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Jkulin

Sh2-174 (Valentine Rose)

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I have been enjoying the challenge of capturing and processing planetary nebula, I'm not sure I can do the beauty of them real justice, I learned many new techniques, a good number I need to develop on. This one really was feint.

I had planned to try and get 30 hours of data, but having just added it up to 16 hours I don't think the extra would improve things with my light polluted skies.

I captured this over the 13/14/15/16/20/21 May 2020

Captured with my GSO/Altair 10" RC Truss, Moravian G2-8300, iOptron 120EC, Pegasus focuser and UPB, Chroma 3nm 2" Filters

Chroma Blue 2" unmounted: 8x390" -20C bin 1x1
Chroma Green 2" unmounted: 8x300" -20C bin 1x1
Chroma Ha 3nm: 22x1200" -20C bin 1x1
Chroma OIII 3nm: 19x1200" -20C bin 1x1
Chroma Red 2" unmounted: 8x348" -20C bin 1x1

More details here: - https://www.astrobin.com/lw3re6/

Information on Sh2-174 is scarce, but I have managed to grab exerts that I have put together for some background information: -

Sh2 -174 is a planetary nebula visible in the constellation of Cepheus

A strange nebula in deep space shines like a cosmic rose unveiled just in time for a past Valentine's Day.

It is one of the northernmost planetary nebulae of the celestial vault; it is located about 3 ° north of Alrai , the γ Cephei and is visible in long exposure photos. Its strongly northern declination means that it can be observed almost exclusively from the northern hemisphere , where, on the other hand, it is circumpolar up to the tropical latitudes.

A planetary nebula is one of the last stages of life for most mid-sized stars. Once a star runs out of fuel, it begins to collapse in on itself, creating the clouds of red and blue in the photo.

As the star sheds layers, it forms into a white dwarf — a densely packed star that has the mass of the sun, but is stuffed into a volume about the size of the Earth.

Usually the white dwarf can be found very near the centre of the planetary nebula, but in the case of Sh2-174 it is off to the right.

The white dwarf star appears as a very blue star in the centre of the blue region of gas in the new image. The off-kilter star arrangement is likely the result of interactions between the nebula and its surroundings.

The cloud, catalogued as a generic emission nebula in the sixties , never showed signs of star formation in progress, nor was the ionizing star of its gases known ; during the nineties the hypothesis was put forward that it was a planetary nebula, the central star of which over time slipped out of the gaseous envelope created by itself, since its dimensions were too small to be an H II region , but comparable to those of a normal planetary nebula. This ionizing star would be the white dwarf catalogued as GD 561, placed outside the cloud. The distance, from which the dimensions were derived, was obtained by studying the radial velocity , and is indicated around 300 parsecs (about 980 light years).

Sh2-174_1200.jpg

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Hi John, that sure is one faint, diffuse PN, you did a good job revealing it. I'm not sure that I've seen any images of it previously, so thanks for sharing it and the narrative which is very interesting.

I'm curious about some of your sub exposure lengths, e.g 390s, 348s. Other than for very short exposures I always shoot in 1m intervals above 2m. In particular 348s is a very precise choice, so how did you arrive at that rather than say 360s (6m). I restrict my exposure lengths according to the dark library that I maintain, so typically 30s, 1m, 2m, 5m, 10m, 15m - that's probably me being lazy, but I'm interested in the reasons for your choices.

TIA

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Crikey, that is faint John, and even after 16 hours.  You did well to get what you did though.

Carole 

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7 hours ago, Jkulin said:

A planetary nebula is one of the last stages of life for most mid-sized stars. Once a star runs out of fuel, it begins to collapse in on itself, creating the clouds of red and blue in the photo.

A beautiful image.  The one correction I'd point out is the above.  Planetary Nebula's and White Dwarfs aren't from a star collapsing in on itself.  This results in Neutron stars, pulsars and black holes.

A White Dwarf is in effect the exposed core of the original star.  To very briefly summarise the process.  Any star with a mass of less than about 10 Suns will follow this route.  The star will continue to burn hydrogen in the core until it runs out of fuel.  This continues until the Helium ash core is too large and the pressure at the edge is not sufficient to burn the Hydrogen and the layers above the core contract slightly onto the core.  This raises the pressure/temperature again at the core boundary instigating a another period of hydrogen burning in the 'shell'.  As the burning is in the shell not the core there is less material between to 'shield' the outer layers from the pressure generated at the shell and hence it bloats to a red giant.  The next stages then depend on the mass of the star.  Assuming > approx. solar mass stars eventually the shell will produce enough helium ash that drops into the core that eventually the pressure and temperature rise high enough to start core burning of helium to carbon.  This shuts down shell burning and hence the outer layers shrink again.  Eventually though this shuts down again and the cycle repeats except now you can get shells of hydrogen and helium burning at different stages.  These ever expanding shells are less and less shielded from the outer layers (and helium burning also produces higher temps/pressures).  These higher pressures therefore exert more force on the outer shells that ultimately lead to it blowing off the outer shells.  This becomes the planetary nebula and as there is no longer any material to continue to burn in the shells this burning shuts down and you are left with a White Dwarf, or the core of the now dead star.  

There's also thinking that planetary nebula only form in a binary/multiple system.  The ejection of the outer layers of a star is thought to be a relatively slow process and hence raises questions as to whether enough material can be ejected quick enough to form the planetary nebula.  In a binary system the shell can be ejected a lot quicker as the expanding shell interacts with the companion through conservation laws.  The companion spirals inwards and this 'energy' is transferred into the shell and ejected.

 

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Named after a famous MotoGP rider?     🙂

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1 hour ago, geoflewis said:

I'm curious about some of your sub exposure lengths, e.g 390s, 348s. Other than for very short exposures I always shoot in 1m intervals above 2m. In particular 348s is a very precise choice, so how did you arrive at that rather than say 360s (6m). I restrict my exposure lengths according to the dark library that I maintain, so typically 30s, 1m, 2m, 5m, 10m, 15m - that's probably me being lazy, but I'm interested in the reasons for your choices.

Hi Geof, Thanks for the comments.

Peter Shah put me onto G2V Star Calibration a few years ago and I think it has helped, the video below explains things better, but essentially you find a star that matches a similar colour to our Sun, then take a number of exposures, I usually test between 0.5, 1, 2, 3 secs and then analyse the star for each RGB filter, it needs to be from an un-saturated image , then using the green as the base you compare the red and the blue, I use Pixinsight, that will then allow me to work out a ratio.

Your supposed to do it on a regular basis, some say even each session, I don't get enough clear night to change, but may well do it during the shorter nights, you need to do it for each OTA, Camera, Filter combination.

@carastro Thanks Carole, Yes when I captured the first test sub in SGP I could see nothing and really did wonder if my platesolving had failed, but after checking and stretching the hell out of the test image I could see a faint crescent, this was the first stack of 11 x 1200s of the Ha and OIII, you could see nothing with the RGB: -

image.png.f79748f64023cd180a703cd5c91b832e.png

and this was 3 of the OIII: -

image.png.06678638162c87ab1a8c71776ee89c73.png

@Whirlwind Thanks for the explanation and clarification, I should have checked my info before posting, but it was late and I never assumed it would be incorrect, thanks once again.👍

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Posted (edited)
5 hours ago, Peter Drew said:

Named after a famous MotoGP rider?     🙂

Is that true Peter, I bow to your far superior knowledge!

Edited by Jkulin

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Unlikely I think but the similarity is there.     🙂

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13 minutes ago, Peter Drew said:

Unlikely I think but the similarity is there.     🙂

I think Valentino would not be quite as subtle though 😁

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At least you knew who I was referring to.   🙂

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This is a faint one John, don't think I will try this a bit beyond my capabilities. Well done on bringing this one out.

Bob.

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4 hours ago, Peter Drew said:

At least you knew who I was referring to.   🙂

There's only one, watched him from when he won his first 125GP

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10 minutes ago, bob-c said:

This is a faint one John, don't think I will try this a bit beyond my capabilities. Well done on bringing this one out.

Bob.

Cheers Bob, with better skies I know I could get a lot better, but with Bortle5/6 its the best I could get.

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Great work on what is obviously a very dim object....

 

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