Experimental image M42 in UV.

[sjastro]

I don't recall ever seeing an amateur UV deep sky image.

This image was to determine if it there are sufficient differences between a UV and white light luminance image. In this case the answer is a clear no.

Anyway here is an uninspiring boring image of M42.
At least I suppose it is unique amongst the thousands of images taken of this object.:)

Full resolution here.
http://members.iinet.net.au/~sjastro/M42uv.html

Clear skies

Steven

[RickS]

Good on you for trying it, Steven! What wavelength was your filter?

[sjastro]

Thanks Rick.

The UV pass filter operates in the 340-400nm region with a 95% transmission.

Regards

Steven

[Merlin66]

Very interesting!
You seem to be picking up some Ha/Hb???
Could it be that the UV filter has some resonance band pass at lower frequencies? ie up in the red???
The Balmer series of Hydrogen are much more difficult below 400nm
May be worth while trialing a combo of a blue pass filter to kill any red response???

Which camera were you using?
Normally there's a significant drop-off in CCD QE below 400nm....

[LightningNZ]

Or it's H-epsilon, -zeta & -eta? http://en.wikipedia.org/wiki/Balmer_series. But yes, best to check the filter characteristics. You might need to combine it with an IR blocker.

Cheers,
Cam

[sjastro]

Thanks Ken and Cam.

I used an ST-10ME (the image was colourized) which has a QE of 50% at 375nm and 60% at 400nm.

The filter is an Astrodon Johnson/Cousins UV photometric filter which (hopefully) shouldn't leak in the IR region.

The image is in fact showing the H-Epsilon emission as per the attachment.
(Note the H-Epsilon line has been incorrectly labelled).

Regards

Steven

[Merlin66]

The Astrondon data I have shows about 60% transmission for the U filter..
Yes the bandwidth sits across the Balmer jump....compared with the Ha intensities the H10 series is much reduced.
Interesting that you achieved such success - well done!

[gregbradley]

Interesting shot Steve. I wonder if we should be using sunblock at night with that much UV coming out of the nebulas!
Greg.

[clive milne]

The UV band might be useful for enhancing the contrast of O-B populations in galaxies, and implicitly therefore, shockwaves and areas of compression. etc

[sjastro]

Astrodon did at one stage sell a Schuler UV filter which gave a 65% transmission in UV.

The current generation has a 95% transmission.

Regards

Steven

[Merlin66]

Steven,
Yes, I have a set of the original Schuler filters....
I didn't realise the new filters were so good!

[sjastro]

Thanks Greg.



Hello Clive.

I've only tried the UV filter on one galaxy at this stage NGC253.
To say the result was disappointing is a bit of an understatement. It was like trying to image the galaxy through a neutral density filter.
Perhaps UV imaging might work on more active galaxies, NGC 5128 springs to mind as being a potential target.

Regards

Steven

[madbadgalaxyman]

An interesting experiment, Steven! The neb may look the same as at longer wavelengths, but the dust lanes are enhanced!

As you know, a Johnson-Cousins (or similar) U -band filter is potentially useful for emphasizing OB stars..... but the extinction is high in this regime, so the reduction of starlight by interstellar dust can greatly negate the impact of the better isolation of hot young stars when using this filter.

Short wavelength filters greatly emphasize the dust distribution within an object or in a galaxy image, and this seems to be the case in your M42 image, which shows the dust distribution in the nebula extremely obviously. Perhaps deep Ultraviolet imaging of this region can show the cold & dark and dusty Orion Molecular Cloud from which stars are forming, as seen against a stellar or nebular background?

Here is a "fun" collection of images of M51, using several individual filters of progressively longer wavelengths, in order to illustrate the effect of isolating progressively longer wavelengths with specific filters. In order, the images are taken with the following filters:

B -band ("blue")
V -band (approximately "visual")
I band (very near infrared, around 800nm)
Near-Infrared (image is a composite of J+H+K bands)(all filters in this composite are >= 1.0 microns)

Given that each colour filter gives a unique image, I will repeat a comment I made in a previous post.... that we actually lose information by adding the images together that are taken with various filters. Your experiments with imaging in various filters are a good illustration of the usefulness of not "adding everything together"!

129573

129574

129575

129576

Note added in later Edit

NGC 253 is noted for being particularly red in its optical colours, compared to the color that would be expected for its optical-wavelengths derived Hubble type; because the the dust screen is so heavy within NGC 253, it does not surprise me that very little ultraviolet light got through to your CCD!!

[Merlin66]

Steven,
I was hoping to find a Hubble UV image of M42 for comparison, but all I can seem to find are "combined" with other wavelengths to give a "OooohhHaaa" image.
The more I think about, the more impressed I am with your results!!!!!

[sjastro]

You are correct the dust lanes are much more pronounced, more so in M43 than M42. I think I suffered from "mind blindness" by concentrating on differences in the highlight areas and failing to note changes in the shadow or dust areas.



A most interesting comparison.



The moral of the story here is that UV imaging requires far more preparatory work than simply finding the RA and Dec of the object you want to image.

The dust lane detail in NGC 5128 is making it a far more interesting proposition to image in UV.

Clear skies

Steven

[sjastro]

Ken,

Given that Hubble is imaging above the Earth's atmosphere I wonder if the images are taken at shorter wavelengths in the UV range.

NASA's Galex probe as an example images in the 135-280nm range.

Regards

Steven

[madbadgalaxyman]

I just tried the GalexView "virtual telescope" interface of the GALEX imaging data (//galex.stsci.edu/GalexView) and it said that it had no ultraviolet imaging available for the Orion Nebula.
This is weird, because you would think that they might have had a go at imaging this object with the satellite, just to see what it would look like in short wavelength UV.

cheers, Robert

[sjastro]

Robert,

Other well known objects that one would expect to be good UV targets are also not available. I couldn't find images of NGC3372 or M1.

Regards

Steven

[Merlin66]

Steven,
sounds like you're "boldly going where few amateurs have gone before............."

[madbadgalaxyman]

Steven,

I still have had little luck finding Ultraviolet images that are easily comparable with yours.

However, here is a preview of a Hubble Space Telescope image of the Orion Nebula that I just downloaded from hla.stsci.edu(the Hubble Legacy Archive), which was taken at similar wavelengths to your image.

This Hubble image is a composite of an F439W filter image (this filter is similar to the standard Johnson B ("blue") filter) and another image taken with the F336W filter (which is very roughly similar to a U filter image)

Both images were taken with the HST and its WFPC2 instrument. The Principal Investigator of the program in which these images were taken was Beckwith, and the Proposal ID is 8894.

129656

(I have not displayed only the UV image, as it is very ratty indeed)

I agree with Ken's comment that you are "boldly going" (!!)
There are always a few individuals who will be in the lead, while the others, like sheep, just go on doing what everybody else is doing.

[sjastro]

Thanks for info Robert.

Regards

Steven

[SkyViking]

What a great effort and result Steven :D
I particularly noticed the complete absence of the multitude of young stars that appear in IR images of this region. That's to be expected of course, but it's still a fascinating contrast if you compare for example with my recent NIR image of M42 here: http://www.iceinspace.com.au/forum/showthread.php?t=100010&highlight=orion+infrared
Your UV version almost looks like a 'starless' rendition in comparison. It really highlights the difference in wavelength that these features are emitting.

I'm thinking it would be pretty cool to create an animation of M42 images, showing the transition through the spectrum from UV to IR.

[Merlin66]

Rolf,
The young O-B stars in the Trapezium and close by are the "powerhouse" which illuminates the M42 gas cloud.....
A lot of the other stars around them are severely dimmed due to the interstellar dust and reddened into the NIR.
I agree, an animation moving across the spectrum would be a very neat project!

[sjastro]

Rolf,

That is an excellent image
An animation would be a great idea.

The enhancement of the dust regions in M43 in the UV image is very apparent when compared to your image.

Clear skies

Steven

[sjastro]

Ken (Merlin66) raised the issue of significant red light leakage reported in UV pass filters. Red light leakage would result in H-Alpha contamination of the M42 image there by making it "not strictly" a UV image.

I am currently taking RGB images of M42. The M42 R images in the nebular regions indicated my ST-X10ME imaging at about 40-50% of full well capacity.

I decided to image a red LED using red and UV pass filters. The red LED has a frequency range of 610-760 nm which conveniently includes the H-Alpha emission at 656nm.
The exposure was adjusted to aim for a 40-50% of full well capacity with the red filter. The ADU counts for both red and UV filters was recorded.
The results and LED images are in the attachment.

The conclusion is while there is red leakage in the UV pass filter, the ADU count is so low that it would be difficult to distinguish this from the statistical and readout an noise in an image, and therefore the H-Alpha contribution is probably lost in the overall noise of the UV image.

Regards

Steven

[Merlin66]

Steven,
A good test!
Certainly shows the current J-C Astrodon filters are much better than their Schuler predecessors.
Well done!

[madbadgalaxyman]

We are getting some very interesting long and short wavelength images, thanks to Steven and Rolf.

I was surprised & amazed by how many extra stars Rolf's infrared image of the Orion nebula "dug out" from the dusty obscuring material in the nebula.

In contrast, the very short wavelengths block the background light from coming through the dust (by means of enhanced processes of scattering and absorption by dust grains), so we see the dark patches enhanced in Steven's near-ultraviolet image.

(UV imaging is good for detecting backlit dusty Protoplanetary Disks, for instance, at least if you have the angular resolution to image them.....)

Robert

[Stevec35]

Interesting stuff Steven. I've done plenty of IR but not UV. Perhaps time to buy another filter.

Cheers

Steve

[seeker372011]

ditto

[sjastro]

Thanks Narayan and Steve.

Clear skies

Steven

[Terry B]

This is very interesting Steven
I decided to hava a similar attempt at this.
I took 4 180 sec frames of the M42 region through an Astrodon U filter and simultaneously took a spectra of the region.
There is certainly lots of emission in the UV. The filter passes between about 3600 and 4000A. There are significant emission in this region as you an see from the spectra. There is emission at H delta and H ep plus there is a broad emission around 3720 that I'm not sure what it is. My spectrograph isn't very accurate in the UV so the measurement might not bee terribly accurate.
Interesting never the less.
Cheers

Terry

[Merlin66]

Terry, there's not much around 370nm....Hg at 366.3/365.5/365.0 and NeIII at 386.9.....

[sjastro]

Thanks for the info Terry.



Could it be from light pollution?

Regards

Steven

[sjastro]

Totally uncharted territory for combining colour with a UV image.

The colour image enhances the differences with "conventional" M42 images.

2hrs L= UV pass (340-400nm) 0.5 hrs R, 0.5hrs G, 0.5 hrs B
Scope BRC-250 ST-X10ME CCD

High resolution image.
http://members.iinet.net.au/~sjastro/M42uv_colour.html

Clear skies

Steven

[Merlin66]

Whooooo!
Certainly shows up the dust cloud, the tighter edges and the hydrogen glow.....
I like it!

[sjastro]

Thanks Ken.

The colour image is also showing the bluish "streamers" which are not defined in the original image.

Regards

Steven

[Terry B]

I think light pollution is unlikely as I am in a very dark spot at 1100m altitude.