Extrasolar Planets and Brown Dwarfs

Supervisory team: Hugh Jones, William Martin, Supriyo Ghosh

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 a series of 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. One final version is destined for delivery to the Thai National Telescope.

We introduce several novel developments including active metrology which enables us to construct a small athermal spectrograph from off-the-shelf parts. We are in the process of developing several accompanying technologies including (1) being able to read out different parts of the array at different speeds allowing arbitrary dynamic range to be reached, (2) developing tapered fibre technologies, (3) optical design without curvature in the spectral orders. The immediate aim of the project is to be able to build a prototype with precision radial velocities of a cm/s and efficiencies to enable a space-based radial velocity instrument. A range of experimental, practical and software skills will be necessary and further developed through this project.

Supervisory team: Hugh Jones, Richard Smart, William Cooper

The brown dwarf regime connects stars to exoplanets  but until recently has been hard to study. It particularly suffers from a lack of  objects having reliable distances and age. The project is to connect high quality Gaia distances and thus brown dwarf brightnesses to the brown dwarf regime through companion objects. EUCLID is a new highly sensitive European infrared telescope which will be used to select brown dwarfs based on companionship with nearby stars which have parallaxes in Gaia. The selection of objects will be based on proper motion, colour, absolute magnitude. Proper motion and colours will come from EUCLID, CatWISE, DESI-LS and be used to establish suitable selections of objects. Crossmatches will be done with the Gaia catalogue to establish nearby stars with suitable matching errors and flags. The Gaia primary stars will then be used calculate absolute magnitudes with the help of integrated EUCLID fluxes as well as those from the new SPHEREx mission. This will enable  connection of Gaia parallaxes from companions yielding benchmarks and multiple brown dwarf systems. Ages for systems will be determined based on  gyrochronology of the primary star. The EUCLID spectra will be particularly valuable at providing spectral discriminators of age and metallicity for example using the shape of H-band peak. This catalogue will provide for a brown dwarf regime filled with a variety of benchmarks. These new objects will be prime candidates for follow-up with new AO and interferometer systems and can resolve the close binary systems.

Supervisory team: David Pinfield, Hugh Jones, Bartek Gauza

Proper motion is the angular velocity at which astronomical objects move across the sky, and can be used to select local or fast-moving objects of interest. However, such objects can also have extreme colours and be much fainter in one wave-band compared to another. So in the fainter wave-band an object may only be detectable in very deep "image stacks" (constructed by adding together many individual images observed over several years). In such “image stacks” high proper motion objects may appear as extended sources at offset positions (due to their movement between individual images in the stack), and a very high proper motion object may even manifest as an apparent "trail" of objects in an image stack.

In this project you will combine deep optical and near infrared/infrared survey data from ground/space-based surveys to search for high proper motion brown dwarfs. Brown dwarfs have extreme colours (e.g optical-NIR or NIR-IR) and can have high proper motion if they are nearby or are members of the thick-disk/halo kinematic populations. You will develop a method to search for brown dwarfs that are point-like objects in one survey but are extended (or forming a trail) in deep-stack survey/s. And you will then explore the nature of these objects using colour/magnitude and proper motions to assess spectra type, distance and age (from e.g. kinematic group membership, companionship, and moving group membership).

Supervisory team: Hugh Jones, Supriyo Ghosh

Our ability to find exoplanets in the radial velocities of stars is currently limited by the problem of distinguishing the gravitational impact of exoplanets from other changes in the atmospheres of stars. Cold and hot sunspots which result from magnetic field and temperature changes in the stellar surface are the main source of uncertainty. We have used high resolution spectra of Sunspots, along with spectra from the normal Sun to identify and model atomic transitions that are changed by the higher magnetic fields in Sunspots through the Zeeman effect (work currently being written up). This provides a list of 1000s of Zeeman sensitive transitions and we can use these to weight/remove spectral regions compromised by magnetic fields from the radial velocity analyses of nearby stars. It should  be possible to further tune this by doing such analysis on systems with high cadence photometry and where there are known transit signals to optimise weightings. This is immediately useful for Sun-like stars but should be applicable at a range of spectral types and particularly perhaps as a route to do radial velocity analyses of stars which are seemingly dominated by activity.