Celestia Forums

I am trying to add the companions of Delta Cygni to Celestia. I create the .stc file, but the stars do not show up? Is it because Delta Cygni is not in the "nearstars" .stc file? Delta Cygni is only in the data file for stars. Can you add stellar companions to stars that only occure in the "nearstars" .stc document?

If you cannot add companions, can someone tell me the exact RA and Dec. of Delta Cygni, or where to find it, so I can use those coordinates to create a barycenter...

Thanx...

This is the general format for a binary barycenter:

(taken from Fridger's binaries file).

The file needs to be an STC file, and you need to put the HIP number you're replacing at the start of the A component. In this example the HIP number is 2762, but for Delta Cygni you'll need to use 97165.

Though delta cygni is a B9.5 III Giant according to Hipparcos - most defniitely not a star that should have any planets around it at all.

The RA and Dec of Del Cyg in Epoch 2000 are:

RA: 19h 44m 58.478s
Dec: +45?° 07' 50.91"
Distance: 170.94913

you'll need to convert that to decimal from hours/degrees though to enter it into the STC.

Thank you so much! I'll see if this format solves the problem.

On a scientific note... I was referring to Delta Cygni's stellar companions. Delta Cygni B is an F1 dwarf with a mean separation of 157 AU. Delta Cygni C is a K star that appears to move with the system with a 2.5 degree separation from Delta Cygni A.

Planets not likely...LOL

This is the code for the Delta Cygni system. It is still not working?

RA should be 19.74958, Dec should be 45.13081.

I don't think you need the "Modify" before the 97165 either.

You may need to add "V" after the spectral types for the companions.

And I'm not entirely sure if Barycenters work in triple systems like that. You might need to find the barycenter of A+B, and then have that orbit another Barycenter made from (A+B) and C.

To generalize Malenfant's comments:

Star and Barycenter RA values are in degrees, not hours.

A leading plus sign (+) will cause a fatal error.

Modify is invalid in an STC catalog, causing a fatal error. It can be used only in an SSC file. When you define an STC object by using an HIP value, its definition completely replaces the existing definition.

While Celestia doesn't care if you define all of the bodies to be orbiting the same Barycenter, that may or may not be valid dynamically, depending on the details of the specific multi-body system.

Thanks for the help! After a correction of these errors, I have a perfectly working Trinary System.

Here's a couple links on the specs of the system

http://www.astro.uiuc.edu/~kaler/sow/deltacyg.html

http://www.alcyone.de/SIT/bsc/HR7528.html

selden wrote:While Celestia doesn't care if you define all of the bodies to be orbiting the same Barycenter, that may or may not be valid dynamically, depending on the details of the specific multi-body system.

Remind me, can you have planets/moons orbiting their own barycenters in a solar system yet?

Malenfant wrote:

selden wrote:While Celestia doesn't care if you define all of the bodies to be orbiting the same Barycenter, that may or may not be valid dynamically, depending on the details of the specific multi-body system.

Remind me, can you have planets/moons orbiting their own barycenters in a solar system yet?

You can define an invisible barycenter object that planets and moons will orbit. This is in fact how the team that discovered the two additional moons of Pluto modeled the four body system in Celestia. There are minor drawbacks to this approach however . . . It will look a bit strange in the solar system browser. And, to use the example of Pluto, you could no longer select Charon as Sol/Pluto/Charon; you'd have to use Sol/Pluto-Charon Barycenter/Charon instead (the exact string depends on what you chose as the barycenter name.)

--Chris

chris wrote:You can define an invisible barycenter object that planets and moons will orbit.

Is it defined in a similar way as for stars though? And would you see the orbits of the bodies around it (that really needs to be fixed for stars - we should have a way to see the orbits around barycenters)?

Or do you just mean the old 'invisible object' style of definition?

Yes, this is a problem. We can't see the orbit for any pair of planets orbiting their center of mass (barycenter). When you look at the solar system from a distance, you can see all the orbits except for the planets moving around their cm. This is very annoying. The trick I'm using is to define a tiny black object as a dummy planet and located on the cm. This way, I could see the missing orbit. But then, there's another problem related to the object's size and the planet's albedo. Sometimes, the planets just suddenly disappear from the view, while moving just a bit around them.

I experienced this problem recently, while working on my Zeta Reticuli SF addon.

When the Hipparcos numbers refer to a multiple system, is it correct to assign the Hipparcos reference to the primary component or to the system as a whole?

Note that barycenters can be assigned Hipparcos numbers (although the OrbitBarycenter parameter does not recognise catalogue references, as I have pointed out in another thread). This issue is one that is preventing a satisfactory implementations for stars which do not have proper names or Flamsteed/Bayer designations and being multiple star systems (e.g. HD 41004, which has a planet around the A component, and the triple star system which contains a planet).