Publications, Grants, & Awards

Peer-Reviewed Publications

3) Silicate grain growth due to ion trapping in oxygen-rich supernova remnants like Cassiopeia A

Authors: Florian Kirchschlager, M. J. Barlow, Franziska D. Schmidt
Journal: ApJ (2020, accepted)
DOI: 1908.10875
Links: arXiv | ADS | Journal

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Core-collapse supernovae can condense large masses of dust post-explosion. However, sputtering and grain-grain collisions during the subsequent passage of the dust through the reverse shock can potentially destroy a significant fraction of the newly formed dust before it can reach the interstellar medium. Here we show that in oxygen-rich supernova remnants like Cassiopeia A the penetration and trapping within silicate grains of the same impinging ions of oxygen, silicon and magnesium that are responsible for grain surface sputtering can significantly reduce the net loss of grain material. We model conditions representative of dusty clumps (density contrast χ = 100) passing through the reverse shock in the oxygen-rich Cassiopeia A remnant and find that, compared to cases where the effect is neglected, as well as facilitating the formation of grains larger than those that had originally condensed, ion trapping increases the surviving masses of silicate dust by factors of up to two to four, depending on initial grain radii. For higher density contrasts (χ ≥ 180), we find that the effect of gas accretion on the surface of dust grains surpasses ion trapping, and the survival rate increases to ~55% of the initial dust mass for χ = 256.

2) Dust survival rates in clumps passing through the Cas A reverse shock I: results for a range of clump densities

Authors: Florian Kirchschlager, Franziska D. Schmidt, M. J. Barlow, Erica L. Fogerty, Antonia Bevan, Felix D. Priestley
Journal: MNRAS (2019)
DOI: 10.1093/mnras/stz2399
Links: arXiv | ADS | Journal

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The reverse shock in the ejecta of core-collapse supernovae is potentially able to destroy newly formed dust material. In order to determine dust survival rates, we have performed a set of hydrodynamic simulations using the grid-based code ASTROBEAR in order to model a shock wave interacting with clumpy supernova ejecta. Dust motions and destruction rates were computed using our newly developed external, post-processing code PAPERBOATS, which includes gas drag, grain charging, sputtering, and grain–grain collisions. We have determined dust destruction rates for the oxygen-rich supernova remnant Cassiopeia A as a function of initial grain sizes and clump gas density. We found that up to 30 % of the carbon dust mass is able to survive the passage of the reverse shock if the initial grain size distribution is narrow with radii around ∼10–50 nm for high gas densities, or with radii around ~ 0.5 – 1.5 μm for low and medium gas densities. Silicate grains with initial radii around 10–30 nm show survival rates of up to 40 % for medium- and high-density contrasts, while silicate material with micron-sized distributions is mostly destroyed. For both materials, the surviving dust mass is rearranged into a new size distribution that can be approximated by two components: a power-law distribution of small grains and a lognormal distribution of grains having the same size range as the initial distribution. Our results show that grain–grain collisions and sputtering are synergistic and that grain–grain collisions can play a crucial role in determining the surviving dust budget in supernova remnants.

1) Dynamical friction for supersonic motion in a homogeneous gaseous medium

Authors: Daniel Thun, Rolf Kuiper, Franziska Schmidt, Wilhelm Kley
Journal: A&A 589, A10 (2016)
DOI: 10.1051/0004-6361/201527629
Links: arXiv | ADS | Journal

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The supersonic motion of gravitating objects through a gaseous medium constitutes a classical problem in theoretical astrophysics. Its application covers a broad range of objects and scales from planets up to galaxies. Especially the dynamical friction, caused by the forming wake behind the object, plays an important role for the dynamics of the system. To calculate the dynamical friction, standard formulae, based on linear theory are often used. It is our goal to check the general validity of these formulae and provide suitable expressions for the dynamical friction acting on the moving object, based on the basic physical parameters of the problem. We perform sequences of high resolution numerical studies of rigid bodies moving supersonically through a homogeneous medium, and calculate the total drag acting on the object, which is the sum of gravitational and hydro drag. We study cases without gravity with purely hydrodynamical drag, as well as gravitating objects. From the final equilibrium state of the simulations, we compute for gravitating objects the dynamical friction by direct numerical integration of the gravitational pull acting on the embedded object. The numerical experiments confirm the known scaling laws for the dependence of the dynamical friction on the basic physical parameters as derived in earlier semi-analytical studies. As a new important result we find that the shock’s stand-off distance is revealed as the minimum spatial interaction scale of dynamical friction. Below this radius, the gas settles into a hydrostatic state, which causes no net gravitational pull onto the moving body. Finally, we derive an analytic estimate for the stand-off distance that can be used to calculate the dynamical friction force.

Manuscripts in Preparation

1) Hydrodynamics Simulations of Core-Collapse Suüernova Remnants: Dust Destruction by the Reverse Shock

Authors: Franziska D. Schmidt et. al

Theses

Hydrodynamics Simulations of Dust Destruction In Supernova Remnants

Authors: Franziska D. Schmidt
Type: PhD Thesis
Date: IN PROGRESS!

Dynamical Friction on Supersonic Gravitating and Non-Gravitating Spheres in a Gaseous Medium

Authors: Franziska D. Schmidt
Type: MSc Thesis
Date: February 2016

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An object travelling through a gaseous medium experiences drag forces pointing in the opposite direction to the object’s trajectory. These drag forces include the hydrodynamic drag force, due to momentum exchange, and the dynamical drag force, due to gravitational interactions between the perturber and an overdense wake of material forming behind it. While the hydrodynamic drag is well understood, the principle of dynamical or gravitational drag still poses many open problems. One of which is the ongoing search for an equation to calculate the dynamical drag force analytically.
In this thesis, building upon the results of previous studies, we will examine the supersonic movement of non-gravitating and gravitating spheres through gaseous media for varying adiabatic indices and varying Mach numbers. Our analyses include, but are not limited to, examinations of the resulting density profiles, shock distances, and individual forces acting on the system.
The obtained results indicate a clear dependence of the standoff distance on the respective Mach numbers and adiabatic indices. This enables us to obtain an analytical approximation of the standoff distance as a function of either the adiabatic index or the Mach number. Furthermore, we find a significant drop in the density profile right behind the object. This reveals that the predominant share of the dynamical drag is caused by gravitational interactions between the sphere and the mass situated within the angle segments between Θ = 100° and Θ = 140°. The spherical object itself moves along Θ = 0°.

Simulation of Bouncing Mechanics on Asteroids with Smooth Particle Hydrodynamics

Authors: Franziska D. Schmidt
Type: BSc Thesis
Date: Oktober 2014

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In late 2014 the Japan Aerospace Exploration Agency (JAXA) is set to launch the unmanned spacecraft Hayabusa 2, which will arrive at its destination, the asteroid 1999 JU3, in 2018. Hayabusa 2 will then release a lander, developed by the German Space Agency (DLR), onto the asteroid surface. The subject of this bachelor’s thesis is the study of the bouncing behaviour of said lander colliding with the regolith covered asteroid surface at a velocity of |v| ≈ 0.1 m/s. This will be accomplished by using a smooth particle hydrodynamics (SPH) code. Several numerical test runs were performed, confirming the integrity of the code and revealing the unlikeness of the lander significantly distorting the asteroid surface at low velocities. Subsequently simulations with varying numbers of SPH particles, asteroid surface densities, lander rotation angles and angles of incident were executed and evaluated with respect to the coefficient of restitution.

Grants & Awards

2020

Grant: HPC Time Allocation (12th DiRAC CALL)

PI: Prof M. J. Barlow (UCL)
Project: ACSP217
Description: 4.5M CPU hours on Data-Intensive Cambridge for ERC project SNDUST.

2019

Grant: HPC Time Allocation (11th DiRAC CALL)

PI: Prof M. J. Barlow (UCL)
Project: ACSP190
Description: 280k CPU hours on Data-Intensive Cambridge for ERC project SNDUST.

Award: Poster Prize (DiRAC Day 2019)

Description: I won the poster prize during the DiRAC Day Conference 2019. See my Meetings page for the poster!