APOD: HFG1 & Abell 6: Planetary Nebulae (2024 Feb 12)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 5370
Joined: Fri Dec 04, 2009 3:27 am

APOD: HFG1 & Abell 6: Planetary Nebulae (2024 Feb 12)

Post by APOD Robot » Mon Feb 12, 2024 5:05 am

Image HFG1 & Abell 6: Planetary Nebulae

Explanation: Planetary nebulae like Heckathorn-Fesen-Gull 1 (HFG1) and Abell 6 in the constellation Cassiopeia are remnants from the last phase of a medium sized star like our Sun. In spite of their shapes, planetary nebulae have nothing in common with actual planets. Located in the bottom left part of the featured photo, HFG1 was created by the binary star system V664 Cas, which consists of a white dwarf star and a red giant star. Both stars orbit their center of mass over about half an Earth day. Traveling with the entire nebula at a speed about 300 times faster than the fastest train on Earth, V664 Cas generates a bluish arc shaped shock wave. The wave interacts most strongly with the surrounding interstellar medium in the areas where the arc is brightest. After roughly 10,000 years, planetary nebulae become invisible due to a lack of ultraviolet light being emitted by the stars that create them. Displaying beautiful shapes and structures, planetary nebulae are highly desired objects for astrophotographers.

<< Previous APOD This Day in APOD Next APOD >>

dougzubenel@gmail.com

Re: APOD: HFG1 & Abell 6: Planetary Nebulae (2024 Feb 12)

Post by dougzubenel@gmail.com » Mon Feb 12, 2024 4:22 pm

This image is unique and fantastic - thanks so much for submitting to APOD!

Regards,
Doug Z

AAVSO
TWAN

User avatar
Ann
4725 Å
Posts: 13421
Joined: Sat May 29, 2010 5:33 am

Re: APOD: HFG1 & Abell 6: Planetary Nebulae (2024 Feb 12)

Post by Ann » Mon Feb 12, 2024 8:44 pm


Am I the only one who can see a similarity between planetary nebula HFG1 and a cat's paw? :wink:

Since I am the Color Commentator, I wondered about this part of the caption:
APOD Robot wrote:

HFG1 was created by the binary star system V664 Cas, which consists of a white dwarf star and a red giant star.
A red giant star? Really? Red giants are typically quite bright (and reddish), and white dwarfs are typically quite faint. Shouldn't the visual light output from this binary system be strongly dominated by the reddish light from the red giant? I don't see any signs of that in planetary nebula HFG1!

I know of only one example of a red giant star with a white dwarf companion, and that is the famous Mira. In visible light, the red giant component outshines its white dwarf companion completely, even though in ultraviolet light the appearance of the binary pair changes dramatically!


Also, and even though this isn't a certainty, isn't there a fairly good chance that the HFG1 system would be a cataclysmic variable, if one of the components is a red giant star? If the white dwarf and the red giant are close enough, matter can start flowing from the red giant onto the white dwarf, which can then have violent nova-like eruptions.


In short, I don't believe that the HFG1 consists of a white dwarf and a red giant. And indeed, the Heckathorn-Fesen-Gull 1 link in today's APOD takes us to a page where yu can read the following:
HFG1 was created by the central star V664 Cas. This is not a single star, but a dense binary star system consisting of a white dwarf and a sun-like star, which are only a few million kilometres apart and orbit every 14 hours.

So the white dwarf doesn't have a bright red giant companion, and instead its partner is a relatively faint sunlike star. And even though the two stars are very close together they don't yet interact, because the sunlike star is small and holds its outer atmosphere close to itself.

But they will interact in the future! Because the sunlike star will turn into a red giant! And then matter will stream from the red giant onto the white dwarf, and then this stellar pair will become a cataclysmic binary.


But so far, HFG1 is a pre-cataclysmic binary. Everything is calm and peaceful in this planetary nebula binary star system! I'm reminded of the medieval guardians who would keep watch from a tower over their cities at night, and blow their horns at night at regular intervals all night, and shout the following soothing words into the night: Everything is calm in the streets of ..... (fill in the name of a suitable city).


(And of course, as the Color Commentator I wonder why the shock front of HFG1 is blue in almost all pictures of this nebula. I guess that the blue color could possibly be OIII, mapped as blue.)

Ann
Color Commentator

Locutus76
Ensign
Posts: 26
Joined: Tue Aug 14, 2018 1:10 pm

Re: APOD: HFG1 & Abell 6: Planetary Nebulae (2024 Feb 12)

Post by Locutus76 » Mon Feb 12, 2024 9:25 pm

Ann wrote: Mon Feb 12, 2024 8:44 pm
(And of course, as the Color Commentator I wonder why the shock front of HFG1 is blue in almost all pictures of this nebula. I guess that the blue color could possibly be OIII, mapped as blue.)
It does say so on the page behind the ‘bluish’ link in the text :ssmile:

User avatar
MarkBour
Subtle Signal
Posts: 1377
Joined: Mon Aug 26, 2013 2:44 pm
Location: Illinois, USA

Re: APOD: HFG1 & Abell 6: Planetary Nebulae (2024 Feb 12)

Post by MarkBour » Sat Feb 17, 2024 2:26 am

Ann wrote: Mon Feb 12, 2024 8:44 pm
1. Yes, that does look like a cat's paw! I can even imagine a claw or two showing in it.
2. Got it. As you indicate, no red giant currently in the nebula.

Interestingly, the system does not settle for one famously confusing term ("planetary"), but is described as a "cometary" system as well.
In
https://ui.adsabs.harvard.edu/abs/2016M ... C/abstract,
Chiotellis, Boumis, Nanouris, Meaburn, and Dimitriadis model that the long, red tail came from the progenitor of the white dwarf half of this pair.
By their modelling, we do see the left-overs of a red giant in the image, but it is smeared out behind HFG1.
I guess the rapid travel through the interstellar medium created both the bow shock and the cometary tail at the same time.
Mark Goldfain

User avatar
Ann
4725 Å
Posts: 13421
Joined: Sat May 29, 2010 5:33 am

Re: APOD: HFG1 & Abell 6: Planetary Nebulae (2024 Feb 12)

Post by Ann » Sat Feb 17, 2024 5:34 am

MarkBour wrote: Sat Feb 17, 2024 2:26 am
Ann wrote: Mon Feb 12, 2024 8:44 pm
1. Yes, that does look like a cat's paw! I can even imagine a claw or two showing in it.
2. Got it. As you indicate, no red giant currently in the nebula.

Interestingly, the system does not settle for one famously confusing term ("planetary"), but is described as a "cometary" system as well.
In
https://ui.adsabs.harvard.edu/abs/2016M ... C/abstract,
Chiotellis, Boumis, Nanouris, Meaburn, and Dimitriadis model that the long, red tail came from the progenitor of the white dwarf half of this pair.
By their modelling, we do see the left-overs of a red giant in the image, but it is smeared out behind HFG1.
I guess the rapid travel through the interstellar medium created both the bow shock and the cometary tail at the same time.
Wow, Mark. We see the leftovers of a red giant in this system? Or at least the long red tail is the leftovers of a red giant?

If so, that suggests to me that the non-degenerate star in the HFG1 system is not a main sequence star at all, but a catastrophically withered-down, faint and sorry version of its former bright and ruddy self, like the puny red giant of the Algol system?


But if the red giant of the HFG1 system has lost so much of its gas, shouldn't it have interacted with its white dwarf companion and caused the white dwarf to act up?

Ann
Color Commentator