Making light work of planet hunting

13 January 2014

Finding a planet the size of Jupiter in the Milky Way is the astronomical equivalent to finding a needle in a haystack. But after a tumultuous year that began with bushfires at the Siding Spring Observatory, collaborators on the HAT-South network have done it - four times!

"HAT-South is a network of telescopes - two telescopes at the Siding Spring Observatory near Coonabarabran, NSW, two in Chile and two in Namibia," says Dr Daniel Bayliss of the Research School of Astronomy & Astrophysics, who manages the HAT-South telescopes at Siding Spring.

"They form a ring around the Southern Hemisphere. It's always night in one of those places, so we can monitor stars for 24 hours per day."

This network of telescopes - the largest exoplanet survey in the Southern Hemisphere -­ is being used to search the sky for giant planets, which appear as tiny specks of darkness transiting across bright stars.

"We measure the light of the star, which is relatively stable, but every now and again the light dims by about one per cent, indicating a planet may be crossing in front and blocking some of the starlight. The dimming usually lasts for about two to three hours. When the planet orbits it happens again and again.

"When we detect a transiting planet we can then find out its mass and size, whether it is orbiting the same way its star is spinning and even what is in its atmosphere - all of which give us clues as to how the planet is formed."

In 2013, Bayliss and his collaborators announced they had discovered four new transiting planets using the HAT-South network, quite an achievement considering only about 150 had been found before, and most of these in the Northern hemisphere.

"For a long time people thought other stars must have planets around them since our sun did, but no one knew for sure until 1995 when the first one was discovered. Astronomy was a very mature field by 1995 but it's just so difficult to find these planets."

The two HAT-South telescopes at Siding Spring are fully automated, allowing Canberra-based Bayliss to manage them remotely.

"When the conditions are good they open up at night - the whole roof comes off. They follow one patch of sky as far as they can then flip over and track a new piece of sky, doing two or three patches of sky a night. Then when they sense it's getting to light they close back up.

"They can also sense the weather - they have sensors for wind, humidity and clouds. Even before it rains, they are closed.

"We have a webcam set up so we can check on them. Part of my job is checking up on these telescopes at Siding Spring and the others in the network around the world."

Bayliss was glued to his computer watching the feed from the webcam on 13 January 2013 when bushfires swept through the Warrumbungle National Park in which the Siding Spring Observatory is located.

"There's nothing you can do," he said. "You're 600 kilometres away.

"We turned everything off and then sat back and watched it. We could see fireballs. We thought it was going to get destroyed."

Bayliss says the fire front was very fast, passing in about 10 minutes.

However as night set in and the webcam started to use a longer exposure, it revealed light trails caused by embers flying over the site.

"The wind picked up and again, we were worried. But by then there were firefighters on the mountain going around putting out spot fires. I suspect they saved the telescopes."

Three buildings were lost at Siding Spring Observatory, but all the telescopes, including HAT-South, survived the fires.

"I went up as soon as I could which was about 10 days after the fire. I had to clean the filters but I got the telescope back online by the end of January, and they were operating in automated mode again."

A year on, HAT-South powers up each night, checks the weather and continues the search.

"We have to monitor thousands of stars before we have a chance of seeing anything," says Bayliss. "But when you do find one, it's very exciting."

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