453 research outputs found
Search for L5 Earth Trojans with DECam
Most of the major planets in the Solar System support populations of
co-orbiting bodies, known as Trojans, at their L4 and L5 Lagrange points. In
contrast, Earth has only one known co-orbiting companion. This paper presents
the results from a search for Earth Trojans using the DECam instrument on the
Blanco Telescope at CTIO. This search found no additional Trojans in spite of
greater coverage compared to previous surveys of the L5 point. Therefore, the
main result of this work is to place the most stringent constraints to date on
the population of Earth Trojans. These constraints depend on assumptions
regarding the underlying population properties, especially the slope of the
magnitude distribution (which in turn depends on the size and albedo
distributions of the objects). For standard assumptions, we calculate upper
limits to a 90% confidence limit on the L5 population of for
magnitude , for , and = 97 for
. This latter magnitude limit corresponds to Trojans 300 m in
size for albedo . At H=19.7, these upper limits are consistent with
previous L4 Earth Trojan constraints and significantly improve L5 constraints.Comment: 17 pages, 12 figures, Accepted to MNRA
First Near-IR Spectroscopic Survey of Neptune Trojans with JWST: Distinct Surface Compositions of Red vs Ultra-Red Neptune Trojans
Neptune's Trojan asteroids have been observed to have a variety of optical
colors, most notably red (g r 0.75), but
the underlying cause of these different color classifications is unknown.
Near-IR spectroscopy can be used as a probe of the surface composition of these
objects, as broad ice bands for a variety of materials are present in the
near-IR. Here, we present the first results of a spectroscopic survey of
Neptune's Trojan asteroids using the NIRSpec instrument on JWST. We compare the
near-IR spectra of eight Neptune Trojans (NTs) based on different optical color
classifications and with model spectra of different ices. We find that most of
our targets are consistent with a surface covered in a thin layer of HO and
CO ices, while the only NT to reliably be classified as ultra-red is
covered in ice tholins in addition to CO. Ice tholins are a known reddening
agent when subjected to irradiation, so these results support the hypothesis
that differences in optical color are due to differences in irradiation of the
surfaces of these bodies. Since NTs have very similar orbits and therefore
generally similar levels of irradiation at the current time, our results
suggest that these objects have unique origins or there is ongoing processing
of the surfaces of these objects through stochastic disturbances such as
impacts.Comment: 10 pages, 2 figures, Submitted to ApJ
Changes in Head, Withers, and Pelvis Movement Asymmetry in Lame Horses as a Function of Diagnostic Anesthesia Outcome, Surface and Direction
Evaluation of diagnostic anesthesia during equine lameness examination requires comparison of com-plex movement patterns and can be influenced by expectation bias. There is limited research about how changes in movement asymmetries after successful analgesia are affected by different exercise condi-tions. Movement asymmetry of head, withers and pelvis was quantified in N = 31 horses undergoing forelimb or hindlimb diagnostic anesthesia. Evaluation on a straight line and a circle was performed with subjective diagnostic anesthesia outcome and quantitative changes recorded. Mixed linear models ( P < .05) analyzed the differences in movement asymmetry before/after diagnostic anesthesia -random fac-tor: horse, fixed factors: surface (soft, hard), direction (straight, inside, outside, inside-outside average), diagnostic anesthesia outcome (negative, partially positive, positive) and two-way interactions. Forelimb diagnostic anesthesia influenced primary movement asymmetry (all head and withers parameters) and compensatory movement asymmetry (two pelvic parameters) either individually ( P <=.009) or in interac-tion with surface ( P <=.03). Hindlimb diagnostic anesthesia influenced primary movement asymmetry (all pelvic parameters) and compensatory movement asymmetry (two head and two withers parameters) ei-ther individually ( P <=.04) or in interaction with surface ( P <=.01;) or direction ( P <=.006). Direction was also significant individually for two pelvic parameters ( P <=.04). Changes in primary movement asymmetries after partially positive or positive outcomes indicated improvement in the blocked limb. Compensatory changes were mostly in agreement with the 'law of sides'. The changes were more pronounced on the hard surface for hindlimb lameness and on the soft surface for forelimb lameness. Withers asymmetry showed distinct patterns for forelimb and hindlimb lameness potentially aiding clinical decision-making.(c) 2022 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/
ArborZ: Photometric Redshifts Using Boosted Decision Trees
Precision photometric redshifts will be essential for extracting cosmological
parameters from the next generation of wide-area imaging surveys. In this paper
we introduce a photometric redshift algorithm, ArborZ, based on the
machine-learning technique of Boosted Decision Trees. We study the algorithm
using galaxies from the Sloan Digital Sky Survey and from mock catalogs
intended to simulate both the SDSS and the upcoming Dark Energy Survey. We show
that it improves upon the performance of existing algorithms. Moreover, the
method naturally leads to the reconstruction of a full probability density
function (PDF) for the photometric redshift of each galaxy, not merely a single
"best estimate" and error, and also provides a photo-z quality figure-of-merit
for each galaxy that can be used to reject outliers. We show that the stacked
PDFs yield a more accurate reconstruction of the redshift distribution N(z). We
discuss limitations of the current algorithm and ideas for future work.Comment: 10 pages, 13 figures, submitted to Ap
Data Deluge in Astrophysics: Photometric Redshifts as a Template Use Case
Astronomy has entered the big data era and Machine Learning based methods
have found widespread use in a large variety of astronomical applications. This
is demonstrated by the recent huge increase in the number of publications
making use of this new approach. The usage of machine learning methods, however
is still far from trivial and many problems still need to be solved. Using the
evaluation of photometric redshifts as a case study, we outline the main
problems and some ongoing efforts to solve them.Comment: 13 pages, 3 figures, Springer's Communications in Computer and
Information Science (CCIS), Vol. 82
Evidence for Color Dichotomy in the Primordial Neptunian Trojan Population
In the current model of early Solar System evolution, the stable members of
the Jovian and Neptunian Trojan populations were captured into resonance from
the leftover reservoir of planetesimals during the outward migration of the
giant planets. As a result, both Jovian and Neptunian Trojans share a common
origin with the primordial disk population, whose other surviving members
constitute today's trans-Neptunian object (TNO) populations. The cold classical
TNOs are ultra-red, while the dynamically excited "hot" population of TNOs
contains a mixture of ultra-red and blue objects. In contrast, Jovian and
Neptunian Trojans are observed to be blue. While the absence of ultra-red
Jovian Trojans can be readily explained by the sublimation of volatile material
from their surfaces due to the high flux of solar radiation at 5AU, the lack of
ultra-red Neptunian Trojans presents both a puzzle and a challenge to formation
models. In this work we report the discovery by the Dark Energy Survey (DES) of
two new dynamically stable L4 Neptunian Trojans,2013 VX30 and 2014 UU240, both
with inclinations i >30 degrees, making them the highest-inclination known
stable Neptunian Trojans. We have measured the colors of these and three other
dynamically stable Neptunian Trojans previously observed by DES, and find that
2013 VX30 is ultra-red, the first such Neptunian Trojan in its class. As such,
2013 VX30 may be a "missing link" between the Trojan and TNO populations. Using
a simulation of the DES TNO detection efficiency, we find that there are 162
+/- 73 Trojans with Hr < 10 at the L4 Lagrange point of Neptune. Moreover, the
blue-to-red Neptunian Trojan population ratio should be higher than 17:1. Based
on this result, we discuss the possible origin of the ultra-red Neptunian
Trojan population and its implications for the formation history of Neptunian
Trojans
The DECam Ecliptic Exploration Project (DEEP) II. Observational Strategy and Design
We present the DECam Ecliptic Exploration Project (DEEP) survey strategy
including observing cadence for orbit determination, exposure times, field
pointings and filter choices. The overall goal of the survey is to discover and
characterize the orbits of a few thousand Trans-Neptunian Objects (TNOs) using
the Dark Energy Camera (DECam) on the Cerro Tololo Inter-American Observatory
(CTIO) Blanco 4 meter telescope. The experiment is designed to collect a very
deep series of exposures totaling a few hours on sky for each of several 2.7
square degree DECam fields-of-view to achieve a magnitude of about 26.2 using a
wide VR filter which encompasses both the V and R bandpasses. In the first
year, several nights were combined to achieve a sky area of about 34 square
degrees. In subsequent years, the fields have been re-visited to allow TNOs to
be tracked for orbit determination. When complete, DEEP will be the largest
survey of the outer solar system ever undertaken in terms of newly discovered
object numbers, and the most prolific at producing multi-year orbital
information for the population of minor planets beyond Neptune at 30 au.Comment: 29 pages, 4 figures and 4 table
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