Nicholas Rattenbury

Dr Nicholas Rattenbury is a Senior Lecturer in the Department of Physics, Faculty of Science, The University of Auckland. He completed his PhD in Physics at The University of Auckland, followed by post-doctoral research at Jodrell Bank Observatory at the University of Manchester.

Dr Rattenbury’s research focuses on astronomy and astrophysics, space systems research, and computational physics. Nick is particularly interested in refining the microlensing technique further to discover more complicated planetary systems, and in the development and use of nanosatellites to develop and test innovative satellite subsystems. He is part of a team of University researchers working towards fostering the New Zealand space industry, and he is active in the Auckland Programme for Space Systems (APSS). His team are members of the Large Synoptic Survey Telescope (LSST), a survey telescope that is currently under construction and will observe a large fraction of the sky frequently and down to faint magnitudes. Further interests include creating algorithms that can analyse observed microlensing data without any human intervention (eg. investigating how graphical processing units (GPUs) may be used to perform the intense numerical calculations necessary for modelling planetary microlensing events) and using data collected from the microlensing databases to improve our understanding of our solar system. He is also leading the design and construction of a satellite ground tracking station to monitor satellite assets.

Nick’s Research

We report the discovery of a planet – OGLE-2014-BLG-0676Lb– via gravitational microlensing. Observations for the lensing event were made by the following groups: Microlensing Observations in Astrophysics; Optical Gravitational Lensing Experiment; Wise Observatory; RoboNET/Las Cumbres Observatory Global Telescope; Microlensing Network for the Detection of Small Terrestrial Exoplanets; and μ-FUN. All analyses of the light-curve data favour a lens system comprising a planetary mass orbiting a host star. The most-favoured binary lens model has a mass ratio between the two lens masses of (4.78 ± 0.13) × 10−3. Subject to some important assumptions, a Bayesian probability density analysis suggests the lens system comprises a 3.09+1.02−1.12 MJ planet orbiting a 0.62+0.20−0.22 M⊙ host star at a deprojected orbital separation of 4.40+2.16−1.46 au. The distance to the lens system is 2.22+0.96−0.83 kpc. Planet OGLE-2014-BLG-0676Lb provides additional data to the growing number of cool planets discovered using gravitational microlensing against which planetary formation theories may be tested. Most of the light in the baseline of this event is expected to come from the lens and thus high-resolution imaging observations could confirm our planetary model interpretation.

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K2 Campaign 9 (K2C9) offers the first chance to measure parallaxes and masses of members of the large population of free-floating planets (FFPs) that has previously been inferred from measurements of the rate of short-timescale microlensing events. Using detailed simulations of the nominal campaign (ignoring the loss of events due to Kepler's emergency mode) and ground-based microlensing surveys, we predict the number of events that can be detected if there is a population of 1 ${M}_{mathrm{Jupiter}}$ FFPs matching current observational constraints. Using a Fisher matrix analysis, we also estimate the number of detections for which it will be possible to measure the microlensing parallax, angular Einstein radius, and FFP mass. We predict that between 1.4 and 7.9 events will be detected in the K2 data, depending on the noise floor that can be reached, but with the optimistic scenario being more likely. For nearly all of these, it will be possible to either measure the parallax or constrain it to be probabilistically consistent with only planetary-mass lenses. We expect that for between 0.42 and 0.98 events it will be possible to gain a complete solution and measure the FFP mass. For the emergency-mode truncated campaign, these numbers are reduced by 20 percent. We argue that when combined with prompt high-resolution imaging of a larger sample of short-timescale events, K2C9 will conclusively determine if the putative FFP population is indeed both planetary and free-floating.

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