M67 Open Cluster

m67Click image for full size version

February 14, 2017; Published in June 2017 Sky & Telescope

June 2017 Sky & Telescope

There are two nice open clusters in Cancer. M67, shown here, is more compact and, to me, appears richer than, M44 in images.  But M44 is usually the “showpiece object” that beginners turn to in this part of the sky.  M67’s stars show lots of colour variation. I find it challenging to tell where the cluster actually ends and “background star field” begins.  

M67 is thought to be about 4 billion years old, implying that its stars are younger than the Sun.  The cluster’s mass is about 1080 times that of the Sun. It has a radius of about 10 light years and appears to be about the size of the full Moon on the sky. Its distance from us is around 2,750 light years. There are many small galaxies visible in this image. I have posted an annotated image to show some of them.

Tekkies:
SBIG STL-11000M camera, Baader LRGB filters, 10″ f/3.6 ASA astrograph, MI-250 mount. Guided with internal guider in main camera. Focused with FocusMax. Acquistion, guiding and calibrationwith Maxim-DL. Registration, integration and all processing with PixInsight. Shot from my SkyShed in Guelph, Ontario.  No moon, average transparency and seeing.  Imaged in February, 2012.

4x3m and 2x5m R, 5x3m G, 5x3m B, 4x5m L unbinned frames (total=72m).

RGB
Creation and cleanup:  L, R, G and B masters were cropped and processed separately with DBE. R, G and B were combined to make an RGB image which was processed with ColorCalibration.

Linear Noise Reduction:  MultiscaleLinearTransform was used to reduce noise in the background areas. A Linear mask and the following Layer settings for threshold and strength were used: Layer 1: 3.0, 0.75   Layer 2: 2.5, 0.62  Layer 3: 2.0, 0.5  Layer 4: 0.5, 0.2, Layer 5: 0.5, 0.1.

Stretching:  HistogramTransformation was applied to make a pleasing yet bright image.

Synthetic Luminance:
Creation and cleanup of SynthL: The cleaned up L, R, G and B masters were combined using the ImageIntegration tool (average, additive with scaling, noise evaluation, iterative K-sigma / biweight midvariance, no pixel rejection).

Linear Noise Reduction:  MultiscaleLinearTransform was used to reduce noise in the background areas. A Linear mask and the following Layer settings for threshold and strength were used: Layer 1: 3.0, 0.75   Layer 2: 2.5, 0.62  Layer 3: 2.0, 0.5  Layer 4: 0.5, 0.2, Layer 5: 0.5, 0.1.

Stretching: HistogramTransformation was applied to make a pleasing yet bright image. 

Nonlinear Noise Reduction: TGVDenoise was applied with a mask to protect stars. The image was re-stretched to reset the black point. 

Combining SynthL with RGB:
The luminance channel of the RGB image was applied with LRGBCombine to make a SynthLRGB image. Colour noise reduction was used at default settings

Final Processing of SynthLRGB:
Background and star brightness, contrast and saturation were adjusted in several iterations using Curves with masks as required.

Image scale is about 2.1 arc sec per pixel.

Share on Facebook68Tweet about this on TwitterShare on Google+0Pin on Pinterest0
By | 2017-04-17T09:34:33+00:00 February 14th, 2017|Open Clusters|1 Comment

About the Author:

An avid astrophotographer who has been hunting deep sky treasures with his camera and telescope for many years now. He enjoys sharing the amazing cosmos with others.

One Comment

  1. Christopher February 14, 2017 at 9:06 pm - Reply

    Very nice Ron. Thank you for the processing explanation.

Leave A Comment