Starship Asterisk*

Cat's Eye Wide and Deep

Explanation: The Cat's Eye Nebula (NGC 6543) is one of the best known planetary nebulae in the sky. Its more familiar outlines are seen in the brighter central region of the nebula in this impressive wide-angle view. But the composite image combines many short and long exposures to also reveal an extremely faint outer halo. At an estimated distance of 3,000 light-years, the faint outer halo is over 5 light-years across. Planetary nebulae have long been appreciated as a final phase in the life of a sun-like star. More recently, some planetary nebulae are found to have halos like this one, likely formed of material shrugged off during earlier episodes in the star's evolution. While the planetary nebula phase is thought to last for around 10,000 years, astronomers estimate the age of the outer filamentary portions of this halo to be 50,000 to 90,000 years. Visible on the left, some 50 million light-years beyond the watchful planetary nebula, lies spiral galaxy NGC 6552.

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That is SOOOO Cool....

I wish I had wide exposure capability...

:---[===] *

The object taking a bow in today's APOD is a planetary nebula! Starsurfer must be happy!

I like the image, too. The outer halo is very impressive. I have to wonder if it is blue for real. It might be, or at least it might be blue-green from OIII. The pink parts are almost certainly pink from Hα emission.

As I was checking NGC 6543 with my software, I found to my surprise that there seemed to be another planetary nebula right next to the Cat's Eye. This other planetary nebula is called IC 4677. Even Simbad's Astronomical Database recognizes IC 4677, but informs us that IC 4677 is a part of NGC 6543, the Cat's Eye! You can see IC 4677 in today's APOD. It is the brightest part of the outer halo of the Cat's Eye, to the right in today's APOD.

I'm sure nobody cares but me, but my software tells me that the central star of the Cat's Eye Nebula is indeed blue, not just intrinsically blue but "visually blue" as well, so that most of the light that reaches us from this star at its 3,000 light-years away residence is indeed blue. The white dwarf central star of NGC 6543 is designated HD 164963, its magnitude is 11.3 and its B-V magnitude is as blue as -0.2, within the limits of uncertainties. Okay, I know, I should shut up about this already!

There is a nice galaxy to the left of the Cat's Eye Nebula, NGC 6552. According to Principal Galaxy Catalog, NGC 6552 may be about 350 million light-years away! So it is not only the Cat's Eye that is far away. NGC 6552 is faint enough (magnitude 14) that it hasn't had its colors measured, apart from its B magnitude and its far infrared magnitude. It appears to be dusty, to be sure: it is almost two magnitudes brighter in far infrared than in blue light. Strangely, though, it doesn't look dusty, since its bar is so big and bright and straight and its ring is so round and regular. Perhaps NGC 6552 is reddened by dust in our own galaxy. And if it is as far away as 350 million light-years, it is bright, too, more than twice as bright as the Milky Way. To all accounts, NGC 6552 is a big, bright and likely quite yellow barred spiral galaxy. It resembles NGC 266. The picture of NGC 266, if you follow the link, is by Gert Gottschalk and Sibylle Froehlich/Adam Block/NOAO/AURA/NSF.

Ann

On a side note, I think its ridiculous that they continue calling these nebulae 'planetary'.

Wesley wrote:On a side note, I think its ridiculous that they continue calling these nebulae 'planetary'.

I have suggested one name in the past because many of them look like bugs: entomic nebulas. Perhaps something more general like pareidolic nebulas would be better.

geckzilla wrote:

Wesley wrote:On a side note, I think its ridiculous that they continue calling these nebulae 'planetary'.

I have suggested one name in the past because many of them look like bugs: entomic nebulas. Perhaps something more general like pareidolic nebulas would be better.

Sure. Pareidolic nebulas sounds like a fine household name.

Ann

We could keep calling them PN for short, too. lol

Ann wrote:The object taking a bow in today's APOD is a planetary nebula! Starsurfer must be happy!

Ann

I'm really happy today! Actually doubly happy because it is a PN with a halo!

geckzilla wrote:We could keep calling them PN for short, too. lol

I have never seen anything wrong with calling them planetary nebula!! An alternative name I can think of is lactea mortis nebulae?

APOD wrote: "At an estimated distance of 3,000 light-years, the faint outer halo is over 5 light-years across."
APOD wrote: " some 50 million light-years beyond the watchful planetary nebula, lies spiral galaxy NGC 6552."
Ann wrote: " According to Principal Galaxy Catalog, NGC 6552 may be about 350 million light-years away! "

Is the APOD distance missing a couple of zeros? 300,000 vs 3,000 light years??

Brian

I like the name planetary nebulae, because they do look like planets, somewhat, and because the name carries history with it! What an irony it is that the only reason Messier is truly remembered, and indeed is famous, is because ... of his list of 'uninteresting objects', i.e., fuzzy patches, such as planetary nebulae, that are not comets.

bls0326 wrote:
APOD wrote: " some 50 million light-years beyond the watchful planetary nebula, lies spiral galaxy NGC 6552."
Ann wrote: " According to Principal Galaxy Catalog, NGC 6552 may be about 350 million light-years away! "

Is the APOD distance missing a couple of zeros?

The APOD is missing a leading "3".

Thanks for the kind words everyone! The image's background, stars, and galaxies are all a straight LRGB blend. The PN is a bicolor HaOIII mixed with the RGB data with a mapping that slightly hued it towards blue. The natural look of the halo is a little more green than shown in the final image, but my preferred mapping of NB data is typically a little more blue.

Maybe someone can tell me if the APOD photos are at original resolution. I would like higher at times.
It's fun to select, copy and paste a detail for closer examination.
I found some interesting features in the recent Mars Rover picture.
I'll check in daily to see any comments and thanks in advance!!!

Taurus1932 wrote:Maybe someone can tell me if the APOD photos are at original resolution. I would like higher at times.
It's fun to select, copy and paste a detail for closer examination.
I found some interesting features in the recent Mars Rover picture.

The image you get when you click on the main page image is normally at the highest resolution provided by the image author. That may or may not be the original resolution. Sometimes there is a link to the webpage with the original image, and that one might be higher resolution than the APOD version.

In general, there are many possibilities and you just have to be a bit clever sometimes to track down higher resolution versions, assuming they even exist.

Sometimes I wonder if the reds and blues ever correspond to the direction of movement relative to the observer ? Red areas from material moving away and blue compressed by rapid motion toward the camera. The idea may, may not, violate the rules of relativity but is based on Doppler physics.

Coil_Smoke wrote:Sometimes I wonder if the reds and blues ever correspond to the direction of movement relative to the observer ? Red areas from material moving away and blue compressed by rapid motion toward the camera. The idea may, may not, violate the rules of relativity but is based on Doppler physics.

The amount of red or blue shift that the Doppler effect creates is much too small to be visually apparent. On deep shots that cover cosmological distances, we can visually see the effect of cosmological redshift, although the choice of color mapping and the nature of the emitting object may not make that obvious in all cases.

APOD Robot wrote:
Planetary nebulae have long been appreciated as a final phase in the life of a sun-like star.

These sun-like stars may not always be so sun-like.
The graph at left of the temperature-magnitude diagram of globular cluster M3 suggests that this cluster still contains stars of the same spectral class as the Sun, even though M3 and its constituent stars are much older than the Sun. How old is M3? Opinions vary, but according to this paper M3 (also known as NGC 5272) is 11.39 billion years old. If that is correct, then the sun-like stars of M3 have survived for 11.39 billion years without even turning into red giants, much less into white dwarfs and planetary nebulas.

In other words, is there a single planetary nebula in the Milky Way that is the remnant of a once a truly sun-like star? Is there a single planetary nebula in the Local Group of galaxies that is the remnant of a star born with the mass of the Sun? Maybe not. Maybe at least 95% of all 1.0 solar mass hydrogen fusing stars ever born in the universe still survive?

Perhaps (almost) all planetary nebulas in the Local Group are remnants of stars that were born with more mass than the Sun. Perhaps the typical planetary nebulas that the universe has seen so far emanate from stars born as F-type main sequence stars, 1½ times as massive as the Sun, like Gamma Virginis, Porrima.

Ann

Chris Peterson,
Thanks much for the tips! Very kind.

Are not planetary nebulae made up, in part, of the remains of any planets orbiting the exploding star? It seems only fitting then to refer to those type of nebulae as "planetary". IMHO

Tszabeau wrote:Are not planetary nebulae made up, in part, of the remains of any planets orbiting the exploding star? It seems only fitting then to refer to those type of nebulae as "planetary". IMHO

Not really. It's entirely possible the planets are still there orbiting more distantly from their parent star, but still there nonetheless. The name gets doubly confusing once you try to talk about protoplanetary nebulas, because it makes it sound like a nebula that forms planets rather than a nebula that is going to form a planetary nebula. The name is dumb, flat out. People stick with it because people are sentimental or just don't care to change it. I believe Nitpicker told me I was tilting at windmills last time I brought it up.

geckzilla wrote:

Tszabeau wrote:Are not planetary nebulae made up, in part, of the remains of any planets orbiting the exploding star? It seems only fitting then to refer to those type of nebulae as "planetary". IMHO

Not really. It's entirely possible the planets are still there orbiting more distantly from their parent star, but still there nonetheless. The name gets doubly confusing once you try to talk about protoplanetary nebulas, because it makes it sound like a nebula that forms planets rather than a nebula that is going to form a planetary nebula. The name is dumb, flat out. People stick with it because people are sentimental or just don't care to change it. I believe Nitpicker told me I was tilting at windmills last time I brought it up.

The name seems to have been coined by William Herschel, who was the first person in humanity (at least since the field of astronomy had been established) to discover a new planet. The planet was Uranus, which looks blue-green through a telescope. It is easy to understand that planets were all the rage after this sensational discovery, and Herschel himself was of course particularly excited.

Herschel conducted very ambitious all-sky surveys, and discovered many small roundish nebulas that were blue-green in color just like Uranus. They were of course the death shrouds of medium mass stars like the Cat's Eye Nebula, which glow blue-green from bright OIII emission. Herschel can be forgiven for thinking that they looked like Uranus, and he called them planetary nebulae.

Ann

The name was fine for a long time. It's still fine now, just less so, due to its currently ambiguous nature.

Also the first PN halo was discovered in 1937 around NGC 6826 but nearly all the currently known haloes have been discovered in the 1980's, 1990's and 2000's. Another point to mention is that there are many faint PN haloes that haven't been officially published by professionals yet. Some good overviews are this paper by Bruce Balick and another by Romano Corradi. Other noteworthy publications are this one and this one. There will hopefully be a new collection this decade, a preview can be seen here.

Also I simply cannot resist including a list of some nice PN haloes:

IC 5148 by Don Goldman
Hen 2-111 by Don Goldman
NGC 5882 by CHART32
NGC 7009 by CHART32
M27 by Fabian Neyer and Robert Pölzl

I notice that no one here has mentioned that the halo is hexagon shaped. How could that have happened?