IC 1805, Melotte 15

10 March, 2025
mono narrowband nebula

Table of contents

Acquisition Details

IC 1805 SII Hα OIII Red Green Blue
Frames 64 51 75 59 60 60
Exp. Time 300s 300s 300s 30s 30s 30s
Darks master darks          
Total 17h 19m 30s          

Final Masters

Synthetic Luminance
Ha
SHO Combined
RGB Combined

Description

I present to you, the heart of the Heart Nebula: Melotte 15 ❤️. After weeks of cloudy skies, I finally had four clear nights to collect data for this image! This deep exposure combines narrowband data (SHO) with broadband (RGB) star data. The final integration time adds up to 17h 20m, making this my longest project in a while!

Processing was done in PixInsight, focusing on balancing the faint structures while keeping a natural starfield. The RGB stars were captured separately on the last night to prevent stars from becoming purple in the calibration process.

Astrometry Calibration

RA center 02h33m22s.8
DEC Center +61°20′38″
Pixel Scale 1.584 arcsec/pixel
Orientation 338.738 degrees
Field radius 0.885 degrees

Data Processing

Processing was done in PixInsight only. Steps of the process are listed below:

  1. SpectrophotometricFluxCalibration,
  2. DynamicBackgroundExtraction,
  3. BlurXTerminator,
  4. SpectrophotometricColorCalibration,
  5. ColorCalibration on Melotte 15 to match the RGB channels levels,
  6. ChannelCombination for merging a SYnthethic Luminance with RGB data,
  7. MaskedStretch for stretching and keeping the bright parts of the nebula under control,
  8. StarXTerminator for removing stars from the SHO data,
  9. Final stretch with HistogramTransformation,
  10. Creation of a so called ‘synthetic luminance’ by combining the SHO data with SNR as the weighting factor. The synthetic luminance was then combined as the CIELab L channel on the SHO data.
  11. NoiseXTerminator on the image using denoise: 1.00:0.91 (color:luminance), low frequency denoise: 1.00:0.80 (color:luminance), frequency scale: 6.6, and 5 iterations.
  12. Used NarrowbandNormalization to balance the SHO data.
  13. Color correction with CurvesTransformation on the background image
  14. Sharpening with UnsharpMask on the background image
  15. Noise reduction with NoiseXTerminator on the background image
  16. Adding the RGB stars on top of the SHO data with PixelMath to prevent purple stars.
  17. FastRotation for better angle :)
  18. ImageSolver for adding the astrometry data to the image.

Final Result

Please check the image in full resolution on my Astrobin post.