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M81 & M82, Bode's Galaxies, LRGB, 4 May 2017

Technical card

Resolution: 4593x3477

Dates: May 4, 2017

Frames:
ZWO Blue 31 mm: 12x300" -20C bin 1x1
ZWO Green 31 mm: 12x300" -20C bin 1x1
ZWO Luminance 31 mm: 36x300" -20C bin 1x1
ZWO Red 31 mm: 12x300" -20C bin 1x1

Integration: 6.0 hours

Avg. Moon age: 8.27 days

Avg. Moon phase: 59.42%

Astrometry.net job: 1569059

RA center: 148.925 degrees

DEC center: 69.292 degrees

Pixel scale: 0.860 arcsec/pixel

Orientation: 89.756 degrees

Field radius: 0.688 degrees

Locations: Mapleton Lateral Observatory, Mapleton, Utah, United States

Description

I wasn't going to post this as it is a bit of a work in progress and a bit of an experiment in processing, but I liked the way it turned out so here it is. It is a little late in the season to image these galaxies from my location because they are dropping down into the Provo, Utah light dome. However, weather prevented me from trying them earlier and after doing NGC 4236, which is part of the same group, I couldn't resist. In processing, there was a pretty good light pollution gradient, which I removed with Gradient XTerminator. I know there's a good deal of IFN in this area and what was left after gradient removal kind of looked like that, but I think it was really just an artifact of the gradient removal; I don't think my skies are dark enough to see the IFN. The other problem was that despite a lot of color in the RGB I tended to lose nearly all of it, especially in the stars, when applying the luminance. So I layered the RGB back on top of the processed LRGB as a color burn layer to bring back the star color, using a layer mask to prevent messing up the galaxies in the process. My attempts to bring up the star color in the original LRGB probably created too much color in M82, but here’s what I got. I may have to revise some more, but I’ve spent too much time on this for now.

Date: 4 May 2017
Subject: M81 & M82, Bode’s Galaxies
Scope: AT8IN + High Point Scientific coma corrector
Filters: ZWO 31 mm diameter unmounted L, R, G, B
Mount: EQ-6 (EQMOD 2.000j)+PEC
Guiding: Orion Thin Off-axis Guider + DSI +PHD 2.6.3.2 (Win 10 ASCOM) using predictive PEC algorithm
Camera: ASI1600MM-Cool, -20 °C, Gain 0 Offset 10
Acquisition: Sequence Generator Pro 2.6.0.21
Exposure: 36x300 L, 12x300 R, 12x300 G, 22x300 B
Stacking: Neb 4.1.5, flats & darks, trans+rot align, Nebulosity 1.5σ stack and align.
Processing: StarTools 1.4.327. Stretched and deconvoluted the luminance. Combined RGB in Neb 4 and stretched, color balanced, and sharpened in StarTools. Layered luminance over RGB in Photoshop CC 2014, boosted the vibrance a lot and saturation a little. Applied GradientXTerminator medium/high. Layered RGB on top of the LRGB as a color burn at ~40%, then masked out the galaxies and gaussian blurred the mask. Topped off with AstroFrame

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Author

David Dearden
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M81 & M82, Bode's Galaxies, LRGB, 4 May 2017, David Dearden

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