Brown Dwarfs... what's with them?

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Brown Dwarfs... what's with them?

Post by NuclearVacuum on 23rd December 2008, 6:51 pm

I already know what a brown dwarf is, but I just don't get them. Why are we mentioning them on Extrasolar Visions? What is it with them that makes them just as interesting as extrasolar planets? Are they interesting because they can harbor moons (maybe Earth-like moons)? I am very puzzled at this, and I am open to anything, so can you please help me out? Sad

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Re: Brown Dwarfs... what's with them?

Post by marasama on 23rd December 2008, 8:04 pm

Brown Dwarf have atmopheres like Jupiters.

Also, since there is really no definate definition of what is a planet, Brown Dwarfs or even Brown Dwarfs at the 12-15Mj range can still be a planet.

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Re: Brown Dwarfs... what's with them?

Post by Sirius_Alpha on 23rd December 2008, 8:25 pm

Indeed, brown dwarfs are substellar, just like planets. They're similar in many respects. And indeed, Earth-like moons are pretty neat, and probably more likely then what would be found around gas planets. Furthermore, like Marasama wrote, there's no clear separation between brown dwarf and planet, though it's usually assumed to be the deuterium fusion mass. Even this may be difficult to use. Is an object a brown dwarf if it's fused even only a single deuterium atom?

Brown dwarfs and gas planet orbits are almost statistically indistinct (except for the existence of the "brown dwarf desert" and the lack of short-period brown dwarfs). Furthermore, there was hints that a star whose name I don't remember (Edasich? would you happen to remember?) that may have two brown dwarfs in a 2:1 resonance.

If I'm not mistaken, there's some uncertainty if brown dwarfs and planets form in separate processes.

Also, take HW Vir. Like Lazarus pointed out, do we call this system a planet + brown dwarf system? Or planet + superplanet?

etc...
etc...

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Re: Brown Dwarfs... what's with them?

Post by NuclearVacuum on 25th December 2008, 12:51 pm

Hm... I never really thought of them as anything besides dim stars. What is the difference between a planet-like brown dwarf and a star-like brown dwarf?



Now that I am getting interested in them, I decided to make a new texture for HD 202206 b (the brown dwarf that most intrigues me). Here is my take on one, what do you think?

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Re: Brown Dwarfs... what's with them?

Post by Sirius_Alpha on 25th December 2008, 2:06 pm

NuclearVacuum wrote:What is the difference between a planet-like brown dwarf and a star-like brown dwarf?
Good question.

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Re: Brown Dwarfs... what's with them?

Post by Edasich on 25th December 2008, 4:38 pm

Sirius_Alpha wrote:
NuclearVacuum wrote:What is the difference between a planet-like brown dwarf and a star-like brown dwarf?
Good question.

Neither scientist have given a really convincing answer so far. alien

However HD 202206 b is relatively "low-mass" and thus could turn out as a super-planet. A massive Jovian.
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Re: Brown Dwarfs... what's with them?

Post by marasama on 26th December 2008, 8:44 pm

Other questions.

Planet -> accreted planetary nebula material -> becomes 13MJ+ = super planet or brown dwarf
Pulsar + Brown Dwarf binary -> Pulsar accreted from BD -> BD is below 13MJ = super planet or brown dwarf

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Re: Brown Dwarfs... what's with them?

Post by Sirius_Alpha on 27th December 2008, 5:12 pm

marasama wrote:Other questions.

Planet -> accreted planetary nebula material -> becomes 13MJ+ = super planet or brown dwarf
Pulsar + Brown Dwarf binary -> Pulsar accreted from BD -> BD is below 13MJ = super planet or brown dwarf

The first one, I would guess would be considered a planet due to the way it formed.
The second one will probably be a star, judging by the SWIFT J1756.9-2508 system (pulsar + 7 M_j white dwarf).

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Re: Brown Dwarfs... what's with them?

Post by Edasich on 27th December 2008, 6:01 pm

I was also thinking about this curious situation *I hope it's not off-topic. If it is, feel free to redirect elsewhere* :

I take a brown dwarf like 15 Sagittae b, a 65 Mj object at 14 AUs (stellar primary is almost a Solar twin, thus habitable zone is just located nearly 1 AU). Assuming inner (undetected so far) planets are barren dwarf jovians (due to orbital placement or eccentricity), the brown dwarf has half-an-Earth-mass moon [because brown dwarfs may likely host such massive satellite]. The satellite is located within 0.005 AUs, in brown dwarf's water zone.
The questions are:

- Is the brown dwarf-satellite system an independent planetary system (15 Sagittae Ba-Bb) or just a "planet"-moon system around a stellar primary?

- Would the moon be habitable nowithstanding the wide orbital zone? Would it be an "Earth-twin" with a dimmer Sun?


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Re: Brown Dwarfs... what's with them?

Post by Sirius_Alpha on 27th December 2008, 7:24 pm

Edasich wrote:- Is the brown dwarf-satellite system an independent planetary system
(15 Sagittae Ba-Bb) or just a "planet"-moon system around a stellar
primary?

Ouch. That's a good one. At first, I want to say the brown dwarf and its satellite are a planetary system... but then again, if 15 Sge B was 20 M_j instead of 65 M_j, then I would probably consider it a planet / moon system.

That one's got me stumped.

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Re: Brown Dwarfs... what's with them?

Post by Lazarus on 3rd January 2009, 1:36 pm

NuclearVacuum wrote:Now that I am getting interested in them, I decided to make a new texture for HD 202206 b (the brown dwarf that most intrigues me). Here is my take on one, what do you think?
Using the parameters given at EPE for this system, the age of the HD 202206 system is 2.04 Gyr. From interpolating the models for a 0.02 solar mass brown dwarf given in this paper, I obtain a temperature of ~690 K from internal heating for HD 202206 b. This does of course assume that the object is not significantly more massive than the lower limit.

Again using the EPE parameters, the temperature from solar heating is roughly 320 K (using the time-averaged flux of solar energy).

HD 202206 b would thus have a temperature of roughly 700 K, so any visible glow would be extremely faint (much less than the lighting of the dayside by solar radiation). If the Sudarsky system applies, it would be a class III object.
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Re: Brown Dwarfs... what's with them?

Post by Darkness nova on 6th January 2009, 2:00 am

Sirius_Alpha wrote:
Edasich wrote:- Is the brown dwarf-satellite system an independent planetary system
(15 Sagittae Ba-Bb) or just a "planet"-moon system around a stellar
primary?

Ouch. That's a good one. At first, I want to say the brown dwarf and its satellite are a planetary system... but then again, if 15 Sge B was 20 M_j instead of 65 M_j, then I would probably consider it a planet / moon system.

That one's got me stumped.
It's a sub planetary system.

Anywho I think somone ((maybe us maybe others)) should CLEARLY work out whats what why where and so and so forth so that we may avoid this confusion in the future.

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Re: Brown Dwarfs... what's with them?

Post by Sirius_Alpha on 6th January 2009, 7:50 pm

Another thing to consider: "Does it mater?"

I think it seems rather apparent that the Universe has made no attempt to neatly sort out objects into two distinct groups, planets and brown dwarfs. It seems that there's a continuum, with either hazy or no boundaries between the two.

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Re: Brown Dwarfs... what's with them?

Post by Darkness nova on 8th January 2009, 5:10 am

Hmmm.

Well then why call then brown dwarves at all......clearly somone had a good reason to separate jovains and brown dwarves int he first place no?

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Re: Brown Dwarfs... what's with them?

Post by Lazarus on 8th January 2009, 7:13 am

If we use the formation distinction between brown dwarfs and planets then there is going to be a difference between the formation of objects around a brown dwarf and around a superplanet, because in the former case the planets form in an independent disc, whereas in the latter case the circumplanetary disc interacts with the circumstellar one.

In fact it turns out that while the solar system has most of its angular momentum in the planetary orbits, for the satellite systems of the giant planets the dominant contribution to the angular momentum is the planet's rotation.
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Re: Brown Dwarfs... what's with them?

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