La Palma and GOTO

Article by: Tom Watts

In collaboration with universities in England, Australia and Thailand, the Armagh Observatory and Planetarium is part of a team operating and commissioning the new Gravitational wave Optical Transient Observatory (GOTO) at the Roque de los Muchachos Observatory on the island of La Palma.

The observatory site as seen from the on site residence.

GOTO, once operational, will try to photograph the optical counterpart of gravitational wave events like the one detected last year, GW170817. It will do this by quickly photographing a large area of the sky in the region where a detected gravitational wave is thought to have come from. A large area of sky needs to be photographed as it is difficult to pinpoint where in the sky a gravitational wave has come from just from the detectors like LIGO and VIRGO. To accomplish this, GOTO will use two separate arrays of 40cm telescopes (relatively small by research standards) to cover 5 square degrees of sky per telescope. Each array is capable of holding 8 telescopes each to eventually cover 80 square degrees.

GOTO open while we checked it over.

As part of Armagh’s contribution, at the start of February I went out to La Palma to “babysit” GOTO while it’s robotic mode was being commissioned. GOTO is able to run in a fully robotic mode, meaning no astronomer needs to sit and manually operate the telescope on site. However while this feature is being tested, the telescope still needs someone to keep an eye on it to make sure it’s doing what it should be.

Unfortunately upon my arrival at the observatory there was an ice storm at the top of the 7,800 ft mountain. This meant it wasn’t possible for several days to even leave the astronomers residence, let alone use the telescope! Eventually the thick fog cleared and the ice began to melt enough to get to the telescope and dome to see how they had fared in the icy conditions. Sadly while I was there the ice didn’t clear enough to allow any observations to be made.

The Nordic Optical Telescope perched on the edge of the mountain.

Due to the high humidity, low temperatures, and freezing temperatures, ice was forming on virtually any surface, from cars to vegetation to telescope buildings. In some of the most exposed places, such as the Nordic Optical Telescope (NOT), we measured ice up to a metre thick and deep.

The 10.4m GTC above the clouds.

While it wasn’t possible to do what I’d gone out there to do, I was fortunate to be able to explore the site and visit some of the telescopes there. The observatory has some of the best facilities in the world, including the world’s largest optical telescope, the Gran Telescopio Canarias (GTC).

I was also show around the 1.2m Belgian Mercator telescope by PhD students from Ku Leuven, and around the 2.56m NOT by a post graduate researcher from Leiden University.

Fellow Armagh PhD student Erin Higgins and me at the summit.

We were also given a tour of the telescope with the largest single mirror at the observatory, the 4.2m William Herschel Telescope (WHT). While the GTC has a larger overall diameter at 10.4m, to achieve such a large aperture a segmented mirror is used. While the mirror for WHT is a single piece of glass, GTC utilizes 36 hexagonal segments positioned together to act as a single mirror.

While we weren’t able to do what we went out there to do because of the weather, it was an incredible experience where lots was learned.

Hopefully next time I’m off somewhere observing the weather will be more cooperative!