Colloquium: Jeff Valentini (STScl)
Inaccurate Abundances for Cool Stars
For many topics in astrophysics, stellar parameters with limited accuracy are sufficient. Some astrophysical problems require better accuracy than is typically achieved today, for example characterizing exoplanet host stars. Decades of research have addressed several issues that limited accuracy in the past, e.g., radiastive transfer algorithms, line data for atoms and molecules, continuous opacities, and non-LTE rate coefficients. A key limitation that still limits accuracy is the treatment of kinematics in cool stellar photospheres. Cool stellar photospheres have velocity fields that are not modeled adequately in 1D and 2D models. 1D models use various approximations that ultimately limit accuracy achievable today. Very common approximations include microturblence and empirical line data, despite availability of more accurate line data. These approximations are unnecessary when the model includes velocity gradients in the photosphere. 3D hydrodynamic models calculate photospheric velocity fields, but are computationally expensive. I will show a novel approach for modeling photospheric velocity gradients in a 1D model. Solar lines can be reproduced without the need for microturbulence or empirical line data. This demonstrates that a key limitation of current 1D models is treatment of velocity fields. One other limitation that needs attention is software development methodology.
Feb. 4, 2021, 2:30 p.m. – 3:30 p.m.
Colloquium zoom room