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Parkes and the LBA

The upper control room at Parkes
Hayride on the Parkes radio telescope (big thanks to Ken and Brett!)  CREDIT: Megan
It's Wednesday evening now and I'm back in Sydney following the observing run at Parkes. It certainly was an educational few days! For some reason the staff here all assumed that, coming from Jodrell, I must be used to observing with large telescopes. I keep having to explain that the Lovell and MERLIN are quite different in that respect: they have dedicated operators to do the actual observing, the astronomer doesn't actually get to use the telescope. Needless to say, I much prefer the Australian method!

So what was I actually doing at Parkes? Well, apart from grinning like a kid, I was there doing VLBI support. VLBI stands for Very Long Baseline Interferometry and is the method we use in radio astronomy to make very high resolution maps of the sky. Normal radio telescopes on their own are pretty pathetic in terms of resolution, even though they are so much bigger than optical telescopes, because the wavelength of light they are looking at is so much larger.

Resolution can be improved in two ways: building a larger telescope, or observing at a shorter wavelength. With radio telescopes, at some point you reach the stage where it would be totally impractical to build a single telescope large enough to get the resolution you want. For example, if you wanted to make a radio telescope large enough to have the same resolution as the Hubble Space Telescope does in the optical part of the spectrum, you would need to build a radio telescope 200 km in diameter. No, that is not a typo, I really mean two hundred kilometres. That's a lot of real estate. This is clearly impractical, so what we do instead is build smaller telescopes that are more practical (and a lot cheaper) and spread them out over a large area. Then, we point them all at the same spot on the sky and record the signals coming from each telescope. These signals are combined in a correlator which does some funky mathematical operations on the data and allows us to synthesise a much larger telescope.

The upper control room at Parkes
The upper control room at Parkes CREDIT: Megan
There are quite a few arrays of radio telescopes around the world using this technique to make accurate maps of the sky. In the UK there is MERLIN, in the US there is the VLA and the VLBA, in Australia they have the LBA. The creatively-named Long Baseline Array is a collection of rather different telescopes that normally have completely independent observing schedules but, four times a year, collaborate to observe as a single instrument. It is made up of three facilities run by the ATNF in Sydney: ATCA (an array of six 22-m dishes near Narrabri in northern NSW), Mopra (a single 22-m antenna located near Coonabarabran in NSW) and Parkes (a 64-m dish near, well, Parkes). Other facilities that also take part in the LBA from time to time are Hobart, Ceduna and Tidbinbilla (actually a deep space tracking station near Canberra).

The European VLBI Network (EVN) works a bit like this, too. It is also a collaboration of independent telescopes that observe together for a few weeks per year, but one big difference is that the EVN facilities all have their own operators. The ATNF telescopes do not have dedicated operators: astronomers who are awarded time on the LBA are encouraged (although not required) to do some observing, which is great for people like me who actually like observing and want to better understand how the whole system works.

Although I wasn't involved with any of the projects observed in this session, some of the ATNF staff knew I was interested in observing, so they invited me over to help out and (of course) I jumped at the chance. Although I've never directly observed with a big telescope before, I have spent a fair bit of time in the control room at Jodrell so quite a bit of the setup was at least familiar. The VLBI-specific stuff was new though, so there was still plenty to learn.

The Parkes staff are a great bunch, and the atmosphere up there was really quite jolly. I just love the fact that there is still a chart recorder in the old control room. It had been relegated to a corner, but John hooked it up during the geodesy experiment and it was interesting comparing the results from the two bands: the telescope floodlights cause quite a large spike when they come on! Watching The Dish in the control room was also quite mad. When I decided I wanted to be an astronomer, I never imagined I'd be doing that! Being left in control of this (relatively) old and rather graceful 1000-tonne telescope was pretty special. No doubt most people will think I'm completely crazy, but standing next to the azimuth track at 3am, watching the telescope move to the next source, was just fantastic. It's times like that when I remember what an utterly brilliant job I have.

Posted by Megan on Wednesday 09th Sep 2009 (11:06 UTC) | 2 Comments | Permalink

Comments: Parkes and the LBA

Much to Claire's chagrin, as she thinks it's a job she might actually be good at, "the ATNF telescopes do not have dedicated operators: astronomers who are awarded time on the LBA are encouraged (although not required) to do some observing". Conversely, the University of Tasmania, who have a contract with the ATNF to provide the services of the Hobart and Ceduna telescopes for each LBA session (which are scheduled to avoid IVS clashes at Hobart), *require* their staff and students who may well have nothing at all to do with VLBI, or even radio astronomy, to observe for these runs, because the ATNF cannot supply staff for all telescopes, and the PIs and others involved in proposals are not required to attend their observations.

I think ATNF do pay UTas some money associated with the support of the telescopes, but unlike IVS observing, the students are not payed for LBA (it's a mandatory service to the astronomical community!), and the university pays to send people to Ceduna - which is why they do their best to remote observe or get help from UAdelaide.

It's a bit of a funny system - no one but the designated CSIRO person is allowed to observe at Tidbinbilla. The PI used to be required to attend one of the sites, but that's no longer the case, meaning, as far as I can make out (*DISCLAIMER: I don't know everything!!*) all observing is now covered at ATNF and UTas' cost by ATNF staff and random astronomers and students willing to help out.

It's great in that you get to learn a lot of stuff about observing, and it gives you the opportunity to go to telescopes even if you don't have any active proposals yourself, and don't get me wrong, it's heaps cool, but it's a bit of a strange set-up, in the case of VLBI I actually think it would make a lot more sense if there *were* dedicated observers.

Alternatively, given it's the background I come from, if *I* have to do it as a service to the astronomy community, why don't other people? Why is it only UTas people who have to step out of their comfort zone and learn how to observe in lots of different modes? I wouldn't be at all opposed to a rolling schedule that all radioastronomers are meant to be on, that they get called occasionally to go to a telescope. That's more or less how DA'ing at the compact array is meant to work.... would decrease the ridiculous observing load on a few staff and give a lot of people the opportunity, like Megan, to learn new things while helping out other astronomers!

That's what I think. :)

Posted by Claire =) on Tuesday 22nd Sep 2009 (07:31 UTC)

The system is a bit odd. I didn't that was the system at UTas! Weird. Trouble with an uber-list of astronomers called on to observe, is you'd end up with a lot of them who observe so infrequently that they have to do the training every time they go. Don't get me wrong, I love that I get the chance to observe here, but the European system of having dedicated telescope operators who are experts does have it's advantages in terms of efficiency....

I love Parkes. I'm a nerd. (and I don't care!)

Posted by Megan on Tuesday 22nd Sep 2009 (11:52 UTC)

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