Viewing Exoplanets using the Virtual Observatory  and Cartes du Ceil (and a telescope !)

NEW 15th January 2017

Revised: 23rd January 2017

 

You can see the star even if you can't see the exoplanet


 Introduction:


Exoplanets and the stars that host them fascinate both the public and astronomers mainly because of the (low ?) probability that they could host life.

 

The number of exoplanets identified continues to rise rapidly, detections being made principally by the transit and radial velocity methods. The database of known exoplanets is available on the internet in 'The Extrasolar Planets Encyclopedia' at http://exoplanet.eu/ , this contains details of all the known exoplanets. If you want to look at these through a telescope or just see where they are on the sky one can type in the co-ordinates of each planet but that can be hard work particularly if you want to show your friends or the public a number of stars hosting exoplanets.

 

Rather than typing in each planet co-ordinates or compiling your own database which will need updating as new discoveries are added the Virtual Observatory offers an easier option. I already have some pages that show how to connect your telescope to the Virtual Observatory for instance the page at http://www.johnmurrell.org.uk/AVO-CdC.htm describes the basics. In this page I look at the specifics of how to connect the Extra Solar Planets database to  Cartes du Ciel (CdC) which is a Planetarium Programme that can be used to control your telescope but also can accept information from the Virtual Observatory.

 

Method:

 

It is not possible to connect the Extra Solar Planets database directly to CdC as the website only allows the complete table to be broadcast, in this case we need to be able to select the appropriate exoplanet location to send to CdC and thus allow the telescope to move to the correct position on the sky. To select the appropriate exoplanet we will use TopCat  ( http://www.star.bris.ac.uk/~mbt/topcat/ ) as has been used in some other examples on this site. The data will be passed from the Extra Solar Planets database to TopCat and then from TopCat to CdC using the  SAMP (Simple Application Messaging Protocol) hub and protocol. The details of how this works should be seamless as long as your PC is connected to the internet.

 

  1. The first operation is to open TopCat either from the website above or from your computer if you have downloaded a local copy. This is done first as TopCat supplies the SAMP hub that enables the connection between the various VO applications.

  2. Stage 2 is to open the Extra Solar Planets catalogue at http://exoplanet.eu/catalog/ , when the page opens the header should show something like this:

  3. At this point the VO Connection line will show as 'Off' you need to click the on box that should result in the line changing to show the TopCat icon to indicate it is now connected to TopCat via the SAMP hub. You might need to authorize this connection depending on your PC's security settings.

  4. The next step is fairly obvious - click the 'send table' button. The TopCat load new table window should pop-up and after a few seconds the table should automatically download.

  5. Next open CdC (you might need to install it first if you have not used it before). CdC does not automatically connect to the SAMP hub - this has to be done using the 'File - SAMP - Connect to SAMP hub option'.

  6. Next go to the TopCat main window - it should be open but minimized. On the main window select the 'Broadcast Row' tick box and then click the 'Activation Action' button. Another menu will pop-up from here select the 'Transmit Coordinates' radio button, also select the Target Application as 'skychart' ( the real name for CdC), this prevents the broadcast row being sent back to the webserver (Astro Tools) which may confuse it. Finally click Ok to set the activation action. Your TopCat window should now show: Though the number of rows and possibly columns may have increased

  7. The next step is to open the data table in TopCat by clicking on the 'Display Table Cell Data' button on the main window. You can now scroll down until the Exoplanet you are interest in is shown, clicking on the row should result in the display in CdC moving to the appropriate position and if you have it connected to your telescope this should also slew to the same location.

  8. If you want to sort the data table in a particular order this is done via the TopCat main window. This window allows you to select only certain items to be shown in the table by creating a 'sub-set'. Instructions on how to do this are in the TopCat help files and in the documentation on the TopCat website. You can also create sub-sets by plotting the data in TopCat and then selecting part of the plot - useful to show objects in a particular part of the sky or with other specific characteristics.

  9. The SkyPlot is quite interesting you can see the Kepler detections very clearly - you can even see the area covered by the CCDs ! ( see the notes below)

  10. That's it - it's far easier and quicker to do than to describe !

   Notes:

  1. The transmission of information from a webpage to an application using SAMP is a piece of VO technology that is not used. The Extrasolar Planets Encyclopedia uses AstroTools (https://github.com/AnotherOneAckap/AstroTools) which is a wrapper around sampjs below.

  2.  The web page table transmission technology is not used that often perhaps the largest application is to transmit catalogues downloaded from Vizier (http://vizier.u-strasbg.fr/viz-bin/VizieR). With Vizier this only downloads the number of Rows set by the max parameter under preferences (default is 50 rows). The extra solar planets encyclopedia downloads the entire (filtered ?) database with no limit on lines.

  3. The transmission of the information used the tool sampjs ( http://astrojs.github.io/sampjs/ ), this page has a number of examples which might help if you want to use this on your own web pages. A search will show some other similar tools including some that are wrappers around sampjs.

  4. Plotting the position of the exoplanets on the sky using TopCat shows the Kepler field quite well, about 2/3 of the exoplanets were discovered using Kepler.

  5. An interesting exercise is to use TopCat to colour the planets by mass, a tip is that you probably need to hide the points without mass otherwise they overwhelm those with mass values. Also a logarithmic colour scale helps as there is a wide range of masses - which is the smallest and largest ?

  6. Instead of or as well as sending the location of the exoplanets to CdC you can send the data to Simbad for a more detailed view of the sky and the objects in the vicinity of the exoplanet. In section 6 you either need to select Aladin as the destination or select all in which case it will be sent to CdC and Aladin.

  7. New - 22/1/2017 The Exoplanet Encyclopedia has a page on using the Encyclopedia with the virtual observatory at http://exoplanet.eu/vo/ . This has links to two pages one to produce simple plots and one to produce more advanced graphics. Both of these use TopCat to produce the plots and are worth looking at even if it is to see what is possible.


John Murrell                                                                                                       © John Murrell 2017

  


 

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