LIST OF POSSIBLE THESIS WITH INAF GRANT FOR XXXIII CYCLE

Supernovae super luminose, Hypernovae and Dark Energy
S. Benetti, F.Bufano

Collaborations: "Public ESO Spectroscopic Survey for Transient Object"(PESSTO);
“NOT Unbiased Transient Survey" (NUTS).
In the last years a new class of extremely energetic transients has been discovered: theSuper Luminous Supernovae (SLSNe). These  transients can be hundred of times more luminous than the most luminous supernovae (Benetti et al. 2014, MNRAS 441, 289). Their central  engine is still unknown, however several hypothesis have been proposed.
The more promising ones are: the pair-instability explosions; the spin-down of a magnetar which is the remnant of the core-collapse of the progenitor star; the interaction of the supernova ejecta with a circum-stellar material expelled by the progenitor star during the final phases of its evolution. The central engine of a SLSNe is in any case associated to a powerful explosion, even more powerful then the explosions connected to long-GRBs (also called hypernovae; Bufano et al. 2012, ApJ 753, 67 ). We, then, proposed to study a sample of SLSNe, hypernovae and also SNe with luminosity in between the two classes. Develop physical models for the different scenarios, and also look for new diagnostic tools (for example, in the radio domain) in order to discriminate among the different proposed scenarios.
The thesis goals will then be:
a) Multi-wavelength monitoring from UV to radio of a sample of energetic SNe with the instruments available to the Padova-Asiago SN group.
b) Data reduction and their analysis.
c) Develop new theoretical tools in collaboration with qualified scientists of our Institutes to probe the different proposed scenarios.
d) Eventually understand the engine supporting these huge explosions, thus checking their use as cosmological standard candles up to z~5.  This in turn could help shedding light into the Dark Energy mystery

Study of the link between planets and circumstellar disks
S. Desidera, F. Marzari, E. Rigliaco

The formation of planets arises in the circumstellar disks. How the disk properties drive the process of planet formation and how planets are responsible of features observed in several disks (spiral arms, rings, belts) is far being understood. The recent development of high-contrast imaging instruments, like SPHERE at VLT, LMIRCAM and in near-future SHARK at LBT)  allows on one hand to extend the sensitivity in the detection of planets and on the other to spatially resolve circumstellar disks with unprecedented details. In this context we propose a PhD program focused on the study of the link between presence of planets and disk characteristics at various evolutionary phases, both on observational and theoretical sides. The observational part will be mostly based on dataset acquired with SPHERE, as part of the GTO program (260 nights, mostly devoted to disk and planets). The PhD student will become member of the SPHERE  Consortium and will contribute to GTO duty activities (observations, data reduction). From the theoretical point of view, the development of dedicated codes for the study of interactions between planets and disks is foreseen.  Specific efforts will be devoted to multi-component debris disks. The presence of planets is the most likely origin of this architecture. The masses and orbital properties of planets that could be responsible for sculpting these belts will be derived. Comparison with observations will allow to address  statistically the hypothesis that the gap between belts is due to the presence of planets.

Resolved stellar populations into the LSST+WFIRST era
L. Girardi, P.Marigo

Abstract: The Large Synoptic Survey Telescope (LSST) and NASA's Wide Field Infrared Survey Telescope (WFIRST) will soon start a new 
revolution in the fields of stellar populations and "Local Group archaelogy", by providing unprecedentedly-deep data for an unprecedently-wide area, from blue to near-infrared wavelengths. LSST will image the Southern sky in 5 passbands every 4 days, providing the largest-ever stellar catalogue after just a few months of operation; at later times it will produce extremely rich information on stellar variability, proper motions, and parallaxes. WFIRST will couple its difraction-limited near-infrared imaging with a very wide  field-of-view, carrying on surveys of large sections of the Milky Way (MW) and also targetted observations of nearly all neighboring galaxies. These data will provide the depth and statistics needed to completely map the MW and everything englobed in its halo out to hundreds of kiloparsecs. We propose a PhD thesis aimed at building the model-fitting tools necessary to convert the LSST+WFIRST data for several billions of stars into stellar population 3D densities and kinematics, star formation histories, constraints to stellar models, etc. The proponents of this thesis are deeply involved in pre-survey simulations of both LSST and WFIRST surveys, and committed to provide stellar models to several of their working groups. The project includes many collaborations around the globe, but mainly with the Seattle's MW working group.

Unraveling the formation of star clusters: a science case for the E-ELT

M. Mapelli

Young star clusters are the places where most stars (and especially massive stars) form in the local Universe. They  host the most massive stars we know (>100 Msun), and give us a unique opportunity to investigate the initial mass function, as well as the dynamics of stars: dense star clusters are the only astrophysical environment where stellar collisions are likely. Our knowledge of dense young star  clusters beyond the Milky Way is  hampered by the resolution of available telescopes. Forthcoming 30m class telescopes (such as the E-ELT) will open a new window on extra-galactic young star clusters, thanks to their exquisite spatial resolution.  The aim of this project is to produce accurate photometric and kinematic models of young dense star clusters in the Local Group, in preparation for E-ELT observations. To reach this goal, the PhD student will investigate the structural and kinematic properties of young massive star clusters  by means of advanced hydro-dynamical simulations. Then, the student will produce mock observations of these models, and will analyze them with the same pipeline that will be used for first-light instruments at E-ELT. More details on our group and on these topics can be found at web.pd.astro.it/mapelli/group.html

Extremely accreting quasars and cosmology  

P. Marziani, P. Mazzei, M. D'Onofrio

Quasars are among the most luminous sources in the Universe. There are still many enigmas on their inner workings; in addition, a large spread in luminosity has hampered their use for cosmological studies. However, several very recent works suggest that it may be possible to exploit a particular class, extremely accreting quasars, as cosmological distance indicators. The student will start from the definition and analysis of a large sample of highly accreting quasars in terms of optical UV and soft-X-ray properties from survey and archival data (SDSS, BOSS, MAST, etc.) and already collected Gran Telescopio Canaries observations. The project will first lead to results on the physical and structural parameters of extremely accreting quasars that are presently poorly understood and that are at the basis of luminosity estimates. Results will then be applied to derive estimates of the principal cosmological parameters with a proper  analysis of statistical and systematic effects. The project involves collaborations with researchers at IAA (Spain) and UNAM (Mexico). In 3 years the student will acquire a culture on important theoretical and phenomenological aspects of quasars, the ability to analyze and measure spectroscopic multifrequency data as well as to apply methods commonly used in observational cosmology. The prospect of the  thesis is to give a relevant contribution to a frontier field that will open further lines of research on AGNs and in observational cosmology.

The hottest stellar atmospheres and their violent outflows
Marina Orio. Possible co-tutoring, to be finalized, by Dr. Jan-Uwe Ness, of the Science Operations Division, Science Operations Department of ESA, ESAC.

This project is based on a rich, challenging and very interesting dataset of novae in outburst, obtained with X-ray gratings between 2000 and 2017 by Orio, her graduate students and collaborators,and by two other groups (now these observations are available in the HEASARC archive). Not all the spectra have been published yet, and in many cases the analysis has been qualitative more than quantitative, for lack of adequate models. We also discovered new spectral lines, that were not predicted yet by current atomic physics. All the data (included those of the other groups) are available in the archives. More spectra will most likely be collected in the course of the thesis, taking advantage of new outbursts of luminous novae in the Galaxy and in the Magellanic Clouds. Thus, the graduate student will practice writing research proposals. Some new data should also be obtained at other wavelengths, because the connection with  the whole electromagnetic spectrum is fundamental. For instance, the optical range gives rich information on the physical parameters of the binary and about the shape of the ejecta, the radio clarifies the dynamics of the mass outflows, and the gamma rays probe the most violent phenomena in the nova ejecta.
The high resolution X-ray spectra show emission from the very hot and luminous  white dwarf of a nova system after the outburst, while it is still burning hydrogen in shell. There is also a residual outflow and the initial ejecta, far from the white dwarf also emit X-rays because of colliding and/or clumpywinds. Thus, a complete model of the spectra involves atmospheric, wind models and models of plasma in collisional ionization equilibrium.
The thesis may have either a phenomenological-theoretical orientation, or focus instead on the atomic physics of the spectra and the observational aspects. Probably the work will be a combination of the two approaches. The student is expected to spend two predoctoral periods of a few months at ESAC in Spain and the University of Wisconsin in the US.

Real supernovae and supernova impostors
A.Pastorello and Padova-Asiago Supernova Group

With the label of "supernova impostors" we refer to a family of eruptive variables with observed properties resembling those of true supernovae. However, contrary to genuine supernova explosions, impostors reach fainter absolute magnitudes (below -15), and the progenitor stars (which are thought to be "luminous blue variables" or -more rarely- early Wolf-Rayet stars) survive the eruptive episodes. Discrimination between impostors and real supernovae is sometimes tricky. Recent observational evidences suggest a tight  correlation between impostors and a class of supernovae whose ejecta interact with dense circum-stellar medium (CSM). These interacting supernovae are of type IIn (when the CSM is hydrogen-rich) and of type Ibn (when the CSM is hydrogen-poor and helium-rich). The former have been linked with luminous blue variable precursors, the latter with Wolf-Rayet stars. Observational evidences suggest that the  progenitors of these supernovae experienced enormous mass loss events a very short time (months to a few years) before the core-collapse.  In some cases, stellar outbursts are observed a short time before the terminal supernova explosion. In other words, real supernovae may occasionally be heralded by an outburst (i.e. supernova impostor). The PhD thesis project consists in analyzing data of recent supernova impostors and/or real interacting supernovae, including the inspection of pre-discovery archive images with the aim of recovering the  pre-burst variability history. The Padova Supernova Group has a strategic role in the "Public ESO Spectroscopic Survey for Transient Object" (PESSTO) collaboration which will provide hundreds of new objects in the next 5 years, and the subject of this thesis proposal well matches one of the key science cases approved by the PESSTO consortium. In addition, our team has independent approved proposals to  a number of telescopes to classify and follow new transient events. The Padova Supernova Group has a strategic role in the "Public ESO Spectroscopic Survey for Transient Object" (PESSTO) collaboration which will provide hundreds of new objects in the next 5 years, and the subject of this thesis proposal well matches one of the key science cases approved by the PESSTO consortium. In addition, our team has  independent approved proposals to a number of telescopes to classify and follow new transient events.

Dissecting galaxy evolution with integral-field spectroscopy
Bianca Poggianti

A PhD project is offered to study galaxies that are losing or accreting gas based on integral-field spectroscopy obtained with the MUSE spectrograph at the VLT. GAS (GAs Stripping Phenomena in galaxies with MUSE) is an ESO Large Program aimed at understanding why and how gas flows in and out of galaxies.
Galaxy evolution is regulated by the availability of gas, and this is one of the hottest topics in extragalactic astronomy today.
The student will have the opportunity to work on state-of-the-art spectroscopic data of excellent quality, and will be part of an international team that, in addition to the VLT Program, has obtained follow-up multi wavelength observations also of the neutral (JVLA) and molecular (APEX, and proposed ALMA) gas. GASP provides MUSE data for 114 galaxies in galaxy clusters, groups and the field in the nearby Universe, and consists of a sample of galaxies with optical signatures for gas removal processes plus a control sample of regular galaxies with no signs of gas disturbance.
The student will analyse the MUSE data to understand the stellar and the ionised gas components of galaxies, and will investigate the link between stellar content, star formation activity, and the various gas phases (ionised, neutral and molecular). He/she will acquire a deep and wide knowledge in this field of research and will gain expertise on observational techniques -- such as integral-field spectroscopy -- that are at the forefront of astrophysical research today.