CU Virginis

Lore & Background

CU Virginis has a stellar classification of Ap Si, with strong lines of silicon and weak helium lines. It is a fast rotator with a period of 0.52 days and an axis inclined to the line of sight from Earth. In 1956, Robert Hardie discovered that the star's brightness varies. Both the spectrum and luminosity vary with rotation, and it is classified as an α2 Canum Venaticorum variable. There is some evidence that the rotation period may vary slightly over a timescale measured in decades, with changes observed to occur in glitches rather than varying constantly.

The star has a strong magnetic field, placing it in the class of magnetic chemically peculiar stars. The polar magnetic field has a strength of about 3 kG, and the magnetic pole may be displaced by 87° from the axis of rotation. The effective magnetic field varies over the course of a rotation, and the mean surface magnetic field varies over a range. CU Virginis is also a radio emitter, with emission modulated by the rotational phase. This emission is believed to be gyrosynchrotron radiation from mildly relativistic electrons trapped in the magnetosphere. Two pulses of 100% circularly polarized radio energy are detected each rotation, possibly produced via an electron cyclotron maser process, and these beams are refracted as they pass through cold plasma in the star's magnetosphere.

Reader's Guide

CU Virginis is significant as one of the best studied Ap stars, providing a key example of a magnetic chemically peculiar star with a strong, oblique magnetic field. Its variability, discovered by Robert Hardie in 1956, established it as an α2 Canum Venaticorum variable, where changes in spectrum and luminosity are tied to rotation. The star's radio emission, modulated by rotation and exhibiting 100% circularly polarized pulses, offers insight into gyrosynchrotron radiation and electron cyclotron maser processes in stellar magnetospheres. Evidence that its rotation period may change in glitches over decades adds to its importance for studying stellar rotational dynamics. The combination of a strong magnetic field, rapid rotation, and radio emission makes CU Virginis a valuable object for understanding the behavior of magnetic fields and particle acceleration in stars.

Did You Know?

• CU Virginis has a rotation period of 0.52 days.
• It emits two pulses of 100% circularly polarized radio energy per rotation.
• The star's magnetic pole may be displaced by 87° from its rotation axis.
• Its rotation period may vary in glitches over decades.