Astronomers have used the Extreme Ultraviolet Imager (EUI) instrument onboard the ESA/NASA Solar Orbiter spacecraft in a new mode of operation to observe the solar corona at extreme ultraviolet wavelengths. This new mode of operation was made possible with a last-minute ‘hack’ to the camera and will almost certainly influence new solar instruments for future missions.
“It was really a hack. I had the idea to just do it and see if it would work. It is actually a very simple modification to the instrument,” said Dr. Frédéric Auchère, an astronomer with the Institut d’Astrophysique Spatiale at the Université Paris-Sud.
“It involved adding a small, protruding ‘thumb,’ weighing a few grams, to the door of the instrument.”
“As the door slides out of the way to let the light into the camera, if it is stopped halfway, the thumb covers the Sun’s bright disk, and EUI can detect the million-times fainter ultraviolet light coming from the surrounding corona.”
Dr. Auchère and his colleagues refer to this as the occulter mode of operation. Tests with the EUI occulter have been on-going since 2021.
In the past, images of the Sun’s corona have been taken with dedicated instruments called coronagraphs.
The value of the new approach is that the coronagraph and the camera can be included in the same instrument.
“We’ve shown that this works so well that you can now consider a new type of instrument that can do both imaging of the Sun and the corona around it,” said Solar Orbiter project scientist Dr. Daniel Müller, a researcher at ESA.
Even before those new instruments, there is a lot of new science to come from EUI.
The occulter mode makes it possible for scientists to see deeper into the Sun’s atmosphere.
This is the region that lies beyond the field of view of classical EUV imagers but it is usually obscured by traditional coronagraphs.
Now, however, EUI’s occulter can image this little-explored region easily.
“Physics is changing there, the magnetic structures are changing there, and we never really had a good look at it before,” said EUI principal investigator Dr. David Berghmans, an astronomer at Royal Observatory of Belgium.
“There must be some secrets in there that we can now find.”
The team’s paper was published in the journal Astronomy & Astrophysics.
F. Auchère et al. 2023. Beyond the disk: EUV coronagraphic observations of the Extreme Ultraviolet Imager on board Solar Orbiter. A&A 674, A127; doi: 10.1051/0004-6361/202346039