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 of radius inflation in stars approaching the slow-rotator sequence

Average stellar radii in open clusters can be estimated from rotation periods and projected rotational velocities under the assumption of random orientation of the spin axis. Such estimates are independent of distance, interstellar absorption, and models, but their validity can be limited by missing data (truncation) or data that only represent upper/lower limits (censoring). We present a new statistical analysis method to estimate average stellar radii in the presence of censoring and truncation. We use theoretical distribution functions of the projected stellar radius $R \sin i$ to define a likelihood function in the presence of censoring and truncation. Average stellar radii in magnitude bins are then obtained by a maximum likelihood parametric estimation procedure. This method is capable of recovering the average stellar radius within a few percent with as few as $\approx$ 10 measurements. Here it is applied for the first time to the dataset available for the Pleiades. We find an agreement better than $\approx$ 10 percent between the observed $R$ vs $M_K$ relationship and current standard stellar models for 1.2 $\ge M/M_{\odot} \ge$ 0.85 with no evident bias. Evidence of a systematic deviation at $2\sigma$ level are found for stars with 0.8 $\ge M/M_{\odot} \ge$ 0.6 approaching the slow-rotator sequence. Fast-rotators ($P$ < 2 d) agree with standard models within 15 percent with no systematic deviations in the whole 1.2 $\ge M/M_{\odot} \ge$ 0.5 range. The evidence found of a possible radius inflation just below the lower mass limit of the slow-rotator sequence indicates a possible connection with the transition from the fast to the slow-rotator sequence.Comment: Accepted by Astronomy and Astrophysics, 11 pages, 6 figure

Evidence of New Magnetic Transitions in Late-Type Dwarfs from Gaia DR2

The second Gaia data release contains the identification of 147 535 low-mass ($\le 1.4 M_{\odot}$) rotational modulation variable candidates on (or close to) the main sequence, together with their rotation period and modulation amplitude. The richness, the period and amplitude range, and the photometric precision of this sample make it possible to unveil, for the first time, signatures of different surface inhomogeneity regimes in the amplitude-period density diagram. The modulation amplitude distribution shows a clear bimodality, with an evident gap at periods $P \le 2$ d. The low amplitude branch, in turn, shows a period bimodality with a main clustering at periods $P \approx$ 5 - 10 d and a secondary clustering of ultra-fast rotators at $P \le 0.5$ d. The amplitude-period multimodality is correlated with the position in the period-absolute magnitude (or period-color) diagram, with the low- and high-amplitude stars occupying different preferential locations. Here we argue that such a multimodality represents a further evidence of the existence of different regimes of surface inhomogeneities in young and middle-age low-mass stars and we lay out possible scenarios for their evolution, which manifestly include rapid transitions from one regime to another. In particular, the data indicate that stars spinning up close to break-up velocity undergo a very rapid change in their surface inhomogeneities configuration, which is revealed here for the first time. The multimodality can be exploited to identify field stars of age $\sim$ 100 -- 600 Myr belonging to the slow-rotator low-amplitude sequence, for which age can be estimated from the rotation period via gyrochronology relationships.Comment: 15 pages, 6 figures, Accepted by Ap

Detection and characterization of stellar magnetic activity with Gaia

The Gaia Data Release 2 (DR2) supplied a catalog of 147,644 late-type stars for which the analysis of the G-band photometric time series allowed the detection of the rotation period and an estimate of the magnetic activity level. The Gaia DR3 will be based on photometric time series spanning a longer time interval and will allow the detection and characterization of about 1 million stars with magnetic activity. In the present work, we show how the Gaia data allows us to study variability phenomena connected to the stellar magnetic activity and occurs on very different timescales. We also show how the Gaia data, combined with long-term photometric surveys such as all sky automated survey (ASAS), can be exploited to detect magnetic activity cycles

Impact of photometric variability on age and mass determination in young stellar objects: the case of the Orion Nebula Cluster

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

4.0 low-tech building systems. BIM-based product-process innovation for corrugated cardboard prefabrication

Construction production chains are facing a profound ecological and digital transformation to support the competitiveness and resilience of the sector against ongoing environmental and socio-economic challenges. In recent years, the development of digital technologies has opened the field to the possibility of transforming prefabricated building production facilities into highly integrated, controlled, environmentally and economically efficient Industry 4.0 systems. CARES research is part of the ongoing debate, developing and implementing an innovative production model of construction elements made of corrugated cardboard, based on the principle of product-process digitalization through the use of BIM tools, aimed at rationalizing the use of resources and reducing the environmental burden of the construction phase

VizieR Online Data Catalog: Differential rotation in solar-like stars (Distefano+, 2016)

The average rotation period, the parameters ωmin ωmax, ∆Ωphot and alphaphot are reported for 111 late-type stars belonging to loose young stellar associations. For each target, the main physical parameters are also reported. The Spectral types, the photometric data and the distances are taken by previous works. The masses, the effective temperatures and the convective turn-over time-scales have been inferred by comparing absolute magnitudes with different sets of theoretical isochrones