Extrasolar Planets and Brown Dwarfs
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Unusual solar systems with massive debris disks
Mark Thompson, Dan Smith
Debris disks are dusty disks of material around main sequence stars, revealed by their far-infrared excess emission. Collisions between asteroids or Kuiper Belt Objects generate small dust particles which absorb starlight from their host stars and reradiate this in the far-IR. Usually the amounts of dust in typical solar systems are very low, on the order of a few Lunar masses or less, however this may be an observational limitation of current debris disk surveys which are tightly focused on solar system analogues. We pioneered a new technique to identify debris disks in far-IR galaxy surveys (Thompson, Smith et al 2010) which uncovered hints of a more massive and colder population of disks than previously known (with the prototypical candidate disk having roughly an Earth mass of dust). This PhD project is to study the sample of ~400 candidate disks that we have identified in the Herschel-ATLAS survey (Bourne et al 2016), using the GAIA DR2 release to determine the distance to these stars and the mass of the disks. You will also use GAIA data to extend the search from the Herschel-ATLAS survey to the entire Herschel legacy catalogue that covers about 10% of the sky. The results of this search will be used to select a sample of disks for high resolution observations with ALMA to reveal their morphology and possible origin.
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Nearby low-mass planets around Solar type stars
Hugh Jones, Fabo Feng
The search for rocky earth-like planets in radial velocity data sets is hampered by stellar activity noise, even in some of the quietest stars that are routinely monitored for radial velocity variations. Although techniques aimed at searching for weak signals in noisy data are now able to detect multiple planet systems, their effectiveness can be augmented with accurate noise models. This project will make use of large archival data sets from precision radial velocity surveys by probing the signatures of stellar activity in spectral lines in an effort to provide improved noise models. This difficult problem will be calibrated by Gaia observations of known systems where their proximity and planet/star mass ratios give rise to relatively large astrometric signals and thus we will work with data from Gaia to make joint astrometric and radial velocity solutions using our newly developed code PEXO (https://github.com/phillippro/pexo/). This provides the opportunity to dramatically improve the robustness and sensitivity of searches for Earth-like planets orbiting nearby stars.
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Brown Dwarfs with Gaia
Hugh Jones, Ricky Smart
Gaia enables reliable distances for a large numbers of brown dwarfs to be discovered and characterised. The research plan is to take spectra for all brown dwarfs in Gaia and to use this to interpret their chemical compositions and ages. These will be used alongside the Gaia information in particular kinematics but also low resolution spectra which is envisaged as a possible data product in future data releases. Scientific exploitation of the Gaia sample will enable a much more secure understanding of brown dwarfs and include derivation of the local luminosity and mass function, characterisation of benchmarks and correlations analyses of physical parameters such as age/mass with photometric/spectroscopic features.
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The exoplanet brown dwarf connection - ultracool companions to Gaia stars
David Pinfield, Bartek Gauza
Ultra-cool companions may be brown dwarfs or planetary mass objects, with known discoveries ranging in effective temperature from ~2700 K down to just a few hundred K. The question of how brown dwarfs and giant planets should be classified/understood is not yet answered, with a full understanding of the "exoplanet brown dwarf connection" being an important goal in the field. Ultracool companions are a crucial ingredient, providing excellent test-beds to helping astronomers understand the complex ultracool atmosphere physics at play. With the recent advent of the Gaia observatory we now have access to an unprecedented set of primary star measurements, which are providing constraints (through association) on companion properties including distance, temperature, surface gravity, mass, age and composition. In this project you will join a team working to fully exploit the powerful combination of Gaia with world-leading infrared surveys, and identify and study ultracool companion populations out to several hundred parsecs (we describe our overall programme in: https://arxiv.org/abs/1706.06038). We are specifically targeting companions with the most extreme properties, such as the youngest planetary mass objects, and the coolest brown dwarfs with temperatures down to room temperature.
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Novel techniques to find cool brown dwarfs in CatWISE
David Pinfield, Bartek Gauza
Very cool brown dwarfs and free-floating planetary mass objects have temperatures of 250-900 K (with late T and Y spectral type). Their temperature depends on both mass and age, but a small fraction have cooled to this state over the full age of the Galaxy. The Galaxy's ancient thick disk and halo populations formed ~10-13 billion years ago, and constituents retain highly characteristic kinematic signatures (with space velocities of 100-300 km/s). The identification of such ancient brown dwarfs is starting to reveal the nature of substellar formation within the primordial environment, and is crucial to our big-picture understanding of galactic star-formation. Our team has an established programme identifying late T/Y dwarfs in imaging data from the WISE observatory, and has identified several of the coolest members of the thick-disk/halo. During the last decade WISE has imaged the whole sky many times, which has led to the (recently released) CatWISE catalogue (a very sensitive mid-infrared motion survey). In this PhD project you will use novel techniques to search CatWISE for cool brown dwarfs, including along obscured sight-lines towards background stars and amongst star clusterings within the galactic plane.