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  #361 (permalink)  
Old 16-November-2008, 11:00 PM
slang slang is offline
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It's so amazing that only fifteen years ago we didn't have one confirmed planet around a star. Now there are so many that it's hard to keep up with all the discoveries.
And I tell people that, when the subject of the Fomalhaut discovery comes up, and they just glaze over. The number of people that are actually fascinated by these discoveries seems to be somewhat low.. or interested, even.
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  #362 (permalink)  
Old 16-November-2008, 11:55 PM
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Originally Posted by timb View Post
That's wrong. The IAU working definition states objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are "planets". Brown dwarfs are not stars, therefore no object orbiting a brown dwarf is a planet. If the brown dwarf orbits a star I suppose you could argue that its satellites also orbit the star, but that would be a special case.
Don't know how you came to this conclusion.

But let me try and work this out:

1. Brown dwarves = greater than 13 Jupiter masses by definition, and burn deuterium - hence, Brown dwarves are stars, not planets
2. An object orbiting a brown dwarf which is less than 13 Jupiter masses and does not burn deuterium is a planet.

An object fitting #3's description has indeed been discovered orbiting an object matching #1's description, so yes:

At least one planet has indeed been discovered orbiting a brown dwarf, which * is * a star according to the IAU definition. It defines an object 13 Jupiter masses or more, deuterium burning, as fitting the description of a star - as that is exactly what a brown dwarf is: between 13 mJ and Red Dwarf in mass, and burning deuterium but not hydrogen and helium.

They are not main-sequence stars but they are indeed stars, IMO and according to the IAU definition you laid out.
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  #363 (permalink)  
Old 17-November-2008, 12:43 AM
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Originally Posted by Drunk Vegan View Post
Don't know how you came to this conclusion.

But let me try and work this out:

1. Brown dwarves = greater than 13 Jupiter masses by definition, and burn deuterium - hence, Brown dwarves are stars, not planets
2. An object orbiting a brown dwarf which is less than 13 Jupiter masses and does not burn deuterium is a planet.
Do you have a reference for that claim? It contradicts the IAU working definition.
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  #364 (permalink)  
Old 17-November-2008, 10:56 AM
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Do you have a reference for that claim? It contradicts the IAU working definition.
Here's one. It's an Internet encyclopedia, but I've seen the same conclusions in many other places on the Internet.

http://www.daviddarling.info/encyclo...rowndwarf.html

A brown dwarf masses between 13 Jupiter masses and 84 Jupiter masses.

Here's a few links on a few brown dwarfs that fit within that mass range.

Kelu 1 is no more than 75 Jupiter masses

http://www.eso.org/public/outreach/p.../pr-07-97.html

Gliese 229 b is between 25 and 65 Jupiter masses

http://www.solstation.com/stars/gl229.htm

And here's a link on an abstract suggesting that the deuterium burning limit may be used to distinguish brown dwarfs from stars.

http://gpd.jhuapl.edu/abstracts/abst...d_abstract.pdf
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Old 17-November-2008, 11:14 AM
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Originally Posted by timb View Post
The IAU working definition states objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are "planets". Brown dwarfs are not stars, therefore no object orbiting a brown dwarf is a planet.
I'm afraid you're reading it incorrectly - it is not an exhaustive definition for extrasolar planets. It says that planetary-mass objects orbiting stars are planets, but does not say that only such objects are planets.

As the WGESP position statement says: "Rather than try to construct a detailed definition of a planet which is designed to cover all future possibilities, the WGESP has agreed to restrict itself to developing a working definition applicable to the cases where there already are claimed detections, e.g., the radial velocity surveys of companions to (mostly) solar-type stars, and the imaging surveys for free-floating objects in young star clusters. As new claims are made in the future, the WGESP will weigh their individual merits and circumstances, and will try to fit the new objects into the WGESP definition of a 'planet', revising this definition as necessary."

I assume frank discussion are now taking place!
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  #366 (permalink)  
Old 17-November-2008, 01:31 PM
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And I tell people that, when the subject of the Fomalhaut discovery comes up, and they just glaze over. The number of people that are actually fascinated by these discoveries seems to be somewhat low.. or interested, even.
This seems to be the case. I believe there is much more opportunity here to make this a big story, but it's not happening. Perhaps this is another frog in the pot analogy. Over the last decade there have been over 300 discoveries of exoplanets. Fomalhaut b is not the first to be imaged, either, and when it was announced, along came the announcment of three planets imaged, as we know. All of these points has kept the frog leaping up and getting everyone's attention.

I suspect something extra has to get the frog out of the pot. In my amateur opinion, I believe Fomalhaut b should be lifted to the proverbial pedestal since it is the first visible exoplanet imaged. This distinction isn't to minimalize the great efforts by others in imaging and infering the others, but I think Fomalhaut b should be given exceptional recognition for the good it should do for astronomy as a whole.

However, it wouldn't shock me if I am missing some points here. Y'all's views are important. I would like to be a part of something special in recognizing this discovery, even if it's just sending flowers or gift certificates to the Fb team.

If this idea has merit in your opinion, we might want to do a thread on what we as supporters can do to help in recognizing such an event.
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  #367 (permalink)  
Old 17-November-2008, 03:11 PM
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And I tell people that, when the subject of the Fomalhaut discovery comes up, and they just glaze over. The number of people that are actually fascinated by these discoveries seems to be somewhat low.. or interested, even.
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This seems to be the case. I believe there is much more opportunity here to make this a big story, but it's not happening.
<Cynic mode on>
I think you may be overestimating the general population. Remember Solid Bismuth's thread? Sadly, most people don't care, and probably won't care until the day a Vulcan drops in to dinner.
<Cynic mode off>

I like your idea of doing something to recognise this achievement George.
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  #368 (permalink)  
Old 17-November-2008, 08:57 PM
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Hey, please keep "what is a planet" stuff out of this thread, this is about extrasolar planet discoveries.

PS. It's "dwarfs", not "dwarves". The latter can be found in Tolkien's books.
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  #369 (permalink)  
Old 17-November-2008, 10:32 PM
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Hey, please keep "what is a planet" stuff out of this thread, this is about extrasolar planet discoveries.
What does that mean?
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  #370 (permalink)  
Old 17-November-2008, 10:34 PM
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Here's one. It's an Internet encyclopedia, but I've seen the same conclusions in many other places on the Internet.

http://www.daviddarling.info/encyclo...rowndwarf.html

A brown dwarf masses between 13 Jupiter masses and 84 Jupiter masses.

Here's a few links on a few brown dwarfs that fit within that mass range.

Kelu 1 is no more than 75 Jupiter masses

http://www.eso.org/public/outreach/p.../pr-07-97.html

Gliese 229 b is between 25 and 65 Jupiter masses

http://www.solstation.com/stars/gl229.htm

And here's a link on an abstract suggesting that the deuterium burning limit may be used to distinguish brown dwarfs from stars.

http://gpd.jhuapl.edu/abstracts/abst...d_abstract.pdf
I don't see the relevance of anything you have posted above to the question of whether objects orbiting brown dwarves are planets.
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  #371 (permalink)  
Old 18-November-2008, 12:15 AM
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<Cynic mode on>
I think you may be overestimating the general population. Remember Solid Bismuth's thread? Sadly, most people don't care, and probably won't care until the day a Vulcan drops in to dinner.
<Cynic mode off>
Agreed, and their apothy is apparent. But, I am not talking of them so much as us -- the ones that really respect what astronomers accomplish. What can we do to express honor?

But, first I want to know if I'm off base on my thinking. From a landmark case perspective, Fomalhaut b may be the most interesting exoplanet to date simply because of the visible imaging (no so much the planet itself).

Either I'm right or wrong, what say thee?

[If I'm right, we can start a new thread. If nothing else, we can send a copy of a congrats thread of all our comments, but I'd love to see something more grand and commencerate to their milestone accomplishment. ]
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  #372 (permalink)  
Old 18-November-2008, 02:35 PM
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I don't see the relevance of anything you have posted above to the question of whether objects orbiting brown dwarves are planets.
Sorry, I misunderstood. I thought you were saying that the definition said that anything over 13 Jupiter masses and burning deuterium was classified, by the definition as being a star. In my own defence, I was suffering from lack of sleep at the time I posted all those links.

And, that's the last thing I'll post about the definition of stars, since we were politely asked to knock if off.

I still disagree, though, with the definition of planets. I think it's more relevant the way an object was formed than what it orbits around. It's silly that you might have two gas giants, formed in exactly the same way, with almost exactly the same composition, with one being classed as a planet (because it orbits, say, a red dwarf) and the other not (because it orbits a brown dwarf). Would Earth suddenly stop being a planet if it were transported to an orbit around a brown dwarf? Would an object around a brown dwarf suddenly become a planet if it were captured a star?
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  #373 (permalink)  
Old 18-November-2008, 03:15 PM
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But, first I want to know if I'm off base on my thinking. From a landmark case perspective, Fomalhaut b may be the most interesting exoplanet to date simply because of the visible imaging (no so much the planet itself).

Either I'm right or wrong, what say thee?
You're not wrong George.
I am a little perplexed though. Is there a reason why everyone is more excited about Fomalhaut b than the three planets around HR8799? Because I thought those images were fantastic. Is it the infrared/visible divide? Becuase that seems like wavelength elitism to me.
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  #374 (permalink)  
Old 18-November-2008, 03:25 PM
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You're not wrong George.
I am a little perplexed though. Is there a reason why everyone is more excited about Fomalhaut b than the three planets around HR8799? Because I thought those images were fantastic. Is it the infrared/visible divide? Becuase that seems like wavelength elitism to me.
My guess is partly due to the fame of the star in question and partly because of the distance. Fomalhaut is much better known, and it has a proper name and not a bunch of letters and numbers. I imagine a lot of people hadn't even heard of HR 8799 before this news broke and it has a designation virtually identical to a lot of other stars out there. Fomalhaut is also much closer, being only 25 light years away, as opposed to Hr 8799's 129 light years.

It's sort of like suddenly finding out something cool about two people, one an acquaintance, someone you've been sort of aware of for some time, who has a unique name, and who lives close by, and one a virtual stranger who lives a fair distance away and who's name is Bob Jones. It's just easier to be interested in the acquaintance.
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  #375 (permalink)  
Old 18-November-2008, 04:34 PM
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Ah. Fair enough.
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  #376 (permalink)  
Old 18-November-2008, 09:16 PM
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Hey, please keep "what is a planet" stuff out of this thread, this is about extrasolar planet discoveries.

PS. It's "dwarfs", not "dwarves". The latter can be found in Tolkien's books.
I'm not sure why you are objecting.

One of the most exciting things about the area of extrasolar planet research is that these objects throw our definitions of planet vs. star vs. brown dwarf into question.

Trying to find the best possible defintion of what each of those things actually is seems entirely relevant to the discussion of interesting extrasolar planet discoveries.
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  #377 (permalink)  
Old 18-November-2008, 09:18 PM
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It probably does boil down to comparing HR8799's to Fomalhaut's exoplanet.

Pros for Fomalhaut b
1) It is the first confirmed directly imaged exoplanet in visible light. [Is it the first direct imaged exoplanet if we go back, since it was imaged in 2004 and I assume even then it was in visible light, right?] This first is unique from the rest and its too late to crank-up the band, I think, for an IR imaged exoplanet.

2) Warmer fuzzies with name familiarity vs. a number designation (as t@nn stated).

2b) "Fomalhaut" is kinda fun to say. [My 3 yr. old niece thought bread pudding made no sense as why make pudding from just bread. Then she said "bread pudding", smiled and said, "That's fun to say!".]

3) The host star is bright and easily visible to the naked eye with mag. of about 1. [HR8799 is not really visible to most naked eyes with its mag. of about 6.]

4) The actual image from Hubble is stunning. Though impressive, the HR8799 image looks like something out of CERN instead of from Keck, at least the few images I've seen.

I still pose the question, repharasing... "Should we wake-up the slumbering cheerleaders and get them to celebrate one of these discoveries, or must we wait till we discover a stargate or something?"
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  #378 (permalink)  
Old 18-November-2008, 10:12 PM