ALFALFA: The Arecibo Legacy Fast ALFA Survey

You may have heard about the recent discovery of an Earth-sized planet that is not quite twice the mass of Earth. Remember, this isn’t an Earth-like planet because it is much too close to the star it orbits to be habitable. I happened to find this announcement especially interesting because I had just attended a talk the day before where Arecibo’s role in exo-planet detection was mentioned. Pulsar B1257+12 was observed at Arecibo and, through close examination of the data, astronomers were able to determine that it hosted two planets, of a few Earth masses, in 1992. Since then, they have detected a third planet and a possible fourth. These extra-solar planets were discovered several years before the “first” exoplanet detection around 51 Pegasi in 1995. I think it’s worth remembering that the first exoplanets, and the first approximately Earth-mass planets, were discovered by the Arecibo radio telescope. Now, you aren’t going to be able to find habitable planets around a pulsar (at least, not habitable to any sort of life we know), but the fact that planets can exist there offers a lot of insight into theories of planet formation and stellar evolution.

When I left you last, Shan and I were headed to Palomar Observatory near sunny San Diego. We were going to look for signs of metals in star forming regions of gas-rich dwarf galaxies. That’s a mouthful, but what it comes down to is that hydrogen gas is what galaxies turn into stars, and stars fuse and burn hydrogen and helium to make the other elements we call metals (some elements can only be formed in supernovae, the final death stages of massive stars, but it comes down to the same thing: star formation sets the whole process in motion).

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It’s been an exciting night of observing here at Arecibo. Of course, exciting means that things are going wrong, which isn’t good. As soon as I tried to start the observations, the program that controls the telescope started sending me error messages. The problem was that it couldn’t adjust the power levels for one of the WAPPs. The WAPPs (Wideband Arecibo Pulsar Processor) are part of the backend of the telescope. Their job is to take the incoming signal and create the spectra we are interested in. In all, there are four WAPPs – one WAPP handles the data for two of ALFA’s beams. (Since ALFA has seven beams, one of the WAPPs handles a single beam twice.)

The WAPPs are somewhat finicky and have been acting up recently, so I wasn’t worried at first. I followed the standard procedure of restarting the WAPPs, hoping to reset them and clear away any errors. Unfortunately, the problem this time couldn’t be fixed that way. As soon at it was clear that the problem wasn’t going to be easily fixed, the telescope operator was on the phone, calling a staff member who is an expert in dealing with the WAPPs. The first step was to determine what type of problem we were having: software or hardware. Sometimes the problem can be a glitch in the software that interfaces with the WAPPs; other times, the problem is with the WAPPs themselves. After some checks, they figured out it was a hardware problem, so the operator headed back to the room containing the WAPPs, talking on the phone to the expert to start figuring out what was wrong. Another expert staff member happened to stop by on his way out for the evening and headed back to help out also. They soon found the problem and a solution, so that the failed WAPP was back up online and running again and observations could start. (One of the WAPPs didn’t have power and the solution was to remove a filter that we don’t need for our observations. The filter wasn’t working and that caused the power to the WAPP to be cut.)

All in all, we lost the first half hour of our observations, which is always frustrating. I was glad to be here at Arecibo, rather than observing remotely, though. This way, I at least knew immediately what was happening and being done to fix the problem. When observing from Cornell, I’d be stuck sitting around, waiting for the phone call to tell me that things are back online and I can start observations. Here, I was able to stick my head into the room containing the WAPPs to ask what was going on. I still couldn’t do anything to help, though, which was personally frustrating for me. I don’t have any experience with hardware, so the nuts and bolts of the WAPPs are a mystery to me. There are many different types of knowledge in this world, and I am always impressed by people who have mastery of a type of knowledge that I don’t. Tonight was a prime example of that. Even though we lost a half hour of observations, the turnaround from noticing a problem to identification of the problem to a solution felt amazing quick. I’m sure it would have seemed longer if I were in Ithaca, having no idea what was happening. Being here to witness the problem and its handling makes me appreciate the staff here that much more. I’m glad to know that they feel as strongly about wasted telescope time as I do.

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After a year of handling my share of ALFALFA observations remotely, scheduling has finally worked out so that I had the chance to come to Arecibo to observe. I’ve been here three days now and have had a blast, from exploring the telescope to meeting all the people who I’ve only interacted with via the internet/telephone until now. There’s a lot I could share, but I wanted to start with just how impressive Arecibo is an an engineering feat. I went up to the platform of the telescope my first day and was blown away.

Above, is a picture I took of the platform and arm of the telescope. The platform is the triangular structure you see suspended in the air. It is supported by cables running to three towers. Below the platform, is a crescent-shaped arm, and on that arm is a line feed and the Gregorian dome. The ALFA receiver is housed in the dome. The arm rotates around the circular track and the dome can move along the arm to control the pointing of the telescope, since the dish is fixed. You can find the details of the telescope with all the numbers here. Suffice it to say, the structures being supported are massive. It’s hard to believe it’s possible sometimes, although that’s not the best thought to have while on the platform, when you’re far above the dish.

Since the night’s observing is about to end, I’ll let pictures do the rest of my talking for now. The pictures I’ve taken at Arecibo Observatory so far are here, and I’ll eventually add descriptions.

At the end of March I had the opportunity to visit Palomar Observatory, near San Diego, with Shan, a younger student in the ALFALFA group. We were there to “follow up” on some detections of dwarf galaxies that we had made with ALFALFA. We can learn a lot about galaxies by observing their neutral gas, which Arecibo helps us find, but when we want to get some information on the stars we need to use an optical observatory, and that’s what took us to Palomar. In particular, we were interested in looking at the star formation histories of these dwarfs and the amount of metals that they contain. Astronomers have this weird habit of referring to pretty much any element that isn’t hydrogen or helium as a “metal,” even though we all know from chemistry that that’s not accurate. What’s important, though, is that these things astronomers call “metals” are the heavier elements that can only be made in stars or, in some cases, in catastrophic stellar death throes called supernovae. These are the important elements that make up your everyday life, like oxygen, carbon, iron, even gold. Since metals are made in stars, looking for metals in galaxies tells you something about the formation of stars in those galaxies over their lifetimes.

The Palomar 200 inch (5 meter) telescope dome.

What, specifically, were we looking for?
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