On this page a 35°×25° wide-field view of the Milky Way in the constellations Perseus, Camelopardalis and Cassiopeia is presented in different color composites.
This region is full of prominent nebulae.
Click on the images to load a full resolution version with more than 100 megapixels using a JavaScript viewer.
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.
This visualization is a pseudo-color image that uses only H-alpha data (including some red continuum). It reveals significantly 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 shown in the legend.
(The legend represents the compression as 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.
An almost-true color image. Unlike the other images, the stars are not subtracted. This improves the visibility of dark nebulae that absorb the light from the stars behind them.
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.
The three largest emission nebulae (red) are (from top to bottom) SH2-202, SH2-199 (aka Soul Nebula) and SH2-190 (aka Heart Nebula).
The faint loop that extends form the Heart Nebula to the right border of the image is the W4 superbubble, sometimes called W4 chimney because it is assumed that hot gas is transferred from the galactic disc to the halo through structures like this, see Lagrois et al..
Parts of the reflection nebula (white) in the top left corner are named LBN 681, LBN 682, and LBN 684.
Many more nebulae can be explored with the JavaScript viewer (click on the images above) by enabling the annotations, either via the menu or by pressing the key '3'.
The large emission nebula close to the center and partly obscured by dark nebulae is DU 71. The brightest part of the large HII region near the bottom border is SH2-205. (The entire nebula is much larger than SH2-205.)
To explore all these nebulae, use the JavaScript viewer (click on the images above) and enable the annotations, either via the menu or by pressing the key '3'.
Pseudo-color visualization of the Soul Nebula (SH2-199), the Heart Nebula (SH2-190), and the W4 superbubble/chimney made from H-alpha data only.
This version shows more details of the emission nebulae than the image above. Especially, the faint northern part of the W4 superbubble/chimney becomes visible.
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: 3h28m, DEC: 57°
Orientation:
Above:
North is right
JavaScript viewer:
North is up
Scale:
10 arcsec/pixel (in center at maximum resolution)
FOV:
35°×25° (RA×DEC, through center)
Exposure times:
Sum of exposure times of all frames used to calculate the image.
H-alpha:
8.7 d
Continuum channels:
5.3 d
Image processing
All image processing steps are deterministic and none of the algorithms use machine learning (often referred to as “AI”), which tends to generate plausible looking fake details.
The software used can be downloaded here.
The image processing steps were:
Bias correction, dark current subtraction, flatfield correction, noise estimation
Alignment and brightness calibration using stars from reference image
Stacking with outlier rejection, background estimation and optimal weighting based on noise estimation
Star subtraction where star positions and intensities are extracted from continuum images
Denoising and deconvolution of both components (stars and residual)
Dynamic range compression using non-linear high-pass filter
Color composition and tonal curve correction
References
Dominic Lagrois and Gilles Joncas.
On the Dynamical Evolution of H II Regions: An Investigation of the
Ionized Component of W4, A Galactic Chimney Candidate. II. Kinematics and
Dynamics in the Latitude Range 3°; < b <= 7°.
ApJ, 693(1):186–206, March 2009.
[ DOI |
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