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NGC 6946 - Fireworks Galaxy - SN 2017eaw

Contains: NGC 6946

Technical card

Resolution: 6543x4897

Dates: July 11, 2017July 12, 2017

Frames:
Astrodon Gen2E B: 12x600" bin 1x1
Astrodon Gen2E G: 14x600" bin 1x1
Astrodon Gen2E L: 30x600" bin 1x1
Astrodon Gen2E R: 15x600" bin 1x1

Integration: 11.8 hours

Avg. Moon age: 16.91 days

Avg. Moon phase: 94.65%

Astrometry.net job: 1654289

RA center: 308.720 degrees

DEC center: 60.153 degrees

Pixel scale: 0.281 arcsec/pixel

Orientation: 179.901 degrees

Field radius: 0.319 degrees

Locations: Ben's Backyard, Federal Way, WA, United States

Description

This is a LRGB image of NGC 6946, the Fireworks Galaxy. It was given this name due to the unusual number of supernovae observed in this galaxy over many years. This year it did not disappoint as SN 2017eaw has been observed. This is a prominent SN, and I have annotated it in a mosaic compilation version of this image. The galaxy is approximately 22 mly distant, located on the border between Cepheus and Cygnus, with apparent magnitude 9.6 and apparent size 11.5 x 9.5 arcmin.

I am impressed with the relatively bright very red (more orange in my image) star, which I have labeled as 3UCAC301-140830 with magnitude 9.53. Stellarium lists it as mag 10.00 with color index 3.50. Cartes du Ciel lists it as UCAC4-751-062996 at mag 10.51 and color index 5.16. Oddly it was not labeled from the Tycho catalog in my annotation. To my knowledge this is the reddest star I've ever imaged in color.

Acquisition Details - Sequence Generator Pro

Nights of 2017-07-10 (L), -11 through -14 (LRGB)
Federal Way, WA - Ben's Backyard - SW of Septic Tank
L: 30 x 600s at 1x1 binning
R: 15 x 600s at 1x1 binning
G: 14 x 600s at 1x1 binning
B: 12 x 600s at 1x1 binning
First use of Optec FastFocus Secondary Mirror Focusing System

Processing Details - PixInsight

L, R, G, B
ImageCalibration with BIAS, DARK, FLAT
SubframeSelector with weighting of SNRWeight, Eccentricity, FWHM
StarAlignment registration
ImageIntegration
DrizzleIntegration
DynamicCrop and VerticalMirror
DynamicBackgroundExtraction - coarse and fine stages

Synthetic L
ImageIntegration of L, R, B, G for Synthetic L
ImageSolver for later plate solving
Deconvolution
MultiscaleLinearTransform
Stretching with HistogramTransformation - matching RGB stretching in multiple stages
HDRMultiscaleTransform
LinearStretch - gentle black color adjustment

RGB
ChannelCombination of R, G, B
DynamicBackgroundExtraction
Linear Stretch - gentle black color adjustment and matching of L
Stretching with HistogramTransformation - matching L stretching in multiple stages
HDRMultiscaleTransform - matching L
CurvesTransformation - for brightening color contrast
Linear Stretch - another gentle tweak
ChannelExtraction - of L, a, b - L was discarded

LRGB
ChannelCombination of Synthetic L and a and b from RGB
SCNR - mild green neutralization at 25%
CurvesTransformation for final LRGB image

Additional Processing
Inverted L image with reverse stretching to flatten the image out a little bit
Annotation of final L image
Creation of Mosaic image with SN circles (done in ImageJ)

Additional Notes
I am still dealing with alignment issues. You may note that the brighter stars show an elongation. I am still trying to diagnose the issue but have my suspicions this may be due to problems with the focal reducer. The other possibility is non-orthogonality between baffle tube and primary. I've been reluctant to dig into this too deeply, particularly as I wish to be imaging at this time.

Overall I'm pleased with the results despite the alignment issue. I will revisit the ColorCalibration step again. I attempted to use eXcalibrator but ran into issue with it not reading my FIT files. I am still investigation this problem. I also note that the HDRMultiscaleTransform produced interesting results and presented the galaxy with different contrast than I'm used to. I may tweak that a little bit because when all is said and done, I feel some detail got washed out with the brightness and the coloring. This is one time where it actually looks better when you blow it up a bit.

Comments

Author

BenKolt
Like

Revisions

B

Synthetic L Image

C

Inverted Synthetic L Image - Reverse Stretched

D

Annotated Image

E

Mosaic Image Highlighting SN 2017eaw

Sky plot

Sky plot

Histogram

NGC 6946 - Fireworks Galaxy - SN 2017eaw, BenKolt

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