Out of Transit telltales of extrasolar planets

A passing shadow and a moving line: these are the ways in which the vast majority of known exoplanets have been discovered and characterised. We look for the small dips in brightness of a star as a planet transits, or for the shifting spectral lines as the star and planet move around their common centre of mass.

These techniques---the "transit method" and "radial velocity method," respectively---are tried and true, and have revealed thousands of exoplanets so far. But only a relative handful of chance-aligned exoplanets, which happen to cast the right shadow on Earth or pull detectably on their host stars, are susceptible to these methods.

But there are many other ways in which planets make their presence evident.

For this project we will focus on Out of Transit (OoT) signals, gradual changes in the apparent brightness of a star over a planet's whole orbit. By building simple, general and robust models of these signals, we can better fit models to known planets and search for whole new populations not yet detected. In particular, we expect to be able to conduct a census of one of the most extreme planet populations: the eccentric hot Jupiters, massive planets on elongated orbits which pass very close to their stars.

We will start from three effects which have been well characterized and observed:
Reflections of the star's light from the planet's surface. This tells us about the size of the planet and its reflectivity, which in turn can inform explorations of the atmospheric and surface composition.
Tidal distortion of the star by the planet. This tells us about the mass of the planet, the shape of its orbit, and the properties of the star, from its mass and radius to hints of its internal composition.
Relativistic beaming of the star and planet's light due to their motion. This lensing effect tells us about the mass and motion of the system, and could even be used to carefully constrain the temperature of the planet.

As well as building and refining the physical models for these effects, we will have to approach the raw data (photometry from space telescopes such as Kepler and TESS) with great care to preserve and highlight these small periodic signals. We will test and implement new detrending methods to remove noise from the raw light curves before we fit our models to the signals beneath.

Using carefully prepared data, new effects, not yet observed in light curves but predicted by theory, such as refraction and scattering of light through planetary atmospheres, may also be within reach.

Each and every one of these signals may be visible in a stellar light curve - and to characterise planets as fully and accurately as possible will require examining all these effects together, giving a holistic view of the expected effect of an orbiting planet. At the same time, taking account of all the signals we have talked about here should give us a full reckoning of all periodic changes in the light from a star caused by an orbiting planet. This should give us the tools to explain and understand every piece of observed light curves, and if it does not it will highlight new areas where we must rethink our current paradigms.

We will produce the models and tools needed to simply and easily draw comparisons between theoretical effects of an extrasolar planet and the observed data. We hope these can be used to better constrain the properties of known exoplanets and to search for new candidates, unseen via existing methods.