Red dwarfs and brown dwarfs

[danielj]

I think there is some confusion about brown dwarfs and red dwarfs.Brown dwarfs are quasi stars,but red dwarfs are really stars with very low mass.So,some textures that are being released are not clearly if it is related to brown dwarfs or red dwars.Actually,a L or Tdwarf is a red or brown dwarf?
Only the brown dwarfs have atmospheres similar to gas giants.
So,I think the textures being released are only from brown dwarfs and there is no texture of red dwarf.What do you think?

[julesstoop]

Red dwarfs now use the standard M-star texture. Do you have reason to believe it is inadequate?

[danielj]

The problem,I think,is that red dwarfs and red giants or supergiants are very different,in terms of composition,starspots and so on.(look to H-R diagram and you??ll se they are in very different positions).Actually,what is exactly a red dwarf?
So,L and Tdwarfs are related to brown dwarfs?

Red dwarfs now use the standard M-star texture. Do you have reason to believe it is inadequate?

[Malenfant]

Personally I hate using 'dwarf' for stars, it's not very accurate. It implies that the object is abnormally small, which isn't the case.

A "red dwarf" is a low mass main sequence (size V) star, between about 0.08 and 0.3 solar masses. It's massive enough to be fusing hydrogen in its interior. It's also relatively small in radius (about 0.1 to 0.3 of the sun''s radius, or between about 70,000 km to 210,000 km in radius - still usually larger than a jovian planet), and luminosity is between 0.00005 Sols and 0.01 Sols. Their lifespan is incredibly long - they'll last for trillions of years, much longer than the current age of the universe. And they're also the most common type of star in the universe, making up about 70% of the stars that exist.

A "brown dwarf" on the other hand is an object that is not massive enough to sustain nuclear fusion in its interior. They're less massive than "red dwarfs", ranging from 13 to 70 jupiter masses (or 0.013 to 0.07 solar masses). The more massive ones can actually fuse deuterium (hydrogen with a proton and a neutron in its nucleus) in their cores for a while, but this shuts down after the first few hundred million years of their lives. Where it gets confusing is that during this initial deuterium fusion stage they look pretty much the same as a small M V star and would actually be classified as such. But after that, they cool off over the next few billion years and go from type M to L to T. As it does so it goes from being red to magenta as more of its radiation shifts into the IR, and clouds and bands start to form as silicon and iron start to condense in the atmosphere, and then eventually it cools enough that methane and water clouds start to form. An old enough brown dwarf that has cooled down completely would just look like a large, very massive jovian planet.


It's entirely possible that the M-star texture - or indeed any star textures - should not apply across the whole range of sizes. We know for example that "red dwarfs" have lots of flares and starspots. Red supergiants also might have them, but they may not necessarily look the same. Though to be honest, it's all a bit of a moot point since I think you'd be blinded by the light even if you looked at a red dwarf to try to see its surface...

[WildMoon]

I think it would be awesome for there to be many different star textures. I might make some, though I have one question: If I give a star a different texture, would it still have the same shining effect?

[selden]

If I give a star a different texture, would it still have the same shining effect?

Yes.

[Malenfant]

I think it would be awesome for there to be many different star textures. I might make some, though I have one question: If I give a star a different texture, would it still have the same shining effect?

I think that's one of the major flaws with Celestia - it doesn't render stars properly. Admittedly you can't render something realistically because the monitor can only output a limited brightness, but I think all these stars will glare significantly - you certainly would never see the surface.

I think stars should really look more like this (ignore everything else):


OK, the lens flare is extreme in this screenshot, but the glare itself captures (a) the colour of the star and (b) the fact that it's really really bright. I suspect that even red dwarfs are probably going to be too bright to look at directly.

But right now, you can look at the sun and all you'd see is a dim, unimpressive yellow ball.

[WildMoon]

Try going to a star and zooming in close to it then stare at it awhile. Don't you think it is kinda bright?

[Malenfant]

Try going to a star and zooming in close to it then stare at it awhile. Don't you think it is kinda bright?

It's not so much a problem if you're right up up close to the star such that it fills the screen - then all the screen is white and you can't really get much brighter than that on a monitor. But when you're further away and can see the disk it's really nowhere near as bright as it should be.

[WildMoon]

Yeah, true, but if it was that bright you'd be blinded and that wouldn't be fun, would it?

[Malenfant]

Yeah, true, but if it was that bright you'd be blinded and that wouldn't be fun, would it?

That screenshot above isn't blinding is it?

It's impossible to be "blinded" by light from a computer monitor. But it is possible to give the illusion of being blinded on one.

[WildMoon]

Ok now I see! Thanks.

[Tech Sgt. Chen]

One of the problems I can never seem to overcome when making star textures is reconciling detail and luminosity. Adding detailed surfaces seems somewhat unrealistic since the photos that expose the detailing are taken with various filters. They're too bright to look at with the naked eye and from the distances attainable (without becoming a slice of bacon) to view them, the details are drowned in bright light.
Additionally, in order to make convection cells on a scale commensurate with their actual size (for me anyway), the texture would have to be of a rediculously large size. Even on my G star textures, the convection cells are too large but, large enough to seem realistic at certain range lengths.
I always end up having to compromise somewhere! I continually experiment with textures trying to find the right blend of detail, transparency and color. Color can be extremely tricky due to the blackbody effect. You create a texture that seems to be just the right shade of yellow, blue or red only to find that it changes drastically when applied to an emissive body.
None of my textures ever seem to turn out the way I want them to but, I seem to always end up with one that's "just good enough" to use in my Celestia program.

[Planet X]

Even though I'm not nearly an expert on stars, I do think each of the star classes should get it's own default texture for Celestia. I would especially like to see different textures for L and T dwarfs. The current default brown dwarf texture currently in Celestia is adequite for the L dwarfs. The T dwarfs need a dark magenta shaded texture, with a gasgiant like banded appearence. Also, these non-fusing T dwarfs should not have extensive flares/halos like other star classes have.

Also, Tech Sgt. Chen, I like your new L brown dwarf texture. I'm currently using it on an L brown dwarf star I have orbiting Betelgeuse. Later!

J P