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Michael Dopita John Hart Peter McGregor Patrick Oates Gabe Bloxham Damien Jones 《Astrophysics and Space Science》2007,310(3-4):255-268
This paper describes the Wide Field Spectrograph (WiFeS) under construction at the Research School of Astronomy and Astrophysics
(RSAA) of the Australian National University (ANU) for the ANU 2.3 m telescope at the Siding Spring Observatory. WiFeS is
a powerful integral field, double-beam, concentric, image-slicing spectrograph designed to deliver excellent throughput, wavelength
stability, spectrophotometric performance and superb image quality along with wide spectral coverage throughout the 320–950 nm
wavelength region. It provides a 25×38 arcsec field with 0.5 arcsec sampling along each of twenty five 38×1 arcsec slitlets.
The output format is optimized to match the 4096×4096 pixel CCD detectors in each of two cameras individually optimized for
the blue and the red ends of the spectrum, respectively. A process of “interleaved nod-and-shuffle” will be applied to permit
quantum noise-limited sky subtraction. Using VPH gratings, spectral resolutions of 3000 and 7000 are provided. The full spectral
range is covered in a single exposure at R=3000, and in two exposures in the R=7000 mode. The use of transmissive coated optics, VPH gratings and optimized mirror coatings ensures a throughput (including
telescope atmosphere and detector) >30% over a wide spectral range. The concentric image-slicer design ensures an excellent
and uniform image quality across the full field. To maximize scientific return, the whole instrument is configured for remote
observing, pipeline data reduction, and the accumulation of calibration image libraries. 相似文献
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CASPIR is a near-infrared spectrometer/imager being built for the Mount Stromlo and Siding Spring Observatories' 2.3 m telescope. The instrument is based on a SBRC 256×256 InSb detector array and uses AR-coated Sapphire, MgO, CaF2, and BaF2 optics to produce two imaging focal plane scales with 0.5/pixel and 0.25/pixel. Spectral resolving powers of 500 will be achieved through a 1×128 slit with three grisms designed for the J, H, and K bands. IJ, JH, and HK cross-dispersed échelle grisms will achieve resolving powers of 1100 through a 1×15 slit. Coronograph and imaging polarimetry modes will also be available. The various observing configurations are selected via five remotely controlled wheels. The instrument design and system architecture are discussed, and preliminary detector performance figures reported. 相似文献
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Summary. The method of stochastic inversion, previously applied to secular variation data, is applied to main field data. Adaptations to the method are required: non-linear, as well as linear, data are used; allowance is made for crustal components in the observatory data; and the prior information is specified differently. The requirement that the models should satisfy a finite lower bound on the Ohmic heating in the core provides strong prior information and gives finite error estimates at the core—mantle boundary.
The new method is applied to data from the epochs 1969.5 and 1980.0. The resulting field models are very much more complex than other models, such as the IGRF models extrapolated to the core, and show considerable small-scale detail which, on the basis of the error analysis, can be believed.
The flux integral over the northern hemisphere is computed at each epoch; the difference between the two epochs is approximately one standard deviation, suggesting that the question as to whether the decay of the dipole is consistent with the frozen-flux hypothesis has been resolved in favour of the hypothesis. 相似文献
The new method is applied to data from the epochs 1969.5 and 1980.0. The resulting field models are very much more complex than other models, such as the IGRF models extrapolated to the core, and show considerable small-scale detail which, on the basis of the error analysis, can be believed.
The flux integral over the northern hemisphere is computed at each epoch; the difference between the two epochs is approximately one standard deviation, suggesting that the question as to whether the decay of the dipole is consistent with the frozen-flux hypothesis has been resolved in favour of the hypothesis. 相似文献
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The non-axisymmetric, non-dipolar magnetic fields of Uranus and Neptune are markedly different from the axially-dipolar dominated fields of the other planets in our Solar System with active dynamos. Stanley and Bloxham [Stanley, S., Bloxham, J., 2004. Nature 428, 151-153] used numerical modeling to demonstrate that Uranus' and Neptune's unusual fields could be the result of a different convective region geometry in these planets. They found that a numerical dynamo operating in a thin shell surrounding a stably-stratified fluid interior produces magnetic field morphologies similar to those of Uranus and Neptune. This geometry for the convective region was initially proposed by Hubbard et al. [Hubbard, W.B., Podolak, M., Stevenson, D.J., 1995. In: Cruickshank, D. (Ed.), Neptune and Triton. Univ. of Arizona Press, Tucson, pp. 109-138] to explain both the magnetic field morphology as well as the low intrinsic heat flows from these planets. Here we examine the influence of varying the stable layer radius in numerical models and compare the results to thin shell models surrounding solid inner cores. We find that a limited range of stable-layer shell thicknesses exist in which Uranus/Neptune-like field morphologies result. This allows us to put constraints on the size of the convective layers in Uranus and Neptune. 相似文献
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Sediments spanning the Olduvai subchron (1.79–1.95 Ma) of ODP Hole 709C in the tropical Indian Ocean were sampled at 5-cm intervals. High-resolution quantitative radiolarian and CaCO3% data have been used as proxies in interpreting palaeoceanographical conditions, an a comparison made with previously obtained oxygen isotope data. Radiolarian data were subjected to principal components analysis, resulting in four varimax factors. Factor 1 accounted for the greatest variation and comprised well-know warm-water and cold-water taxa, with high +ve and - ve scores respectively, which were used in the construction of a temperature index. Results indicate a tripartite temporal division of Olduvai palaeoceanography. In the early Olduvai, prior to 1.895 Ma, and the late Olduvai, approximating the Plio-Pleistocene boundary at 1.81 Ma, divergence-driven equatorial upwelling and high-productivity coincide with isotope-defined ‘interglacials’, and with generally low CaCO3%. However, during the mid-Olduvai, upwelling, productivity and sedimentation rates were all reduced. These changes in palaeoceanography are thought to be linked directly to eccentricity modulated variations in the precession of the Earth's orbit. The early and late Olduvai coincide with periods of minimum eccentricity, when precessional reinforcemnet of the southwest monsoon is weakest, coastal upwelling along the Oman margin is reduced, and zonal wind-driven equatorial divergence upwelling is increased. The mid-Olduvai, however, corresponds with an eccentricity maximum, during which monsoonal activity is stronger and equatorial divergence upwelling weak. 相似文献