I was taking a picture of an IC443 using a Rokinon 135mm lens and ASI 183GT, and wanted to test a new Baader fast F/2 filter set with shorter exposure time that would make any difference compared to longer when using at F/2 speed.

Started this project on 28th Nov 2021 with OIII filter, and due to cloudy weather/Moon and other projects going on this testing got delayed and finally got time to complete Ha on 26th Jan 2022 and SII on 5th Feb 2022.  

After finishing subs from the SHO filter it was time to test, so I completed my staking process in Pixinsight and combined images from 3 filters to check the final result.

After combining images taken from SHO, the final image looks fine to me but I see more noise and think I need a little bit more integration time. I was looking closer at the image to see whether I can see nebula details with less integration time and then  I saw 3 red dots in the image...hmmmm...

I started an investigation.... Is it something wrong with my lens/camera/filter? or I integrated subs with some artifact?

I investigated master Ha and nothing was there, then master OIII and nothing was there.. then SII and found this trail. So now I know that it's with images taken with SII filters and I started checking my subs taken with SII.

When I opened each subs in the Blink tool and saw there is nothing wrong/trailing in each frame and then I found that there is one extra star(Something that looks like star)  present in each of the frames that was taken on that day. I played frames at faster speed and found that the star was moving at very slow speed not noticeable in a single frame .  So now I know why it was red and looks like 3 dots trailing in my final image.

It looks like a star, but I am not sure what it is, tried searching on the net but no luck..
It is possible that it might be a satellite, Asteroid or some space debris..

Let me know in comment if someone knows how to find this kind of things or someone know what it is....

Thanks and Clear Skies......