1,052 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
Efficacy of a T Cell-Biased Adenovirus Vector as a Zika Virus Vaccine
Zika virus (ZIKV) is a major public health concern due to the risk of congenital Zika syndrome in developing fetuses and Guillain-Barre syndrome in adults. Currently, there are no approved vaccines available to protect against infection. Adenoviruses are safe and highly immunogenic vaccine vectors capable of inducing lasting humoral and cellular immune responses. Here, we developed two Adenovirus (Ad) vectored Zika virus vaccines by inserting a ZIKV prM-E gene expression cassette into human Ad types 4 (Ad4-prM-E) and 5 (Ad5-prM-E). Immune correlates indicate that Ad5-prM-E vaccination induces both an anti-ZIKV antibody and T-cell responses whereas Ad4-prM-E vaccination only induces a T-cell response. In a highly lethal challenge in an interferon α/β receptor knockout mice, 80% of Ad5 vaccinated animals and 33% of Ad4 vaccinated animals survived a lethal ZIKV challenge, whereas no animals in the sham vaccinated group survived. In an infection model utilizing immunocompetent C57BL/6 mice that were immunized and then treated with a blocking anti-IFNAR-1 antibody immediately before ZIKV challenge, 100% of Ad4-prM-E and Ad5-prM-E vaccinated mice survived. This indicates that Ad4-prM-E vaccination is protective without the development of detectable anti-ZIKV antibodies. The protection seen in these highly lethal mouse models demonstrate the efficacy of Ad vectored vaccines for use against ZIKV
uvbyCa H beta CCD Photometry of Clusters. VII. The Intermediate-Age Anticenter Cluster Melotte 71
CCD photometry on the intermediate-band uvbyCa H beta system is presented for
the anticenter, intermediate-age open cluster, Melotte 71. Restricting the data
to probable single members of the cluster using the color-magnitude diagram and
the photometric indices alone generates a sample of 48 F dwarfs on the
unevolved main sequence. The average E(b-y) = 0.148 +/- 0.003 (s.e.m.) or
E(B-V) = 0.202 +/- 0.004 (s.e.m.), where the errors refer to internal errors
alone. With this reddening, [Fe/H] is derived from both m1 and hk, using H beta
and b-y as the temperature index, with excellent agreement among the four
approaches and a final weighted average of [Fe/H] = -0.17 +/- 0.02 (s.e.m.) for
the cluster, on a scale where the Hyades has [Fe/H] = +0.12. When adjusted for
the higher reddening estimate, the previous metallicity estimates from
Washington photometry and from spectroscopy are now in agreement with the
intermediate-band result. From comparisons to isochrones of appropriate
metallicity, the cluster age and distance are determined as 0.9 +/- 0.1 Gyr and
(m-M) = 12.2 +/- 0.1 or (m-M)_0 = 11.6 +/- 0.1. At this distance from the sun,
Mel 71 has a galactocentric distance of 10.0 kpc on a scale where the sun is
8.5 kpc from the galactic center. Based upon its age, distance, and elemental
abundances, Mel 71 appears to be a less populous analog to NGC 3960.Comment: Accepted for Astronomical Journal. 38 page latex file includes 11
figures and short version of data table. Full table will appear in online AJ
or may be requested from author
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&
On the structure of the transition disk around TW Hya
For over a decade, the structure of the inner cavity in the transition disk
of TW Hydrae has been a subject of debate. Modeling the disk with data obtained
at different wavelengths has led to a variety of proposed disk structures.
Rather than being inconsistent, the individual models might point to the
different faces of physical processes going on in disks, such as dust growth
and planet formation. Our aim is to investigate the structure of the transition
disk again and to find to what extent we can reconcile apparent model
differences. A large set of high-angular-resolution data was collected from
near-infrared to centimeter wavelengths. We investigated the existing disk
models and established a new self-consistent radiative-transfer model. A
genetic fitting algorithm was used to automatize the parameter fitting. Simple
disk models with a vertical inner rim and a radially homogeneous dust
composition from small to large grains cannot reproduce the combined data set.
Two modifications are applied to this simple disk model: (1) the inner rim is
smoothed by exponentially decreasing the surface density in the inner ~3 AU,
and (2) the largest grains (>100 um) are concentrated towards the inner disk
region. Both properties can be linked to fundamental processes that determine
the evolution of protoplanetary disks: the shaping by a possible companion and
the different regimes of dust-grain growth, respectively. The full
interferometric data set from near-infrared to centimeter wavelengths requires
a revision of existing models for the TW Hya disk. We present a new model that
incorporates the characteristic structures of previous models but deviates in
two key aspects: it does not have a sharp edge at 4 AU, and the surface density
of large grains differs from that of smaller grains. This is the first
successful radiative-transfer-based model for a full set of interferometric
data.Comment: 22 pages, 12 figures, accepted for publication in Astronomy &
Astrophysic
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Mercury separation from aqueous wastes
This project is providing an assessment of new sorbents for removing mercury from wastes at US Department of Energy sites. Four aqueous wastes were chosen for lab-scale testing; a high-salt, acidic waste currently stored at Idaho National Engineering Laboratory (INEL); a high-salt, alkaline waste stored at the Savannah River Site (SRS); a dilute lithium hydroxide solution stored at the Oak Ridge Y-12 Plant; and a low-salt, neutral groundwater generated at the Y-12 Plant. Eight adsorbents have been identified for testing, covering a wide range of cost and capability. Screening tests have been completed, which identified the most promising adsorbents for each waste stream. Batch isotherm tests have been completed using the most promising adsorbents, and column tests are in progress. Because of the wide range of waste compositions tested, no one adsorbent is effective in all of these waste streams. Based on loading capacity and compatibility with the waste solutions. the most effective adsorbents identified to date are SuperLig 618 for the INEL tank waste stimulant; Mersorb followed by lonac SR-3 for the SRS tank waste stimulant; Durasil 70 and Ionac SR-3) for the LIOH solution; and lonac SR-3 followed by lonac SR-4 and Mersorb for the Y-12 groundwater
A gap in the planetesimal disc around HD 107146 and asymmetric warm dust emission revealed by ALMA
While detecting low mass exoplanets at tens of au is beyond current
instrumentation, debris discs provide a unique opportunity to study the outer
regions of planetary systems. Here we report new ALMA observations of the
80-200 Myr old Solar analogue HD 107146 that reveal the radial structure of its
exo-Kuiper belt at wavelengths of 1.1 and 0.86 mm. We find that the
planetesimal disc is broad, extending from 40 to 140 au, and it is
characterised by a circular gap extending from 60 to 100 au in which the
continuum emission drops by about 50%. We also report the non-detection of the
CO J=3-2 emission line, confirming that there is not enough gas to affect the
dust distribution. To date, HD 107146 is the only gas-poor system showing
multiple rings in the distribution of millimeter sized particles. These rings
suggest a similar distribution of the planetesimals producing small dust grains
that could be explained invoking the presence of one or more perturbing
planets. Because the disk appears axisymmetric, such planets should be on
circular orbits. By comparing N-body simulations with the observed visibilities
we find that to explain the radial extent and depth of the gap, it would be
required the presence of multiple low mass planets or a single planet that
migrated through the disc. Interior to HD 107146's exo-Kuiper belt we find
extended emission with a peak at ~20 au and consistent with the inner warm belt
that was previously predicted based on 22m excess as in many other
systems. This warm belt is the first to be imaged, although unexpectedly
suggesting that it is asymmetric. This could be due to a large belt
eccentricity or due to clumpy structure produced by resonant trapping with an
additional inner planet
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
The first ALMA view of IRAS 16293-2422: Direct detection of infall onto source B and high-resolution kinematics of source A
Aims: We focus on the kinematical properties of a proto-binary to study the
infall and rotation of gas towards its two protostellar components. Methods: We
present ALMA Science Verification observations with high-spectral resolution of
IRAS 16293-2422 at 220.2 GHz. The wealth of molecular lines in this source and
the very high spectral resolution offered by ALMA allow us to study the gas
kinematics with unprecedented detail. Results: We present the first detection
of an inverse P-Cygni profile towards source B in the three brightest lines.
The line profiles are fitted with a simple two-layer model to derive an infall
rate of 4.5x10^-5 Msun/yr. This infall detection would rule-out the previously
suggested possibility that source B is a T Tauri star. A position velocity
diagram for source A shows evidence for rotation with an axis close to the
line-of-sight.Comment: Accepted by A&A Letters. 4 pages, 3 figures, 3 appendices (one for
Tables, one for additional figures). This second version includes small
language modifications and changes to keep the letter within the 4 page limi
Multiwavelength analysis for interferometric (sub-)mm observations of protoplanetary disks: Radial constraints on the dust properties of protoplanetary disks
Context. The growth of dust grains from sub-μm to mm and cm sizes is the first step towards the formation of planetesimals. Theoretical models of grain growth predict that dust properties change as a function of disk radius, mass, age, and other physical conditions. High angular resolution observations at several (sub-)mm wavelengths constitute the ideal tool with which to directly probe the bulk of dust grains and to investigate the radial distribution of their properties.
Aims. We lay down the methodology for a multiwavelength analysis of (sub-)mm and cm continuum interferometric observations to self-consistently constrain the disk structure and the radial variation of the dust properties. The computational architecture is massively parallel and highly modular.
Methods. 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.
Results. 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 ~0.88 mm to ~10 mm is available from SMA, CARMA, and VLA. In these disks we find evidence of a decrease in the maximum dust grain size, a_(max), with radius. We derive large a_(max) values up to 1 cm in the inner disk 15 AU ≤ R ≤ 30 AU and smaller grains with a_(max) ~ 1 mm in the outer disk (R ≳ 80 AU). Our analysis of the AS 209 protoplanetary disk confirms previous literature results showing amax decreasing with radius.
Conclusions. Theoretical studies of planetary formation through grain growth are plagued by the lack of direct information on the radial distribution of the dust grain size. In this paper we develop a multiwavelength 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
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