HαHα, More Fun with Hα Images

We got the hoped-for gap in the monsoon clouds this past weekend, so I got more Hα data.

A couple of years ago I was playing with the free planetarium program Stellarium (which I love because it really can mimic what the sky looks like, because it is free, and because it is available for Windows, Mac and Linux), and noticed a patch of nebulosity right on the spine of Cygnus. After a little googling, I realized it was the Tulip Nebula, an emission nebula about 6000 light years away. I tried to image it and was happy to get something, but it was a pretty difficult object for me at the time.  You have to use a little imagination to see a tulip in this (opening toward the bottom left corner). I thought I was also getting Cygnus X-1, the famous X-ray source that is due to a black hole in a binary system, but it's actually right off the left edge of the frame and is nothing to look at anyway. Here's the image:

Date: 14 Aug 2012
Subject: Sh2-101, Tulip Nebula
Scope: AT8IN + 0.5x Antares telereducer
Filter: none
Mount: CG-5 (Synta motors)
Guiding: Orion ST80 + 0.5x Antares telereducer + DSI Ic + PHD
Camera: DSI IIc
Acquisition: Nebulosity 3.1.0
Exposure: 33x240 s
Stacking: Neb 3, bias included, normalize first, trans+rot align, 1.25 SD stack
Processing: crop, color balance, levels & curves, one layer GreyCStoration, unsharp mask another in N3. Layer mask combine the layers, star color enhance, GradientXTerminator, star size reduction, saturation boost all in CS6. 

The Tulip Nebula seemed like it would be a good Hα target because it is mostly Hα emission. It was an easy find after synching on Sadr with the goto dead on. The sky was quite clear and conditions were good save for a bit of gusty wind. I initially had balance issues with the mount and had to rebalance after getting an unsatisfactory PHD2 calibration. The Tulip does show up quite well in Hα (opening toward the upper left corner), with a lot fewer stars and a lot more detail visible in the nebula. I don't think the old RGB data are good enough to bother with combining.

Date: 15 Aug 2014
Subject: SH2-101, Tulip Nebula
Scope: AT8IN+0.5x Antares telereducer
Filter: Baader Planetarium 7 nm H-α
Mount: CG-5 (Synta motors, PicGoto Simplificado)
Guiding: 9x50 Finder/Guider + DSI Ic + PHD 2.3.0 (Win 7 ASCOM)
Camera: DSI IIc chiller at 2.50 A, 14 °C
Acquisition: Nebulosity 3.2.0, no dither
Exposure: 22x600 s
Stacking: Neb 3, bad pixel map, bias included, extract R, normalize, square, trans+rot align, 1.5 SD stack, resize 2x (Bilinear).
Processing: StarTools 1.3.5.279 Crop; Wipe:Color & brightness 75%; Develop 75.54%; HDR:Equalize; Deconvolute 2.7 pix; Life:Moderate; Track RNC 0.01%; CS6 AstronomyTools B&W to Hα; deep space noise reduction; Astro Frame.

That same night I actually started by imaging IC 1275, at one edge of the Lagoon Nebula complex, through the Hα filter, but IC 1275 is pretty close to my southern horizon and I got a late start so I only got about an hour's worth of data before it moved behind my neighbor's trees. This was definitely not enough. So the next night I took more Hα of IC 1275. I got started as soon as it was dark. I synched from λ-Sag and aligned the field of view with the previous night's image. Conditions were excellent: very little wind. I combined the previous night’s data with the new subframes. For now, I'm still converting to false-Hα color, as seen below, but I'm wondering if you can't actually see detail better in these images in greyscale.  I'll have to think about that.

Date: 15, 16 Aug 2014
Subject: IC 1275
Scope: AT8IN+0.5x Antares telereducer
Filter: Baader Planetarium 7 nm H-α
Mount: CG-5 (Synta motors, PicGoto Simplificado)
Guiding: 9x50 Finder/Guider + DSI Ic + PHD 2.3.0 (Win 7 ASCOM)
Camera: DSI IIc chiller at 2.50 A, 16 °C
Acquisition: Nebulosity 3.2.0, no dither
Exposure: 22x600 s
Stacking: Neb 3, bad pixel map, bias included, extract R, normalize, square, trans+rot align, 1.5 SD stack, resize 2x (Catmull-Rom).
Processing: StarTools 1.3.5.279 Crop; Develop 74.99%; HDR:Optimize; Deconvolute 2.7 pix; Track RNC 0.01%; Magic:Shrink 1; CS6 AstronomyTools B&W to Hα dark space; Astro Frame.

Finally, I combined the Hα with an image taken through the UHC-S filter on 22 July 2014. I’m learning more about HαRRGB combining. Interestingly, the scale was slightly different in the Hα and the RGB because in the RGB image I removed the Meade IR cut filter, putting the focal reducer slightly closer to the imaging plane of the camera than it was in the Hα image, where the IR cut filter pushed it away slightly. (I know I don't need the IR cut when using the Hα filter, but I didn't want to change my optical train so I left it in). So I had to translate, rotate, and scale align the Hα and the RGB in Nebulosity. The choice of stars in this alignment is critical; they need to be bright enough to show up in the Hα image, but not bright enough to bloat badly in the RGB. I mainly followed Starizona method 1 for this image, with one major modification: after replacing the original R with HαR, I boosted the red channel using the Photoshop Channel Mixer by 175%. This prevents the image from looking really blue (especially the stars). After that I used the HαR for luminosity, used local contrast enhance, and boosted the saturation a bit. I like the result. The bright Hα emission area at right center looks a lot like a leaping rainbow trout to me, and shows nice contrast with the blue reflection area just below the trout.