My time as a MOA observer

“MOA (Microlensing Observations in Astrophysics) is a Japan/NZ collaboration that makes observations on dark matter, extra-solar planets and stellar atmospheres using the gravitational microlensing technique at the University of Canterbury Mt John Observatory in New Zealand. Further studies are also carried out.” (MOA Page, University of Canterbury)

The MOA telescope is New Zealand’s largest optical telescope with a mirror of 1.8m across. It’s also an exoplanet hunting telescope. I have been fortunate enough to be an observer on this amazing telescope and be involved in the MOA project.

The MOA telescope at Mount John. Credit: Holly McClelland.

The MOA project uses microlensing (that’s what the M in MOA stands for) to hunt for planets around other stars. When two stars come into alignment and the gravity of the star in front causes the background star to be magnified, by looking at this signal you can see what kind of star system if in the middle causing the magnification.

So, what do you do if you are the observer on MOA?

Well you start work at sunset to go set up the telescope and computers. You need to back up the previous night’s data, check the weather conditions, and make sure the telescope is pointing properly at the chosen target.

If the weather is good (no too windy or cloudy) once the sky is dark enough you start taking images.

The galactic bulge – that is the centre of the Milky Way galaxy, is the focus for the telescope’s observations. This is because that is where the most stars are and therefore we get lots of microlensing events in that part of the sky. And the best time for observing it In New Zealand is in winter when the galactic bulge is up nice and high. Just below is one of the Images from the galactic bulge.

The Galactic Bulge (GB). Credit: Holly McClelland.

After the telescope is talking images of the sky, the computer will search for any stars that have increased their brightness and therefore they may be undergoing a microlensing event. The observers’ job is then to go through these events and mark any of them which might have a nice curve that looks like the beginning of a microlensing event. Below is a graph of this happening with a little deviation at the end.

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Light curve of a microlensing event. Credit: Holly McClelland.

Every now and again something wanders into the field of view of the MOA. This happened to me one night when I suddenly saw this new point of light. When we took another image few minutes later it was gone again. After looking up the coordinates in the sky of where we saw it we found out that it was an asteroid named 2050 Elinor, a main belt (between Mars and Jupiter) asteroid named after the astronomer Elinor Gates, the image that MOA got is just below.

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Asteroid Elinor Gates (top right). Credit: Holly McClelland.

The computer will also be measuring the brightness of stars that have already been confirmed as a microlensing events, looking for any anomalies from the model of a lone star moving in front of the background star. An anomaly could be a binary star or perhaps a planet.

One night when I was observing we had the gamma ray burst alarm go off. A gamma ray burst is a high energy event in space. Many researchers are interested in these gamma rays bursts so when one is detected an alert is sent out to observatories so that the observers can turn the telescopes around and catch the light. And of course, at the MOA telescope there is a little blue light that when an alert gets sent out for a gamma ray burst the light will flash and let you know that something is going on. As I was observing, the alarm went off and we captured this image of the sky where the gamma ray burst came from.

Gamma ray burst night. Credit: Holly McClelland.

When the Galactic bulge is too low to observe we look towards the large Magellanic cloud for microlensing events. Observing the Large Magellanic Cloud (LMC) is less action-packed than the galactic bulge (GB) due to the longer exposure time (5 mins for LMC rather than the 1 min for GB) and there are less anomalies in the microlensing. See the timage of the Large Magellanic Cloud (LMC) below with the Tarantula nebula in the lower right.

Large Magellanic Cloud and Tarantula Nebula. Credit: Holly McClelland.

Once every 5 nights we are also taking images of the Small Magellanic Cloud, mainly just to check up on it and see if there is anything interesting happening in there. Here is an image from the Small Magellanic Cloud below.

Small Magellanic Cloud. Credit: Holly McClelland.

This all sounds very exciting but there is also a lot of waiting for the weather to improve and there can be bad runs of clouds, high wind and snow. On these kind of nights, I am still in the control room just in case the weather improves but there is plenty of other work as well so there is never a dull moment.

There are also calibration images that we must take for the telescope. Darks are images were the shutter of the camera is kept close and they give you an image of the noise in the camera. Whereas Flats is taking an image of a white square on the dome lit up evenly to give you an image of the defects in the camera. These are important images in order to make sure the data from the telescope is as good as possible. But they can be a real pain when you have to spend several hours trying to get the camera to work properly to get these calibration images.

I love working with the MOA telescope and I feel excited and proud to contribute to a project where we are discovering new worlds and expanding humanity’s scientific knowledge.