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[show abstract]
[hide abstract]
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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[show abstract]
[hide abstract]
ABSTRACT: Because of a lack of spectral resolution in existing spectroscopic data, current white dwarf atmospheric models cannot explain the atmospheric structure, and resultant extreme-ultraviolet (EUV) emission, of G191-B2B unambiguously. Therefore, a new rocket-borne EUV spectrograph was designed, built, calibrated, and launched. This instrument observed G191-B2B over a bandpass of 254-317 Å and with a resolving power of λ/Δλ ≈ 2800. Highly statistically significant absorption features within the flight spectrum, coupled with metal-rich modeled stellar spectra, provide evidence for blended features of Fe IV/Fe V and Fe IV/O III in G191-B2B's atmosphere. A 3 σ upper limit of 2 × 10-5 has been placed on the photospheric helium abundance, arguing against models that rely on He II as a major EUV opacity source.
The Astrophysical Journal 12/2008; 562(2):992. · 6.02 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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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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K. R. Sembach,
R. Cen,
R. Dave,
T. Cook,
M. Donahue,
D. C. Ebbets, J. C. Green,
E. B. Jenkins,
W. R. Oegerle,
J. P. Ostriker,
J. X. Prochaska,
B. D. Savage,
J. M. Shull,
H. P. Stahl,
T. M. Tripp,
B. D. Oppenheimer,
S. R. Furlanetto,
T. Fang
[show abstract]
[hide abstract]
ABSTRACT: This concept study defines the scientific requirements and instrumental
performance needed for a space mission to detect and characterize the
cosmic web of matter, the processes that produce and govern its
structure, and its influence on the formation and evolution of galaxies.
Our new numerical simulations explicitly track the observational
signatures of the web gas as a function of time (redshift) up to the
present day. The simulations include prescriptions for feedback
interactions between galaxies and the intergalactic medium, and
demonstrate that the ultraviolet O VI lines and the H I Lyman alpha line
are premier diagnostics of low-density cosmic web regions. We define the
field of view, angular resolution, and sensitivity needed to detect the
web filaments in emission and absorption, and the spectral resolution
needed to separate the gas signatures from foreground signals. These
results define the driving science requirements for the Baryonic
Structure Probe and any other future missions seeking to characterize
the cosmic web. The science requirements can be met with a dedicated
observatory in an L2 orbit capable of simultaneously observing both the
faint emissions and weak absorption lines from the cosmic web. Our
mission concept baselines a low risk 5-year core science mission with a
10-year design lifetime. Technological investments that would improve
performance include the development of high quantum efficiency
ultraviolet detectors, large format diffraction gratings, and improved
optical coatings.
11/2005; 37:1197.
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K. R. Sembach,
D. Ebbets,
R. Cen,
T. Cook,
R. Dave,
M. Donahue, J. C. Green,
E. B. Jenkins,
W. R. Oegerle,
J. P. Ostriker,
J. X. Prochaska,
B. D. Savage,
J. M. Shull,
H. P. Stahl,
T. M. Tripp
[show abstract]
[hide abstract]
ABSTRACT: Hydrodynamical simulations of the evolution of the intergalactic medium
provide valuable insights into the probable evolution of baryons in the
presence of cold dark matter as a function of redshift. A primary
prediction of these simulations is that much of the baryonic mass in the
low-redshift universe is in the form of a warm-hot intergalactic medium
(WHIM). Progressing beyond simple detections of the WHIM to a robust set
of observationally testable predictions and a more complete description
of the evolution of the WHIM would have profound implications for
understanding the growth of large scale structure, the formation of
galaxies, and the distribution of dark matter.
The Baryonic Structure Probe will strengthen the foundations of
observational cosmology by directly detecting, mapping, and
characterizing the cosmic web of intergalactic material, its inflow into
galaxies, and its enrichment with the products of stellar and galactic
evolution. This Origins Probe Concept Study will provide a clear
articulation of the scientific priority of these investigations, refine
expectations of the absorption and emission properties of the WHIM,
describe a mission concept capable of making major advances to our
knowledge of cosmic structure, and define a roadmap for investments in
enabling technologies. These will serve as inputs into NASA's strategic
planning process.
11/2004; 36:1509.
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B. P. Wakker,
B. D. Savage,
K. R. Sembach,
P. Richter,
M. Meade,
E. B. Jenkins,
J. M. Shull,
T. B. Ake,
W. P. Blair,
S. D. Friedman, J. C. Green,
R. F. Green,
J. W. Kruk,
H. W. Moos,
E. M. Murphy,
W. R. Oegerle,
D. J. Sahnow,
G. Sonneborn,
E. Wilkinson,
D. G. York
[show abstract]
[hide abstract]
ABSTRACT: We present FUSE observations of OVI absorption in a sample of 100 extragalactic targets and 2 distant halo stars. We describe the details of the calibration, alignment in velocity, continuum fitting, and manner in which contaminants were removed (Galactic H2, absorption intrinsic to the background target and intergalactic Ly-beta lines). We searched for OVI absorption in the velocity range -1200 to 1200 km/s. With a few exceptions, we only find OVI between -400 and 400 km/s; the exceptions may be intergalactic OVI. We discuss the separation of the observed OVI absorption into components associated with the Galactic halo and components at high-velocity, which are probably located in the neighborhood of the Galaxy. We describe the measurements of equivalent width and column density, and we analyze the different contributions to the errors. We conclude that low-velocity Galactic OVI absorption occurs along all sightlines - the few non-detections only occur in noisy spectra. We further show that high-velocity OVI is very common, having equivalent width >65 mAA in 50% of the sightlines and >30 mAA in 70% of the high-quality sightlines. The high-velocity OVI absorption has velocities relative to the LSR of +/-(100--330) km/s; there is no correlation between velocity and absorption strength. We present 50 km/s wide OVI channel maps. These show evidence for the imprint of Galactic rotation. They also highlight two known HI high-velocity clouds (complex~C and the Magellanic Stream). The channel maps further show that OVI at velocities <-200 km/s occurs along all sightlines in the region l=20-150, b<-30, while OVI at velocities >200 km/s occurs along all sightlines in the region l=180-300, b>20 (abbreviated).
08/2002;
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H. W. Moos,
K. R. Sembach,
A. Vidal-Madjar,
D. G. York,
S. D. Friedman,
G. Hebrard,
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,
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, O I, and N I along seven sight lines that probe the local interstellar medium (LISM) at distances from 37 pc 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 HST data, IUE data, and published EUVE measurements. The weighted mean of D I/H I for these five sight lines is (1.52 +/- 0.08) x10-5 (1 sigma 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) x10-2. It is likely that the 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) x10-4, comparable to the weighted mean (3.43 +/- 0.15) x10-4 reported for 13 sight lines probing larger distances and higher column densities (Meyer et al. 1998, Meyer 2001). The FUSE weighted mean of N I/H I for the five sight lines is half that reported by Meyer et al. (1997) 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. Subject Headings: cosmology: observations- ISM: abundances- ISM: evolution - Galaxy:abundances-Ultraviolet:ISM
01/2002;
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W. C. Cash,
L. L. Cowie,
A. F. Davidsen,
A. K. Dupree,
P. D. Feldman,
S. D. Friedman, J. C. Green,
R. F. Green,
C. Gry,
J. B. Hutchings,
E. B. Jenkins
[show abstract]
[hide abstract]
ABSTRACT: The Far Ultraviolet Spectroscopic Explorer satellite observes light in the far-ultraviolet spectral region, 905--1187 A , with a high spectral resolution. The instrument consists of four co-aligned prime-focus telescopes and Rowland spectrographs with microchannel plate detectors. Two of the telescope channels use Al : LiF coatings for optimum reflectivity between approximately 1000 and 1187 A , and the other two channels use SiC coatings for optimized throughput between 905 and 1105 A . The gratings are holographically ruled to correct largely for astigmatism and to minimize scattered light. The microchannel plate detectors have KBr photocathodes and use photon counting to achieve good quantum efficiency with low background signal. The sensitivity is sufficient to examine reddened lines of sight within the Milky Way and also sufficient to use as active galactic nuclei and QSOs for absorptionline studies of both Milky Way and extragalactic gas clouds. This spectral region contains a number of key scientific diagnostics, including O vi,Hi,Di, and the strong electronic transitions of H 2 and HD.
05/2001;
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[show abstract]
[hide abstract]
ABSTRACT: We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the sightline 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)_solar. This value of N(Fe II)/N(H I) implies that the metallicity of complex C along this sightline may be higher than that along the Mrk 290 sightline (0.1 solar) found by Wakker et al. (1999). 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 significan t 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 non-detections 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 H_2 absorption is seen in the high velocity cloud to a limit N(H_2)<2.0x10^14 cm^-2. Future FUSE observations of extragalactic objects behind Galactic high velocity clouds will allow us to better constrain models of HVC origins.
06/2000;
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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,
E. M. Murphy
[show abstract]
[hide abstract]
ABSTRACT: Far-ultraviolet spectra of 11 AGNs observed by FUSE are analyzed to obtain measures of O VI 1031.93 A 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 mid-plane density, n0 = 2x10^(-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 suggest 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.
06/2000;
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J. M. Shull,
J. Tumlinson,
E. B. Jenkins,
H. W. Moos,
B. L. Rachford,
B. D. Savage,
K. R. Sembach,
T. P. Snow,
G. Sonneborn,
D. G. York,
W. P. Blair, J. C. Green,
S. D. Friedman,
D. J. Sahnow
[show abstract]
[hide abstract]
ABSTRACT: We describe a moderate-resolution FUSE mini-survey of H2 in the Milky Way and Magellanic Clouds, using four hot stars and four AGN as background sources. FUSE spectra of nearly every stellar and extragalactic source exhibit numerous absorption lines from the H2 Lyman and Werner bands between 912 and 1120 A. One extragalactic sightline, PKS 2155-304, with low N(HI) shows no detectable H2 and could be the "Lockman Hole" of molecular gas, of importance for QSO absorption-line studies. We measure H2 column densities in low rotational states (J = 0 and 1) to derive rotational and/or kinetic temperatures of diffuse interstellar gas. The higher-J abundances can constrain models of the UV radiation fields and gas densities. In three optically thick clouds toward extragalactic sources, we find n(H) ~ 30-50 cm(-3) and cloud thicknesses of 2-3 pc. The rotational temperatures for H2 at high Galactic latitude, = 107 +/- 17 K (seven sightlines) and 120 +/- 13 K (three optically thick clouds), are higher than those in the Copernicus sample composed primarily of targets in the disk. We find no evidence for great differences in the abundance or state of excitation of H2 between sight lines in the Galaxy and those in the SMC and LMC. In the future, we will probe the distribution and physical parameters of diffuse molecular gas in the disk and halo and in the lower-metallicity environs of the LMC and SMC.
05/2000;
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J. M. Shull,
M. L. Giroux,
S. V. Penton,
J. Tumlinson,
J. T. Stocke,
E. B. Jenkins,
H. W. Moos,
W. R. Oegerle,
B. D. Savage,
K. R. Sembach,
D. G. York, J. C. Green,
B. E. Woodgate
[show abstract]
[hide abstract]
ABSTRACT: We describe a moderate-resolution (20-25 km/s) FUSE study of the low-redshift intergalactic medium. We report on studies of 7 extragalactic sightlines and 12 Ly-beta absorbers that correspond to Ly-alpha lines detected by HST/GHRS and STIS. These absorbers appear to contain a significant fraction of the low-z baryons and were a major discovery of the HST spectrographs. Using FUSE data, with 40 mA (4-sigma) Lyb detection limits, we have employed the equivalent width ratio of Lyb/Lya and occasionally higher Lyman lines, to determine the doppler parameter, b, and accurate column densities, N(HI), for moderately saturated lines. We detect Lyb absorption corresponding to all Lya lines with EW > 200 mA. The Lyb/Lya ratios yield a preliminary distribution function of doppler parameters, with mean = 31.4 +/- 7.4 km/s and median b = 28 km/s, comparable to values at redshifts z = 2.0-2.5. If thermal, these b-values correspond to T(HI) ~ 50,000 K, although the inferred doppler parameters are considerably less than the widths derived from Lya profile fitting, <b(dopp)/b(width)> = 0.52. The typical increase in column density over that derived from profile fitting is Delta[log N(HI)] = 0.3, but ranges up to 1.0 dex. Our data suggest that the low-z Lya absorbers contain sizable non-thermal motions or velocity components in the line profile, perhaps arising from cosmological expansion and infall.
05/2000;
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[show abstract]
[hide abstract]
ABSTRACT: Spectroscopic data obtained from the spectrograph of the Far Ultraviolet
Spectroscopic Explorer (FUSE) during the integration and test phase of
development has been acquired and analyzed. We present the most current
measurement of the resolution of FUSE as a function of wavelength over
the entire bandpass of 905 - 1187 Angstroms. The FUSE instrument outputs
spectra through four channels. Both H2 and PtNe emission line
spectra were studied using an automated routine to determine the full
width at half maximum (FWHM) of more than 100 spectral lines per
channel. The resolution of the instrument has been characterized using a
subset of the emission lines of both H2 and PtNe. The
spectral lines chosen were determined to be unblended, and were
identified as arising from only single molecular transitions. Using
resolution as a diagnostic tool, we have performed a self consistency
check to assure that different channels of the spectrograph image
identical wavelength regions with comparable resolutions. In addition,
we have studied the effects of focal plane motion on the resolution of
FUSE. The results of these studies provide a prediction of the
instrument's performance after launch.
11/1998; 30:1270.
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[show abstract]
[hide abstract]
ABSTRACT: We present initial results of the performance of the Far Ultraviolet
Spectroscopic Explorer (FUSE) spectrograph as measured during alignment
and characterization of the instrument. The measured performance
including resolution, efficiency, and scattered light is discussed along
with the various instrumental effects contributing to the final
performance characteristics. Finally, we present the laboratory spectra
of N2, CO, O2, H2, Ar, and Pt/Ne at 30,000 resolution between 900
Angstroms and 1150 Angstroms as obtained with the spectrograph. These
data are extremely interesting in and of themselves and demonstrate how
powerful an astronomical instrument the FUSE instrument will be once in
orbit.
12/1997; 30:764.
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04/1996; 28:835.
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04/1996; 28:915.
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[show abstract]
[hide abstract]
ABSTRACT: We present two holographic recording solutions that produce gratings suitable for use at grazing incidence in the extreme ultraviolet. The rulings are formed when the interference pattern of two spherical wave fronts is recorded on a planar substrate. Each grating is designed to minimize or eliminate the dominant aberration terms in order to maximize the spectral and spatial resolution of the system. In the first design, the dominant astigmatism term in a power-series expansion of the light path function is eliminated; in the second design, the dominant comatic terms are minimized. Each grating is placed directly in a converging light beam at grazing incidence to provide high system efficiency in the extreme ultraviolet. The aberration control afforded by both recording solutions is excellent, providing detector-limited spatial and spectral resolution over much of the usable bandpass. Furthermore, the aberration control is maintained over a wide range of beam speeds and off-axis angles, thereby outperforming conventional varied line-space gratings for use in the extreme ultraviolet. We discuss the methodology used to develop the recording solutions, model and compare the performance of the gratings, and discuss possible space-based applications for these gratings.
Applied Optics 08/1995; 34(22):4685-96. · 1.41 Impact Factor
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The Astrophysical Journal 10/1993; 418:L41. · 6.02 Impact Factor
