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glen chapman
2003-Jun-11, 01:06 PM
Some years ago - maybe 10 or 15 - there was an article in Astronomy Now, describing the environment of Rigel

In the article they discussed the possibility of this double star actually having a spectroscopic companion orbiting both stars seen from Earth.

Has anyone seen any confirmation of this, if so, would they know of a webpage they could direct me too.

Thanks Glen Chapman

Glom
2003-Jun-11, 03:33 PM
Welcome.

Spectroscopic companion? That does mean one of the same spectral type as the other two?

In you title, you use the Bayer designation for Rigel, but the Bayer designation uses the genitive form of the constellation name. It should be Beta Orionis, literally, beta of Orion.

Emspak
2003-Jun-11, 03:33 PM
http://www.dibonsmith.com/

has a section on Rigel -- here is the text

b Orionis (Rigel) Orion's left foot or leg, is the brightest star in the constellation. In fact the name 'Rigel' means 'Left Leg'.
The star is a binary (Struve 668) with a seventh magnitude visual companion 9.4" from the primary at a position angle of 202. The binary has a slight colour contrast, a bluish-white supergiant and blue companion.
But due to the brightness of the primary you won't be able to resolve the binary with binoculars. It takes a large telescope to split the two.

However there is plenty here for the binoculars to absorb. With Rigel at the centre of your field of vision, you'll note four other bright stars, two to the northeast one to the north-northwest and one to the southwest: binoculars.
To the north-northeast is tau Orionis (a binary with very faint companion) while more to the east of Rigel is 29 Orionis.
Tau Orionis has a visual magnitude of 4.6, 29 Orionis is 4.1. This is exactly one-half a magnitude difference; do you notice the difference? Take your time, study the two for a while and see if you can tell that one is somewhat brighter than the other. This 'somewhat' is exactly half a magnitude.

As mentioned in the introduction, a difference of one magnitude means a brightness difference of two and a half times. A star with a half-magnitude difference has a brightness difference of 1.6. Thus tau Orionis is a bit more than one and a half times brighter than 29 Orionis.

Grand Vizier
2003-Jun-11, 04:07 PM
Spectroscopic companion? That does mean one of the same spectral type as the other two?

No - a spectroscopic companion is detected, not directly, but by doppler shifts of the absorption lines in the primary star's spectrum as it moves around the stars' mutual orbit. The lines will be blue-shifted as the star moves towards us and red-shifted as it moves away. Obviously this method works best if we are looking down the orbital plane. At right angles to the plane, no shifting would be visible.

Similar to a certain exoplanet detection method in fact :)

glen chapman
2003-Jun-12, 01:43 AM
A spectoscopic companion doesn't have to be in the plane of the orbit to detect. The other detection method is an anomoly in the light being presented. Example if we are clearly seeing BO light, but can detect absorbtion line signature of an F3, it will throw an element of doubt as to the star's environment.

Glen

Grand Vizier
2003-Jun-12, 02:37 AM
A spectoscopic companion doesn't have to be in the plane of the orbit to detect. The other detection method is an anomoly in the light being presented. Example if we are clearly seeing BO light, but can detect absorbtion line signature of an F3, it will throw an element of doubt as to the star's environment.


http://www.angelfire.com/on2/daviddarling/speccomp.htm

The pair of stars are often known as a 'spectroscopic binary'.

But, you have a point - complicated spectra can be suggestive of close binaries. But this method is going to be more speculative than the Doppler-shifting I was referring to (cf Capella B). Spectral oddities in singleton stars happen, whereas a wholesale shift in absorption lines is extremely hard to account for - except in terms of orbital motion.

tracer
2003-Jun-14, 02:23 AM
Burnham's Celestial Handbook, which was published a few decades ago, says that Rigel is a trinary star. The B and C components orbit each other very very close together, so close that they can't be resolved as separate point sources and can only be deemed to "collectively" have the spectrum of a B9 main-sequence star. The A component orbits the B-C pair a whopping 9.4 arc-seconds away from them, giving plenty of separation in telescopes. (At Rigel's distance from the Earth, 9.4 arc-seconds works out to a little over 2000 A.U.s.)

eburacum45
2003-Jun-16, 01:10 PM
And Jim Kalers Star of the Week site says it is trinary too-

http://www.astro.uiuc.edu/~kaler/sow/rigel.html
but the companion doesnt really orbit both stars exactly, all three are orbiting the common barycentre wherever that is.

tracer
2003-Jun-16, 08:32 PM
bary = heavy (as in baryon, a heavy subatomic particle)
barycenter = center of mass

Technically, the B and C start are orbiting around their common center of mass, and the A star and the center of mass of the B-C system are in turn orbiting around their common center of mass.