In May, researcher and doctoral student Karina Šķirmante from the Ventspils International Radio Astronomy Centre (VIRAC) led a scientific seminar “Experience in ALMA Data Processing and Its Application in Comet Research”, sharing practical experience on the methodology of processing ALMA (Atacama Large Millimeter/submillimeter Array) data and the use of these data in comet research. The seminar compiled knowledge and practical skills that the researcher acquired by participating in training organised by the European ALMA School. These trainings were organised by the ALMA Regional Centre in Europe “Allegro” together with Leiden Observatory, where advanced methods of ALMA data processing and analysis were studied in depth.

At the beginning of the seminar, the ALMA interferometer was characterized, which operates in the millimetre and submillimetre wavelength range. The antenna arrays that make up ALMA were examined, including the 12‑metre main array, the 7‑metre compact array, and the total power antennas. The researcher informed the audience about ALMA’s sensitivity and angular resolution, which make it possible to study cold molecular gas, dust, star‑forming regions, galaxies, and objects in the Solar System, including comets.

The seminar then explained the methodology of ALMA data processing. It was noted that ALMA does not directly create an image of the sky, but measures visibility data, or samples in the Fourier plane. Since these data are incomplete, as it is not possible to cover the entire visibility plane, image reconstruction is an inverse problem. The seminar outlined the methodology of image reconstruction and its main parameters, discussing data gridding, weighting, and iterative image reconstruction. Special attention was given to the CLEAN algorithm, which is a computational algorithm used in radio astronomy to perform deconvolution of images obtained from radio interferometric observations.

The CASA software is the main tool for ALMA data reduction; therefore, part of the seminar was devoted to reviewing this software, its input parameters, and the resulting images. Using CASA tools, it is possible to inspect MeasurementSet data, select spectral windows, determine molecular line frequencies, and create images or spectral cubes using the tclean function. The seminar also covered various tclean outputs — the primary beam, mask, model, residual image, cleaned image, and primary beam‑corrected image. In addition, the CARTA tool was presented, which is used for the visualisation of FITS data, extraction of spectra, and creation of moment maps.

The second part of the seminar included an overview of the researcher’s obtained results in comet activity modelling and the application of ALMA data for model validation. Comets are remnants from the time of the formation of the Solar System, containing ice, dust, rocks, and various volatile molecules. As a comet approaches the Sun, its nucleus heats up, the ice sublimates, and a coma and tail are formed. Radioastronomical observations, including ALMA observations, are important for determining the molecular composition of comets, for example, identifying molecules such as HCN, HNC, H₂CO, CH₃OH, and others. The thermal model of comet 2P/Encke, the identification of the spatial distribution of the HCN molecule in the cometary coma, and the validation of the model using ALMA archive data were examined in detail. ALMA data were particularly valuable in the researcher’s work, as they made it possible not only to determine the presence of molecules but also to map their spatial distribution within the comet’s coma.

Overall, the seminar provided a practical insight into how ALMA observation data are transformed into scientifically usable images and data products. The seminar was highly valuable, as it ensured the transfer of knowledge and experience by drawing on the expertise of one of the world’s leading radio astronomy observatories in the planning of radio astronomical observations, data analysis and processing, thereby strengthening VSRC’s competence in the use of ALMA data in research and contributing to the long-term development of Latvia’s radio astronomy sector and its integration into the international research environment.

The seminar was organised within the framework of the European Regional Development Fund project No. 1.1.1.5/3/25/I/012 “International Cooperation and Innovation of Ventspils University of Applied Sciences for the Development of Latvia’s Smart Specialisation”.