Extrasolar Planets and Brown Dwarfs

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.

Hugh Jones, Fabo Feng

The programme will focus on the determination of orbital parameters for over 2500 nearby stars which have high precision radial velocity observations along with Gaia and Hipparcos data. Based on our initial work with Gaia DR2 data, astrometric solutions significantly change the determined solutions for more than 23% of nearby stars. The expectation is that future Gaia data releases will allow the existence of significant astrometric signals arising from companions to be probed for most nearby stars. The combination of astrometric and radial velocity data will enable a much wider range of potential exoplanet orbits to be examined and should provide robust constraints on Jupiter analogues around nearby stars. Some of the planets we find will be around the very closest stars and be of immediate interest with facilities such as JWST. The long-term results from the programme can be expected to provide constraint on the variety of “Grand Tack” scenarios for the architectures of Solar Systems with similarities to our own and lead to improvements in the methodologies and available tools for the interpretation of datasets for more distant stars.

This project will make use of large archival data sets from precision radial velocity surveys. In particular, radial velocity data sets are hampered by stellar activity noise and further development of our new software tools to help deal with activity in large datasets will be necessary (e.g., building on Lisogorskyi, Jones, Feng et al. 2020). New Gaia data releases will be used to make joint astrometric and radial velocity solutions using our developing PEXO code (Feng, Lisogorskyi, Jones et al. 2019). This provides the opportunity to dramatically improve the robustness and sensitivity of searches for planets orbiting nearby stars.

Hugh Jones, Ricky Smart

The Gaia project is making an all-sky astrometric survey. UH is part of the follow-up effort identifying new brown dwarfs and taking follow-up spectra (Smart et al. 2019). This project will be concerned with the data reduction and interpretation of astronomical spectra of brown dwarfs. This will involve using a variety of different astronomical software packages as well as the use of atmospheric models. Gaia enables reliable distances for a large numbers of brown dwarfs to be discovered and characterised. Spectra for all brown dwarfs in Gaia can be used along with kinematic information from Gaia to interpret their chemical compositions and ages. These will be used alongside the Gaia information in particular 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. This project is envisaged to include the student becoming a member of the Gaia consortium and also being concerned with the data quality produced for future Gaia data releases.

Hugh Jones, Bill Martin

This project is to realise the so-called EXOhSPEC prototype spectrograph (Exoplanet high resolution spectrograph). It will be entirely built from catalogue components but will utilise technologies not deployed in astronomical spectrographs. EXOhSPEC will be tested on the Sun and local stars both in the laboratory, on local automated telescope as well as with telescopes in the Canaries and Thailand. A final version is destined for delivery to the Thai National Telescope. It is intended to have the fewest possible optical surfaces for a high resolution spectrograph and its efficiency and small size will make it a highly attractive for further development. Among several novel developments that we introduce is active metrology which enables us to construct a small athermal spectrograph from off-the-shelf parts. The long-term aim of the project is to be able to build a prototype to significantly extend the reach of precision radial velocities to higher precisions and efficiencies enabling for example a space-based radial velocity instrument. Papers describing early results and laying out future steps for the project is available (Jones, Martin et al., 2020) along with software to enable iteration through a number of designs. A wide range of experimental, practical and software skills will be necessary and further developed through this project.