HD 66051

Lore & Background

HD 66051 was identified as a peculiar A star with anomalous silicon lines during a spectroscopic survey of southern skies begun in 1967, with preliminary results reported in 1973. It was formally classified as Ap Si in 1978, indicating a chemically-peculiar star. Data from the Hipparcos satellite demonstrated it is a variable star, and further data in 2003 showed it is an eclipsing binary system of the Algol type and an Alpha2 Canum Venaticorum variable, with both variations sharing the same period of 4.74922 days, locked in synchronous rotation.

The system is a double-lined spectroscopic binary with a circular orbit and an orbital period of 4.75 days. The orbital plane is inclined at 84.7° to the plane of the sky, allowing mutual eclipses to be viewed from Earth. The primary eclipse reduces the visual magnitude from 8.79 to 9.12, while the secondary eclipse decreases it to 8.94. The pair are young, near zero-age main sequence stars.

The primary component is a magnetic chemically peculiar Bp star with a highly peculiar composition, somewhat resembling a mercury-manganese star but not belonging to that class. It shows depletion in helium, carbon, magnesium, and aluminium, and overabundance in heavy elements, all iron-group elements except nickel, and high silicon and phosphorus. Its stellar classification indicates it is a helium-weak star. It has a magnetic field with a dipole component inclined 13° to the pole of rotation. The secondary is an Am star with a metallic-lined spectrum, lacking a magnetic field and with non-varying spectra.

Reader's Guide

HD 66051 holds significance as the first early-type magnetic star found in an eclipsing binary system, providing a unique laboratory for studying the interplay between magnetic fields, chemical peculiarity, and binary dynamics. The primary's non-uniform distribution of elements across its surface creates spectral variability as the star rotates, while the secondary's stable, non-magnetic nature allows clear separation of the two stars' contributions. The system's synchronous rotation and circular orbit, with a period of 4.75 days, indicate tidal locking and a relatively evolved binary configuration despite the stars being near zero-age main sequence. The primary's peculiar composition—depleted in light elements like helium and carbon, yet overabundant in heavy elements and iron-group elements—places it among the chemically peculiar stars, though it does not fit neatly into the mercury-manganese class. Its magnetic field, with a dipole component inclined 13° to the rotation axis, adds to its complexity. The eclipses, with primary and secondary events differing in depth, allow precise measurement of stellar parameters and orbital geometry. This system serves as a benchmark for understanding magnetic fields in early-type stars and their effects on binary evolution and atmospheric chemistry.

Did You Know?

• The primary star's composition is depleted in helium, carbon, magnesium, and aluminium, but overabundant in heavy elements and iron-group elements except nickel.
• The orbital plane is inclined at 84.7°, allowing both primary and secondary eclipses to be observed from Earth.
• The system's rotation is synchronized with its orbital period of 4.74922 days.