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55 Cancri

Posted: 20.04.2019, 23:54
by fyr02
I recently made an add-on for the 55 Cancri planetary system, which can be checked out here:
I also wanted to add the red dwarf 55 Cancri B in this addon, since the binary wasn't already present in Celestia 1.6.1.
However, I have no idea how to do this, since I'm kind of a n00b at Celestia and stc files.
I know that doing 55 Cancri B by itself shouldn't be too hard, but I have a few concerns:
How do I incorporate both the new 55 Cancri B and the existing 55 Cancri A into a binary system?
How do I change the name "55 Cancri/Rho1 Cancri" to "55 Cancri A/Rho1 Cancri A"?
How do I work stc files? (Again, I'm a n00b...)
How do I get the existing planets to orbit 55 Cancri A and not the companion/barycenter?
Looking for some help/resources to guide me...

Posted: 21.04.2019, 02:33
by LukeCEL
Hi fyr02,

Before you go through the trouble, please know that I'm working on an exoplanet catalog. It includes definitions for many binary stars, including 55 Cnc AB. Here's the STC code:

Code: Select all

# Parameters for 55 Cnc B from Newton et al. (2016), ApJ 834 (1), 85
# "The Hα Emission of Nearby M Dwarfs and its Relation to Stellar Rotation"
Barycenter "RHO1 Cnc:55 Cnc"
   RA 133.1538407 # mass ratio 0.905:0.255
   Dec 28.3276380
   Distance 41.063

43587 "RHO1 Cnc A:55 Cnc A"
   RA 133.1492139
   Dec 28.3308214
   Distance 41.063
   AppMag 5.95
   SpectralType "G8V"

"RHO1 Cnc B:55 Cnc B"
   RA 133.1702615
   Dec 28.3163402
   Distance 41.063
   AppMag 13.15
   SpectralType "M4V"
   Radius 190000

Essentially, though: you want to write a Barycenter for the 55 Cnc barycenter, then rewrite 55 Cnc A using its HIP index (43587), then make a STC definition for 55 Cnc B.

The HIP index is important because it causes Celestia to automatically replace the star HIP 43587 with the star you wrote ("RHO1 Cnc A"), so you don't get any duplicates. Also, the original extrasolar.ssc file was written so that the planets orbit the star called "HD 75732". Had they been written so they orbit a star called "55 Cnc", this wouldn't have worked, because then the planets would all orbit the barycenter, which in this case is called "55 Cnc".

Posted: 21.04.2019, 02:54
by Lafuente_Astronomy
The exoplanet catalog is interesting. From what catalogs does the exoplanet catalog you're making take from?

Posted: 21.04.2019, 02:58
by fyr02
Thanks so much!
I actually tried doing this myself and although I was able to calculate some pretty good orbital parameters, it was placing 55 Cnc in the middle of Hydra. Looks like my RA was wrong or something.

Posted: 21.04.2019, 14:39
by LukeCEL
Lafuente_Astronomy wrote:From what catalogs does the exoplanet catalog you're making take from?

I'm using the NASA Exoplanet Archive as the main source of host stars and exoplanets, and I'm adding binary stars by hand, with parameters from a bunch of different sources.

Posted: 21.04.2019, 15:19
by Lafuente_Astronomy

Posted: 23.04.2019, 02:35
by selden

The usual cause Celestia drawing a star at the wrong place on the sky is the use of the wrong RA units: using units of Hours instead of Degrees when specifying the RA.

Celestia v1.6.1 STC catalogs require that STar Catalog Right Ascension values be specified in units of Degrees. This is unlike most catalogs (including Celestia's Deep Space Catalogs), which specify the RA value in units of Hours. To convert from Hours to Degrees, you have to multiply the value by 15.0.

In other words, for Rho1 Cnc, one must specify an RA value of more than 133 (degrees) and not a value of almost 9 (hours).

Posted: 27.04.2019, 23:23
by fyr02
Thanks, yeah I know that now, but the difficult thing usually is when an seconds to hours converter wont let me input decimal values for seconds. :(

Posted: 28.04.2019, 03:22
by LukeCEL
fyr02, do you happen to be using as the RA/Dec converter? If so, I recommend using instead, which is more flexible. It allows up to 4 decimal degrees for the arcseconds.

Posted: 29.04.2019, 02:06
by fyr02
Really? Thanks!