General discussions split from Recent Submissions

[tekic545]

Ann,

You frequently express your distaste for planetaries (but sometimes make an exception.) Given that planetaries are among the most vivid and diversely colored objects the in sky, and are among the youngest and most dramatic in their origin, what underlies your disdain for images of them?

Kind Regards,

Bob Gillette

[Ann]

Ann,

You frequently express your distaste for planetaries (but sometimes make an exception.) Given that planetaries are among the most vivid and diversely colored objects the in sky, and are among the youngest and most dramatic in their origin, what underlies your disdain for images of them?

Kind Regards,

Bob Gillette

Good question, Bob. Thank you for asking so kindly, by the way. Well, it all has to do with my color obsession. It is extremely important to me to understand the colors of cosmic objects and understand what they signify. But I also want to know what color cosmic objects "really" are. That is why I love stars. I have spent a lot of time looking at stars simply to discern their colors, so when I see color pictures of star clusters and galaxies, I immediately get a good idea of what kind of stars they contain. Not so with planetaries, however. I have never seen color in a planetary, not that I have ever seen more than one, namely the Ring Nebula. It looked like a grey smoke ring to me. It bothers me that I don't have my own idea of what color planetaries are. And it bothers me even more that I can't understand why some planetaries always seem to photograph as blue-green and others always photograph as mainly red. But even that isn't certain, because planetaries that usually photograph as blue will sometimes look reddish, and vice versa. In short, I don't understand the colors of planetaries, and since colors are so all-important to me, I simply don't like objects whose colors I don't "know" and can't understand.

That's why I will so rarely comment on pictures of planetaries. But Michael Siniscalchi's image shows a planetary that looks the way I think it "ought" to look. I assume that the dark red color is probably mostly hydrogen, possibly mixed with nitrogen or sulphur(?), which is almost the same red color as hydrogen alpha. I assume that the pink color is either hydrogen alpha mixed with hydrogen beta, or else it is possibly hydrogen slightly mixed with doubly ionized oxygen. The dark blue-green color in the center is exactly what I would expect from faint oxygen emission. Also, I think it seems "normal" that a planetary would show both red hydrogen emission and blue-green oxygen emission, and I was happy to see these colors here. I think that the colors of PK164+31.1 /Jones-Emberson 1 "make sense" if the emission results from the gases I have described. And I love the strong blue color of the central star, too. But so many planetaries don't "make sense" to me.

That's what I can say about my feeling about planetaries.

Ann

[tekic545]

Ann,

Thank you! That's a most interesting perspective, and one I sympathize with, as you are, in effect, seeking "truth in imaging." (Which is why I personally am uncomfortable with HST and other artificial narrow-band palettes, even though they do indicate differentiation in gaseous compositions more clearly than RGB images.)

But really, almost all astronomical objects -- galaxies and nebulae alike -- appear in shades of gray when we look at them through a telescope, because the color sensors of our eyes are insufficiently sensitive to see the actual colors. So we have to trust the accuracy of our RGB imaging (and our processing) to preserve an accurate display of colors. Most of us are pretty obsessive about this, using our sun's G2V color balance as the point of reference from which our eyes evolved.

The same truth-in-color standards should (and usually do) apply to images of planetaries. Yet their apparent colors do vary among different, seemingly quite good images. I think the reason is that while planetaries tend overall to be quite bright, nuances of coloration are sometimes captured only with longer exposures.

Thus Michael Siniscalchi's image of J-E 1 is probably a very true representation of its coloration as our eyes would perceive it (if they could),thanks apparently to something like 19 hours of exposure.

Most images of M 27, the Dumbbell, are red and blue; but longer exposures and careful color calibration reveal more of a teal-green color in place of the blue, from the OIII component.

But the dazzling blue NGC 1501 is just that, dazzling blue. It really is. So it is telling us something (which I will leave to the astronomers) about its gaseous make-up. Same with M 57, the Ring Nebula, which has very little real green in it, and not much blue, but significant red and reddish-orange. And the Eskimo, with its unique shades of browns and greens soft orange and almost no blue really looks like that.

I think for the most part that we're seeing the real chemistry of these things represented in their differing colors. I'd be interested to know why, then, the chemistry seems to vary so much from one dying red giant to another.

Best,

Bob

Bob

[Ann]

Thank you for your reply, Bob!

You said:

That's a most interesting perspective, and one I sympathize with, as you are, in effect, seeking "truth in imaging." (Which is why I personally am uncomfortable with HST and other artificial narrow-band palettes, even though they do indicate differentiation in gaseous compositions more clearly than RGB images.)

I agree completely with your assessment of HST images. They are of immense scientific value, but from an aesthetic and even "true-human-color" aspect they are far from ideal.

But really, almost all astronomical objects -- galaxies and nebulae alike -- appear in shades of gray when we look at them through a telescope, because the color sensors of our eyes are insufficiently sensitive to see the actual colors.

That's very true. On the other hand, some planetaries are known for showing color in the eyepiece, such as the Blue Snowball, which, on the other hand, has an irritating tendency to photograph as greenish!

As for galaxies, would you believe that I have actually, really, seen color in a galaxy? It happened in 1970, I was fifteen years old and my eyesight was so much better than it is now. I had just read about the Andromeda galaxy, but I don't think I had seen a single picture of it. I decided to try to see it with my parents' not very big binoculars. I really had no idea what the galaxy would look like, but when I finally found it I knew what it was. It was extended, fuzzy and - yellow! I'm not kidding you. But when I have revisited M31 in later years, it has always looked gray to me.

What did I see when I saw that fuzzy yellow oval? I was seeing the bulge of M31, of course, or maybe just the inner, brighter part of the bulge. But I vividly remember that pale yellow color of it. What is the color index of M31? I don't know if I have ever seen that bit of information, but I would guess it is around 0.9, much like famous star Pollux. When I looked at Pollux through a telescope its color looked much like the pale yellow hue that I remember seeing in Andromeda. And because that glimpse of yellow in Andromeda made such a strong impression on me, I am unable to think of galaxies as gray.

But the dazzling blue NGC 1501 is just that, dazzling blue. It really is. So it is telling us something (which I will leave to the astronomers) about its gaseous make-up. Same with M 57, the Ring Nebula, which has very little real green in it, and not much blue, but significant red and reddish-orange. And the Eskimo, with its unique shades of browns and greens soft orange and almost no blue really looks like that.

I found a homepage, http://www.ngc7000.org/ccd/pn-other.html, where you can see color images of NGC 1501, the Blue Snowball, the Eskimo Nebula and the Owl Nebula, among others. Interestingly, the Blue Snowball looks blue-green, whereas NGC 1501 looks brilliantly blue. However, the Eskimo and the Owl are mostly blue, too!

I think for the most part that we're seeing the real chemistry of these things represented in their differing colors. I'd be interested to know why, then, the chemistry seems to vary so much from one dying red giant to another.

Yes, that must be it. But what could possibly cause the brilliantly blue color of NGC 1501? I guess this planetary has no hydrogen at all, and no other gases that typically glow red. It must certainly contain oxygen, but OIII is blue-green, not pure blue. Could the nebula possibly contain tiny dust particles, so that it glows blue from reflection? Or could it glow blue from helium?

Interesting but frustrating! If I could see "true-color" RGB images of planetaries combined with careful chemical analyses of them and a good explanation for why they show the colors they do, then I would like them a lot, I think!

Ann

[tekic545]

Ann,

My last word on the subject (for now, anyway) is to note the truly unusual and intriguing pale magenta or lavender color across NGC 7008. I hope we provoke a response here from an astrochemist. See http://tinyurl.com/2elr8pr

Bob

[Ann]

Ann,

My last word on the subject (for now, anyway) is to note the truly unusual and intriguing pale magenta or lavender color across NGC 7008. I hope we provoke a response here from an astrochemist. See http://tinyurl.com/2elr8pr

Bob

That's really interesting! The pale magenta or lavender color is in the center of the nebula, where I, at least, would expect the blue-green color of OIII emission. And the blue color is further out from the center, where I would expect the red color of hydrogen emission!

Bob, I took a very quick peek at some of your other pictures (got to rush now, you see). Well, the very blue NGC 1501 is there, I see. And a planetary similar to the Ring Nebula has this magenta or lavender color in the center, but further out it is bright red.

My favorite of your pictures is the closeup of the NGC 206 region in the Andromeda galaxy. That was excellent!

Ann

[tekic545]

Thank you, Ann.

[NoelC]

I have to say, Ann, that I share your feelings regarding object color.

My collaborator Greg Parker and I have made a lot of images using an RGB camera, and I strive to present the "proper" visual colors in the imagery I process. And amazingly, the universe is FULL of wonderful, beautiful color, right in the spectrum our eyes see.

Because a camera can show us the color of something we simply can't see with unaided eyes simply because it's not bright enough is no reason whatsoever not to crave "what does it really look like".

But I don't much mind "false color" imagery unless it's not labeled as such. That just breeds confusion.

-Noel

[Ann]

Ann,

Yes, it is indeed NGC 1514, aka the Crystal Ball Nebula (something it apparently resembles when viewed visually.) IMy apologies, I seem to have dropped the title on the cutting-room floor.

This planetary is unusual, in that it appears to envelop a tightly orbiting pair of stars, one a dying giant, the other an already more-or-less dead white dwarf. Tough luck for any planets in the neighborhood.

Best,

Bob

Couldn't help thinking of something like this when you talked about dropping the title on the cutting-room floor...

Click to view full size image

Like Owlice, I did follow the tinyurl to see the original image and learn that the object in question was planetary nebula NGC 1514. Interestingly, not only does this nebula appears to be unusually blue, but the central star appears to be unusually yellow. That, of course, is because the central star is a binary, and most of the visual light comes from the dying giant, which ought to be of spectral class K or M.

Well, very interesting!

Ann

P.S. I just checked planetary nebula NGC 1514 with my software. My software gives conflicting information about the central star - one source says that the star is of spectral class K0, while the other says that it is of spectral class B8. The B-V index of the light emanating from the central star is given as +0.567, which is very blue for a K0 star and very red for a B8 star. I suppose we are indeed seeing the combined light of a binary star, one very blue but faint, one yellow and brighter.

[tekic545]

Ann,

Thank you for that information about the central binary star of NGC 1514, which goes way beyond what I knew about it. I can claim, however, to have experienced a small rush of curiosity,though one not pursued, as to why the central star was so white, when most often the central stars of planetaries are distinctly blue. I gather the answer is that the colors of the two stars blend to make what we see as white.

Best, Bob

[Ann]

Ann,

Thank you for that information about the central binary star of NGC 1514, which goes way beyond what I knew about it. I can claim, however, to have experienced a small rush of curiosity,though one not pursued, as to why the central star was so white, when most often the central stars of planetaries are distinctly blue. I gather the answer is that the colors of the two stars blend to make what we see as white.

Best, Bob

However, Bob, if the central star is a binary consisting of a K0 star and a B8 star, then neither component is hot enough to ionize any gases around them.

A truly, truly intriguing possibility is that the B8 star is on its way to becoming a hot white dwarf, but that it is still in a transitional stage. It used to be an M giant, but it has shrunk to a B8 star, and it is on its way to becoming even smaller and hotter. In its present stage, it can create a blue reflection nebula, and its companion K0 star can actually provide some blue light too, making the reflection nebula brighter. I have to say that the pure blue color of the nebula suggests a reflection nebula to me, because I expect a planetary nebula to be a bit more turquoise. Of course, it is really unlikely that a reflection nebula would be so sharply defined and bright.

A third possibility is that the central star is triple. There is indeed a hot white dwarf in there, which is providing the ultraviolet light needed to ionize the surrounding gases. But there is a K0 and a B8 star there as well, and the blue light they emit may just possibly be reflected in dust particles in the nebula.

Or not.

Ann

[tekic545]

On the structure of NGC 1514, I found this on the Wide-Field Infrared Survey (WISE) site, which includes a very weird infrared image of the object:

"The object is actually a pair of stars -- one star is a dying giant somewhat heavier and hotter than our sun, and the other was an even larger star that has now contracted into a dense body called a white dwarf. As the giant star ages, it sheds some its outer layers of material to form a large bubble around the two stars. Jets of material from the white dwarf are thought to have smashed into this bubble wall. The areas where the jets hit the cavity walls appear as orange rings in the WISE image. This is because dust in the rings is being heated and glows with infrared light that WISE detects."

http://wise.ssl.berkeley.edu/gallery_NGC1514.html

Bob

[Ann]

On the structure of NGC 1514, I found this on the Wide-Field Infrared Survey (WISE) site, which includes a very weird infrared image of the object:

"The object is actually a pair of stars -- one star is a dying giant somewhat heavier and hotter than our sun, and the other was an even larger star that has now contracted into a dense body called a white dwarf. As the giant star ages, it sheds some its outer layers of material to form a large bubble around the two stars. Jets of material from the white dwarf are thought to have smashed into this bubble wall. The areas where the jets hit the cavity walls appear as orange rings in the WISE image. This is because dust in the rings is being heated and glows with infrared light that WISE detects."

http://wise.ssl.berkeley.edu/gallery_NGC1514.html

Bob

Thanks for the image, Bob! The link gives us a reason for the strange color of the central star. The infrared image shows a dust lane right in front of the central star as seen from our position. The central star has been unusually reddened by dust, purely and simply. My guess is that there is no K0 star here. Instead there may well be a reddened B8 star paired with a small hot white dwarf.

Ann

[tekic545]

Ann,

You're right about the dust lane. I hadn't noticed that. Indeed, that should solve the mystery. Well observed!

Bob