The relation between discs and young companions - Observational studies

The direct imaging technique brings advantages with respect to other, indirect methods of detecting planets. It is sensitive to larger separations, it can detect companions on a variety of orbital configurations, and it allows to simultaneously image both a companion and the circumstellar disc it resides in, thus being the perfect tool to study companion-disc interactions. Direct observations of Hα emission from young planetary and low-mass stellar companions can also shed light on the early gas accretion phase of planet formation. In this Thesis I use the direct imaging technique to study various aspects of planet-disc interaction and planet formation and evolution. I present the detection of a previously unknown low-mass stellar companion around HD 193571, observed as part of the NaCo Imaging Survey for Planets around Young Stars (ISPY). The companion appears to reside within the gap between the host star and its surrounding disc, making this the third low-mass stellar companion discovered within a debris disc. This system is thus the perfect laboratory where to study the relative importance between self- and companion-stirring models in discs. I also present the detection of Hα emission from the known substellar companion around the young star PZ Tel. The derived Hα luminosity, combined with age and disc information, indicates that the emission is likely due to chromospheric activity of the companion. This detection further proves the capability of using high-contrast imaging instruments and techniques to detect Hα signatures from companions around young stars. On a larger scale, I present the L’ band Imaging Survey to find Exoplanets in the North (LIStEN), which targeted ∼30 nearby stars with known and well characterised circumstellar discs. LIStEN focuses on characterising the population of wide-orbit giant planets around disc-hosting stars, as well as studying the intricacies of companion-disc interactions. I present the survey’s scientific goals, data selection and observational strategy, as well as the data reduction and analysis. No new planetary companions were detected, and the mass detection limits derived from the observations are combined with information on the disc size and morphology to constrain the presence of unseen planetary and low-mass stellar companion around these disc-hosting stars

Analyzing directionality of influence among ensemble musicians using Granger Causality

In small musical groups, performers can seem to coordinate their movements almost effortlessly in remarkable exhibits of joint action and entrainment. To achieve a common musical goal, co-performers interact and communicate using non-verbal means such as upper-body movements, and particularly head motion. Studying these phenomena in naturalistic contexts can be challenging since most techniques make use of motion capture technologies that can be intrusive and costly. To investigate an alternative method, we analyze video recordings of a professional instrumental ensemble by extracting trajectory information using pose estimation algorithms. We examine Kansei perspectives such as the analysis of non-verbal expression conveyed by bodily movements and gestures, and test for causal relationships and directed influence between performers using the Granger Causality method. We compute weighted probabilities representing the likelihood that each performer Granger Causes co-performers’ movements. Effects of different aspects of musical textures were examined and results indicated stronger directionality for homophonic textures (clear melodic leader) than polyphonic (ambiguous leadership)

Detection of Hα emission from PZ Telescopii B using SPHERE/ZIMPOL

Hα is a powerful tracer of accretion and chromospheric activity, which has been detected in the case of young brown dwarfs and even recently in planetary mass companions (e.g. PDS70 b and c). Hα detections and characterisation of brown dwarf and planet companions can further our knowledge of their formation and evolution, and expanding such a sample is therefore our primary goal. We used the Zurich Imaging POLarimeter (ZIMPOL) of the SPHERE instrument at the Very Large Telescope (VLT) to observe the known 38−72 MJ companion orbiting PZ Tel, obtaining simultaneous angular differential imaging observations in both continuum and narrow Hα band. We detect Hα emission from the companion, making this only the second Hα detection of a companion using the SPHERE instrument. We used our newly added astrometric measurements to update the orbital analysis of PZ Tel B, and we used our photometric measurements to evaluate the Hα line flux. Given the estimated bolometric luminosity, we obtained an Hα activity (log(LHα/Lbol)) between −4.16 and −4.31. The Hα activity of PZ Tel B is consistent with known average activity levels for M dwarf of the same spectral type. Given the absence of a known gaseous disk and the relatively old age of the system (24 Myr), we conclude that the Hα emission around PZ Tel B is likely due to chromospheric activity

LIStEN:

Context. Planetary systems and debris discs are natural by-products of the star formation process, and they affect each other. The direct imaging technique allows simultaneous imaging of both a companion and the circumstellar disc it resides in, and is thus a valuable tool to study companion-disc interactions. However, the number of systems in which a companion and a disc have been detected at the same time remains low. Aims. Our aim is to increase this sample, and to continue detecting and studying the population of giant planets in wide orbits. Methods. We carry out the L′ band Imaging Survey for Exoplanets in the North (LIStEN), which targeted 28 nearby stars: 24 are known to harbour a debris disc (DD) and the remaining 4 are protoplanetary disc-hosting stars. We aim to detect possible new companions, and study the interactions between the companion and their discs. Angular differential imaging observations were carried out in the L′ band at 3.8 μm using the LMIRCam instrument at the LBT, between October 2017 and April 2019. Results. No new companions were detected. We combined the derived mass detection limits with information on the disc, and on the proper motion of the host star, to constrain the presence of unseen planetary and low-mass stellar companion around the 24 disc-hosting stars in our survey. We find that 2 have an uncertain DD status and the remaining 22 have disc sizes compatible with self-stirring. Three targets show a proper motion anomaly (PMa) compatible with the presence of an unseen companion. Conclusions. Our achieved mass limits combined with the PMa analysis for HD 113337 support the presence of a second companion around the star, as suggested in previous RV studies. Our mass limits also help to tighten the constraints on the mass and semi-major axis of the unseen companions around HD 161868 and HD 8907

Planet populations inferred from debris discs: insights from 178 debris systems in the ISPY, LEECH and LIStEN planet-hunting surveys

We know little about the outermost exoplanets in planetary systems, because our detection methods are insensitive to moderate-mass planets on wide orbits. However, debris discs can probe the outer-planet population, because dynamical modelling of observed discs can reveal properties of perturbing planets. We use four sculpting and stirring arguments to infer planet properties in 178 debris-disc systems from the ISPY, LEECH and LIStEN planet-hunting surveys. Similar analyses are often conducted for individual discs, but we consider a large sample in a consistent manner. We aim to predict the population of wide-separation planets, gain insight into the formation and evolution histories of planetary systems, and determine the feasibility of detecting these planets in the near future. We show that a `typical' cold debris disc likely requires a Neptune- to Saturn-mass planet at 10-100 au, with some needing Jupiter-mass perturbers. Our predicted planets are currently undetectable, but modest detection-limit improvements (e.g. from JWST) should reveal many such perturbers. We find that planets thought to be perturbing debris discs at late times are similar to those inferred to be forming in protoplanetary discs, so these could be the same population if newly formed planets do not migrate as far as currently thought. Alternatively, young planets could rapidly sculpt debris before migrating inwards, meaning that the responsible planets are more massive (and located further inwards) than debris-disc studies assume. We combine self-stirring and size-distribution modelling to show that many debris discs cannot be self-stirred without having unreasonably high masses; planet- or companion-stirring may therefore be the dominant mechanism in many (perhaps all) debris discs. Finally, we provide catalogues of planet predictions, and identify promising targets for future planet searches.Comment: 41 pages, 16 figures, accepted for publication in A&

Musei italiani del dopoguerra (1945-1977). Ricognizioni storiche e prospettive future

Gli anni della ricostruzione nel secondo dopoguerra hanno consegnato al Paese una stagione irripetibile del museo, rinnovato nella sua forma così come nei contenuti. Di quel periodo il volume intende fornire una riflessione storico-critica relativa alla tenuta odierna della proposta culturale e al contempo sui problemi di restauro e di rifunzionalizzazione di quei musei attualmente in corso. L’importanza, riconosciuta a livello internazionale, dei progetti di architetti quali Carlo Scarpa, Franco Albini, Franco Minissi, non sottrae infatti le istituzioni museali nate all’epoca dalle esigenze contemporanee di una loro riorganizzazione dettata da mutati livelli qualitativi e standard di comunicazione aggiornati.Quali possano essere le soluzioni da adottare, nel dovuto rispetto di quanto costituisce tuttora un modello esemplare della museologia e della museografia italiane, è quanto si propongono di verificare i saggi raccolti nel libro, tenendo conto del cambiamento radicale della missione del museo sempre più orientato verso un’ampia accessibilità, nuove pratiche e uno statuto nuovo delle proprie collezioni. Il volume raccoglie i contributi scientifici del primo anno del Corso di Alta Formazione di Museologia e Museografia tenuto a Palazzo Butera a Palermo nel 2020, diretto da Valter Curzi e organizzato dal Dipartimento SARAS dell'Università di Roma "La Sapienza" in convenzione con Palazzo Butera, Francesca & Massimo Valsecchi Collection, con il patrocinio di Fondazione Roma Sapienza, MAXXI, SISCA

ISPY-NACO imaging survey for planets around young stars: Survey description and results from the first 2.5 years of observations

ontext. The occurrence rate of long-period (a ≳ 50 au) giant planets around young stars is highly uncertain since it is not only governed by the protoplanetary disc structure and planet formation process, but also reflects both dynamical re-structuring processes after planet formation as well as possible capture of planets not formed in situ. Direct imaging is currently the only feasible method to detect such wide-orbit planets and constrain their occurrence rate. Aims. We aim to detect and characterise wide-orbit giant planets during and shortly after their formation phase within protoplanetary and debris discs around nearby young stars. Methods. We carry out a large L′-band high-contrast direct imaging survey for giant planets around 200 young stars with protoplanetary or debris discs using the NACO instrument at the ESO Very Large Telescope on Cerro Paranal in Chile. We use very deep angular differential imaging observations with typically >60° field rotation, and employ a vector vortex coronagraph where feasible to achieve the best possible point source sensitivity down to an inner working angle of about 100 mas. This paper introduces the NACO Imaging Survey for Planets around Young stars (NACO-ISPY), its goals and strategy, the target list, and data reduction scheme, and presents preliminary results from the first 2.5 survey years. Results. We achieve a mean 5 σ contrast of ΔL′ = 6.4 ± 0.1 mag at 150 mas and a background limit of L′bg = 16.5±0.2 mag at >1.′′5. Our detection probability is >50% for companions with ≳8 MJup at semi-major axes of 80–200 au and >13 MJup at 30–250 au. It thus compares well to the detection space of other state-of-the-art high-contrast imaging surveys. We have already contributed to the characterisation of two new planets originally discovered by VLT/SPHERE, but we have not yet independently discovered new planets around any of our target stars. We have discovered two new close-in low-mass stellar companions around R CrA and HD 193571 and report in this paper the discovery of close co-moving low-mass stellar companions around HD 72660 and HD 92536. Furthermore, we report L′-band scattered light images of the discs around eleven stars, six of which have never been imaged at L′-band before. Conclusions. The first 2.5 yr of the NACO-ISPY survey have already demonstrated that VLT/NACO combined with our survey strategy can achieve the anticipated sensitivity to detect giant planets and reveal new close stellar companions around our target stars.ISSN:0004-6361ISSN:1432-074