Outer Limits and a Challenge

I continue to have nice imaging weather with no Moon, so I've been trying to take advantage. Our forecast is for things to turn rainy this afternoon, so imaging will likely be on hiatus for a while.

The night before last I decided to revisit the "Outer Limits" Galaxy, NGC 891, so called because it was featured in the introduction to the 60's TV show. I had imaged it a couple of years ago and got what were at the time excellent results, so I wasn't sure I could improve on that. I had some wind gusts that made me doubt even more, but set up the session, focused as well as I could, and went to bed. After stacking and processing the subframes, I was quite happy with the result. I think it's a clear improvement on what I did two years ago. I masked out the fuzzy edges of the galaxy when I deconvoluted, and that prevented them from getting grainy while I was able to process the dust lane aggressively. Here's the old image, then this year's for comparison. The newer image is sharper, better resolved, has tighter stars, and has better color. It's at a slightly smaller scale because I've stopped using my coma corrector (because it doesn't make any visible difference with the tiny imaging chip I'm using:

Maybe I was lucky, but this was a pretty easy find because after my first try with the Telrad I recognized a 3-star asterism and a 2-star asterism that were in the AT8IN field of view chart in AstroPlanner.  So it was a simple matter to move over and find the galaxy.  Since I knew what I was looking for, it was easy to see in 5 s in the imaging scope.  I can also see it in the guide scope at 1.5 s, again because I know where to look.  I'm still guiding at the 4x setting, and I've also loosened up the worm side-to-side adjustment a bit, reasoning that I don't really care about backlash in RA.  So we'll see how this turns out.  Chiller at 7 V, T=5 °C.  Medium RA dither, settling at 0.5.

Date: 7 Nov 2012

Subject: NGC 891 (Outer Limits Galaxy)

Scope: AT8IN+High Point Scientific coma corrector spaced properly

Filter: None

Mount: CG-5 (Synta motors)

Guiding: Orion ST80 + DSI Ic + PHD 1.13.7

Camera: DSI IIc (1.8 A, 7.0 V  T = 5 °C)

Acquisition: Nebulosity 3.1.2, medium RA dither, settling at 0.5

Exposure: 40/44 x 300 s

Stacking: Neb 3, bad pixel map & flats, bias included, normalize first, trans+rot align, 1.5 SD stack

Processing: Neb 3 crop and autocolor balance.  StarTools 1.3 develop, sharpen, color wipe, color saturation, life, magic (star shrink).  CS6 star color enhance, star shrink, curves.

I was a little hesitant to try NGC 891 because I already have a pretty good image of it from 2 years ago, but I decided to see if I could do better. Intermittent wind gusts, but very clear. Synched on γ1 Andromedae and the PicGoto put NGC 891 in my imaging field of view easily. Chiller at 2.5 A, falling from 18 to 11 °C through the night. I must have timed things just right because I went to bed and my imaging session ended just before the mount bumped, while I got a good night's sleep! I tried a bit more sophisticated deconvolution on this image than usual; I masked so I aggressively deconvoluted the dust lane but didn't touch the outer fringes of the galaxy. I probably should have masked the stars a bit more because I got some ringing, so maybe I'll redo the processing.  

Date: 24 Sep 2014

Subject: NGC 891, Outer Limits Galaxy

Scope: AT8IN

Filter: Baader Fringe Killer

Mount: CG-5 (Synta motors, PicGoto Simplificado)

Guiding: 9x50 Finder/Guider + DSI Ic + PHD 2.3.1 (Win 7 ASCOM)

Camera: DSI IIc chiller at 2.50 A, 18-11 °C

Acquisition: Nebulosity 3.2.1, no dither

Exposure: 62x300 s

Stacking: Neb 3, bad pixel map, bias included, no flats, normalize first, trans+rot align, 1.5 SD stack.

Processing: StarTools 1.3.5.289 Crop; Wipe:Color & brightness 75%; AutoDev with ROI; HDR:Optimize; Color:Scientific, 250%; Deconvolute auto mask+block outer parts of galaxy 3.5 pix; Life:Less is more; Track Grain size 5.9 pix; Magic:Shrink 1 pix. Photoshop CC 2014 + Carboni Astronomy Tools Healing brush; Increase star color; Astro Frame.

Last night I got the itch to try a new object. From Kier's 100 Best Astrophotography Targets, NGC 925 was in the right part of the sky. I'd never attempted it before because Kier says it is dim and that "LRGB methods are almost essential", and that even the luminance data might need to be 2x2 binned. That scared me off in the past with my lowly one-shot color camera, but this year I decided I'd give it a try. Kier is right that this galaxy has very low surface brightness. I initially tried 450 sec subframes, and decided that wasn't long enough, so I went to 600 sec, which is the longest I've ever attempted (and I probably couldn't go much longer with my mount). I also tried adjusting my focuser, thinking that it might be the source of the differential flexure I experience near the meridian (it didn't seem to make any difference though). Finally, I used my UHC-S filter, hoping to knock down the background sky glow. In retrospect, perhaps I should have just gone with the UV-IR cut filter. Anyway, I did get something:

This is one of those "don't image from the suburbs, LRGB methods are essential" type objects that I'm crazy enough to try anyway. I do like going after something new every once in a while, and this is a new object for me. Consider it a “challenge” object. Synched from β Tri and found on the first attempt. Some wind gusts & some scattered clouds, but conditions overall were very good. NGC 925 is quite dim, especially the spiral arms (the core is reasonably bright so not terrible to find at 5 s exposures or so). Chose the UHC-S filter, hoping to improve contrast between the galaxy and background sky glow. Used 600 s exposures for the imaging session. Got fairly good data all the way up to the meridian, and finally the mount bumped about 4 AM, ending the session.

Date: 25 Sep 2014
Subject: NGC 925
Scope: AT8IN
Filter: Baader UHC-S
Mount: CG-5 (Synta motors, PicGoto Simplificado)
Guiding: 9x50 Finder/Guider + DSI Ic + PHD 2.3.1 (Win 7 ASCOM)
Camera: DSI IIc chiller at 2.50 A, 18-11 °C
Acquisition: Nebulosity 3.2.1, no dither
Exposure: 40x600 s
Stacking: Neb 3, bad pixel map, bias included, no flats, OSC neb filter extract, normalize, trans+rot align, 1.5 SD stack.
Processing: StarTools 1.3.5.289 Crop; Wipe:Color & brightness 75%; Develop 87.49%; HDR:Optimize; Color:Scientific, 250%; Life:Moderate; Deconvolute auto mask 2.9 pix; Track Grain size 9.1 pix, Scl 1 100%, Scl 2 100%, Scl 3 96%; Magic:Shrink 1 pix (twice). Photoshop CC 2014 + Carboni Astronomy Tools Healing brush; Deep space noise reduction; Levels (darken); Increase star color; Astro Frame.