The planetary graveyard - searching for the remnants of exoplanet systems around dead stars

There is growing evidence that planetary systems are ubiquitous throughout the galaxy. Ground and spaced based surveys have found thousands of planets around stars. They range from Jupiter sized planets so close to the parent star that their atmosphere is being evaporated, to a planetary system made up of seven earth-sized planets around the red dwarf star TRAPPIST-1. Of all the types of isolated stars in the galaxy there is one significant discrepancy where no planets have been detected, White Dwarfs.

97% of stars, including our own Sun, will end their life as the remnant, cooling, cores of stars, known as White Dwarfs. The fate of the planetary systems around these stars is unknown. Planets closest to the parent star are expected to be destroyed as they are engulfed when a main sequence star expands to a red giant, but the fate of those further out are unknown. There is growing evidence that planetary systems do survive to some extent. Contamination of the atmosphere, as well as circumstellar dust and metal rich gas discs have all been observed around White Dwarfs that can only be explained due to the disruption of a rocky body that strayed too close to the star. There is even one system where such a process is being actively monitored, WD1145+017. This system was identified by data from the Kepler Space Telescope, which sees multiple and varying dust clouds transiting across the White Dwarf as the body disintegrates and releases clouds of debris. Not only do such processes provide evidence that planetary systems do survive but they also provide information on the elementary make up of rocky type bodies outside of our own solar system. WD1145+017 is unlikely to be unique and more examples will expand our knowledge of the evolutionary end stage of planetary systems.

Our on-going work has identified many other White Dwarfs with variability that cannot easily be explained but could be due to dusty material accreting onto the White Dwarf. Alternatively such variability could also be due to reflection from or heating of a very short period non-stellar companion, such as a Brown Dwarf or perhaps even a Jupiter sized planet. Our group has recently identified the shortest period known such system: a Brown Dwarf (which is about the same size as Jupiter) orbiting an Earth sized object (the White Dwarf) every ≈70 minutes! These systems can have unique features such as winds and jetstreams transferring heat from the hotter hemisphere to the cooler, as well as allowing us to directly study the Brown Dwarf atmospheres.

We are looking for a proactive student, with a can-do attitude, to search for evidence of ancient planetary systems. You will analyse data from both ground and space based ncluding Kepler and the TESS satellite, due for launch in Spring 2018. You will also analyse White Dwarfs observed by the Next Generation Transit Survey (NGTS), which will eventually observe a significant fraction of the southern hemisphere.