MESARTHIM (Gamma Arietis). Shining third among the stars of the
flat triangle that make the classical figure of Aries, the Ram (for that reason gaining the Gamma
designation), Mesarthim actually takes fourth place in the
constellation after non-named
41 Arietis, which glows softly off to
the northeast. The name (derived from Arabic) originally came from
the same root as that for the Beta star, Sheratan (meaning "the two"), but was
corrupted by mistranslations into its current form. Famed from
history, Mesarthim is also called "the first star of Aries," as
during the ancient times when the stars were being systematically
organized, it was the closest of the Ram's stars to the
vernal
equinox. (Precession, the 26,000 year wobble of the Earth's axis,
has since shifted the equinox westward to Pisces.) Shining at us from a distance of 204 light
years, Mesarthim is one of the classic double stars of the sky, its
two components, of nearly equal brightness, an easily separable 8
seconds of arc apart and known since 1664. Both actually white,
the (just slightly) fainter one (Gamma-1, since it is the more
westerly) has been called "pale grey," which is a visual contrast
effect. Both fifth magnitude (Gamma-1 4.83, Gamma-2 4.75), they
combine to make a mid fourth magnitude (3.9) star. Gamma-1, a
class B (B9) dwarf, is the hotter, its temperature 11,000 Kelvin.
Gamma-2, a bit controversial, has been classed both as an A (A1)
(probably) dwarf and as a B (B9.5) subgiant (meaning that it may be
starting to evolve), the temperature between 9200 and 9800 Kelvin.
Though Gamma-1 is a bit dimmer to the eye, it is actually the more
luminous, as the higher temperature causes more of its light to
shine in the invisible ultraviolet. Gamma 1, around 2.8 solar
masses, radiates 56 or so solar luminosities into space, whereas
Gamma-2 (around 2.5 solar masses) releases somewhere between 43 and
52 times the power of the Sun. While Gamma-
1 is relatively ordinary, Gamma-2 is an "Ap" star,the "p" standing
for (spectrally) "peculiar." It is now known that such stars are
actually highly magnetized, Mesarthim-2's magnetic field roughly
1000 times the strength of Earth's. Like the prototype, Cor Caroli-2, the magnetism is
concentrated into zones in which it aids in the separation of
chemical elements (Gamma-2 notably high in silicon). As the star
rotates, these concentrations swing in and out of view, allowing
the rotation period to be found (in this case 1.609 days) and
causing subtle visual variations. Sophisticated spectroscopic
examination and measures of Doppler shifts allow astronomers to
create "pictures" of the surfaces of such stars, Gamma-2 having the
distinction of being the first to be so treated. The stars of the
pair are separated by at least 500 astronomical units (over a dozen
times Pluto's distance from the Sun), and take at least 5000 years
to orbit each other.