Following heavy storms early in 2012, a team of observatory staff and volunteer researchers set to work repairing the UK's damaged LOFAR station at Chilbolton Observatory, Hampshire. LOFAR is the world's most advanced low-frequency radio telescope, and consists of antenna stations across Europe. The stations can operate together or separately, allowing LOFAR to observe the Universe even as new stations are being built or maintained, and to improve its sensitivity as these stations come online. Christina took the Jodcast crew down to Chilbolton on the 14th of February to see the repairs, and found out about the UK station as the maintenance team dedicated Valentine's Day to caring for the telescope.
Dr Ben Stappers (): LOFAR is the next generation of radio telescopes, in that it's made up of lots of tiny little elements, rather than the large dish like you can see behind me. These elements are combined using fast supercomputers and high-speed internet connections. LOFAR works at low radio frequencies: less than around 240 MHz, all the way down to around about 10 MHz. It consists of elements mainly in a core region in the Netherlands, but also distributed all throughout Europe, with a station based here in the UK.
Christina (): We're here today at the UK LOFAR station in Chilbolton, in the south of England, and today is a maintenance day on the telescope. The dish that you can see behind me is actually used for weather-monitoring, despite looking fairly familiar; the LOFAR station is actually what you can see behind me.
Chrstina (): What sort of maintenance is actually happening?
Derek McKay-Bukowski (): In some cases there are small parts that just need to be replaced. There are also some entire antenna sites that need to be rebuilt from the ground up. In total, there's about a day's worth of work for about 20 people, and you can see in the background, and hear from the hammering behind me, that they're all hard at work.
Christina (): Yeah, and these are all volunteers who are working?
Derek (): They're all volunteers from local universities - so we've got people here from Southampton, Portsmouth, Sussex, Oxford, various other places as well.
Christina (): So, for the placement of the telescopes - are they particularly specific in their placement?
Derek (): They are, actually, yes. So, of the two different arrays of antennas that we have, one array has been tightly packed into a grid, and that is to get the antennas as close together as possible. The other field of antennas that we have, the antennas look like they've been scattered around almost randomly. They're not actually random: in fact, we've carefully chosen those positions so that no two antennas are in the same orientation and at the same distances away from each other. By doing that, you actually get the best possible performance of the antennas in terms of their radio sensitivity on the sky. The radio waves that we're receiving are long-wavelength radio waves, so, therefore, we need to have it accurate to, about, between one-tenth and one-twentieth of a wavelength. However, we can actually do better than that, and the actual position that we're going to put them back onto the field is accurate to about a few centimetres.
Christina (): We're standing amongst the low-band antennae. And, first of all, what are the low-band antennae?
Dr Karen Masters (): So the low-band antennae, they're the antennae that detect the radio waves from the lowest frequency band that LOFAR's sensitive to - that's below FM radio bands. And they're quite simple kit, actually. They have this metal groundsheet, which is actually standard building material from the Netherlands, and just underneath it we've just got this black plastic sheeting to stop weeds growing up. The actual meat of the antenna is these metal wires - they look like they're just holding up the pole, but this is actually it, this is the antenna, this is what detects the radio waves. And then the radio waves go up here to the LNA, which stands for low-noise amplifier - it amplifies the signal. And then it sends it down cables that go down this post and go down under the ground, way over there to the RF container, which is where there's a whole bunch of computers and things in this metal box to stop the radio waves leaking out to the antennae. And it puts together the signal from all of the LBAs here on the field and then sends it down the wire to the Netherlands to be combined with the other stations right across Europe.
Christina (): And given that all of these are anchored to the ground, how do you actually point it at something in the sky?
Karen (): Well it's all done electronically, it's all done by adding in little time delays between the antennas - between when we add up the signal from each of the antennas. If you imagine you were looking at something that was straight up, the radio waves would hit each of these antennas all at exactly the same time, so you wouldn't need a time delay. But if you wanted to look at something, say, over there on the horizon, the radio waves from that would hit these antennas on this side just slightly before the ones way over on the other side. And so you add in this little time delay, and that allows you to point. It's all electronic - it's all done with computers. You know, the kit's very simple - it's very similar to the radio telescopes that were used in the `60s, in the early days of radio astronomy. But without the computer backends, without the high-speed internet to connect to the Netherlands, and without this supercomputer, actually, in the Netherlands running the whole thing - without all of that, it just wouldn't be possible. It's a great telescope.
Christina (): We're now over at the HBAs. Can you tell me a bit more about that?
Karen (): So HBA stands for high-band antenna - this is detecting radio waves from above the FM frequency bands. These, actually, they look a bit funny, but they're actually, in some ways, rather similar to the LBAs. It's just that, because we're doing higher frequencies - so shorter wavelengths - the whole antenna gets shrunk down a bit. Inside of each of these black boxes is a whole lot of, sort of, polystyrene structure that is holding up metal antennas, that also form kind of a cross. There's actually 16 antennas in each box, although we call each one of them one antenna or one HBA.
Christina (): And so how do they work?
Karen (): They work rather similar to the LBAs. So they've got the metal bits, which detect the radio waves. There are amplifiers in there which amplify the signal and add it together from each of the 16 in a box and then from each of the 96. Again, each of these 96 has a cable that goes to the container, and so the signals from all of those are put together and sent to the Netherlands in the container.
Christina (): LOFAR will study the Universe from our own Sun to the earliest and most distant galaxies. LOFAR has 6 key science goals: solar science; cosmic magnetism; deep sky surveys, which will explore distant galaxies; the epoch of reionisation, looking back at the time of the first stars; and more mysterious phenomena, such as ultra-high-energy cosmic rays - and transient sources, which Dr Ben Stappers studies.
Dr Ben Stappers (): What we will do with LOFAR is to study radio pulsars and fast radio transients. This means that we use the telescope to either search for new objects, or we're going to study the known objects, at this unique frequency range. The reason why LOFAR is good for searching for new sources is that it has a very large field of view, plus excellent sensitivity. In that situation, we will use the stations in the core of LOFAR - but we'll also be able to use the stations located around Europe to do very rapid observations and rapid follow-up, because they have this very large field of view, as I mentioned earlier.
|Interviewee:||Dr Ben Stappers|
|Interviewee:||Dr Karen Masters|
|Camera:||Jen Gupta & Libby Jones|
|Editors:||Mark Purver, Jen Gupta, Libby Jones & Christina Smith|
|Opening sequence:||Mike Peel|
|Music:||Susan M. Lockwood & Kevin MacLeod|
|Producers:||Jen Gupta, Libby Jones & Christina Smith|
|Special thanks to:||LOFAR-UK|
|Website:||Mark Purver & Stuart Lowe|
|Cover art:||The LOFAR-UK station at Chilbolton Observatory, Hampshire. CREDIT: STFC/SEPnet|