Welcome to my homepage!

I am a postdoctoral astrophysicist at Charles University in Prague.
My primary interest is the theory of planet formation, hydrodynamics of protoplanetary disks
and planet-disk interactions. This website provides an overview of my current research as well as
previously published papers, meeting contributions and source codes available for the community.

The FARGO_THORIN hydrocode

FARGO_THORIN (or THORIN for short) stands for FARGO with Two-fluid HydrOdynamics, the Rebound integrator Interface and Non-isothermal gas physics. The program is an extension of the standard 2D FARGO code (Masset 2000). The code features are briefly described below, see also Chrenko et al. (2017) for a thorough description of the implemented physics.

!!! The download link has been temporarily disabled !!! I am preparing a new public release of the code which contains several bug fixes and an improved treatment of the update of the pebble velocity field. Please contact me by e-mail if you want to use THORIN before the new version is ready!

The code is publicly available under the terms of this license (see also the GNU General Public License ).
Latest version: Jul 6 2017; first public release (v 1.0)

Research

Highlights from my 2019 paper:

Left: 3D streamline topology near a non-luminous super-Earth-sized protoplanet. Right: the same for a luminous protoplanet. The blue surface indicates the extent of the Hill sphere. Arrows indicate the relative direction of the flow with respect to the protoplanet.

3D gas flow around cold and hot protoplanets

In Chrenko & Lambrechts (2019), we investigated migration of low-mass protoplanets in radiative disks. Our aim was to check how the heating torque (Benítez-Llambay et al. 2015) differs between disks with constant and non-uniform opacities. In the process, we realised that the 3D gas flow around accreting luminous ('hot') protoplanets is significantly different compared to non-luminous ('cold') protoplanets. As shown in the figure on the left, the topology of the horseshoe region profoundly changes and a vertical outflow is established when the protoplanet has a substantial luminosity. The depicted simulation was performed with a constant value of the disk opacity. The distortion of the flow arises because of baroclinic and convective perturbations.

Simulations in Chrenko & Lambrechts (2019) were conducted with Fargo3D (Benítez-Llambay & Masset 2016) into which we implemented the energy equations for gas and radiation.

Flow instability around a luminous protoplanet in a disk with temperature-dependent opacities. The colour scale shows the perturbed gas density, red curves are streamlines. The white circle represents the Hill sphere. See a movie!

Flow instability in disks with temperature-dependent opacities

In disks with temperature-dependent opacities, the gas flow around accreting protoplanets can develop an instability. It arises in disks where the vertical temperature gradient is close to a super-adiabatic stratification. In such a situation, the gas flow never reaches a steady state because of vigorous convective displacements. The figure on the left shows how the (perturbed) gas distribution evolves in the orbital plane of the protoplanet. The overplotted streamlines (shown in the corotating reference frame) are clearly connected to the gas redistribution. The instability has an important impact on the magnitude of the heating torque. The heating torque no longer boosts outward migration and moreover, migration of the protoplanet becomes oscillatory, consisting of alternating inward and outward excursions.

Highlights from my 2017 paper:

Left: Gas temperature in the vicinity of a super-Earth which is heated by pebble accretion and illuminates its surroundings (the circle represents the Hill sphere). The overheated gas forms a hot trail behind the embryo. Right: Evolution of four super-Earths migrating in the disk with accretion heating accounted for.

Evolution of protoplanets growing by pebble accretion

According to recent developments in the planet formation theory, protoplanets form by accretion of small solid particles, known as pebbles, which move through the gaseous media and are decelerated by the aerodynamic drag. Owing to the vigorous material deposition, protoplanets grow rapidly, they become heated and radiate the excessive energy into their surroundings. At the same time, protoplanets migrate due to gravitational interactions with the surrounding disk. I study the evolution of newborn planetary systems while taking into account all the aforementioned phenomena simultaneously, thus providing a realistic feedback between all the system components. Hydrodynamic global-scale simulations are necessary for this purpose.

Closeup of the surface density in an evolving protoplanetary disk consisting of the gas (left) and pebble component (right), interacting with embedded super-Earths.

Two-fluid hydrodynamic code with pebble accretion

I have developed an extension of the 2D FARGO hydrocode. The additional features:

  • Non-isothermal gas disk with the internal energy equation accounting for compressional heating, viscous friction, in-plane radiative diffusion, vertical radiation escape, stellar irradiation and accretion heating.
  • Pebble disk treated as an Eulerian pressureless and inviscid fluid, coupled with the gas disk through the Epstein drag term. Massive bodies accrete from the pebble component self-consistently.
  • Rebound package interface allowing for e.g. 3D high-order orbital integration with adaptive time-stepping (IAS15 integrator), collision search, etc.
  • Gravitational planet-disk interaction calculated by means of a vertically-averaged potential assuming a simple vertical distribution of gas (and pebbles) over the corresponding scale height.

For a detailed code description, see Chrenko et al. (2017).
You can get your own copy of the code on this website!

Publications

Papers in refereed journals

  • Chrenko & Lambrechts (2019) - Oscillatory migration of accreting protoplanets driven by a 3D distortion of the gas flow: ADS entry, publisher
  • Chrenko et al. (2018) - Binary planet formation by gas-assisted encounters of planetary embryos: ADS entry, publisher
  • Brož et al. (2018) - Dynamics of multiple protoplanets embedded in gas and pebble discs and its dependence on Σ and ν parameters: ADS entry, publisher
  • Chrenko et al. (2017) - Eccentricity growth and merging of planetary embryos heated by pebble accretion: ADS entry, publisher
  • Chrenko et al. (2015) - The origin of long-lived asteroids in the 2:1 mean-motion resonance with Jupiter: ADS entry, publisher

Dissertation thesis

  • Early phases of formation and evolution of planetary systems: download pdf

Meeting contributions

  • IAU GA XXX - Evolution of multiplanet systems in 2D and 3D radiative disks (poster): download pdf
  • AAS DPS 2017 - Evolution of migrating protoplanets heated by pebb accretion (talk): ADS entry
  • AAS DPS/EPSC 2016 - Building the giant planet cores by convergent migration of pebble-accreting embryos (poster): ADS entry, download pdf
  • AAS DPS 2015 - Planetesimals embedded in a gaseous disc vs mean-motion resonances (poster): ADS entry, download pdf
  • AAS DPS 2014 - The origin of the long-lived asteroids in the 2:1 mean-motion resonance with Jupiter (talk): ADS entry

Other