A type of chemically peculiar star with unusually large amounts of ionized mercury and manganese in its atmosphere. Such stars can also show excess amounts of other heavy elements such as copper, gallium, xenon, and bismuth. Mercury–manganese stars have spectral types of B6 to A0 and slow rotation rates. Over 150 are known, many of them in young stellar associations. In addition, around two-thirds of the known examples are in double or multiple systems. An example is Iota Coronae Borealis.