14,912 research outputs found
A Collisional Family in the Classical Kuiper Belt
The dynamical evolution of Classical Kuiper Belt Objects (CKBOs) divides into
two parts, according to the secular theory of test particle orbits. The first
part is a forced oscillation driven by the planets, while the second part is a
free oscillation whose amplitude is determined by the initial orbit of the test
particle. We extract the free orbital inclinations and free orbital
eccentricities from the osculating elements of 125 known CKBOs. The free
inclinations of 32 CKBOs strongly cluster about 2 degrees at orbital semi-major
axes between 44 and 45 AU. We propose that these objects comprise a collisional
family, the first so identified in the Kuiper Belt. Members of this family are
plausibly the fragments of an ancient parent body having a minimum diameter of
\~800 km. This body was disrupted upon colliding with a comparably sized
object, and generated ejecta having similar free inclinations. Our candidate
family is dynamically akin to a sub-family of Koronis asteroids located at
semi-major axes less than 2.91 AU; both families exhibit a wider range in free
eccentricity than in free inclination, implying that the relative velocity
between parent and projectile prior to impact lay mostly in the invariable
plane of the solar system. We urge more discoveries of new CKBOs to test the
reality of our candidate family and physical studies of candidate family
members to probe the heretofore unseen interior of a massive, primitive
planetesimal.Comment: final revised version, accepted to ApJ Letters, includes minor caveat
regarding Koronis asteroid famil
The Minimum-Mass Extrasolar Nebula: In-Situ Formation of Close-In Super-Earths
Close-in super-Earths, with radii R = 2-5 R_Earth and orbital periods P < 100
days, orbit more than half, and perhaps nearly all Sun-like stars in the
universe. We use this omnipresent population to construct the minimum-mass
extrasolar nebula (MMEN), the circumstellar disk of solar-composition solids
and gas from which such planets formed, if they formed near their current
locations and did not migrate. In a series of back-of-the-envelope
calculations, we demonstrate how in-situ formation in the MMEN is fast,
efficient, and can reproduce many of the observed properties of close-in
super-Earths, including their gas-to-rock fractions. Testable predictions are
discussed.Comment: Accepted to MNRAS 2013 March
Eccentricity Excitation and Apsidal Resonance Capture in the Planetary System Upsilon Andromedae
The orbits of the outer two known planets orbiting Upsilon Andromedae are
remarkably eccentric. Planet C possesses an orbital eccentricity of e1 = 0.253.
For the more distant planet D, e2 = 0.308. Previous dynamical analyses strongly
suggest that the two orbits are nearly co-planar and are trapped in an apsidal
resonance in which the difference between their longitudes of periastron
undergoes a bounded oscillation about 0 degrees. Here we elucidate the origin
of these large eccentricities and of the apsidal alignment. Resonant
interactions between a remnant circumstellar disk of gas lying exterior to the
orbits of both planets can smoothly grow e2. Secular interactions between
planets D and C can siphon off the eccentricity of the former to grow that of
the latter. Externally amplifying e2 during the phase of the apsidal
oscillation when e2/e1 is smallest drives the oscillation amplitude towards
zero. Thus, the substantial eccentricity of planet C and the locking of orbital
apsides are both consequences of externally pumping the eccentricity of planet
D over timescales exceeding apsidal precession periods of order 1e4 yr. We
explain why the recently detected stellar companion to Upsilon Andromedae is
largely dynamically decoupled from the planetary system.Comment: accepted to Ap
Spectral Energy Distributions of Passive T Tauri Disks: Inclination
We compute spectral energy distributions (SEDs) for passive T Tauri disks
viewed at arbitrary inclinations. Semi-analytic models of disks in radiative
and hydrostatic equilibrium are employed. Over viewing angles for which the
flared disk does not occult the central star, the SED varies negligibly with
inclination. For such aspects, the SED shortward of ~80 microns is particularly
insensitive to orientation, since short wavelength disk emission is dominated
by superheated surface layers which are optically thin. The SED of a nearly
edge-on disk is that of a class I source. The outer disk occults inner disk
regions, and emission shortward of ~30 microns is dramatically extinguished.
Spectral features from dust grains may appear in absorption. However,
millimeter wavelength fluxes decrease by at most a factor of 2 from face-on to
edge-on orientations.
We present illustrative applications of our SED models. The class I source
04108+2803B is considered a T Tauri star hidden from view by an inclined
circumstellar disk. Fits to its observed SED yield model-dependent values for
the disk mass of ~0.015 solar masses and a disk inclination of ~65 degrees
relative to face-on. The class II source GM Aur represents a T Tauri star
unobscured by its circumstellar disk. Fitted parameters include a disk mass of
\~0.050 solar masses and an inclination of ~60 degrees.Comment: Accepted to ApJ, 20 pages, 7 figures, aaspp4.st
On the Plutinos and Twotinos of the Kuiper Belt
We illuminate dynamical properties of Kuiper Belt Objects (KBOs) in the 3:2
(``Plutino'') and 2:1 (``Twotino'') Neptunian resonances within the model of
resonant capture and migration. We analyze a series of numerical integrations,
each involving the 4 migratory giant planets and 400 test particles distributed
throughout trans-Neptunian space, to measure efficiencies of capture as
functions of migration speed. Snapshots of the spatial distribution of resonant
KBOs reveal that Twotinos cluster +/- 75 degrees away from Neptune's longitude,
while Plutinos cluster +/- 90 degrees away. Longitudinal clustering persists
even for surveys that are not volume-limited in their ability to detect
resonant KBOs. Remarkably, between -90 degrees and -60 degrees of Neptune's
longitude, we find the sky density of Twotinos to nearly equal that of
Plutinos, despite the greater average distance of Twotinos. We couple our
findings to observations to crudely estimate that the intrinsic Twotino
population is within a factor of 3 of the Plutino population. Most strikingly,
the migration model predicts that more Twotinos may lie at longitudes behind
that of Neptune than ahead of it. The magnitude of the asymmetry amplifies
dramatically with faster rates of migration and can be as large as 300%. A
differential measurement of the sky density of 2:1 resonant objects behind of
and in front of Neptune's longitude would powerfully constrain the migration
history of that planet.Comment: AJ, in press, to appear in December 2002 issue. For version with
higher resolution figures, see
http://astron.berkeley.edu/~echiang/ppp/ppp.htm
Holographic Duals of Black Holes in Five-dimensional Minimal Supergravity
We examine the dual conformal field theory for extremal charged black holes
in five-dimensional minimal supergravity with 2 independent angular momenta.
The conformal field theory Virasoro algebra, central charge, and temperature
are calculated. Additionally the conformal field theory entropy is calculated
using the Cardy formula and agrees with the Bekenstein-Hawking black hole
entropy. The central charges are directly proportional to the angular momentum
components of the black hole. In five and higher dimensions, rotations of the
spacetime correspond to rotations of the central charges leading to an apparent
symmetry relating the conformal field theories dual to each black hole. A
rotationally invariant central charge, which is proportional to the total
angular momentum, is used to discuss the supersymmetric BMPV black hole limits.Comment: inaccurate descriptions are clarifie
Unitary chiral dynamics in decays into and the role of the scalar mesons
We make a theoretical study of the \J decays into ,
, and using the techniques of
the chiral unitary approach stressing the important role of the scalar
resonances dynamically generated through the final state interaction of the two
pseudoscalar mesons. We also discuss the importance of new mechanisms with
intermediate exchange of vector and axial-vector mesons and the role played by
the OZI rule in the \J\phi\pi\pi vertex, quantifying its effects. The results
nicely reproduce the experimental data for the invariant mass distributions in
all the channels considered.Comment: Prepared for the 10th International Symposium on Meson-Nucleon
Physics and the Structure of the Nucleo
Keck Pencil-Beam Survey for Faint Kuiper Belt Objects
We present the results of a pencil-beam survey of the Kuiper Belt using the
Keck 10-m telescope. A single 0.01 square degree field is imaged 29 times for a
total integration time of 4.8 hr. Combining exposures in software allows the
detection of Kuiper Belt Objects (KBOs) having visual magnitude V < 27.9. Two
new KBOs are discovered. One object having V = 25.5 lies at a probable
heliocentric distance d = 33 AU. The second object at V = 27.2 is located at d
= 44 AU. Both KBOs have diameters of about 50 km, assuming comet-like albedos
of 4%.
Data from all surveys are pooled to construct the luminosity function from
red magnitude R = 20 to 27. The cumulative number of objects per square degree,
N (< R), is fitted to a power law of the form log_(10) N = 0.52 (R - 23.5).
Differences between power laws reported in the literature are due mainly to
which survey data are incorporated, and not to the method of fitting. The
luminosity function is consistent with a power-law size distribution for
objects having diameters s = 50 to 500 km; dn ~ s^(-q) ds, where the
differential size index q = 3.6 +/- 0.1. The distribution is such that the
smallest objects possess most of the surface area, but the largest bodies
contain the bulk of the mass. Though our inferred size index nearly matches
that derived by Dohnanyi (1969), it is unknown whether catastrophic collisions
are responsible for shaping the size distribution. Implications of the absence
of detections of classical KBOs beyond 50 AU are discussed.Comment: Accepted to AJ. Final proof-edited version: references added,
discussion of G98 revised in sections 4.3 and 5.
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