brown dwarf companion question

[doctrellor]

My BD orbiting @ 18 AU around my M3V should be 1200 K, but in Celestia, it shows up as 23 K surface temperature....

I have it as a T1V in the .stc

and the info shows up like a planet instead of a star with luminosity, ect, ect...

any ideas of what I messed up on?

[doctrellor]

I have tried the Brown dwarf in the .ssc, and the .stc (using an orbital barycenter)

so it seems as to keep the BD as a planet instead of a star

[doctrellor]

I made the 2 systems seperate systems and I even took sceenies.. yay

Just in case someone has an answer I must be blind to so I can combine these two..:P

[ajtribick]

Can you post the .stc file?

[selden]

So far as Celestia is concerned, a brown dwarf is a Star and must be defined in an STC catalog file with a SpectralType of M9, L or T, as appropriate. (See stellarclass.cpp)

Unfortunately, Celestia does not currently allow you to specify a body's temperature. It's always calculated from other factors. This for performance and to conserve memory.

All objects defined in SSC files are, by definition, non-luminous and not self-heating. You can specify an SSC class of "planet", "asteroid", "moon", "comet" or "spacecraft". If you don't specify it, Celestia will use the object's radius to try to determine what the class is. The class of an object primarily determines the colors of its orbit path and label, and whether or not it has a cometary tail. Its temperature is calculated assuming it's a perfect black body illuminated by the central star. Most planets' temperatures are modified by their atmospheres, but Celestia does not take this into account since the process is not understood. Celestia also does not yet take into account the heating by several stars if the body is in a multiple-star system.

[buggs_moran]

Creating systems with barcenters isn't too tough if you have the relative masses. The distance r from the center of the main body (1) to the barycenter is r = a/(m2/m1 + m2), m1 and m2 are your masses and a is your separation. Once you have a barycenter set up you can create the two bodies which orbit around it. The code below is from one of the binary systems I am working on.

Code: Select all

Barycenter "V426 OPH"
{
   RA        271.9654167      # (h:m:s)
   Dec       14.11491667    # (deg:m:s)
   Distance    658.52      # light years
}

"V426 OPH Dwarf" # Primary white dwarf component
{
OrbitBarycenter "V426 OPH"
SpectralType "DA"
AbsMag 11.0
Radius 5497.9374   # km

EllipticalOrbit
{
Period        0.0007814282 # years
SemiMajorAxis     0.00457151 # AU
MeanAnomaly     0.0
}

RotationPeriod   4.6
}

"V426 OPH Secondary" # HD 206697 BD +42 4189a
{
OrbitBarycenter "V426 OPH"
SpectralType "K3"
AbsMag 11.0
Radius 545740.9936 # km

EllipticalOrbit
{
Period            0.0007814282 # years
SemiMajorAxis     0.00546033 # AU
MeanAnomaly     180.0
}
}

[Malenfant]

So far as Celestia is concerned, a brown dwarf is a Star and must be defined in an STC catalog file with a SpectralType of M9, L or T, as appropriate. (See stellarclass.cpp)

Unfortunately, Celestia does not currently allow you to specify a body's temperature. It's always calculated from other factors. This for performance and to conserve memory.

There is a set of equations in one of the papers by Adam Burrows (Burrows et al. ,Theory of Brown Dwarfs and extrasolar giant planets, 2001) that one could use to calculate the BD's luminosity, radius, surface gravity, and temperature - however, we need to know the BD's mass and its age.

The equations are actually fairly simple. If it was possible to enter the Age of a BD in an STC, I think it would be trivial to calculate in Celestia.

[ajtribick]

I'll link the Brown dwarf and extra-solar giant planet calculator which implements those equations. It doesn't take into account irradiation or planetary cores though.

Another paper on this issue is On The Radii of Extrasolar Giant Planets by Bodenheimer, Laughlin and Lin, which takes into account cores and irradiation, might be worth investigating.

[doctrellor]

[quote="chaos syndrome"]I'll link the [url=http://zenith.as.arizona.edu/~burrows/cgi-bin/browndwarf3.cgi]Brown dwarf and extra-solar giant planet calculator[/url] .[/quote]

Yeah, that's what I used to get the figures for my 60J BD

Temp 995K
L .00000623636
Mass: .057143 Solar
Age: 4 Gyr
Rad: 58,259 km
Surf Grav: 224,189 (cgs)*

* I'll have to find a similar # for earth or Jupiter to see what this figure would represent

[doctrellor]

[quote="selden"]So far as Celestia is concerned, a brown dwarf is a Star and must be defined in an STC catalog file with a SpectralType of M9, L or T, as appropriate. (See stellarclass.cpp)

.[/quote]

I looked at L in the documentation, and it gave a temp of 1500K to 2000K, and I know M9 is like 2200 K

so that's why I went T since a few of the "nearby" star are T1V or T6V and 1350K & less, so I figured those would be the BD's in our local stellar neighborhood

[doctrellor]

As for my .stc's.

the main star
#######################
#hip500001.stc
#######################
# HIP 500001

500001 "Drem" {


RA 98.0
Dec 5.04
Distance 4.00

SpectralType "M3V"
AbsMag 11.72
Texture "lstar.jpg"

}

#######################

The Companion
#######################
#hip300001.stc
#######################
# HIP 300001

300001 "Nightshadow" {


RA 98.0
Dec 5.04
Distance 150.00

SpectralType "T6V"
AbsMag 38.72
Texture "browndwarf.*"

}

#######################

For the system, I have the BD orbiting at 18.0 AU from the main star, with a period of 141.811 years (I think I did that right)

I'll add the radius to the BD's stc and see how it affects things..

[selden]

I would have specified a Barycenter at the RA and Dec you're using, and then defined the orbits of the two Stars relative to that in the same STC file.

Are you intending to do something like that?

Examples of similar orbital configurations are in Celestia's nearstars.stc catalog file.

[doctrellor]

Yeah, that's what I origianlly did, do the barycenter at that RA/Dec & Distance and have the 2 stars orbit the barycenter

so with the M3V/BD having a 20:1 difference, I wasn't sure how to tweak the period/orbit correctly, even though I read the stc guide like 3 times.

I saw the BD in Celestia, so 'that' works, but for some reason, Celestia gave the BD a 23K temp instead of 1020K like I have now