41 ARI (41 Arietis). Poor 41. In spite of it being the third
brightest star (just over the line into fourth magnitude, 3.63) in
its famous Zodiacal constellation,
Aries (the Ram), not only has it
no proper name, it even carries no Bayer Greek letter, the "41" a Flamsteed number. The most
likely reason is the odd position of the star, which lies far to
the east of the little triangle that represents the horns of the
fabled Ram. 41 Ari, however,
does have the distinction of being
the brightest star within a small set of four that outline an even
smaller triangle that hovers over the back of Aries and that
represents the obsolete constellation of Musca Borealis, the
"Northern Fly." Such defunct constellations abound, and many had
good runs in various star atlases. The Fly, however, was finally
swatted in the early twentieth century when the current 88
constellations were formally adopted. (Musca Australis, now known
just as "Musca," still flits.)
The small figure, easily found,
serves nicely to represent the large set of modern constellations
that are no longer recognized. Physically, 41 Ari is a rather hot
blue-white class B (B8) dwarf star with a surface temperature
estimated at around 12,000 Kelvin (no actual measures exist) that
lies 160 light years away and that radiates 126 times as much
energy as the Sun, from which we deduce a
mass of around 3.2 solar, the star somewhere midway along its
hydrogen-fusing 300 million year lifetime. Like most class B
stars, 41 Ari is a fast rotator, spinning with an equatorial speed
of at least 180 kilometers per second, 90 times faster than the
Sun, which, given its radius of 2.6 times solar, translates into a
rotation period of at most 17 hours. A host of lesser stars flock
around 41, making it seem to be a multiple star. All but one,
however, are line-of-sight accidents. The remaining one, a true
companion, detected by both spectroscopy and interferometry (but
about which nothing is known), lies only 0.2 seconds of arc from 41
itself. Orbiting perhaps 15 AU from 41, the companion would take
some 30 years to make a full orbit. Though listed as "variable,"
modern observations suggest great stability, enough so that 41
Arietis could be used a standard against which to test real
variables.