Milky Way from Taurus to Perseus

On this page a 25°×35° wide-field view of the Milky Way in the constellations Taurus, Auriga and Perseus is presented in different color composites. The region south of the galactic plane is full of Molecular clouds.

The 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 Taurus to Perseus 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 Taurus to Perseus 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 Taurus to Perseus 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 Taurus to Perseus region 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.

Taurus Molecular Cloud and Pleiades — The greenish star cluster at the bottom are the Pleiades (M45, greenish here because blue continuum is mapped to green). Distance is about 130pc (430 light-years). The dust which scatters the light from the stars lies about 0.3pc to 0.7pc (1 to 2 light-years) in front of the stars, see [1]. Most of the other reflection nebulae (greenish to blue) belongs to the Taurus Molecular Cloud (the picture covers most of it) which extends within a distance of about 130pc to 200pc (420 to 650 light-years), see [2]. Thus, Pleiades nebula and and Taurus Molecular Cloud may be associated.

California Nebula behind molecular clouds — The reflection nebulae (blue to green) in top left quarter belong to Taurus Molecular Cloud. The dense structure (partly as dark nebula) in bottom left quarter belong to Perseus Molecular cloud which extends within a distance of about 280pc to 320pc (910 ly to 1040 light years, see [3]. Further molecular clouds that are visible in that image where measured in [4].
These molecular clouds partly obscure a huge HII region (red) which brightest part seems to be the California Nebula (NGC 1499). That structure is analyzed in detail at separate page: HII region around California Nebula (NGC 1499).

Spaghetti Nebula (SH2-240, Simeis 147, supernova Remnant) in false colors made from H-Alpha — The Spaghetti Nebula (SH2-240, Simeis 147) is a supernova remnant.

IC 504 and IC 410 in false colors made from H-alpha — HII region containing IC 405 (Flaming Star Nebula, Sh2-229, the lower bright area in the bottom left quarter) and IC 410 (SH2-236, the upper bright area in the bottom left quarter).

Discoveries

The views above show many 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.
- C1-C11, H1 in H-alpha
- C1-C11, H1 in H-alpha and Continuum
For a detailed description of the object H1, also see the HII region around California Nebula (NGC 1499).
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 (all but CA1) 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.
- CA1-CA6 in H-alpha
- CA7-CA12 in H-alpha

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:
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.
- HII regions can be obscured (i.e. their radiation is scattered and/or absorbed) by molecular clouds that lie in front of them. However, emission nebulae do not obscure molecular clouds. This means that a HII region lies farther away if it appears to be hidden by a visible molecular cloud or a dark nebula. If molecular clouds and HII regions look somehow mixed (pinky red), the HII region is either nearer, or the molecular cloud is very thin. The latter aspect is the reason why it is difficult to determine whether an unobscured HII region lies in front of the molecular cloud.
  An improved visualization of the correlation between HII regions and molecular clouds is planned as soon as better data are available, namely NIR data, which better indicate regions that are optically thick for H-alpha emission.
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: 4h36', DEC: 32°

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:	7.4 d
Continuum channels:	5.8 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