I can be pretty lazy about selecting new targets. I don’t maintain a list of potential targets, though I sometimes have a few interesting objects bouncing around in the back of my mind. More often than not, I finish a target and then scratch my head over what I want to go after next. So, when @Adam Block published his excellent image of NGC 1055, I was finishing up another target and it caught my attention. I love galaxies with interesting features and the extended halo around this galaxy fit the bill. Not only that, it was high in the sky. I have to admit that I feel a little cheap following on Adam’s heals but still, I wondered what I could do with it and as Adam implied, it’s not a trivial target.

NGC 1055 is a nearly edge-on, type SBb spiral galaxy located at a distance of about 52 Mly in the constellation of Cetus. It has an apparent size of 7.6’ x 2. 7’ and an apparent magnitude of 11.4. The extended halo is interesting but so is the detail along the central dust lanes. If you look carefully, you can see evidence of the spiral structure in this extreme edge-on view.

I could see right away that the challenge for my scope would be the two bright stars, HD16835 and HD16786, that have magnitudes of 6.80 and 6.68. These two stars are very close to the galaxy and I knew right away that scattered light and halos from these two stars would be a significant problem. The cropped image below shows the problem. The bight colorful halos and scattered light almost certainly come from strays created by the field flattener in my telescope.

📷 NGC 1055 Full Field.jpgRather than trying to salvage the bright star images, I decided to go for a tighter crop on the galaxy itself. Of course, some of that stray light still extends into the field no matter how tight the crop. So what to do? I tried a few different strategies but settled on simply using the DynamicBackExtraction tool in PI. DBE allows manual selection of sample points so I added a large number of points in the stray light regions. I then use a high order fit (5) to insure a reasonable fit to the odd signal profile and bingo! DBE did a pretty good job of flattening the background. There is a still tiny bit of the glow remaining but it’s minor and within what you’d expect for such bright stars located just outside of the field. I had to do a little hand work to remove the diffraction spikes that extended all the way through the image as well. Overall, I was pretty happy with the result. It’s a tighter crop than I would normally choose but the data supports it—as long as you don’t get overly enthusiastic about pixel peeping. Remember, NGC 1055 is a small object and this is a pretty tight crop of the full field.

Finally, you might wonder why in the world I spent over 82 hours on this thing. First, the seeing was generally pretty poor while I was on this object. I used to sort my data and had I done that, I’m sure that I would have probably tossed out half of the data that I gathered. Now, I just let the weighting factors sort it all out and that means that I list the total amount of data that I took—even though some of it probably contributes very little to the final result. The second reason was that I didn’t have another object on deck and with every passing night the seeing was getting just a little better. So, I hung in there taking more and more data. The best FWHM was about 1.1” and the worst was around 6”. Remember: More data is alway better than less data—and that’s especially true when you are going after something really faint like the halo around this galaxy.

Hope you enjoy it. As always, C&C is always welcome.

John

PS. It was deeply gratifying to see this image receive the IOTD and later a NASA APOD on 11/27/25…Thanksgiving Day! Many thanks to everyone who commented on it. It is a real pleasure to be a part of a community made up of so many world class imagers.