The Research Station for Astrophysics of the Royal Swedish Academy of Sciences runs a 47.5-cm solar telescope on the Canary Island of La Palma. The research in solar physics takes advantage of the superb observing site to study small-scale solar phenomena such as granulation, sunspot structure, and small magnetic elements. This is done with techniques for imaging, spectroscopy, and polarimetry that are being developed in Stockholm and on La Palma to allow sub-arcsecond resolution.
The telescope is used by many guest observers for solar (and planetary) studies. Many of their observing programs are collaborations with the scientific staff based in Stockholm. Essentially all the observational programs are designed to take advantage of the high spatial resolution obtainable. During 1999 there were several observational runs that were coordinated with observations by the SOHO and TRACE spacecraft and other terrestrial telescopes. Notable in this context is the Dutch Open Telescope which is situated close to the SVST and controlled from that building. This telescope, which has an innovative open design, started regular observations this year.
A common subject of the observational projects is small-scale solar magnetic fields as traced by the small photospheric bright points that are especially bright when imaged in the wavelength of the G band. These bright points are barely resolved at the diffraction-limit of the telescope, and the phase-diversity technique for image restorations has been frequently employed in their study. The later technique is currently being refined and developed. (Also with other applications in mind such as the phasing of segmented space telescopes.)
The formation of the G band in magnetic flux tubes (believed to give rise to the bright points mentioned) as well as other spectral diagnostics of these structures is being investigated theoretically as a collaboration project within the European Solar Magnometry Network, wherein our group is one of the nodes.
Other scientific projects include observational and theoretical studies of
photospheric line-formation processes aimed at improving abundance analysis
work, observations of H-
wings for testing photospheric convection
models, observational studies of the structure and dynamics of sunspot
penumbræ, and numerical magnetohydrodynamic modelling of magnetic flux
structures in the solar convection zone and at the solar surface.
An adaptive optical system featuring a bimorph mirror with 18 actuators and a Shack-Hartmann wavefront sensor was installed and used for observations during the year. This is an important preparation for the New Swedish Solar Telescope (NSST) for which funding has been acquired and construction was started during the year. This telescope will have a clear aperture of 95 cm and will be placed in the existing building. It will keep some of the principles from the SVST being a vacuum telescope with a turret construction on top of the tower. The optical system is however different since the objective is a single lens whose chromatic aberration will be corrected by a Schupmann system. The telescope will be equipped with adaptive optics. Current planning calls for observations starting in 2001.