Untangling Magellanic Streams

The Magellanic Stream (MS) is known to contain multiple HI strands and corresponding stellar populations are being discovered. Combining a sample of 17 stars from the H3 (“Hectochelle in the Halo at High Resolution”) survey with 891 stars drawn from the Gaia DR3 catalog, we trace stars along a sub-dominant strand of the MS, as defined by gas content, across 30$^\circ$ on the sky. We find that the corresponding dominant strand at the similar position along the MS is devoid of stars with Galactocentric distance $\lesssim 55$ kpc while the subdominant strand shows a close correspondence to such stars. We conclude that (1) these two Stream strands have different origins, (2) they are likely only close in projection, (3) the subdominant strand is tidal in origin, and (4) the subdominant strand is composed of “disk” material, gas and stars, with a chemical composition that marginally favors it coming from the Small Magellanic Cloud.