168 research outputs found
ALMA observations of polarized emission toward the CW Tau and DG Tau protoplanetary disks: constraints on dust grain growth and settling
We present polarimetric data of CW Tau and DG Tau, two well-known Class II
disk/jet systems, obtained with the Atacama Large Millimeter/submillimeter
Array at 870 m and 0."2 average resolution. In CW Tau, the total and
polarized emission are both smooth and symmetric, with polarization angles
almost parallel to the minor axis of the projected disk. In contrast, DG Tau
displays a structured polarized emission, with an elongated brighter region in
the disk's near side and a belt-like feature beyond about 0."3 from the source.
At the same time the total intensity is spatially smooth, with no features. The
polarization pattern, almost parallel to the minor axis in the inner region,
becomes azimuthal in the outer belt, possibly because of a drop in optical
depth. The polarization fraction has average values of 1.2% in CW Tau and 0.4%
in DG Tau. Our results are consistent with polarization from self-scattering of
the dust thermal emission. Under this hypothesis, the maximum size of the
grains contributing to polarization is in the range 100 - 150 m for CW Tau
and 50 - 70 m for DG Tau. The polarization maps combined with dust opacity
estimates indicate that these grains are distributed in a geometrically thin
layer in CW Tau, representing a settling in the disk midplane. Meanwhile, such
settling is not yet apparent for DG Tau. These results advocate polarization
studies as a fundamental complement to total emission observations, in
investigations of the structure and the evolution of protoplanetary disks.Comment: 8 pages, 5 figures. Accepted for publication in ApJ Letter
The evolution of dust-disk sizes from a homogeneous analysis of 1-10 Myr-old stars
We utilize ALMA archival data to estimate the dust disk size of 152
protoplanetary disks in Lupus (1-3 Myr), Chamaeleon I (2-3 Myr), and Upper-Sco
(5-11 Myr). We combine our sample with 47 disks from Tau/Aur and Oph whose dust
disk radii were estimated, as here, through fitting radial profile models to
visibility data. We use these 199 homogeneously derived disk sizes to identify
empirical disk-disk and disk-host property relations as well as to search for
evolutionary trends. In agreement with previous studies, we find that dust disk
sizes and millimeter luminosities are correlated, but show for the first time
that the relationship is not universal between regions. We find that disks in
the 2-3 Myr-old Cha I are not smaller than disks in other regions of similar
age, and confirm the Barenfeld et al. (2017) finding that the 5-10 Myr USco
disks are smaller than disks belonging to younger regions. Finally, we find
that the outer edge of the Solar System, as defined by the Kuiper Belt, is
consistent with a population of dust disk sizes which have not experienced
significant truncation.Comment: ApJ accepted, 38 pages, 16 figures, 68k compatibl
New insights into the nature of transition disks from a complete disk survey of the Lupus star forming region
Transition disks with large dust cavities around young stars are promising
targets for studying planet formation. Previous studies have revealed the
presence of gas cavities inside the dust cavities hinting at recently formed,
giant planets. However, many of these studies are biased towards the brightest
disks in the nearby star forming regions, and it is not possible to derive
reliable statistics that can be compared with exoplanet populations. We present
the analysis of 11 transition disks with large cavities (>20 AU radius) from a
complete disk survey of the Lupus star forming region, using ALMA Band 7
observations at 0.3" (22-30 AU radius) resolution of the 345 GHz continuum,
13CO and C18O 3-2 observations and the Spectral Energy Distribution of each
source. Gas and dust surface density profiles are derived using the
physical-chemical modeling code DALI. This is the first study of transition
disks of large cavities within a complete disk survey within a star forming
region. The dust cavity sizes range from 20-90 AU radius and in three cases, a
gas cavity is resolved as well. The deep drops in gas density and large dust
cavity sizes are consistent with clearing by giant planets. The fraction of
transition disks with large cavities in Lupus is ~11%, which is inconsistent
with exoplanet population studies of giant planets at wide orbits. Furthermore,
we present a hypothesis of an evolutionary path for large massive disks
evolving into transition disks with large cavities.Comment: 29 pages, 15 figures, Accepted by Ap
The time evolution of in protoplanetary discs as a way to disentangle between viscosity and MHD winds
As the classic viscous paradigm for protoplanetary disk accretion is
challenged by the observational evidence of low turbulence, the alternative
scenario of MHD disk winds is being explored as potentially able to reproduce
the same observed features traditionally explained with viscosity. Although the
two models lead to different disk properties, none of them has been ruled out
by observations - mainly due to instrumental limitations. In this work, we
present a viable method to distinguish between the viscous and MHD framework
based on the different evolution of the distribution in the disk mass
() - accretion rate () plane of a disk population. With
a synergy of analytical calculations and 1D numerical simulations, performed
with the population synthesis code \texttt{Diskpop}, we find that both
mechanisms predict the spread of the observed ratio in
a disk population to decrease over time; however, this effect is much less
pronounced in MHD-dominated populations as compared to purely viscous
populations. Furthermore, we demonstrate that this difference is detectable
with the current observational facilities: we show that convolving the
intrinsic spread with the observational uncertainties does not affect our
result, as the observed spread in the MHD case remains significantly larger
than in the viscous scenario. While the most recent data available show a
better agreement with the wind model, ongoing and future efforts to obtain
direct gas mass measurements with ALMA and ngVLA will cause a reassessment of
this comparison in the near future.Comment: 11 pages, 6 figures, 1 table. Published in ApJ
Is new olive farming sustainable? A spatial comparison of productive and environmental performances between traditional and new olive orchards with the model OliveCan
Olive (Olea europaea L.) is a widely spread tree species in the Mediterranean. In the last decades, olive farming has known major management changes with high economic and environmental impacts. The fast track expansion of this modern olive farming in these recent years casts doubts on the sustainability of such important tree plantation across the Mediterranean. In this work, we performed a spatial modelling analysis to investigate the implications of climate variability and farming management on the productivity and environmental performances of olive orchards around the Mediterranean. Implementation of this research is based on the use of OliveCan; a process-based model able to illustrate responses of water and carbon balances to weather variables, soil characteristics and management techniques enabling the comprehension of olive orchard dynamics under heterogeneous conditions of climate and agricultural practices. Four main intensification levels were adopted to reflect the main olive grove types from traditional to new intensive plantations: low density LD (100 trees ha−1), medium density MD (200 trees ha−1), high density HD (400 trees ha−1) and super high density SHD (1650 trees ha−1). Managements tested were intensification, water supply (rainfed, deficit and full irrigated) and the fate of pruning residues (exported or left on the soil). Two cases studies in two of the main Mediterranean olive-growing regions with contrasting environmental conditions, Tuscany and Jaen regions, focused on mitigation alternative managements for carbon sequestration. Results showed that olive orchards responses in terms of yield and Net Ecosystem Productivity (NEP) vary along with climatic conditions. Water supply was the main driver with a production function that varies for different atmospheric demands. Application of deficit irrigation proved to boost water use efficiency. Besides, intensification from LD to SHD, presented the greatest improvements, 28–73% for yield and 50–100% for NEP. The C sequestration potential of olive orchards was confirmed. In fact, soil organic carbon (SOC) increased continuously over 400 years of simulation, reaching a state of equilibrium. Moreover, intensification and irrigation improved total carbon sequestration. Management of incorporating pruning residues in the soil increased SOC of 10.5 t C ha−1 for Tuscany and 10.8 t C ha−1 for Jaen. Findings of this research enabled the identification of the main drivers influencing the productive and environmental performance of olive groves in the different Mediterranean sub-climates. Impacts of management innovations on olive farming sustainability were also quantified which may help improve production systems for a more sustainable olive cultivation
A multi-objective optimization approach in defining the decarbonization strategy of a refinery
Nowadays, nearly one quarter of global carbon dioxide emissions are attributable to energy use in industry, making this an important target for emission reductions. The scope of this study is hence that to define a cost-optimized decarbonization strategy for an energy and carbon intensive industry using an Italian refinery as a case study. The methodology involves the coupling of EnergyPLAN with a Multi-Objective Evolutionary Algorithm (MOEA), considering the minimization of annual cost and CO2 emissions as two potentially conflicting objectives and the energy technologies’ capacities as decision variables. For the target year 2025, EnergyPLAN+MOEA has allowed to model a range of 0-100 % decarbonization solutions characterized by optimal penetration mix of 22 technologies in the electrical, thermal, hydrogen feedstock and transport demand. A set of nine scenarios, with different land use availabilities and implementable technologies, each consisting of 100 optimal systems out of 10000 simulated ones, has been evaluated. The results show, on the one hand the possibility of achieving medium-high decarbonization solutions at costs close to current ones, on the other, how the decarbonization pathways strongly depend on the available land for solar thermal, photovoltaic and wind, as well as the presence of a biomass supply chain in the region
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