15 Cancri is an α² CVn-type variable star in the zodiac constellation of Cancer, located around 980^[2] light years away. It has the variable star designation BM Cancri (BM Cnc); 15 Cancri (15 Cnc) is the Flamsteed designation. This system is visible to the naked eye as a faint, white-hued star with an apparent visual magnitude of about 5.6. It is moving away from the Earth with a heliocentric radial velocity of 25 km/s.^[6]

Radial velocity measurements taken at the Dominion Astrophysical Observatory in Victoria, British Columbia Canada in 1918 and 1919 led to the determination that 15 Cancri is a single-lined spectroscopic binary system.^[9] The first orbit was calculated in 1973 by Helmut Abt and Michael Snowden with a period of 585 days^[10] however later measurements showed that the orbital period was 635 days.^{[6][note 1]}

15 Cancri A, the visible component, is an Ap star, a chemically peculiar star with an over-abundance of iron peak elements, particularly silicon, chromium, and strontium, in its spectrum.^[11][4]

Like all Ap stars, 15 Cancri has a strong magnetic field. This magnetic field varies as it rotates and in 1968 the visual brightness of the star was shown to vary regularly over about four days.^[12] 15 Cancri was given the variable star designation BM Cancri in 1972 as a member of the α² CVn class of variable stars.^[13] The period has since been measured more accurately at 3.3095 d, believed to be the rotational period of the star.^[14]