MAIA (20 Tauri). The Pleiades, the
Seven Sisters star cluster (one of two naked eye clusters that
belong to Taurus, the other the Hyades), twinkle high in northern
hemisphere autumn and winter skies, while shining closer to the
horizon in the skies of southern hemisphere spring and summer.
Maia, a proper name, is one of the seven mythical daughters of
Atlas and Pleione.
Shining at bright third magnitude (3.87) from
a distance of 385 light years, she ranks fourth brightest after Alcyone, Atlas, and
Electra. Except for
Alcyone (Eta Tauri), the Pleiades' stars carry only Flamsteed numbers, Maia number
20 in the west-to-east parade of numbered naked-eye stars within
the celestial Bull. A blue-white class B (B8) giant star, Maia
radiates 660 times more energy than does the Sun from a warm surface with a rather uncertain
temperature of 12,600 Kelvin. Its radius of 5 1/2 times that of
the Sun gives it true giant status, although the giants in these
hotter stars are nowhere near as large as their cooler orange
cousins like Arcturus and Aldebaran (which lies in front of the Hyades).
As a giant, Maia either has shut down its internal hydrogen fusion
or will do so very shortly, its mass of a bit over four times that
of the Sun giving the star a destiny as a massive white dwarf.
Like the other stars of the cluster, Maia is involved with the
Pleiades reflection nebula that peaks around Merope. Maia appears to be a relatively
slow rotator, and as such has a fairly quiet atmosphere. As a
result, different kinds of atoms drift downward under the pull of
gravity, whereas others are lofted upward by radiation, the effects
making Maia one of the "mercury-manganese stars," in which these
two and other chemical elements are greatly enhanced (manganese in
Maia up by a factor of 160 compared with hydrogen). The star also
has a bit of a curious history. Fifty years ago, the great
astronomer Otto Struve suggested that Maia was slightly variable,
with a period of a few hours. It thence became the prototype of a
whole class of "Maia variables" that included Pherkad (Gamma Ursae Minoris) and that were
in an otherwise stable realm of temperature and luminosity.
Astronomers have argued since then about the reality of the class.
Only recently has the issue been put to rest, when the prototype
(and some others) were found to be stable and not varying at all
(though others in the purported class do vary for other reasons).