Oscillatory migration of accreting protoplanets driven by a 3D distortion of the gas flow

Context. The dynamics of a low-mass protoplanet accreting solids is influenced by the heating torque, which was found to suppress inward migration in protoplanetary disks with constant opacities. Aims. We investigate the differences of the heating torque between disks with constant and temperature-dependent opacities. Methods. Interactions of a super-Earth-sized protoplanet with the gas disk are explored using 3D radiation hydrodynamic simulations. Results. Accretion heating of the protoplanet creates a hot underdense region in the surrounding gas, leading to misalignment of the local density and pressure gradients. As a result, the 3D gas flow is perturbed and some of the streamlines form a retrograde spiral rising above the protoplanet. In the constant-opacity disk, the perturbed flow reaches a steady state and the underdense gas responsible for the heating torque remains distributed in accordance with previous studies. If the opacity is non-uniform, however, the differences in the disk structure can lead to more vigorous streamline distortion and eventually to a flow instability. The underdense gas develops a one-sided asymmetry which circulates around the protoplanet in a retrograde fashion. The heating torque thus strongly oscillates in time and does not on average counteract inward migration. Conclusions. The torque variations make the radial drift of the protoplanet oscillatory, consisting of short intervals of alternating rapid inward and outward migration. We speculate that transitions between the positive and oscillatory heating torque may occur in specific disk regions susceptible to vertical convection, resulting in the convergent migration of multiple planetary embryos.Comment: Accepted for publication in A&A, 19 pages, 18 figure

Accreting luminous low-mass planets escape from migration traps at pressure bumps

We investigate the migration of Mars- to super-Earth-sized planets in the vicinity of a pressure bump in a 3D radiative protoplanetary disc while accounting for the effect of accretion heat release. Pressure bumps have often been assumed to act as efficient migration traps, but we show that the situation changes when the thermal forces are taken into account. Our simulations reveal that for planetary masses $\lesssim$$2\,M_{\oplus}$, once their luminosity exceeds the critical value predicted by linear theory, thermal driving causes their orbits to become eccentric, quenching the positive corotation torque responsible for the migration trap. As a result, planets continue migrating inwards past the pressure bump. Additionally, we find that planets that remain circular and evolve in the super-Keplerian region of the bump exhibit a reversed asymmetry of their thermal lobes, with the heating torque having an opposite (negative) sign compared to the standard circular case, thus leading to inward migration as well. We also demonstrate that the super-critical luminosities of planets in question can be reached through the accretion of pebbles accumulating in the bump. Our findings have implications for planet formation scenarios that rely on the existence of migration traps at pressure bumps, as the bumps may repeatedly spawn inward-migrating low-mass embryos rather than harbouring newborn planets until they become massive.Comment: Accepted in MNRA

Migration of gap-opening planets in 3D stellar-irradiated accretion disks

Context. The origin of giant planets at moderate separations $\simeq$$1$$-$$10$ au is still not fully understood because numerical studies of Type II migration in protoplanetary disks often predict a decay of the semi-major axis that is too fast. According to recent 2D simulations, inward migration of a gap-opening planet can be slowed down or even reversed if the outer gap edge becomes heated by irradiation from the central star, and puffed up. Aims. Here we study how stellar irradiation reduces the disk-driven torque and affects migration in more realistic 3D disks. Methods. Using 3D hydrodynamic simulations with radiation transfer, we investigated the static torque acting on a single gap-opening planet embedded in a passively heated accretion disk. Results. Our simulations confirm that a temperature inversion is established at the irradiated outer gap edge and the local increase of the scale height reduces the magnitude of the negative outer Lindblad torque. However, the temperature excess is smaller than assumed in 2D simulations and the torque reduction only becomes prominent for specific parameters. For the viscosity $\alpha=10^{-3}$, the total torque is reduced for planetary masses ranging from $0.1$ to $0.7$ Jupiter mass, with the strongest reduction being by a factor of $-0.17$ (implying outward migration) for a Saturn-mass planet. For a Jupiter-mass planet, the torque reduction becomes stronger with increasing $\alpha$ (the torque is halved when $\alpha=5\times10^{-3}$). Conclusions. We conclude that planets that open moderately wide and deep gaps are subject to the largest torque modifications and their Type II migration can be stalled due to gap edge illumination. We then argue that the torque reduction can help to stabilize the orbits of giant planets forming at $\gtrsim$$1$ au.Comment: Accepted for publication in A&A, 17 pages, 15 figure

HALT tests

Cieľom tejto bakalárskej práce je vypracovanie rešerše o HALT testoch. Prvá časť práce sa bola zameraná na objasnenie problematiky HALT testov a zariadení potrebných na ich prevedenie. Druhú časť práce som venoval návrhu testovacej procedúry s prihliadnutím na limitujúce možnosti zariadení v Českej republike.The aim of the bachelor thesis is to develop the retrieval about HALT tests. The first part was aimed at making clear the issues of HALT tests and devices which are required for their realization. In the second part of this work the design of the test procedure was taken into account with consideration of limited options in test devices in the Czech Republic.

Stress-strain analysis of real contact surfaces

V súčasnosti má podstatný vplyv na životnosť náhrady bedrového kĺbu opotrebenie artikulujúcich povrchov v kontakte. Je preto žiaduce určiť vplyv určitých aspektov na opotrebenie náhrady. Z toho dôvodu sa diplomová práca zaoberá vplyvom nerovností reálnych povrchov náhrad bedrového kĺbu na jeho opotrebenie. Cieľom je vytvorenie výpočtových modelov, ktoré by zodpovedali reálnemu povrchu nasnímaných náhrad, vykonanie deformačne- napäťovej analýzy a porovnanie s výsledkami bez prítomnosti nerovností.Currently, the wear of the articulating surfaces in contact have a significant influence on the life of hip joint replacement. It is therefore desirable to determine the influence of certain aspects on the wear of replacement. For this reason, master´s thesis deals with the influence of asperities of real surfaces of the hip joint replacement on its wear. The aim is to create computational models that would correspond to the real surface of the scanned prosthesis, performing strain- stress analysis and comparison with the results without the presence of asperities.

On wave interference in planet migration: dead zone torques modified by active zone forcing

We investigate planetary migration in the dead zone of a protoplanetary disk where there are a set of spiral waves propagating inward due to the turbulence in the active zone and the Rossby wave instability (RWI), which occurs at the transition between the dead and active zones. We perform global 3D unstratified magnetohydrodynamical (MHD) simulations of a gaseous disk with the FARGO3D code, using weak gradients in the static resistivity profiles that trigger the formation of a vortex at the outer edge of the dead zone. We find that once the Rossby vortex develops, spiral waves in the dead zone emerge and interact with embedded migrating planets by wave interference, which notably changes their migration. The inward migration becomes faster depending on the mass of the planet, due mostly to the constructive (destructive) interference between the outer (inner) spiral arm of the planet and, the destruction of the dynamics of the horseshoe region by means of the set of background spiral waves propagating inward. The constructive wave interference produces a more negative Lindblad differential torque which inevitably leads to an inward migration. Lastly, for massive planets embedded in the dead zone, we find that the spiral waves can create an asymmetric wider and depeer gap than in the case of $\alpha$-disks, and can prevent the formation of vortices at the outer edge of the gap. The latter could generate a faster or slower migration compared to the standard type-II migration.Comment: 18 pages, 14 figures, accepted for publication in Ap

Physical and dynamical characterization of the Euphrosyne asteroid Family

The Euphrosyne asteroid family occupies a unique zone in orbital element space around 3.15 au and may be an important source of the low-albedo near-Earth objects. The parent body of this family may have been one of the planetesimals that delivered water and organic materials onto the growing terrestrial planets. We aim to characterize the compositional properties as well as the dynamical properties of the family. We performed a systematic study to characterize the physical properties of the Euphrosyne family members via low-resolution spectroscopy using the IRTF telescope. In addition, we performed smoothed-particle hydrodynamics (SPH) simulations and N-body simulations to investigate the collisional origin, determine a realistic velocity field, study the orbital evolution, and constrain the age of the Euphrosyne family. Our spectroscopy survey shows that the family members exhibit a tight taxonomic distribution, suggesting a homogeneous composition of the parent body. Our SPH simulations are consistent with the Euphrosyne family having formed via a reaccumulation process instead of a cratering event. Finally, our N-body simulations indicate that the age of the family is 280 Myr +180/-80 Myr, which is younger than a previous estimate.Comment: 10 pages, 13 figures, accepted to be published in A&