HIP10680/HIP10679: a visual binary in the β\beta Pictoris Association with the fastest rotating member

We present the results of a multi-filter photometric monitoring of the wide binary HIP10680/HIP10679. We found both component to be variable with amplitude up to $\Delta$V = 0.03 mag in the case of HIP10680 and $\Delta$V = 0.07 mag in the case of HIP10679. We could measure the rotation periods P = 0.2396d of the hotter F5V component HIP10680 and P = 0.777d of the cooler G5V component HIP10679. We found that the rotation axes of both components are aligned with an inclination $i$ = $\sim$ 10$^{\circ}$. Although the two components have a mass difference not larger than 15%, they exhibit a significant difference between their rotation periods. Such difference may arise either from different initial rotation periods or to different disc life times. For instance, the slower rotating component HIP 10679 hosts a well know debris disc.Comment: In press by IBVS in Information Bulletin on Variable Stars, 201

Photometric study of HD 155555 C in the β\beta Pictoris Association

We are carrying out a series of photometric monitoring to measure the rotation periods of members in the young $\beta$ Pictoris Association, as part of the RACE-OC project (Rotation and ACtivity Evolution in Open Clusters). In this paper, we present the results for HD 155555C which is believed to be physically associated to the spectroscopic binary V824 Ara (HD155555) and thus constituting a triple system. We collected B, V, and R-band photometric data timeseries and discovered from periodogram analysis the rotation period P = 4.43d. Combined with stellar radius and projected rotational velocity, we find this star almost equator-on with an inclination $i$ $\simeq$ 90$^{\circ}$. The rotational properties of HD155555C fit well into the period distribution of other $\beta$ Pic members, giving further support to the suggested membership to the association and to its physical association to V824 Ara. A comparison with Pre-Main-Sequence isochrones from various models allows us to estimate an age of 20$\pm$15 Myr for this triple system.Comment: 16 pages, 7 figure

Impact of photometric variability on age and mass determination of Young Stellar Objects: A case study on Orion Nebula Cluster

In case of pre-main sequence objects, the only way to determine age and mass is by fitting theoretical isochrones on color-magnitude (alternatively luminosity-temperature) diagrams. Since young stellar objects exhibit photometric variability over wide range in magnitude and colors, the age and mass determined by fitting isochrones is expected to be inaccurate, if not erroneous. These in turn will badly affect any study carried out on age spread and process of star formation. Since we have carried out very extensive photometric observations of the Orion Nebula Cluster (ONC), we decided to use our multi-band data to explore the influence of variability in determining mass and age of cluster members. In this study, we get the amplitudes of the photometric variability in V, R, and I optical bands of a sample of 346 ONC members and use it to investigate how the variability affects the inferred masses and ages and if it alone can take account for the age spread among the ONC members reported by earlier studies. We find that members that show periodic and smooth photometric rotational modulation have their masses and ages unaffected by variability. On other hand, we found that members with periodic but very scattered photometric rotational modulation and members with irregular variability have their masses and ages significantly affected. Moreover, using Hertzsprung-Russell (HR) diagrams we find that the observed I band photometric variability can take account of only a fraction (about 50%) of the inferred age spread, whereas the V band photometric variability is large enough to mask any age spread.Comment: Accepted by MNRAS; 17 pages, 4 Tables, 15 Figure

Evidence from stellar rotation for early disc dispersal owing to close companions

Young low-mass stars of equal-mass exhibit a distribution of rotation periods. At the very early phases of stellar evolution, this distribution is set by the star-disc locking mechanism. The primordial disc lifetime and, consequently, the duration of the disc-locking mechanism, can be significantly shortened by the presence of a close companion, making the rotation period distribution of close binaries different from that of either single stars or wide binaries. We use new data to investigate and better constrain the range of ages, the components separation and the mass ratio dependence at which the rotation period distribution has been significantly affected by the disc dispersal that is enhanced by close companions. We select a sample of close binaries in the Upper Scorpius association (age $\sim$8 Myr) whose components have measured the separation and the rotation periods and compare their period distribution with that of coeval stars that are single stars. We find that components of close binaries have on average rotation periods shorter than single stars. More precisely, binaries with about equal-mass components (0.9 $\le$ M2/M1 $\le$ 1.0) have rotation periods on average by $\sim$0.4 d shorter than single stars; binaries with smaller mass ratios (0.8 $<$ M2/M1 $<$ 0.9) have rotation periods on average by $\sim$1.9 d the primary components, and by $\sim$1.0 d the secondary components shorter than single stars. A comparison with the older 25-Myr $\beta$ Pictoris association shows that, whereas in the latter all close binaries with projected separation $\rho$ $\le$ 80 AU all rotate faster than single stars, in the Upper Scorpius that has happened for about 70% stars, yet. We interpret the enhanced rotation in close binaries with respect to single stars as the consequence of an early disc dispersal induced by the presence of close companions.Comment: 7 pages, 5 figures, 1 table, Accepted by Astronomy & Astrophysic

On the rotation periods of the components of the triple system TYC9300-0891-1AB/TYC9300-0529-1 in the Octans Association

Stellar rotation depends on different parameters. The range of values of these parameters causes the dispersion in the rotation period distributions observed in young stellar clusters/associations. We focus our investigation on the effects of different circumstellar environments on stellar rotation. More specifically, we are searching in stellar Associations for visual triple systems where all stellar parameters are similar, with the only exceptions of the unknown initial rotation period, and of the circum-stellar environment, in the sense that one of the two about equal-mass components has a close-by third 'perturber' component. In the present study we analyse the 35-Myr old visual triple system TYC 9300-0891-1AB + TYC 9300-0529-1 in the young Octans stellar association consisting of three equal-mass K0V components. We collected from the literature all information that allowed us to infer that the three components are actually physically bound forming a triple system and are members of the Octans Association. We collected broad-band photometric timeseries in two observation seasons. We discovered that all the components are variable, magnetically active, and from periodogram analysis we found the unresolved components TYC 9300-0891-1AB to have a rotation period P = 1.383d and TYC 9300-0529-1 a rotation period P = 1.634d. TYC 9300-0891-1A, TYC 9300-0891-1B, and TYC 9300-0529-1 have same masses, ages, and initial chemical compositions. The relatively small 16% rotation period difference measured by us indicates that all components had similar initial rotation periods and disc lifetimes, and the separation of 157AU between the component A and the 'perturber' component B (or vice-versa) has been sufficiently large to prevent any significant perturbation/shortening of the accretion-disc lifetime.Comment: Accepted by New Astronomy 201

Il concetto di 'democrazia ecologica' nel dibattito filosofico e giuspolitico contemporaneo. Tra autorità e libertà, comunità e natura

2013 - 2014My thesis is based on the philosophical-scientific notion of "epistemic complexity" and how that has been "incorporated" in the contemporary environmental law that has already an "interdisciplinary" nature, since on the border between law, science, ethics and economics. It constitutes the "scene" where the need of reweaving the idea of development, unlimited growth and progress manifests both at national and international level through a reorientation of the objectives and the economical political strategies of the last forty years . A key element of this "legal branch" is represented by the precautionary principle (expressly recognized as "mandatory" by the international community since 1992 in the Rio de Janeiro Declaration), which provides a general "duty to act" for the protection of the environment, even if there is no absolute certainty of the risk of serious and irreparable damage. Therefore, several responsibilities arise from both the political decision makers and in the scientific and economic world relatively to the possible risks that a particular "community" could face, accepting the relative consequences. For this reason even not "sectorial" mind-sets appear gradually at substantial legal level of the natural environment, as well as a conception of "strong" environmental sustainability (and "ecological modernization"), not limited to a mere "technical adjustment", nor to precautionary action on an economic cost-benefit analysis of environmental protection; procedurally new "forms" and "spaces" of deliberative "reflexive" democracy (i.e. not simply "pragmatic" ones) are created where rights to information, participation, access to the courts can be practiced more broadly beyond individual preferences of people, not only towards an "individualistic" or "communitarian" perception, but also towards an "ecological" one (inter-relationships between parts and the whole, where the whole has not to be interpreted as the mere sum of the parts). Forms and spaces of an "ecological democracy" which find again in the state, and particularly in a not "interventionist" and not "competitive" state, not enslaved to the logic of competition, market and "financial thinking", their starting point and contemporaneously their "development". At the same time they should and could turn even the state itself into a continuous "process", within "deliberative systems" (on a "transnational" scale), focused on "anthropo-decentralized" ethics. The experiences of Andes neo-constitutionalism (Ecuador and Bolivia cases particularly) finally mark the transition to a new "state based" paradigm oriented to the concept of "multinationality" where "Western" and "indigenous" ideas of “Nature” are harmonized, encouraging to enrich in this way the "systemic" framework for a possible transnational "ecological democracy" towards new ways of considering law, economy, welfare and happiness, different from the material accumulation or simply from the mere "personal life plan"; in other terms towards a new "common sense" and a new "right" to an alternative form of individual and collective life. [edited by Author]XIII n.s

International Student Mobility: An Identity Development Task?

Based on the review of literature on internationalization of education and on identity formation pro cesses in young adults, this cross - sectional study aims to investigate to which extent self - perceived dimensions of identity are associated to the main moti vations to study abroad. The participants in this study were 429 international university students of different nationalities. Findings revealed that the motivation to study abroa d for personal growth is strongly associated to the commitment and in - depth e xploration identity processes, whereas the motivation to study abroad with the aim of changing life style and enlarging job opportunities is positively associated with reconsideration of commitment and in - depth exploration. Furthermore, identity achieved s tudents showed the highest motivation to s tudy abroad for personal growth, while the motivation to study abroad to positively change life - styles and work conditions is strongly associated with the positive facet of identity crisis, which is otherwise calle d searching - moratorium status. Based on these results, the present survey provides useful questions and hypothesis for future researc

The visual binary AG Tri in β\beta Pictoris Association: can a debris disc cause very different rotation periods of its components?

We measure the photometric rotation periods of the components of multiple systems in young stellar associations to investigate the causes of the observed rotation period dispersion. We present the case of the wide binary AG Tri in the 23-Myr young beta Pictoris Association consisting of K4 + M1 dwarfs. Our multi-band, multi-season photometric monitoring allowed us to measure the rotation periods of both components P_A = 12.4d and P_B = 4.66d, to detect a prominent magnetic activity in the photosphere, likely responsible for the measured radial velocity variations, and for the first time, a flare event on the M1 component AG Tri B. We investigate either the possibility that the faster rotating component may have suffered an enhanced primordial disc dispersal, starting its PMS spin-up earlier than the slower rotating component, or the possibility that the formation of a debris disc may have prevented AG Tri A from gaining part of the angular momentum from the accreting disc.Comment: 28 pages, 7 figures, accepted for publication in Astrophysics and Space Science 2015, (ASTR-D-15-00445R2