APOD: Meropes Reflection Nebula (2012 Feb 15)

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APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by APOD Robot » Wed Feb 15, 2012 5:07 am

Image Meropes Reflection Nebula

Explanation: Reflection nebulas reflect light from a nearby star. Many small carbon grains in the nebula reflect the light. The blue color typical of reflection nebula is caused by blue light being more efficiently scattered by the carbon dust than red light. The brightness of the nebula is determined by the size and density of the reflecting grains, and by the color and brightness of the neighboring star(s). NGC 1435, pictured above, surrounds Merope (23 Tau), one of the brightest stars in the Pleiades (M45). The Pleiades nebulosity is caused by a chance encounter between an open cluster of stars and a dusty molecular cloud.

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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by Guest » Wed Feb 15, 2012 5:41 am

What causes the nearly parallel striations in the molecular cloud?

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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by Chris Peterson » Wed Feb 15, 2012 5:45 am

Guest wrote:What causes the nearly parallel striations in the molecular cloud?
Presumably these are shock structures, created by a supernova, nova, or even an active star near the cloud fairly recently.
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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by Ann » Wed Feb 15, 2012 6:26 am

What a lovely image! Congratulations, Leonardo Orazi, you have posted many great images here at Starship Asterisk! :D

As for the "combed hair" structure of the nebula, astrophotographer David Malin wrote (admittedly fifteen years ago or so) that it was caused by dust grains lining up along magnetic lines.

Anyway. The Pleiades is not only one of the loveliest sights in the night-time sky, it is also one of the bluest objects out there. The stars of the Pleiades are certainly not among the most ultraviolet objects in the sky, not compared with the brilliant young stars in Orion and in Scorpius, Lupus, Centaurus, Carina and Vela, for example.

But the Pleiades cluster is just so blue. Unusually for a young cluster, there are no red giants here. All the bright stars emit a lot of blue light. And this blue light gets scattered by the dust grains of the Pleiades nebula. How lovely! :D

In today's APOD, please note the small compact nebula right next to bright star Merope. This nebula is immediately to the lower left of Merope, to the right of the lower left diffraction spike emanating from Merope in this picture.

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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by alter-ego » Wed Feb 15, 2012 6:43 am

Chris Peterson wrote:
Guest wrote:What causes the nearly parallel striations in the molecular cloud?
Presumably these are shock structures, created by a supernova, nova, or even an active star near the cloud fairly recently.
Per the latter suggestion, one hypothesis suggests the striations are formed by the interaction of the star cluster itself and the dust cloud. Analogous to cirrus clouds where clumps of ice crystals settle on a layer a air layer of different wind speed and the shearing action creates long plumes, radiation pressure from the cluster stars decelerate dust particles while gas, unaffected by the radiation, provides the "wind shear" that drags the dust around the stars forming a thin shell.
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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by Chris Peterson » Wed Feb 15, 2012 6:50 am

Ann wrote:As for the "combed hair" structure of the nebula, astrophotographer David Malin wrote (admittedly fifteen years ago or so) that it was caused by dust grains lining up along magnetic lines.
That is unlikely (and was unlikely 15 years ago). Shock structures are much more plausible.
Chris

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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by StefanoDeRosa » Wed Feb 15, 2012 8:16 am

Really a stunning image! congratulations Leonardo :wink:

Stefano

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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by owlice » Wed Feb 15, 2012 8:46 am

A closed mouth gathers no foot.

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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by Boomer12k » Wed Feb 15, 2012 11:25 am

Stunning!!!!

Striations? I thought they were God's Brush Strokes.... :D

Good Job!

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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by Peter R » Wed Feb 15, 2012 11:58 am

Faintly visible and almost touching Merope in a half past six direction is the IC 349 reflection nebula or Barnard's Merope Nebula http://apod.nasa.gov/apod/ap060715.html
It often disappears in the bright glow of Merope so it is nice to see it as well in todays APOD.

/*Peter R

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Tempel's Nebula (2012 Feb 15)

Post by neufer » Wed Feb 15, 2012 3:04 pm

http://leo.astronomy.cz/tempel/tempel.html wrote:
ImageImage
<<Ernst Wilhelm Leberecht Tempel was born on December 4, 1821, at Niedercunnersdorf, near Löbau, in the kingdom of Saxony. His parents were people in poor circumstances, and so he received but a scanty education, which in after years he lost no opportunity of improving. When about twenty years of age he went to Copenhagen, where he worked for about three years as a lithographer, and where his lively manners and his taste for music and art acquired for him many friends, some of whom he never lost sight of. After leaving Copenhagen he went for some time to Christiania, and his roving spirit then brought him to Italy, where he settled at Venice and exercised his art for many years. Having become interested in astronomy he purchased a 4-inch refractor by Steinheil, with which he began exploring the heavens. It was a great encouragement to him to persevere in this occupation (for which he had obtained leave to use the balcony of a Venetian palace), that on April 2, 1859, he succeeded in discovering a comet (1859 I), and thenceforth he remained an enthusiastic observer until his last illness. He was the first to notice (on October 19, 1859) the now well-known nebula around Merope in the Pleiades, the announcement of which, though confirmed by various observers with small instruments, was received with much hesitation, as the object was less readily seen with a larger aperture and higher power.>>
Art Niedercunnersdorffer

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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by orin stepanek » Wed Feb 15, 2012 3:33 pm

Beautiful APOD! 8-) I also liked the illustration of the chance encounter. :D
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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by pstargazer » Wed Feb 15, 2012 10:58 pm

Lovely images, always a delight

saturn2

Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by saturn2 » Wed Feb 15, 2012 11:05 pm

The carbon dust reflecting the blue light from a nearby star. If it emits blue light is a young star.

saturn2

Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by saturn2 » Wed Feb 15, 2012 11:17 pm

This image is very beautiful. Congratulations.

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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by NoelC » Thu Feb 16, 2012 1:55 am

It's a beautiful shot!
saturn2 wrote:If it emits blue light is a young star.
I always wondered about that... If memory serves there are some blue stars, I believe, found in globular clusters. Were those called Blue Stragglers? Can't quite remember if that was the name... Yes, that was it: http://en.wikipedia.org/wiki/Blue_straggler

Are these old? Or newly formed by interactions between cluster members?
M13_Showing_Blue_Stragglers.jpg
-Noel
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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by Ann » Thu Feb 16, 2012 4:40 am

NoelC wrote:It's a beautiful shot!
saturn2 wrote:If it emits blue light is a young star.
I always wondered about that... If memory serves there are some blue stars, I believe, found in globular clusters. Were those called Blue Stragglers? Can't quite remember if that was the name... Yes, that was it: http://en.wikipedia.org/wiki/Blue_straggler

Are these old? Or newly formed by interactions between cluster members?
M13_Showing_Blue_Stragglers.jpg
-Noel
Those are old stars, Noel, but they aren't blue stragglers. There are so many of them, and they are so comparatively bright, that they can't be blue stragglers.
Image
Take a look at this Hubble image of globular cluster 47 Tucanae. You can't judge a cluster by a single picture, because the appearance of the cluster depends on the filters used to take the picture, and recently there was a Hubble/ESA picture of a globular cluster where I, at least, couldn't judge by the color of the stars if there were any genuinely blue stars in it. But I could find other pictures of the same globular (NGC 6752?) and see that other pictures revealed the blue stars in it. When it comes to 47 Tucanae, however, I have never seen any obvious blue stars in this globular, even though you can find several RGB images of it on the net. Even so, 47 Tucanae is famous for containing a moderately large number of blue stragglers! But these stars are too few, too faint and too "barely blue" to stand out in an RGB image.

The blue stars in the picture you posted, Noel, are blue horizontal branch stars. These stars are only found in old and very metal-poor globular clusters. (Actually, there are certainly a number of hot blue horizontal stars mixed with the few hundred billion stars in the disk and bulge of the Milky Way, but how do you find them? In an old globular cluster, these stars really stand out - in the rest of the galaxy, they certainly don't.)
Image
Like I said, it takes a very metal-poor population of stars to create blue horizontal stars. All the Milky Way globulars are more or less metal-poor, but 47 Tucanae isn't metal-poor enough to make these blue stars. 47 Tucanae only makes red horizontal stars.

This is a color-magnitude diagram of the stars in 47 Tucanae. You can see that 47 Tucanae has a very short horizontal branch extending to the left. Left here means blue, but 47 Tucanae's horizontal stars aren't blue.
Image
This, on the other hand, is a typical color-magnitude diagram of a very metal-poor globular cluster. You can see that the horizontal branch extends far to the left. Here is where you find the numerous blue horizontal stars.

You can also see that only the very metal-poor clusters will produce RR Lyrae stars. These are the most important distance indicators in globular clusters. They are located between the blue horizontal stars and the red horizontal stars on the horizontal branch. 47 Tucanae, which is too metal-rich to produce blue horizontal stars, doesn't have RR Lyrae stars either.

You can also see the location of the blue stragglers in the color-magnitude diagram. Note that the blue stragglers are both less bright and less blue than the blue horizontal branch stars. They are also far less numerous.

To summarize, the blue horizontal stage is a normal late evolutionary phase for very metal-poor (and therefore probably very old) stars. The blue straggler stage is a breach of the normal stellar evolution, caused by stars gaining more mass probably during the late stage of their main sequence lifetime. The extra mass allows them to stay on the main sequence longer and shine bluer than their original birth mass would have allowed.

Typically, blue horizontal branch stars are ten billion years old or more. Blue straggler stars, however, can be young or old. So it isn't true that all blue stars are young. Interestingly, the globulars that only produce red horizontal stars are typically younger than the ones that make blue horizontal stars.

Ann
Last edited by Ann on Thu Feb 16, 2012 10:49 am, edited 4 times in total.
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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by Cpatriot » Thu Feb 16, 2012 5:43 am

Now while admittedly being of faint knowledge, compared to you folks who do this for a living, and to satisfy your own curiosity. which is very admirable and enticing. I take a view that demands further explanation of the "Hair Strands" as being a " Chance encounter of a globular structure of stars and a dust cloud". Where might this globular structure be today.?
In what direction would they have been traveling in respect to the dust.? Why are the Pliedies still in the same formation.?
It would seem these phantom stars traveling through here would still be visible somewhere, especially if they are traveling in a different direction than everyone else as it appears from the uniform striations of the dust.
You guys must stay up many many nights trying to put these conundrums in perspective.!
One final question, is our star young or old ? because it looks mighty yellow to me.
This is one great website and I have brought many of my friends here to observe...and wonder. Thanks.!!!

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Re: APOD: Meropes Reflection Nebula (2012 Feb 15)

Post by Chris Peterson » Thu Feb 16, 2012 6:48 am

Cpatriot wrote:Now while admittedly being of faint knowledge, compared to you folks who do this for a living, and to satisfy your own curiosity. which is very admirable and enticing. I take a view that demands further explanation of the "Hair Strands" as being a " Chance encounter of a globular structure of stars and a dust cloud". Where might this globular structure be today.?
In what direction would they have been traveling in respect to the dust.? Why are the Pliedies still in the same formation.?
It would seem these phantom stars traveling through here would still be visible somewhere, especially if they are traveling in a different direction than everyone else as it appears from the uniform striations of the dust.
Open clusters like the Pleiades are loosely bound together by gravity. That means they have relatively long lifetimes before perturbations cause them to dissipate- tens of millions of years, probably (compared with many billions for globular clusters). That's long enough that they become separated from their region of formation, and have opportunities to encounter other bodies or nebulas. It is very difficult to work the dynamics backwards and figure out exactly where they have been, or what other object we can see might once have been near them.

The stars of the Pleiades are in a complex set of orbits around each other. Even though the group stays together, their relative orientation is constantly changing.
Chris

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