The Planet-Disk Connection: Accretion, Disk Structure, and Planet Formation

"How do stars and planetary systems develop and is life exclusive to our planet?" is one of the major questions of humanity, and also one of the Science Challenges proposed by the STFC. In Dundee, we are a small but young and vibrant department with a strong focus in understanding the formation of stars and planets, and the group is growing within the larger context of the Scottish Universities Physics Alliance (SUPA) and the St Andrews Exoplanet Centre.

Our main objective is to explore planet formation environments both observationally and computationally. Planets are born in protoplanetary disks formed around young stars, composed of gas and dust with sizes from very small particles to pebbles. We use multi-telescope, multi-wavelength data and a state-of-the-art computer simulations to track the formation of stars together with protoplanetary disks, to follow the evolution of disks as they disperse, and to study how planetary systems form and evolve out of a dissipating disk. One of the main problems of observationally studying the ongoing planet formation in disks is that the innermost part (which includes the habitable zone, the region where liquid water could enable planets to host life) is too small and too faint to be directly resolved even by the most powerful existing interferometers. Our project will develop special observational techniques to explore the conditions around young stars and in the innermost planet formation regions near the central stars, where many planets are now being discovered. Since observations of disks provide snapshots of disk evolution while observed exoplanets show the end state of planet formation, we also aim to connect the beginning and the end of planet formation (i.e. disks and planets) by using computer simulations, and will compare simulations with both observed disks and exoplanets.

The first key is to explore the velocity and time dimension to track tiny spatial structures: using the Doppler effect and repeated observations over time, we can track the disk material as it orbits, spirals and accretes onto the central star, mapping the innermost regions at few stellar radii and determining the flow of matter throughout the disk. Both quantities are very important to explore whether the star will be quiescent enough in the future to allow for habitable planets, and the way matter moves through the disk in the planet-forming zone. It will also enable us to distinguish observational planetary signatures from those of accretion and activity and thus facilitate the detection of very young planets in the future.

The second key is the "Rosseta Stone" technique, using observations at many different wavelengths (colours), taken with various telescopes. Similar to the different languages of the original Rosetta Stone, each wavelength tells us about aspects of the disk in a slightly different way. By combining them all for large numbers of objects, we can obtain an accurate picture of the global properties of protoplanetary disks and explore the signatures of planet formation.

The third key is to use computer simulations to bridge the gap between protoplanetary disks and exoplanetary systems by exploring the formation of planets over a few million year timescale. We will construct a realistic disk model from our multi-wavelength observations for a large number of disks and use that as the starting point of planet formation simulations. We will then compare the properties of the simulated planetary systems with those of observed ones, which will also help us to rule out or confirm disk properties and physical processes that are not directly observable. Our goals are to put into context the known variety of planets by revealing from which kinds of disks they have originated, and to understand the observed variety of protoplanetary disks by exploring the effect of planet formation on the evolution of the disk.

Our project aims at producing a significant impact in three directions:

1) Scientific impact: Our scientific impact is described in detail in the Academic Beneficiary section. In short, Project 1 will develop emission line tomography for young stars, opening a new door to study accretion processes in various scenarios (e.g. young stars, interacting binaries, accretion onto compact objects). Our public Python-based routines will facilitate the exploitation of existing and future (e.g. Arago) spectral databases and increase our impact in other fields. We will also explore the stellar magnetosphere as a planet migration stopping mechanism. Project 2 will test two popular planet formation models against observed planets and disks by using the state-of-the-art numerical simulations and a realistic disk model constructed from multiwavelength data of protoplanetary disks. Our protoplanetary disk "Rosetta Stone" technique proposes a synergy between the results that can be obtained from different telescope facilities (beating degeneracy in disk structure that cannot be resolved from single observations, and exploring the power and limitations of existing techniques), which are particularly interesting for the development of new instrumentation and observing strategies. Our numerical simulations will help put the known variety of planets and protoplanetary disks into context.

2) Outreach and general impact on society:
Our group has been largely involved in outreach at levels ranging from primary school children, to general public, school teachers, and amateur astronomers, with a special focus on children and young people from less favourable backgrounds and a strong aim to increase the participation of girls in science. We will continue and extend these activities as part of our commitment to the society and the science development.
We will also go a step further in science communication by including artists as project partners for our pathways to impact, similar to previous artist-scientist collaborations in Life Sciences at the University of Dundee (UoD). We will closely communicate with artists at each step of our project so that they become familiar with our scientific methodology and observational techniques as well as the research outcomes. The goal is to have a joint exhibition in year 3, which features pieces of artwork fully based on our project results and methodology along with the scientific research presentations (in form of posters/slides/talks). Using artistic representations can facilitate the understanding of not only our cutting-edge astrophysical research of star and planet formation, but also subtler and more complex concepts such as observational techniques and limitations, multi-telescope data and data processing, time-resolved observations, and computer simulations. By exhibiting the artistic work along with our scientific presentations, we can provide a precise but unique, quantifiable (in REF terms) and memorable insight into our research to the public.

3) Impact for the UoD: Recently, the UoD has opened two new Astrophysics-themed programmes (Physics with Astrophysics, and Mathematics and Astrophysics), which proved to be very popular among undergraduate students. The addition of PDRAs to Dundee will greatly enhance the visibility of our research, encourage active discussion and interaction among undergraduate and post-graduate students, and in general, create a more diverse but strongly focused environment for people considering a career in science. Furthermore, the success of this grant will help us establish Dundee as a UK star and planet formation group and make a strong case for the University to expand the Astrophysics group further. Being led by two female Lecturers, our group will also act as a role model for prospective and future female students, helping to target the interest and to increase the participation of female students in STEM subjects.