2026ApJ..1000...40L

In this study, we investigate the chemical properties of the GD-1 stream using crossmatched, data-driven elemental abundances. The results reveal no clear α-knee in the [Mg/Fe]-[Fe/H] plane, and strong abundance consistency between the thin stream and cocoon, supporting a common origin. The absence of multiple-population signatures (e.g., C-N anticorrelation) suggests a low-mass progenitor. Using a test-particle simulation with the particle spray method and including perturbations from the Sagittarius (Sgr) dwarf galaxy, it shows that Sgr does not significantly heat the stream to form the cocoon, but modifies the intrinsic ϕ₂ distribution, in agreement with observations. The trailing arm is narrowly distributed across the width of the stream, while the leading arm is more diffuse, indicating that a major fraction of cocoon stars are present toward the leading arm. Sgr also drags more stream particles moving toward the Galactic center, producing an excess at V_GSR < 0, consistent with data. Our study confirms that the Sgr has a nonnegligible dynamical influence on the GD-1 stream. Other heating mechanisms (e.g., dark matter subhalo encounters and prestripping process inside the parent halo) remain to be considered, and higher-resolution spectroscopy is needed to further constrain chemical abundances.