Explanation: These brightly outlined flowing shapes look ghostly on a cosmic scale. A telescopic view toward the constellation Cassiopeia, the colorful skyscape features the swept-back, comet-shaped clouds IC 59 (left) and IC 63. About 600 light-years distant, the clouds aren't actually ghosts. They are slowly disappearing though, under the influence of energetic radiation from hot, luminous star gamma Cas. Gamma Cas is physically located only 3 to 4 light-years from the nebulae and lies just above the right edge of the frame. Slightly closer to gamma Cas, IC 63 is dominated by red H-alpha light emitted as hydrogen atoms ionized by the hot star's ultraviolet radiation recombine with electrons. Farther from the star, IC 59 shows less H-alpha emission but more of the characteristic blue tint of dust reflected star light. The field of view spans over 1 degree or 10 light-years at the estimated distance of the interstellar apparitions.
Because the APOD is so large, more than 800 KB, I won't copy it. Instead, let's look at a few other pictures of the illuminating star Gamma Cas, and the "ghosts" named IC 59 and IC 63.Rogelio Bernal Andreo's beautiful portrait of Cassiopeia is a good place to start!
A closer look at Rogelio Bernal Andreo's picture reveals a truly huge and flattened dark "smoke circle" surrounding surrounding Gamma Cas. Inside that dark smoke circle is a smaller red semicircle, and IC 63 and IC 59 are the two bright "outcrops" of this semicircle.
Here is a closer closeup of IC 59 and IC 63 along with their source of illumination and ionization, Gamma Cas:
The huge dark dust circle surrounding Gamma Cas could possibly have been created by Gamma Cas itself, or so I think. (Warning! Amateur guess!) Please note, however, that Wikipedia calls it an eruptive variable star:
Gamma Cassiopeiae is an eruptive variable star, whose apparent magnitude changes irregularly from 1.6 at its brightest to 3.0 at its dimmest. It is the prototype of the class of Gamma Cassiopeiae variable stars. In the late 1930s it underwent what is described as a shell episode and the brightness increased to above magnitude 2.0, then dropped rapidly to 3.4. It has since been gradually brightening back to around 2.2.
Gamma Cassiopeiae is a rapidly spinning star with a projected rotational velocity of 472 km s−1, giving it a pronounced equatorial bulge. When combined with the star's high luminosity, the result is the ejection of matter that forms a hot circumstellar disk of gas. The emissions and brightness variations are apparently caused by this "decretion disk"
So Gamma Cas is ejecting matter that forms a hot circumstellar disk around the star. Isn't it reasonable that IC 63 and IC 59 originated as particularly dense "clumps" that were ejected by Gamma Cas? And now these clumps are located a few light-years away from Gamma Cas, and they are ionized and illuminated by the hot bright star. IC 63 is a little bit closer to Gamma Cas, so it is ionized to glow red, and IC 59 is a little further away, so it is mostly illuminated to reflect a soft shade of blue.
I can't help thinking that Gamma Cas is a very little brother or sister of the mighty and extremely hot Wolf-Rayet stars, which eject huge amounts of matter:
According to Wikipedia, Gamma Cas is 8 million years old. It has 17 times the Sun's mass and is radiating as much energy as 34,000 Suns. Its outer atmosphere has a temperature of 25,000 K, compared with 5778 K for the Sun. And it is ejecting matter. It seems certain (to me at least) that the red semicircle surrounding Gamma Cas could be matter ejected and then ionized by Gamma Cas. The question is if the huge dark circle surrounding it could also have been created by Gamma Cas. Is the star old enough to have flung matter so very far away from it?
Anyway. Because I've been talking about Gamma Cas the whole time now, I can't help thinking of Mama Cass from the Mamas and the Papas. So let's hear it from the Mamas and the Papas!
Click to play embedded YouTube video.
Ann
Re: APOD: Phantoms in Cassiopeia (2024 Oct 26)
Posted: Sat Oct 26, 2024 12:40 pm
by Christian G.
Nice APOD, an otherworldy nebular landscape! And interesting comments, Ann, Gamma Cassiopeiae is a wonderful star! If you look at it and then move to Alpha Cas and then back again, you get a marked blue/red contrast, beautiful. Too bad they're not closer still to one another!
IC 63 looks quite ghostly in this mage:
NASA, ESA, and STScI Acknowledgment: H. Arab (University of Strasbourg)
Re: APOD: Phantoms in Cassiopeia (2024 Oct 26)
Posted: Sat Oct 26, 2024 4:25 pm
by rjansen
Regarding the stated field of view in the final sentence of the description: it should read "spans over 0.5 degree or 5 light-years" rather than
"spans over 1 degree or 10 light-years". The coordinate grid overlay in https://www.astrobin.com/18dwm3/ can be used to verify, where each of the big grid blocks measures 10 arcmin on a side. Also see the APOD of Oct 25 2019 for a field of view that spans more than 1 deg.
Re: APOD: Phantoms in Cassiopeia (2024 Oct 26)
Posted: Sat Oct 26, 2024 5:59 pm
by johnnydeep
Christian G. wrote: ↑Sat Oct 26, 2024 12:40 pm
Nice APOD, an otherworldy nebular landscape! And interesting comments, Ann, Gamma Cassiopeiae is a wonderful star! If you look at it and then move to Alpha Cas and then back again, you get a marked blue/red contrast, beautiful. Too bad they're not closer still to one another!
IC 63 looks quite ghostly in this mage:
IC 63.png
NASA, ESA, and STScI Acknowledgment: H. Arab (University of Strasbourg)
And I take it that neither of those two prominent red and blue stars are Alpha Cas or Gamma Cas.
Christian G. wrote: ↑Sat Oct 26, 2024 12:40 pm
Nice APOD, an otherworldy nebular landscape! And interesting comments, Ann, Gamma Cassiopeiae is a wonderful star! If you look at it and then move to Alpha Cas and then back again, you get a marked blue/red contrast, beautiful. Too bad they're not closer still to one another!
IC 63 looks quite ghostly in this mage:
IC 63.png
NASA, ESA, and STScI Acknowledgment: H. Arab (University of Strasbourg)
And I take it that neither of those two prominent red and blue stars are Alpha Cas or Gamma Cas.
Prominent? Ha! To put things in perspective... find those "prominent" stars. (Gamma Cas is several frame widths to the upper left in my image.)
_
Christian G. wrote: ↑Sat Oct 26, 2024 12:40 pm
Nice APOD, an otherworldy nebular landscape! And interesting comments, Ann, Gamma Cassiopeiae is a wonderful star! If you look at it and then move to Alpha Cas and then back again, you get a marked blue/red contrast, beautiful. Too bad they're not closer still to one another!
IC 63 looks quite ghostly in this mage:
IC 63.png
NASA, ESA, and STScI Acknowledgment: H. Arab (University of Strasbourg)
And I take it that neither of those two prominent red and blue stars are Alpha Cas or Gamma Cas.
Prominent? Ha! To put things in perspective... find those "prominent" stars. (Gamma Cas is several frame widths to the upper left in my image.)
_
hrgb.jpg
I guess you're joking that that they're really not prominent at all, except in that previous image for some reason.
So, where ARE those two in your image? Oops, never mind! There they are just to the upper left of the "G" in "Gamma"!
And I take it that neither of those two prominent red and blue stars are Alpha Cas or Gamma Cas.
Prominent? Ha! To put things in perspective... find those "prominent" stars. (Gamma Cas is several frame widths to the upper left in my image.)
_
hrgb.jpg
I guess you're joking that that they're really not prominent at all, except in that previous image for some reason.
So, where ARE those two in your image? Oops, never mind! There they are just to the upper left of the "G" in "Gamma"!
And the brightest star in that field, up in the upper right, is mag 9.3 - more than 500 times dimmer than gam Cas at mag 2.4.
Prominent? Ha! To put things in perspective... find those "prominent" stars. (Gamma Cas is several frame widths to the upper left in my image.)
_
hrgb.jpg
I guess you're joking that that they're really not prominent at all, except in that previous image for some reason.
So, where ARE those two in your image? Oops, never mind! There they are just to the upper left of the "G" in "Gamma"!
And the brightest star in that field, up in the upper right, is mag 9.3 - more than 500 times dimmer than gam Cas at mag 2.4.
Re: APOD: Phantoms in Cassiopeia (2024 Oct 26)
Posted: Sun Oct 27, 2024 2:58 pm
by florid_snow
I really appreciate the nice pink / magenta Hydrogen Alpha emission
Re: APOD: Phantoms in Cassiopeia (2024 Oct 26)
Posted: Sun Oct 27, 2024 3:08 pm
by Chris Peterson
florid_snow wrote: ↑Sun Oct 27, 2024 2:58 pm
I really appreciate the nice pink / magenta Hydrogen Alpha emission
H-alpha isn't pink! It's deep ruby red. I think what you mean is that you appreciate that you're seeing some combination of H-alpha, H-beta, and continuum radiation that is resulting in a pink color.
Re: APOD: Phantoms in Cassiopeia (2024 Oct 26)
Posted: Mon Oct 28, 2024 2:30 pm
by Chris Peterson
florid_snow wrote: ↑Sun Oct 27, 2024 2:58 pm
I really appreciate the nice pink / magenta Hydrogen Alpha emission
BTW, by coincidence I was imaging this target a couple of nights ago, in H-alpha as well as RGB. Two processed versions here from exactly the same data. One has all of the H-alpha data mapped to the red channel (which is physically where it belongs), the other has 15% of the H-alpha added into the blue channel, to simulate the H-beta presumed present in the same ionized cloud of hydrogen (but poorly captured by the broad blue filter). Which is better is a matter of aesthetic choice, of course. (I expect I know which you prefer, though!)
_
florid_snow wrote: ↑Sun Oct 27, 2024 2:58 pm
I really appreciate the nice pink / magenta Hydrogen Alpha emission
BTW, by coincidence I was imaging this target a couple of nights ago, in H-alpha as well as RGB. Two processed versions here from exactly the same data. One has all of the H-alpha data mapped to the red channel (which is physically where it belongs), the other has 15% of the H-alpha added into the blue channel, to simulate the H-beta presumed present in the same ionized cloud of hydrogen (but poorly captured by the broad blue filter). Which is better is a matter of aesthetic choice, of course. (I expect I know which you prefer, though!)
_
IC63_hrgb.jpg
IC63_hrgb2.jpg
florid_snow wrote: ↑Sun Oct 27, 2024 2:58 pm
I really appreciate the nice pink / magenta Hydrogen Alpha emission
BTW, by coincidence I was imaging this target a couple of nights ago, in H-alpha as well as RGB. Two processed versions here from exactly the same data. One has all of the H-alpha data mapped to the red channel (which is physically where it belongs), the other has 15% of the H-alpha added into the blue channel, to simulate the H-beta presumed present in the same ionized cloud of hydrogen (but poorly captured by the broad blue filter). Which is better is a matter of aesthetic choice, of course. (I expect I know which you prefer, though!)
_
Note how much blue color there is in IC 63 in the Mount Lemmon Skycenter image. It is the amount of blue that lightens the red hue of hydrogen alpha and turns it pink. In your second image, though, Chris, the hydrogen alpha looks pink, but there is little or no blue in the picture. The grey color of IC 63 doesn't look right to me.
A different sort of image is this one by Bill Batchelor:
IC 63 and friends. Credit: Bill Batchelor.
If the Mount Lemmon Skycenter image was very blue, Bill Batchelor's image is very red indeed. It is so red that the bright red rim of IC 63 has turned white, probably from overexposure. That's an interesting phenomenon. Still, it makes sense to me.
I want pictures to feel "real" to me. Your first picture of IC 63 does, Chris, but I have problems with your second one.
florid_snow wrote: ↑Sun Oct 27, 2024 2:58 pm
I really appreciate the nice pink / magenta Hydrogen Alpha emission
BTW, by coincidence I was imaging this target a couple of nights ago, in H-alpha as well as RGB. Two processed versions here from exactly the same data. One has all of the H-alpha data mapped to the red channel (which is physically where it belongs), the other has 15% of the H-alpha added into the blue channel, to simulate the H-beta presumed present in the same ionized cloud of hydrogen (but poorly captured by the broad blue filter). Which is better is a matter of aesthetic choice, of course. (I expect I know which you prefer, though!)
_
I prefer the top one. The second image just doesn't look right to me.
And yet, arguably, the second image is closer to "true color" given that the same hydrogen producing the red H-alpha is also producing blue H-beta, meaning that an ionized hydrogen cloud radiates a color leaning towards magenta. But aesthetically, my preference also leans towards the first image.
florid_snow wrote: ↑Sun Oct 27, 2024 2:58 pm
I really appreciate the nice pink / magenta Hydrogen Alpha emission
H-alpha isn't pink! It's deep ruby red. I think what you mean is that you appreciate that you're seeing some combination of H-alpha, H-beta, and continuum radiation that is resulting in a pink color.
You are absolutely right Chris! I do go on about it from time to time so I should get the scientific words right. H-alpha is ruby red, H-beta would look blue on it's own, and it's only when they mix, and other parts of the spectrum, that give it's characteristic color. But the color words are too subjective and imprecise to me, pink, magenta, neon-red, etc, I'm not sure which one is best for hydrogen continuum radiation.
When I was young my parents took me to several "science demonstration" type of things at our local university. The chemistry demonstrations with burning and electrifying stuff definitely caught my eye. Maybe that's why I'm drawn to a special color of hydrogen emission, what looks most real to me, apparently others have the opposite opinion, it is certainly subjective, I don't begrudge anyone enjoyment of astrophotography, beautiful photos are beautiful, and that's that.
Phantoms in Cassiopeia
