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Planet C sirius


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#1    Corecries

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Posted 08 July 2006 - 01:42 PM


Is it true that there is a third,
or that there is the suspicion of a third ,
aka planet by sirius?

If so where did this come from,

I've read about the Dogon knowing about the dark twin sister.. planet B, but a C is news.
Any input?


#2    Waspie_Dwarf

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Posted 08 July 2006 - 10:43 PM

Firstly Sirius B is not a planet, it is a star (a white dwarf). As far as I am aware there is no evidence of a Sirius C.

Furthermore it now seems likely that the Dogon only added Sirius B into their myths after contact with missionaries who were aware of it's existence.

A good article on the Dogon and Sirius B can be found at the Chandra Space Telescope site: HERE

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#3    frogfish

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Posted 09 July 2006 - 12:51 AM

Yes, Sirius has a binary twin, Sirius B...

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#4    shun

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Posted 11 July 2006 - 10:24 AM

I had to smile, slightly, when Frogfish refered to the Sirius "twins".
Probably more like distant relatives.  

The way I look at it is that yes, there is a companion star. And yes, that could make looking for any planet, more difficult. In theory, one might be obscured. Yet, none has been found.

So, Sirius2 is a binary star system, which follows the pattern, among most stars.

Also, that article Waspy mentioned, on the Dogon in Africa, was very interesting.
Going back to the time of the Greeks, naked eye descriptions of the systems have recorded observing a ruddy hue. That seems to imply reddish, but the author questions the use of the term, and our modern interpretation.

Otherwise, that would mean something was a red giant star, and since Sirius A is younger, and an AV1 blue/white main sequence dwarf, that leaves its companion. If it's companion was a brighter star in the past, and thus discovered in earlier times, it has to be first understood that it is a white dwarf.

So, could it be a white dwarf today, and a red giant hundreds of years ago?

Evidently not, and so the Dogon and others never had a naked eye observation of the companion, Sirius B.

The reason has to do with the mass of Sirius B. It is today on a par with our sun. However, since Sirius B has lost mass, transitioning to a white dwarf, it was originally around 5 solar masses, as a main sequence star.

Since that size star evolves over the course of a couple of hundred million years, there is no chance it was recently a red giant, or seen prior to the use of telescopes. 5 solar mass stars go for about 125 million years, before they fuse helium. Then they heat up and brighten somewhat, and become red giants. That lasts for a time equal to their main sequence- about 125 million years. 75% of the way throught that stage, they expel enough of their mass that they generate a nebula.

The nebula will last for the final 25% of the red giant phase, after which the nebula drifts off, and the star becomes a white dwarf.

125 million years ago Sirius B entered a red giant phase. 30 million years ago, it began forming a nebula.

Even if it had the last vestiges of its nebula during the last 2000 years, the main light to be seen would not include the remnant of any "ruddy" nebula, at that point. The main light at that point would be the white stellar dwarf. And, they are not visible to the naked eye.

What I won't speculate on is how these two stars got together. If Sirius B was a 1 solar mass white dwarf, millions of years ago, then it could be captured into an orbit with its larger companion, Sirius A (2 solar mass). At 2 solar masses, and with its bright luminosity,
Sirius A is about 250 million years old.

It will be another 250 million years before it begins its red giant phase, which will be interesting. When a white dwarf accretes from a red giant, that can lead to the WD getting denser, and going supernova.


If they began orbiting 125 mya, chances are Sirius A (main sequence) accreted material from Sirius B (red giant). Sirius A would be enriched with additional elements.

If they began orbiting 30 mya, then A (main sequence) still accreted material from B (planetary nebula).

Similar enrichment.

The answer to all of this lies in the spectral absorption lines of Sirius A.

Today, they are only detected as lines of various ionized levels of hydrogen.

That could indicate that Sirius A captured a pre-existing white dwarf, Sirius B.
And, furthermore, that Sirius B was never seen as a "ruddy" red giant, or as an atypically
bright planetary nebula, as it orbited Sirius during, man's pre-occupation with the stars.



Some images might include a Hubble Telescope picture of those stars.

Also, examples of mid-life planetary nebulae, and their white dwarf stars, representing how Sirius B might have looked, between 30 mya, and the time it became a white dwarf, before it was captured by Sirius A, IMO.

And, the absorption spectra of Sirius A to show that it is a hydrogen burning main
sequence star.

Incidentally, it was difficult to obtain higher quality spectra on Sirius B, until Hubble Telescope. Even though B is a white dwarf, it has an outer envelope primarily consisting of hydrogen, as indicated by its spectra.

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I just noticed Frogfish posted about the Eskimo Nebula- NGC 2392. So did I, in the link!

Edited by shun, 11 July 2006 - 07:49 PM.


#5    frogfish

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Posted 11 July 2006 - 12:44 PM

Quote

I had to smile, slightly, when Frogfish refered to the Sirius "twins

I know they are not twins...They are very different, but I was at a loss for words original.gif

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