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John L
2005-Jul-13, 08:38 PM
Here (http://planetquest.jpl.nasa.gov/news/tripleSunsets.html) is a link to a story about a new Hot Jupiter discovered in a tight triple binary star system. All three stars fit within the same space as between the Sun and Saturn. The star with the planet is in the center of the system, and the other two orbit in in a binary configuration. The planet has a 3 day orbit around the outer star. The article says that this creates a problem for the migration theory as this Hot Jupiter would have to have started out where the other two stars in the system are for the migration theory to work. Sounds like some fun work in the planet formation field will soon be afoot.

And as half of all stars are in multi-star systems this opens up a whole new area of planet hunting research that could mean the number of planets in the galaxy is a lot higher than anyone previously thought. Before now, it was thought that planets simply could not form in the complex gravitational environment of a tight multi-star system.

VanderL
2005-Jul-13, 09:33 PM
Great find John L, that's an incredible system. I always said our ideas about star and planet formation must be revised (the Nebular theory is untenable, if only by the existence of "hot Jupiters"), but this sytem really takes the cake.

Thanks for this link, it indeed opens up a whole new "can of worms" for mainstream models.

Cheers.

aeolus
2005-Jul-13, 10:21 PM
wow-ee! How cool is this! This is exactly the kind of thing that reminds me why I'm doing an Astro degree.

antoniseb
2005-Jul-13, 10:23 PM
Originally posted by VanderL@Jul 13 2005, 09:33 PM
Thanks for this link, it indeed opens up a whole new "can of worms" for mainstream models.
It is an interesting find. Planetary Migration could also happen in a smaller proto-planetary disk. I'm not sure that this makes a mess of current theories, but it DOES say that planets in multiple star systems CAN form.

VanderL
2005-Jul-14, 08:30 AM
Originally posted by antoniseb+Jul 13 2005, 10:23 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (antoniseb @ Jul 13 2005, 10:23 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-VanderL@Jul 13 2005, 09:33 PM
Thanks for this link, it indeed opens up a whole new "can of worms" for mainstream models.
It is an interesting find. Planetary Migration could also happen in a smaller proto-planetary disk. I&#39;m not sure that this makes a mess of current theories, but it DOES say that planets in multiple star systems CAN form. [/b][/quote]
If the "hot Jupiter" formed according to "nebular" theory, the planet would have formed away from the star it orbits, and then moved closer. The unlikeliness of this process aside (what starts and stops this process?), in this system the close binary orbits at about the distance that Saturn does, and there is no room for the "hot Jupiter" to have formed at all.
The existence of "hot Jupiters" and and the highly "irregular&#39; orbits of most planets can&#39;t be reconciled with the nebular hypothesis, the virtual "fix" is to let more hypothetical planets form and see which one of them survive the subsequent collisions and call that a model. And besides how do you explain the orbiting close binary (heck, any close binary) at it&#39;s current orbit?

Cheers.

astromark
2005-Jul-14, 08:43 AM
The cutting edge. Thanks for this link John. This seems to pave the way for far more complex orbital systmes than we had previously imagined.
The chances of Earth like planets being found has just risen.

antoniseb
2005-Jul-14, 11:04 AM
Originally posted by VanderL@Jul 14 2005, 08:30 AM
The existence of "hot Jupiters" and and the highly "irregular&#39; orbits of most planets can&#39;t be reconciled with the nebular hypothesis
How can you make such a categorical statement without backing it up? Of course it can be reconciled the the &#39;nebular hypothesis". Show me why you believe it can&#39;t.

VanderL
2005-Jul-14, 11:25 AM
Originally posted by antoniseb+Jul 14 2005, 11:04 AM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (antoniseb @ Jul 14 2005, 11:04 AM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-VanderL@Jul 14 2005, 08:30 AM
The existence of "hot Jupiters" and and the highly "irregular&#39; orbits of most planets can&#39;t be reconciled with the nebular hypothesis
How can you make such a categorical statement without backing it up? Of course it can be reconciled the the &#39;nebular hypothesis". Show me why you believe it can&#39;t. [/b][/quote]
I said that in the first paragraph: what makes the planets move towards the star and then stop, what makes them have these eccentricities.

Cheers.

antoniseb
2005-Jul-14, 12:49 PM
Originally posted by VanderL@Jul 14 2005, 11:25 AM
what makes the planets move towards the star and then stop, what makes them have these eccentricities.
Concerning the move in, that is usually attributed to the orbital energy lost to the casting out of other mass in the protoplanetary disk. What stops it is hitting a void in the disk. For this to work, there has to be similar (or more) mass in the local part of the disk as the mass of the planet.

Concerning the eccentricities, I don&#39;t know, and can only guess. Guess one is that there was not enough mass in the disk to circularize the orbit of a captured wanderer. Guess two is that somehow a resonance between protoplanets created a bias as to where the KBOs and comets were being cast out from. These are the first that come to mind, I make no claim that either is the mainstream view.

John L
2005-Jul-14, 02:20 PM
Originally posted by antoniseb+Jul 13 2005, 04:23 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (antoniseb @ Jul 13 2005, 04:23 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-VanderL@Jul 13 2005, 09:33 PM
Thanks for this link, it indeed opens up a whole new "can of worms" for mainstream models.
It is an interesting find. Planetary Migration could also happen in a smaller proto-planetary disk. I&#39;m not sure that this makes a mess of current theories, but it DOES say that planets in multiple star systems CAN form. [/b][/quote]
Well Anton, the problem is that the current migration models are based on large disks, 100 AU or more, with the Jupiter forming in the 10-30AU range and migrating in to the tight Hot Jupiter orbit. As that 10-30AU is occupied by a closely orbiting binary star, each with a mass only somewhat less than the Sun (combined mass more than the central star), these migration theories fall flat. None of them appear to have considered a Jupiter forming in something closer to a 3-5AU orbit and then migrating a few AU into the Hot Jupiter orbit. Anything farther than that, I think, would have either been pulled into orbit around the binary pair of stars, which have a higher mass and therefore gravity, or ejected from the system entirely, which is probably much more likely.

I think what this system, and the continued study of other systems containing Hot Jupiters, is that large planets can form anywhere within the disk of material and only the proto-star switching on stops the process. I think we&#39;ll also find that the planets are well on their way to being fully formed within the proto-stellar cloud before the star ever switches on, but that&#39;s just my own theory.

antoniseb
2005-Jul-14, 02:40 PM
Originally posted by John L@Jul 14 2005, 02:20 PM
I think we&#39;ll also find that the planets are well on their way to being fully formed within the proto-stellar cloud before the star ever switches on, but that&#39;s just my own theory.
I make no claims about the specifics of the timing. You could be right, and not be in conflict with my loose constraints. Personally, I see this system as having the Saturn scale part of the disk[s] completely disrupted by the two stars {counting the close double a single star for the moment). This would mean that the inner disks MIGHT reasonably be able to operate as we might expect for the inner few AU around both stars. It might also leave the outer disk (around all stars) not much more perturbed than if there were just a large gas giant in the Saturn scale orbit.

The biggest difference of course is that the stars aren&#39;t going to migrate in much as they sweep out (if any sweeping was ever needed) the disk lanes at their distances.

Prior to this discovery, and the recent discovery of a planet around a double system containing a white dwarf, I had doubts as to whether there could be planets in a double system, and figured that Alpha Centauri might not have any planets. This gives me hope for us eventually finding something there.

Fraser
2005-Jul-14, 04:34 PM
SUMMARY: A backdrop in many science fiction stories is to have multiple suns in the sky. Astronomers have now found such a world, called HD 188753 Ab. Our heroes couldn&#39;t set foot on this planet, though, since it&#39;s a "hot jupiter"; roughly the mass of Jupiter, but orbiting its parent star every 3.3 days. The other two stars in the system take 25.7 years to orbit the main star (about the distance from the Sun to Saturn), and spin around each other every 156 days,

View full article (http://www.universetoday.com/am/publish/scientist_finds_triple_sunsets.html)

What do you think about this story? Post your comments below.

John L
2005-Jul-14, 04:38 PM
I just wonder, in this particular system, where the point is between the central star and the binary&#39;s orbit where the primary gravitational influence shifts from the central star to the binaries. That would be the point where any proto-planety disk would be cut off. I see the binaries severely truncating the disk from this point outward leaving only the material near the central star to form a planet.

And as you say, and as is pointed out in the article, the only planets found in binary systems before very recently were very wide binaries - stars with separations measured in hundreds or even thousands of AU, and therefore offering little gravitation perturbations. Like you I had assumed that the tighter systems like Centauri would have destroyed in proto-planetary disk during the formation of the stars or would have ejected any planets that did form from gravitational interactions. This discovery could change that, but I would also like to say that I&#39;d prefer some independent confirmation of this discovery. As the article states, the team created some new mathmatical techniques to coax the planet data out of their observations. I would really like to see someone else&#39;s expert opinion on their techniques and how they applied it to the data.

antoniseb
2005-Jul-14, 05:13 PM
Note that there is some discussion about this system already in the "Other Stories" part of the forum. Thanks to JohnL for spotting the story early.

wstevenbrown
2005-Jul-15, 12:01 AM
Curious.

Most stars form in clusters, as the result of the collapse of a dense molecular cloud.

The interval between the formation of the first star and the dispersal of the cluster averages 10-20 MYr.

In the meanwhile, the gravitational tug-of-war drives some systems closer together, and throws some systems completely out of the cluster.

IOW, the double star and the planetary system may have initially formed apart, then been thrown together by cluster dynamics. There was plenty of time for it.

This argument does not apply to really dense but isolated systems like globular clusters, but to more typical star-forming regions such as the Orion Nebula.

I wonder that this point was not brought out, either in the article, or in the Forum discussions-- I don&#39;t see any problem for any of the stellar and planetary evolution models. Best regards-- Steve

bernardz
2005-Jul-15, 03:57 AM
The current theory of planet formation appears to be in trouble.

We have now found large planets much closer to the sun then our theories would allow and now here we have planets like this one.

Svemir
2005-Jul-15, 06:03 AM
IOW, the double star and the planetary system may have initially formed apart, then been thrown together by cluster dynamics. There was plenty of time for it.

This argument does not apply to really dense but isolated systems like globular clusters, but to more typical star-forming regions such as the Orion Nebula.

I wonder that this point was not brought out, either in the article, or in the Forum discussions-- I don&#39;t see any problem for any of the stellar and planetary evolution models. Best regards-- Steve
Good point.
Once again Nature gave us a puzzle.
As I understood that, excentricity of planets orbits (Hot Jupiters, Neptuns etc) is a sign of their youth, because orbits tends to be circular after some time (like in our planetary system). I remember that some of the extrasolar planets are estimated to be mere 100 My old.
Now, in this case, the central star is formed, a planet on, let&#39;s say, 100 AU is formed then it migrated closer to the central star and that the whole system begun to dance with the binary star system.
What is the timeline of this configuration?
Is planets orbit excentric because the planet is young or close orbiting binary pair is disturbing planets orbit (or both)?
Once again, more questions then answers.

Greg
2005-Jul-15, 06:55 AM
Just when you think you understand something about solar system formation, this turns up. We live in exicitng times indeed. Now we can consider that gas giants do not spiral in, but rather form right next to their parent star. Personally I really don&#39;t like this notion considering that ther material near the star would be more likely to form a terrestrial planet than a gas giant. Maybe some stars are constantly unstable and emit alot of radiation that pushes gas out that would normally have fallen into them, enough to form a gas giant on its doorstep. Hopefully Spitzer of the sub-millimeter scopes will weigh in on this and provide some examples. If not, then the spiraling in from a distance theory will prevail.

Greg
2005-Jul-15, 06:57 AM
To clarify that little typo, I meant Spitzer (the infra-red observatory) and the sub-millimeter scopes.

Greg
2005-Jul-15, 07:02 AM
I&#39;ll reiterate briefly what I posted on the main story forum. This is an unsettling find, and just when I was getting comfortable with the planet migration theory. My initial thought are that some stars may be particuarlly unstable early on and emit alot of radiation that may push out gas that normally would fall into them. Perhaps enough gas to form a gas giant. I would greatly appreciate an assist from Spitzer or on of the sub-millimeter telescopes to find such a system early on. Otherwise the migration theory will prevail. I suspect such a find will be forthcoming in the next couple of years. We live in interesting times, indeed&#33;

VanderL
2005-Jul-15, 09:37 AM
Hi all,

You guys seem quite happy to try to fit the data into the existing nebular theory, which has been adapted to include planet migration. Does it occur to any of you that this whole migration business lacks a mechanism? How is it possible to move planets (and Jupiter-plus masses at that) at will through space and let them end up exactly where they are found? I see that even the binary could have formed further out and then moved closer, care to tell how that works? Did anyone consider the energies, or the inherent problem that gravity doesn&#39;t allow abrupt changes because a disturbance in the balance leads to chaos and ejection?

And, this has been a problem from the start, gravitational collapse (the process underlying the nebular theory) has a whole bunch of problems by itself. There is this unexplained step (step 1) that turns gas (plasma) into dust or ice before the whole gravitational circus can start at all. The virtual models all have to assume a "stickiness" to get the process started.

And there is no doubt in my mind that using the current "free parameter" model, someone will come up with a solution, so everybody can go back to business. I think this triple system dramatically shows us that our models are off, and we need something fundamentally different to explain the data. The modifications that are needed to keep the current model (gravitational collapse, planet migration, star migration) have all the characteristics of "epicycling". It works, but somehow all the coincidences necessary to keep model and data in sync keep piling up.

Let me predict something here, we will find evidence of planets orbiting inside a stars&#39; "atmosphere" (or maybe we already have, but didn&#39;t believe the data).
We will find even stranger configurations than the one described in the article, like planets orbiting a close binary, both orbited by another close binary. Planets closely orbiting neutron stars, planets orbiting black holes. Imagine any crazy configuration and we will find them.

We will find planets orbited by a bunch of other planets (that will be tough to find though).

Happy planet hunting,

Cheers.

VanderL
2005-Jul-15, 09:47 AM
I don&#39;t see any problem for any of the stellar and planetary evolution models. Best regards-- Steve


The current theory of planet formation appears to be in trouble.

Hmm, let&#39;s just say we live in interesting times, and be prepared to find many more even stranger star/planet configurations.

Cheers.

antoniseb
2005-Jul-15, 12:34 PM
Originally posted by VanderL@Jul 15 2005, 09:37 AM
Does it occur to any of you that this whole migration business lacks a mechanism? How is it possible to move planets (and Jupiter-plus masses at that) at will through space and let them end up exactly where they are found? I see that even the binary could have formed further out and then moved closer, care to tell how that works?
There IS a mechanism for planet migration, and it has been discussed many times. It is the same mechanism that created the Kuiper Belt and Oort Cloud. However, I would be VERY surprised to see anyone claim that THIS mechanism was able to substantially move the binary in this system. Where did you read THAT?

Let me predict something here, we will find evidence of planets orbiting inside a stars&#39; "atmosphere" (or maybe we already have, but didn&#39;t believe the data). We will find even stranger configurations than the one described in the article, like planets orbiting a close binary, both orbited by another close binary. Planets closely orbiting neutron stars, planets orbiting black holes. Imagine any crazy configuration and we will find them.

I expect you are right about eventually finding a planet orbiting inside a star&#39;s "atmosphere". This will probably be a bloated red giant. We already have evidence in the form of closely orbiting white dwarfs that stars can orbit inside stars... why not Hot Jupiters? As to your other predictions... I guess it COULD happen. They would be strange systems if they were discovered.


The modifications that are needed to keep the current model (gravitational collapse, planet migration, star migration) have all the characteristics of "epicycling".

I disagree. Planet migration has a physical mechanism that explains it, and a natural consequence that was predicted by it and then observed (The Kuiper Belt). Other evidence for it is observed in the proto-planetary disks of nearby new star systems, though much more observation of these objects will help to solidify the theory. Epicycles are mere mathematical constructs to model observed behavior.

VanderL
2005-Jul-15, 01:15 PM
Originally posted by antoniseb+Jul 15 2005, 12:34 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (antoniseb @ Jul 15 2005, 12:34 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-VanderL@Jul 15 2005, 09:37 AM
Does it occur to any of you that this whole migration business lacks a mechanism? How is it possible to move planets (and Jupiter-plus masses at that) at will through space and let them end up exactly where they are found? I see that even the binary could have formed further out and then moved closer, care to tell how that works?
There IS a mechanism for planet migration, and it has been discussed many times. It is the same mechanism that created the Kuiper Belt and Oort Cloud. However, I would be VERY surprised to see anyone claim that THIS mechanism was able to substantially move the binary in this system. Where did you read THAT?


[/b][/quote]
Hi Antoniseb,

(Btw the star migration came from Steve S, his comments are in the Story Comments section, and a quote was copied into this thread.)

Could you tell me more about this mechanism? I hope you don&#39;t mean to say that collisions are responsible? I have no problem with planet migration, but I fail to see a mechanism.




The modifications that are needed to keep the current model (gravitational collapse, planet migration, star migration) have all the characteristics of "epicycling".

I disagree. Planet migration has a physical mechanism that explains it, and a natural consequence that was predicted by it and then observed (The Kuiper Belt). Other evidence for it is observed in the proto-planetary disks of nearby new star systems, though much more observation of these objects will help to solidify the theory. Epicycles are mere mathematical constructs to model observed behavior.

That is the fallacy of the nebular theory; it starts with a number of assumptions and they have become a story, and that story has become dogma. As long as the new pieces fit into the story there&#39;s no problem, but what if there are some loose pieces, like this finding of a triple star planetary system? It doesn&#39;t fit, not even with a planet migration thrown in, it looks as if someone is having fun showing us that our model is fundamentally incorrect. Planet migration, ok, but how do we let them to move in whatever direction we need to fit the observations?

And is your explanation on what an epicycle is meant to show it doesn&#39;t apply here? Because it does, all the steps in planet formation are mathematical constructs.

Cheers.

antoniseb
2005-Jul-15, 01:37 PM
Originally posted by VanderL@Jul 15 2005, 01:15 PM
Could you tell me more about this mechanism? I hope you don&#39;t mean to say that collisions are responsible? I have no problem with planet migration, but I fail to see a mechanism.
The mechanism is that statistically, more massive objects tend to interact with less massive objects in such a way as to fling them out, and thus reduce the orbit of the more massive object. Very massive objects can&#39;t be moved nuch by this mechanism. For Jupiter to have moved inward substantially, it would have to have ejected about a Jupiter Mass of material into long elliptical orbits (the Oort cloud).

This presumes that there was a relatively dense proto-planetary disk early on, and that in cleaning it out, the planets moved inward. There are numerous papers that keep appearing about computer simulations of the orbital dynamics for this mechanism, and it seems pretty well established (it is not just hand-waving).

is your explanation on what an epicycle is meant to show it doesn&#39;t apply here? Because it does, all the steps in planet formation are mathematical constructs.
No, the steps for planet formation are mathematical representations of physical mechanisms. Ptolemaic epicycles were simply a mathmatical means to calculate planetary positions without any physical mechanism that they described. I think it is odd to hear someone decry science because it is supported by mathematics, but that&#39;s what it sounds like you are saying. Do you think that any theory that has mathematics that give quantitative predictions is suspect simply for that reason?

wstevenbrown
2005-Jul-15, 01:41 PM
VanderL:

If you are truly interested in the statistics of multiple-star formation, here is an article whose particular purpose was a population synthesis of binaries containing compact objects; however, in its reference section are quoted the more basic synthesis methods for multiple-star systems of all types:

http://arxiv.org/astro-ph/0102229

This is physics so well-established that the seminal papers predate the electronic archiving system. This particular website, arxiv.org, if you use their Find option, and search the references by author name and year, will call up photostatic copies of the cited works and automatically compile a pdf file for your especial use. Typical execution times are on the order of 20 min.

I hope this helps. Best regards-- Steve

[corrected typo in URL]

wstevenbrown
2005-Jul-15, 02:06 PM
VanderL:

If you are truly interested in the statistics of multiple-star formation, here is an article whose particular purpose was a population synthesis of binaries containing compact objects; however, in its reference section are quoted the more basic synthesis methods for multiple-star systems of all types:

http://arxiv.org/astro-ph/0102229

This is physics so well-established that the seminal papers predate the electronic archiving system. This particular website, arxiv.org, if you use their Find option, and search the references by author name and year, will call up photostatic copies of the cited works and automatically compile a pdf file for your especial use. Typical execution times are on the order of 20 min.

I hope this helps. Best regards-- Steve

Your comments on the "nebular hypothesis" indicate either that you have not read the available literature, or that you don&#39;t understand the physics involved. Had you referred to "accretion disc dynamics", I would have inferred that you had done your homework, understood the issues involved, and were unconvinced by the arguments. Instead: Why must everyone else do the work for you, and present you with a perfect finished product which suits your preconceptions? :huh: S

VanderL
2005-Jul-15, 03:11 PM
Originally posted by wstevenbrown@Jul 15 2005, 01:41 PM
VanderL:

If you are truly interested in the statistics of multiple-star formation, here is an article whose particular purpose was a population synthesis of binaries containing compact objects; however, in its reference section are quoted the more basic synthesis methods for multiple-star systems of all types:

http://arxiv.org/astro-ph/010229

This is physics so well-established that the seminal papers predate the electronic archiving system. This particular website, arxiv.org, if you use their Find option, and search the references by author name and year, will call up photostatic copies of the cited works and automatically compile a pdf file for your especial use. Typical execution times are on the order of 20 min.

I hope this helps. Best regards-- Steve
Hi Steve,

Unfortunately the link doesn&#39;t work, if you mean to say that the models are able to adequately reproduce all the multiple star systems, I won&#39;t try to dispute that they are consistent with the assumptions on which they are based. Could you explain why you don&#39;t see a problem with the new system?

Cheers.

VanderL
2005-Jul-15, 03:18 PM
QUOTE
is your explanation on what an epicycle is meant to show it doesn&#39;t apply here? Because it does, all the steps in planet formation are mathematical constructs.

No, the steps for planet formation are mathematical representations of physical mechanisms. Ptolemaic epicycles were simply a mathmatical means to calculate planetary positions without any physical mechanism that they described. I think it is odd to hear someone decry science because it is supported by mathematics, but that&#39;s what it sounds like you are saying. Do you think that any theory that has mathematics that give quantitative predictions is suspect simply for that reason?

:huh: Looks like we&#39;re saying the same thing here about epicycles, so, no I don&#39;t "decry science because it is supported by mathematics".

Cheers.

VanderL
2005-Jul-15, 03:27 PM
Originally posted by wstevenbrown@Jul 15 2005, 02:06 PM

VanderL:

If you are truly interested in the statistics of multiple-star formation, here is an article whose particular purpose was a population synthesis of binaries containing compact objects; however, in its reference section are quoted the more basic synthesis methods for multiple-star systems of all types:

http://arxiv.org/astro-ph/010229

This is physics so well-established that the seminal papers predate the electronic archiving system. This particular website, arxiv.org, if you use their Find option, and search the references by author name and year, will call up photostatic copies of the cited works and automatically compile a pdf file for your especial use. Typical execution times are on the order of 20 min.

I hope this helps. Best regards-- Steve

Your comments on the "nebular hypothesis" indicate either that you have not read the available literature, or that you don&#39;t understand the physics involved. Had you referred to "accretion disc dynamics", I would have inferred that you had done your homework, understood the issues involved, and were unconvinced by the arguments. Instead: Why must everyone else do the work for you, and present you with a perfect finished product which suits your preconceptions? :huh: S
Steve,

I have tried to get an idea what protoplanetary disk dynamics is all about and when I saw this:




On the stratorotational instability in the quasi-hydrostatic semi-geostrophic limit
O. M. Umurhan

The linear normal-mode stratorotational instability (SRI) is analytically reexamined in the inviscid limit where the length scales of horizontal disturbances are large compared their vertical and radial counterparts. Boundary conditions different than channel walls are also considered. This quasi-hydrostatic, semi-geostrophic (QHSG) approximation allows one to examine the effect of a vertically varying Brunt-Vaisaila frequency, &#036;N^2&#036;. It is found that the normal-mode instability persists when &#036;N^2&#036; increases quadratically with respect to the disc vertical coordinate. However we also find that the SRI seems to exist in this inviscid QHSG extreme only for channel wall conditions: when one or both of the reflecting walls are removed there is no instability in the asymptotic limit explored here. These equations also admit non-normal mode behaviour and under fixed Lagrangian pressure conditions on both radial boundaries there is no normal mode behavior predicted in the QHSG limit. The mathematical relationship between the results obtained here and that of the classic Eady (1949) problem for baroclinic instability is drawn. We conjecture as to the mathematical/physical nature of the SRI.
The general linear problem analyzed without approximation in the context of the Boussinesq equations admits a potential vorticity-like quantity that is advectively conserved by the shear. Its existence means that a continuous spectrum is a generic feature of this system. It also implies that in places where the Brunt-Vaisaila frequency becomes dominant the flow may two-dimensionalize by advectively conserving its vertical vorticity.


I was under the impression that either I&#39;m far too dumb (which is correct, I&#39;m afraid) or that the field is far from clear, which might also be correct, but that&#39;s not based on an extensive study.

Cheers.

P.S. Your link doesn&#39;t work, I am interested in it though, because it&#39;s a review.

Guest
2005-Jul-16, 03:06 AM
That is an extremely abstract abstract. I would have to see the segment in context with some definitions of the acronyms used to get the gist of what this is saying.

Greg
2005-Jul-16, 03:09 AM
That was me. After deleting all of my cookies I was no longer auto-logged when I accessed the website.

wstevenbrown
2005-Jul-16, 05:52 AM
Oops-- my bad. I corrected the typo in both strings. Apologies-- Steve

That&#39;s weird-- the URL shows up correctly on the edit page, but not on the resubmitted page. here is the correct version:

http://arxiv.org/astro-ph/0102229

O, now I get it&#33; You can&#39;t edit within an URL-- must delete the whole bloody thing and retype it entire. S

wstevenbrown
2005-Jul-16, 05:59 AM
Oops-- my bad. I corrected the typo in both strings. Apologies-- Steve

PS That bozo was an obscurantist. They have their fans within their narrow little specialties, but nowhere else. The elitist viewpoint: they thank each other for not wasting each other&#39;s valuable time with English prose which just anyone might have understood. It&#39;s an acquired taste. I haven&#39;t acquired it.

wstevenbrown
2005-Jul-18, 12:17 AM
Today&#39;s crop shows modern thinking on the constraints on planet formation in multiple-star systems:

http://arxiv.org/abs/astro-ph/0507356

Enjoy&#33; S

VanderL
2005-Jul-18, 05:58 AM
Hi Steve,

What do you think about this article (http://xxx.lanl.gov/abs/astro-ph/0507356), it doesn&#39;t involve the 3 star system but it equally shows a planet in a close binary system that cannot have formed in situ. A severe problem, becasue this kind of system can only be explained by "capture", which is one of the least likely scenario&#39;s around, imo.

Cheers.

aeolus
2005-Jul-18, 03:33 PM
Originally posted by VanderL@Jul 18 2005, 05:58 AM
this kind of system can only be explained by "capture", which is one of the least likely scenario&#39;s around, imo.
The conclusion of the paper suggests the ejection of stars that first formed within the system as a possibility for changing the dynamics of the system into it&#39;s current form. This doesn&#39;t require capture of another object does it? This could happen if two of the original stars, say, gradually got closer and closer, and one of them ended up "winning out" and throing the other into space, couldn&#39;t it?

VanderL
2005-Jul-18, 04:00 PM
Originally posted by aeolus+Jul 18 2005, 03:33 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (aeolus @ Jul 18 2005, 03:33 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-VanderL@Jul 18 2005, 05:58 AM
this kind of system can only be explained by "capture", which is one of the least likely scenario&#39;s around, imo.
The conclusion of the paper suggests the ejection of stars that first formed within the system as a possibility for changing the dynamics of the system into it&#39;s current form. This doesn&#39;t require capture of another object does it? This could happen if two of the original stars, say, gradually got closer and closer, and one of them ended up "winning out" and throing the other into space, couldn&#39;t it? [/b][/quote]
Hi Aeolus.

I don&#39;t know if your explanation works, or even if I understand it at all.

Here is the abstract:


The recent discovery of a Jupiter-mass planet in the close binary star system HD188753 poses a problem for planet formation theory. A circumstellar disk around the planet&#39;s parent star would be truncated at 1.3 AU, leaving little material available for planet formation. In this paper, we attempt to model a disk around HD188753, exploring a range of parameters constrained by observations of protoplanetary disks. We find that the in situ formation of the planet around HD188753 is extremely unlikely, and that the planet must have formed before the capture of the close stellar companion.

I think the authors say that the second "stellar companion" was captured after the planet formed around HD188753. Which, as i said seems not very likely to me, especially since this capture didn&#39;t throw out the Jupiter-mass planet. A true mystery.


Cheers.

aeolus
2005-Jul-18, 07:20 PM
Originally posted by VanderL@Jul 18 2005, 04:00 PM
Hi Aeolus.

I don&#39;t know if your explanation works, or even if I understand it at all.
I was referring to this para in the conclusion:



It is more plausible that the planet formed around HD188753A before its stellar companion assumed its present-day orbit. Perhaps it started out as a system with more than two stars, and ejected all but the two seen today, leaving them as a close pair.


This wouldn&#39;t require any capture (which I also think is on the more unlikely side of things) rather an ejection of bodies that originally formed in the system. We have observed binary systems that are &#39;collapsing&#39;, decresing their radius year by year. In this case, when two stars are close enough, one of them might overpower the other, tossing the other into space, and leaving the original system with a different gravity configuration than before.

What are your thoughts about this?

VanderL
2005-Jul-18, 07:36 PM
Originally posted by aeolus+Jul 18 2005, 07:20 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (aeolus @ Jul 18 2005, 07:20 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-VanderL@Jul 18 2005, 04:00 PM
Hi Aeolus.

I don&#39;t know if your explanation works, or even if I understand it at all.
I was referring to this para in the conclusion:



It is more plausible that the planet formed around HD188753A before its stellar companion assumed its present-day orbit. Perhaps it started out as a system with more than two stars, and ejected all but the two seen today, leaving them as a close pair.


This wouldn&#39;t require any capture (which I also think is on the more unlikely side of things) rather an ejection of bodies that originally formed in the system. We have observed binary systems that are &#39;collapsing&#39;, decresing their radius year by year. In this case, when two stars are close enough, one of them might overpower the other, tossing the other into space, and leaving the original system with a different gravity configuration than before.

What are your thoughts about this? [/b][/quote]
Ok, I see the point now, you&#39;re right that ejection from a system is a much more likely event, but your proposal can only be part of the solution (you still need to find a second star). Essentially you want to have a system that can form planets, so you don&#39;t want any other star close by, but if the second star is too close, no planets can&#39;t form, if it&#39;s too far away there won&#39;t be any ejection.

Hmmm, suppose you start with a close binary star system that has a circumbinary disk (I think they have even been found), forming into circumbinary planets (conjecture), maybe disturbing this system could end up with a planet circling one of the stars and ejection of most of the rest?

Dunno, whatever way you look at it, there&#39;s going to be a lot of things happening at a very precise order of events, what do you think?:unsure:

Cheers.

aeolus
2005-Jul-18, 08:16 PM
Originally posted by VanderL@Jul 18 2005, 07:36 PM
Ok, I see the point now, you&#39;re right that ejection from a system is a much more likely event, but your proposal can only be part of the solution (you still need to find a second star). Essentially you want to have a system that can form planets, so you don&#39;t want any other star close by, but if the second star is too close, no planets can&#39;t form, if it&#39;s too far away there won&#39;t be any ejection.

Hmmm, suppose you start with a close binary star system that has a circumbinary disk (I think they have even been found), forming into circumbinary planets (conjecture), maybe disturbing this system could end up with a planet circling one of the stars and ejection of most of the rest?

Dunno, whatever way you look at it, there&#39;s going to be a lot of things happening at a very precise order of events, what do you think?
I&#39;m not sure what I think- that&#39;s why I&#39;m asking :) I&#39;m certainly no expert on the topic, I only read the paper you linked to. Seems like it could happen, and the idea offers a more likely scenario than that of the capture. Personally, I think this stuff is perfect to feed into supercomputers like they do to look into how hurricanes work. I bet we&#39;d learn alot, but come to think of it, end up having even more questions.

VanderL
2005-Jul-18, 09:01 PM
Well, as you know I&#39;m no expert either, but I try to make sense of what I find on the Web, I&#39;m curious what the experts have to say about this system and the 3 star+planet system. I remarked somewhere that you can expect any system imaginable (and some more exotic).

Have you ever seen the intro (outro and intermezzo&#39;s) of 3rd Rock From The Sun?
I think they have the computer model that explains planetary behaviour :D

Cheers.

aeolus
2005-Jul-18, 11:13 PM
Originally posted by VanderL@Jul 18 2005, 09:01 PM
I remarked somewhere that you can expect any system imaginable (and some more exotic).

Have you ever seen the intro (outro and intermezzo&#39;s) of 3rd Rock From The Sun?
I think they have the computer model that explains planetary behaviour :D

With all these new discoveries and different types of systems being found, it wouldn&#39;t be too far off. I&#39;m just hoping Cassini finds a pic of the sheppard moons doing that roller coaster thing on Saturn&#39;s rings... :lol:

wstevenbrown
2005-Jul-19, 02:08 AM
What do you think about this article, it doesn&#39;t involve the 3 star system

VanderL: I linked to that one over in the other string as soon as it hit the arxiv-- it seemed timely.

The key concept regarding capture is this: each time a star is ejected from a cluster, that star gains energy WRT the cluster-- but simultaneously, whatever accelerated it loses energy WRT the cluster, moving it closer to the center, causing the cluster center center to densify, and making capture/collision/interaction more likely. I use &#39;collision&#39; in the elastic sense of &#39;cause the trajectories of both bodies to change&#39;. Detailed population syntheses take this into account.

Planetary formation theories are only in trouble if statistically unlikely numbers of multiple systems with planets start showing up. S

GOURDHEAD
2005-Jul-19, 01:23 PM
Planetary formation theories are only in trouble if statistically unlikely numbers of multiple systems with planets start showing up. I&#39;m not sure I&#39;m capable of appreciating all the fuss about planet formation and migration. Each process occurs in environments which, due to their stochastic nature, defy modeling because of the level of complexity which exceed our current level of technological competence. Starting with the protoplanetary cloud that must collapse in order to produce the menagerie of stellar and planetary objects, the cloud can have a large range of initial angular momenta and histories of transient magnetically powered vortices that can reinforce or oppose the gravitationally powered vortices as well as transfer angular momenta amongst the members prior to as well as after formation of the compact members of the system. Today when we observe whatever we see, we can only guess at such histories not knowing what was there originally. So if one can posit a scenario that will produce whatever is observed, regardless of its unlikelyness, the universe can be counted on to allow it to happen here and there. When we advance to that level of technological competence that allows us to build stellar systems with planet communities to our liking, then we will be interested in optimization of the process; the universe couldn&#39;t care less, isn&#39;t capable of caring at all.

In our system we have Jupiter and Saturn each with quite a set of satellites in orbits with fairly low eccentricities which don&#39;t appear to have been disturbed by the presence of the Sun nor by each other nor the other giants. It seems likely that increasing the mass of the giants and/or their satellites would only increase the system stabilities. If true, we should expect to find loads of planets in multiple star systems provided stellar separations are greater than one AU. I&#39;m not sure about environments where the separations are less.

Here (http://homepage.sunrise.ch/homepage/schatzer/Alpha-Centauri.html) is a link to a concise description of Alpha Centauri; the quote below is from that link.

Visible only from latitudes south of about 25 the star we call Alpha Centauri lies 4.35 light-years from the Sun. But it is actually a triple star system. The two brightest components Alpha Centauri A and B form a binary. They orbit each other in 80 years with a mean separation of 23 astronomical units (1 astronomical unit = 1 AU = distance between the Sun and Earth) [...During their 80-year orbit, the separation between A and B changes from 11 AU to 35 AU.]. The third member of the system Alpha Centauri C lies 13,000 AU from A and B, or 400 times the distance between the Sun and Neptune. This is so far that it is not known whether Alpha Centauri C is really bound to A and B, or if it will have left the system in some million years. Alpha Centauri C lies measurably closer to us than the other two: It is only 4.22 light-years away, and it is the nearest individual star to the Sun. Because of this proximity, Alpha Centauri C is also called Proxima (Centauri). The separations of the stars in this system are sufficiently large that, especially A and B, due to their size could have a great variety of planets in stable orbits, although none have been detected thus far.

wstevenbrown
2005-Jul-19, 03:48 PM
Gourdhead:

Your point about the complexity of star formation is well taken, which is why most population synthesis models take as their starting point a finished cluster, at some specified average density (stars per unit volume), Initial Mass Function (range and frequency of masses) and the assumption of virial status (a thermodynamically balanced range of stellar velocities, dynamically stable). Both the IMF and the virial assumption are still subject to challenge and debate, so the results of any particular model are subject to variation over a binary order of magnitude. A few folks make stronger claims than that, but their standards of proof are... relaxed.

WRT Alpha Centauri, Saturn-mass planets have been ruled out closer than 5 AU for A and B, and something like 20 AU for C, based on the absence of reflex-motion Doppler signatures and proper motion stability. For smaller planets, tho, the possibilities are intriguing. We could find:

1) Planets orbiting A
2) Planets orbiting B
3) Planets orbiting A-B
4) Planets orbiting C
5) Planets orbiting A-B-C

We are very unlikely to detect that last sort unless they are fairly massive or hot, or unless we get very lucky with an occultation.

It&#39;d sure be nice to have neighbors&#33; S

Jakenorrish
2005-Jul-20, 03:23 PM
I read about this earlier and should imagine that as the planet is close enough to its parent star to orbit it within 3 days and that roughly at the distance of our Sun to Saturn there are another 2 stars, you&#39;d need factor 20,000,000,000 sun block to visit there and see a wonderful sunset&#33; B) B) B)

aeolus
2005-Jul-20, 03:44 PM
And probably a heavy duty air conditioner...

Duane
2005-Jul-20, 07:02 PM
Interesting discussion all&#33;

There are many different scenerios for how planetary systems can end up in the configurations they are seen in, not just migration or capture. Having said that, gravitational interaction between bodies is a significant consideration in all cases.

It will also depend on the type of location the star formed in. If the star resulted from the collapse of a Bok globual, there might be much less perturbation between the constituants of the system than if the star formed in a very large cloud, such as Orion.

Furthermore, nearby supernova explosions can also begin the process which leads to interaction between planets, as can the close pass of another star system. Certainly our own system shows evidence of both of these events happening.

I tend to agree with JohnL, in that I would be very surprised to discover that planets did not begin forming in the planetary disk of a proto-star before it ignited/ Having said that, there is recent evidence suggesting that water molecules that are melted and then refreeze after the ignition of the newly born star might be the catalyst that starts the accretion process.

Lets not forget that there must be many free-roaming planets of all sizes out there that were ejected from their home systems. I would think that in a place as crowded as a stellar nursery, interactions between these free-roamers and newly developed or developing systems must be fairly common, as these things go.

Planetwatcher
2005-Jul-24, 07:41 AM
I have merged the string Planet found in Triple Star System with this one.
This string was started first, had the most postings, and had the most recent posting, so I brought the other one to this one.

Also since John L. was the one to break the story in the UT forums, I believe he deserves the credit for the find.

May the combined topic endure long and well.

Nereid
2005-Jul-27, 09:35 PM
Overheard in the corridors of the Astronomy Department of the University of Triton:
"Waddyathink of these recent press stories about triple planet systems and so on?"
"Bah, humbug&#33; Call me an old fuddy-duddy, but all these breathless press releases and sound bites from astronomers who should *****-well know better"
"Oh? But Herr Doktor Professor [name deleted, to protect the innocent - hah&#33;], the observations are good ones, done with all due attention to the systematic errors and confounding effects so well discussed in the literature&#33;"
"It&#39;s not the ***** observations&#33; Of course that young wippersnapper - what&#39;s his name? - knows the difference between a [indistinct - Dobson? Nasmyth?] and a [indistinct - reference to an algorithm in the data processing pipeline?]&#33; It&#39;s the conclusions that those ignoramuses in the marketing department - where the only degrees anyone has are for singing and dancing [Herr Doktor Professor&#39;s shorthand for &#39;marketing&#39;] - make up when they write the release&#33; I mean, hasn&#39;t anyone of them studied astronomy? Don&#39;t they know it takes at least 30 years of hard work to nail down just the broad ranges of the phenomena, let alone the details?"

{end of overheard conversation}

buzzlightbeer
2005-Aug-16, 08:04 PM
dis (http://www.sciencenews.org/articles/20050813/mathtrek.asp) be a story about the orbit and math behind a planet within a triple star system. neato&#33;