How well are we modeling spectra of solar-type stars?
Jeff Valenti (STScI)
For decades synthetic stellar spectra have failed to match high-quality observed spectra of solar-type stars, due to unrealistic physical approximations, inadequate atomic data, and outmoded software development methodologies. These failures limit our ability to measure accurate exoplanet radii, to detect selective accretion onto exoplanet hosts, to predict photochemistry in exoplanet atmospheres, etc. I will show that the main source of error in synthetic line profiles from static 1D atmosphere models is the neglect of velocity gradients due to surface granulation. Classical microturbulence and macroturbulence parameters poorly describe the spectroscopic effects of granulation. I will describe a kinematic 1D approach that may bridge between more realistic 3D hydrodynamic models and more practical 1D models. Next, I will show that atomic line data have improved significantly, but continuous opacities in the ultraviolet are much too low. Model continuum fluxes for solar-type stars are too bright by roughly a factor of two in the near utlraviolet! With collaborators at OSU, I will incorporate modern photoionization cross-sections for neutral metals into a new opacity library and test the results using high-quality HST spectra of cool stars. Finally, I will comment on the vast numbers of hidden parameters that contribute to a synthetic stellar spectrum, the difficulty assessing errors in fitted parameters, and the need for better software development and testing practices.
Coffee and donuts served at 3:30 in 4054 McPherson Laboratory.
