Late type giants ( RGB/AGB stars ) will be important tracers of the Galactic morphology and evolution in the framework of Gaia , as they are intrinsically bright and thus can probe distant stellar populations or those obscured by interstellar extinction .
A realistic representation of their atmospheres and spectra with stellar atmosphere models is thus of crucial importance , both for the design and optimization of Gaia instruments , as well as the interpretation of provided astrophysical data .
Our analysis of synthetic photometric colors of late-type giants based on PHOENIX , MARCS and ATLAS model atmospheres indicates a general agreement between the current theoretical predictions and observations in the framework of stationary 1-D model atmospheres .
Presently available models allow temperature determinations of RGB/AGB stars to an accuracy of \sim \pm 100 K .
In an exploratory study we try to quantify possible residual systematic effects due to the approximations made in 1-D models using full 3-D hydrodynamical models .
We find that differences in broad-band photometric colors calculated with 1-D and 3-D models are significant , translating to the offsets in effective temperature of up to \Delta T _ { eff } \sim 70 K. Clearly , full 3-D hydrodynamical models will help to alleviate such ambiguities in current theoretical modeling .
Additionally , they will allow to study new phenomena , to open qualitatively new windows for stellar astrophysics in the Gaia-era .