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ImagePlanetFormDiscs Report Summary

Project ID: 639889
Funded under: H2020-EU.1.1.

Periodic Reporting for period 1 - ImagePlanetFormDiscs (Imaging the Dynamical Imprints of Planet Formation in Protoplanetary Discs)

Reporting period: 2015-07-01 to 2016-12-31

Summary of the context and overall objectives of the project

Planet formation is a complex process that takes place in the discs around young stars. The dominant fraction of the planet population is believed to form in the inner few astronomical units of these discs. Therefore, it is essential to study the physical processes that take place in these inner disc regions to unveil the initial conditions of planet formation. This will also advance our understanding of how Earth formed and how is able to develop the right conditions for harboring life, addressing one of the oldest questions of mankind. Detailed imaging of the inner disc environment might also reveal planets that are currently in the process of formation and that could be detectable either through the emission from circumplanetary accretion processes, or through the gravitational influence that these planets exert on the disc.

Observational studies of planet formation in protoplanetary discs are primarily limited by the achieved angular resolution that is set by the telescope diameter. Accordingly, most studies of protoplanetary discs could only investigate the outer disc regions, on scales of tens to hundreds of astronomical units. Infrared interferometry offers an elegant way to overcome this resolution barrier by coherently combining the light from separate smaller telescopes that can be spread over hundreds of metres, thereby providing the first direct view into the innermost astronomical unit of protoplanetary discs. The key requirement for obtaining direct images with infrared interferometers is the number of telescopes that are combined, which has so far been limited to 4 telescopes for protoplanetary disc observations. The primary objective of the ERC Starting Grant is to push this barrier by equipping the MIRC beam combiner at the CHARA telescope array with an innovative ultra-low read-noise detector system that will permit us to obtain first 6-telescope interferometric observations of low- and intermediate-mass young stars. Increasing from 4 telescopes to 6 telescopes provides 3.5-times more observables per measurements, while the CHARA array will also provide us about 2.5-times longer baselines than what was achieved in earlier observations. This will enable us to obtain an image in a single night of observing and to study also the time evolution of any resolved structures.

We will use the observational capabilities that will result from our CHARA instrumentation work in order to search for possibly planet-induced structures in the inner regions of protoplanetary discs and to image their temporal evolution. We will combine the interferometric data obtained over a wide wavelength range in order to characterise the resolved structures. Finally, we will search for the signatures of the planets themselves by imaging in accretion-tracing spectral lines.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In the initial 18 months of the project, we made good progress in the optical design of the instrument and in the procurement of the necessary components. We procured an ultra-low read-noise detector system that is based on a novel approach for building infrared detectors. We took test data that confirms the dramatic, order-of-magnitude improvement in sensitivity that we can expect from integrating the detector at CHARA, in particular when using short integration times. For longer integration times, the sensitivity gain will be less pronounced, where the thermal background noise becomes the dominant noise source over the read-out noise.

We expect the delivery of the detector system for March 2017 and we will then work with our collaborators at the University of Michigan on validating the camera performance and on implementing it at the CHARA array. In order to achieve science results as early as possible, we consider staging our implementation in two phases, where “Phase 1” could bring the detector to the CHARA array as early as summer 2017, while the optimised optics would be put into place in “Phase 2” up to one year later.

Besides pushing this instrumentation work ahead, we started implementing the software tools that are necessary in order to interpret our observations in an optimal way. This software tool is optimised for modelling multi-wavelength interferometric data and to extract quantitative physical parameters such as the dust density and 3-dimensional disc structure. Our ERC-funded postdoc is currently applying this model in order to fit the CHARA 3-telescope data from two protoplanetary discs, which should result soon in a first publication using this tool.
We also published interferometric imaging results from CHARA that show the star spots on the surface of a magnetically active star (Roettenbacher et al., 2016, Nature 533, 217). Using the VLTI array we discovered a young high-mass multiple system that is at least 3-times more compact than any previously-unknown high-mass multiple system. The interferometric imaging allowed us to resolved the circumstellar discs around both stars and detect that they are misaligned with respect to each other, which is indicative of the youth of the system (Kraus et al. 2017, ApJ 835, L5).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Our project requires an ultra-fast, ultra-low read-noise infrared detector system that has not been commercially available so far. We worked with a start-up company that was planning to develop and to offer such a system for the first time as a commercial product. We are their first customer and supported them with technical feedback on the optical layout, the optimal read-out strategy, and the measured performances, which will improve their product in general. This new e-APD detector technology has likely applications in manufacturing and medical imaging. Supporting this commercial development in the critical early development phase might therefore have notable future societal impact.

The project is also advancing the state-of-the-art in the field of high-angular resolution studies on planet formation. For instance, we currently analyse an intriguing ALMA interferometry image that show a possibly planet-triggered dust trap. Dust traps are believed to provide the environment for dust grains to grow from micrometer-size to planetesimal size, marking one of the earliest stages of planet formation.

We are happy to engage the general public in our research and to spread general astrophysical knowledge. For this purpose, we engaged in the following six outreach events that targeted a diverse range of audiences:

Jan 2017 (1 evening): Heavitree Squilometre project’s Park in the Dark event. Presented an open-air planetarium show to ~30 people (all ages).
Nov 2016 (1 evening): talk at Torbay Astronomical Society. ~50 attendees. Audience was mainly adults; some secondary school students.
June 2016 (1 evening): talk at Norman Lockyer Observatory. ~30 attendees. Audience predominantly mature adults.
May 2016 (1 evening): talk at Plymouth Astronomical Society: ~50 attendees. Audience was mainly adults; some young teenagers with their parents.
May 2016 (1 day): guest lecture at Merseyside Astronomy Day: ~100 attendees + recorded for distance learning course. Audience of ages 13+.
Dec 2015 (1 day): assisting with the 'Girls into Physics’ day activities. ~200 attendees. All female school children aged 15-17.
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