340 research outputs found
The distribution of accretion rates as a diagnostic of protoplanetary disc evolution
We show that the distribution of observed accretion rates is a powerful
diagnostic of protoplanetary disc physics. Accretion due to turbulent
("viscous") transport of angular momentum results in a fundamentally different
distribution of accretion rates than accretion driven by magnetised disc winds.
We find that a homogeneous sample of 300 observed accretion rates
would be sufficient to distinguish between these two mechanisms of disc
accretion at high confidence, even for pessimistic assumptions. Current samples
of T Tauri star accretion rates are not this large, and also suffer from
significant inhomogeneity, so both viscous and wind-driven models are broadly
consistent with the existing observations. If accretion is viscous, the
observed accretion rates require low rates of disc photoevaporation
(Myr). Uniform, homogeneous surveys of
stellar accretion rates can therefore provide a clear answer to the
long-standing question of how protoplanetary discs accrete.Comment: 10 pages, 8 figures. Accepted for publication in MNRA
Influence of the air inlet configuration on the performances of a paraglider open airfoil
A finite volume flow solver was used to solve the Reynolds averaged Navier-Stokes equations for the 2D flow field on a paraglider open airfoil. The canopy was assumed to be smooth, rigid and impermeable. The parametric study performed concerns the position and the width of the air inlet at the leading edge. The range of values used covers the air inlet geometries from classical ram-air parafoil to sport paraglider airfoil, including transition toward the full closed baseline airfoil. Results are focused both on lift and drag coefficients for performance analysis and on the internal pressure coefficient which can be critical for a real flexible wing regarding the risk of collapse. Depending on the appearance of a separation bubble over the upper edge, two well separated behaviours can be observed. The first behaviour is more typical of ram-air parachutes and the second one corresponds to the design of performance paragliders. For paraglider configurations, it is shown that the aerodynamic coefficients of the open airfoil can be easily deduced from the pressure coefficients of the baseline airfoil without solving the internal flow
HST measures of Mass Accretion Rates in the Orion Nebula Cluster
The present observational understanding of the evolution of the mass
accretion rates (Macc) in pre-main sequence stars is limited by the lack of
accurate measurements of Macc over homogeneous and large statistical samples of
young stars. Such observational effort is needed to properly constrain the
theory of star formation and disk evolution. Based on HST/WFPC2 observations,
we present a study of Macc for a sample of \sim 700 sources in the Orion Nebula
Cluster, ranging from the Hydrogen-burning limit to M\ast \sim 2M\odot. We
derive Macc from both the U-band excess and the H{\alpha} luminosity
(LH{\alpha}), after determining empirically both the shape of the typical
accretion spectrum across the Balmer jump and the relation between the
accretion luminosity (Lacc) and LH{\alpha}, that is Lacc/L\odot =
(1.31\pm0.03)\cdotLH{\alpha}/L\odot + (2.63\pm 0.13). Given our large
statistical sample, we are able to accurately investigate relations between
Macc and the parameters of the central star such as mass and age. We clearly
find Macc to increase with stellar mass, and decrease over evolutionary time,
but we also find strong evidence that the decay of Macc with stellar age occurs
over longer timescales for more massive PMS stars. Our best fit relation
between these parameters is given by: log(Macc/M\odot\cdotyr)=(-5.12 \pm 0.86)
-(0.46 \pm 0.13) \cdot log(t/yr) -(5.75 \pm 1.47)\cdot log(M\ast/M\odot) +
(1.17 \pm 0.23)\cdot log(t/yr) \cdot log(M\ast/M\odot). These results also
suggest that the similarity solution model could be revised for sources with
M\ast > 0.5M\odot. Finally, we do not find a clear trend indicating
environmental effects on the accretion properties of the sources.Comment: 17 pages, 15 figures, accepted for publication in Ap
Dust masses of young disks: constraining the initial solid reservoir for planet formation
In recent years evidence has been building that planet formation starts
early, in the first 0.5 Myr. Studying the dust masses available in young
disks enables understanding the origin of planetary systems since mature disks
are lacking the solid material necessary to reproduce the observed exoplanetary
systems, especially the massive ones. We aim to determine if disks in the
embedded stage of star formation contain enough dust to explain the solid
content of the most massive exoplanets. We use Atacama Large
Millimeter/submillimeter Array (ALMA) Band 6 observations of embedded disks in
the Perseus star-forming region together with Very Large Array (VLA) Ka-band (9
mm) data to provide a robust estimate of dust disk masses from the flux
densities. Using the DIANA opacity model including large grains, with a dust
opacity value of = 0.28 cm g, the median dust
masses of the embedded disks in Perseus are 158 M for Class 0 and 52
M for Class I from the VLA fluxes. The lower limits on the median
masses from ALMA fluxes are 47 M and 12 M for Class 0 and
Class I, respectively, obtained using the maximum dust opacity value
= 2.3 cm g. The dust masses of young Class 0
and I disks are larger by at least a factor of 10 and 3, respectively, compared
with dust masses inferred for Class II disks in Lupus and other regions. The
dust masses of Class 0 and I disks in Perseus derived from the VLA data are
high enough to produce the observed exoplanet systems with efficiencies
acceptable by planet formation models: the solid content in observed giant
exoplanets can be explained if planet formation starts in Class 0 phase with an
efficiency of 15%. Higher efficiency of 30% is necessary if the
planet formation is set to start in Class I disks.Comment: 16 pages, 10 figures, accepted for publication in A&
Constraints on photoevaporation models from (lack of) radio emission in the Corona Australis protoplanetary disks
R. Galván-Madrid, et al., “Constraints on photoevaporation models from (lack of) radio emission in the Corona Australis protoplanetary disks”, Astronomy & Astrophysics, Vol. 570, October 2014. This version of record is available online at: https://doi.org/10.1051/0004-6361/201424630 Reproduced with Permission from Astronomy and Astrophysics, © ESO 2014.Photoevaporation due to high-energy stellar photons is thought to be one of the main drivers of protoplanetary disk dispersal. The fully or partially ionized disk surface is expected to produce free-free continuum emission at centimeter (cm) wavelengths that can be routinely detected with interferometers such as the upgraded Very Large Array (VLA). We use deep (rms noise down to 8 Jy beam in the field of view center) 3.5 cm maps of the nearby (130 pc) Corona Australis (CrA) star formation (SF) region to constrain disk photoevaporation models. We find that the radio emission from disk sources in CrA is surprisingly faint. Only 3 out of 10 sources within the field of view are detected, with flux densities of order Jy. However, a significant fraction of their emission is non-thermal. Typical upper limits for non-detections are Jy beam. Assuming analytic expressions for the free-free emission from extreme-UV (EUV) irradiation, we derive stringent upper limits to the ionizing photon luminosity impinging on the disk surface $\Phi_\mathrm{EUV}Peer reviewe
Correction to:Expanding controlled donation after the circulatory determination of death: statement from an international collaborative (Intensive Care Medicine, (2021), 47, 3, (265-281), 10.1007/s00134-020-06341-7)
The article “Expanding controlled donation after the circulatory determination of death: statement from an international collaborative”, written by Domínguez-Gil, B., Ascher, N., Capron, A.M. et al. was originally published electronically on the publisher’s internet portal on 21 February 2021 without open access. With the author(s)’ decision to opt for Open Choice the copyright of the article changed on 25 March 2021 to © The Author(s) 2021 and the article is forthwith distributed under a Creative Commons Attribution this article is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, which permits any non-commercial use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc/4.0/. The original article has been corrected
Production of Mesons in the Reaction at 3.67 GeV/c
The ratio of the total exclusive production cross sections for
and mesons has been measured in the reaction at
GeV/c. The observed ratio is
from which the exclusive
meson production cross section is determined to be
. Differential cross section
distributions have been measured. Their shape is consistent with isotropic
meson production.Comment: 14 pages, 5 figures, accepted by Phys.Lett.
Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): A Panchromatic View of DO Tau's Complex Kilo-au Environment
While protoplanetary disks are often treated as isolated systems in planet
formation models, observations increasingly suggest that vigorous interactions
between Class II disks and their environments are not rare. DO Tau is a T Tauri
star that has previously been hypothesized to have undergone a close encounter
with the HV Tau system. As part of the DESTINYS ESO Large Programme, we present
new VLT/SPHERE polarimetric observations of DO Tau and combine them with
archival HST scattered light images and ALMA observations of CO isotopologues
and CS to map a network of complex structures. The SPHERE and ALMA observations
show that the circumstellar disk is connected to arms extending out to several
hundred au. HST and ALMA also reveal stream-like structures northeast of DO
Tau, some of which are at least several thousand au long. These streams appear
not to be gravitationally bound to DO Tau, and comparisons with previous
Herschel far-IR observations suggest that the streams are part of a bridge-like
structure connecting DO Tau and HV Tau. We also detect a fainter redshifted
counterpart to a previously known blueshifted CO outflow. While some of DO
Tau's complex structures could be attributed to a recent disk-disk encounter,
they might be explained alternatively by interactions with remnant material
from the star formation process. These panchromatic observations of DO Tau
highlight the need to contextualize the evolution of Class II disks by
examining processes occurring over a wide range of size scales.Comment: 41 pages, 20 figures, accepted by ApJ, reduced data available at
https://zenodo.org/record/640890
Planetary population synthesis
In stellar astrophysics, the technique of population synthesis has been
successfully used for several decades. For planets, it is in contrast still a
young method which only became important in recent years because of the rapid
increase of the number of known extrasolar planets, and the associated growth
of statistical observational constraints. With planetary population synthesis,
the theory of planet formation and evolution can be put to the test against
these constraints. In this review of planetary population synthesis, we first
briefly list key observational constraints. Then, the work flow in the method
and its two main components are presented, namely global end-to-end models that
predict planetary system properties directly from protoplanetary disk
properties and probability distributions for these initial conditions. An
overview of various population synthesis models in the literature is given. The
sub-models for the physical processes considered in global models are
described: the evolution of the protoplanetary disk, the planets' accretion of
solids and gas, orbital migration, and N-body interactions among concurrently
growing protoplanets. Next, typical population synthesis results are
illustrated in the form of new syntheses obtained with the latest generation of
the Bern model. Planetary formation tracks, the distribution of planets in the
mass-distance and radius-distance plane, the planetary mass function, and the
distributions of planetary radii, semimajor axes, and luminosities are shown,
linked to underlying physical processes, and compared with their observational
counterparts. We finish by highlighting the most important predictions made by
population synthesis models and discuss the lessons learned from these
predictions - both those later observationally confirmed and those rejected.Comment: 47 pages, 12 figures. Invited review accepted for publication in the
'Handbook of Exoplanets', planet formation section, section editor: Ralph
Pudritz, Springer reference works, Juan Antonio Belmonte and Hans Deeg, Ed
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