Under the Microscope: GHOSTS & Rainbows (Part 3)

A blog post by Alan McConnachie, Project Scientist for the GHOST spectrometer

GHOST - Commissioning begins for the next great instrument for Gemini Observatory!

More great storytelling with Alan McConnachie, an astronomer with the NRC’s Herzberg Astronomy and Astrophysics Research Centre. Over the last 10 years, Alan has been part of a team that has developed a new instrument for astronomers around the world, called GHOST – the Gemini High Resolution Optical SpecTrograph. GHOST is the new instrument for the Gemini South telescope, one half of the International Gemini Observatory.

Did you miss Part 2? You can read it here.

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Friday, April 29, 2022, Control Room, Gemini South

GHOST allows us to analyze the spectra of astronomical sources. You can think of these spectra as the fingerprints, or maybe the DNA, of objects in which there is encoded information on the chemistry of the object that emitted the light and information on how that object is moving. By looking to see exactly how much light is emitted at every wavelength, we can figure out the temperature of the source. By looking to see if there are specific features, we can figure out chemical composition. And by seeing if all these features are offset in one direction or the other, we can figure out what velocity the object is moving towards or away from us. This is the well-known Doppler effect, and GHOST will be able to see stars moving at a speed equivalent to a human sprinting. And remember it sees this level of subtle movement, even though the very closest star (other than the Sun) is some 41 300 000 000 000-ish kilometres away.

GHOST is not the first instrument to do these things. But in terms of our ability to probe the faintest objects with extremely high resolution, after today I'd say it’s probably going to be the best.

Now that GHOST can produce rainbows, we’ve been fine tuning the positions of all the parts on the table to make sure those rainbows are as sharp as we need and are in the right position on the detector. And we’ve managed to focus the blue camera, so that when we send calibration light down a single circular fibre, we see this:

The image is the calibration light – a Thorium-Xenon light source to be exact – being stretched out into a spectrum (a rainbow), where all the bright features are light emitted at very specific wavelengths. And those dots are very small, very round and very much nearly exactly where they should be.

Back in 2019, this took us many weeks to get. This time around, it took us about a day.

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Saturday, 30 April, 2022

So who knew that today in Chile there was going to be a partial solar eclipse! Astronomers, that’s who! But not this particular astronomer, until my colleague Scott told us.

Step to the fore John B. Aside from his other duties today, he found time to make us all eclipse viewers! So, just before we left the telescope today we observed a solar eclipse from Gemini South (well, that is to say, the car park of Gemini South)!

How to view a solar eclipse:

Never look straight at the Sun. Use a piece of card with a pinhole in it, and project the resulting image onto another piece of card. Who needs that 8-m telescope in the background ;-)

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Friday 6 May, 2022, Control Room, Gemini South?

It’s been a busy week, with no time for posts. We’ve been having some issues with the detectors, especially one of them (the blue) wasn’t behaving just as it should, but Greg, our detector specialist got it sorted (as he always does!). And then lots of fine alignments for both cameras, and making sure that the sciences were oriented in the right way with respect to the optical table.

And now, the result is that every test we have performed shows things are as good as or better than they were in 2019 - which is phenomenally good.?

But today was very special. John’s last day at the telescope for a while. About an hour before he left, John had a not-so-wacky idea, which is how GHOST came to observe its first star around midday on a Friday, while simultaneously confirming the existence of the Sun.

John held the end of the fibre (which we use to send light to the spectrometer) just outside the door to the pier lab. Scott, using precision optics and a careful optical mounting procedure, reflected sunlight from outside of Gemini South towards John, at the door of the pier lab.

I ran a 5 second exposure of GHOST and we recorded the most beautiful rainbow on the detectors that GHOST has yet had the pleasure to see!

These photos show the spectrum of the Sun, as seen by GHOST on its blue and red detector. Each illuminated row is a part of the spectrum, showing the amount of light emitted at each wavelength. Each of the rows overlaps in terms of their wavelength coverage, and each of the detectors overlap in their wavelength coverage. Together, they show all the light emitted from the Sun from a wavelength of about 350 nm to 10300 nm. Our eyes are most sensitive to about 555 nm (green light) and we typically can see wavelengths from about 400nm (blue/violet) to about 800nm (red). Beyond these limits is the ultraviolet and the near-infrared.

I’ll be honest, I wasn’t sure it would work. Now I’m sure GHOST is going to be the best spectrograph in the business!?

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Tuesday, May 10, 2022, La Serena airport?

It’s been great and it’s still going on. But it’ll go on without me being present for a few weeks. Today, I fly out of Chile. Yesterday, Greg and I were voted off the mountain (I keep thinking this whole experience would make a great, if niche, reality TV show). Manuel gave us a ride back to La Serena, and this morning we spent a few hours doing some sightseeing. A beautiful place. Now waiting to get on a plane, at the start of a long journey back to Vancouver Island.

The day before we came down, Jordan, who is in charge of the enclosure that will surround GHOST, came back for round 2, and so did David H., one of our Gemini contacts. John left yesterday. Jennifer, Scott and Jordan will be assembling the enclosure around the newly aligned bench. Jennifer especially still has a long stretch to go.

And so, after the excitement of taking data and observing the solar spectrum, detectors are being warmed up and the electronics are getting unplugged. The clean room around GHOST will be disassembled, and in its place the outer enclosure -– that will keep GHOST stable to tens of thousands of a degree Celsius - will be assembled. And then everything will be reconnected through the enclosure to the bench.

And then we’ll be mostly done, and GHOST will be nearly ready to be put through its paces with nighttime observations (what astronomers call “commissioning”). I’ll be back in Chile for that, at the end of June.

Looking at my notes, this whole experience has been a decade in the making. It was in 2010 when we first heard about the opportunity, first proposals were submitted in 2012, and then it took to 2014 for the dust to settle and for this team to emerge that would take GHOST through to oh-so-near completion. Really, we reached oh-so-near completion in the Fall of 2019, and it would have been completely done by Spring 2020, it might even have been a note-worthy news event in the astronomy world. But it turned out that the news that year would be dominated by something completely different, and 3 years would have to pass before we would be able to reach the finish.

But we are nearly at the finish now. And between now and then, I have no doubt that absolutely nothing will go wrong, right?

Alan’s journey isn’t over yet! Read: “Under the Microscope: GHOSTS & Rainbows Part 4” .

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Whether you’re an astronomer, an engineer, or just interested in science and astronomy – make sure to follow the NRC and #GHOSTinstrument on social media, to learn more.