IOTA CEN (Iota Centauri). Filled with bright hot stars, Centaurus is a centerpiece of "associations" of them, which are vast groups of stars born mostly at the same time from the same huge complex of interstellar clouds. Unbound gravitationally, associations, unlike clusters, expand away into the Galaxy. Among the most famed of these gatherings are the various subgroups that occupy a huge parent system in Scorpius, Centaurus, Lupus, and Crux. Even the sub-associations cross constellation boundaries. But merely belonging to a classical constellation like Centaurus is hardly proof of association membership. There, for example, sits bright third magnitude (2.75, though measured as bright as 2.70) Iota Cen, one of the most northerly of Centaurus's stars, which (unlike most of them) lies close to us, a mere 59 light years away, vastly closer than any of the sub-associations, which go from 380 light years for Lower Centaurus-Crux to 470 light years for Upper Centaurus-Lupus and Upper Scorpius: showing once again that the sky has three dimensions, not two. Here we see a typical white class A (A2) dwarf with a temperature of 9100 Kelvin, which together with distance yields a luminosity 71 times that of the Sun, a radius 3.4 times solar, and a mass 2.5 to 2.6 solar depending on the exact state of evolution: which may be more like a subgiant (a star that is giving, or has given, up core hydrogen fusion) than a dwarf, the star's age falling between 500 and 600 million years. A projected equatorial rotation speed of 86 kilometers per second gives a rotation period of under two days. A barely detectable magnetic field comes in at around 100 times the strength of Earth's, but with a large uncertainty. Iota Cen is identified as a "Vega-like" star, one with a surrounding infrared-radiating dusty "debris-disk" that might attest to collisions in a kind of planetary system (the champion of which is Beta Pictoris). It's also referred to as a "high proper motion" star ("proper motion" being the angular movement across the line of sight). The high movement, however, is the result of the star's closeness and that its true movement of 30 kilometers per second is almost perfectly perpendicular to the line of sight, its distance from us hardly changing at all.
Written by Jim Kaler 6/15/07. Return to STARS.