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.

 

Touring the Telescope

As Ann mentioned in the last post, the ALFALFA Undergraduate Workshop was taking place last week at Arecibo Observatory.  This was my first time attending the workshop, and I enjoyed the experience a lot – meeting various members of the ALFALFA Undergraduate Team and hearing about ongoing work.  One of the best parts was, of course, a tour of the telescope.  I have a feeling that every time I’m shown the telescope I’ll manage to learn something new.  Between the impressive engineering and long history that go into Arecibo, I think there will always be a new story to hear or new fact to learn.

I was part of the last tour group from the workshop that went up to the telescope platform.  They were planning on doing some radar tests once we were done with the tours.  When they want to run the radar, they have to place covers on all the other receivers on the telescope because enough power is transmitted through the radar that it would fry the other receivers.  Since, we were the last group visiting the receiver room up on the telescope platform, they started preparations while we were still up there.  First, they rotated the floor of the receiver room to move ALFA into place for putting the cover on.  We went down to look at the receivers and to see ALFA in person.  While there, we decided to help out by placing the cover on ALFA.  It took us a bit to figure out which way the cover fit on, but eventually we got it.  A few pictures of this process are below.

 

The ALFALFA Workshop at Arecibo

This week we’re holding the ALFALFA Undergraduate Team workshop on-site at the observatory, so there are about 30 ALFALFA team members roaming around. We have three nights of observing while we’re here, from 2 a.m. until 7:15 a.m., and at the moment I’m right in the middle of the first observing run. Most of the time, we observe remotely, from our office in Ithaca, so being here is always a different (and wonderful) experience. This time through, I’m particularly enjoying the amazing weather, since Ithaca has had some temperatures in the single digits and Arecibo is in the mid-70s, clear, sunny, and beautiful. If I had to choose just one thing, I’d say the best part is falling asleep and waking up with the windows open, a breeze coming through the room and the sound of coquis and other wildlife outside.

While we’re here, we’re taking a look at a part of the ALFALFA survey that includes some pretty interesting objects, and that was all part of our workshop observing proposal that was written by the dedicated team of undergraduates working on the survey, in particular Nicholas Crump, Steven Margell, and Tess Senty. We’ll cover part of the Leo Cluster of galaxies; Leo is an especially “rich” cluster, which is the term extragalactic astronomers use to describe clusters with many galaxies. Because there are so many galaxies in the cluster, and so many of them with lots of neutral hydrogen gas, the galaxies are interacting with each other and with the hot gas in between them. This can strip gas off of the galaxies, but it can also cause intense periods of star formation, making a cluster like Leo a very interesting place to learn about galaxy evolution.

Since this was our first night of observing for a while, I’m on a strange schedule; I got up as usual this morning, but after dinner tonight I slept from about 9 a.m. until 1 a.m. In the morning, some other ALFALFA observers might come in and relieve me around 5:30, at which point I’ll head back to my cabin and grab as much sleep as I can before I head in to the workshop. It can be a strange schedule, but the great thing about coming to Arecibo is that observing and working becomes your life, so you can tune everything else out and grab sleep whenever you get the chance!

 

No, we are not really “telescope vultures”!

Here’s a blog post from Martha about some recent observing time we lucked into. Enjoy!

Although the majority of the observing time at Arecibo goes to passive radio astronomy, observers also make use of its powerful transmitters to do radar astronomy (remote sensing of the Moon, planets and their satellites and rings) and atmospheric science, especially incoherent scatter radar to study the Earth’s ionosphere. The atmospheric sciences experiments are organized as large campaigns (“World Day’s”) making use of simultaneous experiments using a “chain of radars”, one of which is Arecibo and conducted over a week or so. But they depend on the use of the transmitter, and once in a while, the transmitter fails and cannot be fixed in the short run. If towards the end of an ionosphere campaign, there is a hardware breakdown and it is clear that it cannot be fixed, the telescope schedule is quickly reassigned to other programs (so that the telescope does not go unused). The ALFALFA observing program (A2010) is one of those that is “on call”, ready to fill in on short notice.

So, on Dec 14th, we were notified that we could observe on two nights rather unexpectedly. Since we were notified late in the day and it was during the week of final exams for many students and also snowing (which complicates travel and parking; fortunately MH and RG have vehicles which drive well in the snow), Martha decided the best thing to do was to run the observing herself.

The first issue was “What should we observe”? The time allocation was also for the “spring block”, 07h30 < R.A. < 16h30, and we had not really been expecting to observe before January. Scheduling a many-year survey in an optimally-efficient manner is not always as easy as one might think. Since we only observe at night (the Sun is a strong radio source which moves through the sky and therefore interferes with our "minimum intrusion" observing technique), the time we were assigned covered only 07h30 < R.A. < 11h50; we will have to observe the rest of the block later. Martha also realized that since AUDS (program A2133, another large scale survey using Arecibo) was not scheduled before (as is normally the case), it would be an ideal night to observe south of zenith. The AUDS target is north of zenith, so if we follow them, the telescope has to be slewed all the way around to the other half of the sky. Because of her quick thinking, we got in two south of zenith runs, almost completing what we need south of the zenith strip.

It is rumored that the atmospheric scientists think of us as "telescope vultures", circling nearby, hoping that their experiment fails. But, that is not really true, though indeed, their disaster becomes our opportunity. We point out that on occasion there is reciprocity: if a target-of-opportunity (like a potential Earth-impacting asteroid) needs immediate observing time, then our allocated runs can be (and have been on occasion) preempted at the last minute. The main point is that telescope time is a precious resource, best used to maximum efficiency, which sometimes requires last-minute changes to the schedule.

 

600th Observing Session

We recently celebrated the 600th observing session of the ALFALFA survey. This landmark occurred during Thanksgiving week, so we had a large contingent of observers at Arecibo taking advantage of the break from university classes. Two of the institutions from the ALFALFA Undergraduate Team, Humboldt State University and Colgate University, were represented. The observers, including two faculty advisors and seven undergraduate students, met in the control room for a celebration before observations started. Pictures, courtesy of Tom Balonek, are featured below. You can also find the pictures on the ALFALFA website located here.

600 observing sessions completed and 79% of the survey observations completed – we’re nearing completion of the observations for the survey. There’s still plenty of science to do, though!

 

ALFA’s Back!

The receiver we use for our observations, ALFA (more details here), is back in use after being out of commission for a month and a half for service. ALFA was put back into place at the beginning of the month and has been working ever since; we’ve been observing over the last two weeks and things seem to be mostly working.

Servicing ALFA is no simple task. You want to get the receiver into the shop so that it can be tinkered and twiddled with easily, but it’s installed in a dome that is suspended 400 ft above the dish of the telescope and kept chilled to very cold temperatures (well below freezing). You want to have a very good reason for needing to service the receiver. There’s the hassle of uninstalling and reinstalling the receiver, but also the risk that every time you let it warm up to room temperature when it’s in the shop that it might not cool back down without breaking. Then there’s also all of the observing time you lose while the receiver is in the shop. (Of course, Arecibo was still being used for observations, it’s just that any of the projects using ALFA – including us – couldn’t observe.) In this case, ALFA was taken down for servicing because several programs that use the receiver needed it be to improved and tweaked a little bit so that they could actually make the observations they wanted.

Unfortunately, like with everything, once you fix one problem, another appears. In this case, one of the beams of ALFA has been acting up. Fortunately, it seems like this isn’t a problem that will require ALFA coming off the telescope again to fix. Instead, it seems to be something that can be fixed while ALFA is installed in the dome, allowing the problem to be worked on during telescope maintenance time without impacting observations.

 

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.