LAMBDA CET (Lambda Ceti, the former "Menkar"). Except for those
that belong to the brighter or otherwise prominent stars, proper names, while charming, can be
problematic if not downright confusing. Many are the duplications.
Think first of Deneb, Deneb Algedi, Denebola, Deneb
Kaitos, and the multitudinous rest of them. Then there are the
real duplications. There is a Gienah in
Corvus, another in Cygnus. At least they are in different constellations. Worse are the numerous stars
WITHIN a constellation that share a name. Zeta and Epsilon Aquilae are both "Deneb al
Okab," a situation moderated by respectively calling them
"Australis" and "Borealis." Then there are Lambda and Alpha Ceti, both within the head of Cetus, the Whale or Sea Monster. Rather
faint fifth magnitude (4.70) Lambda was the original "Menkar,"
which from Arabic refers to the Beast's nostrils. Someone in
medieval times, however, took it upon himself to transfer the name
to brighter, nearly-second-magnitude Alpha, which is in Cetus's
jaw. The wrongful title stuck, and Lambda lost out. Alpha,
whether properly of not, is "Menkar." The long story rather makes
up for the relative lack of knowledge about the star itself, which
falls in league in the neglected category with Beta Equulei and Beta Piscis Austrini. And rather too bad.
As a relatively hot (13,400 Kelvin) class B (B6) giant (but see below) 576 light
years away (give or take 18), it's rather out of place, as it is
well off the path of the Milky Way, the
natural home of youthful class B stars. And it's really quite an
impressive star (surely deserving of keeping its more ancient
mythological title) with a total luminosity (including a lot of
ultraviolet radiation and a small ten-percent correction for
interstellar dust) 920 times that of the Sun. From temperature and brightness, we find
a radius of just 5.4 solar, not much for a "giant,' an ill-
determined projected rotation speed of 128 kilometers per second
(appropriate for the class) yielding a rotation period of under two
days. Theory gives an impressive mass between 4.5 and 4.8 Suns
(depending on exact details of internal structure) and shows the
star to be more a subgiant (one that has given up, or soon will
give up, core hydrogen fusion). Youthful indeed, the star is only
100 to 125 million years old. Its fate is to become a fairly white dwarf of about 0.85
solar masses (white dwarfs the cores of the once far more massive
stars), massive for such a leftover remnant, but not quite up to
the classic example, Sirius B.
Written by Jim Kaler 1/22/10. Return to STARS.