APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Comments and questions about the APOD on the main view screen.
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APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by APOD Robot » Tue Oct 22, 2013 4:06 am

Image A Massive Star in NGC 6357

Explanation: For reasons unknown, NGC 6357 is forming some of the most massive stars ever discovered. One such massive star, near the center of NGC 6357, is framed above carving out its own interstellar castle with its energetic light from surrounding gas and dust. In the greater nebula, the intricate patterns are caused by complex interactions between interstellar winds, radiation pressures, magnetic fields, and gravity. The overall glow of the nebula results from the emission of light from ionized hydrogen gas. Near the more obvious Cat's Paw nebula, NGC 6357 houses the open star cluster Pismis 24, home to many of these tremendously bright and blue stars. The central part of NGC 6357 shown spans about 10 light years and lies about 8,000 light years away toward the constellation of the Scorpion.

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by Beyond » Tue Oct 22, 2013 4:12 am

Ahh, i spotted the cave easily in this one. It's illuminated by the massive star. :yes: :content:
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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by Ann » Tue Oct 22, 2013 4:40 am

This is really a most fascinating area of star formation. The stars that already exist here, and the stars being born here, are fantastic. It is a great Hubble picture, too.

Of course I keep wondering about the colors. As can be seen from this larger photo of the same area, the star that is seen "inside the nebular cave", so that it should be more reddened than the other stars, is instead seen to be the bluest. Is that because of the filters used and how the filters were mapped? This page lists several filters used for this image, among them a 550 nm filter mapped as blue, and a 547 nm filter, very slightly bluer than the first one, which is mapped as green. Does this have anything to do with the confusing colors?

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by Case » Tue Oct 22, 2013 5:26 am

http://en.wikipedia.org/wiki/NGC_6357 wrote:Pismis 24
[NGC 6357] includes the open cluster Pismis 24, which is home to several massive stars. One of the brightest stars in the cluster, Pismis 24-1, was thought possibly to be the most massive on record, until it was discovered to be a binary system.[5]

Southeast Asia

Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by Southeast Asia » Tue Oct 22, 2013 6:03 am

My question for this APOD entry would be: exactly how, or even roughly how massive is this massive star in NGC 6357?

Compared to say, our Sun?

Thanks always for all the insight and reader education.

jmaiz

Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by jmaiz » Tue Oct 22, 2013 6:24 am

Hi, I am the author of this image. Can you please correct my name? It is "J. Maíz Apellániz", not "J. M. Apellániz". Maíz is part of my family name, not my middle name, and should be spelled out completely. You can learn more about Spanish names at [https://en.wikipedia.org/wiki/Spanish_names][https://en.wikipedia.org/wiki/Spanish_names]. Also, you can verify this information by going to my web site: [http://jmaiz.iaa.es][http://jmaiz.iaa.es]. Thank you.

PhilT

Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by PhilT » Tue Oct 22, 2013 6:49 am

That is one heck of a heliosphere compared to our own Suns :roll:

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by Boomer12k » Tue Oct 22, 2013 7:07 am

Always a WOW Moment!!!!

Another CAVE Nebula? Or is it CASTLE GREYSKULL???

And "Ultra Cosmic Man" with his pointy helmet...lifting UP the maw of the cave!

I love the Clam-like lower part of the "Cavern" ....with a "PEARL" inside.....just awe inspiring...

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by orin stepanek » Tue Oct 22, 2013 11:30 am

Beyond wrote:Ahh, i spotted the cave easily in this one. It's illuminated by the massive star. :yes: :content:
Agreed! 8-)
Orin

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by dmjhardman » Tue Oct 22, 2013 12:13 pm

Beautiful. And thank you for posting these pictures -- I so missed them during the shutdown and want you to know that some of us do very much appreciate NASA and all of you who contribute to making these pictures possible. They are my 'morning fix' each day. Thank you.

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by bentsn » Tue Oct 22, 2013 12:46 pm

It appears that the image is a composite. The diffraction spikes on the two lowest bright stars are rotated about 45 degrees from those in the rest of the image. In addition the bottom right corner of the image has very low resolution.

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by geckzilla » Tue Oct 22, 2013 1:00 pm

jmaiz wrote:Hi, I am the author of this image. Can you please correct my name? It is "J. Maíz Apellániz", not "J. M. Apellániz". Maíz is part of my family name, not my middle name, and should be spelled out completely. You can learn more about Spanish names at [https://en.wikipedia.org/wiki/Spanish_names][https://en.wikipedia.org/wiki/Spanish_names]. Also, you can verify this information by going to my web site: [http://jmaiz.iaa.es][http://jmaiz.iaa.es]. Thank you.
I sent an email to RJN about it.
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by geckzilla » Tue Oct 22, 2013 1:01 pm

bentsn wrote:It appears that the image is a composite. The diffraction spikes on the two lowest bright stars are rotated about 45 degrees from those in the rest of the image. In addition the bottom right corner of the image has very low resolution.
Deep space photos invariably are. It's a long process.
Just call me "geck" because "zilla" is like a last name.

jmaiz

Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by jmaiz » Tue Oct 22, 2013 2:00 pm

geckzilla wrote:
bentsn wrote:It appears that the image is a composite. The diffraction spikes on the two lowest bright stars are rotated about 45 degrees from those in the rest of the image. In addition the bottom right corner of the image has very low resolution.
Deep space photos invariably are. It's a long process.
Not only are there two orientations involved but two cameras. The image is a combination of ACS and WFPC2 data.

jmaiz

Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by jmaiz » Tue Oct 22, 2013 2:01 pm

geckzilla wrote:
jmaiz wrote:Hi, I am the author of this image. Can you please correct my name? It is "J. Maíz Apellániz", not "J. M. Apellániz". Maíz is part of my family name, not my middle name, and should be spelled out completely. You can learn more about Spanish names at [https://en.wikipedia.org/wiki/Spanish_names][https://en.wikipedia.org/wiki/Spanish_names]. Also, you can verify this information by going to my web site: [http://jmaiz.iaa.es][http://jmaiz.iaa.es]. Thank you.
I sent an email to RJN about it.
Thanks.

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by RJN » Tue Oct 22, 2013 2:07 pm

jmaiz wrote:Hi, I am the author of this image. Can you please correct my name? It is "J. Maíz Apellániz", not "J. M. Apellániz".
OK. Fixed. Sorry. - RJN

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by BDanielMayfield » Tue Oct 22, 2013 2:31 pm

APOD Robot wrote:Image A Massive Star in NGC 6357

Explanation: For reasons unknown, NGC 6357 is forming some of the most massive stars ever discovered.
One reason shouldn’t be an unknown, for it seems obvious that to get really massive stars there would have had to have been an unusually rich, dense supply of dust and gas to have formed them.
Just as zero is not equal to infinity, everything coming from nothing is illogical.

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by Chris Peterson » Tue Oct 22, 2013 2:52 pm

Ann wrote:Of course I keep wondering about the colors. As can be seen from this larger photo of the same area, the star that is seen "inside the nebular cave", so that it should be more reddened than the other stars, is instead seen to be the bluest. Is that because of the filters used and how the filters were mapped? This page lists several filters used for this image, among them a 550 nm filter mapped as blue, and a 547 nm filter, very slightly bluer than the first one, which is mapped as green. Does this have anything to do with the confusing colors?
The short answer is yes, that's why the colors aren't natural.

There's really no excuse for them to put together such a poor page as that, which doesn't properly identify the filters used. If forces anybody who is interested to go out and track them down. The actual filters used, with their central wavelength and passband, were:

ACS 550M - 558 nm (54.7 nm) mapped to blue
ACS 658N - 658.4 nm (7.3 nm) mapped to red
ACS 850LP - 944.5 nm (122.9 nm) mapped to red
WF 547M - 548.3 nm (48.4 nm) mapped to green
WF 656N - 656.4 nm (2.2 nm) mapped to red

To fully understand the represented color, you need to consider the passband of each filter (a broad filter with a central wavelength associated with a particular color may not appear that color at all). You also need to understand how the individual channels were weighted before being mapped to RGB color channels- information which isn't available on the image page.

Of course, just noting that a moderately narrow "green" filter is being mapped to blue, that the blue and green channels are almost identical, and that invisible IR wavelengths are being mapped to red should tell you that you aren't seeing an image reflective of natural colors.
Chris

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by geckzilla » Tue Oct 22, 2013 3:01 pm

I've found the spacetelescope.org pages to be a lot more informative than other outreach sites. Most of them don't even include filter information.
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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by Chris Peterson » Tue Oct 22, 2013 3:10 pm

geckzilla wrote:I've found the spacetelescope.org pages to be a lot more informative than other outreach sites. Most of them don't even include filter information.
IMO, a site that claims to be involved in scientific outreach, that doesn't, at a minimum, identify the actual filters used as well as the mappings between them and RGB, is an embarrassment. It just reflects the dumbing down of science in America today (although I've noticed that ESA sites are often particularly poor when it comes to providing the most basic of information needed to understand an image).

Often, these sites put up some sort of press-release quality text that isn't very informative and is only moderately accurate, as well. Seems to be more about PR than actual education.
Chris

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by Ann » Tue Oct 22, 2013 3:12 pm

Southeast Asia wrote:My question for this APOD entry would be: exactly how, or even roughly how massive is this massive star in NGC 6357?

Compared to say, our Sun?

Thanks always for all the insight and reader education.
http://en.wikipedia.org/wiki/Pismis_24-1 wrote:

When originally discovered and thought to be a single star, Pismis 24-1 was calculated to have a mass around 300 times the sun, but as currently known all three components have masses less than 100 times the sun.
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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by geckzilla » Tue Oct 22, 2013 3:23 pm

Chris Peterson wrote:
geckzilla wrote:I've found the spacetelescope.org pages to be a lot more informative than other outreach sites. Most of them don't even include filter information.
IMO, a site that claims to be involved in scientific outreach, that doesn't, at a minimum, identify the actual filters used as well as the mappings between them and RGB, is an embarrassment. It just reflects the dumbing down of science in America today (although I've noticed that ESA sites are often particularly poor when it comes to providing the most basic of information needed to understand an image).

Often, these sites put up some sort of press-release quality text that isn't very informative and is only moderately accurate, as well. Seems to be more about PR than actual education.
The text is blue for the filter used in the blue channel, green for the next, and red for the other three. The only thing they didn't include were whether they were narrow, wide, medium, or whatever LP stands for (is that polarized?) longpass.
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by Chris Peterson » Tue Oct 22, 2013 3:44 pm

geckzilla wrote:
Chris Peterson wrote:
geckzilla wrote:I've found the spacetelescope.org pages to be a lot more informative than other outreach sites. Most of them don't even include filter information.
IMO, a site that claims to be involved in scientific outreach, that doesn't, at a minimum, identify the actual filters used as well as the mappings between them and RGB, is an embarrassment. It just reflects the dumbing down of science in America today (although I've noticed that ESA sites are often particularly poor when it comes to providing the most basic of information needed to understand an image).

Often, these sites put up some sort of press-release quality text that isn't very informative and is only moderately accurate, as well. Seems to be more about PR than actual education.
The text is blue for the filter used in the blue channel, green for the next, and red for the other three. The only thing they didn't include were whether they were narrow, wide, medium, or whatever LP stands for (is that polarized?) longpass.
Other important information not included, which IMO every page should include: orientation (all astronomical images are assumed to be north up, east left unless otherwise noted), field of view of one or both axes, identifiers of the source images. (I understood the way color mapping was identified- the comment about mapping wasn't in regards to this particular page, just a general observation.)

BTW, this page isn't very good, but it's far from the worst I've seen. And while I would suggest that every astroimager provide this sort of information for their own work (far too many don't!), my quibble here is with sites specifically devoted to educational outreach, and probably supported by a combination of taxes and mandatory allotments from the primary research grants involved in collecting the data.
Chris

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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by geckzilla » Tue Oct 22, 2013 3:55 pm

Yeah, I think their strategy differs from yours a little. They want to draw people in with an amazing image and show the least confusing information possible so that the average Joe looking at the site comes away feeling that the continued funding of Hubble is a worthy cause. It's definitely more about being inspiring and rapid avulsion of socks through mere viewing of images. It's sort of funny that when viewing a Hubble image it's almost guaranteed that north isn't up because it almost always looks more presentable if the image is rotated so that the areas without data can be nicely cropped of. I get happy on the rare occasion I don't have to rotate them away from north up.
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Re: APOD: A Massive Star in NGC 6357 (2013 Oct 22)

Post by Chris Peterson » Tue Oct 22, 2013 4:32 pm

geckzilla wrote:Yeah, I think their strategy differs from yours a little. They want to draw people in with an amazing image and show the least confusing information possible so that the average Joe looking at the site comes away feeling that the continued funding of Hubble is a worthy cause. It's definitely more about being inspiring and rapid avulsion of socks through mere viewing of images. It's sort of funny that when viewing a Hubble image it's almost guaranteed that north isn't up because it almost always looks more presentable if the image is rotated so that the areas without data can be nicely cropped of. I get happy on the rare occasion I don't have to rotate them away from north up.
Of course, I'm not suggesting that they fill the main caption with excessive detail about the imaging process itself. But there's already a sidebar for technical information. That's the place to provide details- more than they typically do. Avulsion of socks is great, but it shouldn't come at the expense of avulsion of basic information.

I don't care if the images are displayed north up. When the intent is aesthetic (or partly so) it's fine to rotate the image. But tell us the rotation angle and image scale! I can't count the times over the years that myself or somebody else has had to painfully work that out for an APOD image in order to identify some secondary feature.
Chris

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