HD 66051

This was identified as a peculiar A star with anomalous lines of silicon during a spectroscopic survey of southern skies begun in 1967, with preliminary results reported in 1973.^[10] Data from the Hipparcos satellite demonstrated it is a variable star.^[11] It was formally classified as Ap Si in 1978,^[6] indicating a chemically-peculiar star. In 2003, further data showed this is an eclipsing binary system of the Algol type and an Alpha2 Canum Venaticorum variable. The period of both variations is the same, 4.74922 days, and it is locked in synchronous rotation.^[12]

HD 66051 is a double-lined spectroscopic binary.^[13] It is a young star system with components that are near zero-age main sequence. The pair have an orbital period of 4.75 days in a circular orbit, with a separation of 20.4 times the radius of the Sun. The orbital plane is inclined at an angle of 84.7° to the plane of the sky,^[5] allowing their mutual eclipses to be viewed from Earth. During the primary eclipse, the visual magnitude of the pair decreases from 8.79 to 9.12. The secondary eclipse decreases the visual magnitude to 8.94.^[12]

The composition of the more massive primary component is highly peculiar and somewhat resembles a mercury-manganese star,^[11] although it does not belong to that class.^[8] It shows depletion in certain light elements, including helium, carbon, magnesium, and aluminium. In contrast, it is overabundant in heavy elements and all members of the iron group except nickel. Silicon and phosphorus are also high in abundance. The resulting stellar classification is kB9 hB7 V He-w SiCrSrEuHg, indicating this is a helium-weak star.^[11] It has a magnetic field with a dipole component that is inclined 13° to the pole of rotation, and a polar field strength of 600 G.^[8]

The primary is a magnetic chemically peculiar Bp star with a non-uniform distribution of elements across its surface.^[8] It was the first early-type magnetic star to be found in an eclipsing binary system.^[14] These chemical spots create a variability in the spectrum as the star rotates. It has 3.2 times the mass of the Sun and 2.8 times the Sun's radius. The rotation rate is synchronized with the orbital period of 4.75 days.^[8]

The secondary is an Am star,^[13] displaying a metallic-lined spectrum, but lacks a magnetic field and its spectra does not vary.^[8] It has 1.75 times the mass of the Sun and 1.39 times the Sun's radius.^[8]