New Star Textures

[Tech Sgt. Chen]

I've been working on some new star textures for Celestia. These are detailed textures taken from hires images of solar granulation and sunspots. They are 4096X2048 size and the granulation detail show up quite nicely on my monitor. They don't seem to cause too much of a drain on my system and I've experienced no jitters on close-ups at increased circulation speeds.
So far I have a G-Star:


And a B-Star:


I'm experimenting with additional sunspots on the B-Star.

[ajtribick]

Those textures look great, I'm just wondering about whether you can get sunspots on B-class stars: don't they have a different structure near the "surface", which makes their magnetic fields behave differently or something...

[Tech Sgt. Chen]

I'm not aware of any phenomenon that would prevent sunspots on B Class stars. Are far as I know, magnetic fields are what causes these spots. I know that B Class stars burn hotter, hence the blue hue but, mass and the resulting gravitational forces are existent in all stars. I don't believe the mass of a B Class star precludes it from having sunspots but, if anyone out there knows more about it, please chime in since I'm aiming for realism here.

[danielj]

Ver nice,but since is a 4k texture,you should provide close-up views.
Another thing:I would like to know if your G texture is based in rthovald??s texture of the Sun.It is very similar to it.

[quote="Tech Sgt. Chen"]I've been working on some new star textures for Celestia. These are detailed textures taken from hires images of solar granulation and sunspots. They are 4096X2048 size and the granulation detail show up quite nicely on my monitor. They don't seem to cause too much of a drain on my system and I've experienced no jitters on close-ups at increased circulation speeds.

[Spaceman Spiff]

Hi Tech Sgt. Chen,

I'm afraid chaos syndrome has a point. Stars from about F5 through A, B and O or W won't have starspots. In more detail, it's like this (which I learnt in stellar astrophysics):

Sunspots are caused by magnetics field lines getting tangled due to turbulent convection of the plasma in the Sun's outer layer (which extends down below the Sun's surface by about 10% of the Sun's radius).

Stellar modelling shows that this is because the most efficient heat transportation method in this region out of the three possibilities: conduction, convection or radiation, is the second: convection. Otherwise it's by radiation (or rather radiative transfer, conduction not being possible in a plasma) in the inner 90% of the sun.

This changes for lighter and heavier stars. The heavier a star, the thinner this outer convective layer gets, until at F5 type stars it's about gone. Without such convection, there's no turbulence, no magnetic field lines twist up, and no starspots form (though actually, a new layer of convection starts to grow in the core of heavier stars).

For lighter stars, the convective layer extends further down the lighter a star is, until the whole star is fully convective for M-type dwarves. That's why these stars can be so long lived: they can potentially fuse 100% of their hydrogen, not the usual 10% like the Sun.

It's not an obvious result, so many people try and draw F-O stars with starspots. A disappointing result for exciting piccies maybe, but surely compensated by the other overlooked fact that K and M type dwarves have larger starspots, sometimes covering from pole to equator in size. Their flares are quite something to... These have actually been observed by astronomers, so it's not just theoretical prediction.

Spiff.

[eburacum45]

Yes, every star type will look quite different, alyhough I am not sure what B class stars would look like-
I made a texture for Betelgeuse myself, available in the OA add-on;
http://img66.echo.cx/img66/1382/betelgeuse3uh.jpg

this was based on the images from this page
http://www.astro.uu.se/~bf/movie/movie.html
although to be more accurate the whole star needs to be modelled as an irregular mesh (or several)

[Tech Sgt. Chen]

Whew! I had a hard time accessing the forum today. One minute the pages are loading fine, the next minute, I can't reconnect. Ok, here are some close-ups of the solar granulation and NO, I did not copy off of anyone's textures. These were made by me, from scratch, using high resolution solar images. As a matter of fact, Selden provided me texture sample links with which to reference well over a year ago, long before rthovald??s beautiful version of an animated Sol (you may notice my past posts inquiring about star textures). It is probable that rthovold and I used the same methods for transferring and applying the texture. I have accumulated many more texture samples to date. Unfortunately, I had to drop the project and visits to the forum due to an extended, family, medical emergency.
To Spaceman Spiff: Are you referring to Wolf-Rayet, Cepheid Variables or Chemically Peculiar B stars? And, can you provide references to your understanding of The Presence Of Spots On Other Stars.
OK, here are some close-ups to portray the surface granulation. Note that these images had to be deflated for quick loading and may not accurately portray the actual detail. The only drawback to the detailing is a file size, approximate, of 10 MB. Still, it loads quickly on my system:





Post Script: eburacum45 - Yes, I have that same image from the Hubble space telescope. It's labeled as the first detailed image of a star other than our Sun. There was another forum member who provided a fictional texture, quite detailed, for Betelgeuse. I can't remember who it was...Rassilon?...praesepe? I'm not sure but, you may still find a link to the texture in the forum archives. I know I have it somewhere on one of my computers. I've just started making an Mstar texture. If I like the results when I'm finished, I may do my own version of Betelgeuse.

[Spaceman Spiff]

To Spaceman Spiff: Are you referring to Wolf-Rayet, Cepheid Variables or Chemically Peculiar B stars? And, can you provide references to your understanding of The Presence Of Spots On Other Stars.

By W I do mean Wolf-Rayet stars, which have such strong radiation pressure at their surfaces, that they are blowing their surfaces off into space. I think the general principle applies to Cepheids and chemically peculiar B stars too, but I was refering to main sequence stars in general. Giant stars could be different..

Googling for references won't turn much up, you'll have to look up astrophysical text books in a library, but you could have a look at the findings of the AIP (http://www.aip.de/groups/activity/DI/DopplerImaging.html)

Spiff.

[Tech Sgt. Chen]

Wow, talk about a puzzling lack of info on the subject. Though, I am not refuting Spaceman Spiff's assertion that, all stars within their respective spectral classes of "F5 through A, B and O or W won't have starspots", I could find absolutely nothing to substantiate it. And, this involved 12 straight hours of research and Googling! I did however find this:

Why are the Stars in the Pleiades so Blue?
They conclude that these young stars are rapidly rotating, and furthermore, since rapidly rotating stars tend to have many "sunspots" (areas of coolertemperatures on their surfaces) they also have spotty surfaces that make their emitted light fluctuate. They suggest that in fact all are young age. Their result is significant because, of course, our own Sun rotates and has sunspots, and understanding these processes on other stars helps scientists understand the phenomena on our own Sun. Furthermore their conclusion, if supported, means that the astronomers who are trying to measure the ages of other stars must recognize that, at least in stars like these, they must tread with extra caution because of the importance of rotation in modifying the stellar colors.

Ref: http://www2.si.edu/research/spotlight/1_25.htm

Starspots
If the Sun has spots, the natural question to ask is: what about other stars? From a theoretical point of view at least, the answer is clear. Cool stars ?€” those with convective zones ?€” will probably have spots if they rotate fast enough to generate magnetism. Hot stars, on the other hand, lacking convective motion, are expected to be spotless. With very few exceptions, the stars are too distant to allow us to directly test this theory. But despite the great gulfs that separate us from our stellar neighbors, astronomers now know for certain that some of them do indeed harbor dark "starspots," similar to the Sun?€™s. The trick is to look for features that on the Sun ?€” and presumably on other stars as well ?€” hint at magnetic activity. And the obvious place to look is in a star?€™s spectrum.

Ref: http://www.space-art.co.uk/markgarlick/ ... _starspots

A theorist's view of the A-star laboratory
Two topics concerning A-type stars are discussed: starspots associated the strong magnetic fields, and prospects of asteroseismology. Considering starspots on the analogy of sunspots is misleading. It is logically concluded that the level of the photosphere of starspots of magnetic A-stars is higher than the normal photosphere, contrary to the sunspots. As for prospects of asteroseismology, it is demonstrated how well (or poorly) we can probe the internal structure of the distant stars using the limited number of p-mode frequencies. Though the detectable eigenmodes must be limited to be , if the observational error is of the order of , inversion has still some hope.

Ref: http://www.astro.uwo.ca/apn/Archive/ApN_42/AAP/
These are but a few of the many references I've accumulated.

IN summary, I admit that many things have changed since I took courses in Astronomy and the Physical Sciences. There are many things that I must, literally, learn all over again. All of the references that I found on this matter lead ME to thisconclusion: The assertion that "all stars in the F, A, B, O and W classes lack spots" is conjecture and theoretical at best.
I'm not saying I'm correct. I'm only saying that all the references I was able to find point to this conclusion. I certainly would appreciate solid references to the contrary.

[Don. Edwards]

Spaceman Spiff,
Brown Dwarf's don't fuse hydrogen at all. They may fuse Deuterium, an exotic form of Hydrogen when they first form but once all the Deuterium is burned off there isn't enough heat and pressure to maintain critical mass and fusion then stops. They will of course continue to convect and radiate heat. But they will gradually cool down over billions of years until they are cold and dark. I would guess that eventually even the convection would stop once they reached an internal temperature that is equal to their surrounding space.

[Spaceman Spiff]

Wow, talk about a puzzling lack of info on the subject. ... [snip] ... , this involved 12 straight hours of research and Googling!

12!? I gave up after 2! I suspect it's because this kind of research gets published as single studies of individual stars over the years, and then there might be a few review papers, and then a text book is written by an academic who reviews the reviews. Not much of this really makes it onto the web, and what I found tended to be only for K and M dwarves.

What I also remember now is that generally for main sequence stars, those in that F5-O range generally tend to remain fast rotators, while the cooler stars get slower with age. While faster rotation is supposed to mean stronger magnetism, it's convection that's needed to tangle the magnetic field lines to get starspots to form at all: sunspots are where the tangled magnetic field lines push out through the Sun's photosphere. In cooler stars, the magnetic field lines were presumed to loop out into any surrounding protoplanetary disk and allow the stars to shed angular momentum more efficiently (magnetic braking effect). Thus, there was supposed to be an inferred correlation of starspot activity to this convective outer layer, because the 'knee' in the rotation speed curve is about where the outer convective layer reaches zero depth.

It would be good news that there's evidence for something on the hotter stars, and it's true that faster rotation is in general supposed to mean greater magnetic activity. If you read them carefully, I don't think those links are saying hotter stars have been found with (darker) starspots like in the pictures you present. The first seems garbled (and had an incomplete sentence I note you corrected!), but also to be talking about the F,G, K dwarves of the Pleiades. The extra blue can't comes from starspots (which are redder because cooler), but could come from faculae and plages. So that one doesn't make sense. The second one isn't clear if it's saying hotter stars or any stars have been found to have starspots. It could just mean the M dwarves I've already mentioned. Still, the third makes it sound like it would be a different mechanism from the Sun's sunspots, so I wonder what they'd really look like.

Spaceman Spiff,
Brown Dwarf's don't fuse hydrogen at all.

Yes, you're right. Sigh. Oh why oh why didn't I spot that non sequitur? Off to the edit button with me! I included brown dwarves because I was thinking pof mentioning that they too are susceptible to the same convective magnetic entanglement to creat 'starspots' on them too. At least, one brown drawf has been observed to flare in X-rays...

Oh, and I forgot to say to texture maker's in general: I don't think there should be a mandatory 'reality' audit for Celestia textures, so I don't mind B star textures with starspots, but I thought I'd raise the possibility that hot stars may actually be featureless, and cool (young) stars may have very large starspots.

Spiff.

P.s. tardy reply due to slow forum server.

[Tech Sgt. Chen]

I have seen sparse, scattered suggestions of the theory supporting, somewhat, the idea of the existence of certain stars within different spectral catagories that lack spots. Though I saw allusions of various forms that such a train of thought existed, it seemed no one was serious enough to put solid references about it anywhere on the web. I personally never heard the theory but, like I said, it's been a long time since schooling for me. Many things change.

I'm not genius here but, these inferences suggest that massive stars with slow rotational periods lack the magnetic fields (due to the slow rotations) needed to produce sun like spots. I find this reasoning difficult to comprehend. Especially in light of the fact that, a star is an extremely massive object! So massive in fact, that it produces enough gravity to significantly affect space around it out to distances in the astronomical units! It also produces enough gravity to congeal incomprehensible volumes of gas. Think of what it takes (here on Earth) to bring a small amount of gas down to a liquid or almost solid state.
Yet, stars are succeed effortlessly in turning these gases into thick, boiling, gelatinous oceans on sheer gravitational power!!! If that weren't enough, the gravity pulls the atoms into a compact state to the point of fusional temperatures.

All this mass, exerting all of this gravity, and not being able to produce magnetic fields? Yet, everyone seems to have no problem agreeing that all stars (SEEM) to have opposite poles. If that doesn't sound like a giant magnet to me, then I may as well toss all my papers and books into the air right now. I miss you Dr. Carl Sagan!!!

Most of the references included above, along with many others that I saved was not so much to show that blue stars have spots. Rather, almost every reference I found, save for the second one above, alluded to the common consensus that they "Just Don't Know". The first reference mentions "taking extra care" in calculating, the second clearly states that stars lacking motion are "EXPECTED to lack spots" and the third, dealing with specific measurement (unrelated to sun-like spot) directly infers that they don't know! I would speculate that there are scientists on both sides of the bleachers in this stadium!

[Don. Edwards]

I miss Carl Sagan as well. To think of all the things he spoke of and has come to pass and things he thought would happen and or we would find and haven't. He was lost to us before his time.

[Spaceman Spiff]

I'm not genius here but, these inferences suggest that massive stars with slow rotational periods lack the magnetic fields (due to the slow rotations) needed to produce sun like spots. I find this reasoning difficult to comprehend.

You don't have to be because you've put your finger on something here. Before I get to that though, a couple of clarifications:

1. No, it's that massive stars tend to remain fast rotators, and it's thought that that's because they do not have outer convective zones which generate twisted magnetic fields and starspots.

2. Yes, the high mass stars do have strong magnetism in them, but it's buried within the turbulent convective cores which we can't see, and which can't produce starsorts on the surface. They can produce a dipole magentic field which itself permeates the whole star and beyond. Massive stars can have magnetic fields which are large and global, sunspots have magnetic fields that are small and local.

Remember, sunspots (and starspots on those red dwarves) are where bundles of highly twisted magnetic fields have pushed through the star's photosphere, and repulsed the plasma there so that it's cooled. It's the coolness that makes them darker (and redder).

Now the interesting point you raise. I'm sure one thing Carl Sagan frequently pointed out in his explaining of how science works (and science is a method, not a resulting body of knowledge) is that it's looking for the unexpected that is important. If you (foolishly!*) still accept Francis Bacon's description of the scientific method, you'll look for starspots where you expect them: low mass stars. If you (wisely!*) accept Karl Popper's description of the scientific method, you'll look for starspots where you don't expect them: high mass stars.

Perhaps what has happened for starspot astronomy are kinds of 'selection effects'. If astronomers are learning this cliched theory that only low mass stars are likely to have have starspots, then because of limited finance and observation time (where scientists have to justify the research they do based on the 'positive results' they promise to find!!!) they will clearly prefer look at low mass stars to study starspots. Also, it is much easier to detect large starspots on small, low mass stars than small starspots on large, high mass stars. Yet, it would be much more scientific and profound if someone were to discover that large, high mass stars do have starspots (or some other unexpected surface features) instead. I noticed that all the literature I was finding seemed to deal only with small dwarves when it came to starspot studies - because they seem to be the easiest subjects.

You see, I wanted to make you aware of this 'current understanding' by astronomers that it's expected that stars of different masses will have different numbers and sizes of starspots (from none at all, to several giant spots), and that stars won't have the same old sunspotty-type starspots again and again. Yet I don't want to 'ban' people from producing starspotted B types star textures in the name of 'scientific accuracy', because... well, we seem not to know for sure... In a way, I'm appealing for increased imagination about starspot appearance.

Spiff.

* Call me biased. I know I'm right .

[Tech Sgt. Chen]

I've been feverishly working on my new website so that I can upload the textures for, anyone interested, to download. I can easily upload two versions of various spectral classes that include or exclude spots peculiar to each class. Unfortunately, I believe Celestia will only render 1 of the two textures for each class. I wish there was a way for Celestia to differentiate say, a B-class star texture according to it's size or rotational speed but, it won't which makes all this a moot point. Stars, to me anyway, are the easiest of the texture catagories to create. Maybe when my skills advance, I can graduate to some decent planet or cloud textures. And, yes Don, I have every intension of viewing or downloading your tutorials. So, don't remove their acccessiblity. Time constraints, and DUN, severely rule my priorities. I know HTML quite well but, it's still a pain in the arse! I'm a heavy user of nested tables which really tailor a website but, just try keeping track of all the individual <tr>,<td>, tags; even with all the comments I use to keep track! I hope to have SOMETHING published within a few days.

[Tech Sgt. Chen]

Well, the M Star texture is just about finished. Luckily I saved a B&W star texture template from which to colorize. It really speeds up the process. I then add new -OR- modify old sunspot textures that I add as a transparent layer. Here are a couple of samples:

And a Close Up:

Again, these photos are a bit deflated but, the detailing still shows up quite well here! I forgot to tone down the brightness setting in photoshop and resultingly, the photos appear less red than the actual texture.

[eburacum45]

Well, my own ideas about Betelgeuse are taking a quite a different direction.
Here is my texture applied to an irregular mesh;
http://img66.imageshack.us/img66/159/betelgeuse1yj.jpg

this is based on this movie
http://www.astro.uu.se/~bf/movie/dst35g ... _I1blm.mpg

although I will have to increase the number of convection cells visible in the texture.
It seems that a massive red giant like this would have relatively few such cells, although whether there would be another layer of detail smaller than the cells shown in the movie I couldn't say.

This is after all a very big star.

[Tech Sgt. Chen]

I've been thinking about creating a Betelgeuse texture. I'm not sure yet where exactly I would begin. I've seen some articles indicating the existence of an active core that can actually be observed through semi-transparent layers of ash and gas. Supposedly, bright objects behind Betelgeuse can also be seen through this semi-transparent layer. I'll have to do a lot more research before even starting.
I'm creating a new post for the link where my star textures can be downloaded if desired.

[Joey P.]

Anyone knows what happened to these star textures? If you have them, send me a copy under a .zip file. Thanks!