Welcome to ALFALFA!

ALFALFA is a blind survey using the Arecibo telescope designed to detect neutral hydrogen in other galaxies. A brief overview of the survey is available in the About page. If that’s not nearly enough information for you, don’t worry! Future posts will describe various aspects of the survey, data, and follow-up observations in detail. Another goal of this blog is to share the excitement (and trials) of ALFALFA, including observing reports and summaries of new science and papers as they’re published.

We’d also love to hear from you. Do you have a general question about ALFALFA that you would like answered? Post it in the comment section of this entry, and we’ll do our best to answer it. Are you a member of the ALFALFA team and would like to contribute content to this blog? Contact Betsey and your help will be gratefully accepted.

 

Arecibo is Awesome

Arecibo is an amazing, amazing telescope. It’s often easy to forget just how impressive it is, but I had the point driven home the other day, and I wanted to share. The sensitivity of a telescope is driven by the collecting area of the dish (or mirror, for optical telescopes) since a dish with a bigger collecting area can collect more photons from distant objects. Arecibo has a 300 meter diameter – it is the world’s largest telescope and hence is extremely sensitive.

I realized just how sensitive Arecibo is last week. I was working on a proposal to observe some sources from the ALFALFA survey with the Very Large Array (VLA) in New Mexico in order to see structure in these sources more clearly. (I talk here about how the VLA achieves better resolution of astronomical sources.) In order to write this proposal, I had to calculate how long we needed to observe my sources in order to have a good detection. These were all objects that were strong detections in the ALFALFA survey where they were observed for only 43 seconds in all (less than a minute!) by Arecibo. I calculated that in order to have a decent detection level with the VLA, it would take upwards of 10 hours of observation time. This strong difference comes from the vast difference in collection areas; the VLA only has twenty-seven 25 meter dishes while Arecibo is a 300 meter dish. I had always known that Arecibo is an awesome facility, but looking at this difference in time necessary to detect the same sources really impressed upon me what an amazing and unique facility Arecibo is.

43 seconds or 10 hours? I know which I’d choose.

 

The 5BAA Tour, Part Two

The 5BAA tour has successfully ended – Sabrina is all settled in and starting her new job. The trip went extremely smoothly, including having nice weather the whole time. We took one day of slight detours to visit Bryce Canyon and Zion National Parks. The scenery and rock formations were spectacular. We thought of our planetary science colleagues at Cornell who could explain the formation processes behind everything, but we were happy to just enjoy the views.

A view of Bryce Canyon.

Chewie enjoying the view at Bryce Canyon.

A view at Zion National Park.

Chewie and Bella enjoying the sand at Zion National Park.

 

The 5BAA Tour

Sabrina recently (five days ago) defended her dissertation to her committee. She gave a very excellent talk on her work over the last few years to a full room. (Once she has some time, I’ll try to convince her to write a brief explanation for here.) Now that she’s done with her graduate work, Sabrina is off to start a post-doctoral position at CalTech in Pasadena, CA where she’ll be working with data from the Spitzer and Herschel space telescopes.

Now, Sabrina has two lovely bulldogs that need to move across the country with her. Rather than leaving her to handle the drive with two dogs by herself, Ann and I are along for the ride (actually, a lot of the driving). We’ve been referring to this trip as the 5BAA Tour: The Five B’s Across America Tour. The five B’s are:

Brie (Sabrina)
Banana (Ann)
Betsey (That’s me!)
Bella (The beautiful bulldog.)
Bad Dog (Chewie, the other bulldog.)

We’ve done two long days of driving to make it part way into Kansas and have three days of shorter drives ahead of us. The internet access is spotty, but I’ll try to include a picture or two at some point.

 

Papers!

I’m going to do some bragging for Ann and Sabrina here. They both have had papers recently accepted to astronomical journals for publication (and Sabrina’s has been published online already because I’m a little slow), which means they posted these papers to the astro-ph arXiv. The arXiv is an online preprint server where scientists post their papers before publication so that the community can see exciting results as soon as possible.

Ann’s paper is a presentation of a catalog of sources from the ALFALFA survey. Ann took a strip of the survey area and found all the sources – both galaxies and high velocity clouds. This work is part of the legacy aspect of the survey. The catalog is made available to the community so that people can use the information about the hydrogen content of that part of the sky in future scientific work.

Sabrina’s paper also includes a catalog but is focused on examining the Leo Group. The Leo Group is a relatively nearby collection of galaxies. This means that lots of small galaxies were found in this region that would be too faint to see if they were further away. Sabrina also found a number of small galaxies that had a substantial portion of their mass in gas, but are so faint optically that they hadn’t been found in previous optical searches. Since the Leo Group is a bound collection of galaxies, Sabrina was able to look at the distribution of galaxy masses and compare the number of big galaxies to small galaxies. This helps us understand how structure forms in the universe. (For example, see Ann’s post explaining the HI Mass Function.)

 

Around the World in 80 Telescopes

If you haven’t heard, 2009 is the International Year of Astronomy and, accordingly, lots of events are planned for the year. About a month ago, ESO (the European Southern Observatory) organized an event called “Around the World in 80 Telescopes” which had live webcasts from eighty telescopes in twenty-four hours. Of course, you can’t visit eighty telescopes and not include Arecibo Observatory. I can’t get the embedding to work right now, so head here to watch the video on Arecibo.

Of course, you should check out all the other telescopes, too. I’m making my way through them slowly.

 

The HI Mass Function: What Do We Do With All These Galaxies?

As Betsey has mentioned, ALFALFA is a great way to find hydrogen-rich galaxies regardless of their stellar content. With ALFALFA, we can find lots of galaxies, including a lot that have very few stars and are therefore incredibly dim. This is just another way to learn about the incredible diversity and structure in the Universe around us, and when we’re done we’ll have a big pile of about 30,000 galaxies to work with. There’s a lot that we can learn about the Universe in this way, but I’d like to tell you about just one: the HI Mass Function. We call it the HIMF for short.

 

Observing at Arecibo

I’ve been back from observing at Arecibo for a bit now, but I thought I would summarize the observing experience. Mostly, observing at Arecibo isn’t much different from observing remotely in Ithaca. The biggest difference in terms of running the observations is that I get many more monitors to watch, as you can see in the pictures below. When observing in Ithaca, I have two monitors (running with one computer) for everything – one to display the program that controls the telescope and one for data monitoring. At Arecibo I have two computers, one with six monitors (telescope and observations control) and one with two (data monitoring). The set-up with all the monitors is very nice, especially because a lot of programs that monitor the status of the telescope and system set-up are displayed (the four peripheral monitors). Occasionally though, the different set-up would cause me to have a mild panic. I would glance at the data monitoring, for example, and then become uneasy when I didn’t see the program controlling the observations and telescope out of the corner of my eye. I managed to keep forgetting that it was on another set of monitors, a few feet away. All that extra monitor space could be disturbing at times.

The computer, and all its monitors, used to control the telescope.

The computer for monitoring data quality.

While the observing set-up is nicer at Arecibo and slightly more responsive since there’s no remote connection delay, that’s not the motivation for traveling all that way. The real reason to travel to Arecibo is to interact with people. Now, there are lots of people to meet at the observatory, but, in terms of observing, it was great to finally meet the telescope operators. The telescope operators are there to help make science observations run as smoothly as possible, which means they help with telescope set-up and are the first people you turn to for help when troubleshooting. When observing remotely, I would call the operator about fifteen minutes before the start of our observations to let him know that I was ready to take control of the telescope and to request the telescope be slewed to our desired position. What this means is that the extent of my interaction with the operators had been occasional 30-60 second phone conversations and snippets of dialog through a chat window in the telescope control program. One of the most productive parts of my trip was having the opportunity to meet the telescope operators in person and chat with them (especially during the long nights). It wasn’t just that it was nice to be able to put faces to the names of the operators I had worked with remotely; having interacted with the operators more has left me more confident of dealing with observing troubles remotely. Now, if I have to call the operator because of troubles (WAPP failures, network failures, etc.), it’s not calling a stranger and explaining the situation from scratch. Instead, I know the operators and they know me, and we can jump right into solving the problem and starting observations as soon as possible.

 

Arecibo and Exo-planets

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.

 

Dwarf Galaxies from ALFALFA: Followup at Palomar, Part 2

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).

 

An Exciting Night

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.