Celestia Forums

Well,
Since I couldn't recover my Blue Supergiant texture from CD, I had to recreate it from scratch. I actually like it better than the old one, much more detail! Unfortunately, I lost my Wolf-Rayet texture as well and have to recreate it also. Darn, that one took a real long time to create!
Anyway, here's the progress so far on the new Supergiant. I'm not sure I like this sunspot though. No matter how many times I tweak it, I just can't get it's color to conform to the star's.


Here's a closeup of the stellar spot including some granular detail:


See what I mean about the color? I may just end up using a different sunspot.

Is there any particular reason why the sunspot is so darn huge relative to the star? (I mean if that's a supergiant then it looks like the spot itself is several times larger than the Sun!). I've never heard of any blue supergiants that have such a big sunspot (it'd show up as a variation in their luminosity as the star rotates)

As there is definitely a hotspot shown in the Hubble photo of Betelgeuse that is many times larger than our sun, couldn't there be a large cool spot as well?

I think you might have this the wrong way round, actually; I am obviously not an astronomer, like some people here are; but it seems likely to me that red giants like Betelgeuse will have huge spots and very few convection cells- see this APOD for a possible model
http://antwrp.gsfc.nasa.gov/apod/ap001222.html

(on the other hand, this paper describes an unsuccessful search for these giant convection cells)
http://origins.colorado.edu/cs12/procee ... grayxx.pdf

Perhaps blue stars will have very very small convection cells compared to the size of the star, particularly as the convective layer on a blue star is smaller compared to the diameter - in fact according to this page convection only occurs in the core
http://www.bramboroson.com/astro/apr3.html
an image from that site
http://www.bramboroson.com/astro/images ... ection.jpg

I might herefore be the case that the surfaces of blue giants have no detail at all comparable to that found on our Sun- it could instead have fierce patches of hotter or cooler surface due to magnetic effects perhaps (I'm guessing here) or rotation effects if it is a fast spinner like Dschubba or Regulus.

Sorry; I'm rambling; what we need is a proper' stronomer I think.

Tech Sgt. Chen wrote:Well,
Since I couldn't recover my Blue Supergiant texture from CD, I had to recreate it from scratch. I actually like it better than the old one, much more detail! Unfortunately, I lost my Wolf-Rayet texture as well and have to recreate it also. Darn, that one took a real long time to create!
Anyway, here's the progress so far on the new Supergiant. I'm not sure I like this sunspot though. No matter how many times I tweak it, I just can't get it's color to conform to the star's.


Here's a closeup of the stellar spot including some granular detail:


See what I mean about the color? I may just end up using a different sunspot.

If you ask me, that sunspot appears waaaay too big for a star like that, IMO.

From all the research I've done, it appears that the general consensus is that Supergiant stars possess equally giant convection cells and stellar spots. Here are some models I found during that research.


Here is a model that represents the convection cells for a Red Supergiant.

Of course, since no close-up pictures of these stars are possible, these models are based on actual astronomical theory however, this is how scientists expect them to appear.

I'm no astrophysicist... but a convection cell larger than Jupiter's orbit ? Wouldn't that break up as it rises through the layers of the star. You don't see huge bubbles rising to surface in water - water turbulence breaks it up into smaller bubbles. Wouldn't a convection cell in a star undergo the same sort of disintegration? Isn't that why we get a group of sunspots?

I could be wrong. I never really looked into it. I just assumed we get groups of sunspots because a single "spot" was distrubed as it rose to the surface.

Anyway... I like it... reminds me of a giant blue eye. Are there any constellations with blue supergiants representing the figure's eye? No? Too bad.

It's been a while since I was doing any physics, so I had a look at the Wikipedia. It looks like a Red supergiant and a blue supergiant are completely different beasts. The convection patterns of one probably have very little to do with the other.
By blue supergiant I assume you mean a type O Ia... (like zeta Puppis?), with temperatures in excess of 30,000K.

Red giants, supergiants or red stars of *any* mass have temperatures below 3,500K.

Big difference.

Red supergiants or giants are also much less dense - they are typically stars at the end of their life that have left the main sequence by puffing up in response to running low on primary nuclear fuel.

So all this data and theory on the physics Red supergiants' convection physics demonstrates nothing *prima face* about that of Blue supergiants. I'm not saying they couldn't turn out to be similar, just that you can't simply infer the physics of one from the other. Just because they both happen to be referred to as 'supergiant' in English doesn't make them part of the same natural kind.

Sources:
http://en.wikipedia.org/wiki/H-R_diagram
and links leading therefrom.

Anyway, for the record, I think the big spot looks cool.

Yeah. Red and Blue supergiants are totally different in structure and in 'evolutionary position' during a star's life. It would be wrong to use red SGs to define what Blue SGs should look like.

Try leaving the pattern grey. I think Celestia colourises stars, so the same greyscale texture would adopt the colour of the star. If that's not good enough, take your screenshot and use the colour dropper (to grab the RGB values) on the atmosphere, and colorise the greyscale texture with that.

By the way, we discussed the relation of outer convective zones and starspots before when Tech. Sgt. Chen first produced some star textures. I raised the matter for technical accuracy, but could only write concerning main sequence stars though, being less sure about giant or supergiant stars - apart from red supergiants as I know about Betelgeuse' supersized convection cells.

However, surely there's also the matter of aesthetic merit. I mean several people have produced planets textures with garish colours or something that looks like a crumpled paper texture. I find people tend to accept these, and though I prefer strong realism, I wouldn't want to deflate someone's sense of achievement so I keep quiet. I find people generally like having exciting textures whether they're realistic or not.

Still, that blue supergiant star colourised orangy-yellow would make an excellent texture for a red dwarf like Gliese 876.

Spiff.

I can't help but grin upon reading many of the questions/comments posted in regard to my proposed Supergiant. Most of these questions are the same ones that came to mind when I first learned of the current theories regarding giant stars and starspots. And, yes, most of these questions/theories came to light when researching my last star texture discussion initiated by Spaceman Spiff. There are those of us in the Celestia community who require strict adherence to astronomical standards and those who prefer the aesthetics alone.

As I said before, I am hardly the last authority on astronomy or stellar physics and, I certainly am not in agreement with the current theories regarding giant convection cells and stellar spots. However, these do appear to be the current theories none-the-less, whether I agree with them or not.
The models I presented above were not the only ones I found during my research but, the only ones I saved for reference.
I personally, prefer the traditional theories regarding stellar constants and relative convection cell/spot sizes.
I already had decided to create another standard version of the texture and post both on my website.
I do (highly) appreciate the comments and suggestions that without, I would never have any idea what was preferred.
I certainly would like to hear from someone who is an authority on the subject, to clarify the theories.

ogg wrote:

By blue supergiant I assume you mean a type O Ia... (like zeta Puppis?), with temperatures in excess of 30,000K

So all this data and theory on the physics Red supergiants' convection physics demonstrates nothing *prima face* about that of Blue supergiants. I'm not saying they couldn't turn out to be similar, just that you can't simply infer the physics of one from the other

Yes, that would fit the type though, the color of this paticular texture was more the B0 (I) type.
Consequently, the first B/W model posted is of a Blue star with a giant Polar spot. Most of the consensus seems to indicate that convection cell size rises, commensurate with star size. The larger the star, the larger the convection cell size. Not too surprising when you realize that Earth can usually fit (several, easily) into a sunspot on Sol (a yellow, dwarf!).

Isn't sunspot size (and presence) related more to the presence and strength of a stellar magnetic field than to convection cell size though?

Tech Sgt. Chen wrote:I Most of the consensus seems to indicate that convection cell size rises, commensurate with star size. The larger the star, the larger the convection cell size. Not too surprising when you realize that Earth can usually fit (several, easily) into a sunspot on Sol (a yellow, dwarf!).

The size of the star is not the only consideration; the depth of the convective layer is muuch more important.

If I understand the theory correctly (bearing in mind of course I am only reading other peoples' research, not doing the maths myself) cooler stars have very thick convective layers, and so have large cells and presumably large sunspots (starspots); your texture would be good for a red dwarf or even perhaps a red giant.
Hotter stars have larger actively fusing cores and the convecting layer gets thinner, so K-type stars have smaller cells than M - type stars,

F-type have smaller cells than G-type and so on; when you get to class O supergiants or LBVs there probably is no surface convective layer at all, so no recognisable cells or sunspots.

But there might be other features we don't suspect yet, so they might not be completely blank...

From what I have read so far and after doing a bit of research...

Red supergiants have radiative cores (past the H fusion core) then convective shells (so we see granulation like the boiling bubbles on water) and Blue supergiants have convective cores (past the C fusion core) and very large radiative shells, hence very little suface features. However, cooler spots would still look darker than their surrounding regions and probably granulated depending on how cool they could get, but probably nothing like a sunspot... which is, as most of you know, just a few thousand degrees cooler than the surrounding granulated area, hence darker. However, I still like your texture Chen...

Sorry Guys,
I've have been reading your replies and have taken note. I'm trying to keep up with the pace of the forum while working 12 hour night shifts!
Trying to read and reply at 6:00AM EST (US) after pulling an All-Nighter just isn't cutting it!
A couple of times I've tried to read/answer replies but, have been too tired to understand what I'm reading or who I'm replying to. I'm obviously going to have to do more research (it certainly wouldn't be the first time my wires have crossed). Now, I'm beginning to find (what appears to be) good research papers on convection properties of hotter, massive stars except, I have to download and install a postscript viewer (.ps file extension) in order to read them. If need be, I should have no problem decoloring/recoloring the texture to remediate the spectral class (i.e., Blue to Red Giant).
Thanks for the input and insight. I'll be back shortly...
Gentlemen, I moving this discussion (for now) to the Physics And Astronomy section under the title, "Stellar Convection Properties".
Please meet me there as I need further discussion, input and references.
Post Script: I just woke up (literally).[/b]

Well,
I'm certainly glad that all of you voiced your opinions on this matter because it helped to point me in the direction of the specific fields of research needed.
I've come to the conclusion that there simply is not enough data (at least, none that I can find) to support my original concept for the Blue Supergiant.
On the contrary, despite scant references to the existence of giant convection cells in A-type stars, their structure is still quite different from Blue Giants and Supergiants. Additionally, despite a consensus to suggest the possiblities of giant convection cells in cooler, red, supergiants; there is still a wide discrepancy in agreement concerning their properties and proportions. Though my research suggested (to me) that there probably is a defined surface structure to Blue Supergiants, the only solid information I could find indicated the presence of a convective layer that lies beneath the photosphere.
In regard to giant stellar spots, the consensus appears to suggest their existance on cooler stars and discrepancies appeared to exist on their exact size. Additionally, though stellar spots can be influenced by rotational speeds AND, there is proof to suggest high speed rotation in hot, blue stars; there appeared to be inconsistencies regarding the stellar rotation speed /To /magnetic field influence ratio.
For Example: I found reference suggesting that fast rotation speeds account for stellar spots in hot, blue, stars but, also reference indicating that most supergaints rotate slowly and slower rotation accounts for higher electromagnetic influence.
I have to agree with ogg, eburacum45 and all of you that, there simply isn't enough data to extrapolate the conclusions I suggested in my texture.
The good news is, I can easily turn the blue supergiant into a red one.
THANKS for all the input and references!!!