Dr John D. Ilee

About

I am an STFC Ernest Rutherford Fellow and Associate Professor in Astrophysics at the School of Physics & Astronomy, University of Leeds. My research is focused on understanding the properties and evolution of disks around young stars. I use a variety of observational and theoretical techniques to explore how dust grains and molecular gas behave in these disks, with the ultimate goal of improving our understanding of both star and planet formation. Before my current role, I held postdoctoral research positions at the Institute of Astronomy at the University of Cambridge and the University of St Andrews, Scotland.

Team Members

• Isaac Radley - PhD student
• Zoe Parker - PhD student
• Anastasia Topalidou - PhD student
• Katelyn Jordaan - MSc student, University of Pretoria, South Africa
• Dr Linus Labik - Simons Foundation PIVOT Fellow, KNUST, Ghana

Research

My research is focused on understanding the physical and chemical properties of disks around young stars. I study these disks across the stellar mass range – from those forming planets around Sun-like stars, all the way up to the precursors of the most massive stars in the Universe. Below are some brief highlights, but for all the details please see my NASA ADS publication list.

Observing Protoplanetary Disks with the SKA

The SKA-Mid array, currently being constructed in the Karoo area of South Africa, will have unprecedented sensitivity and high spatial resolution at centimeter wavelengths. These capabilities will enable detailed imaging of dust continuum emission as well as the detection complex molecules in protoplanetary disks. We have been working to understand exactly how SKA-Mid will provide crucial constraints on the processes that govern planet formation. This has involved a combination of theoretical simulations and observational campaigns. I performed the first realistic simulations of how SKA-Mid would observe 'pebbles' in a protoplanetary disk (see above) demonstrating that we can expect high fidelity images of disks at 10's of GHz for the first time. I also showed that a possible extension to the SKA-Mid receivers up to 25 GHz would significantly improve it's ability to detect and characterise large, complex molecules.

My group is continuing to set the stage for SKA-Mid observations of young stars. PhD student Isaac Radley is using the Karl G. Jansky Very Large Array (VLA) to characterise the Ophiuchus star forming region at the highest spatial resolution possible before SKA-Mid comes online. Isaac is combining these data with observations from the James Webb Space Telescope (JWST) and the Atacama Large Millimetre/submillimetre Array (ALMA) for a full multi-wavelength characterisation of the young stellar objects across this region. PhD student Anastasia Topalidou will be using the combined JWST-ALMA-VLA datasets to produce comprehensive models of each of the star/disk systems to allow us to predict what SKA-Mid will (and won't) be able to observe.

Finding the youngest exoplanets in disks

The exoALMA Large Program was a survey with ALMA that targeted 15 protoplanetary disks to map gas and dust distributions with high spatial and spectral resolution. It used molecular line and continuum observations to characterize disk structure and kinematics and examine processes that cause disk substructures. The datasets were large and complex, requiring development of careful calibration and imaging techniques, which set a new standard for the analysis of molecular line observations of protoplanetary disks.

Using these images were able to perform a systematic survey to identify perturbations consistent with embedded planets across several disks for the first time. These perturbations manifest in a characteristic 'lightning bolt' shape in the channel maps of molecular lines, which we found in six disks: AA Tau, SY Cha, J1842, J1615, LkCa 15, and HD 143006. Comparison with hydrodynamical and radiative transfer simulations suggested the planets were located at large radii (80-130 au) and had masses between 1-5 times the mass of Jupiter.

Characterising the chemical complexity of disks

The Molecules with ALMA at Planet-forming Scales (MAPS) Large Program studied 50 molecular lines in five protoplanetary disks to characterize the radial and vertical chemical structures that influence planet formation and disk evolution. We specifically looked at the location and characteristics of several complex organic molecules, specifically HC₃N, CH₃CN, and c-C₃H₂. We found the molecules in most of the disks, with varied patterns such as central peaks and rings, and showed that they are concentrated close to the disk midplane and in regions where planets and comets are expected to form. The relative abundances of these organics are similar to those seen in comets in our own Solar System, suggesting that the raw chemical ingredients for life-relevant compounds are common in planet-forming environments.

I've also studied our nearest protoplanetary disk, TW Hya, using some of the most sensitive ALMA observations ever obtained. I found evidence for a faint outer disk of large dust grains that had been predicted by theoretical models of disk evolution. Using the same dataset, I also studied the distribution and properties of another key complex molecule methanol (CH₃OH). The methanol emission is concentrated close to the disk regions with millimetre-sized dust grains, and comparisons with chemical models indicate that processes such as photodesorption and grain surface chemistry help release methanol from ices into the gas phase, though existing models cannot fully reproduce the observed abundance and radial profile. These results imply that the interplay between ice chemistry and dust evolution plays a key role in shaping the availability of complex organic molecules in planet-forming regions.

Contact

If you'd like to get in touch, please send me an email at:

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