2,918 research outputs found
ALMA Observations of Circumstellar Disks in the Upper Scorpius OB Association
We present ALMA observations of 106 G-, K-, and M-type stars in the Upper
Scorpius OB Association hosting circumstellar disks. With these data, we
measure the 0.88 mm continuum and CO = 32 line fluxes of disks
around low-mass ( ) stars at an age of 5-11 Myr. Of the
75 primordial disks in the sample, 53 are detected in the dust continuum and 26
in CO. Of the 31 disks classified as debris/evolved transitional disks, 5 are
detected in the continuum and none in CO. The lack of CO emission in
approximately half of the disks with detected continuum emission can be
explained if CO is optically thick but has a compact emitting area ( au), or if the CO is heavily depleted by a factor of at least
relative to interstellar medium abundances and is optically thin. The continuum
measurements are used to estimate the dust mass of the disks. We find a
correlation between disk dust mass and stellar host mass consistent with a
power-law relation of . Disk dust
masses in Upper Sco are compared to those measured in the younger Taurus
star-forming region to constrain the evolution of disk dust mass. We find that
the difference in the mean of between Taurus and
Upper Sco is , such that is lower in Upper
Sco by a factor of .Comment: 18 pages of text, 11 Figures, 5 Tables. Published in Ap
Measurement of Circumstellar Disk Sizes in the Upper Scorpius OB Association with ALMA
We present detailed modeling of the spatial distributions of gas and dust in
57 circumstellar disks in the Upper Scorpius OB Association observed with ALMA
at sub-millimeter wavelengths. We fit power-law models to the dust surface
density and CO = 3-2 surface brightness to measure the radial extent of
dust and gas in these disks. We found that these disks are extremely compact:
the 25 highest signal-to-noise disks have a median dust outer radius of 21 au,
assuming an dust surface density profile. Our lack of CO detections in
the majority of our sample is consistent with these small disk sizes assuming
the dust and CO share the same spatial distribution. Of seven disks in our
sample with well-constrained dust and CO radii, four appear to be more extended
in CO, although this may simply be due to higher optical depth of the CO.
Comparison of the Upper Sco results with recent analyses of disks in Taurus,
Ophiuchus, and Lupus suggests that the dust disks in Upper Sco may be
times smaller in size than their younger counterparts, although we caution that
a more uniform analysis of the data across all regions is needed. We discuss
the implications of these results for disk evolution.Comment: 15 pages of text, 7 figures, 3 tables. Accepted in Ap
Opportunity to Test non-Newtonian Gravity Using Interferometric Sensors with Dynamic Gravity Field Generators
We present an experimental opportunity for the future to measure possible
violations to Newton's 1/r^2 law in the 0.1-10 meter range using Dynamic
gravity Field Generators (DFG) and taking advantage of the exceptional
sensitivity of modern interferometric techniques. The placement of a DFG in
proximity to one of the interferometer's suspended test masses generates a
change in the local gravitational field that can be measured at a high signal
to noise ratio. The use of multiple DFGs in a null experiment configuration
allows to test composition independent non-Newtonian gravity significantly
beyond the present limits. Advanced and third-generation gravitational-wave
detectors are representing the state-of-the-art in interferometric distance
measurement today, therefore we illustrate the method through their sensitivity
to emphasize the possible scientific reach. Nevertheless, it is expected that
due to the technical details of gravitational-wave detectors, DFGs shall likely
require dedicated custom configured interferometry. However, the sensitivity
measure we derive is a solid baseline indicating that it is feasible to
consider probing orders of magnitude into the pristine parameter well beyond
the present experimental limits significantly cutting into the theoretical
parameter space.Comment: 9 pages, 6 figures; Physical Review D, vol. 84, Issue 8, id. 08200
Molecular outflow launched beyond the disk edge
One of the long-standing problems of star formation is the excess of angular
momentum of the parent molecular cloud. In the classical picture, a fraction of
angular momentum of the circumstellar material is removed by the
magneto-centrifugally driven disk wind that is launched from a wide region
throughout the disk. In this work, we investigate the kinematics in the
envelope-disk transition zone of the Class I object BHB07-11, in the B59 core.
For this purpose, we used the Atacama Large Millimeter/submillimeter Array in
extended configuration to observe the thermal dust continuum emission
( 1.3 mm) and molecular lines (CO, CO and HCO),
which are suitable tracers of disk, envelope, and outflow dynamics at a spatial
resolution of AU. We report a bipolar outflow that was launched at
symmetric positions with respect to the disk (80~AU in radius), but was
concentrated at a distance of 90--130~AU from the disk center. The two outflow
lobes had a conical shape and the gas inside was accelerating. The large offset
of the launching position coincided with the landing site of the infall
material from the extended spiral structure (seen in dust) onto the disk. This
indicates that bipolar outflows are efficiently launched within a narrow region
outside the disk edge. We also identify a sharp transition in the gas
kinematics across the tip of the spiral structure, which pinpoints the location
of the so-called centrifugal barrier.Comment: 5 pages, 5 figures, Accepted for publication in A&A Letter
ALMA Observations of the Orion Proplyds
We present ALMA observations of protoplanetary disks ("proplyds") in the
Orion Nebula Cluster. We imaged 5 individual fields at 856um containing 22
HST-identified proplyds and detected 21 of them. Eight of those disks were
detected for the first time at submillimeter wavelengths, including the most
prominent, well-known proplyd in the entire Orion Nebula, 114-426. Thermal dust
emission in excess of any free-free component was measured in all but one of
the detected disks, and ranged between 1-163 mJy, with resulting disk masses of
0.3-79 Mjup. An additional 26 stars with no prior evidence of associated disks
in HST observations were also imaged within the 5 fields, but only 2 were
detected. The disk mass upper limits for the undetected targets, which include
OB stars, theta1Ori C and theta1Ori F, range from 0.1-0.6 Mjup. Combining these
ALMA data with previous SMA observations, we find a lack of massive (>3 Mjup)
disks in the extreme-UV dominated region of Orion, within 0.03 pc of O-star
theta1Ori C. At larger separations from theta1Ori C, in the far-UV dominated
region, there is a wide range of disk masses, similar to what is found in
low-mass star forming regions. Taken together, these results suggest that a
rapid dissipation of disk masses likely inhibits potential planet formation in
the extreme-UV dominated regions of OB associations, but leaves disks in the
far-UV dominated regions relatively unaffected.Comment: ApJ, in pres
ALMA Measurements of Circumstellar Material in the GQ Lup System
We present ALMA observations of the GQ Lup system, a young Sun-like star with
a substellar mass companion in a wide-separation orbit. These observations of
870 m continuum and CO J=3-2 line emission with beam size
( AU) resolve the disk of dust and gas surrounding the primary star, GQ
Lup A, and provide deep limits on any circumplanetary disk surrounding the
companion, GQ Lup b. The circumprimary dust disk is compact with a FWHM of
AU, while the gas has a larger extent with a characteristic radius of
AU. By forward-modeling the velocity field of the circumprimary
disk based on the CO emission, we constrain the mass of GQ Lup A to be , where is a known distance, and
determine that we view the disk at an inclination angle of
and a position angle of . The
upper limit on the 870 m flux density of any circumplanetary
disk associated with GQ Lup b of mJy implies an upper limit on the dust
disk mass of for standard assumptions about optically thin
emission. We discuss proposed mechanisms for the formation of wide-separation
substellar companions given the non-detection of circumplanetary disks around
GQ Lup b and other similar systems.Comment: 11 pages, 4 figure
ALMA Observations of Asymmetric Molecular Gas Emission from a Protoplanetary Disk in the Orion Nebula
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations
of molecular line emission from d216-0939, one of the largest and most massive
protoplanetary disks in the Orion Nebula Cluster (ONC). We model the spectrally
resolved HCO (4--3), CO (3--2), and HCN (4--3) lines observed at 0\farcs5
resolution to fit the temperature and density structure of the disk. We also
weakly detect and spectrally resolve the CS (7--6) line but do not model it.
The abundances we derive for CO and HCO are generally consistent with
expected values from chemical modeling of protoplanetary disks, while the HCN
abundance is higher than expected. We dynamically measure the mass of the
central star to be which is inconsistent with the
previously determined spectral type of K5. We also report the detection of a
spatially unresolved high-velocity blue-shifted excess emission feature with a
measurable positional offset from the central star, consistent with a Keplerian
orbit at . Using the integrated flux of the feature in
HCO (4--3), we estimate the total H gas mass of this feature to be at
least , depending on the assumed temperature. The
feature is due to a local temperature and/or density enhancement consistent
with either a hydrodynamic vortex or the expected signature of the envelope of
a forming protoplanet within the disk.Comment: 19 pages, 12 figures, accepted for publication in A
A Machine-Learning Based Microwave Sensing Approach to Food Contaminant Detection
To detect contaminants accidentally included in packaged foods, food industries use an array of systems ranging from metal detectors to X-ray imagers. Low density plastic or glass contaminants, however, are not easily detected with standard methods. If the dielectric contrast between the packaged food and these contaminants in the microwave spectrum is sensible, Microwave Sensing (MWS) can be used as a contactless detection method, which is particularly useful when the food is already packaged. In this paper we propose using MWS combined with Machine Learning (ML). In particular, we report on experiments we did with packaged cocoa-hazelnut spread and show the accuracy of our approach. We also present an FPGA acceleration that runs the ML processing in real-time so as to keep up with the throughput of a production line
Preliminary laboratory multi-scale investigation on performance of pervious concrete pavements and vegetated elements as storm water bio-filters and retention systems
The growing population in urban areas worldwide is having a severe impact on the environment and quality of life of inhabitants. To alleviate the impact on traditional transportation infrastructures, existing and future urban facilities must be more environmentally friendly and sustainable. One solution is to develop new “green transportation infrastructures” (GTI) as part of the urban storm water management system.
Although technologies for GTI have been well-investigated, there is limited experience of their potential benefits globally and, specifically, in Italy. This work, funded by the Regione Piemonte in 2015 and supported by different areas of expertise, aimed at promoting new urban storm water systems through the retention, filtration, and restoration of natural soil water content.
To this end, a laboratory investigation of porous road pavements (Figure 1), and vegetated boxes (Figure 2 and 3) that filter runoff pollutants from impervious pavements was conducted to examine ecological, hydraulic, and mechanical performance levels.
Three different experimental scales (samples, columns, and boxes) for the two GTI technologies were considered. Samples were used to assess the permeability, void content, strength, and pollution reduction potential of different materials used to build full-scale bio-filter systems. The pollutant reduction was determined by the reduction in suspended solids and hydrocarbon concentration, with results confirming that it depends on filter type and permeability. The preliminary results are encouraging and show a high reduction in total suspended solids and hydrocarbon concentrations (from 65% to 99%).
Concrete pervious pavements and vegetated bio-filter systems were reproduced in columns and boxes, combining materials and supports for biofilm bacteria (geotextile, plastic caps) to assess the abatement potential of pre-developed biofilm bacteria compared to systems where bacteria are present naturally. Hydraulic parameters (percolation time, void content, outflow rate) were estimated so as to provide basic design parameters for full-scale applications
Inner edges of planetesimal belts: collisionally eroded or truncated?
The radial structure of debris discs can encode important information about
their dynamical and collisional history. In this paper we present a 3-phase
analytical model to analyse the collisional evolution of solids in debris
discs, focusing on their joint radial and temporal dependence. Consistent with
previous models, we find that as the largest planetesimals reach collisional
equilibrium in the inner regions, the surface density of dust and solids
becomes proportional to within a certain critical radius. We
present simple equations to estimate the critical radius and surface density of
dust as a function of the maximum planetesimal size and initial surface density
in solids (and vice versa). We apply this model to ALMA observations of 7 wide
debris discs. We use both parametric and non-parametric modelling to test if
their inner edges are shallow and consistent with collisional evolution. We
find that 4 out of 7 have inner edges consistent with collisional evolution.
Three of these would require small maximum planetesimal sizes below 10 km, with
HR 8799's disc potentially lacking solids larger than a few centimeters. The
remaining systems have inner edges that are much sharper, which requires
maximum planetesimal sizes km. Their sharp inner edges suggest they
could have been truncated by planets, which JWST could detect. In the context
of our model, we find that the 7 discs require surface densities below a
Minimum Mass Solar Nebula, avoiding the so-called disc mass problem. Finally,
during the modelling of HD 107146 we discover that its wide gap is split into
two narrower ones, which could be due to two low-mass planets formed within the
disc.Comment: Accepted for publication in MNRAS, 21 pages, 11 figure
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