MINTAKA (Delta Orionis). Orion is
defined by his great
belt, three bright second magnitude stars in a row that the ancient
Arabs called "the string of pearls," which is the meaning of the
name of the middle star,
Alnilam. The two flanking stars, eastern
Alnitak and western Mintaka, both come
from Arabic phrases that mean "the belt of the Central One," the
Central One the Arabic personification of our Orion, a woman lost
to history. Though (at magnitude 2.21)
Mintaka is the seventh brightest star in Orion,
and the faintest of the three belt stars, it still received the
Delta designation from Bayer, who lettered the belt stars in order
from west to east before dropping down to Orion's lower half to
continue the process. Of the sky's brightest stars, first through
third magnitude, Mintaka is closest to the celestial equator, only
a quarter of a degree to the south, the star rising and setting
almost exactly east and west. The star is wonderfully complex. A
small telescope shows a seventh magnitude companion separated by
almost a minute of arc. At Mintaka's distance of 915 light years
(very nearly the same as Alnitak at the eastern end of the belt),
the faint companion orbits at least a quarter of a light year from
the bright one. In between is a vastly dimmer 14th magnitude
component. The bright star we call Mintaka (whose solo magnitude
is 2.23) is ALSO double, and
consists of a hot (30,000 Kelvin) class B, slightly evolved, giant
star and a somewhat hotter class O star, each radiating near
90,000 times the solar
luminosity (after correction for a bit of interstellar dust
absorption), each having masses somewhat over
20 times the solar mass. This pair is too close to be separated
directly. The duplicity is known through the star's spectrum (its
rainbow of light), which detects two stars orbiting each other
every 5.73 days, and also because the stars slightly eclipse each
other, causing a dip of about 0.2 magnitudes. Mintaka is most
famed. however, as a background against which the thin gas of
interstellar space was first detected, when the German astronomer
Johannes Hartmann in 1904 discovered absorptions in the star's
spectrum that could not be produced by the orbiting pair. From
this discovery, and others that followed, we now know that all of
the Galaxy's interstellar space contains an enormously complex
medium of gas and dust that is the birthplace of new stars.
Mintaka will also, to some distant generation of astronomers, be
famed in death, as each of its components is so massive that their
only fate is to explode violently as supernovae.