Welcome! 

I am a PhD student in Time-domain astronomy group of Ondřej Pejcha at Charles University in Prague. I am particularly interested in theory of (binary) stars. Before working in the field of astronomy, I worked in the field of continuum mechanics under the supervision of Vít Průša.

If you wish to contact me, please use my email: jakub.cehula@mff.cuni.cz

RESEARCH

To see my publications, please visit my Google Scholar profile.

Theory of mass transfer in binary stars

Calculation of the mass transfer (MT) rate Mdot of a Roche lobe overflowing star is a fundamental task in binary star evolution theory. Most of the existing MT prescriptions are based on a common set of assumptions that combine optically-thick and optically-thin regimes with different flow geometries.

I developed a new model of MT based on the assumption that the Roche potential sets up a nozzle converging on the inner Lagrangian point and that the gas flows mostly along the axis connecting both stars, see https://arxiv.org/abs/2303.05526. In this paper, we derived a set of 1D hydrodynamic equations governing the gas flow. We obtained algebraic solution for the polytropic equation of state (EOS), which gives Mdot within a factor of 0.9 to 1.0 of existing optically-thick prescriptions and which reduces to the existing optically-thin prescription for isothermal gas. For a realistic EOS, we found that Mdot differs by up to a factor of 4 from existing models. We illustrated the effects of our new MT model on 30 Msun low-metallicity star undergoing intensive thermal time-scale MT and found that it is more likely to become unstable to L2 overflow and common-envelope evolution than for existing MT prescriptions. Our model provides a framework for including additional physics such as radiation or magnetic fields.

Origami-like structures made of light activated shape memory polymers

Light activated shape memory polymers (LASMPs) are smart materials with the ability of remembering a deformed state (temporary shape) due to exposure to UV light and returning to the permanent (original) shape by the exposure to UV light with a different wavelength. Regarding the shape of smart materials frequent inspiration is taken from the art of origami, the Japanese art of folding paper into various shapes. 

I developed a code for computer modelling of such origami-like structures made of LASMPs, see Cehula & Průša (2020, Int. J. Eng. Sci. 150, 103235). The code is a modification to the state-of-the-art code for simulations of elastic origami-like structures developed by Liu & Paulino (2018, Origami, 7, 1167-1182). The original code is called MERLIN2, my modification is called MERLIN2.LUX.

MISCELLANEOUS

May 2021

Feb 2021

Jan 2021

Aug 2020

Mar 2020

Oct 2019