My time at the Compact Array

A special report by Katie Barnard on her work experience at Narrabri

So there I was, quietly flagging data, and Naomi came up to me: "Oh by the way Katie, I've volunteered you to do a research talk"... WHAT!? And so, work experience student that I was, I ended up giving a research talk to a group of PhD astrophysicists, and others, about astronomy. There's something not quite right with that picture...

But that was only one of the exciting things I did in my three weeks at the ATCA. The purpose of the work experience was basically to see what it's like to be an astronomer. I am in the process of trying to decide what to do at university next year, having finished year 12 last year, I decided to take a year off to enjoy life and figure out what I want to do as a career. I have been interested in astronomy for some time, and so I thought work experience would be a good idea to see what it was really like. And so, with the help of Raymond Haynes from the ATNF, in mid-July I was on my way up to Narrabri!

In my time at the ATCA, I worked with Naomi McClure-Griffiths, a PhD student from the university of Minnesota. Having done no university-level study, it was a little bit difficult at first to understand what was going on. For the first couple of days I felt a little overwhelmed by it all, but through Naomi's patient explanations and diagrams I soon began to grasp the basic ideas.

It was really interesting finding out about the telescope and how it worked, learning how radio waves from space are collected and then transformed into pictures of what is there. Whilst I was there I was able to do some observing by myself, which was a little scary at first (having a $50 million telescope under my control!), but I need not have worried as everything went relatively smoothly. I also learned about all the processing the data has to go through before it can be seen as a picture. Naomi showed me how to load the data onto the computer and how to flag it (i.e. take out the bad data) before it is turned into a picture.

However, I think the most exciting thing I did whilst I was there was looking for, and then analysing shells. A shell is a huge `bubble' in space - a large area which contains very little gas and dust, and is surrounded by `walls' of relatively dense areas of gas and dust. Naomi gave me some `cubes' (seen as movies) of different sections of the sky, from observations at Parkes, to look through and identify possible shells.

To identify them as shells, the first thing is to look for areas of non-emission with what looks like walls of swept-up mass on the sides. I also looked at the velocity profiles, looking for a dip with a peak on either side in the profile. The peaks indicate the walls of emission and the dips show the empty centres of the shells. I then worked out the basic properties for each _ the centre coordinates, central velocity, angular diameter and angular height.

Having looked through all the different cubes, I chose the most interesting one (cube 295) to study further. For this, I identified three different shells which I named `Shelby' (from Shell B) `Teddy Bear' (because of it's shape) and `Small' (because of it's size relative to the others).

I then worked out more properties of these three; their physical height and diameter, distance, column densities, ambient density, swept-up mass, expansion energy, kinetic energy and expansion velocity. I also looked for front and back caps for the shells. The distances involved I find hard to comprehend. `Small' has a diameter of 630 pc, or 2054 light years, which of course means that if you were travelling at the speed of light, it would take you 2054 years to get form one side to the other. I find that absolutely incredible!

There are a number of computer programs which are used to work out the properties, or look at the shells in different ways. One such program makes a 3D picture of the cube, and turns it around so you can see it from all different angles. This was really good for visualising the shells, and seeing how they all seem to join up, which I had noticed in the movie. I also plotted where the shells are on a map of our galaxy and was quite surprised by how far out they are. The most distant of the three (Small) is 15.7 kpc from us, and the closest, (Shelby) is 11.5 kpc, which poses an interesting question of why they are so far out in the galaxy.

Having done all this work on the shells, they became the topic of my research talk. It was a little difficult, in that I'm still trying to get my head around a lot of the `basic' concepts, but it went well.

Another highlight of my time at the ATCA was a tour of one of the antennas. It was an amazing experience actually going up onto the dish. The antennas, while looking huge from the ground, seemed even higher from the top, with an incredible view in all directions. Of course I didn't spend all the time working, I had fun playing volleyball, table tennis, appreciating the countryside and just enjoying being out in the country _ a lovely change from the city!

Thanks to all the people that made this work experience possible. Especially to Raymond Haynes for organising it all for me, to Dave McConnell, Robin Wark and all the staff at Narrabri for making me feel welcome, and of course to Naomi for all the time and effort she put into explaining things to me and showing me around. I had a really fantastic time, and it showed me just how fascinating astronomy really is!