Extragalactic and Galactic Surveys with the Balloon-Borne Large Aperture Sub-Millimeter Telescope

Mass loss in evolved massive stars is one of the least understood yet fundamental aspects of stellar evolution. HOW and WHEN do massive stars lose their H-envelopes? This central question motivates this proposal. We request a continuation of our successful NuSTAR campaign that led to the first detection of a H-poor extragalactic SN in the hard X-rays. We request NuSTAR observations to map the unique situation of the interaction of the H-stripped SN2014C with a H-rich shell ejected by its progenitor star, as part of our approved gamma-ray to radio follow up. Our goal is to complete the mapping of the density profile of the H-rich material at R>7d17 cm to determine its location and total mass, and hence the mass-loss history of the progenitor in the years before stellar death.