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M. A. Barstow,
M. P. Kowalski,
R. G. Cruddace,
K. S. Wood,
F. Auchere,
N. J. Bannister,
M. F. Bode,
G. E. Bromage,
M. R. Burleigh,
A. C. Cameron, [......],
S. A. Matthews,
M. Orio,
E. Pace,
I. Pagano,
K. J. H. Phillips,
M.-F. Ravet,
J. H. M. M. Schmitt,
B. Y. Welsh,
K. Werner,
G. Del Zanna
[show abstract]
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ABSTRACT: This paper describes a proposed high resolution soft X-ray and Extreme Ultraviolet spectroscopy mission to carry out a survey
of Stellar and Galactic Environments (SAGE). The payload is based on novel diffraction grating technology which has already
been proven in a sub-orbital space mission and which is ready to fly on a satellite platform with minimal development. We
discuss the goals of a SAGE base-line mission and demonstrate the scientific importance of high resolution spectroscopy in
the Extreme Ultraviolet for the study of stars and the local interstellar medium.
Experimental Astronomy 04/2012; 23(1):169-191. · 1.82 Impact Factor
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[show abstract]
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ABSTRACT: We report the first high-resolution (R = 4000) spectroscopic observation of the binary DA white dwarf Feige 24 in the extreme-ultraviolet band 220-250 Å. A stellar atmosphere model assuming a homogeneous element distribution yields a best fit to the data that excludes a significant abundance of photospheric helium. The upper limit on the photospheric helium abundance is 2.5 × 10–6 (90% confidence), equivalent to a lower limit of 1.2 × 10–13 M ☉ on the overlying layer of hydrogen. An ionized interstellar He component (3.9 × 1017 cm–2) is clearly present along the line of sight, which implies an He ionization fraction of 0.72, considerably higher than is typical of the local interstellar medium. However, some of this material may be associated with circumstellar gas, which has been detected by analysis of the C IV absorption line doublet in a Hubble Space Telescope/Space Telescope Imaging Spectrograph spectrum.
The Astrophysical Journal 03/2011; 730(2):115. · 6.02 Impact Factor
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R. G. Cruddace,
M . P. Kowalski,
D. Yentis,
C. M. Brown,
H. Gursky,
M. A. Barstow,
N. P. Bannister,
G. W. Fraser,
J. E. Spragg, J. S. Lapington,
J. A. Tandy,
B. Sanderson,
J. L. Culhane,
T. W. Barbee,
J. F. Kordas,
W. Goldstein,
and G. G. Fritz
[show abstract]
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ABSTRACT: We report a high-resolution (R = 3000-4000) spectroscopic observation of the DA white dwarf G191-B2B in the extreme-ultraviolet band 220-245 Å. A low-density, ionized He component is clearly present along the line of sight, which if completely interstellar implies a He ionization fraction considerably higher than is typical of the local interstellar medium. However, some of this material may be associated with circumstellar gas, which has been detected by analysis of the C IV absorption-line doublet in a Hubble Space Telescope/Space Telescope Imaging Spectrograph spectrum. A stellar atmosphere model assuming a uniform element distribution yields a best fit to the data that includes a significant abundance of photospheric He. The 99% confidence contour for the fit parameters excludes solutions in which photospheric He is absent, but this result needs to be tested using models allowing abundance gradients.
The Astrophysical Journal 12/2008; 565(1):L47. · 6.02 Impact Factor
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M. A. Barstow,
R. G. Cruddace,
M. P. Kowalski,
N. P. Bannister,
D. Yentis, J. S. Lapington,
J. A. Tandy,
I. Hubeny,
S. Schuh,
S. Dreizler,
T. W. Barbee
[show abstract]
[hide abstract]
ABSTRACT: We have continued our detailed analysis of the high-resolution (R= 4000) spectroscopic observation of the DA white dwarf G191-B2B, obtained by the Joint Astrophysical Plasmadynamic Experiment (J-PEX) normal incidence sounding rocket-borne telescope, comparing the observed data with theoretical predictions for both homogeneous and stratified atmosphere structures. We find that the former models give the best agreement over the narrow waveband covered by J-PEX, in conflict with what is expected from previous studies of the lower resolution but broader wavelength coverage Extreme Ultraviolet Explorer spectra. We discuss the possible limitations of the atomic data and our understanding of the stellar atmospheres that might give rise to this inconsistency. In our earlier study, we obtained an unusually high ionization fraction for the ionized He ii present along the line of sight to the star. In the present paper, we obtain a better fit when we assume, as suggested by Space Telescope Imaging Spectrograph results, that this He ii resides in two separate components. When one of these is assigned to the local interstellar cloud, the implied He ionization fraction is consistent with measurements along other lines of sight. However, the resolving power and signal-to-noise available from the instrument configuration used in this first successful J-PEX flight are not sufficient to clearly identify and prove the existence of the two components.
Monthly Notices of the Royal Astronomical Society 08/2005; 362(4):1273 - 1278. · 4.90 Impact Factor
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N. P. Bannister,
E. J. Bunce,
S. W. H. Cowley,
R. Fairbend,
G.W. Fraser,
F. J. Hamilton, J.S. Lapington,
J.E. Lees,
M. Lester,
Steve E. Milan,
J. F. Pearson,
G.J. Price,
R. Willingale
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N. P. Bannister,
E. J. Bunce,
S. W. H. Cowley,
R. Fairbend,
G.W. Fraser,
F. J. Hamilton, J.S. Lapington,
J.E. Lees,
M. Lester,
S. E. Milan,
J. F. Pearson,
G.J. Price,
R. Willingale
[show abstract]
[hide abstract]
ABSTRACT: A comprehensive understanding of the solar wind interaction with Earth's coupled magnetosphere-ionosphere system requires an ability to observe the charged particle environment and auroral activity from the same platform, generating particle and photon image data which are matched in time and location. While unambiguous identification of the particles giving rise to the aurora requires a Low Earth Orbit satellite, obtaining adequate spatial coverage of aurorae with the relatively limited field of view of current space bourne auroral imaging systems requires much higher orbits. A goal for future satellite missions, therefore, is the development of compact, wide field-of-view optics permitting high spatial and temporal resolution ultraviolet imaging of the aurora from small spacecraft in low polar orbit. Microchannel plate optics offer a method of achieving the required performance. We describe a new, compact instrument design which can observe a wide field-of-view with the required spatial resolution. We report the focusing of 121.6 nm radiation using a spherically-slumped, square-pore microchannel plate with a focal length of 32 mm and an F number of 0.7. Measurements are compared with detailed ray-trace simulations of imaging performance. The angular resolution is 2.7±0.2° for the prototype, corresponding to a footprint ~33 km in diameter for an aurora altitude of 110 km and a spacecraft altitude of 800 km. In preliminary analysis, a more recent optic has demonstrated a full width at half maximum of 5.0±0.3 arcminutes, corresponding to a footprint of ~1 km from the same spacecraft altitude. We further report the imaging properties of a convex microchannel plate detector with planar resistive anode readout; this detector, whose active surface has a radius of curvature of only 100 mm, is shown to meet the spatial resolution and sensitivity requirements of the new wide field auroral imager (WFAI).
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R. G. Cruddace,
M. P. Kowalski,
D. J. Yentis,
G. G. Fritz,
H. Gursky,
M. A. Barstow,
N. P. Bannister,
G. W. Fraser,
J. E. Spragg, J. S. Lapington,
J. A. Tandy,
B. Sanderson,
J. L. Culhane,
T. W. Barbee,
J. F. Kordas,
W. Goldstein
264:38.
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M. A. Barstow,
M P Kowalski,
R. G. Cruddace,
K. S. Wood,
Frédéric Auchere,
N.J. Bannister,
M. F. Bode,
G. E. Bromage,
M. R. Burleigh,
A.C. Cameron, [......],
S.A. Matthews,
M. Orio,
E. Pace,
I. Pagano,
K. J. H. Phillips,
Marie-Françoise Ravet-Krill,
J. H. M. M. Schmitt,
B. Y. Welsh,
K. Werner,
G. Del Zanna
Experimental Astronomy.
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M. A. Barstow,
M. R. Burleigh,
N.J. Bannister, J.S. Lapington,
M P Kowalski,
R. G. Cruddace,
K. S. Wood,
Frédéric Auchere,
M. F. Bode,
G. E. Bromage, [......],
Rosine Lallement,
D. de Martino,
S.A. Matthews,
K. J. H. Phillips,
G. Del Zanna,
M. Orio,
E. Pace,
I. Pagano,
J. H. M. M. Schmitt,
B. Y. Welsh
Astrophysics and Space Science.
