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 Post subject: Re: TRAPPIST-1
PostPosted: Sun, 26-02-17, 15:55 GMT 
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My money would be on the bolometric correction being off, it's based on an approximate relationship between effective temperature and bolometric correction which may not be valid for ultracool dwarfs. The property is intended to help with Celestia estimating the radius but since I supply the radius anyway it doesn't need to be in the .stc file.

Usually it's easier to estimate the luminosity from radius and effective temperature anyway.


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 Post subject: Re: TRAPPIST-1
PostPosted: Sun, 26-02-17, 16:09 GMT 
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Well, here comes the promised sequence of steps for transit hunting in celestia.Sci. Of course the example of choice is the TRIPLE transit in the TRAPPIST-1 system.

  • Goto Earth, enter the TRAPPIST-1 star as selection into the command line and
    mouse click on the tooth-wheel icon (Preferences, marked pink). The time settings page pops up (may be moved anywhere). Fill in the desired Julian Date. For the triple transit it is BJD=2457367.58 d. Look at the corresponding figure:

    [click on images by all means, followed by your browser's fullscreen key (F11)]
    Attachment:
    transit_hunt_Sci1.jpg
    transit_hunt_Sci1.jpg [ 214.66 KiB | Viewed 255 times ]
  • Hit Set simulation date/time in the dialog. This gives Dec 11 2015 as expected. Next hit G (goto). As a result the observer is (only) 417600 km away from the TRAPPIST-1 star.
    Attachment:
    transit_hunt_Sci2.jpg
    transit_hunt_Sci2.jpg [ 176 KiB | Viewed 255 times ]
  • Now using CTRL+mousedrag, move the star away from the observer to about 0.2 AU. Close the preferences dialog by clicking again on the tooth wheel.This looks like so
    Attachment:
    transit_hunt_Sci3.jpg
    transit_hunt_Sci3.jpg [ 144.86 KiB | Viewed 255 times ]
  • Finally zoom back using SHIFT+mousedrag until you have the triple transit right in front of you ;-) . Switch on the orbits (O) and the labels (Shift+L) whence you find the planet names from left to right: e-f-c.
    Attachment:
    transit_hunt_Sci4.jpg
    transit_hunt_Sci4.jpg [ 208.62 KiB | Viewed 255 times ]
Enjoy,
Fridger

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 Post subject: Re: TRAPPIST-1
PostPosted: Sun, 26-02-17, 16:14 GMT 
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ajtribick wrote:
My money would be on the bolometric correction being off, it's based on an approximate relationship between effective temperature and bolometric correction which may not be valid for ultracool dwarfs. The property is intended to help with Celestia estimating the radius but since I supply the radius anyway it doesn't need to be in the .stc file.

Usually it's easier to estimate the luminosity from radius and effective temperature anyway.


BoloCorrection doesn't seem to work when the get:info().luminosity key is called through CELX. Luminosity seem related to the AppMag only. My aforementioned correction has been performed manually, since I get the same value either or not BoloCorrection string is present within the .stc.

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Last edited by fenerit on Sun, 26-02-17, 16:28 GMT, edited 2 times in total.

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 Post subject: Re: TRAPPIST-1
PostPosted: Sun, 26-02-17, 16:25 GMT 
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Hi Fridger: hope you did acknowledge the southern solar eclipse, by the way... :°

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 Post subject: Re: TRAPPIST-1
PostPosted: Sun, 26-02-17, 16:30 GMT 
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ajtribick wrote:
My money would be on the bolometric correction being off, it's based on an approximate relationship between effective temperature and bolometric correction which may not be valid for ultracool dwarfs. The property is intended to help with Celestia estimating the radius but since I supply the radius anyway it doesn't need to be in the .stc file.

Usually it's easier to estimate the luminosity from radius and effective temperature anyway.


I have a number of neat respective simulation ideas that I'll start coding soon.

First of all: the TRAPPIST-1 system certainly merits a "Workflow" entry in celestia.Sci!

Step one is to convert the "transit hunting" results within celestia.Sci into a continuous "photometry" simulation display (using Qwt real time plotting that Dawoon also used for Microlensing display!). The attenuation of the radiated flux from TRAPPIST-1 by planetary transits is mainly a normalized ratio of star and planetary areas...
Then the interested celestia.Sci users could go on extracting the corresponding radii! ;-)

How about this?

Fridger

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 Post subject: Re: TRAPPIST-1
PostPosted: Sun, 26-02-17, 16:31 GMT 
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fenerit wrote:
Hi Fridger: hope you did acknowledge the southern solar eclipse, by the way... :°


Absolutely, Fenerit! Remember there is also an Eclipse finder in Celestia/celestia.Sci

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 Post subject: Re: TRAPPIST-1
PostPosted: Sun, 26-02-17, 17:06 GMT 
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t00fri wrote:
Well, here comes the promised sequence of steps for transit hunting in celestia.Sci. Of course the example of choice is the TRIPLE transit in the TRAPPIST-1 system.

  • Goto Earth, enter the TRAPPIST-1 star as selection into the command line and
    mouse click on the tooth-wheel icon (Preferences, marked pink). The time settings page pops up (may be moved anywhere). Fill in the desired Julian Date. For the triple transit it is BJD=2457367.58 d. Look at the corresponding figure:

    [click on images by all means, followed by your browser's fullscreen key (F11)]
    Attachment:
    The attachment transit_hunt_Sci1.jpg is no longer available
  • Hit Set simulation date/time in the dialog. This gives Dec 11 2015 as expected. Next hit G (goto). As a result the observer is (only) 417600 km away from the TRAPPIST-1 star.
    Attachment:
    The attachment transit_hunt_Sci2.jpg is no longer available
  • Now using CTRL+mousedrag, move the star away from the observer to about 0.2 AU. Close the preferences dialog by clicking again on the tooth wheel.This looks like so
    Attachment:
    The attachment transit_hunt_Sci3.jpg is no longer available
  • Finally zoom back using SHIFT+mousedrag until you have the triple transit right in front of you ;-) . Switch on the orbits (O) and the labels (Shift+L) whence you find the planet names from left to right: e-f-c.
    Attachment:
    The attachment transit_hunt_Sci4.jpg is no longer available
Enjoy,
Fridger


Thanks, but I don't have the lower tool bar!
I did get a chance to do the double transit.


Attachments:
11 Dec 2015 - 013113 UTC.jpg
11 Dec 2015 - 013113 UTC.jpg [ 86.89 KiB | Viewed 249 times ]

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 Post subject: Re: TRAPPIST-1
PostPosted: Sun, 26-02-17, 17:18 GMT 
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Fine!

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 Post subject: Re: TRAPPIST-1
PostPosted: Sun, 26-02-17, 17:57 GMT 
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t00fri wrote:
Fine!

Fridger


I went through your steps in 1.6.1 as best I could.
It doesn't have a "Set Simulation" date/time.

Attached is the result.


Attachments:
Celestia 1.6.1 Step Through.jpg
Celestia 1.6.1 Step Through.jpg [ 81.28 KiB | Viewed 242 times ]

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 Post subject: Re: TRAPPIST-1
PostPosted: Sun, 26-02-17, 18:25 GMT 
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stardust wrote:
t00fri wrote:
Fine!

Fridger


I went through your steps in 1.6.1 as best I could.
It doesn't have a "Set Simulation" date/time.

Attached is the result.


Very well, Thanks!
Of course, celestia.Sci enjoys many new functionalities!
I coded the entire time settings pannel from scratch a little while ago. There are many more interesting mutual events to check within celestia.Sci / Celestia. Hence such a time settings facility is very useful...

These applications are a lot of fun: So-called "mutual events"

Fridger

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 Post subject: Re: TRAPPIST-1
PostPosted: Sun, 26-02-17, 21:39 GMT 
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Love that!
I downloaded the paper pub015.pdf. I will read it this evening.

For now I have a Pluto/Charon eclipse.


Attachments:
PlutoCharon Eclipse.jpg
PlutoCharon Eclipse.jpg [ 102.15 KiB | Viewed 227 times ]

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 Post subject: Re: TRAPPIST-1
PostPosted: Mon, 27-02-17, 8:57 GMT 
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Nice eclipse, stardust!

Some of you might have wondered why I did not activate the LT flag (<->Light Travel delay) when hunting for planetary transits of TRAPPIST-1 some 40 ly away! The reason was that the transits were given in modern Barycentric Julian Dates (BJD_TDB) which "divides out" such special relativity effects.

Here is a pro-level converter applet from BJD_TDB to JD_UTC which I used for checking: http://astroutils.astronomy.ohio-state. ... d2utc.html

The best-fit BJD_TDB time for the triple transit was 2457367.58 d (<= NATURE paper). The converter calculated that the JD_USB equivalent is 2457367.579463134 d, and hence we don't have to apply any further corrections.

For people interested in understanding these time concepts/formats in more depth, have a look here: http://astroutils.astronomy.ohio-state. ... ation.html
along with the research paper by the authors of the above converter applet:
https://arxiv.org/pdf/1005.4415.pdf

Enjoy
Fridger

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 Post subject: Re: TRAPPIST-1
PostPosted: Mon, 27-02-17, 14:29 GMT 
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OUPS

https://en.wikipedia.org/wiki/TRAPPIST-1

Apparent magnitude (V) 18.80

Absolute magnitude (MV) 18.4 ± 0.1

Luminosity (bolometric) 0.000525±0.000036 L☉

Luminosity (visual, LV) 0.00000373 L☉


https://en.wikipedia.org/wiki/TRAPPIST-1#Notes

N°2 => Taking the absolute visual magnitude of TRAPPIST-1


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 Post subject: Re: TRAPPIST-1
PostPosted: Mon, 27-02-17, 19:18 GMT 
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Gaia DR1 (Gaia Collaboration, 2016) (tgas) => NOT

Gaia DR1 (Gaia Collaboration, 2016) (gaia) => YES

Gaia DR1 (Gaia Collaboration, 2016) (qso) => NOT

Gaia DR1 (Gaia Collaboration, 2016) (tgasptyc) => NOT

source: 2635476973180461312

RA(h:m:s): 23 06 29.1499
DE(d:m:s): -05 02 23.384

mag: 18.414

;)


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 Post subject: Re: TRAPPIST-1
PostPosted: Tue, 28-02-17, 15:12 GMT 
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I discussed with Andrew about the proper SpecularColor for the TRAPPIST-1f planet.
While presumably, we may copy much of the Earth atmosphere settings into the trappist-1.ssc file, the SpecularColor should be some appropriate reddish shade (rather than grayish).

Clearly, for the given temperature of 2550 K, the specular color should be proportional to the star color, that is displayed in celestia.Sci or in Celestia. Here things start getting different:

In celestia.Sci I have added a ToolButton allowing to quickly switch between the 2 different color versus temperature tables in the source file starcolors.cpp. See here:
Attachment:
colorTB.jpg
colorTB.jpg [ 12.6 KiB | Viewed 172 times ]

In Celestia there is a hard-coded default choice also depending on the used Celestia version. The older table variant (StarColors_Enhanced) utilizes only 41 temperature entries, while the new table (StarColors_Blackbody_2deg_D65) uses 401 support values. This has massive implications also to the star coloration and the color distributions in globular clusters in case of celestia.Sci. I did very extensive data analyses in this context already years ago.

I used Maple to quickly yet precisely interpolate the various temperature <-> color data from starcolors.cpp. First, consider
StarColors_Blackbody_2deg_D65 (<=> Vivid blackbody colors)
====================================================

While the red fraction is 1.0 throughout in this temp range, here are the displays for green and blue:
Attachment:
vivid_green.jpg
vivid_green.jpg [ 22.55 KiB | Viewed 172 times ]

Attachment:
vivid_blue.jpg
vivid_blue.jpg [ 23.82 KiB | Viewed 172 times ]

++++++++++++++++++++++++++++++++++
Numerically for 2550 K:
Result: rgb(255, 100, 17) or with fractions rgb(1.0, 0.3924, 0.0661) or as Hex #FF6411
++++++++++++++++++++++++++++++++++

Next consider the older table:
StarColors_Enhanced (<=> Weak classic colors)
==========================================
Also here the red fraction is 1.0 throughout the range of interest. In this table, however, we only have 4 data points between 1000 K and 4000 K for an interpolation of the green and blue fractions at 2550 K.
Attachment:
weak_green.jpg
weak_green.jpg [ 22.31 KiB | Viewed 172 times ]

Attachment:
weak_blue.jpg
weak_blue.jpg [ 20.09 KiB | Viewed 172 times ]

+++++++++++++++++++++++++++++
Numerically for 2550 K:
Result: rgb(255,144,144) or as fractions: rgb(1.0, 0.565, 0.565) or Hex #FF9090
+++++++++++++++++++++++++++++
In direct comparison the two interpolated colors differ substantially:
Attachment:
colorschemes_2550k.png
colorschemes_2550k.png [ 51.12 KiB | Viewed 172 times ]

where the left one refers to the modern StarColors_Blackbody_2deg_D65 table, with 11 support data between 2000K and 3000K!

The actuall celestia.Sci display of TRAPPIST-1 looks less intense but essentially matches.

E.g. the weak classic colors setting: gives
Attachment:
realcolor.jpg
realcolor.jpg [ 27.89 KiB | Viewed 172 times ]


The RGB triplet of preference can now be scaled down by a common factor to obtain the proper rgb entries for SpecularColor.

E.g. for the modern, vivid colorscheme and an earthlike atmosphere, the planet f then looks like so with SpecularColor [ 0.75 0.2943 0.0496 ]
[Click on image by all means]
Attachment:
vivid_f_specular2.jpg
vivid_f_specular2.jpg [ 98.09 KiB | Viewed 167 times ]


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