ZANIAH (Eta Virginis). An old term -- before we understood that
stars do move -- referred to the "fixed stars," the phrase really
meant to distinguish real stars from the "wandering stars," the
planets. The names applied to stars sometimes appear about as
fixed as the stars themselves, that is they, or at least some of
them, move around too. "Zaniah," the Eta star of Virgo, the Virgin, refers an angel, the "angel of a-
awwa" (the meaning unknown, and with apologies to Arabic readers
for leaving out the necessary accents), and was originally applied
to Porrima (Gamma Virginis), and later
fell to dimmer (mid-fourth magnitude, 3.89) Eta. In a rather
special place, Zaniah, to the west of Porrima, is squeezed between
the celestial equator and the ecliptic. Of the brighter stars that
make the constellation figures, Zaniah is one of the closest to the
equator, only 2/3 of a degree to the south of it, and only 5
degrees to the east of the autumnal equinox, the point where the
Sun crosses the equator on its way south in September. Zaniah, 250
light years away, is classed as an A (A3) subgiant, the latter
meaning that the star seems to be about to give up its central
hydrogen fusion, if it has not already. From its surface
temperature of 8800 Kelvin (and of course its distance) we can
calculate a luminosity 130 times that of the Sun. The star's status and properties,
however, are seriously compromised by its seeming triple nature.
None of the components can be resolved by eye at the telescope.
Ultrashort imaging (to avoid smearing of the image by twinkling) in
addition to occultations by the Moon reveal a pair of stars (one
fourth magnitude, the other fifth) separated by but 0.12 seconds of
arc, or around 10 Astronomical Units. One of them, probably the
brighter, is revealed by the spectrograph to be a much closer
double with a period of 72 days and an average separation of only
half an astronomical unit. This very close double is then orbited
by the third outer star. It would seem impossible for a planet to
survive the gravitational onslaught of the trio. All three seem to
be class A stars, and one or more may be slightly variable. Though
individually, each would become a relatively massive white dwarf,
the proximity of the close pair will probably disrupt the flow of
evolution as the more-massive of them will expand first and will
encroach upon the other, a common scenario among close pairs.