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Modern Solar Facilities – Advanced Solar Science, 69–76 F. Kneer, K. G. Puschmann, A. D. Wittmann (eds.) c  Universitätsverlag Göttingen 2007 SUNRISE: High resolution UV/VIS observations of the Sun from the stratosphere A. M. Gandorfer1,* , S. K. Solanki1 , P. Barthol1 , V. Martı́nez Pillet2 , W. Schmidt3 , A. M. Title4 , M. Knölker5 , and the SUNRISE team 1 Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany 2 Instituto de Astrofı́sica de Canarias, La Laguna, Tenerife, Spain 3 Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany 4 Lockheed-Martin Solar and Astrophysics Lab., Palo Alto, CA, USA 5 High Altitude Observatory, Boulder, CO, USA * Email: gandorfer@mps.mpg.de Abstract. SUNRISE is an international project for the development, construction, and operation of a balloon-borne solar telescope with an aperture of 1 m, working in the UV/VIS spectral domain. The main scientific goal of SUNRISE is to understand the structure and dynamics of the magnetic field in the atmosphere of the Sun. SUNRISE will provide near diffraction-limited images of the photosphere and chromosphere with an unpredecented resolution down to 35 km on the solar surface at wavelengths around 220 nm. The focal-plane instrumentation consists of a polarization sensitive spectrograph, a Fabry-Perot filter magnetograph, and a phase-diverse filter imager working in the near UV. The first stratospheric long-duration balloon flight of SUNRISE is planned in summer 2009 from the Swedish ESRANGE station. SUNRISE is a joint project of the German Max-Planck-Institut für Sonnensystemforschung (MPS), Katlenburg-Lindau, with the Kiepenheuer-Institut für Sonnenphysik (KIS), Freiburg, Germany, the High-Altitude Observatory (HAO), Boulder, USA, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto, USA, and the Spanish IMaX consortium. In this paper we will present a brief description of the scientific and technological aspects of SUNRISE. 1 Introduction: Science with SUNRISE The solar atmosphere is pervaded by magnetic fields which are at the root of the many fascinating phenomena grouped together under the name solar activity. The magnetic processes that govern solar activity locally determine ‘space weather’ as well as being potentially significant drivers of terrestrial climate variability on a time scale of decades to centuries. If we are to understand these fundamental processes, we must learn how the magnetic field interacts with the solar plasma and must uncover the conversion of energy between its mechanical , magnetic, radiative, and thermal forms. The solar photosphere represents the key interaction region: Thermal, kinetic and magnetic energy all are of the same order of magnitude and transform easily from one form into another. The interaction between convection, radiation and magnetic field in the electrically conducting solar plasma leads to the creation of a rich variety of magnetic structure, from huge sunspots down to intense magnetic field concentrations on length scales down to a few tens of km, as illustrated in Fig. 1. 70 A. Gandorfer et al.: SUNRISE In order to best address these major scientific questions the SUNRISE instruments should provide images of the magnetic structure and measurements of the magnetic field, the flow velocity, and thermodynamic properties of the plasma ... • . . . with a spatial resolution down to 35 km on the Sun, • . . . on a sufficiently large field of view to cover the magnetic connectivity in the solar atmosphere ( 30 Mm), • . . . over a sufficiently long time to follow the evolution of magnetically active regions (i.e., several days), and • . . . simultaneously in different heights of the solar atmosphere. This leads to the concept of a diffraction-limited operation of a telescope of 1 m aperture in the visible and UV spectral ranges (down to 220 nm), with in-flight alignment capability, equipped with a filter imager, a polarimetric spectrograph, and an imaging magnetograph, on long-duration stratospheric balloon flights in the framework of NASA’s LDB program. 2 SUNRISE mission concept Ground based observations of the Sun are suffering from several limitations. The Earth’s atmosphere does not allow access to the interesting solar UV radiation between 220 nm and 370 nm. In addition, atmospheric turbulence usually is creating image blur, so that high resolution imaging is possible only occasionally. Long term and high resolution observations especially in the UV are therefore conducted from space-borne instruments. Avoiding the high costs associated with space missions, but taking the advantages of being above 99% of the Earth’s atmosphere, SUNRISE shall be flown as a balloon-borne stratospheric solar Figure 1. High resolution image of a magnetic solar region...

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