Equation of State Studies Using SOHO Data

Principal Investigator / Institution: Werner Dappen, USC

This is a new task to use the SOHO data to obtain constraints on the equation
 of state while pre-helioseismic solar models were quite adequately using
 simple ideal-gas equations of state, it turned out that non-ideal corrections 
had to be included in order to match the constraints from solar oscillation 
frequencies.  in particular, the effect of the Coulomb pressure correction in 
the solar plasma became clearly evident.  Finer non-ideal effects are 
emerging in analyses of current observational data.  The finer effects in 
the equation of state are subject of current controversial physical models 
of plasmas.  A helioseismic analysis effectively allows experiments to be 
carried out on the physics of the plasma at this level of detail.  This is a 
severe test of theory.  Although the non-ideal effects are relatively small 
corrections (typically 1-10% of the pressure), the extraordinary 
observational accuracy makes the helioseismic data sensitive to them, 
imposing stringent constraints on their theoretical computation to the 
required level.  In this way, the subtle quantum many-body effects that 
contribute to the small, but theoretically challenging non-ideal corrections 
in the equation of state, can be studied in the Sun.  Knowledge about these 
non-ideal corrections will have astrophysical implications for higher 
densities plasmas of low-mass stars, brown dwarfs, and giant planets.  
So far, the P.I. has been carrying out solar modeling and inversion tasks 
in collaboration with Joergen Christensen-Dalsgaard (Aarhus).  To enable 
the higher cadence required by the flurry of the SOI/MDI data, this proposal 
requests support to develop solar modeling and inversion capabilities at USC, 
in order to analyze the data for equation of state effects.  In this way, SOHO 
data will make a contribution to solar physics, stellar astrophysics, and 
basic physics.