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Old 26-05-2012, 04:36 PM
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madbadgalaxyman (Robert)
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CCDs with high sensitivity at near 1 micron

An interesting recent development in CCDs is some CCDs that have their maximum sensitivity in the near-infrared.

CCDs used in the Jasmine Space Astrometry mission will have a 90% quantum efficiency at 0.9 micrometers wavelength.

I don't think these are the exotic "infrared only" CCDs with all their attendant problems.

This could enable amateurs to do near-infrared imaging, a useful thing for Milky Way objects which are highly obscured by dust, as the infrared photons have a habit of getting past the dust grains.
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Old 27-05-2012, 09:06 AM
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Effects of increased wavelength on dust lanes

As I am talking about long wavelength (towards 900-1000nm) CCD sensitivity, I thought I would share with you these three images of M51;
In order, the central wavelength of each filter that was used is :
(1) 435nm (near photometric B band)
(2) 555nm (near photometric V band)
(3) 814nm (near photometric I band)

But , said Virginia, "The amount of visible dust decreases; so what? Why is that important to astronomers?"

Answer: Because you get to see what is behind the dust!

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Old 27-05-2012, 11:01 AM
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Quote:
Originally Posted by madbadgalaxyman View Post
An interesting recent development in CCDs is some CCDs that have their maximum sensitivity in the near-infrared.

CCDs used in the Jasmine Space Astrometry mission will have a 90% quantum efficiency at 0.9 micrometers wavelength.

I don't think these are the exotic "infrared only" CCDs with all their attendant problems.

This could enable amateurs to do near-infrared imaging, a useful thing for Milky Way objects which are highly obscured by dust, as the infrared photons have a habit of getting past the dust grains.
I have done NIR imaging using a ST-X10ME which has QE of around 65% at 0.75 microns and drops to around 30% at 0.9 microns.

Recently I tried a test image of the emission nebula RCW71 which is located behind the Coalsack in near infrared but found the results disappointing. An unfiltered luminance image was much brighter.

I suspect that I will have far better luck on obscured objects which have a continuous spectrum such as galaxies and globular clusters.

Regards

Steven
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Old 27-05-2012, 01:42 PM
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Quote:
Originally Posted by sjastro View Post
I have done NIR imaging using a ST-X10ME which has QE of around 65% at 0.75 microns and drops to around 30% at 0.9 microns.

Recently I tried a test image of the emission nebula RCW71 which is located behind the Coalsack in near infrared but found the results disappointing.
Steven,

Your experiment with NIR imaging is interesting.

Even though I am currently writing an article about the Coalsack, I haven't actually considered the case of RCW 71. (though I have seen this nebula on various images.)

It seems to me that you are right that the nebular emission being mainly output at a few specific spectral lines (mainly OIII and H-alpha) might be a reason for there being little signal at near-infrared wavelengths.

Abell (ACO) 3627, the rich but obscured cluster of galaxies in Triangulum Australe, could be an interesting test object for NIR imaging, as the member galaxies will have plenty of emission at red and infrared wavelengths
(note: I ran a thread recently as to why this cluster is referred to, even by professional astronomers, as the Norma Cluster)

cheers,
Robert

Here are a couple of links relevant to 700nm - 1000nm sensitive CCDs:

http://www-ccd.lbl.gov

http://snap.lbl.gov/ccdweb/ccdpapers.html
(several papers about CCDs with extended infrared sensitivity)

The book "Optics in Astrophysics", (2005), by Foy and Foy, contains a section on how CCDs are optimized for various wavelengths. Some of it is available at Google Books

Last edited by madbadgalaxyman; 27-05-2012 at 01:58 PM. Reason: more
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Old 27-05-2012, 05:50 PM
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Originally Posted by madbadgalaxyman View Post
Steven,

Your experiment with NIR imaging is interesting.

Even though I am currently writing an article about the Coalsack, I haven't actually considered the case of RCW 71. (though I have seen this nebula on various images.)

It seems to me that you are right that the nebular emission being mainly output at a few specific spectral lines (mainly OIII and H-alpha) might be a reason for there being little signal at near-infrared wavelengths.

Abell (ACO) 3627, the rich but obscured cluster of galaxies in Triangulum Australe, could be an interesting test object for NIR imaging, as the member galaxies will have plenty of emission at red and infrared wavelengths
(note: I ran a thread recently as to why this cluster is referred to, even by professional astronomers, as the Norma Cluster)

cheers,
Robert

Here are a couple of links relevant to 700nm - 1000nm sensitive CCDs:

http://www-ccd.lbl.gov

http://snap.lbl.gov/ccdweb/ccdpapers.html
(several papers about CCDs with extended infrared sensitivity)

The book "Optics in Astrophysics", (2005), by Foy and Foy, contains a section on how CCDs are optimized for various wavelengths. Some of it is available at Google Books
Thanks for the links.

I'll check out Abell (ACO) 3627 as I am interested in imaging obscure (that is off the beaten track) objects.

The Circinus galaxy is coming into imaging season, I'll try the NIR filter on this one. I have an LRGB image of this object.

Regards

Steven
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Old 27-05-2012, 09:16 PM
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Steven,
You have probably seen the thread about ACO 3627 entitled "Why is the Norma Cluster not in Norma?"

It is definitely an object of mystery, visually quite unassuming due to high extinction, but comparable in its properties to the Coma Cluster of galaxies. The brightest three or four galaxies are quite prominent, but everything else is much much fainter.

The galaxy fields to the south and east of this cluster extend for a long way (all the way to Pavo), and are part of the same supergalactic structure (seen in part of this map by Anthony Fairall);

Click image for larger version

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See also: "A Catalogue of Galaxies behind the southern Milky Way", (2001, Astronomy and Astrophysics, vol. 380, p.441, by Woudt and Kraan-Korteweg.)
This paper has got some really cool maps showing how inhomogeneous is the sky distribution of galaxies in the southern sky.....due to various large-scale structures.
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Old 28-05-2012, 03:34 AM
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Within sane prices there is no CCD with such high QE at 900-1000 nm, but many DS cameras have quite decent QE within that range.

889 nm is used for methane band imaging (Jupiter, Saturn, Uranus) and 1010 nm is used for Venus night side thermal emission imaging. Aside of that deep IR is rarely used by "amateurs". There are for example Astrodon NIR tricolor imaging filters but they aren't popular.
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Old 28-05-2012, 07:24 AM
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NGC 7793 using visible and NIR luminance

To illustrate the difference in visible and NIR here are images of NGC 7793.
Both images use the same RGB colour data, the luminance data for visible and NIR is 2 hrs for each.

The left hand image is the visible luminance.

Regards

Steven
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Old 28-05-2012, 02:37 PM
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Good to hear from one of our European "astro cousins". Your blog is a goldmine of information!
I am sure that you are right about no infrared-optimized CCDs "within sane prices", but then some of us spend so much money on our hobby that our wives (or husbands) may question our sanity!
(galaxy morphology benefits from longer wavelength imaging, so "maybe I burn down the house for the insurance money" to get NIR CCD)

Steven's images of NGC 7793 are a good illustration of one of the principal advantages of near-infrared imaging;

Sbc to Sd - type galaxies contain a lot of dust and star-formation activity and OB stars that might just be a transient state in the evolution of a galaxy, and this extreme population one material only contributes a small amount to the total mass of a galaxy.("somewhat like the icing on a cake")
By minimizing the influence of dust and OB stars in astronomical imaging of galaxies, near-infrared imaging can better show the underlying structure of spiral arms and bar structures, which are often clearly imprinted in the old & mass-dominant stellar population.
Some galaxies (e.g. NGC 253, NGC 2903) contain such a heavy dust distribution, and/or such a chaotic structure of dust and OB stars, that it is impossible to discern the overall structure of the galaxy without using NIR imaging.

cheers,
Mad Bad galaxy man

In Sd galaxies such as NGC 7793 and NGC 300, the spiral structure is usually low contrast and/or chaotic, and the HII regions and OB stars can be distributed in a
highly entropic manner; it is often hard to discern the structure of one of these galaxies without recourse to longer wavelength imaging (preferably at 2 microns or longer!!)

The nuclear star cluster in N7793 also is much more prominent in Steven's NIR image.

Last edited by madbadgalaxyman; 28-05-2012 at 02:52 PM. Reason: more
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