Astr384 Photography Projects, Spring 2004

M57 Ring Nebula, Andrew Vanden Heuvel

Image Analysis

There are a number of things one can learn by carefully (or even casually) examining this image. Most noticeable is the distinct coloration. The red and green regions are clearly distinct from one another (albeit overlapping in some places). This is highly suggestive of both the nature of the formation of the object as well as the composition of the material that constitutes it. The ordering of layers suggests the stratification of the stellar interior prior to the dramatic creation of the object.
The haze within the interior of the ring suggests that the ‘ring’ is likely not a two-dimensional ring that we happen to see directly face on, but rather that it is a three-dimensional sphere of which we are seeing a 2D projection on the sky. We see only wispiness when looking through the center of the hollow sphere, but when we look to the edges, we see much more material since a single line of sight will pass through many more layers of material at the edges of the sphere (much like how a soap bubble is transparent in the center, yet visible at the edges). Finally, the bright blue star in the center is indicative of the ultimate fate of a star after it has shed its outer layers in the final throws of fusion. It’s hot.

One aside: the image is cropped with the Ring Nebula offset. This reveals the fuzzy object in the upper right corner, the barred spiral galaxy IC 1296. Look for the faint spiral arms protruding from the top and bottom of the core and winding counterclockwise. Although near to the Ring nebula in direction, at 71 million light years distant, it is at least 36,000 further.

Image Processing

The Images: The images used to create this image were taken on three separate nights, April 14, April 27, and May 1, 2004. Images were taken using each of the b, v, and r filters. All images were five minute long exposures.

Calibration: All images were individually dark subtracted and flat-fielded using MaxIm 4’s group calibration feature. All relevant biases, darks, and flats were averaged using the ‘sigma clip’ algorithm in order to create a master bias, dark, and flat. These were then applied to each raw image.

Averaging: All of the reduced images of a given filter were then aligned with each other and averaged together again using the ‘sigma clip’ averaging algorithm. At this point in the processing, we had three reduced averaged images--one for blue, visual, and red.

Digital Development: On each of the three images, I ran digital development using the following settings:
Filter Type: FFT Low-Pass
FFT Hardness: Mild
DDP parameters: Default
This made use of the high signal to noise by greatly improving the detailed structure within the ring as well as the dynamic range of the image--it brought out many more faint stars and made both bright and faint features on the Ring Nebula simultaneously visible.

Color Combination: Next, I used the Combine Color feature to put all three images together into a single color image. I found that by using an LRGB conversion type and using the red image for both the luminance and red, I was able to get a highly detailed image while maintaining what seems like a natural coloration of the object. I set the color ratios to be Red: 1, Green: 1, Blue: 1.2.

Unsharp Mask: The last step was to unsharp mask the completed color image. I used an FFT-LowPass filter with a Hardness of Hard.

I then cropped and converted my image to a JPEG.