The Sigma Ori Multiple Star System
Sigma Ori lies about
a degree to the southwest of Alnitak, the easternmost star in the "belt"
or Orion. This system of five stars puts on a great show in telescopes
both large and small.
The closest pair (AB)
consists of two gravitationally bound stars, the 3.8 magnitude Sigma Ori
itself, and it's 5.3 magnitude close companion. Currently a mere 0.24"
apart, these stars take 170 years to complete one orbit about one-another.
A larger aperture instrument, excellent seeing, and high magnitification
are required to see this pair.
The 10th magnitude star C
lies 11" to the SW. To the NE lies the 6.9 magnitude star D (13" away).
Further to the NE, at a distance of 42", lies the 6.5 magnitude star E.
This star is the variable star V1030 Ori, an SX Ari type variable with
a range of ~0.15 magnitude over a period of 1.2 days.
A full orbit of the AB
pair.
The view in a 90mm ETX with
a Meade 12.5mm SP eyepiece from a dark location. Only those objects visible
in this scope are simulated. The Sigma Ori system is at the center. Another
system lies at the top right.
The view in a 90mm ETX
showing the best possible resolution.
Millennium Star Atlas Vol
I Chart 254
Sky Atlas 2000 Chart 11
Uranometria 2000 Vol I&II
Chart 226