Stellar Atmospheric Parameters: The Four-Step Program and Gaias Radial Velocity Spectrometer

The determination of atmospheric parameters is the first and most fundamental step in the analysis of a stellar spectrum. Current and forthcoming surveys involve samples of up to several million stars, and therefore fully automated approaches are required to handle not just data reduction but also the analysis, and in particular the determination of atmospheric parameters. We propose that a successful methodology needs, at the very least, to pass a series of consistency tests that we dub the four-step program. This and related issues are discussed in some detail in the context of the massive data set to be obtained with the Radial Velocity Spectrometer onboard Gaia