RUI: Multi-wavelength Spectroscopic and Spectropolarimetric Diagnostics of the Solar Atmosphere

This 3-year project aims to develop data analysis techniques to infer the thermodynamic and magnetic structure of the solar atmosphere from the photosphere to a height of about 2-5 Mm using simultaneous multi-wavelength observations of spectral lines formed at different heights. Many current analysis approaches yield only simplified results instead of stratifications of physical properties.

The project will develop an automatic, semi-empirical method to convert such results of lower complexity to atmospheric stratifications wherever they cannot be directly derived from an inversion of spectra. The method will be tested on observations of sunspots, where additional constraints on the magnetic field topology, connectivity and the gas density are available from the well-organized spatial structuring and magnetic field extrapolations.

The results will enable one to address nearly all currently open questions in relation to the lower solar atmosphere, e.g., understanding the fine-structure and the properties of mass flows and oscillations inside sunspots from deep in the photosphere to the chromosphere. This will add to our understanding of the basic properties of sunspots, which are some of the most enigmatic objects in astrophysics.

Sunspots are an integral part of late-type stars, play a vital role in stellar evolution and can influence life-supporting exoplanets including the Earth through space weather events that are rooted in sunspots and the active regions that host them.

The method to infer the thermodynamic and magnetic structure of the solar atmosphere will be based on a piece-wise analysis of different photospheric and chromospheric spectral lines with already available inversion codes and the additional tools developed during the project. For any spectral line where current analysis methods do not provide stratifications of physical parameters of the solar atmosphere, e.g., the prominent chromospheric spectral line of neutral Hydrogen Alpha at 656 nm, a semi-empirical method using external constraints from magnetic field extrapolations will be employed to convert the results retrieved from a simplified modeling of the radiative transfer to stratifications.

A major effort will be to consistently convert and combine the stratifications from different height regimes into a single atmospheric stratification of all relevant thermodynamic and magnetic parameters from 0 to about 5 Mm in the solar atmosphere. The resulting atmospheric model is expected to be in hydrostatic equilibrium, to provide all physical parameters on a geometrical height scale and to reproduce all observed spectral lines when a spectral synthesis of the model atmosphere is executed.

A successful demonstration of the reliability of the approach on sunspot observations, where additional constraints are available because of the spatial continuity of the magnetic field topology, will allow one to decide on its suitability for observations of arbitrary solar targets. Any scientific question that requires accurate physical properties of the lower solar atmosphere can potentially be addressed with the results of the analysis approach.

The tool developed through this project will be freely available to the community of solar researchers and will help in fully exploiting the observations with the NSF’s 4-meter class Daniel K. Inouye Solar Telescope. The participation of underrepresented students at California State University Northridge to both analyze and visualize the high-resolution spectropolarimetric data will prepare a future generation of the scientific workforce in solar physics.

The research and EPO agenda of this project supports the Strategic Goals of the AGS Division in discovery, learning, diversity, and interdisciplinary research.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.