APOD: NGC 7789: Caroline's Rose (2024 Jul 06)

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APOD: NGC 7789: Caroline's Rose (2024 Jul 06)

Post by APOD Robot » Sat Jul 06, 2024 4:05 am

Image NGC 7789: Caroline's Rose

Explanation: Found among the rich starfields of the Milky Way, star cluster NGC 7789 lies about 8,000 light-years away toward the constellation Cassiopeia. A late 18th century deep sky discovery of astronomer Caroline Lucretia Herschel, the cluster is also known as Caroline's Rose. Its visual appearance in small telescopes, created by the cluster's complex of stars and voids, is suggestive of nested rose petals. Now estimated to be 1.6 billion years young, the galactic or open cluster of stars also shows its age. All the stars in the cluster were likely born at the same time, but the brighter and more massive ones have more rapidly exhausted the hydrogen fuel in their cores. These have evolved from main sequence stars like the Sun into the many red giant stars shown with a yellowish cast in this color composite. Using measured color and brightness, astronomers can model the mass and hence the age of the cluster stars just starting to "turn off" the main sequence and become red giants. Over 50 light-years across, Caroline's Rose spans about half a degree (the angular size of the Moon) near the center of the sharp telescopic image.

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Re: APOD: NGC 7789: Caroline's Rose (2024 Jul 06)

Post by AVAO » Sat Jul 06, 2024 7:10 am

APOD Robot wrote: Sat Jul 06, 2024 4:05 am Image NGC 7789: Caroline's Rose

Explanation: Found among the rich starfields of the Milky Way, star cluster NGC 7789 lies about 8,000 light-years away toward the constellation Cassiopeia. A late 18th century deep sky discovery of astronomer Caroline Lucretia Herschel, the cluster is also known as Caroline's Rose. Its visual appearance in small telescopes, created by the cluster's complex of stars and voids, is suggestive of nested rose petals. Now estimated to be 1.6 billion years young, the galactic or open cluster of stars also shows its age. All the stars in the cluster were likely born at the same time, but the brighter and more massive ones have more rapidly exhausted the hydrogen fuel in their cores. These have evolved from main sequence stars like the Sun into the many red giant stars shown with a yellowish cast in this color composite. Using measured color and brightness, astronomers can model the mass and hence the age of the cluster stars just starting to "turn off" the main sequence and become red giants. Over 50 light-years across, Caroline's Rose spans about half a degree (the angular size of the Moon) near the center of the sharp telescopic image.

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Beautiful shot by the astrophotographer!
...In the IR the area is almost a bit more spectacular. Note the radioactive star IRAS 23580+5633 in the upper left shown in red in the IR.

NASA /ESA (WISE) jac berne (flickr)

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Re: APOD: NGC 7789: Caroline's Rose (2024 Jul 06)

Post by AVAO » Sat Jul 06, 2024 7:28 am

APOD Robot wrote: Sat Jul 06, 2024 4:05 am Image NGC 7789: Caroline's Rose

Explanation: Found among the rich starfields of the Milky Way, star cluster NGC 7789 lies about 8,000 light-years away toward the constellation Cassiopeia. A late 18th century deep sky discovery of astronomer Caroline Lucretia Herschel, the cluster is also known as Caroline's Rose. Its visual appearance in small telescopes, created by the cluster's complex of stars and voids, is suggestive of nested rose petals. Now estimated to be 1.6 billion years young, the galactic or open cluster of stars also shows its age. All the stars in the cluster were likely born at the same time, but the brighter and more massive ones have more rapidly exhausted the hydrogen fuel in their cores. These have evolved from main sequence stars like the Sun into the many red giant stars shown with a yellowish cast in this color composite. Using measured color and brightness, astronomers can model the mass and hence the age of the cluster stars just starting to "turn off" the main sequence and become red giants. Over 50 light-years across, Caroline's Rose spans about half a degree (the angular size of the Moon) near the center of the sharp telescopic image.

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Nice Link https://science.nasa.gov/mission/hubble ... -clusters/


Thousands upon thousands of stars illuminate this breathtaking image of star cluster Liller 1, imaged with Hubble’s Wide Field Camera 3. This stellar system, located 30,000 light-years from Earth, formed stars over 11 billion years.


Look at that. Crazy ZOOM IN: https://esahubble.org/images/potw2221a/zoomable/

ESA/Hubble & NASA, F. Ferraro

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Re: APOD: NGC 7789: Caroline's Rose (2024 Jul 06)

Post by Ann » Sat Jul 06, 2024 8:28 am

I like today's APOD, but because it is so large that I can only post it as an attachment, and since I have other attachments to post, I will post two much smaller pictures of Caroline's Rose that I found on the net.


As you can see, Caroline's Rose cluster appears to be quite rich and contain many member stars. But the stars are mostly faint, so the cluster doesn't stand out that clearly against the background. In the Wikisky image you can see that all the brightest stars are red, but the red giant stars are not that much brighter than their cluster siblings, which means that the red giant stars are not extremely bright in themselves.

All of this, taken together, suggests that NGC 7789 is somewhat old-ish. And yes, 1.6 billion years is actually somewhat old for an open cluster.

So let's compare Caroline's Rose with other rich open clusters of different ages! Let's start with a cluster that is older than Caroline's Rose:


According to Wikipedia, NGC 2158 is believed to be 2 billion years old. You can see that it is very rich, much richer than Caroline's Rose. You can also see that the brightest stars of NGC 2158 are red giants that seem to stand out more in brightness than the brightest stars of Caroline's Rose. A word of caution, though: The NGC 2158 image is an SDSS one, and SDSS tends to "exaggerate" the brightness of the reddest stars. (To be more precise, the SDSS channel that is mapped as red is actually an infrared one, and since the reddest stars are typically very infrared, they do look extra bright in SDSS images.)

You can see small blue stars scattered in NGC 2158. According to this source, NGC 2158 is a metal-poor cluster, which could mean, theoretically, that the small blue stars could be blue horizontal branch stars similar to the blue stars of globular clusters. But I doubt it. In my opinion, the small blue stars of NGC 2158 could be early F-type stars or blue stragglers that have gained mass from another star and become hotter. (The bright blue star at lower left that appears to be a member of NGC 2158 is almost certainly a foreground star and an outlier of cluster M35.)


A rich cluster that is young is M11, the Wild Duck Cluster, in Scutum.

1024px-Eso1430a[1].jpg
M11, the Wild Duck Cluster. Credit: ESO.

M11 is believed to be 316 million years old, according to Wikipedia. (Don't ask me how they know it's not 315 or 317 million years old instead. :wink: )

As you can see, M11 is rich, and most of the brightest stars are blue. However, there are many red giant stars in M11 too. The blue stars of M11 are most likely spectral class A, and the blue giants may also typically be spectral class A. Neither the red giants nor the blue giants of M11 are supergiants.


A cluster than is about the same age as M11 is NGC 3532. In a brilliant picture by Velimir Popov and Emil Ivanov, you can really see the mixture of red and blue stars in a rich cluster of this age:



Much younger than M11 and NGC 3532 are the Double Cluster in Perseus:


The stars of the Double Cluster of Perseus are believed to be only 14 million years old. As you can see, most of the brightest stars are blue, but there are five prominent red giant stars. Or, correction, these red stars are not mere giants but supergiants, as are the brightest blue stars of the clusters. The brightest blue and red stars of the Double Cluster of Perseus are much more massive than any stars found in M11, NGC 3532, NGC 2158 or Caroline's Rose.


Let's take a look at an even younger cluster:

NGC 6231 Capella Observatory Josef Pöpsel Stefan Binnewies.png
NGC 6231. Credit: Josef Pöpsel, Stefan Binneweis/ Capella Obersvatory


NGC 6231 is believed to be only 2-7 million years old. All its brightest stars are blue, and it contains no red giant stars at all. The bright yellow star at upper left is a foreground star, as is the small very red star at lower right. If you ask me, an age of 2 million years seems more reasonable than 7 million years, because I suspect that at least one of the massive blue stars of this cluster would have run out of its core fuel and turned into a red supergiant if it was 7 million years old.

Let me finish by showing you a picture of open cluster Trumpler 5:

Trumpler 5 Photocommunity Deutschland.png
Trumpler 5. Credit: Photocommunity Deutschland.

So, based on the appearance of this cluster, how old do you think it is? It's extremely hard (or impossible) to judge Trumpler 5's exact age from its appearance, but what do you think? (I guess you can cheat if you want and google it!) :D

Ann

EDIT: Okay! I couldn't help myself. I googled "Trumpler 5 age" and got a few different answers, among them Log Age, 9.61. (What does that mean, Chris? I have an idea, but I think that would perhaps make the cluster too old.)

Another answer to the age of Trumpler 5 was 125 million years. That is dead wrong! Okay, fellow Starshippers and Asteriskers, can you tell me why that age is dead wrong for Trumpler 5?
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Re: APOD: NGC 7789: Caroline's Rose (2024 Jul 06)

Post by Christian G. » Sat Jul 06, 2024 4:12 pm

A lovely cluster with a lovely name! And a discussion page with plenty more beauties! Star clusters are so enchanting...

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Re: APOD: NGC 7789: Caroline's Rose (2024 Jul 06)

Post by Chris Peterson » Sat Jul 06, 2024 4:41 pm

Ann wrote: Sat Jul 06, 2024 8:28 am EDIT: Okay! I couldn't help myself. I googled "Trumpler 5 age" and got a few different answers, among them Log Age, 9.61. (What does that mean, Chris? I have an idea, but I think that would perhaps make the cluster too old.)
It means log(age in years). So 9.61 means 4.07 billion years, similar to the Sun. I have no opinion as to the accuracy of that value.
Chris

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Re: APOD: NGC 7789: Caroline's Rose (2024 Jul 06)

Post by Ann » Sat Jul 06, 2024 6:38 pm

No takers? No one wants to guess why Trumpler 5 can't be 125 million years old?

Trumpler 5 Photocommunity Deutschland.png
Trumpler 5. Credit: Photocommunity Deutschland.

Let's look at a cluster that is reasonably close to 125 million years old, NGC 2516, which is believed to be 135 million years:


Do Trumpler 5 and NGC 2516 look similar? They don't.


No, Trumpler 5 looks similar to NGC 2158, in that both clusters are very rich, very yellow, full of small stars and devoid of bright blue stars.



Of course, Trumpler 5 and NGC 2516 are not directly comparable, because Trumpler 5 is so much richer than NGC 2516. Also Trumpler 5 is undoubtedly more reddened by foreground dust than NGC 2516. For all of that, we would be justified in saying that very few stars in Trumpler 5 are the least bit blue, whereas the majority of the bright stars in NGC 2516 are bluish. Also the bright stars of NGC 2516 stand out against the background.

Wikipedia said that NGC 2158 is about 2 billion years old, and this source said that Trumpler 5 is about 2.4 billion years old. Whatever! Trumpler 5 and NGC 2158 do look similar to me! I'm happy to consider these two clusters "contemporaries", or more or less so, anyway!

NGC 2158 and Trumpler 5 as two old men.png

Ann
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Re: APOD: NGC 7789: Caroline's Rose (2024 Jul 06)

Post by johnnydeep » Sat Jul 06, 2024 11:41 pm

Ok, where are the "small telescope views" that show "nested rose petals"?
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Re: APOD: NGC 7789: Caroline's Rose (2024 Jul 06)

Post by Chris Peterson » Sat Jul 06, 2024 11:58 pm

johnnydeep wrote: Sat Jul 06, 2024 11:41 pm Ok, where are the "small telescope views" that show "nested rose petals"?
https://knuklhdsobsrv.wordpress.com/wp- ... etch-1.jpg
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Re: APOD: NGC 7789: Caroline's Rose (2024 Jul 06)

Post by Avalon » Sun Jul 07, 2024 2:24 am

I find it interesting how many concentric arcs of stars appear in this cluster. It truly looks like a cosmic rose.

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Re: APOD: NGC 7789: Caroline's Rose (2024 Jul 06)

Post by johnnydeep » Sun Jul 07, 2024 5:35 pm

Chris Peterson wrote: Sat Jul 06, 2024 11:58 pm
johnnydeep wrote: Sat Jul 06, 2024 11:41 pm Ok, where are the "small telescope views" that show "nested rose petals"?
https://knuklhdsobsrv.wordpress.com/wp- ... etch-1.jpg
Thanks. But I think it takes quite a leap of poetic imagination to see that as "nested rose petals"! I see only two, maybe three "petals" at best, and they look more like simple arcs.
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