Related papers: A possible dividing line between massive planets a…
Recent discoveries of extrasolar planets at small orbital radii, or with significant eccentricities, indicate that interactions between massive planets and the disks of gas and dust from which they formed are vital for determining the final…
The dominant formation mechanism of brown dwarfs and planetary mass objects in star-forming regions is presently uncertain. Do they form like stars, via the collapse and fragmentation of cores in Giant Molecular clouds, or do they form like…
Doppler velocity measurements from the Anglo-Australian Planet Search reveal planetary mass companions to HD23127, HD159868, and a possible second planetary companion to HD154857. These stars are all G dwarfs. The companions are all in…
Self-gravitating protostellar discs are unstable to fragmentation if the gas can cool on a time scale that is short compared to the orbital period. We use a combination of hydrodynamic simulations and N-body orbit integrations to study the…
Substellar objects, like planets and brown dwarfs orbiting stars, are by-products of the star formation process. The evolution of their host stars may have an enourmous impact on these small companions. Vice versa a planet might also…
We report the discovery of a giant planet in the OGLE-2017-BLG-1522 microlensing event. The planetary perturbations were clearly identified by high-cadence survey experiments despite the relatively short event timescale of $t_{\rm E} \sim…
Massive early-type stars vary; low-mass late-type brown dwarfs vary, too. I will make a short, but illustrative, summary of my previous studies on stellar and sub-stellar photometric variability (including the discovery of the most variable…
In near-infrared NaCo observations of the young brown dwarf 2MASS J0041353-562112, we discovered a companion a little less than a magnitude fainter than the primary. The binary candidate has a separation of 143 mas, the spectral types are…
Neutron stars and stellar-mass black holes are the remnants of massive stars, which ended their lives in supernova explosions. These exotic objects can only be studied in relatively rare cases. If they are interacting with close companions…
We have measured high-precision parallaxes for a large sample of candidate young (~10-100 Myr) and intermediate-age (~100-600 Myr) ultracool dwarfs, with spectral types ranging from M8 to T2.5. These objects are compelling benchmarks for…
Brown dwarfs bridge the gap between stars and planets, providing valuable insight into both planetary and stellar formation mechanisms. Yet the census of transiting brown dwarf companions, in particular around M dwarf stars, remains…
Increasing numbers of sub-stellar companions are now being discovered via direct imaging. Orbital elements for some of these objects have been derived using star--companion astrometry, and several of these appear to have eccentricities…
Direct imaging searches have begun to detect planetary and brown dwarf companions and to place constraints on the presence of giant planets at large separations from their host star. This work helps to motivate such planet searches by…
Studying the earliest stages in the birth of stars is crucial for understanding how they form. Brown dwarfs with masses between that of stars and planets are not massive enough to maintain stable hydrogen-burning fusion reactions during…
The observational properties of brown dwarfs pose challenges to the theory of star formation. Because their mass is much smaller than the typical Jeans mass of interstellar clouds, brown dwarfs are most likely formed through secondary…
The "Disk Substructures at High Angular Resolution Project" (DSHARP) has revealed an abundance and ubiquity of rings and gaps over a large sample of young planet-forming disks, which are hypothesised to be induced by the presence of forming…
We have conducted an angular differential imaging survey with NIRC2 at Keck in search of close-in substellar companions to a sample of seven systems with confirmed planetary-mass companions (PMCs) on wide orbits (>50 AU). These…
Co-orbital planets have not yet been discovered, although they constitute a frequent by-product of planetary formation and evolution models. This lack may be due to observational biases, since the main detection methods are unable to spot…
The observational properties of brown dwarfs pose challenges to the theory of star formation. Because their mass is much smaller than the typical Jeans mass of interstellar clouds, brown dwarfs are most likely formed through secondary…
Brown dwarfs bridge the gap between the stellar and planetary mass regimes. Evolving from conditions very similar to the lowest-mass stars, the atmospheres of older brown dwarfs closely resemble those expected in close-in extrasolar giant…