M82 | Arp337 - Cigar Galaxy
M82 Cigar Galaxy - Click here for full resolution
Messier 82 (also known as Cigar Galaxy) is a starburst galaxy approximately 12 million light-years away in the constellation Ursa Major. It is the second-largest member of the M81 Group, with the D25 isophotal diameter of 40,800 light-years. It is about five times more luminous than the Milky Way and its central region is about one hundred times more luminous. The starburst activity is thought to have been triggered by interaction with neighbouring galaxy M81. As one of the closest starburst galaxies to Earth, M82 is the prototypical example of this galaxy type.
source: Wikipedia
NGC/IC:
Other Names:
Object:
Constellation:
R.A.:
Dec:
Transit date:
Transit Alt:
NGC 3034
Arp337, Cigar Galaxy
Galaxy
Ursa Major
09h 55m 53s
+69º 40.8’
28 Feb
74º N
Conditions
M82 is visible all year round, with highest altitudes reached in the winter. During five successive sessions M82 was photographed under near new moon conditions. Still not the best of conditions though, as from the Backyard in Groningen, The Netherlands, the Northern Sky is heavily light polluted from the city glow. Occasionally passing high clouds limited imaging time as well. Other than that conditions were good with low humidity and temperatures just above freezing.
Equipment
M82 is a close neighbour of M81 and often they are photographed at the same time. However, an image of M81 was already made at an earlier occasion, so the focus here was on M82 alone. The TOA-130 with ASI1600MM Pro had just around the right FoV, although M81 was still a bit visible in the corner.
Telescope
Mount
Camera
Filters
Guiding
Accessoires
Software
Takahashi TOA-130, 67FL Field Corrector, Sesto Senso
10Micron GM1000HPS, Berlebach Planet
ZWO ASI1600MM Pro, cooled to -25 ºC
1.25” mounted Astrodon LRGB filters
Unguided
Fitlet2, Linux Mint, DIY Power distribution box, Alnitak Flip-Flat, MBox
KStars/Ekos, INDI Library, Mountwizzard4, PixInsight 1.8.9-2
Imaging
M82 is a pretty standard LRGB target. Imaging was done using unity gain setting of 139 for all filters. Exposure times were also kept constant between filters. In total around 6h of RGB and 6h of luminance images were collected.
Resolution
Focal length
Pixel size
Resolution
Field of View
Rotation
Image center
3464 × 2384 px (8.3 MP)
1000 mm @ f/7.7
3.8 µm
0.78 arcsec/px
45' 8.8" x 31' 4.2"
40 degrees
RA: 9º 55’ 56.043”
Dec: +69º 40’ 50.15”
Processing
All images were calibrated using Darks (50) and Flats (25), registered and integrated using the WeightedBatchPreProcessing (WBPP) script in PixInsight to R, G, B and L images respectively. M81 was very visible in the corner as a very bright spot, so this needed to be cropped out. To that purpose, all images were first rotated by 90 degrees and subsequently cropped, just enough to eliminate any visibility of M81.
GraXpert was used to remove gradients from the individual color channels before combining them into an RGB image. It would be possible to combine first and then run GraXpert once. But it is so easy to run GraXpert these days, that it does not take much more time. And gradients of an individual channel must be simpler than gradients of three combined channels. One thing I did was to show the background model. It gives just a bit more peace of mind by understanding of what is happening, rather than just a black box. After deconvolution using BlurXTerminator (BXT), the stars were removed with StarXTerminator (SXT), just so that in stretching all attention can be focused on the galaxy itself. It also allowed to CloneStamp away a little blob in the background, most probably a not fully calibrated out dust-mote. After stretching using GeneralisedHyperbolicStretch (GHS), noise was removed using NoiseXTerminator (NXT). The stars were stretched as well and put back in using Pixelmath. In stretching both the galaxy and the stars, under colour Mode, the option ‘Colour’ was chosen, with a 60-70% RGB Blend. This way the colour of both the galaxy and the stars could be maintained very well without adjusting saturation at some point.
The Luminance image was treated in a very similar way, with cropping away the M81 in the corner, removing the gradient with GraXpert and deconvolving with BXT. Also here the stars were removed for a short while, mostly to accommodate the stretching. After the stretch a bit of extra contrast was added using CurvesTransformation. Stars were stretched separately and put back in.
Luminance was now combined into the RGB image using LRGBCombination, and the resulting outcome looked pretty good. No further corrections were made, other than a quick calibration of the background level to 0.07.
One bright star to the right of the image had a typical diffraction pattern of the ZWO ASI1600MM camera. This has been reported by others several times, and is probably related to either the sensor or the cover-glass used in this camera.
Processing workflow (click to enlarge)
This image has been published on Astrobin.
