Research :: PhD Topics for 2014 :: Planets

Topics under the thematic lineTowards the detection and characterization of other Earths” available for the 2014 Call (6 PhD Topics):

  • 2014/101 – Exoplanet detection in metal-poor stars: a fundamental test for planet formation models
  • 2014/102 - Characterizing the atmosphere of exoplanets through transmission and reflected light spectroscopy
  • 2014/103 – From ESPRESSO to Plato: detecting and characterizing Earth-like planets in the presence of stellar noise
  • 2014/104 – Toward the statistical validation of Earth-like planets
  • 2014/105 – Galactic stellar populations and planet formation with the Gaia-ESO Survey data
  • 2014/106 – Towards exoplanetary atmospheres: new data reduction methods for the nIR

For further details, please see the listing below, with abstracts and advisors.

2014/101 – Exoplanet detection in metal-poor stars: a fundamental test for planet formation models

AdvisersNuno C. Santos (CAUP) and Pedro Figueira (CAUP)

The detection of rocky, Earth-like planets within the habitable zones (HZ) of their host stars is one of the holy grails of exoplanetary research. Although these are at the limit of current observational capabilities, the number of detected super-Earths and Neptune-mass planets has been growing steadily, some of which are in the HZ. These discoveries are allowing us to do a first census of Earth-like planets in our Galaxy, but also to better constraint the planet formation models. In this respect, present models strongly suggest that lighter planets should be frequent around low metallicity stars, contrarily to what is the case for giant planets. The search for planets around metal-deficient stars is thus key in all this discussion.

The present PhD thesis proposal focuses in this specific aspect. In particular, we aim to explore data from an ongoing radial velocity (RV) survey led by our team (an ESO Large Program), which uses the HARPS spectrograph to search for low mass exoplanets around 109 solar-type, moderately metal-poor stars. In this context, the proposed project has two main tasks (that will run in parallel). In a first task, the student will investigate new data analysis methods, including statistical methods using both frequentist and Bayesian approaches, in order to develop new tools that are necessary to detect very low mass planets through RV measurements. The development of these tools is fundamental to interpret the low amplitude signals (close to the measurement precision) expected in the data, and thus to fully exploit the data of the referred Large Program. In a second task the student will then make use the developed tools, together with already implemented methods, to characterize the frequency of planets down to the Earth-mass limit in our sample of metal-poor stars. With this dual approach, this project also serves as a preparatory program for our scientific participation in the analysis of data coming from the future state-of-the-art instruments like the ESPRESSO spectrograph.

Notes: This is a closed project.

2014/102 - Characterizing the atmosphere of exoplanets through transmission and reflected light spectroscopy

AdvisersPedro Figueira (CAUP) and Nuno C. Santos (CAUP)

We propose to study the reflected light from exoplanets with the goal of characterizing their atmospheres. It has been shown that in the optical, even in the best-case scenarios, the planet/star flux ratio will be smaller than 1/10000. As a consequence the planet’s signal will be buried amidst the noise of the stellar spectrum, and the detection of such a signal is a very difficult observational challenge.

To enhance the minute planet’s signal and make it surface above the stellar noise, we will use a technique demonstrated in Martins et al. (2013), applied to real data. This technique will permit us to measure directly the planet’s reflected light and reconstruct its albedo function. The collected data will allow to constrain atmosphere models, both in composition and dynamics, as well as exoplanet orbital parameters, to which the aforementioned technique is particularly sensitive.

Notes: This is a closed project.

2014/103 – From ESPRESSO to Plato: detecting and characterizing Earth-like planets in the presence of stellar noise

AdvisersNuno C. Santos (CAUP)

While the number and variety of discovered extra-solar planets is still an important asset for exoplanet research, the focus of extrasolar planet researchers is now moving towards two main lines: i) the detection of lower and lower mass planets, with the goal of finding an Earth sibling, and ii) the finest characterization of planets orbiting other stars, including their interior structures and atmospheres.

Despite the development of a whole new generation of instruments and space missions (like ESO- ESPRESSO and ESA’s CHEOPS and PLATO missions, on which our team is deeply involved), these goals are not easy to achieve. In particular, the “noise” introduced by stellar activity has been shown to be a strong source of difficulties for planet search and characterization programs using both high precision radial velocity or photometric transit observations.

The present project proposes to investigate the impact and role of stellar activity in precise planet search and characterization projects. For this, we expect the student to develop a tool to simulate the effects of stellar activity on precise photometric (transit) and radial velocity measurements. The tool will then be applied to real data (e.g. HARPS and Kepler). The impact of stellar activity on the derivation of precise planet parameters will be investigated in detail. The results of this project have crucial consequences for the full success of instruments like ESPRESSO, CHEOPS, and PLATO.

2014/104 – Toward the statistical validation of Earth-like planets

AdvisersAlexander Santerne (CAUP)

Detecting a planet like the Earth is one of the main challenge of the next decade. To find such planets, new outstanding instrumentations are going to be built with an unprecedented precision (such as the ESPRESSO spectrograph for the ESO – VLT and the PLATO space mission from ESA). Their precision will make possible the detection of an exoearth signal. However, other astrophysical scenarios are able to mimic the signal of an Earth signal, like stellar variability (stellar activity, magnetic cycle, …), or multiple stellar systems.

The announcement of the first Earth-twin planet will thus require strong evidence that the detected signal is indeed of planetary origin. This can be done by statistically validating the planet signals. In this context, the PASTIS software is a unique, fully-Bayesian, tool that is able to validate small-size planets. However, today, the PASTIS tool is not able to statistically validate an Earth-analog planet without relying on their occurrence rate and statistics of physical properties. Statistics of such planets are however extremely poor since only one is known so far (the Earth).

The goal of this PhD will be to improve the capabilities of PASTIS to validate planets, down to Earth-size ones. This can be done by improving the constraints from the data on the various astrophysical scenarios. This will require to develop or implement more accurate models of the scenarios, accounting for all the available data (photometry, spectroscopy, radial velocity, asteroseismology, etc…). Then, the improved PASTIS software will be used by the PhD student to validate Earth-size planets already detected by the CoRoT and Kepler space telescopes and/or that will be detected by the future TESS space mission (NASA). It will also be used to prepare the validation of the Earth-size planets that will be detected by the PLATO space mission.

The PhD student will work within a young and dynamic team of researchers who have developed the PASTIS software.

*PASTIS: Planet Analysis and Small Transit Investigation Software

Notes: This is a topic requiring a mixed fellowship (3-6 months per year in France/Switzerland).

2014/105 – Galactic stellar populations and planet formation with the Gaia-ESO Survey data

AdvisersVardan Adibekyan (CAUP) and Sérgio Sousa (CAUP)

The on-going Gaia-ESO Survey is a very ambitious project which uses ESO/VLT to obtain detailed spectra of about 100000 stars from all the Galactic stellar populations. We propose to use the data from this survey (for which we have privileged access) to study the chemical and kinematic properties of stellar populations. The goal is to understand the formation and evolution of the distinct populations that we can identify with the data. In addition, we propose to investigate the observed planet hosting stars to understand possible links between the different stellar populations and planet formation processes. This latter study should help us to better estimate the frequency of the different type of planets for each stellar population and in our Galaxy in general.

Notes: This topic is also offered as topic 203, under the thematic line on Stars.

2014/106 – Towards exoplanetary atmospheres: new data reduction methods for the nIR

Advisors: Nuno C. Santos (CAUP), Cláudio Melo (ESO), Pedro Figueira (CAUP)

The search for extrasolar planets has as one of its crowns the study of exo-atmospheres. This goal has been shaping Science and scientific instrumentation for the last decade. In this project we provide a gradual approach to developing and perfecting of methodologies required for the detection and characterization of exo-atmospheres.

Building up on current in-house knowledge, we propose to develop the methodologies required for the extraction of the maximum of information, and in particular the minute signals of exoplanets from nIR spectra. The risk of this ambitions program will be minimized by a thorough and gradual pathway to this objective. The intermediary tasks and objectives have been laid out and a significant amount of observational data has already been acquired and is fully available to be explored from day one.

The expertise gained through this project will give the PhD the ability to efficiently reduce and explore nIR spectroscopic data, an emerging field in astronomy, in particular in the domain of extrasolar planets. The results of this project will be used for the science verification of two upgraded infrared instruments: CRIRES+ and VISIR (both at the VLT-ESO).

Notes: This topic requires a mixed fellowship (up to one year in ESO-Chile). This topic is also offered as topic 501, under the thematic line on Instrumentation.