Celestia Forums

Some stars are very non-spherical; Regulus is one famous example. I've made a model of this rapidly spinning B class star.



I've made this image by putting an oblate shell on the outside of the
star, with a thick atmosphere
(see this page-
http://en.wikipedia.org/wiki/Regulus
The star is oblate (not rugby-ball shaped, as some news items
maintained a few years ago)
The star exhibits gravity darkening because the poles have a higher
gravity, so fusion runs hotter under the poles; the surface is much
closer to the fusing core at the poles than at the equator.
I got this effect by darkening the texture at the equator, by the way.

I am sure there is a way of replacing the star with a model rather than simply covering it with a luminous shell; any ideas?


I have an ambition to make a model of a B emitter class star next,
like Dschubba
http://www.astro.uiuc.edu/~kaler/sow/dschubba.html
these very rapidly spinning stars have a disk around the equator which
emits radiation; by merging a star and a black-hole accretion disk I
think I could make a reasonable model of such a beast.
Incidentally here is an old image of a shell I put round the outside of Betelgeuse a while ago; not entirely successful, but it looks good from a distance-


Betelgeuse apparently is very irregular in form, although extraordinarily big.

eburacum45 wrote:I am sure there is a way of replacing the star with a model rather than simply covering it with a luminous shell; any ideas?

Wouldn't the STC parameter
SemiAxes 4.16 4.16 3.14
do what you want?
It has been available since v1.4.0.

http://www.lepp.cornell.edu/~seb/celest ... eters.html

or you can use an arbitrarily shaped Mesh

Thanks; that is just what I am looking for.
Has anyone else tried this? Someone might have already made a whole bunch of oblate stars for Celestia, or know of some data concerning oblate stars.

Medusa created an STC for two close orbiting stars
http://www.celestiaproject.net/forum/viewtopic.php?p=78334&

It also causes Celestia to display several visual anomalies. i.e. several rendering bugs are apparent.

Here is Dschubba, made using the SemiAxes declaration and with an emitter disk added around the equator. Does anyone have any more info on these bright, irregular stars? Just how oblate should Dschubba be?

That looks pretty cool with the emitter disk. (Don't put it anywhere near earth though, or you'll start a wave of UFO sightings! )

Accoring to that page by Jim Kaler, Dschubba is a quadruple star; one close companion at about Mercury's distance, one at Saturn's distance, and one way out. Actually there is a very nearby star in the 2 Million star database, so I haven't bothered modellingthat one.

Reading a little more about gravity darkening, I found that the temperature and therefore
the 'bolometric flux' of the star would cool at the equator of a spinning star. So I've made a new texture,
with distinct yellowing around the middle; the emitter disk is now white instead of grey, although to be honest,
I haven't got any data on the colour of the disk yet.
Also visible is one of the companion stars at Mercury's distance.

eburacum45 wrote:... So I've made a new texture, with distinct yellowing around the middle; the emitter disk is now white instead of grey, although to be honest, I haven't got any data on the colour of the disk yet.

Hello eburacum45, very nice and interesting.
Is it already available for download?
BTW, I prefer the first version of the emitter disk, the grey one, IMHO it looks more credible and smoother than the second one.
Well done.
Bye

Andrea

ANDREA wrote:

eburacum45 wrote:... So I've made a new texture, with distinct yellowing around the middle; the emitter disk is now white instead of grey, although to be honest, I haven't got any data on the colour of the disk yet.

Hello eburacum45, very nice and interesting.
Is it already available for download?
BTW, I prefer the first version of the emitter disk, the grey one, IMHO it looks more credible and smoother than the second one.
Well done.
Bye

Andrea

I agree in some respects with Andrea, the emitter disk is smoother in the first, however, to some extent, the overall effect of the second is perhaps better as the emitter disk merges more smoothly and seamlessly with the star....

....in short, I like aspects of them both!

Looking forward to this addon.

I'll make it available, but you will have to bear in mind that it is an impression of the Dschubba system, based on the scant information that is available on the 'Net. I don't have reliable information on how oblate Dschubba A is, or exactly how far out B and C orbit. (or in what plane; so it would not satisfy Dr Schrempp).

However it looks nice; the ragged edge of the emitter disk is now exactly how I imagined it when I first read Jim Kaler's description. Here is a litlle movie of the three main stars;
http://www.orionsarm.com/movies/dschubba.wmv

eburacum45 wrote:I'll make it available, but you will have to bear in mind that it is an impression of the Dschubba system, based on the scant information that is available on the 'Net. I don't have reliable information on how oblate Dschubba A is, or exactly how far out B and C orbit. (or in what plane; so it would not satisfy Dr Schrempp).
However it looks nice; the ragged edge of the emitter disk is now exactly how I imagined it when I first read Jim Kaler's description. Here is a litlle movie of the three main stars;

Happy to know it will be available, thank you (and yes, I know that it will not satisfy Fridger, but it's so nice...)
Regaring the emitter disk, could you make available a second version with the smoother edges? Please.
And the movie is very nice, appreciated!
Thanks a lot.
Bye

Andrea

And now for something completely different; a moving model of Betelgeuse, based on the simulations of Bernd Freytag

http://www.youtube.com/watch?v=_LXI9VijaYQ


(see here for Freytag's movies)
http://www.astro.uu.se/~bf/movie/dst35g ... movie.html

Betelgeuse set to Pink Floyd's Echos? None-the-less very interesting!