Two Fraunhofer lines in the ultraviolet part of the spectrum, at 396.8 and 393.4 nm respectively, due to singly ionized calcium (Ca II). They are prominent in the spectrum of solar-type and cooler stars. Emission at the H and K lines is frequently found in stars where there is enhanced magnetic activity (e.g. flare stars and RS Canum Venaticorum stars).
Subjects: Astronomy and Astrophysics.