1.2k citations · 2.7k across the 21 of their papers we have counts for
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Time evolution of gaps in stellar streams in axisymmetric Stäckel potentials
Helmer H. Koppelman, Amina Helmi
When a subhalo interacts with a cold stellar stream it perturbs its otherwise nearly smooth distribution of stars, and this leads to the creation of a gap. The properties of such g…
Frequencies, chaos and resonances: a study of orbital parameters of nearby thick disc and halo stars
Helmer H. Koppelman, Jorrit H. J. Hagen, Amina Helmi
We study the distribution of nearby thick disc and halo stars in subspaces defined by their characteristic orbital parameters. Our aim is to establish the origin of the structure r…
Galactic potential constraints from clustering in action space of combined stellar stream data
Stella Reino, Elena M. Rossi, Robyn E. Sanderson +4
Stream stars removed by tides from their progenitor satellite galaxy or globular cluster act as a group of test particles on neighboring orbits, probing the gravitational field of…
A massive mess: When a large dwarf and a Milky Way-like galaxy merge
Helmer H. Koppelman, Roy O. Y. Bos, Amina Helmi
Circa 10 billion years ago the Milky Way merged with a massive satellite, Gaia-Enceladus. To gain insight into the properties of its debris we analyse in detail the suite of simula…
Determination of the escape velocity of the Milky Way using a proper motion selected halo sample
Helmer H. Koppelman, Amina Helmi
The {\it Gaia} mission has provided the largest catalogue ever of sources with tangential velocity information. However, using this catalogue for dynamical studies is difficult bec…
The Reduced Proper Motion selected halo: methods and description of the catalogue
Helmer H. Koppelman, Amina Helmi
The Gaia mission has provided the largest ever astrometric chart of the Milky Way. Using it to map the Galactic halo is helpful for disentangling its merger history. The identifica…