depicting Ursa Major's stars for Epsilon Ursae Majoris, plotted from
TESS data According to
Hipparcos, Epsilon Ursae Majoris is from the
Sun. Its
spectral type is
A1p; the "p" stands for
peculiar, as its
spectrum is characteristic of an
α2 Canum Venaticorum variable. Epsilon Ursae Majoris, as a representative of this type, may harbor two interacting processes: first, the star's strong
magnetic field separating different elements in its
hydrogen 'fuel'; second, a rotation axis at an angle to the magnetic axis may be spinning different bands of magnetically sorted elements into the line of sight between Epsilon Ursae Majoris and the Earth. The intervening elements react differently at different frequencies of light as they whip in and out of view, causing Epsilon Ursae Majoris to have very strange
spectral lines that fluctuate over a period of 5.1 days. The
kB9 suffix to the spectral type indicates that the
calcium K line is present and representative of a B9 spectral type even though the rest of the spectrum indicates A1. Epsilon Ursae Majoris's rotational and magnetic poles are at almost 90 degrees to one another. Darker (denser) regions of
chromium form a band at right angles to the equator. It has long been suspected that Epsilon Ursae Majoris is a
spectroscopic binary, possibly with more than one companion. A 2008 study suggested Alioth's 5.1-day variation may be due to a substellar object of about 14.7
Jupiter masses in an eccentric orbit (e=0.5) with an average separation of 0.055
astronomical units. It is now thought that the 5.1-day period is the rotation period of the star, and no companions have been detected using the most modern equipment. Observations of Alioth with the
Navy Precision Optical Interferometer also did not detect a companion. Epsilon Ursae Majoris has a relatively weak magnetic field for a variable of this type, 15 times weaker than
α Canum Venaticorum, but it is still 100 times stronger than
that of the Earth. ==Name and etymology==