Time-domain astronomy group at Charles University, Prague
Our PhD students Mara, Marco and Chad and Master student Jan participated in 21st Heidelberg Summer School on Cosmic Multiplicity: Evolution and Fate of Binary Stars organized by IMPRS for Astronomy and Cosmic Physics at the University of Heidelberg.
We welcome two starting PhD students: Mara Čutura is joining us from Geneva University and Cheuk Nam Chong from Chinese University of Hong Kong.
This July, we had the honor to host two summer students. Krzysztof Król from University of Warsaw worked on 3D simulations of circumbinary decretion disks with Athena++. Jakub Hadač (our own recent Bachelor graduate) explored applications of automatic differentiation in Astrophysics with JAX.
Our group recently graduated two new Bachelor students. Jakub Hadač defended his thesis on Simulations of mass transfer in binary star systems with the effect of radiation pressure. Jakub will continue with Master studies in Astronomy at Heidelberg University. Šimon Brunovský also defended his thesis on Circumbinary disks around stellar mergers. Congratulations to both!
Our group participated at the annual meeting of the European Astronomical Society in Lausanne. Ondřej Pejcha gave a contributed talk and chaired one of the plenary sessions and Marco Laversveiler presented a poster.
The workshop was held in Cheb, Czech Republic, and I gave an invited talk on the Evolution of binary stars leading up to high-energy sources.
I spent the past week at IAUS406: Future landscape of astrophysical transients, where I gave a contributed talk on Luminous Red Novae, met many new people, and did not fall off the boat.
It was great to visit Cambridge for the first time, give a talk on common envelope evolution, and reconnect with old friends and meet new ones.
We invite applications for multiple ERC-funded PhD positions to perform computer simulations of binary stars. You can find more details and application process on a separate website. Deadline for applications is January 15 2026!
We have good reasons to think that Luminous Red Novae (LRNe) signal the merger of two stars. But what powers the light curves of the brightest extragalactic events? Using radiation transport module developed by Diego Calderón for moving-mesh code JET by Paul Duffell we performed 2D simulations of LRNe powered by shock interaction with a “disky” structure left behind by pre-merger processes. Compared to homologously expanding spheres, shock-powered events are a factor of ~10 brighter and can be about twice as long. Amazing to see how the shock feeds the energy to the rest of the ejecta for reprocessing, while remaining hidden inside. But the photosphere is not spherical and can dramatically change shape if the shock encounters a well-defined outer edge of the CSM, like what can be seen in the raytraced images in the movie below. Signs of this might be found in spectral line profiles and/or polarimetry.
Other issues considered: hydrogen+helium equation of state, tabulated opacites, low effective temperatures, dust formation, irradiation by the central merger remnant.
Accepted to ApJL, this work marks the end of my ERC StG that finished in the summer but I hope it is also just a beginning on the path of making LRNe useful probes of binary evolution!
https://arxiv.org/abs/2508.09257