177 research outputs found
Influence of final state interaction on incoherent pion photoproduction on the deuteron in the region of the Delta-resonance
The influence of final state - and pi N-rescattering in incoherent pion
photoproduction on the deuteron has been investigated. For the elementary
photoproduction operator an effective Lagrangian model is used which describes
well the elementary reaction. The interactions in the final two-body subsystems
are taken in separable form. While NN-rescattering shows quite a significant
effect, particularly strong for neutral pion production, pi N-rescattering is
almost negligible. Inclusion of such effects leads to an improved and quite
satisfactory agreement with experiment.Comment: 18 pages revtex4 including 16 postscript figure
Reassessing the formation of the inner Oort cloud in an embedded star cluster
We re-examine the formation of the inner Oort comet cloud while the Sun was
in its birth cluster with the aid of numerical simulations. This work is a
continuation of an earlier study (Brasser et al., 2006) with several
substantial modifications. First, the system consisting of stars, planets and
comets is treated self-consistently in our N-body simulations, rather than
approximating the stellar encounters with the outer Solar System as hyperbolic
fly-bys. Second, we have included the expulsion of the cluster gas, a feature
that was absent previously. Third, we have used several models for the initial
conditions and density profile of the cluster -- either a Hernquist or Plummer
potential -- and chose other parameters based on the latest observations of
embedded clusters from the literature. {These other parameters result in the
stars being on radial orbits and the cluster collapses.} Similar to previous
studies, in our simulations the inner Oort cloud is formed from comets being
scattered by Jupiter and Saturn and having their pericentres decoupled from the
planets by perturbations from the cluster gas and other stars. We find that all
inner Oort clouds formed in these clusters have an inner edge ranging from 100
AU to a few hundred AU, and an outer edge at over 100\,000 AU, with little
variation in these values for all clusters. All inner Oort clouds formed are
consistent with the existence of (90377) Sedna, an inner Oort cloud dwarf
planetoid, at the inner edge of the cloud: Sedna tends to be at the innermost
2% for Plummer models, while it is 5% for Hernquist models. We emphasise that
the existence of Sedna is a generic outcome. We define a `concentration radius'
for the inner Oort cloud and find that its value increases with increasing
number of stars in the cluster, ranging from 600 AU to 1500 AU for Hernquist
clusters and from 1500 AU to 4000 AU for Plummer clusters...Comment: Accepted Icarus 201
Planet Four: Terrains - Discovery of Araneiforms Outside of the South Polar Layered Deposits
We present the results of a systematic mapping of seasonally sculpted
terrains on the South Polar region of Mars with the Planet Four: Terrains (P4T)
online citizen science project. P4T enlists members of the general public to
visually identify features in the publicly released Mars Reconnaissance Orbiter
CTX images. In particular, P4T volunteers are asked to identify: 1) araneiforms
(including features with a central pit and radiating channels known as
'spiders'); 2) erosional depressions, troughs, mesas, ridges, and
quasi-circular pits characteristic of the South Polar Residual Cap (SPRC) which
we collectively refer to as 'Swiss cheese terrain', and 3) craters. In this
work we present the distributions of our high confidence classic spider
araneiforms and Swiss cheese terrain identifications. We find no locations
within our high confidence spider sample that also have confident Swiss cheese
terrain identifications. Previously spiders were reported as being confined to
the South Polar Layered Deposits (SPLD). Our work has provided the first
identification of spiders at locations outside of the SPLD, confirmed with high
resolution HiRISE imaging. We find araneiforms on the Amazonian and Hesperian
polar units and the Early Noachian highland units, with 75% of the identified
araneiform locations in our high confidence sample residing on the SPLD. With
our current coverage, we cannot confirm whether these are the only geologic
units conducive to araneiform formation on the Martian South Polar region. Our
results are consistent with the current CO2 jet formation scenario with the
process exploiting weaknesses in the surface below the seasonal CO2 ice sheet
to carve araneiform channels into the regolith over many seasons. These new
regions serve as additional probes of the conditions required for channel
creation in the CO2 jet process. (Abridged)Comment: accepted to Icarus - Supplemental data files are available at
https://www.zooniverse.org/projects/mschwamb/planet-four-terrains/about/results
- Icarus print version available at
http://www.sciencedirect.com/science/article/pii/S001910351730055
An Oort cloud origin for the high-inclination, high-perihelion Centaurs
We analyse the origin of three Centaurs with perihelia in the range 15 AU to
30 AU, inclinations above 70 deg and semi-major axes shorter than 100 AU. Based
on long-term numerical simulations we conclude that these objects most likely
originate from the Oort cloud rather than the Kuiper Belt or Scattered Disc. We
estimate that there are currently between 1 and 200 of these high-inclination,
high-perihelion Centaurs with absolute magnitude H<8.Comment: Accepted for publication in MNRA
Potential Backup Targets for Comet Interceptor
Comet Interceptor is an ESA F-class mission expected to launch in 2028 on the
same launcher as ESA's ARIEL mission. Comet Interceptor's science payload
consists of three spacecraft, a primary spacecraft that will carry two smaller
probes to be released at the target. The three spacecraft will fly-by the
target along different chords, providing multiple simultaneous perspectives of
the comet nucleus and its environment. Each of the spacecraft will be equipped
with different but complementary instrument suites designed to study the far
and near coma environment and surface of a comet or interstellar object (ISO).
The primary spacecraft will perform a fly-by at ~1000 km from the target. The
two smaller probes will travel deeper into the coma, closer to the nucleus. The
mission is being designed and launched without a specific comet designated as
its main target. Comet Interceptor will travel to the Sun-Earth L2 Lagrangian
point with ARIEL and wait in hibernation until a suitable long-period comet
(LPC) is found that will come close enough to the Sun for the spacecraft to
maneuver to an encounter trajectory. To prepare for all eventualities, the
science team has assembled a preliminary set of backup targets from the known
Jupiter family comets, where a suitable fly-by trajectory can be achieved
during the nominal mission timeline (including the possibility of some launch
delay). To better prioritize this list, we are releasing our potential backup
targets in order to solicit the planetary community's help with observations of
these objects over future apparitions and to encourage publication of archival
data on these objects.Comment: Accepted to RNAA
Planet Hunters VII. Discovery of a New Low-Mass, Low-Density Planet (PH3 c) Orbiting Kepler-289 with Mass Measurements of Two Additional Planets (PH3 b and d)
We report the discovery of one newly confirmed planet ( days,
) and mass determinations of two previously
validated Kepler planets, Kepler-289 b ( days,
) and Kepler-289-c ( days,
), through their transit timing variations
(TTVs). We also exclude the possibility that these three planets reside in a
Laplace resonance. The outer planet has very deep (), high
signal-to-noise transits, which puts extremely tight constraints on its host
star's stellar properties via Kepler's Third Law. The star PH3 is a young
( Gyr as determined by isochrones and gyrochronology), Sun-like star
with , , and
K. The middle planet's large TTV amplitude (
hours) resulted either in non-detections or inaccurate detections in previous
searches. A strong chopping signal, a shorter period sinusoid in the TTVs,
allows us to break the mass-eccentricity degeneracy and uniquely determine the
masses of the inner, middle, and outer planets to be ,
, and , which we designate PH3 b, c, and
d, respectively. Furthermore, the middle planet, PH3 c, has a relatively low
density, g/cm for a planet of its mass, requiring a
substantial H/He atmosphere of by mass, and joins a
growing population of low-mass, low-density planets.Comment: 21 pages, 10 figures, 5 tables, accepted into Ap
The TAOS Project: Statistical Analysis of Multi-Telescope Time Series Data
The Taiwanese-American Occultation Survey (TAOS) monitors fields of up to
~1000 stars at 5 Hz simultaneously with four small telescopes to detect
occultation events from small (~1 km) Kuiper Belt Objects (KBOs). The survey
presents a number of challenges, in particular the fact that the occultation
events we are searching for are extremely rare and are typically manifested as
slight flux drops for only one or two consecutive time series measurements. We
have developed a statistical analysis technique to search the multi-telescope
data set for simultaneous flux drops which provides a robust false positive
rejection and calculation of event significance. In this paper, we describe in
detail this statistical technique and its application to the TAOS data set.Comment: 15 pages, 14 figures. Submitted to PAS
First measurements of the ^16O(e,e'pn)^14N reaction
This paper reports on the first measurement of the ^16O(e,e'pn)^14N reaction.
Data were measured in kinematics centred on a super-parallel geometry at energy
and momentum transfers of 215 MeV and 316 MeV/c. The experimental resolution
was sufficient to distinguish groups of states in the residual nucleus but not
good enough to separate individual states. The data show a strong dependence on
missing momentum and this dependence appears to be different for two groups of
states in the residual nucleus. Theoretical calculations of the reaction using
the Pavia code do not reproduce the shape or the magnitude of the data.Comment: 10 pages, 11 figures, 2 tables, Accepted for publication in EPJ
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