420 research outputs found
The time evolution of dusty protoplanetary disc radii: Observed and physical radii differ
Proto-planetary disc surveys conducted with ALMA are measuring disc radii in
multiple star forming regions. The disc radius is a fundamental quantity to
diagnose whether discs undergo viscous spreading, discriminating between
viscosity or angular momentum removal by winds as drivers of disc evolution.
Observationally, however, the sub-mm continuum emission is dominated by the
dust, which also drifts inwards, complicating the picture. In this paper we
investigate, using theoretical models of dust grain growth and radial drift,
how the radii of dusty viscous proto-planetary discs evolve with time. Despite
the existence of a sharp outer edge in the dust distribution, we find that the
radius enclosing most of the dust increases with time, closely
following the evolution of the gas radius. This behaviour arises because,
although dust initially grows and drifts rapidly onto the star, the residual
dust retained on Myr timescales is relatively well coupled to the gas.
Observing the expansion of the dust disc requires using definitions based on
high fractions of the disc (e.g. 95 per cent) and very long
integrations with ALMA, because the dust grains in the outer part of the disc
are small and have a low sub-mm opacity. We show that existing surveys lack the
sensitivity to detect viscous spreading. The disc radii they measure do not
trace the mass radius or the sharp outer edge in the dust distribution, but the
outer limit of where the grains have significant sub-mm opacity. We predict
that these observed radii should shrink with time
On the millimetre continuum flux–radius correlation of proto-planetary discs
A correlation between proto-planetary disc radii and sub-mm fluxes has been
recently reported. In this Letter we show that the correlation is a sensitive
probe of grain growth processes. Using models of grain growth and drift, we
have shown in a companion paper that the observed disc radii trace where the
dust grains are large enough to have a significant sub-mm opacity. We show that
the observed correlation emerges naturally if the maximum grain size is set by
radial drift, implying relatively low values of the viscous parameter
. In this case the relation has an almost universal
normalisation, while if the grain size is set by fragmentation the flux at a
given radius depends on the dust-to-gas ratio. We highlight two observational
consequences of the fact that radial drift limits the grain size. The first is
that the dust masses measured from the sub-mm could be overestimated by a
factor of a few. The second is that the correlation should be present also at
longer wavelengths (e.g. 3mm), with a normalisation factor that scales as the
square of the observing frequency as in the optically thick case
Involvement of the phosphoinositide 3-kinase/Akt signaling pathway in the resistance to therapeutic treatments of human leukemias.
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
Constitutively active Akt1 protects HL60 leukemia cells from TRAIL-induced apoptosis through a mechanism involving NF-kappaB activation and cFLIP(L) up-regulation.
Are inner disc misalignments common? ALMA reveals an isotropic outer disc inclination distribution for young dipper stars
Dippers are a common class of young variable star exhibiting day-long dimmings with depths of up to several tens of per cent. A standard explanation is that dippers host nearly edge-on (id ≈ 70°) protoplanetary discs that allow close-in (10 au) disc resolved by ALMA and that inner disc misalignments may be common during the protoplanetary phase. More than one mechanism may contribute to the dipper phenomenon, including accretion-driven warps and ‘broken’ discs caused by inclined (sub-)stellar or planetary companions
Gas Density Perturbations Induced by One or More Forming Planets in the AS 209 Protoplanetary Disk as Seen with ALMA
The formation of planets occurs within protoplanetary disks surrounding young
stars, resulting in perturbation of the gas and dust surface densities. Here,
we report the first evidence of spatially resolved gas surface density
() perturbation towards the AS~209 protoplanetary disk from the
optically thin CO () emission. The observations were carried out
at 1.3~mm with ALMA at a spatial resolution of about 0.3\arcsec
0.2\arcsec (corresponding to 38 25 au). The CO
emission shows a compact (60~au), centrally peaked emission and an outer
ring peaking at 140~au, consistent with that observed in the continuum emission
and, its azimuthally averaged radial intensity profile presents a deficit that
is spatially coincident with the previously reported dust map. This deficit can
only be reproduced with our physico-thermochemical disk model by lowering
by nearly an order of magnitude in the dust gaps. Another
salient result is that contrary to CO, the DCO () emission
peaks between the two dust gaps. We infer that the best scenario to explain our
observations (CO deficit and DCO enhancement) is a gas
perturbation due to forming-planet(s), that is commensurate with previous
continuum observations of the source along with hydrodynamical simulations. Our
findings confirm that the previously observed dust gaps are very likely due to
perturbation of the gas surface density that is induced by a planet of at least
0.2~M in formation. Finally, our observations also show the
potential of using CO isotopologues to probe the presence of saturn mass
planet(s)
High quality superconducting niobium films produced by Ultra High Vacuum Cathodic Arc
The vacuum arc is a well-known technique to produce coating with enhanced
adhesion and film density. Many cathodic arc deposition systems are actually in
use in industry and research. They all work under (high) vacuum conditions in
which water vapor pressure is an important source of film contamination,
especially in the pulsed arc mode of operation. Here we present a Cathodic Arc
system working under Ultra High Vacuum conditions (UHVCA). UHVCA has been used
to produce ultra-pure niobium films with excellent structural and electrical
properties at a deposition temperature lower than 100oC. The UHVCA technique
therefore opens new perspectives for all applications requiring ultra-pure
films or, as in the case of Plasma Immersion Ion Implantation, ultra-pure
plasmas.Comment: submitted to AP
A multi-wavelength analysis for interferometric (sub-)mm observations of protoplanetary disks: radial constraints on the dust properties and the disk structure
Theoretical models of grain growth predict dust properties to change as a
function of protoplanetary disk radius, mass, age and other physical
conditions. We lay down the methodology for a multi-wavelength analysis of
(sub-)mm and cm continuum interferometric observations to constrain
self-consistently the disk structure and the radial variation of the dust
properties. The computational architecture is massively parallel and highly
modular. The analysis is based on the simultaneous fit in the uv-plane of
observations at several wavelengths with a model for the disk thermal emission
and for the dust opacity. The observed flux density at the different
wavelengths is fitted by posing constraints on the disk structure and on the
radial variation of the grain size distribution. We apply the analysis to
observations of three protoplanetary disks (AS 209, FT Tau, DR Tau) for which a
combination of spatially resolved observations in the range ~0.88mm to ~10mm is
available (from SMA, CARMA, and VLA), finding evidence of a decreasing maximum
dust grain size (a_max) with radius. We derive large a_max values up to 1 cm in
the inner disk between 15 and 30 AU and smaller grains with a_max~1 mm in the
outer disk (R > 80AU). In this paper we develop a multi-wavelength analysis
that will allow this missing quantity to be constrained for statistically
relevant samples of disks and to investigate possible correlations with disk or
stellar parameters.Comment: 19 pages, 15 figures, accepted for publication in A&
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