One of the many treasures of Cepheus, one of the most beautiful planetary nebulae - DeHt 5 / PK 111 + 11.1 along with the nearby supernova remnant - SNR 110.3 + 11.3.

I collected almost twice as much Hydrogen Alpha as I planned because I wanted to show the SNR reasonably well- it is a very dim structure. Also, I desired to show as much of the DeHt5 tail, which is even dimer, as possible. Furthermore, I also collected twice as much Oxygen III as I planned. For the frame to be aesthetically pleasing, the oxygen heart of the nebula had to be most conspicuous.

Inverted Ha monochrome:




Inverted OIII Monochrome (there are traces of OIII in the SNR, but extremely faint):



A. Workflow

1. DynamicCrop,
2. BlurXterminator,
3.StarXterminator,
4. DynamicBackgroundExtraction,

I separated the files for color and L.LUM:

1. NoiseXterminator , gently,
2. Combination of Ha and OIII in Pixelmath (a*(1-(1- OIII)* (1-HA)) + (1-a)*HA), "a" value selected iteratively,
3. EZSoftStretch to pre-stretch, finished with GHS.

RGB:

1. NoiseXterminator, a solid dose,
2. Assembling two different color variants in PixelMath and mixing them to taste,
3. Stretching Ha and OIII using HistogramTransformation with settings as in STF.

LRGB:

1. LRGCombination , " Lightness " and " Saturation " sliders adjusted accordingly,
Endless work on colors and contrast, both in Pix and PS, using various masks and tools…

Stars:

1. Preparing two versions in PIX, using BlurXterminator - one with the "halo" parameter at 0.00, the other at maximum.
2. SPCC,
3. Stretched with GHS,
4.StarXterminator,
5. Both versions uploaded to PS, corrected colors, saturation, cosmetics.
6. Mixing both versions by applying the version with max halo to the version without halo with the "lighten" function and adjusting the opacity with the slider.


B. Life cycle of the DeHt 5 nebula


1. Central star, properties, location, orbit

Central star is a white dwarf- WD 2218+706. It is located roughly in the center of the Cepheus "triangle", at a distance of approximately 1,200 light-years, in close proximity to VDB 152.
Spectral type - uncommon and mysterious DAe - further reading: https://arxiv.org/pdf/2307.09186.pdf
Temperature: ~76500 K
Mass: ~0.57 M ⊙
The star, and therefore the main mass of the nebula, moves at a speed of ~59 km/s through the interstellar medium.
The star's orbit is in the so-called thin disk of the Milky Way, thus very close to the galactic plane plane.

/// Source: Faraday Rotation in the Tail of the Planetary Nebula DeHt 5, RR Ransom, R. Kothes , M. Wolleben , TL Landecker , https://doi.org/10.48550/arXiv.1009.3284 ///

2. Interaction of the star with the interstellar medium

The star and nebula are moving at a speed of ~59 km/s relative to the interstellar medium (ISM). This results in a bow-shock structure in front of the nebula. We don't see anything resembling a well-defined bow-shock like in HFG-1 here, because DeHt5 is moving towards us - we see it a little from the front, a little to the side. It's a very old (evolved) nebula. Its structure has been significantly disturbed because of the interactions with ISM.

A star that once resembled our Sun was finishing the penultimate stage of its life cycle- so called AGB star- star on the asymptotic giant branch of the Hertzsprung -Russell diagram. The interaction with the ISM began then- perhaps ~200-250 thousand years ago, before the star turned into a WD and the PN appeared.

3. Two tails – two phases in the life of the nebula and its central star

3.1 AGB phase

After exhausting the hydrogen fuel in the core, stars similar in mass to our Sun swell, become red giants and increase their brightness many times over.
The end of the AGB phase is characterized by a significant loss of mass from the star in the form of a stellar wind moving with moderate velocity but scattering prodigious mass into space.
This wind at the end of the AGB phase is likely the source of the first of the two tails of the nebula, when the lost mass entered into the first currently observable interactions with the ISM.
For many PNs, this phase results in the formation of spatially extensive halos of very low brightness and/or scattered tails. A good example is Sh2-200 and its huge hydrogen halo.

3.2 WD & PN phase

Marking the end of the AGB phase, the star sheds its outer shell - this is a large amount of hot, ionized, fast-moving stellar wind - the actual PN. What remains is an extremely compressed, hot and bright white dwarf that emits intense UV radiation (sometimes even X-rays, as in the case of the central star MWP 1), ionizing nearby material. WD is composed of degenerate matter, held from further collapse by electron degeneracy pressure.

In most cases, the PN is much denser than the surrounding ISM and can move quickly - as in this case. Such an object leaves a trail behind it - a tail, which may consist of disturbed material from the ISM, stellar wind remnants from the AGB phase and also material from the PN itself.

Tail’s shape, length and durability depend on many factors - the speed of the PN in the ISM, the density of the ISM, magnetic fields, the density of the PN itself, etc.

The evolution of PN and the matter it encounters along the way may look, for example, like this:



This is a simulation for an object moving at a speed of 50 km/s relative to the ISM. Of course, this does not completely match DeHt5, which is older than 30,000 years (panel d) and moves faster. But it shows the disruption and breakdown of the original structure and the formation of the tail.

/// Source : The interaction of planetary nebulae and their asymptotic giant branch progenitors with the interstellar medium, CJ Wareing,1,2, Albert A. Zijlstra1, and TJ O'Brien1, https://doi.org/10.1111/j.1365- 2966.2007.12459.x  ///

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To understand how the virtually invisible tails of the nebula were detected and why it is important from a scientific point of view - as an example of the interaction of PNe with magnetic fields in the ISM, I must mention two issues - magnetic fields in the ISM and the Faraday effect. Are you still on board? Let’s continue:
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4. Magnetic fields in the interstellar medium

The ISM is the matter and radiation that fills the space between the stars in the galaxy. It's not nebulae, or not only nebulae. The vacuum is not that empty, although the density of matter in many places in the galaxy is lower than in the best vacuum chambers. There are neutral and ionized atoms, dust, cosmic radiation, but also magnetic fields that are detectable both on smaller and larger scales - the so-called galactic magnetic fields.

Planetary nebulae moving in relation to these magnetic fields and the ISM will interact with them.

This may result in changes in the structure of the nebula, taking the form of stripes/waves, such as in Sh2-216, Sh2-200, PuWe-1, because the presence of a magnetic field affects the movement of ionized gas.

But the ionized clump of matter also affects the magnetic field lines, distorting them, as DeHt5 illustrates. And this phenomenon allows us to detect its normally invisible tails.

/// Source: Theory of the Interaction of Planetary Nebulae with the Interstellar Medium, Ruth Dgani , https://doi.org/10.48550/arXiv.astro-ph/0001004  ///

5. Faraday effect (magneto-optic Faraday effect)

The effect involves the rotation of the plane of polarization of linearly polarized light as it passes through a magnetic field.

Visually, it works like this:



β – twist angle,
B – magnetic induction in the direction of light propagation,
d – length at which light interacts with the magnetic field,
Verdet's constant - does not apply in the case of the interstellar medium; what matters is the orientation of the fields and the density of free electrons, which determine the intensity of the effect.

/// Source: https://en.wikipedia.org/wiki/Faraday_effect  ///

The Faraday effect is an important tool for astronomers. Polarimetric measurements, which allow visualizing the presence and parameters of a magnetic field by examining the shifting polarization of light, are very sensitive. Definitely more sensitive than simple optical measurements - they allow us to show the presence of structures that are extremely difficult to discover optically, as long as they are associated with magnetic fields.

They also allow us to visualize the "thin" tail of DeHt5, which is nigh-invisible, does not fit in my image, and was probalby formed during the AGB phase of the star's life.

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6. PN and its two tails - structure visualized using the Faraday effect.

The source of all the following information and illustrations is this brilliant publication:

/// FARADAY ROTATION IN THE TAIL OF THE PLANETARY NEBULA DeHt 5, R. R. Ransom, R. Kothes , M. Wolleben and T. L. Landecker , https://doi.org/10.48550/arXiv.1009.3284  ///



In the center of the circle is the star WD2218+706 - the central star of the nebula.
The circle covers most of the nebula's visible surface.
The arrow shows the trajectory of the star's movement, and therefore the nebula's, from our point of view. The length of the arrow represents the distance the star will travel over the next ~50,000 years.
The dashed lines show the inaccuracy of the estimated trajectory.
The orientation of the illustration is similar to my photo.



Panel (a) illustrates the degree of polarization and panel (b) the polarization angle.
Orientation as above.

While in my photo you can see part of the "thick tail", the "thin tail" is optically indistinguishable from the background and extends beyond the frame.
However, polarimetric measurements show a changed magnetic field that modifies the polarization of light - that is why these structures can be detected using the technique.
The arrow shows the star's trajectory over the next 200-250 thousand years from our point of view.

To conclude the topic of the spatial arrangement of the nebula, tails and the magnetic field, the last illustration follows, showing the spatial location of the nebula, its tails, the magnetic field in the medium and us - the observer:



A word of explanation - it is as if you were looking not from Earth, but "from above" at the system of the nebula, its tail, and the Earth.
Here you can see how the nebula moving in relation to the ISM and the magnetic field permeating it interacts with it. And why polarimetric measurements show what they show.

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7. SNR 110.3+11.3


Since the main subject of the photo is the PN and there is little information about the supernova remnant in the frame- the object is mostly unexplored, I will only mention that it is a small fragment of a huge structure catalogued as SNR 110.3 + 11.3, which covers a large part of Cepheus and is located approx . 1200 light years from Earth.These are filaments and membranes typical of SNR, like Veil, but much dimer.

Interestingly, I was able to record trace amounts of OIII that coincide with Ha in the SNR. However, the weak OIII signal does not allow it to be shown in the color composite image, despite 20 hours of exposure.

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Thanks in advance for any comments - both positive and negative.