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Binaries Escorted By Orbiting Planets

Periodic Reporting for period 2 - BEBOP (Binaries Escorted By Orbiting Planets)

Reporting period: 2020-05-01 to 2021-10-31

In the past two decades, thousands of planets have been detected in orbit around nearby stars. Their many properties, architectures and configurations is allowing to compare our solar system to all other planetary systems and find out how typical, or atypical the formation of planets within the solar system was. While we have improved our understand of the physical processes behind planet formation there are still many questions than answered. The main reason for this is that exoplanetary research is still quite recent, but also because we have identified systems very different from what was anticipated, and it is difficult to explain how varied planetary systems are, including our own.

One approach to enhance our understand of planet formation is to gain somewhat control on the many properties that affect planet formation. One way to do this is to look at circumbinary planets. Those are planets that have two suns in orbit of another, at the centre of the system, rather than just one. This strange and unusual configuration was not thought to be possible until 10 years ago. Having two stars at the centre of the system affects how the dust and the gas that eventually create to planets moves, which in turn affects how planets are created from it. It was thought that the presence of two stars would disturb the dust too much, preventing it from accumulating into a planet. Yet circumbinary exist, and therefore there is something we do not fully understand behind planet formation, but particularly on how dust accumulates to make planets.

Understanding how those strange planets managed to be created will tell us which physical processes are the most important behind the formation of planets. Our hope that once we know that, we will also get to know better how planet form around single stars like the Sun, and therefore complete the story about our Earth came to be, and the story of the origin of life.

The goal of the project is to increase how well we know circumbinary planets, and therefore investigate planetary formation. The only forward to detect new circumbinary planets (only two handfuls are known at this stage), which we have been doing in the past two and half years and which is set to continue.
The main objective was to collect data on nearby binary stars and start the search for planets orbiting them. Data access was the most important objective fulfilled by the project thus far. We had to apply to various observatories and we won competitions that award time to the most interesting astronomical projects. The second, also very important achievement was to identify our first candidate exoplanets, and well as show that indeed, circumbinary planets can be detected using regular telescopes (all have so far been identified using space telescopes). While this work is not public yet, we have detected for the first circumbinary planets using ground-based telescopes. We did this in northern hemisphere using the most recognised detection method: radial velocities. We have also done that in the Southern Hemisphere. In addition, we made the first detection of a transit, when the planet passes in front of one of the two stars, using a telescope in Antarctica.

Meanwhile, we have also participated in multiple investigations that discovered planets orbiting single stars. The reason we are engaged in such activities, is because we wish to compare the properties of circumbinary planets to the properties of planets orbiting single stars. For instance we wish to know whether they have the same typical masses, the same orbital periods etc, or whether they are distinct. Each similarity and difference will be used to refine the theory of planet formation.

In addition, we have worked in refining what we know about the binary stars we target themselves. Doing so, our most important discovery thus far is that of a rare pair of stars called brown dwarfs, that orbiting one another and eclipse one another. This configuration allowed to measure their mass and radius. In addition, we could know their luminosity and age and as such were able to refine theoretical developments made in the 1990s and that had remained mostly unvalidated by data since then.
We communicate these results regularly at scientific conferences, but also communicate our results to the public in various events, some to schools, some of groups of adults. Our main result so far was also the subject of a pr
At the start of the project, circumbinary planets had only been detected using spacecrafts. Our data now shows it is possible to detect some at a much reduced cost, using ground-based telescopes, pushing the state of the art of what is feasible using traditional telescopes. In addition, a serendipitous discovery allowed us to validates models of stellar evolutions developed decades ago.

In the next phase of the project, we expect announcing multiple discoveries and producing revised occurence rates for circumbinary planets. Early results appear to show a significant difference between the mass distribution of planets orbiting stars and binary stars. We will seek to confirm whether this is true.
In addition, we expect the data from ESA’s Gaia satellite to become available, which will assist our detection of circumbinary companions.

Finally, work done at the onset of the project established that detecting the reflected light from a habitable rocky planets orbiting a very low mass star is not that different from measuring the flux contribution from the secondary stars of the binaries we are monitoring. Work is being done now to explore this route further and show a new detection method for exoplanets that could also provide information about the planets’ atmospheric composition.
Illustration for the discovery of a pair of eclipsing brown dwarfs.
Illustration of the SPECULOOS telescopes in Chile, one of which is partly used for the project.
Illustration of the ASTEP telescope, in Antarctica, which is partly used for the project.