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ABSTRACT: Impurity sources and confinement times in the central cell of TMX were examined by studying the extreme ultraviolet (EUV) emissions from intrinsic and injected impurities. Impurity ions from gases puffed radially toward the central-cell plasma showed very little radial penetration into the plasma. The confinement times of highly ionized intrinsic and injected impurities in the central cell were of the order of or less than the deuterium ion confinement times; the ambient density ratios of O V to O VI indicate overall O VI confinement times near the axis of 0.3 to 3 ms. Impurities introduced into the central-cell plasma were not detected in either end-cell plasma, indicating that axial losses of impurities from the central cell were small. This result agrees with theoretical calculations of the axial confinement times and suggests that most of the losses were radial. The radial flux of impurity ions determined from the measured radial profiles of the ambient impurity ion densities is primarily outward; the magnitude of these fluxes also implies a short confinement time for impurity ions.
Nuclear Fusion 01/2011; 23(12):1675. · 4.09 Impact Factor
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A. B. Schultz,
F. Allard,
M. Clampin,
M. McGrath,
F. C. Bruhweiler,
J. A. Valenti,
P. Plait,
S. Hulbert,
S. Baum,
B. E. Woodgate,
C. W. Bowers,
R. A. Kimble,
S. P. Maran, H. W. Moos,
and F. Roesler
[show abstract]
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ABSTRACT: We report the first Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) CCD spectroscopy of the bona fide brown dwarf Gliese 229B. The optical spectrum shows absorptions of Cs I at 8944 Å and water vapor bands at 9300-9600 Å. Strong CaH, FeH, TiO, and VO bands observed in late M dwarfs are absent from the spectrum of Gliese 229B. The formation of dust grains may explain the absence of strong atomic lines and molecular bands of these refractory elements. The broad spectral coverage obtained helps resolve current speculations about the presence of dust clouds in the atmosphere of cool brown dwarfs. We find the slope of the STIS/CCD spectrum and the lack of flux detected shortward of 8000 Å strongly supports the presence of dust hazes suspended in the photosphere of Gl 229B rather than a complete settling of the grains to regions below the photosphere.
The Astrophysical Journal 01/2009; 492(2):L181. · 6.02 Impact Factor
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G. Sonneborn,
C. S. J. Pun,
R. A. Kimble,
T. R. Gull,
P. Lundqvist,
R. McCray,
P. Plait,
A. Boggess,
C. W. Bowers,
A. C. Danks,
J. Grady,
S. R. Heap,
S. Kraemer,
D. Lindler,
J. Loiacono,
S. P. Maran, H. W. Moos,
and B. E. Woodgate
[show abstract]
[hide abstract]
ABSTRACT: Visual and ultraviolet spatially resolved (~01) spectra of SN 1987A obtained on days 3715 and 3743 with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope show that the high-velocity supernova debris is colliding with circumstellar gas. Very broad Lyα emission with velocities extending to ~±20,000 km s-1 originates inside the inner circumstellar ring and appears to fill most of the surface area within 067 ± 003 (0.14 pc at a distance of 50 kpc) of the ring's center. The observed Lyα flux from the shocked ejecta is (1.85±0.53) × 10−13 and (1.25±0.51) × 10−12 ergs cm-2 s-1 after correcting for extinction. A spatially unresolved blueshifted emission feature was discovered in Hα (and other lines) on the inner ring at position angle 31°±8°. The Hα emission extends to -250 km s-1 with no corresponding redshifted emission. This highly localized interaction appears to be the initial contact of the supernova blast wave with an inward protrusion of the inner ring. The broad Lyα emission and the "hot spot" are separate interaction phenomena associated with the reverse and forward shocks, respectively. We also find that the size of the inner ring in forbidden lines of oxygen has a dependence on ionization potential, in agreement with photoionization models of the ring.
The Astrophysical Journal 01/2009; 492(2):L139. · 6.02 Impact Factor
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K. R. Sembach,
B. P. Wakker,
T. M. Tripp,
P. Richter,
J. W. Kruk,
W. P. Blair, H. W. Moos,
B. D. Savage,
J. M. Shull,
D. G. York,
G. Sonneborn,
G. Hébrard,
R. Ferlet,
A. Vidal-Madjar,
S. D. Friedman,
and E. B. Jenkins
[show abstract]
[hide abstract]
ABSTRACT: Using Far Ultraviolet Spectroscopic Explorer (FUSE) and Hubble Space Telescope observations of the QSO PG 1259+593, we detect D I Lyman series absorption in high-velocity cloud Complex C, a low-metallicity gas cloud falling onto the Milky Way. This is the first detection of atomic deuterium in the local universe in a location other than the nearby regions of the Galactic disk. We construct a velocity model for the sight line based on the numerous O I absorption lines detected in the ultraviolet spectra. We identify eight absorption-line components, two of which are associated with the high-velocity gas in Complex C at ≈-128 and ≈-112 km s-1. A new Westerbork Synthesis Radio Telescope (WSRT) interferometer map of the H I 21 cm emission toward PG 1259+593 indicates that the sight line passes through a compact concentration of neutral gas in Complex C. We use the WSRT data together with single-dish data from the Effelsberg 100 m radio telescope to estimate the H I column density of the high-velocity gas and to constrain the velocity extents of the H I Lyman series absorption components observed by FUSE. We find N(H I) = (9.0 ± 1.0) × 1019 cm-2, N(D I) = (2.0 ± 0.6) × 1015 cm-2, and N(O I) = (7.2 ± 2.1) × 1015 cm-2 for the Complex C gas (68% confidence intervals). The corresponding light-element abundance ratios are D/H = (2.2 ± 0.7) × 10-5, O/H = (8.0 ± 2.5) × 10-5, and D/O = 0.28 ± 0.12. The metallicity of Complex C gas toward PG 1259+593 is approximately 1/6 solar, as inferred from the oxygen abundance [O/H] = -0.79 ±. While we cannot rule out a value of D/H similar to that found for the local ISM (i.e., D/H ~ 1.5 × 10-5), we can confidently exclude values as low as those determined recently for extended sight lines in the Galactic disk (D/H < 1 × 10-5). Combined with the sub-solar metallicity estimate and the low nitrogen abundance, this conclusion lends support to the hypothesis that Complex C is located outside the Milky Way, rather than inside in material recirculated between the Galactic disk and halo. The value of D/H for Complex C is consistent with the primordial abundance of deuterium inferred from recent Wilkinson Microwave Anisotropy Probe observations of the cosmic microwave background and simple chemical evolution models that predict the amount of deuterium astration as a function of metallicity.
The Astrophysical Journal Supplement Series 12/2008; 150(2):387. · 13.46 Impact Factor
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B. D. Savage,
K. R. Sembach,
E. B. Jenkins,
J. M. Shull,
D. G. York,
G. Sonneborn, H. W. Moos,
S. D. Friedman,
J. C. Green,
W. R. Oegerle,
W. P. Blair,
J. W. Kruk,
and E. M. Murphy
[show abstract]
[hide abstract]
ABSTRACT: Far-ultraviolet spectra of 11 active galactic nuclei observed by Far Ultraviolet Spectroscopic Explorer (FUSE) are analyzed to obtain measures of O VI λ1031.93 absorption occurring over very long paths through Milky Way halo gas. Strong O VI absorption is detected along 10 of 11 sight lines. Values of log[N(O VI) sin |b|] range from 13.80 to 14.64, with a median value of 14.21. The observations reveal the existence of a widespread but irregular distribution of O VI in the Milky Way halo. Combined with estimates of the O VI midplane density, n0 = 2 × 10-8 cm-3, from the Copernicus satellite, the FUSE observations imply an O VI exponential scale height of 2.7 ± 0.4 kpc. We find that N(C IV)/N(O VI) ranges from ~0.15 in the disk to ~0.6 along four extragalactic sight lines. The changing ionization state of the gas from the disk to the halo is consistent with a systematic decrease in the scale heights of Si IV, C IV, N V, to O VI from ~5.1 to ~2.7 kpc. While conductive heating models can account for the highly ionized atoms at low |z|, a combination of models (and processes) appears to be required to explain the highly ionized atoms found in the halo. The greater scale heights of Si IV and C IV compared to O VI suggests that some of the Si IV and C IV in the halo is produced in turbulent mixing layers or by photoionization by hot halo stars or the extragalactic background.
The Astrophysical Journal 12/2008; 538(1):L27. · 6.02 Impact Factor
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[show abstract]
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ABSTRACT: We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the sight line toward the Seyfert 1 galaxy Markarian 876, which passes through high-velocity cloud (HVC) complex C. This sight line demonstrates the ability of FUSE to measure ionic absorption lines in Galactic HVCs. High-velocity absorption is clearly seen in both members of the O VI doublet. This is the first detection of O VI in a neutral hydrogen HVC. One component of HVC complex C is resolved in multiple Fe II lines from which we derive N(Fe II)/N(H I) = 0.48 (Fe/H)☉. This value of N(Fe II)/N(H I) implies that the metallicity of complex C along this sight line may be higher than that along the Mrk 290 sight line (0.1 solar) found by Wakker et al. On the other hand, if the metallicity of complex C is also 0.1 solar along this line of sight, the observed value of N(Fe II)/N(H I) suggests there may be a significant amount of H+ along the line of sight. In any case, little, if any, iron can be depleted into dust grains if the intrinsic metallicity of complex C is subsolar. Absorption from complex C is also seen in C II, N I, and N II, and upper limits based on nondetections can be determined for Ar I, P II, and Fe III. Although molecular hydrogen in the Milky Way is obvious in the FUSE data, no H2 absorption is seen in the HVC to a limit N(H2) < 2.0 × 1014 cm-2. Future FUSE observations of extragalactic objects behind Galactic HVCs will allow us to better constrain models of HVC origins.
The Astrophysical Journal 12/2008; 538(1):L35. · 6.02 Impact Factor
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G. Hébrard,
M. Lemoine,
A. Vidal-Madjar,
J.-M. Désert,
A. Lecavelier des Étangs,
R. Ferlet,
B. E. Wood,
J. L. Linsky,
J. W. Kruk,
P. Chayer,
S. Lacour,
W. P. Blair,
S. D. Friedman, H. W. Moos,
K. R. Sembach,
G. Sonneborn,
W. R. Oegerle,
and E. B. Jenkins
[show abstract]
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ABSTRACT: We present a deuterium abundance analysis of the line of sight toward the white dwarf WD 2211-495 observed with the Far Ultraviolet Spectroscopic Explorer (FUSE). Numerous interstellar lines are detected on the continuum of the stellar spectrum. A thorough analysis was performed through the simultaneous fit of interstellar absorption lines detected in the four FUSE channels of multiple observations with different slits. We excluded all saturated lines in order to reduce possible systematic errors on the column density measurements. We report the determination of the average interstellar D/O and D/N ratios along this line of sight at the 95% confidence level: D/O = (4.0 ± 1.2) × 10-2 and D/N = (4.4 ± 1.3) × 10-1. In conjunction with FUSE observations of other nearby sight lines, the results of this study will allow a deeper understanding of the present-day abundance of deuterium in the local interstellar medium and its evolution with time.
The Astrophysical Journal Supplement Series 12/2008; 140(1):103. · 13.46 Impact Factor
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[show abstract]
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ABSTRACT: Far-Ultraviolet Spectroscopic Explorer (FUSE) spectra of 100 extragalactic objects and two distant halo stars are analyzed to obtain measures of O VI λλ1031.93, 1037.62 absorption along paths through the Milky Way thick disk/halo. Strong O VI absorption over the velocity range from -100 to 100 km s-1 reveals a widespread but highly irregular distribution of O VI, implying the existence of substantial amounts of hot gas with T ~ 3 × 105 K in the Milky Way thick disk/halo. The integrated column density, log [N(O VI) cm-2], ranges from 13.85 to 14.78 with an average value of 14.38 and a standard deviation of 0.18. Large irregularities in the gas distribution are found to be similar over angular scales extending from <1° to 180°, implying a considerable amount of small- and large-scale structure in the absorbing gas. The overall distribution of O VI is not well described by a symmetrical plane-parallel layer of patchy O VI absorption. The simplest departure from such a model that provides a reasonable fit to the observations is a plane-parallel patchy absorbing layer with an average O VI midplane density of n0(O VI) = 1.7 × 10-8 cm-3, a scale height of ~2.3 kpc, and a ~0.25 dex excess of O VI in the northern Galactic polar region. The distribution of O VI over the sky is poorly correlated with other tracers of gas in the halo, including low- and intermediate-velocity H I, Hα emission from the warm ionized gas at ~104 K, and hot X-ray-emitting gas at ~106 K. The O VI has an average velocity dispersion, b ≈ 60 km s-1, and standard deviation of 15 km s-1. Thermal broadening alone cannot explain the large observed profile widths. The average O VI absorption velocities toward high-latitude objects (|b| > 45°) range from -46 to 82 km s-1, with a high-latitude sample average of 0 km s-1 and a standard deviation of 21 km s-1. High positive velocity O VI absorbing wings extending from ~100 to ~250 km s-1 observed along 21 lines of sight may be tracing the flow of O VI into the halo. A combination of models involving the radiative cooling of hot fountain gas, the cooling of supernova bubbles in the halo, and the turbulent mixing of warm and hot halo gases is required to explain the presence of O VI and other highly ionized atoms found in the halo. The preferential venting of hot gas from local bubbles and superbubbles into the northern Galactic polar region may explain the enhancement of O VI in the north. If a fountain flow dominates, a mass flow rate of approximately 1.4 M yr-1 of cooling hot gas to each side of the Galactic plane with an average density of 10-3 cm-3 is required to explain the average value of log [N(O VI) sin |b|] observed in the southern Galactic hemisphere. Such a flow rate is comparable to that estimated for the Galactic intermediate-velocity clouds.
The Astrophysical Journal Supplement Series 12/2008; 146(1):125. · 13.46 Impact Factor
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S. D. Friedman,
J. C. Howk,
P. Chayer,
T. M. Tripp,
G. Hébrard,
M. André,
C. Oliveira,
E. B. Jenkins, H. W. Moos,
W. R. Oegerle,
G. Sonneborn,
R. Lamontagne,
K. R. Sembach,
and A. Vidal-Madjar
[show abstract]
[hide abstract]
ABSTRACT: We present measurements of the column densities of interstellar D I and O I made with the Far Ultraviolet Spectroscopic Explorer (FUSE) and of H I made with the International Ultraviolet Explorer (IUE) toward the sdOB star Feige 110 [(l,b) = (7409, - 5907); d = 179 pc; z = -154 pc]. Our determination of the D I column density made use of curve-of-growth fitting and profile fitting analyses, while our O I column density determination used only curve-of-growth techniques. The H I column density was estimated by fitting the damping wings of the interstellar Lyα profile. We find log N(D ) = 15.47 ± 0.06, log N(O ) = 16.73 ± 0.10, and log N(H ) = 20.14 (all errors 2 σ). This implies D/H = (2.14 ± 0.82) × 10-5, D/O = × 10-2, and O/H = (3.89 ± 1.67) × 10-4. Taken with the FUSE results reported in companion papers and previous measurements of the local interstellar medium (LISM), this suggests the possibility of spatial variability in D/H for sight lines exceeding ~100 pc. This result may constrain models which characterize the mixing timescales and length scales of material in the LISM.
The Astrophysical Journal Supplement Series 12/2008; 140(1):37. · 13.46 Impact Factor
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[show abstract]
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ABSTRACT: We use Far Ultraviolet Spectroscopic Explorer (FUSE) observations to study interstellar absorption along the line of sight to the white dwarf WD 1634-573 (d = 37.1 ± 2.6 pc). Combining our measurement of D I with a measurement of H I from Extreme Ultraviolet Explorer data, we find a D/H ratio toward WD 1634-573 of D/H = (1.6 ± 0.5) × 10-5. In contrast, multiplying our measurements of D /O = 0.035 ± 0.006 and D /N = 0.27 ± 0.05 with published mean Galactic interstellar medium (ISM) gas-phase O/H and N/H ratios yields D/HO = (1.2 ± 0.2) × 10-5 and D/HN = (2.0 ± 0.4) × 10-5, respectively. Note that all uncertainties quoted above are 2 σ. The inconsistency between D/HO and D/HN suggests that either the O I/H I or the N I/H I ratio toward WD 1634-573 must be different from the previously measured average ISM O/H and N/H values. The computation of D/HN from D I/N I is more suspect, since the relative N and H ionization states could conceivably vary within the local ISM, while the O and H ionization states will be more tightly coupled by charge exchange.
The Astrophysical Journal Supplement Series 12/2008; 140(1):91. · 13.46 Impact Factor
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A. Vidal-Madjar,
D. Kunth,
A. Lecavelier des Etangs,
J. Lequeux,
M. André,
L. BenJaffel,
R. Ferlet,
G. Hébrard,
J. C. Howk,
J. W. Kruk,
M. Lemoine, H. W. Moos,
K. C. Roth,
G. Sonneborn,
and D. G. York
[show abstract]
[hide abstract]
ABSTRACT: The metal-deficient starburst galaxy I Zw 18 has been observed with the Far Ultraviolet Spectroscopic Explorer (FUSE) in a search for H2 molecules. The spectrum obtained with an aperture covering the full galaxy shows no absorption lines of diffuse H2 at the radial velocity of the galaxy. The upper limit for the diffuse H2 column density is found to be very low, N(H2) 1015 cm-2 (10 σ), unlike our Galaxy where H2 is generally present for even low H I column densities. Although the H I column density here is as high as N(H I) ≈ 2 × 1021 cm-2, we observe 2N(H2)/N(H I) 10-6. We cannot exclude the possibility that some H2 could be in very dense, small, and discrete clumps that cannot be detected with the present observation. However, the remarkable absence of diffuse H2 in this metal-poor galaxy can be explained by the low abundance of dust grains (needed to form this molecule from H atoms), the high ultraviolet flux, and the low density of the H I cloud surrounding the star-forming regions. Thus, having eliminated diffuse H2 as a significant contributor to the total mass, it appears that the gas of the galaxy is dominated by H I and that the high dynamical mass is not composed of cold and diffuse baryonic dark matter.
The Astrophysical Journal 12/2008; 538(1):L77. · 6.02 Impact Factor
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K. R. Sembach,
B. D. Savage,
J. M. Shull,
E. B. Jenkins,
E. M. Murphy,
D. G. York,
T. Ake,
W. P. Blair,
A. F. Davidsen,
S. D. Friedman,
B. K. Gibson,
J. W. Kruk, H. W. Moos,
W. R. Oegerle,
D. Sahnow,
and G. Sonneborn
[show abstract]
[hide abstract]
ABSTRACT: We have used moderate-resolution (FWHM ≈ 25 km s-1) spectra of active galactic nuclei and QSOs observed by the Far Ultraviolet Spectroscopic Explorer to make the first definitive measurements of absorption by hot gas in high-velocity clouds (HVCs) at large distances from the Galactic plane. Seven of the 11 sight lines studied exhibit high-velocity ( > 100 km s-1) O VI λ1031.93 absorption with log N(O ) ≈ 13.79-14.62. High-velocity O VI absorption is detected in the distant gas of H I HVC complex C, the Magellanic Stream, several HVCs believed to be in the Local Group, and the outer Galaxy. The fraction of O VI in HVCs along the seven sight lines containing high-velocity O VI averages ~30%, with a full range of ~10%-70%. The O VI detections imply that hot (T ~ 3 × 105 K), collisionally ionized gas is an important constituent of the HVCs since O VI is difficult to produce by photoionization unless the path lengths over which the absorption occurs are very large (>100 kpc). The association of O VI with H I HVCs in many cases suggests that the O VI may be produced at interfaces or mixing layers between the H I clouds and hot, low-density gas in the Galactic corona or Local Group. Alternatively, the O VI may originate within cooling regions of hot gas clouds as they are accreted onto the Galaxy.
The Astrophysical Journal 12/2008; 538(1):L31. · 6.02 Impact Factor
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R. L. Shelton,
J. W. Kruk,
E. M. Murphy,
B. G. Andersson,
W. P. Blair,
W. V. Dixon,
J. Edelstein,
A. W. Fullerton,
C. Gry,
J. C. Howk, [......],
K. C. Roth,
D. J. Sahnow,
R. Sankrit,
B. D. Savage,
K. R. Sembach,
J. M. Shull,
O. H. W. Siegmund,
A. Vidal-Madjar,
B. Y. Welsh,
and D. G. York
[show abstract]
[hide abstract]
ABSTRACT: We report the first Far-Ultraviolet Spectroscopic Explorer measurements of diffuse O VI (λλ1032, 1038) emission from the general diffuse interstellar medium outside of supernova remnants or superbubbles. We observed a 30'' × 30'' region of the sky centered at l = 3150 and b = -413. From the observed intensities (2930 ± 290 [random] ± 410 [systematic] and 1790 ± 260 [random] ± 250 [systematic] photons cm-2 s-1 sr-1 in λλ1032 and 1038, respectively), derived equations, and assumptions about the source location, we calculate the intrinsic intensity, electron density, thermal pressure, and emitting depth. The intensities are too large for the emission to originate solely in the Local Bubble. Thus, we conclude that the Galactic thick disk and lower halo also contribute. High-velocity clouds are ruled out because there are none near the pointing direction. The calculated emitting depth is small, indicating that the O VI-bearing gas fills a small volume. The observations can also be used to estimate the cooling rate of the hot interstellar medium and to constrain models. The data also yield the first intensity measurement of the C II 3s 2S1/2-2p 2P3/2 emission line at 1037 Å and place upper limits on the intensities of ultraviolet line emission from C I, C III, Si II, S III, S IV, S VI, and Fe III.
The Astrophysical Journal 12/2008; 560(2):730. · 6.02 Impact Factor
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M. Lemoine,
A. Vidal-Madjar,
G. Hébrard,
J.-M. Désert,
R. Ferlet,
A. Lecavelier des Étangs,
J. C. Howk,
M. André,
W. P. Blair,
S. D. Friedman, [......], H. W. Moos,
K. Sembach,
P. Chayer,
E. B. Jenkins,
D. Koester,
J. L. Linsky,
B. E. Wood,
W. R. Oegerle,
G. Sonneborn,
and D. G. York
[show abstract]
[hide abstract]
ABSTRACT: High-resolution spectra of the hot white dwarf G191-B2B, covering the wavelength region 905-1187 Å, were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). These data were used in conjunction with existing high-resolution Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) observations to evaluate the total H I, D I, O I, and N I column densities along the line of sight. Previous determinations of N(D I) based upon GHRS and STIS observations were controversial as a result of the saturated strength of the D I Lyα line. In the present analysis the column density of D I has been measured using only the unsaturated Lyβ and Lyγ lines observed by FUSE. A careful inspection of possible systematic uncertainties tied to the modeling of the stellar continuum or to the uncertainties in the FUSE instrumental characteristics has been performed. The column densities derived are log N(D ) = 13.40 ± 0.07, log N(O ) = 14.86 ± 0.07, and log N(N ) = 13.87 ± 0.07, quoted with 2 σ uncertainties. The measurement of the H I column density by profile fitting of the Lyα line has been found to be uncertain. If additional weak, hot interstellar components are added to the three detected clouds along the line of sight, the H I column density can be reduced quite significantly, even though the signal-to-noise ratio and spectral resolution at Lyα are excellent. The new estimate of N(H I) toward G191-B2B reads log N(H ) = 18.18 ± 0.18 (2 σ), so that the average D/H ratio on the line of sight is D/H = × 10-5 (2 σ).
The Astrophysical Journal Supplement Series 12/2008; 140(1):67. · 13.46 Impact Factor
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J. W. Kruk,
J. C. Howk,
M. André, H. W. Moos,
W. R. Oegerle,
C. Oliveira,
K. R. Sembach,
P. Chayer,
J. L. Linsky,
B. E. Wood,
R. Ferlet,
G. Hébrard,
M. Lemoine,
A. Vidal-Madjar,
and G. Sonneborn
[show abstract]
[hide abstract]
ABSTRACT: We present an analysis of interstellar absorption along the line of sight to the nearby white dwarf star HZ 43A. The distance to this star is 68 ± 13 pc, and the line of sight extends toward the north Galactic pole. Column densities of O I, N I, and N II were derived from spectra obtained by the Far Ultraviolet Spectroscopic Explorer (FUSE), the column density of D I was derived from a combination of our FUSE spectra and an archival Hubble Space Telescope (HST) GHRS spectrum, and the column density of H I was derived from a combination of the GHRS spectrum and values derived from Extreme Ultraviolet Explorer (EUVE) data obtained from the literature. We find the following abundance ratios (with 2 σ uncertainties): D /H = (1.66 ± 0.28) × 10-5, O /H = (3.63 ± 0.84) × 10-4, and N /H = (3.80 ± 0.74) × 10-5. The N II column density was slightly greater than that of N I, indicating that ionization corrections are important when deriving nitrogen abundances. Other interstellar species detected along the line of sight were C II, C III, O VI, Si II, Ar I, Mg II, and Fe II; an upper limit was determined for N III. No elements other than H I were detected in the stellar photosphere.
The Astrophysical Journal Supplement Series 12/2008; 140(1):19. · 13.46 Impact Factor
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D. J. Sahnow, H. W. Moos,
T. B. Ake,
J. Andersen,
B-G Andersson,
M. Andre,
D. Artis,
A. F. Berman,
W. P. Blair,
K. R. Brownsberger, [......],
K. C. Roth,
R. Sankrit,
K. R. Sembach,
R. L. Shelton,
O. H. W. Siegmund,
C. J. Silva,
G. Sonneborn,
S. R. Vaclavik,
H. A. Weaver,
and E. Wilkinson
[show abstract]
[hide abstract]
ABSTRACT: The launch of the Far Ultraviolet Spectroscopic Explorer (FUSE) has been followed by an extensive period of calibration and characterization as part of the preparation for normal satellite operations. Major tasks carried out during this period include the initial coalignment, focusing, and characterization of the four instrument channels and a preliminary measurement of the resolution and throughput performance of the instrument. We describe the results from this test program and present preliminary estimates of the on-orbit performance of the FUSE satellite based on a combination of these data and prelaunch laboratory measurements.
The Astrophysical Journal 12/2008; 538(1):L7. · 6.02 Impact Factor
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H. W. Moos,
K. R. Sembach,
A. Vidal-Madjar,
D. G. York,
S. D. Friedman,
G. Hébrard,
J. W. Kruk,
N. Lehner,
M. Lemoine,
G. Sonneborn, [......],
C. Oliveira,
K. Roth,
D. J. Sahnow,
B. D. Savage,
J. M. Shull,
T. M. Tripp,
E. J. Weiler,
B. Y. Welsh,
E. Wilkinson,
and B. E. Woodgate
[show abstract]
[hide abstract]
ABSTRACT: Observations obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) have been used to determine the column densities of D I, N I, and O I along seven sight lines that probe the local interstellar medium (LISM) at distances from 37 to 179 pc. Five of the sight lines are within the Local Bubble, and two penetrate the surrounding H I wall. Reliable values of N(H I) were determined for five of the sight lines from Hubble Space Telescope (HST) data, International Ultraviolet Explorer (IUE) data, and published Extreme Ultraviolet Explorer (EUVE) measurements. The weighted mean of D I/H I for these five sight lines is (1.52 ± 0.08) × 10-5 (1 σ uncertainty in the mean). It is likely that the D I/H I ratio in the Local Bubble has a single value. The D I/O I ratio for the five sight lines within the Local Bubble is (3.76 ± 0.20) × 10-2. It is likely that O I column densities can serve as a proxy for H I in the Local Bubble. The weighted mean for O I/H I for the seven FUSE sight lines is (3.03 ± 0.21) × 10-4, comparable to the weighted mean (3.43 ± 0.15) × 10-4 reported for 13 sight lines probing larger distances and higher column densities. The FUSE weighted mean of N I/H I for five sight lines is half that reported by Meyer and colleagues for seven sight lines with larger distances and higher column densities. This result combined with the variability of O I/N I (six sight lines) indicates that at the low column densities found in the LISM, nitrogen ionization balance is important. Thus, unlike O I, N I cannot be used as a proxy for H I or as a metallicity indicator in the LISM.
The Astrophysical Journal Supplement Series 12/2008; 140(1):3. · 13.46 Impact Factor
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ABSTRACT: We present a new D/H measurement along the sightline to REJ 1738+665, one of the hottest DA stars (T eff ~ 76,000 K, log g ~ 7.85), probing a line of sight in the direction (l = 9689, b = 3195) and extending over a path-length of ~243 pc. Hot DA stars are useful sources for mapping interstellar absorption because of the lack of metal lines, which can lead to systematic errors, making REJ 1738+665 an attractive target for measuring D/H at distances and column densities intermediate between those in the Local Bubble (LB) and the more distant targets studied by the Far Ultraviolet Spectroscopic Explorer (FUSE). The FUSE spectrum towards REJ 1738+665 is rich in interstellar features (H I, H2, D I, C II, N I, N II, O I, Si II, P II, Ar I, and Fe II) and offers another opportunity to probe D/H and D/O outside the LB. We determine the column densities of the species mentioned above. N(H I) is determined using archival Hubble Space Telescope data in conjunction with model atmospheres and synthetic spectra computed in non-local thermodynamic equilibrium in order to better define the stellar continuum in the vicinity of Lyα. Our analysis yields D I/H I = (1.78 ± 0.28 0.25) × 10–5 and D I/O I = (5.25 ± 0.93 0.82) × 10–2 along this sight line (errors stated at the 1σ level). The D/H ratio is consistent with the LB value, while the D/O ratio is only marginally consistent with the LB value (1.6σ above). We find O I/H I = (3.39 ± 0.65 0.57) × 10–4, consistent with that measured in the local interstellar medium (ISM) and N I/H I = (5.01 ± 0.86 0.77) × 10–5, somewhat lower than typical values measured in the ISM..
The Astrophysical Journal 12/2008; 690(2):1045. · 6.02 Impact Factor
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C. A. Grady,
E. F. Polomski,
Th. Henning,
B. Stecklum,
B. E. Woodgate,
C. M. Telesco,
R. K. Piña,
T. R. Gull,
A. Boggess,
C. W. Bowers, [......],
R. A. Kimble,
S. Kraemer,
D. Lindler,
J. L. Linsky,
S. P. Maran, H. W. Moos,
P. Plait,
F. Roesler,
J. G. Timothy,
and D. Weistrop
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ABSTRACT: Coronagraphic imaging of the nearest Herbig Be star with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope, Ks (2.15 μm) imaging with ADONIS at the 3.6 m telescope at La Silla, and mid-infrared imaging with OSCIR using the 4 m Blanco Telescope at Cerro Tololo Inter-American Observatory confirm the detection of the disk reported by Pantin et al. and map the disk out to 5'' (~515 AU) in the optical and at Ks. While the source is unresolved at 10 and 18 μm, it can be traced to 15 at 11.7 μm. We confirm the change in the radial dependence of the disk surface brightness near 27 seen at 1.6 μm by Augereau et al. at Ks. No such break in the power law is seen in the optical. The STIS data reveal spiral dark lane structure, making HD 100546 the third near–zero-age main-sequence Herbig Ae/Be star with structure more than 100 AU from the star. We also optically detect a low surface brightness envelope extending 10'' (1000 AU) from the star, in addition to nebulosity, which is probably associated with DC 292.6-7.9. The survival of the envelope through essentially the entire pre–main-sequence lifetime of the star, coupled with the absence of physical companions within 1500 AU of the star, suggests that envelope lifetimes owe more to the star-forming environment than to mass-loss activity from the Herbig Ae/Be star.
The Astronomical Journal 12/2007; 122(6):3396. · 4.03 Impact Factor
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D. V. Bowen,
E. B. Jenkins,
T. M. Tripp,
K. R. Sembach,
B. D. Savage, H. W. Moos,
W. R. Oegerle,
S. D. Friedman,
C. Gry,
J. W. Kruk,
E. Murphy,
R. Sankrit,
J. M. Shull,
G. Sonneborn,
D. G. York
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ABSTRACT: 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 Galaxy in a way that is consistent with an exponential scale height of 3.2 kpc at negative latitudes or 4.6 kpc at positive latitudes. Average volume densities of OVI along different sight lines exhibit a dispersion of about 0.26 dex, irrespective of the distances to the target stars. This indicates that OVI does not arise in randomly situated clouds of a fixed size and density, but instead is distributed in regions that have a very broad range of column densities, with the more strongly absorbing clouds having a lower space density. Line widths and centroid velocities are much larger than those expected from differential Galactic rotation, but they are nevertheless correlated with distance and N(OVI), which reinforces our picture of a diverse population of hot plasma regions that are ubiquitous over the entire Galactic disk. The velocity extremes of the OVI profiles show a loose correlation with those of very strong lines of less ionized species, supporting a picture of a turbulent, multiphase medium churned by shock-heated gas from multiple supernova explosions. Comment: Accepted for publication in ApJS. Preprint with full resolution images and all 148 spectra available at http://www.astro.princeton.edu/~dvb/o6
11/2007;
