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A source coincident with the position of the type IIb supernova (SN) 2008ax is identified in pre‐explosion  Hubble Space Telescope  ( HST ) Wide Field Planetary Camera 2 observations in three optical filters. We identify and constrain two possible progenitor systems: (i) a single massive star that lost most of its hydrogen envelope through radiatively driven mass‐loss processes, prior to exploding as a helium‐rich Wolf–Rayet star with a residual hydrogen envelope, and (ii) an interacting binary in a low‐mass cluster producing a stripped progenitor. Late time, high‐resolution observations along with detailed modelling of the SN will be required to reveal the true nature of this progenitor star.

The type IIb SN 2008ax: the nature of the progenitor