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



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
G. Piotto, V. Nascimbeni

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 and (spectro-)photometry, which allows us to probe the atmospheres of transiting planets hosted by bright and nearby stars on short orbits. Low- and high-resolution spectrographs in the visible and near-infrared range are highly complementary, enabling us to retrieve both the planetary continuum (that carries information about the presence of aerosols and clouds) at low resolution, and spectral lines (that can be exploited to get atomic/molecular abundances and to constrain the atmospheric vertical structure and dynamics) at high resolution.

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, being involved in the scientific preparation of satellites such as CHEOPS, PLATO and especially ARIEL, and finally having access to proprietary data from MODS@LBT and other low-resolution spectrographs at top-class observatories. A thesis is offered with the aim of improving the reduction and analysis techniques to extract and interpret transmission spectra, and testing those tools to optimally exploit proprietary and archival data in a homogeneous way. Such an approach would be particularly valuable to maximize the scientific yield of other freshly-commissioned or forthcoming facilities such as CARMENES, ESPRESSO, PEPSI, CRIRES+, JWST and, in perspective, ARIEL.

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

The Transiting Exoplanet Survey Satellite (TESS) has already discovered hundreds of small planetcandidates that transit bright, nearby stars in the Southern hemisphere, and in the next few months it will start observing the Northern hemisphere. 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.

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, in preparation for CHEOPS and PLATO.
TESS is successfully mapping the sky, and will complete its first (close to) all sky survey next year. The monitored regions cover many stellar clusters and there will be the unprecedented opportunity to search for transits in front of cluster stars. Our group has a well-documented expertise on high precision photometry in clusters that is priceless for exoplanetary studies because their age, chemistry and distance can be estimated way better than for field stars.
The work 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 K2 and then TESS in preparation for future planet-hunting and characterization of space missions such as PLATO  and ARIEL.  The main task of the PhD student will be to prepare the software, and then use it to exploit TESS data. TESS exoplanet candidates may also be followed-up by CHEOPS. CHEOPS is and ESA mission, scheduled for a launch in the second half of 2018. 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.

The PLATO Input Catalog
G. Piotto, M. Montalto

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 catalog 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
G. Piotto, V. Nascimbeni, L. Borsato

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 (Holman+ 2005, Science 307, 1288), 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. The PhD thesis will start from the developed expertise, and extend it to forthcoming (2018) 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.