Annotate unknown stars problem?
Stacking program, astrometric (plate) solver, fits file viewer
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han59
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Hi.
Today I decided to check how the “Annotate unknown stars in selected files” feature works. I put together several dozens of monochrome images from a set of variable star observations. And ASTAP found 3 unknown “stars” on it. One object turned out to be a distant galaxy, it was easily found out by Online query - Browser query Hyperleda. But the other two objects were clearly stars, and quite bright. I was surprised that Online query - Browser query Simbad didn't give any results, because Simbad doesn't know any stars at these places. But then I noticed that ASTAP transmits the coordinates of the objects to SIMBAD as 177.4103886370d+19.0084203268d
And if you remove this “d” from the coordinates, then everything is correct! At the same time, other objects are correctly located in Simbad even with this “d” in the coordinate line. I don't know what the problem is, but it needs to be fixed somehow.
Thanks, Han, for a great program with so many useful features.
Last edit: Aleh 2025-03-25
As I understood, the problem arises because the request to Simbad is sent with an accuracy of 5”, and on the edges of the frame due to optical distortions the deviation of objects can be greater than this value. Maybe increase this parameter or make it customizable?
Hi Aleh,
Can you copy and paste the link which doesn't work with the "d" in your reply. With or without "d" seems to work both but I'm not sure if it is wise to remove the "d" at this moment.
You can increase the tolerance/search area by pulling a square around it. Hold the right mouse button and pull a square. Then release the button and select in the popup "Online query", ....
For distortion, did you check mark "Add SIP coefficient". See attached. After solving the positions should be more accurate.
Finding unknown stars is in most cases just a typical star or galaxy so a "false alarm" but it helps to find nova or asteroids.
If you find any problem please report. That helps.
Cheers, Han
The missing attachment
That's great advice, Han. With SIP enabled, all stars including those at the edge of the field of view are now recognized correctly.
As for the presence or absence of “d” in the coordinates - it was a false alarm. ASTAP was sending a request to Simbad to search for a star within 5 angular seconds and getting a negative response. I manually removed the “d” from the coordinates and clicked search. But now the search was within a radius of 2 arc minutes, which is how Simbad searches by default. And the right star was found, of course. So it wasn't the “d”.
Thanks for your help.