Melotte 15

Melotte 15 – Open Star Cluster in the IC 1805 Nebula
Melotte 15 is a very young star cluster in the IC 1805 nebula, also known as the Heart Nebula. It is comprised of OB stars, approximately 1.5 myr old and is one of the core clusters of the Cas OB6 stellar association.

Surrounding IC 1805 nebula glows bright in the red portion of the visible spectrum as the hydrogen is ionized by ultraviolet light from OB stars. This image captures this H II emission via narrowband filter centered at 656.3 nm wavelength. Clouds of neutral and atomic hydrogen appear as dark streaks and globules.

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Image Data

Telescope: 10″ Aries f/15 Maksutov-Cassegrain on Astro-Physics 900GTO German Equatorial
Accessories: Moravian G1-0300 as Off-Axis Guider, 0.67X Astro-Physics CCD Telecompressor
Focal Length and Resolution: 2692 mm, 0.52″/pixel
Instrument: QSI 532wsg at -20 deg. C
Exposures: 3nm Narrowband [H II]: 6.75 hours [O III]: 6 hours, total: 12.75 hours
Filter(s): Astrodon Narrowband and Tru-Balance E-Series
Exposure Date: September 24 to October 2, 2011
Seeing, FWHM: Not Measured
Processing Software: MaximDL, PixInsight, Photoshop
Image Acquisition Software: MaximDL, TheSky6, CCDAutoPilot, FocusMax, PinPoint

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Object Data

Constellation: Cassiopeia
Type: Open Star Cluster, type III 3 p n
Distance: 7,500 ly
Dimensions: 21′
Magnitude: ~ 6.5 (V)

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Processing Procedure

LRGB Combination (R=[H II], G=[O III], B=[O III])
Histogram Transformation
Split to RGB
ATrousWaveletTransform on G and B channels (K-Sigma Noise Thresholding) to denoise
Generate Star Mask
ATrousWaveletTransform to bring details out (with noise suppression)
Resample to 1600px horizontal (resample mask too)
ATrousWaveletTransform to bring details out (with noise suppression)
Create Grayscale Layer via Desaturate
Overlay Grayscale as Luminosity over RGB Layer
Select stars, expand 5 pixels, feather 5 pixels, invert
Shadows 1%, Width 56%, Radius 300px, Highlights 0%, Midtone Contrast +30
Flatten, Levels (Subjective)
Noise Filter – selective low luminosity (low SNR) parts, Unsharp Mask


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Czech Astrophotography of the Month
8Mag Astrophotographer of the Month
MF Dnes Newspaper



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