LESATH (Upsilon Scorpii). Lesath, Scorpius's Upsilon star, is
intimately related in the observer's eye to Shaula (Lambda Scorpii), the two making the
Scorpion's famed, and very real-looking, stinger. Bright third
magnitude (2.69), the star is a magnitude fainter than its apparent
companion, the stinger trailing off at its end. Though the two
stars were originally tied together by name ("Shaula," meaning "the
Scorpion's stinger," at one time referring to them both), the name
"Lesath" really has nothing to do with the frightful beast, and is
a vivid lesson in how star names can become corrupted. The name
originally came from a Greek word that means "foggy," and according
to recent scholarship most likely refers to the fuzzy objects of
the Milky Way, notably to the naked-eye cluster Messier 7, which is
nearby (and to which the stinger points; look up and to the left).
The name was then translated into Arabic, badly re-translated to
Latin, and mistranslated back into Arabic to a word that meant
"sting," Lesath's origin a mismatch of three languages. Like so
many in Scorpius, Lesath is a hot (22,400 Kelvin) class B star (B2
IV) that is spectrally identical to Shaula. The two are really
related in that they both belong to the huge and nearby Scorpius-
Centaurus association of O and B stars, an enormous group with
several subgroups. Though born roughly at the same time, the
association's stars are not gravitationally bound, and the
association is rapidly expanding. The relation between Shaula and
Lesath stops there, however. Though Shaula and Lesath appear very
close (less than a degree apart) on the sky, they do not constitute
a double: Lesath, 520 light years away, is 180 light years the
nearer of the two. From Lesath, Shaula would appear at magnitude -
1.3, while from Shaula, Lesath would shine at magnitude zero
(+0.42), the Sun a small nearby dot of the
11th magnitude! Physically Lesath is a "subgiant" with a huge
luminosity 12,300 times that of the Sun (accounting for a large
amount of ultraviolet radiation) and a radius 7.5 times solar. It
is listed in catalogues of "Be" stars, which means it is surrounded
by a cloud of matter, though it seems to be rotating slower than
most (73 kilometers per second), most likely because its rotation
pole is tipped toward us. There is some suggestion that it may
have a companion, but that has never been confirmed. Lesath has
either just shut down its internal hydrogen fusion or will soon do
so. It will then begin its evolution to become a red supergiant.
With a mass 10 times solar, the star is on the dividing line at
which stars explode. It will most likely survive that fate, and
instead turn into a rare massive neon-oxygen white dwarf.