Starship Asterisk*

TheOtherBruce wrote: ↑Sat Aug 15, 2020 3:49 pm

orin stepanek wrote: ↑Fri Aug 14, 2020 12:21 pm Crazy thing about nebulas; You can look at them and imagine a face or 2; then look at them later and see something else!

I blame those pesky Klingons and their dubious industrial safety record in moon mining...

orin stepanek wrote: ↑Fri Aug 14, 2020 12:21 pm Crazy thing about nebulas; You can look at them and imagine a face or 2; then look at them later and see something else!

neufer wrote: ↑Fri Aug 14, 2020 11:50 am

https://hubblesite.org/contents/media/images/2012/49/3125-Image.html wrote:

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NGC 5189 (Gum 47, IC 4274, nicknamed Spiral Planetary Nebula) is a planetary nebula in the constellation Musca. Observations with the Southern African Large Telescope have finally found a white dwarf companion in a 4.04 day orbit around the rare low-mass Wolf-Rayet type central star of NGC 5189. NGC 5189 [90 × 62 arcsec] is estimated to be 546 parsecs or 1,780 light years away from Earth. Other measurements have yielded results up to 900 parsecs (~3000 light-years).

https://en.wikipedia.org/wiki/Wolf%E2%80%93Rayet_nebula wrote:

AB7 is one of the highest-excitation nebulae in the Magellanic Clouds, two satellite galaxies of the Milky Way

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<<A Wolf–Rayet nebula is a nebula which surrounds a Wolf–Rayet star.

WR nebulae have been classified in various ways. One of the earliest was by the nature and origin of the nebula:

• HII regions
  ejecta-type nebulae
  wind-blown bubbles

This classification requires detailed study of each nebula and more recent attempts have been made to allow quick classification of nebulae based purely on their appearance. WR nebulae frequently are ring-shaped in appearance, possibly spherical. Others are irregular, either disrupted shells or formed from clumpy ejection. Examples of this type of nebula include NGC 6888, NGC 2359, and NGC 3199.>>

https://en.wikipedia.org/wiki/WR_104 wrote:

WR 104

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<<WR 104 is a triple star system located about 7,500 light-years from Earth. The primary star is a Wolf–Rayet star, abbreviated as WR, with a B0.5 main sequence star in close orbit and another more distant fainter companion.

The WR star is surrounded by a distinctive spiral Wolf–Rayet nebula, often referred to as a pinwheel nebula. The rotational axis of the binary system, and likely of the two closest stars, is directed approximately towards Earth. Within the next few hundred thousand years, the Wolf–Rayet star is predicted to probably become a core-collapse-supernova with a small chance of producing a long duration gamma-ray burst.

The possibility of a supernova explosion from WR 104 having destructive consequence for life on Earth stirred interest in the mass media, and several popular science articles have been issued in the press since 2008. Some articles decide to reject the catastrophic scenario, while others leave it as an open question. Scientists currently believe the odds of WR 104 posing a risk to be small.

The Wolf–Rayet star that produces the characteristic emission line spectrum of WR 104 has a resolved companion and an unresolved spectroscopic companion, forming a triple system.

The spectroscopic pair consists of the Wolf–Rayet star and a B0.5 main sequence star. The WR star is visually 0.3 magnitudes fainter than the main sequence star, although the WR star is typically considered the primary, as it dominates the appearance of the spectrum and is more luminous. The two are in a nearly circular orbit separated by about 2 AU, which would be about one milli-arcsecond at the assumed distance. The two stars orbit every 241.5 days with a small inclination (i.e. nearly face-on).

The visually resolved companion is 1.5 magnitudes fainter than the combined spectroscopic pair and almost one arc-second away. It is thought to be physically associated, although orbital motion has not been observed. From the colour and brightness, it is expected to be a hot main sequence star.

The rotational axis of the binary system is directed approximately towards Earth at an estimated inclination of 0 to 16 degrees. This provides a fortunate viewing angle for observing the binary system and its dynamics.

WR 104 is surrounded by a distinctive dusty Wolf–Rayet nebula over 200 astronomical units in diameter formed by interaction between the stellar winds of the two stars as they rotate and orbit. The spiral appearance of the nebula has led to the name Pinwheel Nebula being used. The spiral structure of the nebula is composed of dust that would be prevented from forming by WR 104's intense radiation were it not for the star's companion. The region where the stellar wind from the two massive stars interacts compresses the material enough for the dust to form, and the rotation of the system causes the spiral-shaped pattern. The round appearance of the spiral leads to the conclusion that the system is seen almost pole on, and an almost circular orbital period of 220 days had been assumed from the pinwheel outflow pattern.

WR 104 shows frequent eclipse events as well as other irregular variations in brightness. The undisturbed apparent magnitude is around 12.7, but the star is rarely at that level. The eclipses are believed to be caused by dust formed from expelled material, not by the companion star.>>

Ann wrote: ↑Fri Aug 14, 2020 7:34 pm

johnnydeep wrote: ↑Fri Aug 14, 2020 6:35 pm

APOD Robot wrote: ↑Fri Aug 14, 2020 4:05 am NGC 5189: An Unusually Complex Planetary Nebula

Explanation: Why is this nebula so complex? When a star like our Sun is dying, it will cast off its outer layers, usually into a simple overall shape. Sometimes this shape is a sphere, sometimes a double lobe, and sometimes a ring or a helix. In the case of planetary nebula NGC 5189, however, besides an overall "Z" shape (the featured image is flipped horizontally and so appears as an "S"), no such simple structure has emerged. To help find out why, the Earth-orbiting Hubble Space Telescope has observed NGC 5189 in great detail. Previous findings indicated the existence of multiple epochs of material outflow, including a recent one that created a bright but distorted torus running horizontally across image center. Hubble results appear consistent with a hypothesis that the dying star is part of a binary star system with a precessing symmetry axis. NGC 5189 spans about three light years and lies about 3,000 light years away toward the southern constellation of the Fly (Musca).

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So, I've read Neufer's and Ann's additional text and links, but I'm still not sure if the WR star that is the cause of the NGC 5189 nebula is visible in the photos I've seen (or any others). However, we apparently do know that this WR star has a binary companion, which means that the existence of both are indeed inferrable, if not actually conveniently visible.

Planetary nebula Abell 43 and its strikingly blue central star. Photo: Ed Walendowski/Adam Block/NOAO/AURA/NSF.

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A very good color picture might give the central star away, because it would be so strikingly blue (because it is so hot). Take a look at planetary nebula Abell 43 and its very blue central star to see what I mean.

Then again, the central star of NGC 5189 might not be so blue, since it is a Wolf-Rayet type of central star. I posted a spectrum of a Wolf-Rayet star in a previous post, and if you look at it, you can see that a Wolf-Rayet star has a very bright emission nebula in the blue part of the spectrum, but it also has two bright emission lines in the green and yellow parts of the spectrum. Therefore, the central star might not give itself away by its blue color in any case.

NGC 5189 by Volker Wendel and Bernd Flach-Wilken.

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I agree with you, neither the APOD nor the picture I posted by Robert Gendler helps us pick out the central star of NGC is 5189. But I did find a fine and very true-color-looking picture by Volker Wendel and Bernd Flach-Wilken, which just might give us a clue.

As you can see, one of the stars inside NGC 5189 does look much bluer than any other stars in the picture. So is it the central star? I don't know, because I don't like the fact that it appears to be situated off-center. But it is possible that Volker Wendel and Bernd Flach-Wilken have caught this blue star red-handed.

And if you want a more centrally placed central star for NGC 5189, you might want to check out this Hubble picture of NGC 5189 which has had a grid mark placed all over it. As you can see, there is a star right at what appears to be the center of the nebula, judging by the grid mark.

Ann

johnnydeep wrote: ↑Fri Aug 14, 2020 6:35 pm

APOD Robot wrote: ↑Fri Aug 14, 2020 4:05 am NGC 5189: An Unusually Complex Planetary Nebula

Explanation: Why is this nebula so complex? When a star like our Sun is dying, it will cast off its outer layers, usually into a simple overall shape. Sometimes this shape is a sphere, sometimes a double lobe, and sometimes a ring or a helix. In the case of planetary nebula NGC 5189, however, besides an overall "Z" shape (the featured image is flipped horizontally and so appears as an "S"), no such simple structure has emerged. To help find out why, the Earth-orbiting Hubble Space Telescope has observed NGC 5189 in great detail. Previous findings indicated the existence of multiple epochs of material outflow, including a recent one that created a bright but distorted torus running horizontally across image center. Hubble results appear consistent with a hypothesis that the dying star is part of a binary star system with a precessing symmetry axis. NGC 5189 spans about three light years and lies about 3,000 light years away toward the southern constellation of the Fly (Musca).

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So, I've read Neufer's and Ann's additional text and links, but I'm still not sure if the WR star that is the cause of the NGC 5189 nebula is visible in the photos I've seen (or any others). However, we apparently do know that this WR star has a binary companion, which means that the existence of both are indeed inferrable, if not actually conveniently visible.

APOD Robot wrote: ↑Fri Aug 14, 2020 4:05 am NGC 5189: An Unusually Complex Planetary Nebula

Explanation: Why is this nebula so complex? When a star like our Sun is dying, it will cast off its outer layers, usually into a simple overall shape. Sometimes this shape is a sphere, sometimes a double lobe, and sometimes a ring or a helix. In the case of planetary nebula NGC 5189, however, besides an overall "Z" shape (the featured image is flipped horizontally and so appears as an "S"), no such simple structure has emerged. To help find out why, the Earth-orbiting Hubble Space Telescope has observed NGC 5189 in great detail. Previous findings indicated the existence of multiple epochs of material outflow, including a recent one that created a bright but distorted torus running horizontally across image center. Hubble results appear consistent with a hypothesis that the dying star is part of a binary star system with a precessing symmetry axis. NGC 5189 spans about three light years and lies about 3,000 light years away toward the southern constellation of the Fly (Musca).

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orin stepanek wrote: ↑Fri Aug 14, 2020 5:05 pm

TheZuke! wrote: ↑Fri Aug 14, 2020 3:39 pm Hell Dog Nebula?

[edit]Okay, since a "Wolf"-Rayet star is involved, (thanks neufer) it could be a Hell Wolf Nebula.

Well a wolf is (?) a dog; kinda!
++++++++

TheZuke! wrote: ↑Fri Aug 14, 2020 3:39 pm Hell Dog Nebula?

[edit]Okay, since a "Wolf"-Rayet star is involved, (thanks neufer) it could be a Hell Wolf Nebula.

neufer wrote: ↑Fri Aug 14, 2020 11:50 am

https://hubblesite.org/contents/media/images/2012/49/3125-Image.html wrote:

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NGC 5189 (Gum 47, IC 4274, nicknamed Spiral Planetary Nebula) is a planetary nebula in the constellation Musca. Observations with the Southern African Large Telescope have finally found a white dwarf companion in a 4.04 day orbit around the rare low-mass Wolf-Rayet type central star of NGC 5189. NGC 5189 [90 × 62 arcsec] is estimated to be 546 parsecs or 1,780 light years away from Earth. Other measurements have yielded results up to 900 parsecs (~3000 light-years).

Wikipedia wrote:

Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very high surface enhancement of heavy elements, depletion of hydrogen, and strong stellar winds. Their surface temperatures range from 30,000 K to around 210,000 K, hotter than almost all other stars. They were previously called W-type stars referring to their spectral classification.

Classic (or Population I) Wolf–Rayet stars are evolved, massive stars that have completely lost their outer hydrogen and are fusing helium or heavier elements in the core...

A separate group of stars with WR spectra are the central stars of planetary nebulae (CSPNe), post-asymptotic giant branch stars that were similar to the Sun while on the main sequence, but have now ceased fusion and shed their atmospheres to reveal a bare carbon-oxygen core.

orin stepanek wrote: ↑Fri Aug 14, 2020 12:21 pm Crazy thing about nebulas; You can look at them and imagine a face or 2; then look at them later and see something else!

https://hubblesite.org/contents/media/images/2012/49/3125-Image.html wrote:

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NGC 5189 (Gum 47, IC 4274, nicknamed Spiral Planetary Nebula) is a planetary nebula in the constellation Musca. Observations with the Southern African Large Telescope have finally found a white dwarf companion in a 4.04 day orbit around the rare low-mass Wolf-Rayet type central star of NGC 5189. NGC 5189 [90 × 62 arcsec] is estimated to be 546 parsecs or 1,780 light years away from Earth. Other measurements have yielded results up to 900 parsecs (~3000 light-years).

https://arxiv.org/abs/1501.03373 wrote:
A radial velocity survey for post-common-envelope Wolf-Rayet central stars of planetary nebulae: First results and discovery of the close binary nucleus of NGC 5189

Rajeev Manick, Brent Miszalski, Vanessa McBride [Submitted on 14 Jan 2015]

<<The formation of Wolf-Rayet central stars of planetary nebulae ([WR] CSPNe) whose spectroscopic appearance mimics massive WR stars remains poorly understood. Least understood is the nature and frequency of binary companions to [WR] CSPNe that may explain their H-deficiency. We have conducted a systematic radial velocity (RV) study of 6 [WR] CSPNe to search for post-common-envelope (post-CE) [WR] binaries. The spectacular nebular morphology of NGC 5189 fits the pattern of recently discovered post-CE PNe extremely well with its dominant low-ionisation structures (e.g. as in NGC 6326) and collimated outflows (e.g. as in Fleming 1). The anomalously long 4.04 d orbital period is either a once-off (e.g. NGC 2346) or it may indicate there is a sizeable population of [WR] binaries with massive WD companions in relatively wide orbits, perhaps influenced by interactions with the strong [WR] wind.>>