White Dwarfs binary J0806

[Cham]

There's an interesting white dwarfs binary, described here :

http://chandra.harvard.edu/press/05_rel ... 53005.html

Here's some technical info about its location :

http://chandra.harvard.edu/photo/2005/j0806/

I'm making a small addon for this binary, but I'm having two problems (I always forget the conventions in Celestia ). Here's my stc file :


Barycenter "J0806"
{
RA 8.1064444 # 08h 06min 23.20sec
Dec 15.4583888889 # 15deg 27min 30.20
Distance 1600 # approx 1600 LY
}


995002 "J0806 A" # component A
{
OrbitBarycenter "J0806"
SpectralType "WC"
AbsMag 9
SemiAxes [1 0.87 0.87]

EllipticalOrbit {
Period 1.01863258e-5 # 321.5 sec
SemiMajorAxis 2.6737967914e-4 # half 80000 km, approx.
Eccentricity 0
Inclination 0
AscendingNode 0
ArgOfPericenter 0
MeanAnomaly 0
}

RotationPeriod 0.0893055556 # 321.5 sec
}

995003 "J0806 B" # component B
{
OrbitBarycenter "J0806"
SpectralType "WC"
AbsMag 9
SemiAxes [1 0.87 0.87]

EllipticalOrbit {
Period 1.01863258e-5 # 321.5 sec
SemiMajorAxis 2.6737967914e-4 # half 80000 km, approx.
Eccentricity 0
Inclination 0
AscendingNode 0
ArgOfPericenter 180
MeanAnomaly 0
}

RotationPeriod 0.0893055556 # 321.5 sec

}


First, can somebody confirm the RA and DEC coordinates I defined for Celestia ? The real coordinates are indicated in hours, minutes and sec, but I'm not sure of their value for Celestia (that's the kind of stuff I forget easily after two months).

Second, how can I make the two stars bulges aligned ? See the picture below, they aren't oriented properly (the red bars aren't aligned).

[Cham]

Here's a picture of a quick hack for this addon wanabe :

[selden]

In STC files, RA is in degrees: multiply your values by 15. (There are 15 degrees per hour of RA.)

[Cham]

In STC files, RA is in degrees: multiply your values by 15. (There are 15 degrees per hour of RA.)

So is this right :

RA 120.1064444 # 08h 06min 23.20sec

?

And what about the bulges orientation ?

[selden]

So is this right :

RA 120.1064444 # 08h 06min 23.20sec

?

yes.

And what about the bulges orientation ?

I've never gotten that to work right in an STC file. A workaround is to make the two of them one model and rotate it. Although the stars then will not be rotating separately, they doubtless are tidally locked anyhow.

[Cham]

Actually, the bulges are rotating at the right angular velocity. However, they aren't oriented properly in front of each other, I have to manually set some weird RotationOffset, and I don't understand why. I had to do the same thing with some of my black hole addons, by trial and error. There's surrely a way to do it properly.

By the way, there's a superb animation there, that we will be able to reproduce in Celestia, if I can get this addon right :

http://chandra.harvard.edu/photo/2005/j0806/wd_lg.mov

[PlutonianEmpire]

what about Obliquity and EquatorAscendingNode? Can we do those in stc files like we do in ssc files?

[Guckytos]

Hi there,

as far as i remember from writing the updated STC Guide, yes Obliquity and EquatorAscendingNode can be used as in SSC-Files.
Hmmmm, probably i should go and rework the Guide once again, but i will probably wait until the 1.4.0 final (whenever that will be).

RotationOffset, PrecissionRate and Orientation should also be supported.

If anyone has a good and easy description of those parameters, i'd like to hear/have it. If there is an example explaining those things even better. At the moment i just pasted the SSC explanation.

Regards,

Guckytos

[Cham]

I found the solution to my bulge problem. In Celestia, the year has 365.25 days, and not 365.3 which I used. Here's the new .stc code for the RX J0806 white dwarfs binary :

Code: Select all

#
# Two white dwarfs rotating around their barycenter with a period of 5min 30sec.
# This addon is based on some info found here : http://chandra.harvard.edu/photo/2005/j0806/index.html
# I suggest to run the addon with a 10x or 100x time scale, to "accelerate" the rotation.
#

Barycenter "J0806"
{
   RA  120.1064444        # 08h 06min 23.20sec
   Dec  15.4583888889   # 15deg 27min 30.20
   Distance  1600       # approx 1600 LY
}


995002 "J0806 A" # component A
{
OrbitBarycenter "J0806"
SpectralType "WC"
AbsMag  8.9
SemiAxes [1 0.87 0.87]

        EllipticalOrbit {
                Period             1.0187720232e-5  # 321.5 sec
                SemiMajorAxis      2.6737967914e-4  # half 80000 km, approx.
                Eccentricity       0
                Inclination        0
                AscendingNode      0
                ArgOfPericenter    0
                MeanAnomaly        0
        }

   RotationPeriod 0.0893055556   # 321.5 sec
}

995003 "J0806 B" # component B
{
OrbitBarycenter "J0806"
SpectralType "WC"
AbsMag 8.9
SemiAxes [1 0.87 0.87]

        EllipticalOrbit {
                Period             1.0187720232e-5  # 321.5 sec
                SemiMajorAxis      2.6737967914e-4  # half 80000 km, approx.
                Eccentricity       0
                Inclination        0
                AscendingNode      0
                ArgOfPericenter    180
                MeanAnomaly        0
        }

   RotationPeriod 0.0893055556   # 321.5 sec
}


Also, here's the .ssc code to define the "accretion" disk around this double system. This is the source of the x-rays, according to many sources I've found on the web.

Code: Select all

"Disk" "J0806"
{
   Mesh "J0806.3ds"
   Radius 1000000
   Emissive true

   EllipticalOrbit
      {
      Period 9E12
      SemiMajorAxis 1E-12
      }

   RotationPeriod 0.0893055556
}