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20 July 2010 The Irkutsk Barium filter for narrow-band wide-field high-resolution solar images at the Dutch Open Telescope
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Abstract
A wide-field birefringent filter for the barium II line at 455.4nm is developed in Irkutsk. The Barium line is excellent for Doppler-shift measurements because of low thermal line-broadening and steep flanks of the line profile. The filter width is 0.008nm and the filter is tunable over 0.4nm through the whole line and far enough in the neighboring regions. A fast tuning system with servomotor is developed at the Dutch Open Telescope (DOT). Observations are done in speckle mode with 10 images per second and Keller-VonDerLühe reconstruction using synchronous images of a nearby bluecontinuum channel at 450.5nm. Simultaneous observation of several line positions, typically 3 or 5, are made with this combination of fast tuning and speckle. All polarizers are birefringent prisms which largely reduced the light loss compared to polarizing sheets. The advantage of this filter over Fabry-Perot filters is its wide field due to a large permitted entrance angle and no need of polishing extremely precise surfaces. The BaII observations at the DOT occur simultaneously with those of a fast-tunable birefringent H-alpha filter. This gives the unique possibility of simultaneous speckle-reconstructed observations of velocities in photosphere (BaII) and chromosphere (H-alpha).
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Robert H. Hammerschlag, Valery I. Skomorovsky, Felix C. M. Bettonvil, Galina I. Kushtal, Vyacheslav L. Olshevsky, Robert J. Rutten, Aswin P. L. Jägers, Guus Sliepen, and Frans Snik "The Irkutsk Barium filter for narrow-band wide-field high-resolution solar images at the Dutch Open Telescope", Proc. SPIE 7735, Ground-based and Airborne Instrumentation for Astronomy III, 773585 (20 July 2010); https://doi.org/10.1117/12.858450
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