1,322 research outputs found
Physical Characterization of Warm Spitzer-observed Near-Earth Objects
Near-infrared spectroscopy of Near-Earth Objects (NEOs) connects diagnostic
spectral features to specific surface mineralogies. The combination of
spectroscopy with albedos and diameters derived from thermal infrared
observations can increase the scientific return beyond that of the individual
datasets. To that end, we have completed a spectroscopic observing campaign to
complement the ExploreNEOs Warm Spitzer program that obtained albedos and
diameters of nearly 600 NEOs (Trilling et al. 2010). Here we present the
results of observations using the low-resolution prism mode (~0.7-2.5 microns)
of the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). We also
include near-infrared observations of ExploreNEOs targets from the MIT-UH-IRTF
Joint Campaign for Spectral Reconnaissance. Our dataset includes near-infrared
spectra of 187 ExploreNEOs targets (125 observations of 92 objects from our
survey and 213 observations of 154 objects from the MIT survey). We identify a
taxonomic class for each spectrum and use band parameter analysis to
investigate the mineralogies for the S-, Q-, and V-complex objects. Our
analysis suggests that for spectra that contain near-infrared data but lack the
visible wavelength region, the Bus-DeMeo system misidentifies some S-types as
Q-types. We find no correlation between spectral band parameters and
ExploreNEOs albedos and diameters. We find slightly negative Band Area Ratio
(BAR) correlations with phase angle for Eros and Ivar, but a positive BAR
correlation with phase angle for Ganymed. We find evidence for spectral phase
reddening for Eros, Ganymed, and Ivar. We identify the likely ordinary
chondrite type analog for a subset of our sample. Our resulting proportions of
H, L, and LL ordinary chondrites differ from those calculated for meteorite
falls and in previous studies of ordinary chondrite-like NEOs.Comment: 6 Tables, 9 Figure
De-biased Populations of Kuiper Belt Objects from the Deep Ecliptic Survey
The Deep Ecliptic Survey (DES) discovered hundreds of Kuiper Belt objects
from 1998-2005. Follow-up observations yielded 304 objects with good dynamical
classifications (Classical, Scattered, Centaur, or 16 mean-motion resonances
with Neptune). The DES search fields are well documented, enabling us to
calculate the probability of detecting objects with particular orbital
parameters and absolute magnitudes at a randomized point in each orbit.
Grouping objects together by dynamical class leads, we estimate the orbital
element distributions (a, e, i) for the largest three classes (Classical, 3:2,
and Scattered) using maximum likelihood. Using H-magnitude as a proxy for the
object size, we fit a power law to the number of objects for 8 classes with at
least 5 detected members (246 objects). The best Classical slope is
alpha=1.02+/-0.01 (observed from 5<=H<=7.2). Six dynamical classes (Scattered
plus 5 resonances) are consistent in slope with the Classicals, though the
absolute number of objects is scaled. The exception to the power law relation
are the Centaurs (non-resonant with perihelia closer than Neptune, and thus
detectable at smaller sizes), with alpha=0.42+/-0.02 (7.5<H<11). This is
consistent with a knee in the H-distribution around H=7.2 as reported elsewhere
(Bernstein et al. 2004, Fraser et al. 2014). Based on the Classical-derived
magnitude distribution, the total number of objects (H<=7) in each class are:
Classical (2100+/-300 objects), Scattered (2800+/-400), 3:2 (570+/-80), 2:1
(400+/-50), 5:2 (270+/-40), 7:4 (69+/-9), 5:3 (60+/-8). The independent
estimate for the number of Centaurs in the same H range is 13+/-5. If instead
all objects are divided by inclination into "Hot" and "Cold" populations,
following Fraser et al. (2014), we find that alphaHot=0.90+/-0.02, while
alphaCold=1.32+/-0.02, in good agreement with that work.Comment: 26 pages emulateapj, 6 figures, 5 tables, accepted by A
Believing in Credibility Measures:Reviewing Credibility Measures in Media Research From 1951 to 2018
Believing in Credibility Measures:Reviewing Credibility Measures in Media Research From 1951 to 2018
Optical Guidance System /OGS/ for rendezvous and docking Final report
Optical guidance system for Apollo rendezvous and dockin
The Size Distribution of Trans-Neptunian Bodies
[Condensed] We search 0.02 deg^2 for trans-Neptunian objects (TNOs) with
m<=29.2 (diameter ~15 km) using the ACS on HST. Three new objects are
discovered, roughly 25 times fewer than expected from extrapolation of the
differential sky density Sigma(m) of brighter objects. The ACS and other recent
TNO surveys show departures from a power law size distribution. Division of the
TNO sample into ``classical Kuiper belt'' (CKB) and ``Excited'' samples reveals
that Sigma(m) differs for the two populations at 96% confidence. A double power
law adequately fits all data. Implications include: The total mass of the CKB
is ~0.010 M_Earth, only a few times Pluto's mass, and is predominately in the
form of ~100 km bodies. The mass of Excited objects is perhaps a few times
larger. The Excited class has a shallower bright-end size distribution; the
largest objects, including Pluto, comprise tens of percent of the total mass
whereas the largest CKBOs are only ~2% of its mass. The predicted mass of the
largest Excited body is close to the Pluto mass; the largest CKBO is ~60 times
less massive. The deficit of small TNOs occurs for sizes subject to disruption
by present-day collisions, suggesting extensive depletion by collisions. Both
accretion and erosion appearing to have proceeded to more advanced stages in
the Excited class than the CKB. The absence of distant TNOs implies that any
distant (60 AU) population must have less than the CKB mass in the form of
objects 40 km or larger. The CKB population is sparser than theoretical
estimates of the required precursor population for short period comets, but the
Excited population could be a viable precursor population.Comment: Revised version accepted to the Astronomical Journal. Numerical
results are very slightly revised. Implications for the origins of
short-period comets are substantially revised, and tedious material on
statistical tests has been collected into a new Appendi
Possible Observational Criteria for Distinguishing Brown Dwarfs from Planets
The difference in formation process between binary stars and planetary
systems is reflected in their composition as well as their orbital
architecture, particularly orbital eccentricity as a function of orbital
period. It is suggested here that this difference can be used as an
observational criterion to distinguish between brown dwarfs and planets.
Application of the orbital criterion suggests that with three possible
exceptions, all of the recently-discovered substellar companions discovered to
date may be brown dwarfs and not planets. These criterion may be used as a
guide for interpretation of the nature of sub-stellar mass companions to stars
in the future.Comment: LaTeX, 11 pages including 2 figures, accepted for publication in the
Astrophysical Journal Letter
Do Proto-Jovian Planets Drive Outflows?
We discuss the possibility that gaseous giant planets drive strong outflows
during early phases of their formation. We consider the range of parameters
appropriate for magneto-centrifugally driven stellar and disk outflow models
and find that if the proto-Jovian planet or accretion disk had a magnetic field
of >~ 10 Gauss and moderate mass inflow rates through the disk of less than
10^-7 M_J/yr that it is possible to drive an outflow. Estimates based both on
scaling from empirical laws observed in proto-stellar outflows and the
magneto-centrigugal disk and stellar+disk wind models suggest that winds with
mass outflow rates of 10^-8 M_J/yr and velocities of order ~ 20 km/s could be
driven from proto-Jovian planets. Prospects for detection and some implications
for the formation of the solar system are briefly discussed.Comment: AAS Latex, accepted for Ap
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