MU TAU (Mu Tauri). In Taurus, the
Zodiacal Bull, the eye focuses on the Pleiades, which is not a part of the constellation's outline, and then on the
larger cluster, the Hyades, which makes the animal's
vee-shaped head and that seems to contain bright Aldebaran (the star actually not part of
the cluster). The "vee" extends to the southwest through Lambda to Omicron
Tau. South of that line are scattered remains that lie north of
Eridanus and that include a couple of stars
that still bear Greek letters, fourth
magnitude Nu (3.91, an A0 dwarf 117 light years away) and
fainter but still fourth magnitude (4.29) Mu Tauri, a blue, hot
(16,980 Kelvin), much more distant (456 light years plus or minus
22) class B (B3) subgiant
(but see below). It's a bit unusual to see such a hot star lying
that far (28 degrees) off the centerline of the Milky Way, but hardly unheard of, and at least
a part of the explanation lies in the star's membership. Also
surprising is the fairly large amount of interstellar dust absorption, half
a magnitude. When we correct for that (the unoccluded magnitude
3.78) and a pretty good bit of ultraviolet light, the star is
seen to shine with a total luminosity of 1960 Suns, which in turn yields a radius 5.1 times
that of the Sun. The iron content relative to hydrogen is about 70
percent solar, nothing unusual. With an equatorial rotation speed
of at least 89 kilometers per second (rather low for a B star), the
rotation period must be under 2.9 days. The spin axis may be pointing
more or less towards us, though the star is likely not a really fast
rotator as there is no emitting equatorial disk. Application of
theory yields a mass of close to six times that of the Sun and shows
that though the star is still a dwarf, it is well along on its 50
million year hydrogen-fusing lifetime and will become an actual
subgiant before very long, finally ejecting its outer layers and
turning into a white
dwarf of about 0.9 or so solar masses.
Youthful stars have not moved that far from their birthplaces, and
therefore define loose associations and streams. Complex, the
streams commonly overlap, with old ones generating new ones as their
massive stars explode and drive further star formation. Mu Tauri
belongs to the dispersing Cassiopeia-Taurus association, one of 83 class B
stars whose center consistently lies at about the same distance as
Mu and has about the same age. From the name alone, Cas-Tau must
span a huge angular diameter in the sky, from Taurus to Cassiopeia (indeed well beyond) with Perseus more or less in the middle. Indeed
at the core of Cas-Tau is a "halo" surrounding the Alpha Persei cluster, a bound group with
Alpha Persei (Alfirk) near its center.
Cas-Tau, which may be some 4000 light years across, is related to,
and may in part be the parent of, many of the local associations of
O and B stars that in turn create the tilted "Gould Belt" of hot,
young, blue stars that lies off the midline of the Milky Way. Though
also recognized by John Herschel, the Gould Belt is named after B.
A. Gould (1824-1896), an astronomer who for a time directed the Dudley
Observatory in Albany, New York (hometown of thy author) and helped
pioneer South American astronomy. Gould founded the prestigious
"Astronomical Journal," in 1849. Now a publication of the American
Astronomical Society, in December of 2014 the Journal ceased paper
publication and became all-electronic, starkly revealing the
revolution not only in scientific publishing but in life in general,
something to ponder while admiring Mu Tauri, which began this tale
Written byJim Kaler 3/13/15. Return to STARS.