This observation of M4 was part of an attempt to use Sequence Generator Pro to automatically image multiple targets; M4 was the first target. A nearly full Moon was nearby, creating nasty gradients that made this image even harder to process than a globular cluster usually is. (I remember when I used to regard globulars as easy. No more!) The experiment was not successful (I had some trouble getting the second target, M12, and had to manually intervene, and the 3rd target, M13, was in the field of view but failed to center (plate solve error), causing the sequence to abort after I had retired to bed), but this first image turned out OK despite persistently poor guiding and some nasty color gradients (some of which are still apparent); it’s much better than any of my previous attempts of M4. I kept subframes short to avoid blowing out the core. A few interesting facts I learned from Wikipedia: M4 is one of the closest globulars to Earth, was the first to be resolved into individual stars, and apparently consists of at least 2 stellar populations, suggesting at least 2 distinct star-forming events.
Date: 17-18 Jun 2016
Subject: M4, Cat’s Eye Globular Cluster
Scope: AT8IN+High Point Scientific Coma Corrector
Filter: Baader Planetarium Fringe Killer
Mount: EQ-6 (EQMOD)+PEC
Guiding: Orion ST-80 + Antares 0.5x focal reducer + DSI Ic + PHD 2.6.1.1 (Win 10 ASCOM)
Camera: DSI IIc, no chiller CCD 15 °C
Acquisition: Sequence Generator Pro 2.5.1.14 with Nebulosity 4.0.4 ASCOM camera driver
Exposure: 47x120 s
Stacking: Neb 4, bad pixel map, bias included, 33 flats, match histograms, trans+rot align, Neb 4 40-60%tile stack.
Processing: StarTools 1.4.316: Crop; Wipe; Develop: 74.28%; HDR
ptimize; Color:Scientific, 300% saturation, red bias reduce 1.29; Deconvolute: 3.0 pix; Track: Smoothness 87%, 4.5 pix;. Photoshop CS6 + Astronomy Tools: Levels; layer masked Levels; Gradient Xterminator; Unsharp mask; Increase star color; Astroframe.
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