ALMA 879 μm continuum observations of the triple protostellar system L1448 IRS3B with the difference continuum sources marked. The left colored image is zoomed in on IRS3B and is plotting with a log color stretch. The inner binary is separated by 0.″25 (75 au) and has a circumbinary disk with spiral structure, and the tertiary is separated from the binary by ∼0.″8 (230 au) within one of the arms. The “protostars” are the continuum positions previously discovered in Tobin et al. (2016a), while the “clump” is a new feature, resolved in these observations. The “deficit” indicates the location of depression of flux between IRS3B-a and the “clump.” This is discussed in Sections 3.1 and 6. The beam size of each panel is shown in the lower right (0.″11 × 0.″05 using a Briggs robust parameter of 0.5).