From Wikipedia, the free encyclopedia Sigma Orionis
Sigma Orionis
Sigma Orionis A/B/C/D/E a blue O-type star with an apparent visual magnitude
Observation data of +4.2. Sigma Orionis B is a B-type star with an apparent
Epoch J2000 Equinox J2000 visual magnitude of +5.1. The pair orbit each other every
Constellation Orion
170 years at a distance of about 90 AU. A and B have very
hot surfaces, around 32,000 and 29,600 kelvins, radiating
Right ascension 05h 38m 44.80s at about 35,000 and 30,000 solar luminosities, respective-
Declination −2° 36’ 00.0" ly. Temperature and luminosity give masses of 18 and
13.5 solar masses, making the close AB pair among the
Apparent magnitude (V) 4.2/5.1/8.79/6.62/6.66 most massive of visual binaries.
Characteristics The next brightest stars in the system are Sigma Ori-
onis D and E, which lie about 4,600 and 15,000 AU respec-
Spectral type O9V/B0.5V/A2V/B2V/B2Vp
tively from the AB pair. Both are seven solar mass B-type
U−B color index ?/?/−0.25/−0.87/−0.86 dwarf stars with magnitudes of 6.62 and 6.66. Sigma Ori-
onis E is a prototype of the strange "helium-rich" stars,
B−V color index ?/?/−0.02/−0.20/−0.18
which have significantly large amounts of helium.
Variable type No/No/No/No/Yes The last star in the system is Sigma Orionis C, an A-
Other designations
type dwarf star. C is the closest to the AB pair, about 3,900
AU away.
Sigma Orionis, Sigma Ori, σ Orionis, σ Ori, 48 Orionis, 48 Ori, While the orbit of the AB pair is stable, the orbits of
BD-02°1326, HD 37468, HR 1931, HIP 26549, SAO 132406 the other three are not, and long before they die they will
Database references probably be gravitationally sped up and forced out of the
system.
SIMBAD data
Sigma Orionis or Sigma Ori (σ Orionis, σ Ori) is a five-star References
system in the constellation Orion, just to the south of Al-
[1] "Sigma Ori". Jim Kaler’s Stars. University of Illinois,
nitak. It is approximately 1,150 light years from Earth.[1]
Urbana-Champaign Campus. 2009. Archived from
The primary component is the binary Sigma Orion-
the original on 2011-12-03.
is AB, with the two stars being a mere 0.25 arcseconds
http://www.webcitation.org/63fFuXOB2. Retrieved
apart. Both stars are hydrogen-fusing dwarfs only a few
2011-12-03.
million years old. The brighter one, Sigma Orionis A, is
Retrieved from "http://en.wikipedia.org/w/index.php?title=Sigma_Orionis&oldid=465628576"
Categories:
• Orion constellation
• Multiple star systems
• O-type main sequence stars
• B-type main sequence stars
• A-type main sequence stars
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