High-resolution transmission spectroscopy has revolutionized exoplanet atmospheric characterization since the detection of sodium in HD 209458 b. However, high-resolution fiber-fed spectrographs like HARPS and ESPRESSO failed to reproduce this detection, revealing that stellar effects—particularly the Rossiter-McLaughlin (RM) effect and center-to-limb variations—can mask atmospheric signals, especially in projectedly aligned hot Jupiters.

The RM effect, while complicating atmospheric studies, simultaneously provides crucial measurements of projected spin-orbit angles, offering insights into planetary formation. This is particularly valuable for understanding Neptune-sized planets and their puzzling population features (desert, savanna, ridge). The ATREIDES program addresses this through systematic RM measurements of nearly 60 short-orbit Neptunes.

This thesis presents my contributions to high-resolution spectroscopy through data from HEARTS, ESPRESSO GTO, and ATREIDES programs, investigating atmospheric characterization while probing planetary architectures. I also developed a transit observation planning tool that facilitated ATREIDES's extensive observing campaign.