Exoplanets and exoplanetary systems

Search and characterization of exoplanets using SPHERE and other direct-imaging instruments. Search for extrasolar planets
S. Desidera, R. Gratton , R. Claudi, M. Turatto



In the coming years a dramatic improvement in the capabilities for direct detection and characterization of exoplanets is expected, thanks to the availability of new, dedicated instrumentation. SPHERE at VLT, whose commissioning is in progress, will have a leading role in this new era. OAPD team is heavily involved in the SPHERE GTO survey (260 VLT nights over 5 years) with relevant contribution on various themes, from selection and characterization of targets, to data analysis for planet detection, planet characterization and survey statistical analysis, on which there is ample room for a PhD thesis. The activities of the team are complemented with ongoing observations using the AO system at LBT and with the technical and science definition of the next-generation planet imager EPICS for E-ELT, then ensuring a long-time perspective for the work. A second possible thesis concerns the possibility to implement a high-resolution spectroscopic mode in the integral field spectrograph (IFS) for the high contrast imager PCS for E-ELT. The goal of this method is to detect molecular bands such as those due to O2 or H2O by cross-correlating template spectra with individual spectra obtained with the IFS. In principle, this method allows coupling the best possible techniques for planet detection, and it appears as the best possible method to achieve the high prized goal of characterizing life friendly atmospheres. The thesis will examine various points:
 a) the technical feasibility of the method and the specifications to be put on the instrument; this includes a preliminary opto-mechanical design of the instrument and a discussion of the main sources of noise, including photon, detector, thermal background, and speckle noise;
 b) the best possible spectral bands to be used - taking into consideration the impact of absorption due to the Earth atmosphere on the observations - and the information about the actual presence of life that can be retrieved from their use;
 c) the practical realization and scopes of forerunners on 8 meter telescopes, such as a high spectral resolution mode for SPHERE. For this thesis, we plan to have long term stays in Leiden (to work with the team of I. Snellen), Oxford (to work with the team of N. Thatte) and Garching (to work with the responsible of the PCS project M. Kasper).

Searching for planets around young stars using GIARPS
S. Desidera,R. Claudi, R. Gratton, L. Malavolta

Discovery of young planets is a crucial step to understand the formation and migration mechanisms affecting planets at formation epochs. Magnetic activity of young stars represents a strong limitation for the search of such planets using the radial velocity (RV) method. New perspectives in this field are now open by the recent availability of GIARPS (GIAno & haRPS-n), the new common feed for both the high-resolution spectrographs of the Telescopio Nazionale Galileo (TNG) in La Palma (Canary Islands), i.e. HARPS-N in the visible (VIS) and GIANO in the near-infrared (NIR). The unique chance of simultaneous VIS+NIR high-precision RV measurements allows the exploitation of the wavelength dependence of activity-related signals (which are expected to be significantly lower in the NIR) to disentangle the origin of RV variations of young stars and characterize planetary masses with unprecedented precision.
We propose a PhD program focused on the search for exoplanets around young stars using GIARPS. The PhD candidate will develop new activity indices over the whole VIS+NIR spectrum and test their performances at varying observing conditions and spectral types. He will also explore multi-wavelength modeling of activity and planetary signals using state-of-the-art statistical tools (Bayesian analysis, Gaussian processing, etc.)
The PhD student will become member of the GAPS Collaboration and will have the possibility of carrying out observation at the TNG. First scientific outcomes on the main science goals are expected within the PhD horizon.


Planets around the Monster
M. Mapelli

Recent theoretical models by our group and recent radio observations indicate that protoplanetary discs exist in the central parsec of our Galaxy. Such protoplanetary discs are exposed to intense ultra-violet radiation from the massive stars in the Galactic center and can be affected by super-massive black hole tidal shear. The student will perform hydrodynamical simulations of protoplanetary discs, to understand whether they can survive and lead to the formation of planets in the Galactic center. Moreover, the student will perform N-body simulations and analytical calculations, to estimate the probability that such planets are captured and disrupted by the supermassive black hole. These results will give important predictions for future X-ray missions (ATHENA) and for the 30m class telescopes (e.g. E-ELT).
 More details on our group and on these topics can be found at web.pd.astro.it/mapelli/group.html



Exoplanet migration by interaction with the circumstellar disk
F. Marzari

The presence of giant planets orbiting very close to their star and compact super-Earth planetary systems, like the Trappist one, can be explained only by invoking planet migration. The bodies originally formed in the outer regions of the circumstellar disk and migrated inside by dynamically interacting with the surrounding gas of the disk in which they are embedded. The PhD project will focus on the different aspects of the two type of migration: type I typical of low mass planets and type II characteristic of giant planets carving a gap in the disk. Hydrodynamical simulations will be performed, either with fixed grid codes like PLUTO and FARGO or with SPH codes (Phantom or Seren), to investigate the coupled evolution of two planets, their potential resonance trapping or the occurrence of planet-planet scattering while performing convergent migration. The dependence of the different dynamical evolutionis on the thermal structure of the disk will be investigated, in particular including the effects of stellar heating which may be relevant in aged disks. The effects of one or two resonant planets on the dust distribution within the disk will also be explored to outline potential observable features revealing the presence of the planet from disk images.

Astrometric search for exo-planets using observations collected with Hubble Space Telescope observations of the closest neighbors of the Sun.
A.Milone, L. Bedin

Located at 2.0 pc, the L8+T1 dwarfs system Luhman16AB is the third closest system    known to Earth, making it a key benchmark for detailed investigation of brown dwarf  atmospheric properties, thermal evolution, multiplicity and planet-hosting        frequency. We have collected HST data in spatial-scanning mode to obtain the most accurate annual    parallax of any brown dwarf to date, achieving an unprecedented accuracy of 1 part   in 10000 (50 micro-arcsecond) for each of the two components of Luh16, and to  constrain their absolute space motions with similar accuracy. Most importantly, we   will be able to confirm the giant planet candidate and to search for faint           companions co-moving with the targets, either resolved or through astrometric perturbations of the A-B orbital motion, the latter probing down to few              Earth masses.  Present-day ground-based direct imaging and AO facilities have fundamental limitations (field of view, PSF stability, differential chromatic effects, visibility) which introduce systematic and seasonal errors that are hard to          quantify, and which have already resulted many times in clamorous false alarm in the recent past. This is particularly true for faint and red objects.                                                                                                         Luhman 16A and B will be problematic for GAIA (faint, color, crowding, visibility),  and the collected (and pending) HST spatial-scanning mode observations will actually be an important complementary validation of the final GAIA catalog itself (expected 2020).  We expect the PhD student involved in this project to have a major and leading role in developing,  calibrate and testing the new techniques for these accurate measurements with HST.

Atmospheres of Extrasolar Planets
L. Malavolta, G. Piotto

Although thousands of confirmed extrasolar planets are known to date, a clear and consistent picture of how they formed and evolved is still missing. Planetary systems discovered so far have revealed an astonishing diversity, not only in the physical/orbital parameters of the individual planets (mass, radius, density, eccentricity), but also in their overall architecture. Crucial information about the environment where planets formed, their subsequent migration, and their interaction with the host star is somehow encoded in the present physical state and chemical composition of their atmospheres. For this purpose, the most promising investigation technique is transmission spectroscopy, which allows us to probe the atmospheres of transiting planets hosted by bright and nearby stars on short orbits. High-resolution spectrographs in the visible and near-infrared range allow the detailed study of the spectral lines of the exoplanetary atmosphere, that can be exploited to get atomic/molecular abundances and to constrain the vertical structure and dynamics of the atmosphere.
Our group is actively involved in both types of observations, being part of the GAPS collaboration for the exploitment of GIARPS@TNG with privileged access to data, and part of several projects involving ESPRESSO@VLT. A thesis is offered with the aim of improving the reduction and analysis techniques to extract and interpret transmission spectra, in order to perform a homogeneous comparison of the properties of exoplanetary atmospheres of several planets in
a rigorous Bayesian framework. Such an approach would be particularly valuable to maximize the scientific yield of other freshly-commissioned or forthcoming facilities such as CARMENES@CAHA, PEPSI@LBT and CRIRES+@VLT, JWST and, in perspective, ARIEL.


Confirmation of Earth-like planets detected by TESS
L. Malavolta, G. Piotto

The Transiting Exoplanet Survey Satellite (TESS) has already discovered hundreds of small planet candidates that transit bright, nearby stars. While TESS can provide precise radii and orbital periods for many Earth-size planets, a spectroscopic follow-up from the ground is required in order to measure their mass and ultimately constrain their internal composition. As part of the HARPS-N Guaranteed Time Observations, our research group has access to 40 nights/semester at one of the most precise spectrograph in the world committed to the characterization of Earth-like planets using the radial velocity (RV) method, with already a large record of publications. A precise mass determination however has to take into account the fact of stellar activity, since the presence of spots and faculae on the stellar surface can introduce spurious signals in the RV time series and hamper our ability of detecting small planets.
We propose a PhD project that will guide the student through all the steps of planet discovery and characterization, starting from the identification of periodic signals in the TESS light-curve and vetting of the most promising targets for spectroscopic observations, followed by the determination of the photospheric parameters of the host star, the assessment of the stellar activity level, and finally the measurement of planetary mass and radius for each planet of the system to unveil their internal composition by comparing their position with respect to theoretical models in the mass-radius diagram. The student will become familiar with the most recent and experimental techniques to model the stellar interference in light curve and RV datasets, and he/she will become an expert on the state-of-the-art statistical tools applied to exoplanet science, including Bayesian analysis and Gaussian Processes. As part of this project, the PhD candidate will have the possibility of carrying out observations at the Italian 3.6m telescope Telescopio Nazionale Galileo (TNG) in La Palma (Canary Islands) and other facilities.
Statistical validation and ranking of exoplanetary candidates from
space-based missions

Validation and ranking of exoplanetary candidates from space-based missions
M. Montalto, G. Piotto

The advent of photometric, large scale, space-based surveys like TESS  (and in the upcoming future PLATO)  is dramatically increasing the number of known exoplanets and exoplanetary systems.
Currently,  our group is working on the follow-up of several planetary candidates,  mainly identified on TESS images with independent photometric analysis,  thanks  to our expertise on photometric data reduction. Efficient follow-up  strategies (e.g. radial velocities, for mass measurement) require candidate validation and ranking through a battery of different tests that can be initially performed on a statistical basis
comparing several candidates' properties with the ones of known  exoplanets. This is an essential tool that permits to identify the most promising  candidates and avoid waste of precious  observing time. The student is expected to first  analyze planetary candidates with state of the art publically  available software, and then to further improve it  specializing it to the case of TESS and PLATO and including  additional, complementary information avalable from  different sources (e.g. Gaia). He/she will be also actively involved  in the follow-up activities that our group is promoting, including observation at telescope.

Exoplanet search using TESS in preparation for CHEOPS and PLATO
G. Piotto, D. Nardiello

This is a thesis to exploit TESS data, mainly for the search of exoplanets based on the transit method. The main purpose of the work is searching for CHEOPS and radial velocity grondbased follow-up candidates.
TESS is successfully mapping the sky, and will complete its first (close to) all sky survey next on July 2020. Extension for 2 years of TESS operations has been approved.  Our group has a well-documented expertise on high precision photometry on space data that is priceless for exoplanetary studies. The proposed thesis project will allow the student to gain expertise on data reduction and analysis, starting from the techniques our group has developed to exploit crowded environments imaged by Kepler, K2 and then TESS. The main task of the PhD student will be to exploit TESS data. TESS exoplanet candidates may also become targets for CHEOPS follow-up. CHEOPS is an ESA mission, now in full operation, since April 2020. The gained expertise will also be of fundamental importance for the preparation of PLATO, an ESA space mission for exoplanet search, expected to be launched in 2026.
The PhD student will become part of a large international collaboration, as members of our group have top level responsabilities in both in CHEOPS and PLATO missions, as well as groundbased radial velocity follow-up facilities

The PLATO Input Catalog
M. Montalto, G. Piotto

Our group is deeply involved in PLATO (Planetary Transits and Stellar Oscillations), an ESA M3 space mission to be launched in 2026. PLATO will survey about half of the whole sky with exquisite photometric precision, aiming at discovering and characterizing thousands of transiting exoplanetary systems hosted by bright, nearby stars. Its main targets, dwarf and subgiant stars with a spectral type later than F5, must be selected in advance in order to optimize the observing strategy and the mission design. No existing catalogs of stellar parameters is both deep and wide enough to this purpose, but Gaia already started  delivering at least part of the needed information, and forthcoming GAIA data releases is expected to play a major role the preparation of the PLATO Input Catalog (PIC). A thesis is offered to identify PLATO targets and obtain their most relevant parameters using GAIA catalog as a basis, and then complementing the information with other photometric and spectroscopic catalogs. During the thesis, the student will also develop the algorithms for stellar classification which will be used both for the PIC, but, also and more in general, for stellar astrophysics studies.

Exoplanet search using the TTV/TDV method

L. Borsato, V. Nascimbeni, G. Piotto

A PhD thesis on TTV search of exoplanets is offered. The transit time variation (TTV) technique is a method to search for and characterize (including mass and orbital parameters) exoplanets in multiple exoplanet systems. Basically, it uses the variations of orbits - which cause changes in the transit times - due to the gravitational perturbations in a multiple-planet system. We have an ongoing observational program for the detection of planets using the TTV technique, and we have developed and are presently extending a program to interpret the TTV signal. A huge number of nights at Asiago, Teide and La Palma, as well as CTIO and La Silla telescopes have been assigned. This data set, and observations coming from TESS represent a formidable data base for TTV investigations. The TTV analysis software has already been applied to Kepler/K2 data. Two programs of observations with CHEOPS, based on TTV analysis of multiple transits observed by the satellite are under our responsibility. The PhD thesis will start from the developed expertise, and extend it to CHEOPS and TESS data, also in preparation for PLATO and ARIEL. The student will be trained for observations at the telescope. The student will be inserted in an international collaboration, as our group is responsible for the TTV analysis of CHEOPS, PLATO and ARIEL missions.