Magnetic Stars

Magnetic Stars 

stars on whose surfaces there exist magnetic fields stronger than a few hundred gauss.

The magnetic fields of stars were first measured by the American astronomer H. W. Babcock in 1948 from the Zeeman splitting in the spectrum of a star. The strongest magnetic field measured thus far is for the star HD 215441 and is equal to 34,000 gauss. All known magnetic stars have an anomalous abundance of chemical elements in their atmospheres—a great excess of rare-earth elements (Eu, La) and an excess of elements of the iron group (Fe, Mn, Cr) and lighter elements (Si, Cl, P). On the basis of this characteristic, magnetic stars belong to the group of peculiar A-type stars.

The magnetic field intensity and the chemical composition of the atmospheres of magnetic stars, which is determined on the basis of the stars’ spectra, periodically vary. This is due to the rotation of the stars, which are characterized by a nonuniform distribution of the magnetic field and chemical composition on the surface.

On the Hertzsprung-Russell diagram, magnetic stars lie on the main sequence in the region of spectral classes from FO to B5 and constitute about 10 percent of all stars in these classes. The strong magnetic field of such stars may arise either during the star’s formation (compression of the partially ionized gas, which initially had a weak magnetic field, leads to intensification of the field) or by way of the hydromagnetic dynamic processes in a rotating star. The origin of the anomalies of chemical composition has not been determined.

REFERENCE

Eruptivnye zvezdy. Moscow, 1970. Chapter 7.

V. L. KHOKHLOVA