bandhead

Bandhead is a term used in molecular spectroscopy and astrophysics to denote the short-wavelength boundary of a molecular absorption or emission band. It marks the point in a vibrational-rotational band where individual rotational lines become tightly spaced and merge into a quasi-continuous feature. Bandheads are particularly prominent in infrared spectra of diatomic and small polyatomic molecules, such as carbon monoxide (CO), cyanogen (CN), and water (H2O). The precise position and shape of a bandhead depend on the molecular species, the involved vibrational transition, rotational temperature, and Doppler broadening. Observers use bandhead features to constrain physical conditions in astronomical environments, including stellar atmospheres, circumstellar disks, and star-forming regions. Analyzing bandheads can yield estimates of temperature, velocity fields, and chemical composition.

In non-scientific usage, bandhead can refer informally to the leader or the most prominent member of a musical band, i.e., the person who organizes performances or is the public face of the group. The term is regional and casual, and its exact meaning can vary with context.