I’m currently in Socorro, New Mexico at the Array Operations Center for the VLA (Very Large Array). The VLA is a large array of radio telescopes, consisting of 27 dishes with diameters of 25 meters (82 feet). If you’re trying to place where you might have seen or heard of the VLA, it is featured in the movie Contact; when Jodie Foster sits in the desert listening to her headphones, she is at the VLA. (See here for a good breakdown of SETI in the movie Contact and in real life.)
Array observations are very interesting because they offer a nice complement to observations with large single dish telescopes. Arecibo is much more sensitive (can see fainter objects) than the VLA, but the VLA offers much better spatial resolution (objects aren’t as blurry). This means that ALFALFA can identify interesting faint galaxies, and follow-up observations with the VLA can help to determine the structure of these galaxies. I hope to explain a little bit more about how radio telescope arrays work later in the week, but I don’t want to delve into that topic right now. Instead, I’ll talk about what I’m doing in Socorro.
Now, this trip is not exciting as you might think (except for the fact that I’m not in Upstate New York in February). The VLA is actually about a hour’s drive from Socorro, so I haven’t even seen the telescope yet. Of course, there are advantages to not being at the telescope site, such as being able to use a microwave. (Those are a no-no on-site as they produce radiation at wavelengths that the telescope observes at.) We do plan to make the time for a trip out to the VLA, as it would be nice to see the array that we’re using.
Of course, this isn’t an observing trip, either, which also removes some excitement (in the form of time pressure). I’m out here to learn how to reduce data that was taken a couple of months ago. (It’s actually for a non-ALFALFA project, but I will hopefully have time to also reduce some follow-up VLA observations of ALFALFA galaxies. And if not, I’ll be bringing my skills back to Ithaca.) It’s actually not unusual for observers to travel to Socorro for reduction but not observations. Partially, this is due to the nature of observing with the VLA; an observing plan is submitted to the telescope operator and does not require the presence of an observer. However, dealing with data from arrays is challenging because you need to combine the information from all the different antennas. Originally, the limitations were on computing power; people traveled to Socorro for access to computers that were powerful enough to handle the data processing. Currently, travel reasons have more to do with expertise. By traveling out here, I’m able to learn how to use this program from an expert, which means much less time spent trying to understand the manual. This is especially helpful, as the program used to reduce VLA data ( AIPS – Astronomical Imaging Process System) was first developed in the 70’s and has many quirks that are best learned from someone familiar with it. This process of learning from an expert has worked well, as we had a rough map of our data by the end of today – our first day!