- 2019/137 - Mitigate stellar activity to characterise Earth-size planets
- 2019/138 - Composition of Earth-size planets
- 2019/139 – Unveiling the composition of exoplanets atmospheres with CHEOPS and ESPRESSO
- 2019/140 – Emission and transmission spectra of exoplanet atmospheres
For further details, please see the listing below, with abstracts and advisors. Prospective candidates are welcome to contact directly the proposers of the topics for inquiries and further details.
2019/137 - Mitigate stellar activity to characterise Earth-size planets
Advisers: Susana Barros (IA U.Porto)
The detection of terrestrial mass planets is a major goal in astrophysics. This has recently become possible due to two space-based transit surveys, namely CoRoT and Kepler and improvements in the precision of radial velocity measurements. Future space based missions (e.g. CHEOPS, PLATO) and new high-resolution spectrographs such as ESPRESSO (Pepe+2010) and NIRPS (Wildi+2017) are being planned to detect and characterise Earth-like planets around bright nearby stars. This research project aims to improve the accuracy and precision of planetary parameters derived from transits and radial velocities obtained with these future facilities, which our institute has privileged access.
One of the project goals is to develop tools and methods that are essential to explore the data from these missions. A second more general goal of this project is to study the effect of stellar activity in observations of small sized planets. The student will investigate how the stellar activity biases planetary parameter measurements and develop methods to correct for it. The corrections will be implemented in an already existing tool to derive mass and radii of exoplanets. Then he/she will apply the new tool to new observations of exoplanets obtained with CHEOPS, EXPRESSO and NIRPS. This is crucial to improve the accuracy of the measurements of mass and radii of planets in the range from Earth-Neptune size. Accurate masses and radii are essential to derive the composition of very low mass planets and gain insight into planetary structure. This will provide constrains on planetary formation and evolution theories. Moreover, bright systems allow further characterisation of the planets. Optionally the student can also be involved in developing stellar activity corrections for observations of Rossiter–McLaughlin effect to measure the relative angle between the planet orbit and the stellar spin or observations of planetary atmospheres.
2019/138 - Composition of Earth-size planets
Many transiting small exoplanets where found and are waiting to be found by the K2 mission (Barentsen+2018). Our group has developed tools to reduce K2 data, compute high precision light curves and search for planetary transits. Using these tools, we already discovered multiplanetary systems (Barros+2017) and a planet smaller than the Earth (Santerne+2018).
This project consists in optimizing and using these tools to create a complete list of transiting planetary candidates from K2 data; prioritize them for follow-up observations and confirm them using state-of-the-art spectrographs: HARPS, ESPRESSO, NIRPS. The recently launched TESS satellite is also providing transiting candidates, which can also be included in the priority list for follow-up. The student will thus have the unique opportunity to discover and characterize new exoplanets. One important part of the project is the development of tools to prioritize the planetary candidates using all the available information.
The second part of the project involves combining the transit observations from K2 and TESS with the radial velocity observations taken with HARPS, ESPRESSO and NIRPS. This will allow deriving the mass and radii of the planets and hence constrain their composition. Our group already has its own code to derive the planetary parameters but the student is expected to optimize it.
The tools developed here will also be important for future surveys like PLATO. Our group is responsible for their development for the ESA mission PLATO giving the opportunity for the student to be involved in this extra-ordinary mission which gather most of the European exoplanet community.
Possible developments of this project are:
- Optimizing the photometry of TESS data
- Detecting exoplanet of prime-interest for atmospheric characterization: exoplanet with extended atmospheres, in the verge of evaporation or rocky planet around very bright stars.
- Statistical studies about the occurrence rate of different types of planets as a function of stellar properties.
2019/139 - Unveiling the composition of exoplanets atmospheres with CHEOPS and ESPRESSO
Although several thousands of exoplanets have already been detected (see exoplanet.eu), our understanding of their atmospheres is still very limited. In most of the cases, our knowledge of an exoplanet can be reduced to its mass and radius (see Demangeon+2018). The last years have, however, seen considerable developments in terms of instrumentation. New missions like the ESA-CHEOPS satellite (Fortier+2014), the ESA-ARIEL project (Tinetti+2016) and the high resolution spectrograph ESPRESSO@ESO-VLT (Pepe+2014) will shed new lights on exoplanets and their atmospheres.
CHEOPS, ARIEL and ESPRESSO will provide complementary information. On one side, CHEOPS will probe the atmosphere of “hot jupiters” providing broad spectral measurement of the light reflected by these planets. ARIEL will complement that with low resolution spectra in the infra-red. On the other side, ESPRESSO will provide high resolution observation of these planets and their host stars, from which transmission spectra and specific spectral signatures can be extracted.
For this PhD project, the laureate will be involved in CHEOPS, ARIEL and ESPRESSO science team activities. The first objective will be to focus on the interpretation of CHEOPS and ESPRESSO data. A second step will be to participate to the scientific definition of the ARIEL mission whose launch is planned for 2028. Using state-of-the art models, inspired from those used to simulate the atmosphere of Solar System planets, the laureate will infer several properties of the observed atmospheres: their reflective properties (albedo, presence/characteristics of clouds, e.g. Demory+2013, Martins+2018), their temperature, the molecules and atoms which compose them (e.g. Birkby+2017). Due to the unprecedented precision and flexibility offered by CHEOPS and ESPRESSO on one side and the importance of the ESA-ARIEL mission for the future of exoplanet sciences. The results from this thesis will constitute landmarks in the field of exoplanetary atmospheres and help to shape the future of the field.
The supervisors of this project, along with the team which will host the laureate, has a deep involvement and expertise in both CHEOPS, ARIEL and ESPRESSO. They will guarantee the laureate access to the data, to sophisticated 3D atmospheric models and involvement in the science team’s activities.
2019/140 - Emission and transmission spectra of exoplanet atmospheres
With more than 3800 extra-solar planets discovered so far, one of the main focus of exoplanet research is the detailed characterization of exoplanets, and specifically their atmospheres. This represents a first effort that should ultimately lead the the detection of life signatures in other worlds.
ESPRESSO, NIRPS and SPIROU are a new generation of high-resolution spectrographs dedicated to exoplanet research. Installed at ESO’s VLT, ESPRESSO (Pepe+2014) started its observations in September 2018 and for the next 4/5 years will dedicate 1/3 of its guaranteed observation time (or about 70 nights) to exoplanetary atmosphere studies. NIRPS (Bouchy+2017) and SPIROU (Simon+2012) will start observation within the next year and will also reserve a significant fraction of their time to exoplanetary atmosphere sciences. ESPRESSO observes at visible wavelengths, while NIRPS and SPIROU observe in near infra-red. The observations from these different facilities will thus be complementary, and allow to approach the study of exoplanet atmospheres from a unique perspective.
Different observational strategies can be used for this objective depending on the exoplanet studied. When the exoplanet transits in front of its parents star, we are able to observe the minute color dependent changes in the spectra produced by the different fractions of the stellar light passing through the exoplanet’s atmosphere (Wyttenbach+2017). From such observation a low resolution transmission spectra of the atmosphere can be extracted. In some cases, the detection of strong absorption lines of molecules like CO is also possible (Désert+2009). For hot exoplanets orbiting close to their parent stars, the spectra of the light emitted by the atmosphere can also be detected (Stevenson+2010).
The main objective of this PhD project is to extract robust observational constraints on the atmospheres of exoplanets as observed with ESPRESSO, NIRPS, and SPIROU. For this, the candidate is expected to perform and optimize the data analysis processes to extract the minute planetary signal and derive the properties of exoplanet atmospheres.
The supervisor and co-supervisor of this project are deeply involved in ESPRESSO, NIRPS, and SPIROU. They will offer to the laureate both access to the data and science teams, as well as expertise on the instrument and the observational techniques required for this project.