Milky Way in Cygnus

On this page a 26°×32° wide-field view of the Milky Way in the constellation Cygnus is presented in different color composites. This region is full of emission nebulae which are partially obscured by dark nebulae near the galactic plane.

All pictures below are downscaled versions. Full resolution images with more than 100 megapixels can be loaded with a Javascript viewer by clicking on the images in the first section. Selected details are shown in the second section. The third section presents some discoveries. Image and instrument data can be found at the end of this page.

Full views

Click on the images to load a full resolution version with more than 100 megapixels using a JavaScript viewer.

Milky Way in Cygnus in H-alpha, blue continuum and red continuum — This image is a false color composite in which H-alpha (including red continuum) is mapped to red, blue continuum (including [OIII] and H-beta emissions) is mapped to green, and red continuum (without H-alpha) is mapped to blue. Reflection nebulae appear green to blue, while HII regions are red. Stars in the continuum channels are partially subtracted to make the faint nebulae visible.

Milky Way in Cygnus in H-alpha — This visualization is a pseudo-color image that only uses the H-alpha data (including some red continuum). It shows many more details of the emission nebulae than the image above.

**Color composition:** After partial star subtraction, the dynamic range was compressed using a non-linear high-pass filter. This results in a compression ratio r, which is used to calculate the color as depicted in the legend. (The legend shows the compression c:=1-r). Blue regions are compressed the least, while white regions are compressed the most. Luminance is determined by the tonal curve-corrected result of the dynamic range compression.

Legend for false color image of Milky Way in Cygnus in H-alpha — This visualization is a pseudo-color image that only uses the H-alpha data (including some red continuum). It shows many more details of the emission nebulae than the image above.

**Color composition:** After partial star subtraction, the dynamic range was compressed using a non-linear high-pass filter. This results in a compression ratio r, which is used to calculate the color as depicted in the legend. (The legend shows the compression c:=1-r). Blue regions are compressed the least, while white regions are compressed the most. Luminance is determined by the tonal curve-corrected result of the dynamic range compression.

Milky Way in Cygnus in RGB — An almost-true color image. Unlike to the other images, the stars are not subtracted. This improves the visibility of dark nebulae that absorb the light from the stars behind.

Due to the limited resolution of continuum channels, the image is only presented at half resolution.

Selected details

Here are a few details that also can be seen using the JavaScript viewer.

SH2-117 (North America Nebula and the Pelican Nebula) in H-alpha and continuum — SH2-117 which is obscured by a band of dark dust. That dark nebula separates the HII region into two parts, the North America Nebula (NGC 7000) and the Pelican Nebula (IC 5070). It is assumed that the ionization source is J205551.27+435224.3 ([1]) which lies behind the dark nebula in a distance of about 2500 light years (Gaia EDR3).

Also see the observations section of an interactive presentation of these objects using the Javascript Viewer.

SH2-117 (North America Nebula and the Pelican Nebula), Crescent Nebula (NGC 6888, SH2-105) and SH2-112 in H-alpha and continuum — A wider view which shows more HII regions. The nebula above NGC 7000 is SH2-119 which is ionized by 68 Cygni (the bright star in the center of the nebula). Its distance according the Gaia EDR3 is about 2200 light years. The nebula in the lower half of the image is just a small part of a huge HII region in background. It is ionized by the Cygnus OB2 association whose average distance is about 5000 light years (Gaia EDR3). Smaller objects that can be seen in this image are the Crescent Nebula (NGC 6888, SH2-105) and SH2-112

Also see the observations section of an interactive presentation of these objects using the Javascript Viewer.

SH2-117 (North America Nebula and the Pelican Nebula), Crescent Nebula (NGC 6888, SH2-105) and SH2-112 in H-alpha — Similar view as above but here as as pseudo-color image using H-alpha data only. That visualization emphasizes the complex structures of the nebulae.

Supernova remnant SH2-103 (Veil Nebula) in H-alpha — The Veil Nebula (SH2-103) is a supernova remnant which exploded about 10,000 to 20,000 light years ago and which lies in a distance of about 2500 light years ([2]).

Observations and discoveries

Click on the following links for presentations of interesting observations using the JavaScript Viewer.

The views above shows some nebulae that cannot be found in catalogs. (The JavaScript Viewer allows identifying objects using catalogs or SIMBAD and defining new objects.) Some (probably not all) of these unexplored nebulae have been collected in the list below. Click on the following links for a presentation.

Objects that are not cataloged by now and objects the are related to them (the list does not contain objects that are only minor extensions of known structures):
- G1-G8, E5 in H-alpha and Continuum
- G1-G5, E5 in H-alpha
Uncataloged HII rings and arcs. Some of these structures may be random, some may be projections of spherical shells (bubbles). Such structures are always circular in the image because stereographic projection was used. The outlines of these structures are completed to circles. It may be helpful to toggle these plots on and off by pressing the '2' key in order to improve the visibility.
- GA1-GA5 in H-alpha
- GA1-GA5 in H-alpha and continuum

Notes

In the JavaScript viewer, the object outlines can be toggled on and off by pressing the '2' key. This can be helpful to make certain structures (e.g. rings) visible.
False color images containing H-alpha and continuum:
- H-alpha is mapped to red, blue continuum is mapped to green, and red continuum (without H-alpha) is mapped to blue.
- Color of molecular clouds and reflection nebulae in the false color image is something between green (bluish in reality) and blue (reddish in reality).
- HII regions (ionized hydrogen) appear red to orange, depending on the amount of OIII (doubly ionized oxygen) detected by the blue continuum filter.
SIMBAD queries for certain object types can be made easily in the JavaScript Viewer by drawing a circle and pressing a shortcut key or via the menu
A repository with the discoveries can also be found on GitHub

Image data

Images where captured with a camera array which is described on the instruments page.

Image data are:

Projection type:

Stereographic

Center position:

RA: 20h36, DEC: 39°

Orientation:

Above:	North is right
JavaScript viewer:	North is up

Scale:

10 arcsec/pixel (in center at maximum resolution)

FOV:

32°×26° (RA×DEC, through center)

Exposure times:

Sum of exposure times of all frames used to calculate the image.

H-alpha:	9.1 d
Continuum channels:	6.0 d

Image processing

All image processing steps are deterministic, i.e. there was no manual retouching or any other kind of non-reproducible adjustment. The software which was used can be downloaded here.

Image processing steps where:

Bias correction, dark current subtraction, flatfield correction
Alignment and brightness calibration using stars from reference image
Stacking with masking unlikely values and background correction
Star subtraction
Denoising and deconvolution both components (stars and residual)
RGB-composition (same factor for stars and residual for the true color composite)
Dynamic range compression using non-linear high-pass filter
Tonal curve correction

References

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