LMC imaged in near UV

[sjastro]

One of the issues of NUV (near UV) imaging is selecting a target that is sufficiently different from imaging in the visual range to make it worth the effort.

One of the problems of imaging in NUV, unlike narrowband imaging is there is no contrast enhancement due to reduction in natural and artificial light pollution, in fact contrast is reduced due to near UV in the upper atmosphere.

The other problem is the low QE in NUV in amateur CCDs plus the absorption of UV in optical glass.
I used my ST-10XME which has moderate sensitivity in near UV plus a pancake lens design to minimize absorption.

The LMC was selected due to it being subjected to tidal forces by our galaxy and the SMC. Collisions due to tidal stress emit radiation in UV. Hot young stars also emit UV.

Image details.
Imaged with a 70mm Pentax pancake lens at f/4 and ST-10XME.
1 hr R, 1 hr G, 1 hr B and 2 hrs NUV.
The NUV and B data were combined to form a RG(B+NUV) image.
The B+NUV combination enhances the blue regions in the LMC and are areas in the LMC where NUV emissions occur.

Large resolution image here.
http://members.iinet.net.au/~sjastro/LMC_NUV.html

Clear skies

Steven

[Paul Haese]

Interesting look Steven, sounds like an interesting idea to image in NUV.

[sjastro]

Originally Posted by Paul Haese

Interesting look Steven, sounds like an interesting idea to image in NUV.

Thanks Paul.

NUV imaging doesn't have the photographic impact of narrowband imaging, but it reveals more of the dynamics of star formation in galaxies.
It also makes dark nebulae look a lot "darker" as NUV cannot penetrate these regions.

Regards

Steven

[marco (Marco Lorenzi)]

Indeed interesting Steve, it would be nice to see the UV channel alone, just to better appreciate what is actually present there that is less visible in the RGB classical images..

Clear skies
Marco

[atalas]

Good work Steven!

[sjastro]

Originally Posted by atalas

Good work Steven!

Thanks Louie

Originally Posted by marco

Indeed interesting Steve, it would be nice to see the UV channel alone, just to better appreciate what is actually present there that is less visible in the RGB classical images..

Clear skies
Marco

Near UV image only attached.
Even with a 2hr exposure in NUV the LMC is a "faint" object.

Incidentally NASA APOD did a comparison between the LMC in middle and far UV with a visible light image. (Middle and far UV imaging require satellites).

http://apod.nasa.gov/apod/ap130610.html

Clear skies

Steven

[Stevec35 (Steve)]

Interesting shot Steven. It seems to show the blue stars more prominently which is I suppose what you would expect.

Cheers

Steve

[sjastro]

Originally Posted by Stevec35

Interesting shot Steven. It seems to show the blue stars more prominently which is I suppose what you would expect.

Cheers

Steve

That's correct Steve.

Blue stars of spectral type O and B have blackbody curves that peak in UV and therefore emit light in the NUV range.

It's the reason why I combined the NUV and B colour data which accentuated the blue colour in the image without wrecking the colour balance as NUV is progressively weaker in types A, F, G, K and M stars.

Clear skies

Steven

[sjastro]

Sorry if most people find this stuff boring.

Total NUV luminance exposure is now 6 hrs.
Given the higher S/N ratio it is now possible to add an NUV luminance image and have the B channel now composed only of NUV data.

(NUV)RG(NUV) image.
6 hrs NUV, 40 minutes R, 40 minutes G.
70mm Pentax Pancake lens used at f/4.

The image now reveals structures that are clearly due to NUV emissions.

Higher resolution here.
http://members.iinet.net.au/~sjastro/LMC_lumUV.jpg

Clear skies

Steven

[SkyViking (Rolf)]

There is certainly an emphasis on the O/B stars with UV, it looks quite different from optical.
A nice and interesting project Steve!

[Shiraz (Ray)]

nice work Steven - very interesting approach. You have overcome some difficult technical issues.

[sjastro]

Thanks Ray and Rolf.

Another problem with NUV imaging is that NUV is more sensitive to atmospheric extinction than visible light. This was quite noticeable as the S/N ratio was lower at the end of the imaging sesion when compared to the start.

Clear skies

Steven

[Regulus (Trevor)]

Steven, how do you get Near UV? A particular filter?

Trevor

[sjastro]

Originally Posted by Regulus

Steven, how do you get Near UV? A particular filter?

Trevor

Trevor,

I use a 340nm-400nm UV pass filter that is commonly used for photometry.
Visible, near infra-red and infra-red light is filtered out.

Regards

Steven

[Merlin66 (Ken)]

Late coming to the thread...
but once again some excellent results!!
Well done.
I hope your work encourages others to move towards a more "scientific" interpretation of their normal AP images....

[sjastro]

Originally Posted by Merlin66

Late coming to the thread...
but once again some excellent results!!
Well done.
I hope your work encourages others to move towards a more "scientific" interpretation of their normal AP images....

Thanks Ken,

I can only vouch for myself here.
There is a conflict between scientific value and "pretty pictures".
The greater the artistic license put into an image, the lesser the scientific value.
I attempt to strike a balance between the two for my images in general.

The LMC in UV image is an exception. It wouldn't win an astrophotography award by any stretch of the imagination, but it has far greater scientific value than anything else I have produced.

Regards

Steven