Have you ever wondered what graduate students do for the summer? Besides catching up on research, the summer is a great time to get away from the office and attend meetings, conferences, and workshops. I recently attended the 20th NRAO Synthesis Imaging Workshop (SIW), which occurred May 15-22, 2024, in Socorro, New Mexico, USA, just an hour away from the Jansky Very Large Array (VLA) site. This workshop is designed for both new and experienced users of the VLA, Very Long Baseline Array (VLBA), and the Atacama Large Millimeter/submillimeter Array (ALMA) to learn about how the technique of interferometry is used in radio astronomy. SIW began in 1983, shortly after the VLA finished construction, to support a new user base and has happened approximately every two years since then. Thousands of students have attended SIW, many of whom have since pursued professional careers in radio astronomy. Almost all the lecturers in this edition had either attended SIW as students or were previous lecturers!
The workshop is made up of three main components: introductory lectures, advanced lectures, and tutorials. The schedule typically spans a weekend to break up the basic and advanced lectures, and the tutorials generally are in the second week. The initial lectures assume that students are familiar with the wavelike nature of electromagnetic radiation, the concept of interferometry (e.g., Young’s double slit experiment), and the Fourier transform. Although mathematical topics, students are not expected to understand all of the detailed derivations of these topics, and only a familiarity with the concepts is necessary to begin appreciating the content presented in the lectures. Some lectures will present math and equations for completeness. Still, the workshop’s goal is for students to get practice in data reduction, so only the bare minimum background content is presented, and the remaining lecture content will focus on practical applications. The introductory lectures are designed to be useful to anyone. I highly recommend reviewing them to understand how radio astronomy works, even if you will never use radio data in your research.
The advanced lectures and tutorials make up the majority of the second week. These lectures focus on specific experimental designs and data products and how users might produce what they need from a VLA observation. In my first tutorial, I attended the “VLA Manual Calibration and Imaging” session, which taught users how to calibrate VLA data using the CASA software package. The second component was to create a continuum image, or an image combining all the data from all the observed frequencies, using standard data reduction techniques like CLEAN. My second tutorial was essentially the same goal, but to use data from the VLBA and reduce it with the AIPS program, which comes with its own unique challenges that are different from VLA data. Everyone attends the advanced lectures, but they are designed to focus on specific science cases. For example, one lecture was about using non-imaging analysis, and another focused on spectral line work and its applications at both low and high frequencies.
And, of course, the weekend includes a tour of the VLA site. I climbed one of the antennas on a tour led by Rick Perley, the project scientist of the EVLA upgrade project, the first postdoctoral researcher at NRAO, and an accomplished radio astronomer. The antenna surface is safe to walk on, so we started at the top and worked our way down to the receiver room. We stopped at various points through the antenna to discuss how it works. After the antenna climb, we visited the operator building, where the telescope operators oversee the array and decide which schedule is observed. The VLA is relatively unique because the array operator makes the final call about what programs are observed; most other major observatories have automated queue observations. The operator building is also where the supercomputer that enables the VLA’s interferometric mode called the correlator, is housed, which must handle ~120 Gb/sec of data from each of the 27 antennas. The VLA site has several other exciting attractions, including a Long Wavelength Array (LWA) station. Check out their live radio all sky feed!
This workshop is well-led and one of the best-organized events, owing to its long history and dedicated lecturers. Radio astronomy is filled with professionals who are also passionate about sharing their knowledge with the next generation of astronomers, and SIW embodies that to its greatest extent. I highly recommend attending this workshop, even if you aren’t planning to do radio astronomy in your career.
If you’re interested in more information, check out the Resources page of the workshop website to find textbook suggestions and links to online resources from previous SIW sessions. You can also see the slides and recordings of every lecture from the workshop on the Program page. Be sure to subscribe to the NRAO eNews to find out when the next workshop will happen!
Astrobite edited by: Cole Meldorf
Featured image credit: NRAO/AUI/NSF, Jeff Hellerman
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