MENKIB (Xi Persei). The naming of stars was hardly systematic,
some bright ones (like Gamma
Cassiopeia) having no proper names at all, at least within our
own culture. Perseus (the Hero) may be
the champion not only of Andromeda
but also of unnamed stars as well. The top two, Mirfak (Alpha) and Algol (Beta) have proper names, and then the
list stops until we arrive at number 10, a fourth magnitude star
called "Atik" and Bayer's "Omicron" star. Fainter yet is number 12
in brightness, mid-fourth magnitude Menkib (Bayer's "Xi"). They
both refer to a larger Arabic construction in which Atik is the
"collarbone" of the Pleiades and Menkib
the "shoulder" (Caph in Cassiopeia representing the "hand." Why these dim
stars of Perseus, rather than some of the brighter ones, were
chosen is a mystery. In terms of real significance, however, the
old Arabians chose well. Though Menkib is not terribly bright to
the eye, it is nevertheless quite the spectacular star. One of the
very few naked eye stars that falls into the hottest of stellar
categories (class O), it shines with a sparkling blue-white light.
Indeed it is one of the hottest stars to be seen without the aid of
a telescope, its surface temperature around 37,000 Kelvin, over six
times hotter than the Sun. Its apparent
faintness is caused by a combination of its uncertain distance of
around 1600 light years and by the absorption of its light by
interstellar dust in the Milky Way, which cuts its brilliance about
in half. When these are taken into account, we see that to the eye
the star would shine 13,500 times brighter than the Sun. And when
we take into account the ultraviolet light from Menkib's hot gases,
the figure climbs to 330,000 times! To receive the same amount of
energy as we do, an orbiting planet would have to be 15 times
Pluto's from the Sun away. (Menkib does have a companion: a much
smaller star, about which nothing is known, in a 7-day orbit).
Menkib is slightly unstable, changing its brightness by about five
percent, and is also blowing a fierce wind, causing it to lose
about a millionth of a solar mass per year, ten million times the
rate in the solar wind. It is one of the naked-eye sky's most
massive stars, weighing in at birth at around 40 solar masses.
Though the star's status is rather uncertain, some observers
calling it a "giant," others a "supergiant," it has almost
certainly shut down core hydrogen fusion, and may even be fusing
helium, already having lost some 10 percent of its original mass.
Still only a few million years old, its only recourse is to explode
sometime in the next million years or so. Fortunately for us,
stars like this are very rare, none nearby. Menkib, like Naos in Puppis, is
also one of the sky's few "runaway" stars. For reasons still
uncertain, it is zipping at high speed from its birthplace in a
group known as the "Perseus OB2 association (which oddly contains
it sister star Atik), the acceleration caused either by a close
encounter with another star or by the explosion of a now-dead and
even more massive companion.