Brown Dwarf Catalogue

[Cham]

Hello guys.

There's a database of Brown Dwarfs at this page :

http://charon.nmsu.edu/~crom/bdwarfs/catindex.html

Is it possible to convert it in some usable file for Celestia ?

[selden]

Cham,

Unfortunately that database does not include any distance information.

[Cham]

Hmmm ! Yep, I noticed this too. Too bad.

I would be glad to have a file with lots of Brown Dwarfs and White Dwarfs in Celestia.

[Bob Hegwood]

Would just like to ask...

Is there a specific star or stars currently provided with Celestia upon
which we can apply Brown Dwarf textures? Or, have there been some
Brown Dwarf stars already included with Celestia? Would just like to be
able to see the effect.

Sorry, don't know if this is a Brain-Dead question or not... Simply have
not seen or heard of Brown Dwarves before.

Thanks, Bob

[selden]

The very last star in Grant's nearstars.dat (included in Celestia v1.4.0pre6) is a brown dwarf.

Code: Select all

"Alula Australis Bb::XI UMa Bb:53 UMa Bb:Gliese 423 Bb"
{
        OrbitBarycenter "Alula Australis B"
        SpectralType "L"  # brown dwarf
        AbsMag 21         # for approximate radius in Celestia

        EllipticalOrbit {
                Period          0.0109 # 3.98dy
                SemiMajorAxis   0.056  # mass ratio 1.05:0.08
                Eccentricity    0
        }
}

[Evil Dr Ganymede]

Last time I tried to explain something to Bob, he didn't follow . So is this any more understandable?

Brown Dwarfs are "failed stars" - objects that have 13-70 jupiter masses... but it's all crammed into an object that is basically the same size as Jupiter. This means that they're actually (a) VERY dense (several tens of times denser than Earth) and their gravitational field at the surface is huge (up to several hundred times that at earth's surface!).

However, they fail as stars because they're not massive enough to fuse hydrogen in their cores as stars do to get their energy - what happens instead is that the pressure in their cores only gets high enough to burn deuterium - a heavy form of hydrogen. But they're not even massive enough to sustain this for long, and the fusion shuts down after the first few hundred millions of their lives. At this stage, they're probably emitting enough red light to glow visibly - in fact, they may just look like red dwarf stars. After that, they just cool off over time - a brown dwarf that is several billion years old would probably look pretty much like an ordinary gas giant, feebly emitting infrared radiation and illuminated only by nearby stars. As they cool, they start to look more and more like gas giants - bands form in their atmospheres as things like silicates and iron condense out to form clouds (yes, they can have clouds made of rock. Kooky, huh?). They also very slowly get smaller over time too, since there's no outward pressure from internal fusion keeping them 'fluffed up" anymore.

Basically, you can think of the size sequence like this:

Terrestrial World (Earth, Venus, Mars)
Small gas giant (0.01 to 0.5 Jupiter masses - Uranus, Neptune)
Large gas giant (0.5 to 2 Jupiter masses - Jupiter, Saturn)
Superjovian (2-12 Jupiter masses - Ups And d)
Brown Dwarf (13-70 Jupiter masses - Gliese 229B)
Red Dwarf star (80-300 Jupiter masses - Proxima Centauri, Barnard's Star)
...and then you go up to bigger stars.

This gives you an idea of what they look like:
http://spider.ipac.caltech.edu/staff/da ... rison.html

[Dollan]

Small gas giant (0.01 to 0.5 Jupiter masses - Uranus, Neptune)

Isn't a Jupiter mass of 0.01 only 3 Earth masses or so?


...John...

[Evil Dr Ganymede]

Well, OK, the bottom end of that is a bit fuzzy . About 8-10 Earth Masses (0.03 Jupiter Masses) would probably be better, that seems to be the upper limit for the Panthalassic worlds described by Leger et al.

[Michael Kilderry]

Isn't there also a category inbetween the Panthalassics and the Small Gas Giants, called Gas Dwarfs. These worlds are like gas giants, but they are smaller and have larger cores compared to the size of the planet then bigger gas giants.

Michael Kilderry

[Dollan]

I haven't heard of this. Any links?

...John...

Isn't there also a category inbetween the Panthalassics and the Small Gas Giants, called Gas Dwarfs. These worlds are like gas giants, but they are smaller and have larger cores compared to the size of the planet then bigger gas giants.

Michael Kilderry

[chaos logged out]

LP 944-20 is in the nearstars.stc file - it's a young brown dwarf, still hot enough to be spectral type M, so I suppose you could add a texture declaration to the file...

[Evil Dr Ganymede]

Isn't there also a category inbetween the Panthalassics and the Small Gas Giants, called Gas Dwarfs. These worlds are like gas giants, but they are smaller and have larger cores compared to the size of the planet then bigger gas giants.

There probably could be, but none have been discovered or described in detail. I'd imagine they'd be rather rare. I was just listing the things that we knew about and it wasn't supposed to be a complete list anyway.

[Bob Hegwood]

Last time I tried to explain something to Bob, he didn't follow .

Thanks for reminding me...

I understood the explanation above just fine. Thanks for taking
pity on me. <hee, hee> Thanks for the explanation too. Was educational.

Take care, Bob

[Bob Hegwood]

The very last star in Grant's nearstars.dat (included in Celestia v1.4.0pre6) is a brown dwarf.

Forever in your debt, Selden...

Thanks again, Bob

[Evil Dr Ganymede]

I understood the explanation above just fine. Thanks for taking pity on me. <hee, hee> Thanks for the explanation too. Was educational.

Yay!

[Michael Kilderry]

I haven't heard of this. Any links?

...John...

Isn't there also a category inbetween the Panthalassics and the Small Gas Giants, called Gas Dwarfs. These worlds are like gas giants, but they are smaller and have larger cores compared to the size of the planet then bigger gas giants.

Michael Kilderry

The original idea of a gas dwarf came from a solar system generating program called Star Gen. It also includes Panthalassic planets, but it calls them "Ocean" worlds. I can't remeber the web site address, but type "StarGen" into the Google search engine and it should come up.

I don't know about Gas Dwarfs being particularly rare, as they are the link between Panthalassics and the Minature Jovians.

Michael Kilderry

[Evil Dr Ganymede]

I don't know about Gas Dwarfs being particularly rare, as they are the link between Panthalassics and the Minature Jovians.

Yes, and how many Panthalassic worlds do we know of (I'll give you a clue - none ). Panthalassics have only been theorised to exist. A Gas Dwarf (I call them "Subgiants" myself) would have to be a massive rocky or icy planet that can retain hydrogen and helium, yet somehow NOT snowball into a fully-fledged jovian (and it can't really do that by spiralling closer to the sun, because if it gets warm enough to lose its hydrogen and helium, then it'll lose all of it).

So I figure they're going to be quite rare in planetary systems, because it would require a very unusual set of circumstances to form them (e.g. protoplanetary nebula being blown off before they can fully become gas giants).

They are certainly theorised to exist as free-floating bodies OUTSIDE planetary systems, as rogue worlds cast out by gravitational interactions (see Stevenson's paper on Interstellar planets for details). But within planetary systems it's very hard to get the right circumstances to form them.

[Dollan]

Yeah, I have several versions of Stargen either bookmarked or downloaded. Great programs, but I discovered that most of them started to repeat results if you ran them enough times. One of them, running off of BASIC I think it was, actually reproduced a system exactly if your original parameters for generation were exactly the same. All the others, though, did not have this flaw.

As for gas dwarfs... I suppose I could see them forming and surviving in a system, but the circumstances needed to keep them in "pristine" shape would require so many coincidences, I doubt that they would be very plentiful at all. I agree with Consty... they might make a great idea for a rogue planet.

There's a question: Can Celestia have a planet unattached to a star?

...John...

[Michael Kilderry]

Maybe one could exist in a close double gas giant system, where the gas dwarf is the smaller giant, and so the bigger one strips away a lot of it's gas through gravity, like some close stellar binaries do.

Michael Kilderry

[selden]

John wondered

Can Celestia have a planet unattached to a star?

V1.4 can!

But it does have to be attached to a Barycenter. Which is invisible, so that's OK.