Celestia Forums

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).

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

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

selden wrote: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 ?

Cham wrote:
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.

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

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

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

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 :




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.