Milky Way from Perseus to Cassiopeia

On this page a 35°×25° wide-field view of the Milky Way in constellations Perseus, Camelopardalis and Cassiopeia is presented in different color composites. This region is full of known and unknown nebulae.

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 from Perseus to Cassiopeia 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 from Perseus to Cassiopeia 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 from Perseus to Cassiopeia 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 from Perseus to Cassiopeia 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.

Man emission nebulae (including SH2-202, SH2-199 and SH2-190) and the reflection nebulae LBN 681, LBN 682 and LBN 684 SH2-131 — 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 [1]. 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'.

Many emission nebulae (including DU 71 and SH2-205) — 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'.

SH2-199 (Soul Nebula) and SH2-190 (Heart Nebula) and W4 superbubble/chimney in H-alpha — 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.

Discoveries

The views above show many HII regions 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.

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: 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. There was no manual retouching or any other kind of non-reproducible adjustment. No AI was used; the images shown here are the results of deterministic calculations and not hallucinations of an AI.

Image processing steps where:

Bias and dark current subtraction, flatfield correction, noise estimation
Alignment and brightness calibration using stars
Stacking with masking unlikely values and background correction
Extracting stars from the emission line images using information from continuum images
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

[1]: 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 ]

This work made use of the SIMBAD database, maintained by CDS, Strasbourg, France, and the Gaia public archive.