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.