What causes these 'squiggles' in stacked data?

[swag72]

I have been working on a target and so far have over 20 hours of Ha and OIII. Today is the first time I have tried to process it and I have found I have little squiggles all over the place. It's showing in both the Ha and OIII data, all of which was taken over about 5 different nights. I can not see anything in each sub.

I stacked them in Maxim (as I always do) using the sigma clip method (whcih I always use) - So can anyone suggest what would cause this?

[RogerTheDodger]

Dithered hot pixels?

[Zakalwe]

Hot pixels. They stay in the smae place in each frame, but the stars might move. When they are stacked, the stacking process aligns the stars and this makes the hot pixels into a trail.

[davew]

They look like dithered hot pixels from two different nights imaging.

Try SD Mask. Works for me

Dave.

[swag72]

Brilliant thanks, I'll have a restack!

[steppenwolf]

Have to agree, they look just like hot pixels to me!

[swag72]

Just looked and I stacked in something different to usual - Doh!!!!

[davew]

I don't know !!

Bottom line...... Have you got rid of the squiggles ?

I still tend to use SD mask anyway. Experiment - get say 10 Ha subs and stack in one then the other and see which looks best. I did it some time ago and Sigma clip wasn't as good.

Dave.

[steppenwolf]

Glad to hear you have a solution but I'm with Dave as I also use SD Mask - 3 passes and 0.5 Sigma Factor

[swag72]

Snap on the settings and squiggles have gone!! Don't know why I changed the setting!'

[davew]

Sorted.

Also credit to Roger, Zakalwe and Steve

Dave.