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Nowadays, there is a rising interest in the packaging industry regarding more environment‐friendly (i.e. biodegradable and/or compostable) polymer‐based solutions, especially for film blowing applications. However, replacing traditional, fossil resource‐based polymers typically used for such applications is not an easy task, since the more environment‐friendly solutions must have adequate features in terms of processability and final properties. In this work, three commercial biodegradable (and, at least partially, biobased) polymers were investigated by a preliminary rheological and mechanical analysis, in order to perform film manufacturing experiments in laboratory equipment. Furthermore, oxygen and water vapour barrier properties were studied by permeability measurements. The investigation was ultimately performed on films produced in industrial equipment, and the results were compared to those for a typical, standard polypropylene (PP) film used in flexible packaging applications. It was found that the mechanical properties were adequate (in some cases, even up to 25–30% higher than for the PP counterpart), as well as oxygen permeability. On the other hand, water permeability was significantly higher than that of PP films, and this should be taken into account in cases where high water vapour barrier properties are required. © 2024 Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]

Space-born missions designed to search for exo-planets are providing us with high-precision photometric time series very well suited to measure the rotation period of solar- and lower-mass stars. Considering the large number of stars monitored during the mission life, the possibility to inspect each periodogram is out of question and, therefore, each method to search for rotation periods applied either individually or in combination is designed to automatically select the best rotation period estimate. In the case of unresolved binary stars it is possible to measure the rotation period of both components, when these are both variable and have comparable magnitude. On the other hand, the detection of two different rotation periods from the same photometric timeseries can represents a tool to unveil the binary nature of the star. In this paper, we present the case of the star TWA 23, a member of the young TWA association, as just one example of numerous cases. These may occur when the star is an unresolved binary and the variability of the secondary component is present in the time series. However, the frequency of the primary and dominant power peak in the periodogram, originating from the primary component, needs to be pre-whitened to allow the frequency of the secondary component to be detected. Considering the possible presence of undiscovered close binaries in the input catalogs of various ongoing or future missions aimed at exoplanet search, it becomes advisable to follow routinely this filtering approach to prevent to miss relevant information on the true binary nature of stars. [ABSTRACT FROM AUTHOR]

Context. Direct imaging of debris discs gives important information about their nature, their global morphology, and allows us to identify specific structures possibly in connection with the presence of gravitational perturbers. It is the most straightforward technique to observe planetary systems as a whole. Aims. We present the first resolved images of the debris disc around the young F-type star HD 160305, detected in scattered light using the VLT/SPHERE instrument in the near infrared. Methods. We used a post-processing method based on angular differential imaging and synthetic images of debris discs produced with a disc modelling code (GRaTer) to constrain the main characteristics of the disc around HD 160305. All of the point sources in the field of the IRDIS camera were analysed with an astrometric tool to determine whether they are bound objects or background stars. Results. We detect a very inclined (~82°) ring-like debris disc located at a stellocentric distance of about 86 au (deprojected width ~27 au). The disc displays a brightness asymmetry between the two sides of the major axis, as can be expected from scattering properties of dust grains. We derive an anisotropic scattering factor g > 0.5. A second right-left asymmetry is also observed with respect to the minor axis. We measure a surface brightness ratio of 0.73 ± 0.18 between the bright and the faint sides. Because of the low signal-to-noise ratio (S/N) of the images we cannot easily discriminate between several possible explanations for this left-right asymmetry, such as perturbations by an unseen planet, the aftermath of the breakup of a massive planetesimal, or the pericenter glow effect due to an eccentric ring. Two epochs of observations allow us to reject the companionship hypothesis for the 15 point sources present in the field. [ABSTRACT FROM AUTHOR]

M stars are ideal targets to search for Earth-like planets. However, they usually have high levels of magnetic activity, which could affect their habitability and make difficult the detection of exoplanets orbiting around them. Unfortunately, long-term variability of dM stars has not been extensively studied, due to their low intrinsic brightness. For this reason, in 1999 we started the HKα project, which systematically observes the spectra of a large number of stars, in particular dM stars, at the Complejo Astronómico El Leoncito (CASLEO). In this work, we study the long-term activity of the young active dM1 star AU Microscopii. We analyse the Mount Wilson index S derived from CASLEO spectra obtained between 2004 and 2016, which we complement with the S -index derived from HARPS, FEROS, and UVES public spectra. We also analyse the simultaneous photometric counterpart provided by the ASAS public data base for this star between 2000 and 2009, and our own photometry. In both totally independent time series, we detect a possible activity cycle of period ∼5 yr. We also derived a precise rotation period for this star P rot = 4.85 d, consistent with the literature. This activity cycle reflects that an αΩ dynamo could be operating in this star. [ABSTRACT FROM AUTHOR]

Very young stars, like the Orion Nebula Cluster (ONC) members analysed in the present study, exhibit photometric variability with a wide range of amplitudes. Such a prominent variability reflects in the inferred values of stellar colours and luminosities and, in turn, in the inferred stellar ages and masses. In this study, we measure the amplitudes of the photometric variability in V, R and I optical bands of a sample of 346 ONC members. We use these measurements to investigate how this variability affects the inferred masses and ages and whether it alone can account for the age spread among ONC members reported by earlier studies. We make use of colour-magnitude and Hertzprung-Russell (HR) diagrams. We find that members that show periodic and smooth photometric rotational modulation have masses and ages that are unaffected by variability when theoretical isochrones and evolutionary mass tracks are used in either colour-magnitude or HR diagrams. On the other hand, members with periodic but very scattered photometric rotational modulation and non-periodic members have masses and ages that are significantly affected. Moreover, using HR diagrams, we find that the observed I-band photometric variability can take account of only a fraction (~50 per cent) of the inferred age spread, whereas the V-band photometric variability is large enough to mask any age spread. [ABSTRACT FROM AUTHOR]

Very young stars, like the Orion Nebula Cluster (ONC) members analysed in the present study, exhibit photometric variability with a wide range of amplitudes. Such a prominent variability reflects in the inferred values of stellar colours and luminosities and, in turn, in the inferred stellar ages and masses. In this study, we measure the amplitudes of the photometric variability in V, R and I optical bands of a sample of 346 ONC members. We use these measurements to investigate how this variability affects the inferred masses and ages and whether it alone can account for the age spread among ONC members reported by earlier studies. We make use of colour-magnitude and Hertzprung-Russell (HR) diagrams. We find that members that show periodic and smooth photometric rotational modulation have masses and ages that are unaffected by variability when theoretical isochrones and evolutionary mass tracks are used in either colour-magnitude or HR diagrams. On the other hand, members with periodic but very scattered photometric rotational modulation and non-periodic members have masses and ages that are significantly affected. Moreover, using HR diagrams, we find that the observed I-band photometric variability can take account of only a fraction (-50 per cent) of the inferred age spread, whereas the V-band photometric variability is large enough to mask any age spread. [ABSTRACT FROM AUTHOR]

Since 2004, we have been engaged in a long-term observing programme to monitor young stellar objects (YSOs) in the Orion Nebula Cluster (ONC). We have collected about 2000 frames in V, R and I broad-band filters on more than 200 nights distributed over five consecutive observing seasons. The high-quality and time-extended photometric data give us an opportunity to address various phenomena associated with young stars. The prime motivations of this project are (i) to explore various manifestations of stellar magnetic activity in very young low-mass stars, (ii) to search for new pre-main-sequence eclipsing binaries and (iii) to look for any EXor and FUor-like transient activities associated with YSOs. Since this is the first paper on this programme, we give a detailed description of the science drivers, the observation and the data reduction strategies as well. In addition to these, we also present a large number of new periodic variables detected from our first 5 yr of time-series photometric data. Our study reveals that about 72 per cent of classical T Tauri stars (CTTS) in our field of view are periodic, whereas only 32 per cent of weak-lined T Tauri stars (WTTS) are periodic. This indicates that inhomogeneity patterns on the surface of CTTS of the ONC stars are much more stable than on WTTS. From our multiyear monitoring campaign, we found that the photometric surveys based on single season are incapable of identifying all periodic variables. And any study on evolution of angular momentum based on single-season surveys must be carried out with caution. [ABSTRACT FROM AUTHOR]

CoRoT-2a is a young (≈0.5 Gyr) G7V star accompanied by a transiting hot-Jupiter, discovered by the CoRoT satellite (Alonso et al. Astron Astrophys 482:L21, 2008; Bouchy et al. Astron Astrophys 482:L25, 2008). An analysis of its photospheric activity, based on spot modelling techniques previously developed by our group for the analysis of the Sun as a star, shows that the active regions on CoRoT-2a arised within two active longitudes separated by about 180° and rotating with periods of 4.5221 and 4.5543 days, respectively, at epoch of CoRoT observations (112 continous days centered at ≈2007.6). We show that the total spotted area oscillates with a period of about 28.9 days, a value close to 10 times the synodic period of the planet with respect to the active longitude pattern rotating in 4.5221 days. Moreover, the variance of the stellar flux is modulated in phase with the planet orbital period. This suggests a possible star–planet magnetic interaction, a phenomenon already seen in other extrasolar planetary systems hosting hot-Jupiters. [ABSTRACT FROM AUTHOR]

We constrain the properties of the spotted regions on the photosphere of the active late-type star DX Leonis by comparing the observed amplitudes of light and color variations with synthetic amplitudes obtained by means of Dorren's spot model and computed for a grid of values of spot temperatures, areas and latitudes. [ABSTRACT FROM AUTHOR]