Mark McCaughrean

‎“יְהִי אוֹר‎ – fiat lux – let there be light”

Here are the first engineering images from #ESAEuclid, our mission to study the dark universe.

Each shows the full Euclid field, with 36 CCDs for the visible camera, VIS, & 16 HgCdTe detectors for the near-IR imager & spectrometer, NISP, plus zooms to show more detail.

This is just the beginning 🖖🤘

Full story & links to the very large full-res zoom images:

https://www.esa.int/Science_Exploration/Space_Science/Euclid/Euclid_test_images_tease_of_riches_to_come

#Astrodon #SpaceExploration #SpaceScience #DarkUniverse

Euclid test images tease of riches to come

Euclid’s two instruments have captured their first test images. The mesmerising results indicate that the space telescope will achieve the scientific goals that it has been designed for – and possibly much more.

Jul 31, 2023 at 12:50pmIceCubesApp
Show threadAkaSci 🛰️Jul 31, 2023
Hi @markmccaughrean
In the VIS, are the 4kx4k detectors (there are 36 of them), actually composed of four 2kx2k CCDs, as seems to be implied by the zoomed-in image from VIS?
Show threadMark McCaughreanJul 31, 2023

@AkaSci No, they’re contiguous 4k x 4k devices, namely CCD 273-84 from e2v. They are accessed via 4 parallel read-outs, which probably explains the quadrants, but I have to admit that I don’t understand why there are gaps – I asked the same question myself when I saw the images last week, but don’t have an answer yet.

http://www.e2v.com/resources/account/download-datasheet/3837

https://arxiv.org/pdf/1608.08603.pdf

Show threadMark McCaughreanJul 31, 2023
@AkaSci It’s possible that they’ve just been displayed this way, thanks to the four readouts, but actually are contiguous. I’ll check with our team to see if I can get an answer.
Show threadAkaSci 🛰️Jul 31, 2023
@markmccaughrean
Also, what is the cause of the thin streaks from multiple directions visible in the zoomed-in image?
Cosmic rays/particles? If so, I presume they can be removed in post-processing during science operations.
Are the number of streaks consistent with theory and the design of the telescope?
Thanks as always for your deep insights.
Show threadΣ(i³) = (Σi)²Jul 31, 2023
@AkaSci @markmccaughrean yeah, my first thought was that's a lot of cosmics. Assuming those aren't particularly long-duration exposures those look worrying - but I'd think they know what they're doing there ( had enough time to plan for those )
Show threadMark McCaughreanJul 31, 2023

@SvenGeier @AkaSci Yes, they're cosmic rays. Most hit the detectors at high incidence angles & only corrupt a few pixels, but occasionally they hit near-parallel to the detector & create streaks.

They're not an issue & get removed by stacking multiple images which may also be dithered. And they can also be removed using clever read-out techniques in IR arrays – that's how JWST does it.

I expect the rate is exactly as predicted after many years of operating Gaia at L2.

Show threadMark McCaughreanJul 31, 2023

@SvenGeier @AkaSci To state the obvious, they have *not* been removed in these images simply because they're engineering data.

But again, they're fully anticipated & the survey strategy & processing pipeline will deal with them just fine.

Show threadAkaSci 🛰️Jul 31, 2023

@markmccaughrean @SvenGeier
Thanks!
This web-page has some more detail on what you so concisely described - https://www.euclid-ec.org/public/mission/vis/

I presume Euclid will also be able to image areas in the gaps between the 36 detectors via dithering.
The cosmic ray streaks probably have some usefulness as well; e.g., to characterize them and to measure bursts from distant energetic cosmic events.

VIS – Euclid Consortium

Show threadMark McCaughreanJul 31, 2023

@AkaSci @SvenGeier I believe that describes filling the gaps between the 36 CCDs via dithering – there's no mention of the fact that each CCD was displayed in the PR as a quad of images.

As for cosmic rays in such CCD images, I'm unaware of anyone trying to use them for astrophysics. They come from everywhere, the solar wind, Milky Way, extragalactic, secondary events in the spacecraft etc., & come constantly. Plus there's precious litle directional or energy information.

Show threadAkaSci 🛰️Jul 31, 2023
@markmccaughrean @SvenGeier
For analysis of cosmic ray streaks on CCD images, I was reminded of this article on Gaia, where the streaks are used, through post-analysis, as a (crude) particle counter.
Also, streaks caused by interaction of gamma rays with CCD material.
https://www.cosmos.esa.int/web/gaia/iow_20221109
IoW_20221109 - Gaia - Cosmos

Show threadMark McCaughreanJul 31, 2023
@AkaSci @SvenGeier Indeed, although that particular GRB was the BOAT (brightest of all time) & most probably wouldn't noticed. We have other more optimised GRB spotters up there, with directional sensitivity too 🙂