Comet C/2023 P1 (Nishimura)
C/2023 P1 (Nishimura) - Click here for full resolution
Comet C/2023 P1 was discovered by Hideo Nishimura on 12 August 2023 using a 200-mm f/3 telephoto lens mounted on a Canon EOS 6D. It is rather unique that an amateur astronomer is discovering a new comet with so many global sky survey programs going on. Upon discovery the comet was magnitude 11.5. Maximum brightness expected is around magnitude 2.5 mid September.
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C/2023 P1 (Nishimura)
Comet
Cancer
09h 21m 49.620s
+24º 25.8’
n.a.
n.a.
Conditions
Observations were made from a holiday location in Duns, Scotland. Observing the Comet was rather challenging. At the time of observation, it would rise above the horizon at around 03:00h in the morning. At 04:00h it was around 8° above the horizon, ready to be photographed. But angular distance from the sun was only 28° and quickly the observation window would close due to the sun rising. Maximum brightness of the comet was expected mid September, but by then it would be even closer to the sun and the observation window would be extremely narrow.
Equipment
As the imaging was done during a period abroad, the only telescope available was the travel setup based on the Takahashi FS-60CB. The 370mm of this scope in combination with the APS-C sized OSC camera turned out to be a perfect fit to capture the full tail of the comet with room to spare. Setup and polar alignment were done the evening before.
Telescope
Mount
Camera
Filters
Guiding
Accessoires
Software
Takahashi FS-60CB, 1.04x multi-flattener (370mm @ f/6.2), PrimaluceLab Esatto 2”
Rainbow Astro RST-135E, Gitzo GT5533S tripod
QHY268C, cooled to -15 ºC
Astronomik L3, 2” mounted, Baader filter drawer
Askar FMA180 with reducer (180mm @ f/4.5), ZWO ASI290MM
Fitlet2, Linux Mint 20.04, Pegasus Powerbox Advance
KStars/Ekos 3.6.3, INDI Library 2.0.0, PixInsight 1.8.9-2
Imaging
Imaging was started at around 04:00h in the morning. But unfortunately the outer edge of a tree was still just in the way of the comet. While waiting for the comet to appear, flats were taken. At around 04:40h the comet appeared and the imaging started. Imaging was continued until well after 05:00h, but everything after 05:00h was pretty much unusable due to too much interference with the rising sun.
Resolution
Focal length
Pixel size
Resolution
Field of View
Rotation
Image center
4500 × 3000 px (13.5 MP)
370 mm @ f/6.2
3.76 µm
2.096 arcsec/px
2º 37’ x 1º 45’
-11.6 degrees
RA: 09h 21m 49.620s
Dec: +24º 25’ 48.30”
Processing
Processing followed essential the same workflow as the second image of C/2022 E3 (ZTF). A stars-only image is prepared by integrating the star-aligned images and follow a basic RGB image workflow, extracting the stars at the end. A comet-only image is prepared by aligning a set of starless images on the comet and process from there. As a final step the stars-only and comet-only image are combined to create the final image.
The stars-only image starts with a regular image integration of star-aligned images. A default DynamicBackgroundExtraction and ColorCalibration are then applied. The white balance values from the color calibration are noted, as they are used later for the comet-only image. The optical quality of the scope made the star field look pretty good, even while the image was severely under sampled at 2 arcsec/px. Still applied a deconvolution using BlurXTerminator, tightening the stars up ever so slightly. A number of iterations of GeneralisedHyperbolicStretch were applied to stretch the stars without clipping the highlights and trying to maintain color as much as possible. StarXTerminator was now applied to create a star-only image. In that image there was still a small artefact present from the comet, which was cloned out of the image using CloneStamp.
The comet-only image starts with running StarXTerminator in batch mode. This creates 17 starless images with only the comet visible. The revised process CometAlign is able to register these starless images on the nucleus of the comet. The 17 individual comet-only images were now combined using a regular ImageIntegration. The resulting image was cropped to the same dimensions as the stars-only image. There was a huge gradient in the background caused by the fact that imaging was done shortly before sunrise. A DynamicBackgroundExtraction was performed which took care of most of it. The color was adjusted using the old ColorCalibration process in manual mode. The white balance factors for each of the three color channels that were obtained from SPCC in the stars-only image were used for that. Unfortunately the background still had some imperfections. Some of the frames had a shadow from a tree still in the corner, which caused some irregular patterns in the background in the final stack. Also the extraction of the stars had left some residual signal that smeared out to little stripes in the integrated image. The clone stamp tool was used to eliminate both imperfections. HistogramTransformation was used to stretch the image. Further enhancement of the tail of the comet was obtained by applying some CurvesTransformations and an AutomaticBackgroundExtraction to eliminate some residual gradients. Noise reduction was the final step to complete the comet-only image. This had to be done very carefully though, as too strong noise reduction would eliminate some of the structure of the comet’s tail.
With a processed stars-only and comet-only image, PixelMath was used to combine them into one image. Only some additional mild noise reduction was applied to get to the final image.
Processing workflow (click to enlarge)
This image has been published on Astrobin.
