13 October 2021 at 12:36 pm #575068Tim HaymesParticipant
From a Planoccult listserver note, i read news of ESO highlighting these VLT observations. https://www.eso.org/public/unitedkingdom/news/eso2114/ and the detailed paper can be read here: https://www.eso.org/public/archives/releases/sciencepapers/eso2114/eso2114a.pdf
Many asteroid 3d-shapes have been deduced from amateur observed occultations and light curve measurement over the last 10 years or so, but the detail from VLT is something else ! As an example, the asteroid (130) Elektra has been observer twice from the UK by BAA members in 2010 and 2018 occulting different stars. The 3d calculated shape can now be compared to the image in the paper. Its a big step forward in determining the shape of the larger main belt asteroids.
Euraster credit: E Frappa.
Enyoy…13 October 2021 at 5:47 pm #584779Alex PrattParticipant
I missed that, in between all the Pallas reports. The paper contains the barest mention of occultations. I suggest posting your message to IOTAoccultations and UKoccultations, to bring it to a wider audience. Also the taster video:
Alex.13 October 2021 at 6:14 pm #584780Tim HaymesParticipant
Great video – thanks for the link Alex,
For those who may inquire, why telescopes shine lights into the sky? Well from what i understand this is part of the adaptive optics feed-back system. It doesn’t effect the images. A wiki would be the best place to seek further info on this.
Tim14 October 2021 at 9:44 am #584787Dr Paul LeylandParticipant
The aim is to create an artificial star of known size and shape. A very narrow laser beam tuned to exactly the same wavelength of sodium light stimulates fluorescence at the same wavelength from sodium in the upper atmosphere. (Incidentally, that sodium comes primarily from sea salt.)
A telescope looking at that fluorescent spot should see an immobile spot with a shape and diameter set by the resolution of the optics. In practice it sees a large shimmering moving blob because of the atmosphere. Clever software quickly works out what distortions should be made to the telescope to return that blob to its undistorted shape and very fast mechanical actuators then make the corresponding movements to an optical element. Voila, diffraction-limited images through adaptive optics.14 October 2021 at 10:35 pm #584788Richard MilesParticipant
You can tell we are well into the 21st Century when you see detailed images of asteroids measuring small fractions of an arcsecond in size. The paper includes density measurements of these bodies, which is rather amazing.
There again, the latest BAA Journal has some amateur images of Mars, Uranus and Neptune that were unthinkable say 50 years ago!15 October 2021 at 11:22 am #584789Robin LeadbeaterParticipant
Looking at the full paper, I see that they found deconvolving the images using the actual measured stellar point spread function gave artifacts so they resorted to tuning the PSF using a parameterised function. The reference to the validation of the technique using Vesta might be interesting for planetary imagers.16 October 2021 at 4:36 pm #584792Dr Paul LeylandParticipant
Thanks for posting this. A fascinating paper.
Likely useful not just for planetary observers. Obvious DS applications are to clean up globular clusters and galaxy clusters.
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