifts 2.0 to 2.6), implied by their line widths, are too low for collisional ionization to be a dominant process. We estimate the oxygen abundance under the assumption of photoionization; a striking result is the bimodal distribution of [O/H] with median values close to 0.01 (0.5) solar for the metal-poor (metal-rich) populations. We present the first estimate of the…
We use spectroscopic data from HST and FUSE to study the wide range of ionization states of the "highly ionized high-velocity clouds". Studied extensively in OVI absorption, these clouds are usually assumed to be infalling gas in the Galactic halo at distances less than 50 kpc. An alternative model attributes the OVI (and OVII X-ray absorption) to cosmological structures of low-density, shock-heated intergalactic gas, distributed over 1-3 Mpc surrounding the Milky Way. The latter interpretation is unlikely, owing to the enormous required mass of gas (4x10^12 M_solar). Our detection, in 9 of 12…
We present a high resolution (R~500) X-ray spectrum of the bright quasar H1821+643 (z=0.297), obtained in a 470 ksec Chandra observation. We search for X-ray absorption by highly ionized metal species, OVII and OVIII in particular, at the redshifts of the six intervening OVI absorption systems known from UV studies. We detect features with >~2-sigma significance at the predicted OVII and OVIII wavelengths of one OVI system, at the OVII wavelength of a second, and at the NeIX wavelength of a third. We find two additional features of comparable strength (one OVII and one OVIII) within 1000 km/s …
We present a detailed model for the ionized absorbing gas evident in the 900 ksec Chandra HETGS spectrum of NGC 3783. The analysis was carried out with PHASE a new tool designed to model X-ray and UV absorption features in ionized plasmas. The 0.5-10 keV intrinsic continuum of the source is well represented by a single power law (Gamma=1.53) and a soft black-body component (kT=10 keV). The spectrum contains over 100 features, which are well fit by PHASE with just six free parameters. The model consists of a simple two phase absorber with difference of 35 in the ionization parameter and differe…
We present long-slit HST/STIS measurements of the ionized-gas kinematics in the nucleus of three disk galaxies, namely NGC 2179, NGC 4343, NGC 4435. The sample galaxies have been selected on the basis of their ground-based spectroscopy, for displaying a strong central velocity gradient for the ionized gas, which is consistent with the presence of a circum nuclear keplerian disk (CNKD, Bertola et al. 1998; Funes et al. 2002) rotating around a super massive black hole (SMBH). For each target galaxy we obtained the H_alpha and [NII] 6583 AA kinematics along the major axis and two 0"25 parallel of…
Recent ultraviolet and X-ray observations of intergalactic OVI and OVII absorption systems along lines of sight to bright quasars have opened a new window onto the ``warm-hot intergalactic medium'' (WHIM). These systems appear to provide a significant reservoir for baryons in the local universe, and comparison to cosmological simulations suggests that their abundance roughly matches theoretical predictions. Here we use analytic arguments to elucidate the physical properties of the absorbers and their role in structure formation. We first show that if the absorbers result from structure-formati…
Recent Chandra and XMM observations of distant quasars have shown strong local (z~0) X-ray absorption lines from highly ionized gas, primarily He-like oxygen. The nature of these X-ray absorbers, i.e., whether they are part of the hot gas associated with the Milky Way or part of the intragroup medium in the Local Group, remains a puzzle due to the uncertainties in the distance. We present in this paper a survey of 20 AGNs with Chandra and XMM archival data. About 40% of the targets show local OVII He-alpha absorption with column densities around 10^16 cm^-2; in particular, OVII absorption is p…
Intergalactic absorbers along lines of sight to distant quasars are a powerful diagnostic for the evolution and content of the IGM. In this study, we search known low-z Ly-alpha absorption systems for equivalent absorption in higher Lyman lines as well as the important metal ions OVI and CIII. OVI absorption is detected roughly half the time and shows a smaller range of column density than HI. This implies a multi-phase IGM with warm neutral and hot ionized components. We use our OVI detection statistics to determine that the fraction of intergalalctic mass at 10^5-10^6 K is at least 5% of the…
A survey of diffuse interstellar sight lines observed with the Far Ultraviolet Spectroscopic Explorer has led to the serendipitous discovery of a high-ionization nebula around the hot white dwarf KPD 0005+5106. The nebula has an OVI 1032A surface brightness of up to 25,000 photons/s/cm^2/sr, making it the brightest region of extended OVI emission in our survey. Photoionization models using the incident white dwarf continuum successfully reproduce the observed OVI intensity. The OVI emission arises in the highly ionized inner region of a planetary nebula around KPD 0005+5106. This newly discove…
X-ray absorption lines of highly-ionized species such as OVII at about zero redshift have been firmly detected in the spectra of several active galactic nuclei. However, the location of the absorbing gas remains a subject of debate. To separate the Galactic and extragalactic contributions to the absorption, we have obtained Chandra LETG-HRC and FUSE observations of the black hole X-ray binary LMC X--3. A joint analysis of the detected OVII and Ne IX Kalpha lines, together with the non-detection of the OVII Kbeta and OVIII Kalpha lines, gives the measurements of the temperature, velocity disper…
We present observations of the UV absorption lines in the luminous Seyfert 1 galaxy Mrk 509, obtained with the medium resolution (lambda/Delta-lambda ~ 40,000) echelle gratings of the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. The spectra reveal the presence of eight kinematic components of absorption in Ly-alpha, C IV, and N V, at radial velocities of -422, -328, -259, -62, -22, +34, +124, and +210 km s^-1 with respect to an emission-line redshift of z = 0.03440, seven of which were detected in an earlier Far Ultraviolet Spectrographic Explorer (FUSE) spectrum. The co…
We present observations of the intrinsic absorption in the Seyfert 1 galaxy NGC 3783 obtained with the STIS/HST and FUSE. We have coadded multiple STIS and FUSE observations to obtain a high S/N averaged spectrum spanning 905-1730 A. The averaged spectrum reveals absorption in O VI, N V, C IV, N III, C III and the Lyman lines up to LyE in the three blueshifted kinematic components previously detected in the STIS spectrum (at radial velocities of -1320, -724, and -548 km/s). The highest velocity component exhibits absorption in Si IV. We also detect metastable C III* in this component, indicati…
With a column density log N(OVI) = 14.95+/-0.05, the OVI absorber at z_abs~0.2028 observed toward the QSO PKS0312-77 (z_em=0.223) is the strongest yet detected at z<0.5. At nearly identical redshift (z_abs=0.2026), we also identify a Lyman limit system (LLS, log N(HI)=18.22). Combining FUV and NUV spectra of PKS0312-77 with optical observations of galaxies in the surrounding field (15'x32'), we present an analysis of these absorbers and their connection to galaxies. The observed OI/HI ratio and photoionization modelling of other low ions indicate the metallicity of the LLS is [Z/H]_LLS=-0.6 an…
We present the results from ASCA observations of NGC 3783 carried out during 1993 and 1996. Variability is observed both between the two epochs and within the individual observations, the latter due to a non-stationary process. We find the spectra at both epochs to contain features due to absorption by ionized material, predominantly due to Ovii and Oviii. We find the opacity for such material to decrease by a factor approx 2 in the approx 0.7--1.0 keV band between the epochs while the photoionizing flux increases by approx25%. By comparison with detailed photoionization models we show this be…
We report on the multiphase absorption-line system detected at a redshift z = 3.021 in the spectrum of the quasi-stellar object CTQ 325 (z_em = 3.212). The system is displaced by ~14,000 km/s to the blue of the systemic velocity defined by the center of the symmetric OI quasar emission line. It consists of shallow and broad (~700 km/s, FWHM) absorption lines of HI 1215, CIV 1548,1550, and OVI 1032,1038, produced by collisionally ionized gas and of narrow absorption lines (FWHM < 20 km/s) of Ly-alpha, Ly-beta, ..., Ly-6, SiIII 1206, and CIII 977 produced by photoionized gas. Possible origins of…
The observed intergalactic OVI absorbers at z>0 have been regarded as a significant reservoir of the ``missing baryons''. However, to fully understand how these absorbers contribute to the baryon inventory, it is crucial to determine whether the systems are collisionally ionized or photoionized (or both). Using the identified intergalactic OVI absorbers as tracers, we search for the corresponding X-ray absorption lines, which are useful for finding the missing baryons and for revealing the nature of the OVI absorbers. Stacking the Chandra grating spectra along six AGN sight lines, we obtain th…
We present a detailed analysis of the intergalactic metal-line absorption systems in the archival HST/STIS and FUSE ultraviolet spectra of the low-redshift quasar PKS1302-102 (z_QSO = 0.2784). We supplement the archive data with CLOUDY ionization models and a survey of galaxies in the quasar field. There are 15 strong Lya absorbers with column densities logN_HI > 14. Of these, six are associated with at least CIII 977 absorption (logN(C^++) > 13); this implies a redshift density dN_CIII/dz = 36+13/-9 (68% confidence limits) for the five detections with rest equivalent width W_r > 50 mA. Two sy…
We present the results of a 4 day ASCA observation of the Seyfert galaxy MCG-6-30-15, focussing on the nature of the X-ray absorption by the warm absorber, characterizd by the K-edges of the intermediately ionized oxygen, OVII and OVIII. We confirm that the column density of OVIII changes on a timescale of $\sim 10^4$~s when the X-ray continuum flux decreases. The significant anti-correlation of column density with continuum flux gives direct evidence that the warm absorber is photoionized by the X-ray continuum. From the timescale of the variation of the OVIII column density, we estimate that…
Intergalactic absorbers along lines of sight to distant quasars are a powerful diagnostic for the evolution and content of the intergalactic medium (IGM). In this study, we use the FUSE satellite to search 129 known lya absorption systems at z<0.15 toward 31 AGN for corresponding absorption from higher Lyman lines and the important metal ions OVI. We detect OVI in 40 systems over a smaller range of column density than seen in HI. The co-existence of OVI and HI suggests a multiphase IGM, with warm photoionized and hot ionized components. With improved OVI detection statistics, we find a steep d…
X-ray absorption spectroscopy provides a potentially powerful tool in determining the metal abundances in various phases of the interstellar medium (ISM). We present a case study of the sight line toward 4U 1820-303 (Galactic coordinates l, b=2.79, -7.91 and distance = 7.6 kpc), based on Chandra Grating observations. The detection of OI, OII, OIII, OVII, OVIII, and NeIX Kalpha absorption lines allows us to measure the atomic column densities of the neutral, warm ionized, and hot phases of the ISM through much of the Galactic disk. By comparing these measurements with the 21 cm hydrogen emissio…
We report on high resolution spectra of the bright QSO HS0747+4259 (zem = 1.90, V = 15.8) observed to search for intermediate redshift OVI absorption systems. The spectra were obtained by means of the Space Telescope Imaging Spectrograph (STIS) at the Hubble Space Telescope (HST) and the High Resolution Echelle Spectrometer (HIRES) at the W. M. Keck telescope. We identify 16 OVI systems in the range 1.07 <= z <= 1.87. Among them, six systems with zabs = 1.46-1.8 exhibit a sufficient number of lines of different ionic transitions to estimate the shape of the ionizing radiation field in the rang…
We present results on the X-ray spectrum of the quasar PG 1114+445 from an ASCA observation performed in 1996 June, and a ROSAT observation performed 3 years earlier. We show good agreement between all the datasets can be obtained if the underlying continuum in the 0.2--10 keV band is assumed to be a powerlaw (photon index Gamma approx 1.8) absorbed by photoionized material. The ionized gas imprints deep absorption edges in the observed spectrum <~ 2 keV due to Ovii and Oviii, from which we determine its column density (approx 2E22 cm^{-2}) and ionization parameter (Ux approx 0.1) to be simila…
We report the detection of highly-ionized gas at z~0 seen in resonant UV and X-ray absorption lines toward the z=0.03 blazar Mkn 421. A total of 13 X-ray and 3 UV lines were measured (or upper limits derived), including three lines in the OVII K-series and Kαtransitions from neon, carbon, and nitrogen. From the three OVII lines we derive a 2σDoppler parameter constraint of 24<b<55 km/s. The FUSE spectrum shows strong Galactic low--velocity OVI 1032A absorption as well as a possible weak OVI high-velocity component (HVC). The Doppler parameter of the low-velocity OVI measured with FUSE is ~3σhi…
We present HST/STIS and FUSE spectra of the QSO PG 1211+143 (z_em = 0.081) and a galaxy survey of the surrounding field. This sightline shows two strong intergalactic absorption systems at cz ~ 15,300 and 19,300. This sightline addresses the nature and origin of the OVI absorbers, and their connection to galaxies. We explore the relationship of these absorbers to the nearby galaxies and compare them to other OVI-bearing absorbers in diverse environments. At 15,300 km s^-1, we find four distinct HI components and associated CII, CIII, CIV, SiII, SiIII, SiIV, NV, and OVI, lying near a spiral-dom…
We investigate the physical processes occuring in the multiphase gas of a damped Lyαsystem (DLA). We base our analysis on a high quality Keck HIRES spectrum of the QSO J1211+0422 in which a DLA is detected at z=2.377. There is little contamination of the high-ion (OVI, NV, CIV, SiIV) absorption, allowing us to explore the properties of the highly ionized gas and its connection to other gas-phases. The metallicity ([Z/H]=-1.41+/-0.08), HI column density (log N(HI)=20.80+/-0.10), full-width velocity (Δ(v_ neut)=70 km/s) and relative abundances ([Si/Fe]=+0.23+/-0.05 and [N/Si]=-0.88+/-0.07) of th…
We report the results of a survey of OVI 1032 absorption along the lines of sight to 25 white dwarfs in the local interstellar medium (LISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). We find that interstellar OVI absorption along all sightlines is generally weak, and in a number of cases, completely absent. No OVI absorption was detected with significance greater than 2 sigma for 12 of the 25 stars, where the 1 sigma uncertainty is 4 mA, equivalent to an OVI column density of ~3 x 10^12 cm^-2. Of the remaining stars, most have column densities N(OVI) < 10^13 cm^-2 and no…
(Abridged) With the goal of investigating the nature of OVI absorbers at high redshifts, we study the effects of proximity to the background quasar. In a sample of sixteen quasars at z(QSO) between 2.14 and 2.87 observed at 6.6 km/s resolution with VLT/UVES, we detect 35 OVI absorption-line systems lying within 8000 km/s of z(QSO). The systems can be categorized into 9 strong and 26 weak OVI absorbers. The strong absorbers are defined by the presence of either broad, fully saturated OVI absorption or partial coverage of the continuum source, and have log N(OVI)>~15.0; these systems are intrins…
We present highlights and an overview of 20 FUSE and HST/STIS observations of the bright symbiotic binary EG And. The main motivation behind this work is to obtain spatially-resolved information on an evolved giant star in order to understand the mass-loss processes at work in these objects. The system consists of a low-luminosity white dwarf and a mass-losing, non-dusty M2 giant. The ultraviolet observations follow the white dwarf continuum through periodic gradual occultations by the wind and chromosphere of the giant, providing a unique diagnosis of the circumstellar gas in absorption. Unoc…
The X-ray bright z=0.116 quasar PKS 2155-304 is frequently observed as a Chandra calibration source, with a total of 483 ksec of Low Energy Transmission Grating (LETG) exposure time accumulated through May 2006. Highly-ionized metal absorption lines, including numerous lines at z=0 and a putative OVIII K-alpha line at z=0.055, have been reported in past Chandra studies of this source. Using all available Chandra LETG spectra and analysis techniques developed for such z=0 X-ray absorption along other sightlines, we revisit these previous detections. We detect 4 absorption lines at >3σsignifican…
Hydrodynamic simulations of growth of cosmic structure suggest that 30-50% of the total baryons at z=0 may be in a warm-hot intergalactic medium (WHIM) with temperatures ~10^5-10^7K. The O VI λλ1032, 1038 absorption line doublet in the FUV portion of QSO spectra provides an important probe of this gas. Utilizing recent hydrodynamic simulations, it is found that there should be ~5 O VI absorption lines per unit redshift with equivalent widths >= 35 mA, decreasing rapidly to ~0.5 per unit redshift at >= 350 mA. About 10% of the total baryonic matter or 20-30% of the WHIM is expected to be in the…
To probe the distribution and physical characteristics of interstellar gas at temperatures T ~ 3e5 K in the disk of the Milky Way, we have used the Far Ultraviolet Spectroscopic Explorer (FUSE) to observe absorption lines of OVI toward 148 early-type stars situated at distances 1 kpc. After subtracting off a mild excess of OVI arising from the Local Bubble, combining our new results with earlier surveys of OVI, and eliminating stars that show conspicuous localized X-ray emission, we find an average OVI mid-plane density n_0 = 1.3e-8 cm^-3. The density decreases away from the plane of the Galax…
I examine some of the evidence relevant to the idea that high-velocity clouds (HVCs) are gas clouds distributed throughout the Local Group, as proposed by Blitz et al. (1999) and Braun & Burton (1999). This model makes several predictions: a) the clouds have low metallicities; b) there should be no detectable Halpha emission; c) analogues near other galaxies should exist; and d) many faint HVCs in the region around M31 can be found. Low metallicities are indeed found in several HVCs, although they are also expected in several other models. Halpha emission detected in most HVCs and, when examin…
We have studied the abundance of oxygen in the IGM by analyzing OVI, CIV, SiIV, and HI pixel optical depths derived from a set of high-quality VLT and Keck spectra of 17 QSOs at 2.1 < z < 3.6. Comparing OVI and CIV optical depth ratios to those in realistic, synthetic spectra drawn from a hydrodynamical simulation and comparing to existing constraints on [Si/C] places strong constraints on the ultraviolet background (UVB) model using weak priors on allowed values of [Si/O]: for example, a quasar-only background yields [Si/O] ~ 1.4, highly inconsistent with the [Si/O] ~ 0 expected from nucleosy…
We study the physical conditions, elemental abundances, and kinematics of the high-velocity clouds (HVCs) along the sight lines toward active galaxies HE0226-4110 and PG0953+414 using Hubble Space Telescope Imaging Spectrograph and Far Ultraviolet Spectroscopic Explorer data. Our observations reveal multiple components of HVC absorption in lines of HI, CII, CIII, CIV, OVI, SiII, SiIII, and SiIV in both directions. We investigate whether photoionization by the extragalactic background radiation or by escaping Milky Way radiation can explain the observed ionization pattern. We find that photoion…
Results are presented for our search for warm-hot gas towards the quasar Q 0329-385. We identify ten OVI systems of which two are within 5000 km/s of z_em and a third one should be of intrinsic origin. The seven remaining systems have HI column densities 10^13.7<N(HI)<10^15.6 cm^-2. At least ~1/3 of the individual OVI sub-systems have temperatures T<1x10^5 K and cannot originate in collisionally ionized gas. Photoionization by a hard UV background field reproduces well the ionic ratios for metallicities in the range 10^-2.5 - 10^-0.5 solar, with possibly sub-solar N/C relative abundance. For […
We present Hubble Space Telescope Imaging Spectrograph (HST/STIS) and Far Ultraviolet Spectroscopic Explorer (FUSE) observations of high ion interstellar 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 low Galactic halo, -1.3 kpc from the plane of the Galaxy in the direction l = 304.9, b = -16.1. The STIS E140H grating observations provide high-resolution (FWHM = 2.7 km/s) spectra of the resonance doublets of Si IV, C IV, and N V. These data are complemented by medium-resolution (FWHM = 20 km/s) FUSE spectra of O VI. We find evid…
The star HD72089 is located behind the Vela supernova remnant and shows a complex array of high and low velocity interstellar absorption features arising from shocked clouds. A spectrum of this star was recorded over the wavelength range 1196.4 to 1397.2 Angstroms at a resolving power lambda/Delta lambda = 110,000 and signal-to-noise ratio of 32 by STIS on the Hubble Space Telescope. We have identified 7 narrow components of C I and have measured their relative populations in excited fine-structure levels. Broader features at heliocentric velocities ranging from -70 to +130 km/s are seen in C …
We report on detailed Monte Carlo inversion analysis of five OVI systems from the spectrum of the bright quasar HE 0515-4414 (z_e = 1.71). The associated system at z_a = 1.697 with the neutral hydrogen column density N(HI)= 4.4 10^{13} cm^{-2} shows pronounced absorption from highly ionized transitions of CIII, CIV, NV, OVI, SiIV, and probably SVI. We found that only a power law type ionizing spectrum (J_nu propto nu^{-1.5}) is consistent with the observed sample of the line profiles, i.e. the system is definitely intrinsic. The relative metal abundances give almost the solar pattern and the m…
(Abridged) We present high-resolution spectra of the interstellar NaI and CaII absorption lines for 3 early-type stars along the line-of-sight towards the Shajn 147 SNR. These are supplemented with far-UV aborption spectra of HD 36665 and HD 37318 recorded with the NASA FUSE satellite. The observations reveal intermediate-velocity (IV) absorption features at V_helio = +92 km/s towards HD 37318 and -65 & -52 km/s towards HD 36665. These IV components can be associated with the expansion of the SNR. The observations suggest that the IV component at +92 km/s towards HD 37318 is composed mainly of…
We present HST/STIS and FUSE spectra of the quasar RXJ1230.8+0115 (V=14.4, z=0.117). In addition to Galactic, Virgo, and intervening absorption, this quasar is host to a remarkable intrinsic absorption complex. Four narrow absorption line systems, strong in CIV, NV, and OVI, lie within 5000 km/s of the QSO redshift. Three of the systems appear to be line-locked, two in NV, and two in OVI, with the common system residing in between the other two (in velocity). All three systems show signs of an intrinsic origin -- smooth wind-like profiles, high ionization, and partial coverage of the central e…
We present a high-resolution spectral analysis of Betelgeuse (M2 Iab). Between 1998 January and 1999 March four spatially resolved raster scans (http://cfa-www.harvard.edu/cfa/ep/pressrel/alobel0100.html) have been obtained with the STIS on the Hubble Space Telescope. The near-UV echelle spectra reveal double-peaked permitted emission lines of neutral and singly ionized metals, with self-absorbed line cores. We observe reversals in the intensity of both emission line components when scanning across the UV disk, for four unsaturated lines of Si I, Fe I, Al II], and Fe II. We model the Si I lam2…
We present results from an analysis of FUSE and HST/STIS spectroscopy of the z_em=0.57 quasar PKS0405-123. We focus on the intervening metal-line systems identified along the sightline and investigate their ionization mechanism, ionization state, and chemical abundances. We identify six OVI absorbers to a 3sigma equivalent width (EW) limit of 60mA. This implies an incidence dN/dz = 16^{+9}_{-6} consistent with previous OVI studies. In half of the OVI systems we report positive detections of CIII suggesting the gas is predominantly photoionized, has multiple ionization phases, or is in a non-eq…
High resolution optical (HIRES/Keck) and UV (STIS/HST) spectra, covering a large range of chemical transitions, are analyzed for three single-cloud weak MgII absorption systems along the line of sight toward the quasar PG 1634+706. Weak MgII absorption lines in quasar spectra trace metal-enriched environments that are rarely closely associated with the most luminous galaxies (>0.05L^*). The two weak MgII systems at z=0.81 and z=0.90 are constrained to have >=solar metallicity, while the metallicity of the z=0.65 system is not as well-constrained, but is consistent with >1/10th solar. These wea…
We present an analysis of interstellar and intergalactic absorption lines in the FUSE spectrum of the low-redshift quasar PG0804+761 (z=0.100) at intermediate resolution (FWHM=25 km/s) in the direction l=138.3, b=31.0. With a good signal-to-noise ratio and the presence of several interesting Galactic and extragalactic absorption components along the sight line, this spectrum provides a good opportunity to demonstrate the ability of FUSE to do both interstellar and extragalactic science. Although the spectrum of PG0804+761 is dominated by strong absorption from local Galactic gas, we concentrat…
(Abridged) We present computations of the metals photoionization structures of pressure supported gas clouds in gravitationally dominant DM minihalos in the extended Galactic halo or LG environment. We consider low-metallicity (0.1-0.3 solar) clouds that are photoionized by the metagalactic radiation field, and which are pressure-confined by a hot external medium. We study the properties of LCDM Burkert (and NFW) minihalos with circular velocities 12-30 km/s. We present results for the volume densities and projected column densities of low-ions, CII, NI, OI, SiII and SII, produced in the neutr…
We have searched for evidence of soft X-ray absorption by hot metals in the vicinity of the Galaxy in the spectra of a small sample of fifteen Type I AGN observed with the high resolution X-ray gratings on board Chandra. This is an extension of our previous survey of hot OVII and OVIII absorbing gas in the vicinity of the Galaxy. The strongest absorption signatures within a few hundred km/s of their rest-frame energies are most likely due to warm absorbing outflows from the nearest AGN, which are back-lighting the local hot gas. We emphasize that absorption signatures in the spectra of some di…
Using new HST/FOS, NTT/EMMI, and Keck/HIRES spectra of the gravitationally-lensed double QSO HE 1104-1805 AB (z=2.31, θ=3.2), and assuming UV photoionization by a metagalactic radiation field, we derive physical conditions (ionization levels, metal abundances and cloud sizes along the lines of sight) in five CIV+MgII absorption systems clustered around z=1.66 along the two lines of sight. Three of these systems are associated with a damped Ly-alpha (DLA) system with logN(HI)=20.85, which is observed in A. The other two systems are associated with a Lyman-limit system with logN(HI)=17.57 (B). T…
We obtained far-ultraviolet spectra of the Seyfert 1 galaxy NGC 7469 using the FUSE on 1999 December 6. Our spectra cover the wavelength range 990-1187 A with a resolution of 0.05 A. We see broad emission lines of CIII, NIII, OVI, and HeII as well as intrinsic absorption lines in the OVI 1032,1038 resonance doublet. The absorption arises in two distinct kinematic components at systemic velocities of -569 km/s and -1898 km/s. Both components are very highly ionized- no significant Ly beta absorption is present. The higher blueshift component is not quite saturated, and it has a total OVI column…
We have obtained low-dispersion spectra of NGC 3227 with the Space Telescope Imaging Spectrograph (STIS) to study the intrinsic UV absorption and the reddening of the nucleus in this Seyfert 1 galaxy. The UV spectra show a wealth of absorption lines at the systemic redshift that span a wide range in ionization state (Mg I to N V). The equivalent widths of the lines are consistent with our earlier prediction that a ``lukewarm absorber'' (T= 18,000 K at the ionized face) with a substantial column of gas [N(H) = 2 x 10^21 cm^-2] is present and likely responsible for the reddening of the nucleus. …
We used HIRES/Keck profiles (R=6 km/s) of MgII and FeII in combination with FOS/HST spectra (R=230 km/s) to place constraints on the physical conditions (metallicities, ionization conditions, and multi-phase distribution) of absorbing gas in three galaxies at z=0.9254, 0.9276, and 0.9343 along the line of sight to PG 1206+459. The chemical and ionization species covered in the FOS/HST spectra are HI, SiII, CII, NII, FeIII, SiIII, SiIV, NIII, CIII, CIV, SVI, NV, and OVI, with ionization potentials ranging from 13.6 to 138 eV. The multiple MgII clouds exhibit complex kinematics and the CIV, NV a…
We present new FUSE spectroscopy of the dwarf starburst galaxy NGC 625. These observations probe multiple phases of the interstellar medium, including the coronal, ionized, neutral and molecular gas. This nearby (D = 3.9 +/- 0.2 Mpc) system shows a clear detection of outflowing coronal gas as traced by OVI 1032 Angstrom absorption. The centroid of the OVI profile is blueshifted with respect to the galaxy systemic velocity by ~ 30 km/sec, suggesting a low-velocity outflow. The implied OVI velocity extent is found to be 100 +/- 20 km/sec, which is fully consistent with the detected HI outflow ve…
