Help, please?

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Ann
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Help, please?

Postby Ann » Thu May 28, 2015 1:50 am

For various reasons I just felt the urge to check up starbursting dwarf galaxy NGC 1569. I found this page, complete with information about filters used for the image. Unfortunately for me, the image focuses on the nebulas and ionized gaseous outflows of the galaxy, whereas I would like to concentrate on the two super star clusters in the galaxy. These clusters show up quite well in this image. But unfortunately I can't seem to find any information about the filters used for that image.

Can anyone help me?

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Chris Peterson
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Re: Help, please?

Postby Chris Peterson » Thu May 28, 2015 3:58 am

Ann wrote:For various reasons I just felt the urge to check up starbursting dwarf galaxy NGC 1569. I found this page, complete with information about filters used for the image. Unfortunately for me, the image focuses on the nebulas and ionized gaseous outflows of the galaxy, whereas I would like to concentrate on the two super star clusters in the galaxy. These clusters show up quite well in this image. But unfortunately I can't seem to find any information about the filters used for that image.

From the Fast Facts for that release, F336W (U), F555W (V), F658N (H-alpha), F814W (I). Unfortunately, the mapping to RGB isn't given. The image is a "pretty picture" not used for science, so the processing details may not be available. There's a paper published analyzing the data used to produce the image (which included other filters, as well). But as is typical, each channel was analyzed separately. Usually, combining channels into a color image of some kind obfuscates the science.
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Re: Help, please?

Postby bystander » Thu May 28, 2015 4:32 am

ESA Hubble (HEIC) has some mapping information:

F336W (U) blue, F555W (V) green, F658N (H-alpha) and F814W (I) red
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Ann
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Re: Help, please?

Postby Ann » Thu May 28, 2015 4:35 am

Thank you for your help!

Ann
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geckzilla
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Re: Help, please?

Postby geckzilla » Thu May 28, 2015 7:39 am

There's some exquisite data hidden in the archive on those clusters. It's from Hubble's old ACS/HRC (Advanced Camera for Surveys / High Resolution Channel) which, sadly, is no longer functional. This observation of NGC 1569 called for three wideband channels: F814W, F555W, and F330W. So that's a near-infrared, green, and near-ultraviolet image.

Chris Peterson wrote:Usually, combining channels into a color image of some kind obfuscates the science.

This is so very true. It takes a special kind of processing for it to be scientifically useful. I don't claim my processing below is that kind of useful, but it treats the stars a lot more fairly than the previous images supplied in this thread. I tried to balance the colors so that none of them is overwhelming and the values are left dark so that the relative brightnesses of each cluster and star are preserved and the histogram doesn't get clamped. It definitely requires a dark background and viewing at 100% resolution to enjoy.

NGC1569_ACS_HRC_IR_G_UV.jpg


This is an alternative version which replaces the F814W with an ACS/WFC [NII] (F658N) filter. It had to be scaled up by 200% to match the HRC data, though. The interpolation isn't especially noticeable, so that's nice. Surprisingly, some of the stars have strong [NII] signals. I presume that is because they are tightly wrapped in a bubble of emission nebula, but if there is another explanation available I'd be open to it of course.
NGC1569_ACS_HRC_NII_G_UV.jpg


Some interesting features I noticed which are visible as yellowish fuzzballs are visible in both images. If I had to, I would guess globular clusters...
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Ann
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Re: Help, please?

Postby Ann » Thu May 28, 2015 8:39 am

Thanks, Geck, that is so very interesting! It really shows the star clusters brilliantly. While one of them (clearly the oldest one) emits quite a lot of UV light and almost certainly still contains quite few hot bright stars, it is surrounded by large numbers of red supergiants. The other cluster, which is a sort of Siamese Double Cluster, is much bluer and therefore younger than the other large cluster and is surrounded by small blue dots.

Absolutely fascinating! I quite agree, your image contains so much more information than the prettified picture produced for public consumption. Even though I don't question the beauty of it.

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Re: Help, please?

Postby geckzilla » Thu May 28, 2015 8:50 am

The press release image is alright, but it is also a bit overprocessed, if you ask me. When the contrast is increased so much it looks good in thumbnail view but it becomes garish when viewed up close. I'm going to do my own version.
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Re: Help, please?

Postby geckzilla » Sat May 30, 2015 6:58 am

Here's an animation I made of variable stars in the galaxy. This isn't near the clusters or really anything in particular. It's just a small section of the two exceptionally high quality data sets taken a year apart which makes the variable stars easy to spot. It's fun to watch for a moment, anyway.

http://www.geckzilla.com/astro/NGC1569_var_stars.html
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Ann
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Re: Help, please?

Postby Ann » Sat May 30, 2015 7:57 am

geckzilla wrote:Here's an animation I made of variable stars in the galaxy. This isn't near the clusters or really anything in particular. It's just a small section of the two exceptionally high quality data sets taken a year apart which makes the variable stars easy to spot. It's fun to watch for a moment, anyway.

http://www.geckzilla.com/astro/NGC1569_var_stars.html


Really fascinating!

There are many variable stars in that field. What kind of variables do you think they are?

There is one relatively bright star that almost winks out as it is pulsating. What could it be?

Do you think there are any Cepheids in the field?

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Re: Help, please?

Postby geckzilla » Sat May 30, 2015 8:24 am

It's hard to say. I am not sure why the two epochs are so far apart. I suspect it might have something to do with waiting so that the telescope could rotate exactly 90° for the second one. The rotation helps to deal with the charge bleeds and probably some other niggling details. It's possible that no astronomer has bothered to look at the data for the purpose of studying the variables since it wasn't originally observed with that intention in mind. Obviously, one needs to take a set number of observations over a given time frame to discover the periodicity of variable stars. I doubt much can be done with these two. Maybe I'm wrong! That relatively bright one that nearly winks out could just be a lucky catch of the star at nearly minimum and maximum brightness. I would be surprised if none of them were Cepheids.
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