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 Post subject: TRAPPIST-1
PostPosted: Mon, 02-05-16, 20:49 GMT 
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ESO: Three Potentially Habitable Worlds Found Around Nearby Ultracool Dwarf Star

So, how do we get there? ;)


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 Post subject: Re: TRAPPIST-1
PostPosted: Tue, 03-05-16, 4:15 GMT 
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Location: N 42.38846 W 83.45456
Quote:
So, how do we get there?

quote from Cheech and Chong (Santa Clause And His Old Lady)

"some magic dust, man."



Quote:
Cm: Oh, well, man, he had some magic dust, man.

Tc: Some magic dust?

Cm: Yeah, magic dust, y'know? He used ta give a little bit to da reindeer, a
Little bit to Santa Claus, a little bit more for Santa Claus, a little
Bit more...

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 Post subject: Re: TRAPPIST-1
PostPosted: Tue, 03-05-16, 13:20 GMT 
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Someone made a SSC for these planets ? Is the star in Celestia's database ?

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 Post subject: Re: TRAPPIST-1
PostPosted: Wed, 04-05-16, 11:10 GMT 
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The star is not in the Hipparcos database (it's too dim and was too recently discovered) and it's more than 25LY away, so it's not included in Celestia.

The star's parameters are available at
http://simbad.u-strasbg.fr/simbad/sim-i ... 28-0502285
and
https://en.wikipedia.org/wiki/TRAPPIST-1

Most of the planets' orbital parameters are not well measured, but see
http://www.openexoplanetcatalogue.com/p ... APPIST-1b/

Here are some first approximations:
Code:
# trappist-1.stc
"TRAPPIST-1:2MASS+J23062928-0502285"
{
   Radius 79310 # 0.114 * sun
   RA 346.5042 #23 06 30.34
   Dec  5.0335 #05 02 36.44
   Distance 39.5
   SpectralType "M8"
   AppMag 18.8
   }


Code:
# trappist-1.ssc
"TRAPPIST-1b" "TRAPPIST-1" {
Radius 7071 # 1.11 * earth 6371
EllipticalOrbit {
SemiMajorAxis 0.0111 Period 0.0041363 # 1.5108 days
}}

"TRAPPIST-1c" "TRAPPIST-1" {
Radius 6690 # 1.05 * earth
EllipticalOrbit {
SemiMajorAxis 0.0152 Period 0.0066304 # 2.4218 days
}}

"TRAPPIST-1d" "TRAPPIST-1" {
Radius 7390 # 1.16 * earth
EllipticalOrbit { SemiMajorAxis 0.271 Period 0.49828  # 18.20 days
}}


Notes:
1. Due to gaps in observations, the period and sma of TRAPPIST-1d are poorly defined.
2. Orbital eccentricities are unknown.

Exercises left for the student ;)
1. Since these planets were detected using the transit method, the common inclinations of the orbits can be determined from the star's position on the sky.
2. The planets' positions in their orbits (MeanAnomaly, etc) could be determined from the times of the observations.
3. Appropriate surface textures

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 Post subject: Re: TRAPPIST-1
PostPosted: Wed, 04-05-16, 13:07 GMT 
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Thanks Selden ! :)

I would suggest to add a venuslike texture :

Code:
"b" "TRAPPIST-1" {
   Radius 7071  # 1.11*Earth 6371
   Texture "venuslike.*"

   EllipticalOrbit {
      SemiMajorAxis 0.0111
      Period 0.0041363  # 1.5108 days
   }
}

"c" "TRAPPIST-1" {
   Radius 6690  # 1.05*Earth
   Texture "venuslike.*"

   EllipticalOrbit {
      SemiMajorAxis 0.0152
      Period 0.0066304  # 2.4218 days
   }
}

"d" "TRAPPIST-1" {
   Radius 7390  # 1.16*Earth
   Texture "venuslike.*"

   EllipticalOrbit {
      SemiMajorAxis 0.271
      Period 0.49828  # 18.20 days
   }
}

That system is nice in Celestia.

And what is fun with it, is we can easily find the star's mass, using my good'old LUA Plugins :


Attachments:
trappist.jpg
trappist.jpg [ 82.07 KiB | Viewed 2603 times ]

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 Post subject: Re: TRAPPIST-1
PostPosted: Wed, 04-05-16, 18:25 GMT 
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Selden wrote:
Exercises left for the student ;)
1. Since these planets were detected using the transit method, the common inclinations of the orbits can be determined from the star's position on the sky.
2. The planets' positions in their orbits (MeanAnomaly, etc) could be determined from the times of the observations.
3. Appropriate surface textures

The first two of these are handled automatically by my script that processes the NASA Exoplanet Archive. Unfortunately, TRAPPIST-1 isn't in the archive (yet).

The relevant files can nevertheless be created by supplying a CSV with the same columns as would come from the archive, giving the following:

stc file:
Code:
"TRAPPIST-1"
{
   RA<deg> 346.622012
   Dec<deg> -5.041275
   Distance<pc> 12.1
   AppMag 18.8
   SpectralType "M7.5V"
   Temperature 2550
   BoloCorrection -4.85
   Radius<rS> 0.114
}


ssc file:
Code:
"b" "TRAPPIST-1"
{
   Radius<rE> 1.113

   EllipticalOrbit {
      SemiMajorAxis<AU> 0.01111
      Period<d> 1.51085

      Epoch 2457322.518000 # transit midpoint
      MeanAnomaly 90.000

      ArgOfPericenter<deg> 180.000 # unknown, 0 assumed
      Inclination<deg> 1.224
      AscendingNode<deg> 255.734 # unknown, using ecliptic
   }

   UniformRotation {
      Inclination<deg> 1.224 # to match orbit
      AscendingNode<deg> 255.734 # to match orbit
   }
}

"c" "TRAPPIST-1"
{
   Radius<rE> 1.049

   EllipticalOrbit {
      SemiMajorAxis<AU> 0.01522
      Period<d> 2.42185

      Epoch 2457362.805000 # transit midpoint
      MeanAnomaly 90.000

      ArgOfPericenter<deg> 180.000 # unknown, 0 assumed
      Inclination<deg> 1.134
      AscendingNode<deg> 255.734 # unknown, using ecliptic
   }

   UniformRotation {
      Inclination<deg> 1.134 # to match orbit
      AscendingNode<deg> 255.734 # to match orbit
   }
}

"d" "TRAPPIST-1"
{
   Radius<rE> 1.163

   EllipticalOrbit {
      SemiMajorAxis<AU> 0.058 # from Kepler's 3rd law
      Period<d> 18.202

      Epoch 2457294.774000 # transit midpoint
      MeanAnomaly 90.000

      ArgOfPericenter<deg> 180.000 # unknown, 0 assumed
      Inclination<deg> 0.734
      AscendingNode<deg> 255.734 # unknown, using ecliptic
   }

   UniformRotation {
      Inclination<deg> 0.734 # to match orbit
      AscendingNode<deg> 255.734 # to match orbit
   }
}


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 Post subject: Re: TRAPPIST-1
PostPosted: Wed, 04-05-16, 19:24 GMT 
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Thanks Andrew!

just gave exo b a venus surface texture. Here are 3 screen shots using your orbit parameters...

[click on image (1920x1080) and then hit your browser's fullscreen key (F11 on FF)]
The TRAPPIST-1 system is still a very symmetrical one...The nearby irregular dwarf galaxy is LMC.
Attachment:
trappist_system.jpg
trappist_system.jpg [ 181.25 KiB | Viewed 2585 times ]


[click on image (1920x1080) and then hit your browser's fullscreen key (F11 on FF)]
Landed on exo b. No "sunsets" yet on exo b at this point ;-)
Attachment:
trappist_b.jpg
trappist_b.jpg [ 140.93 KiB | Viewed 2585 times ]


and finally exo b and exo c dancing around their star ...
Attachment:
trappist_b_c.jpg
trappist_b_c.jpg [ 53.82 KiB | Viewed 2582 times ]


Fridger

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 Post subject: Re: TRAPPIST-1
PostPosted: Wed, 04-05-16, 21:17 GMT 
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Just to indicate that the parameters in Andrew's code above for the 3rd planet give some relatively large discrepencies for the central body's mass, compared to the values from the first and second planets.

Mass of star according to planet b : 83.9 Jupiter
Mass of star according to planet c : 83,7 Jupiter,
Mass of star according to planet d : 82,3 Jupiter.

My LUA pluggins can clearly show the effect of uncertainties here.

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 Post subject: Re: TRAPPIST-1
PostPosted: Wed, 04-05-16, 21:37 GMT 
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Pretty clearly a rounding effect.

For the inner two planets I provided the semimajor axes reported in the paper in the input file, and the script takes these as-is (no rounding applied).

For the third planet, only the range of semimajor axes for the complete range of allowed orbital periods is given, so I didn't supply the semimajor axis in the input. The comment "# from Kepler's 3rd law" is added in the output when the script computes a semimajor axis missing in the input.

If I do the calculation myself, I get a semimajor axis of 0.0583565... AU for the orbital period of 18.202 days and a stellar mass of 0.080 solar masses (83.8 Jupiter masses).

Rounding that to 0.058 AU (as the output from my script does) and solving for the stellar mass using the 18.202 day period, I get 82.3 Jupiter masses, which matches your Lua plugin.


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 Post subject: Re: TRAPPIST-1
PostPosted: Thu, 05-05-16, 0:16 GMT 
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Andrew,

since Grant ceased the updating of the exoplanets database, did you completed it using your script ?
If so, is it possible for you to publish your version for Celestia ?

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 Post subject: Re: TRAPPIST-1
PostPosted: Thu, 05-05-16, 4:22 GMT 
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slightly OT but goes with the ssc

an odd result from a hack test gave me this heightmap
I was NOT expecting this

2k reduced -- use it , do not use it , whatever

Image

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 Post subject: Re: TRAPPIST-1
PostPosted: Thu, 05-05-16, 11:20 GMT 
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Cham wrote:
since Grant ceased the updating of the exoplanets database, did you completed it using your script ?
If so, is it possible for you to publish your version for Celestia ?

Given the rapid rate of discovery I haven't been doing this so far. To stay as up-to-date as possible it is necessary to run the script to generate the files. Nevertheless, I've now put a release up on the GitHub project with the generated files, see this page. (Note these files do NOT contain the TRAPPIST-1 system as they were not present in the NASA Exoplanet Archive)

There is definitely room for improvement. Probably will want to switch to the Open Exoplanet Catalogue as a data source in future as it is able to represent binary stars (the NASA Exoplanet Archive lacks the information to properly represent circumbinary planets).


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 Post subject: Re: TRAPPIST-1
PostPosted: Thu, 05-05-16, 13:29 GMT 
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Thanks Andrew.

I'm toying with the files.

I noticed that there are several systems which don't show the same orbits as in Grant's database.
See for example 55 Cnc (which is well known), Kepler-11, Kepler-32, Kepler-33, and HIP 94931 (there are several others).
Actually, the orbits appear to be tilted. Why such differences ?

Also, HD 219134 is not in Grant's database, but it has two weirdness : planet "b" has a tilted orbit relative to other planets, which seems odd, and "e" is missing while there are "d", "g" and "h".

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 Post subject: Re: TRAPPIST-1
PostPosted: Thu, 05-05-16, 15:11 GMT 
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I've extracted all systems which have 4 exoplanets or more and that aren't in Grant's database.
This gave me 37 "new" systems.

Most of them are interesting. Here's a view :
Attachment:
Kepler.jpg
Kepler.jpg [ 83.68 KiB | Viewed 2533 times ]


This is Grant's database + 37 systems from Andrew's files

Two of these "new" systems are puzzling :

All 5 planets of Kepler-296 have a large eccentricity of 0.33.
I wonder how we could have this info from occulting bodies.
(This page says eccentricity smaller than 0.33 : http://exoplanetarchive.ipac.caltech.ed ... pler-296+f)

The 5 planets of Kepler-186 are showing some large discrepencies in the central star mass.
From inner to outer planet : 0.36, 0.23, 0.36, 0.35, 0.64 solar mass.

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 Post subject: Re: TRAPPIST-1
PostPosted: Thu, 05-05-16, 19:04 GMT 
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My script uses a different method to "fill in the blanks" when it comes to missing orbital elements.

The orientation of the orbit is given by three parameters: ω (argument of periastron), i (inclination) and Ω (longitude of the ascending node). For a planet that is only known by RV, only ω is known. For a transiting planet, we also get i. The question is what to use for the missing ones. For the case where only ω is known, I make the same choice as Grant Hutchison did: choose i and Ω such that the orbit ends up in the ecliptic plane, which makes the Inclination and AscendingNode parameters in the .ssc file 0.

Where we differ is the case of transiting planets. Grant Hutchison chose to set Ω to 0, whereas I use Ω from the ecliptic plane. From what I observe, this tends to result in less severe mutual inclinations in the case where transiting and non-transiting planets exist in the same system. I do not yet have any special handling for this case: my intention is to eventually use the invariable plane of planets with more fully-specified orbits. This results in different orientations of the orbits for transiting planets, but both should be consistent with the known orbital elements.

As for eccentricity, this is an issue I'm aware of: the NASA Exoplanet Archive occasionally gives limits (e.g. eccentricity < 0.3) but the script does not yet parse the relevant field. This means that a planet whose eccentricity is given as <0.3 will end up being represented with an eccentricity of 0.3, rather than 0 which is probably a more sensible representation in the majority of cases.

The discrepant stellar masses for Kepler-186 are in line with the parameters given in the NASA Exoplanet Archive for this system: planets b, d and e come out near 0.36 solar masses, while c and f get 0.23 and 0.64 solar masses respectively. The parameters for planet f are taken from a different reference to the other planets, but the semimajor axis of c looks like an error in the catalogue: going to the referenced paper for the planetary properties the given semimajor axis is 0.0520 AU rather than the 0.0451 AU value given in the NASA database.


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