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Supersharp Images from New VLT Adaptive Optics

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Re: Supersharp Images from New VLT Adaptive Optics

#31

Post by eisstrom »

skykooler wrote: post #26
eisstrom wrote: post #15

Earlier quoted context omitted.

We can achieve a very high resolution from the ground but only in a very small field of view. To cover one typical HST image with MUSE at the VLT, we would need a mosaic of hundreds of exposures. The reason for this are the four artificial guiding stars from the lasers. The closer they are together on the sky, the more atmospheric distortion you can correct. Here is an image of them: https://www.eso.org/public/united…

Do the lasers create light pollution problems for the telescopes?

Absolutely! When the lasers are used, MUSE uses a filter at the correct wavelength (Natrium D) to get rid of the laser photons.

Only one telescope is currently equipped with lasers. The other ones can't observe the same region of the sky when the lasers are activated.

Re: Supersharp Images from New VLT Adaptive Optics

#32

Post by semaphoreP »

appleflaxen wrote: post #8
eisstrom wrote: post #5

I'm a PhD student working with data of globular clusters from this instrument for quite some time now. I will be happy to answer your questions!

the article makes it sound like the approach is so effective that it makes space-based telescopes unnecessary. is that true? does this mean that we should simply use ground-based 'scopes with adaptive optics?

Adaptive optics is really only effective in the infrared. And really only in the near-infrared, as past 5 microns, we can't really see through the atmosphere. In the visible, ground-based can't match space observatories (in the visible, the atmospheric turbulence is way harder to correct for).

Re: Supersharp Images from New VLT Adaptive Optics

#33

Post by SiempreViernes »

eisstrom wrote: post #30
SiempreViernes wrote: post #27

Earlier quoted context omitted.

The Hubble field of view is pretty small too, something like 25 arcseconds the internet tells me.

I was comparing it to HST WFC3 with a field of view of 160 x 160 arcsec^2 ( https://www.spacetelescope.org/about/general/instruments/wfc... ). Thats about 450 times larger than the MUSE narrow-field mode FOV. I think you mean the high-resolution mode of the ACS instrument ( https://www.spacetelescope.org/about/general/instruments/acs... ) but that is broken and it was not repaired during the last HST service mission.

Actually what I was looking at was the field of view of an individual MAMA detector in the Space Telescope Imaging Spectrograph, that instrument has about ~ 100 x 100 arcsec2 of total field of view apparently.

Re: Supersharp Images from New VLT Adaptive Optics

#34

Post by welterde »

semaphoreP wrote: post #32
appleflaxen wrote: post #8

Earlier quoted context omitted.

the article makes it sound like the approach is so effective that it makes space-based telescopes unnecessary. is that true? does this mean that we should simply use ground-based 'scopes with adaptive optics?

Adaptive optics is really only effective in the infrared. And really only in the near-infrared, as past 5 microns, we can't really see through the atmosphere. In the visible, ground-based can't match space observatories (in the visible, the atmospheric turbulence is way harder to correct for).

> In the visible, ground-based can't match space observatories (in the visible, the atmospheric turbulence is way harder to correct for).

The image this article is about is mostly in the optical (MUSE only goes from 465nm to 930nm; and the synthetic filters used in the MUSE image [4] seem to be quite close to the used HST filters).

> And really only in the near-infrared, as past 5 microns, we can't really see through the atmosphere.

Not quite true [1] (at least if only considering absorption), it's just that the background becomes more and more of a problem (both continuum and narrow emission lines), and one has less nicely defined windows of transmission and lots of strongly variable absorption lines (picking dry places for the telescopes and selecting nights with low water vapour column densities helps). At the VLT for example there is VISIR [2], which does mid-IR imaging and spectroscopy.

Of course the sensitivty from the ground is much lower than from space or somewhere in between (for example there is SOFIA [3] which is a 2.5m telescope on an airplance) and some bands of interest are indeed absorbed. But there are indeed projects that involve mid-IR observations that can be done from the ground.

[1] https://www.gemini.edu/sciops/telescopes-and-sites/observing... [2] http://www.eso.org/sci/facilities/paranal/instruments/visir/... [3] https://en.wikipedia.org/wiki/Stratospheric_Observatory_for_... [4] https://www.eso.org/public/unitedkingdom/images/eso1824c/

Re: Supersharp Images from New VLT Adaptive Optics

#35

Post by vanderZwan »

eisstrom wrote: post #21
vanderZwan wrote: post #14

Earlier quoted context omitted.

> With this new capability, the 8-metre UT4 reaches the theoretical limit of image sharpness and is no longer limited by atmospheric blur. Theoretical limit as in diffraction limited? How will this technology "scale" to other frequencies and resolutions? Related to this diffraction limit: is there any overlap in the advances in microscopy and astronomy? For example, do advances in super-resolution microscopy[0] affec…

Yes, the diffraction limit is meant here. The VLT has four 8 m mirrors, for each of them the angular resolution limit is = wavelength/diameter = 8 * 10^(-8) rad. The practical resolution of the new narrow-field mode is about 4*10^(-7) rad, and it was one order of magnitude larger before. Adaptive optics is the key invention here. As far as I know, it works better in the near-infrared than in the red part of the optic…

> The practical resolution of the new narrow-field mode is about 4 * 10^(-7) rad, and it was one order of magnitude larger before.

Amazing! :)

> As far as I know, it works better in the near-infrared than in the red part of the optical range, and it gets worse toward the blue part.

Do you know what is the reason for this? Noise from Rayleigh scattering? EDIT: Already answered here: https://news.ycombinator.com/item?id=17559121

> It's funny that your mention super-resolution microscopy because Stefan Hell, one of the Nobel Prize winners for advances in that field, works in the same city as we do. So far, I don't think we have any overlap with what he does.

Why not arrange a kind of meet-up? :) Surely exchanging ideas would lead to interesting ideas, and in the worst case you can at least by inspired by geeking out over mega- and micro-optics together.

Re: Supersharp Images from New VLT Adaptive Optics

#36

Post by vanderZwan »

eisstrom wrote: post #16
Jaruzel wrote: post #10

Earlier quoted context omitted.

Are the images natural colour, or have they been 'enhanced' in any way? i.e. is Neptune really that blue?

The advantage of MUSE is that you get all color information, i. e. the flux at any wavelength from blue to red. In principle, one can use this together with the sensitivity curve for our eyes to construct a natural image. In this case, I think, they tried to imitate the color scheme from the Hubble image which is more limited. In short: Not sure how realistic this is, but one could make a realistic image from the new…

Could one use that information the other way around to make estimates for expected "missing data" in Hubble images taken in areas where VLT has not looked yet, for example to decide where to look next?

Re: Supersharp Images from New VLT Adaptive Optics

#37

Post by arriu »

This is very exciting. I'd love to see some of this make its way into amature equipment.

Technology has helped us go past what would have been though of as possible with similar optics equipment 50 years ago. For the most part, optical mirrors and lenses are the same but what we can now do with them has changed quite a bit.

For example, here is a video of Mars through a small telescope: http://i.imgur.com/8juHPdn.gifv

If we take the best parts of each video frame in that video and combine them in a smart way, a process called lucky imaging, we can reduce the impact of the atmosphere: http://i.imgur.com/CzLZTlv.png

Re: Supersharp Images from New VLT Adaptive Optics

#38

Post by Osmium »

Jaruzel wrote: post #10
eisstrom wrote: post #5

I'm a PhD student working with data of globular clusters from this instrument for quite some time now. I will be happy to answer your questions!

Are the images natural colour, or have they been 'enhanced' in any way? i.e. is Neptune really that blue?

I see this question a lot. I used to have an obsession with 'true color'; images felt fake otherwise. Artificial.

I'm a working scientist now, and my view has changed. I realize how limited our senses are. How much of the world--of the universe--I'd miss by restricting it to just what my eyes can see natively. Even among colors that I can see, but perhaps the signal is too faint ... I'm a lot more tolerant of color-mapped images now. I don't see them as artificial anymore, but as beautiful and transcendental. A window into a hyper-spectral world normally invisible to me. It's really something special. I wish I could share this perspective with more people.

Re: Supersharp Images from New VLT Adaptive Optics

#40

Post by anon1253 »

eisstrom wrote: post #5

I'm a PhD student working with data of globular clusters from this instrument for quite some time now. I will be happy to answer your questions!

How does it compare to my amateur attempts with a 12" Newton https://www.flickr.com/photos/joelkuiper/42502865635/ :p ?

All kidding aside, do you think there is some scientific value in the efforts of hobby astronomers and astrophotographers around the world?

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