Summer student programme 2025

Hi! My name is Juno (Ha-Eun) Choi and I am a recent graduate of Colgate University in the United States with a bachelors degree in Astronomy/Physics. There, I worked under the NANOGrav collaboration on a research project focused on pulsars and the ISM.

This summer, I worked on a similar project with Dr. Aurélien Chalumeau and Dr. Nina Gusinskaia. The motivation of this work was to utilize both Nançay and Meerkat data to model the effects of the ISM through scintillometry (scintillation + interferometry) and to compare that with results from pulsar timing. This was done in the aims to refine PTA noise characterization and obtain higher precision in pulsar timing. By the end of my summer I was able to extract the scintle widths, scattering timescales, and scattering indexes from numerous pulsars and make several analytical comparisons. It was particularly interesting to compare the scattering time scales from the scintillometry work to the dm time series determined from timing. I learned so many new skills!

Outside of the research, I had an absolutely wonderful time with the other summer students and getting to travel around the Netherlands. My favorite cities that I got to visit were Groningen, Rotterdam, and Zwolle! The surrounding nature was very lovely as well. I definitely recommend taking every opportunity to go out and explore!

The summer student program at ASTRON was absolutely unforgettable. I am so grateful for the time I had there and am so excited for all of the future students that will get to experience it as well.

Hello, my name is Seung Yeon Lee from South Korea. I am currently pursuing a Master’s degree at UNIST. In fact, I first came to JIVE in the Netherlands in February 2024, and at that time I never imagined that I would return. But I was fortunate to be given this opportunity, and here I am again. Wow!

During the summer programme, I enjoyed a range of experiences. I went stargazing with my fellow summer students, participated in various field trips, and visited many of the Netherlands’ museums, seeing famous paintings in live. Can you believe I visited around ten different regions and museums?

Here, I studied H I absorption in active galactic nuclei (AGNs). Although I had already been researching AGN in Korea, I had always worked only with continuum data, and this was my very first experience analyzing H I absorption. The aim of my project was to understand AGN feedback. AGN feedback, which arises from the interaction between the central supermassive black hole (SMBH) and the interstellar medium (ISM) of the host galaxy, plays a crucial role in understanding galaxy evolution. To this end, we investigated the radio AGN J1435+5051, which has a jet, through parsec-scale VLBI phase-referencing observations with the VLBA, EVN, eMERLIN, and GBT. We successfully resolved the source on parsec scales, which had remained unresolved in previous kiloparsec-scale studies using MERLIN and in H I studies with the WSRT. In the continuum image, the source shows an unusual curved U-shaped morphology, and weak H I absorption at the ∼2σ level was detected in the brightest region and along the adjacent jet. From the H I absorption spectral profile, we found that the observed cold gas does not exhibit the rotation expected from a regular disc, and that the H I gas near the center appears diffuse,
with tentative evidence for clumpiness.

Although it was difficult at first and I felt frustrated when the results did not come out as expected, as I continued I began to see more results, which became exciting. Over these two months, I feel that I have learned so much. I wish I could stay longer, but now it is time to go back. I believe there will be another chance to come back someday, and until then I will continue working hard.

Finally, I want to thank my supervisors Suma, Zsolt, Raffaella, and Gabor, as well as Junghwan, Leonid, Yvonne, and many others who cared for me. I am also grateful to Hamish, Jacksen, Long, Marta, Param, Tuva, and Juno for sharing this Summer Programme together. See you again!

Hello everyone! I am Param Joshi, a physics master’s student from the National Institute of Technology Rourkela, India. Being selected for the ASTRON/JIVE summer programme 2025 was like a dream come true. In short, this was the most memorable and exciting summer for me till date, and I have already started to miss the place.

I worked with Sanne Bloot, David Konijn and Joe Callingham on studying the radio emissions of M dwarf stars. For this project, I targeted a particular M dwarf star V374 Peg, as it is behaving strangely in its radio emissions and we cannot fully understand the emission mechanism involved with these emissions. I used the VLA archival datasets to analyse the star’s emissions, and we did detect atleast 3 confirmed radio bursts. I performed reduction, calibration and imaging the data using CASA, and subsequent python scripts for radio lightcurves which shows the bursts from the star. Note that we detect the bursts in only stokes I, but not stokes V, which shows the peculiar behaviour of the emissions as it is not usual to see circularly unpolarized bursts from an M dwarf as they mostly produce ECMI emissions which are highly circularly polarised. Our interpretation of what might be going on is that, as per a study on massive stars, there can be frequency dependence of the detection of circular polarisation fraction from radio emissions due to perfect alignment of the Left and the Right circularly polarised bursts (originating from the dipoles of the star’s magnetic field independently at both locations) at higher frequency which looks like having a total circularly unpolarised burst. There’s definitely a need for further diving into the properties and analysis of the radio emissions to understand the theory properly.

Apart from the project and work, I also got to roam around various cities nearby in the Netherlands as well as France, Belgium and Germany, along with lots of amazing trips with all the summer students, organised by the program coordinators such as a trip to the European Space Agency, the Westerbork and LOFAR telescope sites, nearby Planetarium and beaches along with the Wadlopen(walking in the sea on a low tide), all memorable and exciting in itself. Overall, it was a lot of fun and learning in the summer and I would like to thank my supervisors and the program coordinators for giving me such a wonderful opportunity! I would highly recommend anyone interested in radio astronomy to apply for this program to get the best opportunity for summer research. I am looking forward to visiting ASTRON again in the future:)

Hi! My name is Jacksen, I’m from Colombia. I’m a first-year Master’s student in scientific computing at Memorial University of Newfoundland, Canada. This summer I had the opportunity to participate in the ASTRON internship, and it was an incredible experience! For me, it was the first time working directly in radio astronomy, and I found myself fascinated by it!

I worked on implementing fringe-fitting calibration for LOFAR long baselines under the supervision of Tammo and Mattia. In Very Long Baseline Interferometry (VLBI) such as LOFAR with international stations, the phase of visibilities changes rapidly, making it difficult to capture variations in both frequency and time. Fringe fitting corrects these phase residuals by approximating the expected rate of change, which allows visibilities to be coherently combined over longer intervals and improves the signal-to-noise ratio. This technique is widely used in VLBI, in software like CASA and AIPS, but is not yet implemented in the LOFAR software framework (e.g., DP3). During the internship, we developed a stand-alone fringe-fitting pipeline (Python/C++) and tested it on EVN and LOFAR data from point-like sources. Our fringe fitting code improved the data quality, increasing the source’s flux by over an order of magnitude relative to the background and transformed initially blurry structures into well-defined point sources.

Throughout the summer, I also had the chance to travel around the Netherlands. And ofc! I had the privilege of making great friends, with whom I shared many fun moments: group dinners, movie nights, and stargazing. I’ll miss those days.

For all of this, I’m very grateful to the ASTRON/JIVE team, particularly to my supervisors for their time, patience, and everything I learned from them. And to all the friends I made along the way, you made this summer unforgettable!

Hi, my name is Marta, and I’m a master’s student at Nicolaus Copernicus University in Toruń, Poland. During the summer, I worked with Xiaoxi Song, Aditya Parthasarathy and Joeri van Leeuwen on the mode-changing pulsar J0904-4246, whose emission pattern switches between two distinct modes.

The data I analysed were collected over five years using the highly sensitive MeerKAT telescope as part of the Thousand-Pulsar-Array (TPA) programme. From the ∼13,000 single pulses, each pulse was classified as belonging to either the Weak or Bright mode based on its intensity profile. This classification allowed us to identify differences between the two modes regarding intensity, pulse shape, and polarimetric properties.

During the project, I learned and developed new skills, including working with tools such as PSRSALSA. My supervisors were very supportive, and everyone at ASTRON/JIVE was friendly. Besides the project, there were many extra activities, such as lectures and trips to the LOFAR core, the Westerbork radiotelescope, the Eisinga Planetarium, and wadlopen. It was a great experience, and I would recommend it to everyone.