Principal Investigator: Mathias Maercker, Sven Wedemeyer

Institute: OSO, Sweden & University of Oslo, Norway

Abstract:

ALMA offers diagnostic possibilities for the study of our Sun, which have not been available before. In particular, ALMA's ability to serve as an essentially linear thermometer of the atmospheric gas at unprecedented spatial resolution in this wavelength range has great diagnostic potential. Consequently, solar ALMA observations will contribute significantly to answering long-standing questions about the structure, dynamics and energy balance of the outer layers of the solar atmosphere and thus promise high-impact results. In contrast to many other astronomical sources, the Sun does fill the primary beam of ALMA with a complex emission pattern on a large range of spatial scales, which evolves on extremely short time scales of only seconds and even below. Fully exploiting ALMA's possibilities therefore requires imaging at very high cadence, possibly down to 100ms. Such a high-cadence imaging capability, which is the topic of the development study proposed here, has yet to be investigated and developed. The first regular observation of the Sun in Cycle 4 are limited to integration times of 2s.

We propose to investigate a potential high-cadence imaging mode by using state-of-the-art numerical simulations as basis for a solar simulation pipeline. The simulations, which provide realistic test cases with precisely know properties, are then input in the to-be-developed Solar ALMA Simulator, which produces artificial visibilities. The simulator tool will allow to investigate the influence of different instrumental effects and set-ups on the final reconstructed data. Comparisons between the input and output of the simulation pipeline will then reveal how well imaging at high cadence performs. The main study result will be the evaluation of the potential performance of this new capability and recommendations for observing and post- processing strategies. Next to the deliverables, further by-products of the study are the Solar ALMA Simulator, reviewed data reduction routines, and a well-defined solar simulation pipeline, which can also be used to investigate other potential solar observing modes in the future.