719 research outputs found
The Yarkovsky Drift's Influence on NEAs: Trends and Predictions with NEOWISE Measurements
We used WISE-derived geometric albedos (p_V) and diameters, as well as
geometric albedos and diameters from the literature, to produce more accurate
diurnal Yarkovsky drift predictions for 540 near-Earth asteroids (NEAs) out of
the current sample of \sim 8,800 known objects. As ten of the twelve objects
with the fastest predicted rates have observed arcs of less than a decade, we
list upcoming apparitions of these NEAs to facilitate observations.Comment: Accepted for publication by The Astronomical Journal. 41 pages, 3
figure
A revised asteroid polarization-albedo relationship using WISE/NEOWISE data
We present a reanalysis of the relationship between asteroid albedo and
polarization properties using the albedos derived from the Wide-field Infrared
Survey Explorer. We find that the function that best describes this relation is
a three-dimensional linear fit in the space of log(albedo)-log(polarization
slope)-log(minimum polarization). When projected to two dimensions the
parameters of the fit are consistent with those found in previous work. We also
define p* as the quantity of maximal polarization variation when compared with
albedo and present the best fitting albedo-p* relation. Some asteroid taxonomic
types stand out in this three-dimensional space, notably the E, B, and M Tholen
types, while others cluster in clumps coincident with the S- and C-complex
bodies. We note that both low albedo and small (D<30 km) asteroids are
under-represented in the polarimetric sample, and we encourage future
polarimetric surveys to focus on these bodies.Comment: 16 pages, Accepted to Ap
Revising the age for the Baptistina asteroid family using WISE/NEOWISE data
We have used numerical routines to model the evolution of a simulated
Baptistina family to constrain its age in light of new measurements of the
diameters and albedos of family members from the Wide-field Infrared Survey
Explorer. We also investigate the effect of varying the assumed physical and
orbital parameters on the best-fitting age. We find that the physically allowed
range of assumed values for the density and thermal conductivity induces a
large uncertainty in the rate of evolution. When realistic uncertainties in the
family members' physical parameters are taken into account we find the
best-fitting age can fall anywhere in the range of 140-320 Myr. Without more
information on the physical properties of the family members it is difficult to
place a more firm constraint on Baptistina's age.Comment: 27 pages, 16 figures, accepted to Ap
Space-Based Thermal Infrared Studies of Asteroids
Large-area surveys operating at mid-infrared wavelengths have proven to be a
valuable means of discovering and characterizing minor planets. Through the use
of radiometric models, it is possible to derive physical properties such as
diameters, albedos, and thermal inertia for large numbers of objects. Modern
detector array technology has resulted in a significant improvement in spatial
resolution and sensitivity compared with previous generations of space-based
infrared telescopes, giving rise to a commensurate increase in the number of
objects that have been observed at these wavelengths. Space-based infrared
surveys of asteroids therefore offer an effective means of rapidly gathering
information about small body populations' orbital and physical properties. The
AKARI, WISE/NEOWISE, Spitzer, and Herschel missions have significantly
increased the number of minor planets with well-determined diameters and
albedos.Comment: Chapter for Asteroids IV book (accepted for publication
NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results
The NEOWISE dataset offers the opportunity to study the variations in albedo
for asteroid classification schemes based on visible and near-infrared
observations for a large sample of minor planets. We have determined the
albedos for nearly 1900 asteroids classified by the Tholen, Bus and Bus-DeMeo
taxonomic classification schemes. We find that the S-complex spans a broad
range of bright albedos, partially overlapping the low albedo C-complex at
small sizes. As expected, the X-complex covers a wide range of albedos. The
multi-wavelength infrared coverage provided by NEOWISE allows determination of
the reflectivity at 3.4 and 4.6 m relative to the visible albedo. The
direct computation of the reflectivity at 3.4 and 4.6 m enables a new
means of comparing the various taxonomic classes. Although C, B, D and T
asteroids all have similarly low visible albedos, the D and T types can be
distinguished from the C and B types by examining their relative reflectance at
3.4 and 4.6 m. All of the albedo distributions are strongly affected by
selection biases against small, low albedo objects, as all objects selected for
taxonomic classification were chosen according to their visible light
brightness. Due to these strong selection biases, we are unable to determine
whether or not there are correlations between size, albedo and space
weathering. We argue that the current set of classified asteroids makes any
such correlations difficult to verify. A sample of taxonomically classified
asteroids drawn without significant albedo bias is needed in order to perform
such an analysis.Comment: Accepted to Ap
WISE/NEOWISE Observations of the Jovian Trojans: Preliminary Results
We present the preliminary analysis of over 1739 known and 349 candidate
Jovian Trojans observed by the NEOWISE component of the Wide-field Infrared
Survey Explorer (WISE). With this survey the available diameters, albedos and
beaming parameters for the Jovian Trojans have been increased by more than an
order of magnitude compared to previous surveys. We find that the Jovian Trojan
population is very homogenous for sizes larger than km (close to the
detection limit of WISE for these objects). The observed sample consists almost
exclusively of low albedo objects, having a mean albedo value of .
The beaming parameter was also derived for a large fraction of the observed
sample, and it is also very homogenous with an observed mean value of
. Preliminary debiasing of the survey shows our observed sample is
consistent with the leading cloud containing more objects than the trailing
cloud. We estimate the fraction to be N(leading)/N(trailing) , lower than the value derived by others.Comment: Accepted for publication in Astrophysical Journal. Electronic table
will be available at the publishers websit
Using Narrow Band Photometry to Detect Young Brown Dwarfs in IC348
We report the discovery of a population of young brown dwarf candidates in
the open star cluster IC348 and the development of a new spectroscopic
classification technique using narrow band photometry. Observations were made
using FLITECAM, the First Light Camera for SOFIA, at the 3-m Shane Telescope at
Lick Observatory. FLITECAM is a new 1-5 micron camera with an 8 arcmin field of
view. Custom narrow band filters were developed to detect absorption features
of water vapor (at 1.495 microns) and methane (at 1.66 microns) characteristic
of brown dwarfs. These filters enable spectral classification of stars and
brown dwarfs without spectroscopy. FLITECAM's narrow and broadband photometry
was verified by examining the color-color and color-magnitude characteristics
of stars whose spectral type and reddening was known from previous surveys.
Using our narrow band filter photometry method, it was possible to identify an
object measured with a signal-to-noise ratio of 20 or better to within +/-3
spectral class subtypes for late-type stars. With this technique, very deep
images of the central region of IC348 (H ~ 20.0) have identified 18 sources as
possible L or T dwarf candidates. Out of these 18, we expect that between 3 - 6
of these objects are statistically likely to be background stars, with the
remainder being true low-mass members of the cluster. If confirmed as cluster
members then these are very low-mass objects (~5 Mjupiter). We also describe
how two additional narrow band filters can improve the contrast between M, L,
and T dwarfs as well as provide a means to determine the reddening of an
individual object.Comment: 43 pages, 17 figures. Accepted for publication in the Astrophysical
Journal 27 June 200
The Euphrosyne family's contribution to the low albedo near-Earth asteroids
The Euphrosyne asteroid family is uniquely situated at high inclination in
the outer Main Belt, bisected by the nu_6 secular resonance. This large, low
albedo family may thus be an important contributor to specific subpopulations
of the near-Earth objects. We present simulations of the orbital evolution of
Euphrosyne family members from the time of breakup to the present day, focusing
on those members that move into near-Earth orbits. We find that family members
typically evolve into a specific region of orbital element-space, with
semimajor axes near ~3 AU, high inclinations, very large eccentricities, and
Tisserand parameters similar to Jupiter family comets. Filtering all known NEOs
with our derived orbital element limits, we find that the population of
candidate objects is significantly lower in albedo than the overall NEO
population, although many of our candidates are also darker than the Euphrosyne
family, and may have properties more similar to comet nuclei. Followup
characterization of these candidates will enable us to compare them to known
family properties, and confirm which ones originated with the breakup of (31)
Euphrosyne.Comment: Accepted for publication in Ap
Characterization of Active Main Belt Object P/2012 F5 (Gibbs): A Possible Impacted Asteroid
In this work we characterize the recently discovered active main belt object
P/2012 F5 (Gibbs), which was discovered with a dust trail > 7' in length in the
outer main belt, 7 months prior to aphelion. We use optical imaging obtained on
UT 2012 March 27 to analyze the central condensation and the long trail. We
find nuclear B-band and R-band apparent magnitudes of 20.96 and 19.93 mag,
respectively, which give an upper limit on the radius of the nucleus of 2.1 km.
The geometric cross-section of material in the trail was ~ 4 x 10^8 m^2,
corresponding to a dust mass of ~ 5 x 10^7 kg. Analysis of infrared images
taken by the Wide-Field Infrared Survey Explorer in September 2010 reveals that
the object was below the detection limit, suggesting that it was less active
than it was during 2012, or possibly inactive, just 6 months after it passed
through perihelion. We set a 1-sigma upper limit on its radius during this time
of 2.9 km. P/2012 F5 (Gibbs) is dynamically stable in the outer main belt on
timescales of ~ 1 Gyr, pointing towards an asteroidal origin. We find that the
morphology of the ejected dust is consistent with it being produced by a single
event that occurred on UT 2011 July 7 20 days, possibly as the result of
a collision with a small impactor.Comment: 29 pages, 5 figures. Accepted for publication in Ap
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