Sirius B ?

[Cham]

On this site :

http://www.celestiaproject.net/gallery/view_al ... epe&page=2

there is some nice Sirius B pictures, which I think is a real object not included in Celestia's database. Can someone give here a complete ssc definition (with colors and glow) for this white dwarf ?

[Cham]

Okay, I've found the info on this forum, on an old discussion :

http://www.celestiaproject.net/forum/viewtopic ... ght=sirius

The only problem is , temperature doesn't fit.

[granthutchison]

Here's the definition with a correctly orientated orbit:

Code: Select all

"Sirius B" "Sirius"
{
   Texture "bstar.jpg"
   Radius 5800

   Emissive true

   EllipticalOrbit {
      Period          50.09
      SemiMajorAxis   19.8
      Eccentricity    0.592
      Inclination   97.51
      AscendingNode   161.33
      ArgOfPericenter 184.56
      MeanAnomaly     40.89
   }

   RotationPeriod 0.5 # plausible guess
}


Grant

[danielj]

I borrowes a texture from the Activity "Life and death of the stars".I put the whitedwarfwhite.jpg texture for Sirius B.I don?t know if it is more accurate.Why the temperature not fitting is a problem?

[granthutchison]

Why the temperature not fitting is a problem?

Just because Celestia displays Sirius B's temperature as something like 100K, instead of the real value of 27000K.

Grant

[danielj]

OK,but what texture is more accurate for Sirius B :"whitedwarf2.jpg" borrowed for the activity "Life and Death of the Stars" or "bstar.jpg"?

Why the temperature not fitting is a problem?

Just because Celestia displays Sirius B's temperature as something like 100K, instead of the real value of 27000K.

Grant

[granthutchison]

OK,but what texture is more accurate for Sirius B :"whitedwarf2.jpg" borrowed for the activity "Life and Death of the Stars" or "bstar.jpg"?

I have no idea what the surface of a white dwarf looks like, and have never seen whitedwarf2.jpg, so that makes things a bit tricky ...
But at 27000K Sirius B should look distinctly blue, like an early B star, which is why I chose the texture I did. See here for an approximate rendering of some star colours versus temperature.

Grant

[Cham]

How much oblateness (I guessed 0.09) for a white dwarf that rotate with a period of about 0.002 hours (exagerate guess?), with a radius of about 5800 km (is that too small?) ?

Do you have an idea ?

[granthutchison]

Seems an extraordinarily fast rotation - a number of transverse velocities of close to 30km/s have been measured, implying a rotation period of around 20 minutes. At that speed the equatorial "centrifugal" force is about 1/10000th of the surface gravity. Compare Earth, where the equatorial "centrifugal" force is a 300th of the surface gravity, and results in an oblateness of only 0.003. These white dwarfs should be almost indistinguishable from spherical.

Grant

[Cham]

I think you're right, but astronomers are discovering that many stars may have a "big" oblateness, more than expected.

And the Earth is a pasty liquid with a hard crust. A white dwarf is more gazeous-liquid (I'm not sure about this). So the rotation may have a stronger effect on them. And as I can tell (not sure), a white dwarf is not so far away of a neutron star state, which may be spinning very fast.