What is going on with these stars?!

[Datalord]

I am processing some data from last night, trying some more bin4 processing, but after stacking I notice this in the subs:

What is going on? I've never seen anything like it before. It is only on the large stars, none of the smaller has it, so I'm guessing it has something to do with well depth?

[vlaiv]

That looks like bloom.

Most CCDs nowadays have ABG - anti blooming gate - which prevents this from happening. It is electrons from pixel well overflowing into adjacent pixels and filling them up as well.

Maybe in bin x4 on your CCD (and I'm assuming these images are from CCD) ABG is not working 100% properly and lets "a few" electrons (enough to fill adjacent pixel well to a certain level) escape?

Btw - here is what bloom looks like:

It is usually a streak in direction of CCD columns (same direction CCD is being read out by shifting electrons from pixel to pixel until it reaches end of a column).

 

[Datalord]

yeah, I figured it had something to do with that. I just thought that only happened when the wells would fill up, but that's clearly not the case here.

[MarkAR]

I've come across the term blooming a few times, nice to know what it actually looks like.

[DaveS]

Seen blooming plenty of times with old-style CCD video cameras. a bright light in the FoV would throw a spike usually in a downward direction.