1,128 research outputs found
ALMA observations of the debris disk around the young Solar Analog HD 107146
We present ALMA continuum observations at a wavelength of 1.25 mm of the
debris disk surrounding the 100 Myr old solar analog HD 107146. The
continuum emission extends from about 30 to 150 AU from the central star with a
decrease in the surface brightness at intermediate radii. We analyze the ALMA
interferometric visibilities using debris disk models with radial profiles for
the dust surface density parametrized as i) a single power-law, ii) a single
power-law with a gap, and iii) a double power-law. We find that models with a
gap of radial width AU at a distance of AU from the central
star, as well as double power-law models with a dip in the dust surface density
at AU provide significantly better fits to the ALMA data than single
power-law models. We discuss possible scenarios for the origin of the HD 107146
debris disk using models of planetesimal belts in which the formation of
Pluto-sized objects trigger disruptive collisions of large bodies, as well as
models which consider the interaction of a planetary system with a planetesimal
belt and spatial variation of the dust opacity across the disk. If future
observations with higher angular resolution and sensitivity confirm the
fully-depleted gap structure discussed here, a planet with a mass of
approximately a few Earth masses in a nearly circular orbit at AU
from the central star would be a possible explanation for the presence of the
gap.Comment: (38 pages, 7 figures, accepted for publication in ApJ
Laser-induced ultrafast electron emission from a field emission tip
We show that a field emission tip electron source that is triggered with a femtosecond laser pulse can generate electron pulses shorter than the laser pulse duration (~100 fs). The emission process is sensitive to a power law of the laser intensity, which supports an emission mechanism based on multiphoton absorption followed by over-the-barrier emission. Observed continuous transitions between power laws of different orders are indicative of field emission processes. We show that the source can also be operated so that thermionic emission processes become significant. Understanding these different emission processes is relevant for the production of sub-cycle electron pulses
NGC7538 IRS1 -- an O star driving an ionized jet and giant N-S outflow
NGC 7538 IRS 1 is a very young embedded O star driving an ionized jet and
accreting mass with an accretion rate > 10^-4 Msun/year, which is quenching the
hypercompact HII region. We use SOFIA GREAT data, Herschel PACS and SPIRE
archive data, SOFIA FORCAST archive data, Onsala 20m and CARMA data, and JCMT
archive data to determine the properties of the O star and its outflow. IRS 1
appears to be a single O-star with a bolometric luminosity > 1 10^5 Lsun, i.e.
spectral type O7 or earlier. We find that IRS 1 drives a large molecular
outflow with the blue-shifted northern outflow lobe extending to ~ 280" or 3.6
pc from IRS 1. Near IRS 1 the outflow is well aligned with the ionized jet. The
dynamical time scale of the outflow is ~ 1.3 10^5 yr. The total outflow mass is
~ 130 Msun. We determine a mass outflow rate of 1.0 10^-3 Msun/yr, roughly
consistent with the observed mass accretion rate. We observe strong high
velocity [CII] emission in the outflow, confirming that strong UV radiation
from IRS 1 escapes into the outflow lobes and is ionizing the gas. Many O stars
may form like low mass stars, but with a higher accretion rate and in a denser
environment. As long as the accretion stays high enough to quench the HII
region, the star will continue to grow. When the accretion rate drops, the HII
region will rapidly start to expand.Comment: 21 pages, 19 figures. Accepted for publication in The Astrophysical
Journa
A Resolved Ring of Debris Dust around the Solar Analog HD 107146
We present resolved images of the dust continuum emission from the debris disk around the young (80-200 Myr) solar-type star HD 107146 with CARMA at λ = 1.3 mm and the CSO at λ = 350 μ. Both images show that the dust emission extends over an approximately 10" diameter region. The high-resolution (3") CARMA image further reveals that the dust is distributed in a partial ring with significant decrease in a flux inward of 97 AU. Two prominent emission peaks appear within the ring separated by ~140° in the position angle. The morphology of the dust emission is suggestive of dust captured into a mean motion resonance, which would imply the presence of a planet at an orbital radius of ~45-75 AU
Dynamically Driven Evolution of the Interstellar Medium in M51
We report the highest-fidelity observations of the spiral galaxy M51 in CO
emission, revealing the evolution of giant molecular clouds (GMCs) vis-a-vis
the large-scale galactic structure and dynamics. The most massive GMCs
(so-called GMAs) are first assembled and then broken up as the gas flow through
the spiral arms. The GMAs and their H2 molecules are not fully dissociated into
atomic gas as predicted in stellar feedback scenarios, but are fragmented into
smaller GMCs upon leaving the spiral arms. The remnants of GMAs are detected as
the chains of GMCs that emerge from the spiral arms into interarm regions. The
kinematic shear within the spiral arms is sufficient to unbind the GMAs against
self-gravity. We conclude that the evolution of GMCs is driven by large-scale
galactic dynamics --their coagulation into GMAs is due to spiral arm streaming
motions upon entering the arms, followed by fragmentation due to shear as they
leave the arms on the downstream side. In M51, the majority of the gas remains
molecular from arm entry through the inter-arm region and into the next spiral
arm passage.Comment: 6 pages, including 3 figures. Accepted, ApJ
Observing the Sun with Atacama Large Millimeter/submillimeter Array (ALMA): High Resolution Interferometric Imaging
Observations of the Sun at millimeter and submillimeter wavelengths offer a
unique probe into the structure, dynamics, and heating of the chromosphere; the
structure of sunspots; the formation and eruption of prominences and filaments;
and energetic phenomena such as jets and flares. High-resolution observations
of the Sun at millimeter and submillimeter wavelengths are challenging due to
the intense, extended, low- contrast, and dynamic nature of emission from the
quiet Sun, and the extremely intense and variable nature of emissions
associated with energetic phenomena. The Atacama Large Millimeter/submillimeter
Array (ALMA) was designed with solar observations in mind. The requirements for
solar observations are significantly different from observations of sidereal
sources and special measures are necessary to successfully carry out this type
of observations. We describe the commissioning efforts that enable the use of
two frequency bands, the 3 mm band (Band 3) and the 1.25 mm band (Band 6), for
continuum interferometric-imaging observations of the Sun with ALMA. Examples
of high-resolution synthesized images obtained using the newly commissioned
modes during the solar commissioning campaign held in December 2015 are
presented. Although only 30 of the eventual 66 ALMA antennas were used for the
campaign, the solar images synthesized from the ALMA commissioning data reveal
new features of the solar atmosphere that demonstrate the potential power of
ALMA solar observations. The ongoing expansion of ALMA and solar-commissioning
efforts will continue to enable new and unique solar observing capabilities.Comment: 22 pages, 12 figures, accepted for publication in Solar Physic
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&
COVID-19 model-based practice changes in managing a large prostate cancer practice: following the trends during a month-long ordeal
Coronavirus (COVID-19) has been a life-changing experience for both individuals and institutions. We describe changes in our practice based on real-time assessment of various national and international trends of COVID-19 and its effectiveness in the management of our resources. Initial risk assessment and peak resource requirement using the COVID-19 Hospital Impact Model for Epidemics (CHIME) and McKinsey models. Strengths, weaknesses, opportunities, and threats (SWOT) analysis of our practice\u2019s approach during the pandemic. Based on CHIME the community followed 60% social distancing, the number of expected new patients hospitalized at maximum surge would be 401, with 100 patients requiring ventilator support. In contrast, when the community followed 15% social distancing, the maximum surge of hospitalized new patients would be 1823 and 455 patients would require a ventilator. on April 15, the expected May requirement of ICU beds at peak would be 68, with 61 patients needing ventilators. The estimated surge numbers improved throughout April, and on April 22 the expected ICU bed peak in May would be 11.7, and those requiring ventilator would be 10.5. Simultaneously, within a month, our surgical waitlist grew from 585 to over 723 patients. Our SWOT analysis revealed our internal strengths and inherent weakness, relevant to the pandemic. A graded and a guarded response to this type of situation is crucial in managing patients in a large practice
Australian Opportunities in a Circular Economy for Metals: Findings of the Wealth from Waste Cluster
The Circumstellar Disk and Asymmetric outflow of the EX Lup Outburst System
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations
at 0.3 arcsec-resolution of EX Lup, the prototype of the EXor class of
outbursting pre-main sequence stars. The circumstellar disk of EX Lup is
resolved for the first time in 1.3mm continuum emission and in the =2--1
spectral line of three isotopologues of CO. At the spatial resolution and
sensitivity achieved, the compact dust continuum disk shows no indications of
clumps, fragments, or asymmetries above 5-sigma level. Radiative transfer
modeling constrains the characteristic radius of the dust disk to 23 au and a
total dust mass of 1.010 M (33 M_earth), similar to
other EXor sources. The CO and CO line emission trace the disk
rotation and are used to constrain the disk geometry, kinematics, and a total
gas disk mass of 5.110 M. The CO emission extends
out to a radius of 200 au and is asymmetric, with one side deviating from
Keplerian rotation. We detect blue-shifted, CO arc-like emission located
0.8 arcsec to the north-west, and spatially disconnected from the disk
emission. We interpret this extended structure as the brightened walls of a
cavity excavated by an outflow, which are more commonly seen in FUor sources.
Such outflows have also been seen in the borderline FU/EXor object V1647 Ori,
but not towards EXor objects. Our detection provides evidence that the outflow
phenomenon persists into the EXor phase, suggesting that FUor and EXor objects
are a continuous population in which outflow activity declines with age, with
transitional objects such as EX Lup and V1647 Ori
- …