M63- Sunflower Galaxy
M63 - Sunflower Galaxy. Click here for full resolution image.
The Sunflower galaxy M63, also known as NGC5055, is a spiral galaxy in the constellation of Canes Venatici. The distance to earth is approximately 29.3 million lightyears. It is a member of the M51 group, a group of galaxies which includes the Whirlpool Galaxy M51.
The galaxy is classified as an SAbc galaxy, which means that there is no central bar feature and loosely wound arms. In visible light the individual arms are difficult see, but in infrared, a clear two-arm structure is seen, wrapping symmetrically around the galaxy, extending 13,000 lightyears from the nucleus.
The galaxy is weakly active, but in 1971, a supernova (SN 1971 I) was observed that reached a magnitude of 11.8.
Planning
Object
Visual Magnitude: 8.52
Apparent size: 11.8 x 7.2 arcmin
R.A.: 13h 16m 39.90s
Dec.: 41º 55’ 47.4”
Conditions
Astr. night: 22:27
Astr. dawn: 04:42
Moon: 6 %
Moon set: 22:34
Humidity: 67-77 %
Pressure: 1010-1018 hPa
The sunflower galaxy is a typical galaxy to observe during ‘Galaxy season’, more or less in spring-time. While the galaxy is not particularly bright, it is decent in size and has a nice structure to it, making it a rewarding galaxy to photograph.
Images were captured during two session, on April 7 and 9, 2019, respectively. While close together, these were two separate sessions with equipment being installed and dismantled each time. The moon was pretty much absent during these nights, so perfect conditions for broadband imaging.
Capturing
The galaxy is not a very active galaxy, so adding H-alpha data to the dataset to highlight star formation would probably not have much effect. The galaxy was photographed as an LRGB-image. Because the galaxy is a relatively dim object, slightly longer exposure times were chosen. Luminance was shot at 180s per frame and the color channels were shot at a longer exposure of 300s per frame to compensate for the smaller bandwidth.
Framing was kept rather simple, with just the galaxy right in the middle of the frame. The TOA-130 + ASI1600 combination had more than enough field of view to adjust rotation during processing.
There was quite a bit of wind especially during the second night. While normally the flip-flat would be installed, it was taken off this time, as it caught too much wind. After it was taken off, the telescope kept stable much better.
In total over the two nights about 9h of usable exposures was acquired. The total observation time was somewhat longer, but several frames got lost due to user error in programming the schedule and a new ‘Remember job progress’ setting in the Ekos scheduler, which was not set properly. In the end about 50% of frames was luminance and 50% of frames was colour, as planned.
Technical details
Telescope
Mount
Camera
Sensor Temp.
Takahashi TOA-130 + 35 flattener
10Micron GM1000HPS
ZWO ASI1600MM Pro
-25ºC
Exposures
Luminance
Red
Green
Blue
Total Exposure
88 x 180s @ Gain 139/21
17 x 300s @ Gain 139/21
19 x 300s @ Gain 139/21
19 x 300s @ Gain 139/21
9.0h
Processing
All frames were calibrated with Bias (100), Dark (50) and Flat (25) frames, registered and stacked using the BatchPreprocessing script. Looking at the stacked channels, it seemed that rotating the image by 90 degrees clockwise would give a more pleasing image. This meant that a crop had to be applied, loosing about 50% of the total frame. This was no problem as the field of view was large enough to still have a very good overview of the galaxy.
Noise was then reduced in all channels using the MureDenoise script. While the results were good, the use of the MureDenoise tool on earlier objects had seen more significant effects. The luminance channel was now deconvoluted to sharpen up the stars and bring out just a little bit more detail in the galaxy. On this particular image the deconvolution had quite a significant effect on the details in the spiral arms of the galaxy. Deconvolution is not always easy to execute and results can vary quite a bit. But for this image it really had a significant positive effect on the final result. Below are detailed images of the galaxy before and after deconvolution.
The colour channels were combined and followed a separate track of linear processing. With the crop being applied earlier, there was not much of a background gradient, but still out of routine a DynamicBackgroundExtrection was applied, followed by a PhotometricColorCorrection. The resulting image had still quite a bit of green in the background which was removed by SCNR.
The RGB and Luminance image were stretched to the non-linear state by repeatedly applying a series of HistogramTransformations. Next the channels were combined by applying the Luminance channel to the RGB image using LRGB Combination. This is always a very rewarding moment. Suddenly the image starts to speak and shows so much detail and rich colours. From here it is important to apply only very subtle effects. It is very easy to over-cook the image. One example of that is LocalHistogramEqualization. A powerful tool to bring out detail in an image, but also a tool that can quickly ruin the image. It was applied here with kernel radius of 120, contrast limit of 1.5 and an amount of 0.5. With these settings the spiral arms got a little more contrast against a darker background, revealing overall more detail. This was further enhanced a tiny bit using DarkStructureEnhance. Some high frequency noise was removed using TGVDenoise. Inevitably it makes the image a bit softer which was then restored again by sharpening using MultiscaleLinearTransform. Final touches were applied using CurvesTransformation and Saturation to darken the background and bring out a tiny bit more pop in the colours of the galaxy.
This image has been published on Astrobin and received Top Pick status.
