APOD: Planetary Nebula Abell 36 (2014 May 30)

[APOD Robot]

Planetary Nebula Abell 36

Explanation: The gorgeous, gaseous shroud of a dying sunlike star, planetary nebula Abell 36 lies a mere 800 light-years away in the constellation of Virgo. At that distance it spans over 1.5 light-years in this sharp telescopic view. Shrugging off its outer layers, the nebula's central star is contracting and becoming hotter, evolving towards a final white dwarf phase. In fact, in Abell 36, the central star is estimated to have a surface temperature of over 73,000 K, compared to the Sun's present 6,000 K temperature. As a result, the intensely hot star is much brighter in ultraviolet light, compared to its visual appearance here. The invisible ultraviolet light ionizes hydrogen and oxygen atoms in the nebula and ultimately powers the beautiful visible light glow.

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[geckzilla]

I get the feeling that the older planetary nebulas are fuzzy like this one. If there was some way to measure the nebulousness of a planetary nebula it might be easier to measure the dimensions and distance of the nebula based on how old it is. Something like how tree rings can be read to tell how old a tree is.

[Boomer12k]

Such a beautiful end....yet maybe supplying new and heavier elements for another system....

:---{===] *

[neufer]

I get the feeling that the older planetary nebulas are fuzzy like this one. If there was some way to measure the nebulousness of a planetary nebula it might be easier to measure the dimensions and distance of the nebula based on how old it is. Something like how tree rings can be read to tell how old a tree is.

• Probably more complicated than that.

Perhaps a middle aged matter bounded nebula with a very hot massive central star:

<<Nebulae may be described as matter bounded or radiation bounded. In the former case, there is not enough matter in the nebula to absorb all the UV photons emitted by the star, and the visible nebula is fully ionized. In the latter case, there are not enough UV photons being emitted by the central star to ionize all the surrounding gas, and an ionization front propagates outward into the circumstellar envelope of neutral atoms.

It has been determined that the more massive stars produce more irregularly shaped nebulae.>>

<<Abell 36 is a planetary nebula in the constellation of Virgo... estimated to [have an] age ranging from 4,700 to 8,000 years. [The planetary nebula phase is relatively short-lived, perhaps only 10,000 years.] There is a very faint, extended, ionizing halo stretching nearly 5 degrees that was recently discovered. It is much larger than image shown above, and too faint to be seen with this equipment and exposure time.

Stars greater than 8 solar masses are likely to end their lives in a supernova explosion, like the Veil or Vela nebulae. Smaller stars, down to about 0.8 solar masses, will likely produce a planetary nebula - an ionized and hence, visible cloud of gas surrounding a small, hot star. The star, after spending most of its life on the main branch, runs out of hydrogen to burn in its core, which becomes incredibly hot due to gravitational compression. The star becomes a huge red giant as the outer layers expand and cool. Helium fusion tends to go in pulses, building up until they become powerful enough the eject a large part of the star's atmosphere into the interstellar medium. The ejected material forms a cloud around the now exposed, hot core. As more of the core is exposed and the temperature reach 30,000 K, enough ultraviolet photons become available to ionize the ejected cloud, making it glow and visible to our telescopes and instruments. The cloud becomes the planetary nebula that we see. Our narrowband filters, such as H-alpha, OIII, NII and He detect this glow and highlight different structures.

In the final stages the star heats up and then cools down to the point where it no longer can produce enough ultraviolet radiation to ionize the increasingly distant cloud of ejected gas. The star becomes a white dwarf and the nebula disappears from sight.>>

More at http://www.astrodonimaging.com/gallery/ ... ?imgID=241

[Ironwood]

"At that distance it spans over 1.5 light years...". That doesn't make sense. Wouldn't it span 1.5 light years no matter how far away it was? Did they mean degrees instead of light years? Distance does affect angular size.

[Chris Peterson]

"At that distance it spans over 1.5 light years...". That doesn't make sense. Wouldn't it span 1.5 light years no matter how far away it was? Did they mean degrees instead of light years? Distance does affect angular size.

My reading of this is that at an assumed distance of 800 ly, its angular size implies a span of 1.5 ly. That is, our estimate of actual size is tied to our estimate of distance.

[LocalColor]

Such a beautiful end....yet maybe supplying new and heavier elements for another system....

:---{===] *

My thoughts too.

[geckzilla]

"At that distance it spans over 1.5 light years...". That doesn't make sense. Wouldn't it span 1.5 light years no matter how far away it was? Did they mean degrees instead of light years? Distance does affect angular size.

Planetary nebulas are hard to accurately measure distance to. Since there is some uncertainty about it and distances to many things in the Universe it makes sense that possibility of error would be reflected in the wording of things even if it's not explicitly stated.

[geckzilla]

I get the feeling that the older planetary nebulas are fuzzy like this one. If there was some way to measure the nebulousness of a planetary nebula it might be easier to measure the dimensions and distance of the nebula based on how old it is. Something like how tree rings can be read to tell how old a tree is.

• Probably more complicated than that.

Yeah, with PNe that is nearly always the case. Maybe with those perfectly spherical ones.

[starsurfer]

I get the feeling that the older planetary nebulas are fuzzy like this one. If there was some way to measure the nebulousness of a planetary nebula it might be easier to measure the dimensions and distance of the nebula based on how old it is. Something like how tree rings can be read to tell how old a tree is.

You're right that older planetary nebulae are more diffuse and featureless whilst younger planetary nebulae exhibit many internal structures such as jets and FLIERs. Distances to planetary nebulae are difficult to determine but I think it is easier for planetary nebulae with a binary central star.

Also for anyone wondering what the grayish haze in the rest of the image is, this is an imaging artefact.

[Psnarf]

Doctor Adam Block created that image with a 32" telescope? LRGB = 7:3:3:3 I don't know what that means. The grayish haze is probably the result of high-altitude dust. Tucson had some rip-snorting wind storms blowing in from Texas last month, 50mph+ gusts and all. Could be high altitude smoke from the San Diego-area fires? Trying to imagine what would be an "Astrophotography with Adam Block" experience. Pretty sure most of the work is in post-processing. Before that, aim the telescope, set it to auto-track, open the CCD shutter, then play a couple of hands of whist or a round of cribbage? I jest. Dr. Block has posted enough images herein to be declared an expert at what he does. All I can do is gaze in awe at his images. Lessee, millions of stars in a globular cluster, the many background galaxies in his images,... I have rather poor brains for playing count-the-stars.

[Boomer12k]

Why....the purpley and blue colors???

:---[===] *

[Chris Peterson]

Doctor Adam Block created that image with a 32" telescope? LRGB = 7:3:3:3 I don't know what that means.

It means that the luminance channel exposure time was 7 units (hours, perhaps), and the RGB channel exposures were 3 units each.

The grayish haze is probably the result of high-altitude dust.

Probably not. At a dark site, haze, dust, fog all make the sky darker, not lighter.

The background is NOT an artifact. It is real. The sky does not produce zero signal between light emitting objects. The upper atmosphere glows, and depending on the object, there may be interstellar dust adding signal, as well.

In processing, we typically set the black point just below the sky background level. That results in the background not being clipped to black, but just a touch above that. We want to just barely see the noise floor. In today's image, the background has a count of around 10, and is almost completely neutral, which demonstrates good processing.

[ta152h0]

whoa, 1.5 LY across. That is big. It only takes about 16 light hours to cross the solar system and we all know how big that is.

[BDanielMayfield]

It would give me the blues except for the fact that it has some nice purple in it.

[Ann]

I'm just thinking that this nebula shouldn't be blue at all. It must be very OIII-rich, and Chris has just taught me that OIII is really this color.

Ann

[geckzilla]

Unless I misread it or it's mislabeled, an OIII filter wasn't used to produce the image. It's just a wideband RGB picture.

[Ann]

So where does the blue light come from in this image? Is it scattered starlight?

Ann

[Beyond]

I used to have sunglasses that were called 'blue blockers'. They blocked the blue light from the sun (sorry Ann) and everything looked less fuzzy and sharper.

[DavidLeodis]

Doctor Adam Block created that image with a 32" telescope? LRGB = 7:3:3:3 I don't know what that means.

In the information brought up through the "this sharp telescopic view" it states "Exposure LRGB = 7:3:3:3 hours" thus the units are hours. I think LRGB stands for Luminance Red Green Blue filters (I'm unsure though about the L).

[geckzilla]

So where does the blue light come from in this image? Is it scattered starlight?

Ann

It's a mix of ionized hydrogen and oxygen atoms like the description says. Because it's wideband it all merges together resulting in a somewhat muddy appearance. I don't really know what kind of processing was done, though. I expect PNe to be greener but I haven't done any wideband RGB processing of them. Wideband sure, but never these particular filters which are supposed to be biased to human eye perception.

[Chris Peterson]

I'm just thinking that this nebula shouldn't be blue at all. It must be very OIII-rich, and Chris has just taught me that OIII is really this color.

The Ha line falls entirely within the passband of a red astronomical filter, with no energy in the green or blue. [OIII], however, is a different story. Astronomical RGB filters normally have a finely tuned overlap between the G and B filters that includes 500 nm. That means that [OIII] typically creates a signal with approximately equal amounts of green and blue, which is why it commonly appears as cyan in broadband images. But the actual hue is very sensitive to the final color balancing (often based on stars), and can therefore be substantially shifted towards either blue or green. This is then confounded by the fact that we seldom see [OIII] in isolation, but mixed with both narrowband and broadband sources. And of course, the actual color may be dominated more by luminosity than by hue.

[starsurfer]

So where does the blue light come from in this image? Is it scattered starlight?

Ann

Bright Ha and OIII emission is visible with broadband LRGB filters. Ha and OIII emission that is too faint for LRGB is only visible with exposures taken through Ha and OIII filters.
Colours of a planetary nebula and other objects with Ha and OIII are dependent on the distribution of the ionized gases, see below:
1. Areas that have only Ha.
2. Areas that have only OIII.
3. Areas that have both Ha and OIII where Ha is more than OIII.
4. Areas that have both Ha and OIII where OIII is more than Ha.
5. Areas that have both Ha and OIII where both are almost equal.

Abell 36 has overlapping Ha and OIII around the edges, which is why that part appears purple and the inner part contains more OIII, which is why it is blue.