What happens in the innermost disk at the time of planet formation? While direct mapping cannot access these regions, emission (and absorption) lines in young stars trace their winds, accretion-related structures, spots, and innermost disk. In the optical, a large number of species with various excitation potentials can provide information on the temperature, density, and velocity of hot and tiny structures. Using time-resolved spectroscopy covering several rotational and disk orbital periods, we can obtain a very detailed view of the structure and variability of accretion columns and spots and information on the presence and launching points of stellar/disk winds in young stars. In outbursting sources, the temperature variation allows us to spectroscopically access an even larger region of the disk and surroundings. Here we present the results on several young stars with different properties, discussing what we can learn from "reading between their (spectral) lines" and how to achieve this with the STAR-MELT Python package, which will be publicly released soon (see Poster and video by Justyn Campbell-White for further details).

{"references": ["Sicilia-Aguilar, A., et al. (2015), A&A, 580, A82", "Sicilia-Aguilar, A., et al. (2017), A&A 607, 127", "Sicilia-Aguilar, A., et al. (2020a), A&A 633, 37", "Sicilia-Aguilar, A., et al. (2020b), A&A 643, 29", "Campbell-White, Sicilia-Aguilar, Matsumura, et al. in prep."]}