IIb

IIb is a designation used in various domains to denote a specific subclass within a broader category designated as Type II or Class II. In astronomy, IIb refers to a subclass of core-collapse supernovae known as Type IIb. These events begin with spectra showing hydrogen lines, which fade over weeks as helium lines become prominent, indicating partial loss of the progenitor’s outer hydrogen envelope. They are considered transitional between Type II and Type Ib/c supernovae. Progenitors are massive stars that have shed much of their hydrogen, often through binary interaction. A well-studied example is SN 1993J in the galaxy M81. Light curves and spectra help distinguish IIb from other supernova types.

In military history, Type IIb denotes a subclass of German U-boats used during World War II. Part of the broader Type II family, the IIb variant featured refinements over earlier II designs, including greater range and improved habitability, making them capable of operations beyond immediate coastal waters. They served mainly in the North Sea and adjacent waters before larger, more capable designs replaced them.

In other domains, the label IIb may appear as a regional or stage designation within larger classification schemes, with the precise meaning dependent on the specific system. If you are seeking information on a different IIb context, specifying the field or domain can yield more targeted details.