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.
Written by Jim Kaler. Return to STARS.