High-resolution spectra of the hot white dwarf G191-B2B, covering the
wavelength region 905-1187A, were obtained with the Far Ultraviolet
Spectroscopic Explorer (FUSE). This data was used in ...conjunction with existing
high-resolution Hubble Space Telescope STIS observations to evaluate the total
HI, DI, OI and NI column densities along the line of sight. Previous
determinations of N(DI) based upon GHRS and STIS observations were
controversial due to the saturated strength of the DI Lyman-alpha line. In the
present analysis the column density of DI has been measured using only the
unsaturated Lyman-beta and Lyman-gamma 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(DI)
= 13.40 +/-0.07, log N(OI) = 14.86 +/-0.07, and log N(NI) = 13.87 +/-0.07
quoted with 2-sigma uncertainties. The measurement of the HI column density by
profile fitting of the Lyman-alpha line has been found to be unsecure. If
additional weak hot interstellar components are added to the three detected
clouds along the line of sight, the HI column density can be reduced quite
significantly, even though the signal-to-noise ratio and spectral resolution at
Lyman-alpha are excellent. The new estimate of N(HI) toward G191-B2B reads: log
N(HI) = 18.18 +/-0.18 (2-sigma uncertainty), so that the average (D/H) ratio on
the line of sight is: (D/H) = 1.66 (+0.9/-0.6) *10^-5 (2-sigma uncertainty).
We report the first Far Ultraviolet Spectroscopic Explorer (FUSE)
measurements of diffuse O VI (lambda,lambda 1032,1038) emission from the
general diffuse interstellar medium outside of supernova ...remnants or
superbubbles. We observed a 30arcsec x 30arcsec region of the sky centered at l
= 315 and b = -41. From the observed intensities
(2930+/-290(random)+/-410(systematic) and 1790+/-260(random)+/-250(systematic)
photons/cm/cm/s/sr in the 1032 and 1038 Angstrom emission lines, 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 constrain models.
The data also yield the first intensity measurement of the C II 3s2 S1/2 to 2p2
P3/2 emission line at 1037 Angstroms 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.
Science 293:1112-1116,2001 The neutral hydrogen and the ionized helium absorption in the spectra of
quasars are unique probes of structure in the early universe. We present
Far-Ultraviolet ...Spectroscopic Explorer observations of the line of sight to the
quasar HE2347-4342 in the 1000-1187 A band at a resolving power of 15,000. We
resolve the He II Ly alpha absorption as a discrete forest of absorption lines
in the redshift range 2.3 to 2.7. About 50 percent of these features have H I
counterparts with column densities log N(HI) > 12.3 that account for most of
the observed opacity in He II Ly alpha. The He II to H I column density ratio
ranges from 1 to >1000 with an average of ~80. Ratios of <100 are consistent
with photoionization of the absorbing gas by a hard ionizing spectrum resulting
from the integrated light of quasars, but ratios of >100 in many locations
indicate additional contributions from starburst galaxies or heavily filtered
quasar radiation. The presence of He II Ly alpha absorbers with no H I
counterparts indicates that structure is present even in low-density regions,
consistent with theoretical predictions of structure formation through
gravitational instability.
Analyses of spectra obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, together with spectra from the Copernicus and IMAPS instruments, reveal an unexplained very wide range ...in the observed deuterium/hydrogen (D/H) ratios for interstellar gas in the Galactic disk beyond the Local Bubble. We argue that spatial variations in the depletion of deuterium onto dust grains can explain these local variations in the observed gas-phase D/H ratios. We present a variable deuterium depletion model that naturally explains the constant measured values of D/H inside the Local Bubble, the wide range of gas-phase D/H ratios observed in the intermediate regime (log N(H I} = 19.2-20.7), and the low gas-phase D/H ratios observed at larger hydrogen column densities. We consider empirical tests of the deuterium depletion hypothesis: (i) correlations of gas-phase D/H ratios with depletions of the refractory metals iron and silicon, and (ii) correlation with the molecular hydrogen rotational temperature. Both of these tests are consistent with deuterium depletion from the gas phase in cold, not recently shocked, regions of the ISM, and high gas-phase D/H ratios in gas that has been shocked or otherwise heated recently. We argue that the most representative value for the total (gas plus dust) D/H ratio within 1 kpc of the Sun is >=23.1 +/- 2.4 (1 sigma) parts per million (ppm). This ratio constrains Galactic chemical evolution models to have a very small deuterium astration factor, the ratio of primordial to total (D/H) ratio in the local region of the Galactic disk, which we estimate to be f_d <= 1.19 +/-0.16 (1 sigma) or <= 1.12 +/- 0.14 (1 sigma) depending on the adopted light element nuclear reaction rates.
We have used moderate-resolution (FWHM ~ 25 km/sec) spectra of AGNs and QSOs
observed by the Far Ultraviolet Spectroscopic Explorer (FUSE) 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 (|V(LSR)| > 100 km/sec) O VI 1031.93 A absorption with
log N(O VI) = 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 about 30
percent, with a full range of 10-70 percent. The O VI detections imply that hot
(log T(K) = 5-6) 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.
Using Far Ultraviolet Spectroscopic Explorer and Hubble Space Telescope observations of the QSO PG1259+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. A new Westerbork Synthesis Radio Telescope (WSRT) interferometer map of the H I 21 cm emission toward PG1259+593 indicates that the sight line passes through a compact concentration of neutral gas in Complex C. We find D/H = (2.2+/-0.7)x10^-5, O/H = (8.0+/-2.5)x10^-5, and D/O = 0.28+/-0.12. The metallicity of Complex C gas toward PG1259+593 is approximately 1/6 solar, as inferred from the oxygen abundance O/H = -0.79 (+0.12, -0.16). While we cannot rule out a value of D/H similar to that found for the local ISM, we can confidently exclude values as low as those determined recently for extended sight lines in the Galactic disk. 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. Abbreviated abstract
Lipid composition of prototropic and histidine-dependent strains of Candida tripicalis D-2 was studied by the method of gas and thin layer chromatography. Essential differences are shown in the ...quantitative composition of neutral lipids and fatty acids of the studied strains.
Astrophys.J.538:L7-L11,2000 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 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 this data and prelaunch laboratory
measurements.
