Starship Asterisk*

Re: Diffraction spikes... I'm trying my hardest not to make another window pane joke. :lol:

[list][size=150][b][url=http://www.universetoday.com/2009/09/09/just-how-good-is-the-new-hubble-lets-compare/]Just How Good is the "New" Hubble? Let's Compare[/url][/b][/size]

[url=http://www.universetoday.com/2009/09/09/just-how-good-is-the-new-hubble-lets-compare/writing-images3/][img]http://www.universetoday.com/wp-content/uploads/2009/09/Writing-Images3.jpg[/img][/url]
[i]Hubble images of Omega Centauri starfield from 2002, left, and 2009, right. (HST WFC3/UVIS)[/i][/list]

[size=85][i]Thanks, Art[/i][/size]

[quote="BMAONE23"]Looking at [url=http://imgsrc.hubblesite.org/hu/db/images/hs-2009-25-q-full_jpg.jpg]this 36mb file[/url] of the Omega cluster, I have to wonder why the Red Giant stars have a Tripled diffraction spike appearance while even the Largest (brightest) Blue stars only have singular diffraction spikes?[/quote]

Could it be something structural in the filter itself? Perhaps the filter that created the triple-difraction spikes is a three-layer filter whereas the other is a single layer one?

Rob

Good question.
I was looking for the binary systems in the large image. Sometimes they can be noticed in the doubling of the diffraction spikes in the images. I noticed though, that ALL the larger red stars have trippled spikes. Even the largest blue star in the image has single spikes and it is easily as impressive in presance as the red stars.

Why would the diffraction spikes even be tripled? Maybe the blue has tripled spikes but they are closer together so it looks like one fat spike instead of three thin ones. Red represents infrared and blue represents one of the UV filters, right? Maybe wavelength has something to do with it.

Looking at [url=http://imgsrc.hubblesite.org/hu/db/images/hs-2009-25-q-full_jpg.jpg]this 36mb file[/url] of the Omega cluster, I have to wonder why the Red Giant stars have a Tripled diffraction spike appearance while even the Largest (brightest) Blue stars only have singular diffraction spikes?

In reply to JXP; indeed the red and blue stars are cluster members. They're stars which have evolved off the main sequence, and thus become much brighter than main sequence stars of the same or lesser mass.

For karlhein; that's a good question, and globular cluster formation is not well understood. Many globular clusters do seem to have some overall rotation. The key issue is that star formation in galaxies is driven by the molecular clouds, and the clouds had time (since the galaxy began to form) to settle to the midplane of the galaxy in near-circular orbits. So new stars are made there. Globular clusters are made very quickly, in extremely dense molecular clouds in single (well, this point is somewhat debated--but if multiple, VERY close in time) epochs of star formation. So GCs don't form stars in a plane like spiral galaxies do. It's thought that some elliptical galaxies form very quickly (sort of like globular clusters), and they also don't show strong planar geometry.

Very nice post on the globular cluster Omega Centuri. Is there any thought on why globular clusters are globular rather than being flattened spirals like them more typical galaxy? Obviously it involves rotation around the communal center of mass, which one anticipates that globular clusters don't do; but why the lack of rotation that causes flattening?

This is a fantastic photo. My question is: are the prominent red and blue
stars likely cluster members? We were always taught that globular clusters
were pop II stars. Given the age of the cluster, both red giants and bright
blue stars would have to be either acquired recently or formed as mergers.
I'd appreciate links if an "answer" is not apparent.

Thanks,
John-

A couple points of interest:
*The bright blue stars in the picture actually aren't blue stragglers, as implied by the caption; they're at a stage called the horizontal branch, in between two red giant stages. The HST press release for this image gets this small detail correct:
http://hubblesite.org/newscenter/archive/releases/2009/25/image/q/
*The binary stars will be among the faint blue stars (most of which are white dwarfs). However, I don't know which of the faint blue stars are the two binary stars. It's not possible to tell just from looking at this picture; they were identified by cross-correlating X-ray source positions with stars with unusual combinations of colors in particular bands. It would take me quite a while to figure out which they were in this image (if they're actually within this image), by comparing this image with images and positions in the professional astronomical literature.
*As for the planetary nebulae, that's a good question. Planetary nebulae expand fairly quickly (~10 km/s), so they achieve relatively large sizes fairly quickly (for instance, the famous Ring Nebula is about ~0.16 pc in radius, or 34000 x the distance between the Earth and Sun). The typical distances between stars in globular clusters are much less than that; so the Ring Nebula would have been destroyed by interactions with passing stars before it could attain its current age. There are some (small, young) planetary nebulae in globular clusters (http://apod.nasa.gov/apod/ap000804.html), but they don't last as long as in the rest of the Galaxy.

Can anyone tell me why, with so many red giants in the picture, there are no planetary nebulas? Shouldn't some of the red giants have evolved to the white dwarf stage? Is extreme radiation causing planetaries to be so short lived that they don't show-up?

I like apodman's re-saying of my idea in the appropriate technical parlance. Thank you.

And then he volunteers. Cool.

I guess the layers could be numbered so that we could remove or add them sequentially.


[quote="apodman"]APOD wiki. The graphic anyone can annotate. Make it multi-layered so annotations can be selected separately or in combination. And naturally we want zero image degradation with repeated edits and saves. It should be trivial for one of our experts to write the software for a graphical wiki. All we need then is an administrator, a couple of moderators, and a volunteer for each constellation; I'll take the teapot so that leaves only 87 constellations for the rest of you.[/quote]

APOD wiki. The graphic anyone can annotate. Make it multi-layered so annotations can be selected separately or in combination. And naturally we want zero image degradation with repeated edits and saves. It should be trivial for one of our experts to write the software for a graphical wiki. All we need then is an administrator, a couple of moderators, and a volunteer for each constellation; I'll take the teapot so that leaves only 87 constellations for the rest of you.

[quote="peter_from_nyc"]Is there some way, even a wikipedia type way, that someone can annotate the stars?[/quote]
I like the idea of an APOD wiki. A place for annotations or even corrections. It would probably need to be kept seperate from APOD, but accessible from there.

Other Omega Centauri photos in this release.

http://hubblesite.org/newscenter/archive/releases/2009/25/image/q/
http://hubblesite.org/newscenter/archive/releases/2009/25/image/r/
http://hubblesite.org/newscenter/archive/releases/2009/25/image/s/
http://hubblesite.org/newscenter/archive/releases/2009/25/image/t/
http://hubblesite.org/newscenter/archive/releases/2009/25/image/u/
http://hubblesite.org/newscenter/archive/releases/2009/25/image/v/
http://hubblesite.org/newscenter/archive/releases/2009/25/image/w/

[quote="peter_from_nyc"]Is there some way, even a wikipedia type way, that someone can annotate the stars?[/quote]
Certainly, but somebody has to do it, and that somebody is whoever provides the source material. The editors of APOD don't have the time to actually create annotated images. In fact, some APODs do provide annotation, including mouse-over annotation. But most do not simply because no annotation was available.

Sometimes, annotated versions are provided on this forum because somebody here takes on that job.

[quote="peter_from_nyc"] But wouldn't it be cool (pun intended) to circle the binary stars? [/quote]
http://apod.nasa.gov/apod/ap090914.html

I'd like to know which were the binaries also.

Orin

http://apod.nasa.gov/apod/ap090914.html

I'm about 60 years old, and with 2 MIT degrees. I love reading APOD every day.

But sometimes, I can [b]NOT [/b]figure out what you guys are pointing at.

Is there some way, even a wikipedia type way, that someone can annotate the stars?

E.g. with the "The Center of Globular Cluster Omega Centauri " of 2009 September 14
someone could point to the red stars, the blue stars, the binary stars.

Yeah I can see the difference between red and blue. But wouldn't it be cool (pun intended) to circle the binary stars? Or number them?

This is a bit conceited, but here it goes: if I can't tell the difference, there are probably thousands of people who can't.

Peter

PS: I like it when you put your cursor over the photo and the constellations appear. I can never name them (except for Big Dipper, and Orion's belt). But something like that on a routine basis. If there were some tool, and if people could do it to help others, and maybe like wikipedia, there would be gradients of editorial supervision.

And think of the education opportunities: A high school class trying to document a photo. A second HS class trying to find mistakes, and correct them. And yearly awards for groups who have helped others in those tasks.