Ground-Based Solar Research An Assessment and Strategy for the Future (1998) / Chapter Skim
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Appendix H: A Large-Aperture Solar Telescope
Appendix H: A Large-Aperture Solar Telescope
Pages 83-104
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Appendix H A Large-Aperture Solar Telescope NOTE: The material in this appendix is reprinted from material distributed to the Task Group on Ground-based Solar Research on April 28, 1997, and later revised by the scientific staff of the National Solar Observatory.
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Our conclusion is that an aperture of about three meters is the least that will meet the need to study the Sun adequately with the scientifically required angular resolution and sensitivity. Approaching the diffraction limit of such an aperture in the near infrared and blueward into the visible is feasible using a combination of adaptive optics and image reconstruction techniques.
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· The Sun presents us with many important unsolved mysteries and unexplored domains that challenge science. I.2 Key Goals for Solar Research The key goals for solar physics have been compiled by numerous study groups in recent years.
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what heats and cools the chrome sphere, prominences, and low corona. the three-dimensional structure of coronal magnetic fields and its relation to the corona's thermal and dynam*
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In the rest of the report, we select some of the specific goals for more extensive discussion. · magnetic fields and mass motions - test models of magnetoconvection (e.g.
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Scales as small as 0.2 arcsec can be glimpsed in the blue end of the spectrum. Application of image restoration techniques such as differential speckle and phase diversity speckle have allowed high-angular-resolution time series observations of granulation and photospheric magnetic fields to be obtained (e.g.
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Flare Energy Buildup and Release Solar flares represent the most dramatic examples of magnetic field instabilities. According to current ideas, the shearing and twisting of coronal magnetic fields by photospheric convective motions stores energy in coronal electrical currents.
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4.l Representative Goals Requiring Low Scattered Light Coronal M agnetic Fields It is difficult to overestimate the importance of coronal magnetic fields for the physics of the corona. The field is responsible for the highly inhomogeneous structure, with scales ranging from sub arcsec (November and Koutchmy 1996, Golub et al.
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1990; Hassler and Moran 1993) in coronal spectrum lines, but periodic Doppler shifts have not.
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How is the equilibrium temperature related to the loop's magnetic field strength? A large aperture coronagraph could isolate individual structures and investigate the relationship between field strength and equilibrium temperature.
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Infrared observations from space with useful angular resolution are impractical, and only one ground-based telescope in the world currently accesses the full infrared spectrum. This unique capability, exploited using modern detectors, has given us a new window on solar physics.
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We confine ourselves here to the briefest reminder that the infrared spectrum offers proven advantages for measuring the "bread-and-butter" quantities of stellar physics: temperature, density, and chemical composition, as well as magnetic field strength. Temperature At photospheric temperatures, the intensity of the thermal infrared continuum closely approximates a Rayleigh-leans distribution.
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used infrared intensities to demonstrate a relationship between temperature and magnetic field strength in sunspots (the Tower contrast and stray-light contamination of sunspots in the {R was an additional advantage)
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is under construction to take advantage of possible future flight opportunities (Title 19961. Given the difficulties experienced in placing even moderate aperture solar telescopes in space, at present, the ground is the only option for a large-aperture telescope.
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For these cases, space is the obvious solution. However, even with these limitations, the high angular resolution provided by a large aperture ground-based solar telescope equipped with adaptive optics will be a stunning breakthrough for solar research.
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To measure the line-of-sight component of a uniform magnetic field to I gauss requires about 5000, and the transverse component to 30 gauss about 10,000. The exact values depend on the spectrum lines and techniques used to fit polarized line profiles.
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angular resolution in the thermal infrared through direct imaging. However, some general statements can be made.
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At longer wavelengths, solar infrared measurements with useful angular resolution are logically done from the ground. The photon flux in the infrared is reasonably well matched to the attainable apertures.
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~ arcsec requires nearly diffraction-limited performance by an aperture no smaller than 3 meters, from the near infrared to as far blueward as possible. Such performance is attainable at a good site on the ground by using a combination of adaptive optics and image reconstruction techniques.
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1994, in Infrared Solar Physics (IAU Symp.
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end Lindsey, C., eds. 1994, Infrared Solar Physics (TAU Symp.
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A sky background of 10 x 10-6 and an overall efficiency of 0.1 are assumed. A loop lifetime of 1000 seconds enforces a need to use large apertures to reach expected magnetic field strengths.
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