Showing extended objects on astronomical images with Aladin & Simbad
New October 2016
Opening your VOTABLE in Aladin and showing the extended objects
Having generated a VOTABLE containing the extended ISM objects we now need to open this in Aladin. The steps are quite simple and are similar to those used in page 1.
I used the following query to generate a VOTABLE for the area around Gamma Cygni:
otypes = ISM & dimmajor > 0.1 & region(box,gamma cygni,20d 20d)
This gives something similar to the image below:
You should be able to zoom in and out and pan the image and the ISM should be shown as long as the centre is within the 20 degree box defined in the VOTABLE query.
As the bubble / nebula does not have an ISM identity and we have no star labels in out list how can we find out what the star in the centre is allowing us to investigate further ?
There is a useful feature in Aladin that will help us - if you have the mode set to 'select' the pointer will normally be an arrow. If the tip of the pointer is placed over an object such as the star in the centre of the bubble / nebula a pop-up should appear with the identifier and brief that are stored in Simbad.
This should show the star is HD 192163 -- a Wolf-Rayet Star, it is probable the hot winds from this star are creating a bubble in the ISM
Why is the nebula not shown ?
The nebula around the star is NGC 6888, the crescent nebula. Opening the relevant Simbad page here shows that there are no measurements for the major / minor diameters of the ellipse so our filter has eliminated this object both from the VOTABLE catalogue and from being displayed !
This all goes to prove that any astronomical data must be used with caution.
The methods described on these pages can be used as a basis to generate catalogues and filters to show other types of objects for instance you could show only high proper motion stars, those within a certain radius or those of a particular spectral type as well as showing quasars only.
If you have any comments on these pages or require assistance in the use of The Virtual Observatory please contact me via the mail link on my home page.
John Murrell 10th October 2016
(c) John Murrell 2016
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