1,641 research outputs found
Trans-Neptunian Objects with Hubble Space Telescope ACS/WFC
We introduce a novel search technique that can identify trans-neptunian
objects in three to five exposures of a pointing within a single Hubble Space
Telescope orbit. The process is fast enough to allow the discovery of
candidates soon after the data are available. This allows sufficient time to
schedule follow up observations with HST within a month. We report the
discovery of 14 slow-moving objects found within 5\circ of the ecliptic in
archival data taken with the Wide Field Channel of the Advanced Camera for
Surveys. The luminosity function of these objects is consistent with previous
ground-based and space-based results. We show evidence that the size
distribution of both high and low inclination populations is similar for
objects smaller than 100 km, as expected from collisional evolution models,
while their size distribution differ for brighter objects. We suggest the two
populations formed in different parts of the protoplanetary disk and after
being dynamically mixed have collisionally evolved together. Among the objects
discovered there is an equal mass binary with an angular separation ~ 0."53.Comment: 16 page, 10 figures, accepted by Ap
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
Theoretical Transmission Spectra During Extrasolar Giant Planet Transits
The recent transit observation of HD 209458 b - an extrasolar planet orbiting
a sun-like star - confirmed that it is a gas giant and determined that its
orbital inclination is 85 degrees. This inclination makes possible
investigations of the planet atmosphere. In this paper we discuss the planet
transmission spectra during a transit. The basic tenet of the method is that
the planet atmosphere absorption features will be superimposed on the stellar
flux as the stellar flux passes through the planet atmosphere above the limb.
The ratio of the planet's transparent atmosphere area to the star area is
small, approximately 10^{-3} to 10^{-4}; for this method to work very strong
planet spectral features are necessary. We use our models of close-in
extrasolar giant planets to estimate promising absorption signatures: the
alkali metal lines, in particular the Na I and K I resonance doublets, and the
He I - triplet line at 1083.0 nm. If successful, observations
will constrain the line-of-sight temperature, pressure, and density. The most
important point is that observations will constrain the cloud depth, which in
turn will distinguish between different atmosphere models. We also discuss the
potential of this method for EGPs at different orbital distances and orbiting
non-solar-type stars.Comment: revised to agree with accepted paper, ApJ, in press. 12 page
Orbital migration and the frequency of giant planet formation
We present a statistical study of the post-formation migration of giant
planets in a range of initial disk conditions. For given initial conditions we
model the evolution of giant planet orbits under the influence of disk,
stellar, and mass loss torques. We determine the mass and semi-major axis
distribution of surviving planets after disk dissipation, for various disk
masses, lifetimes, viscosities, and initial planet masses. The majority of
planets migrate too fast and are destroyed via mass transfer onto the central
star. Most surviving planets have relatively large orbital semi-major axes of
several AU or larger. We conclude that the extrasolar planets observed to date,
particularly those with small semi-major axes, represent only a small fraction
(~25% to 33%) of a larger cohort of giant planets around solar-type stars, and
many undetected giant planets must exist at large (>1-2 AU) distances from
their parent stars. As sensitivity and completion of the observed sample
increases with time, this distant majority population of giant planets should
be revealed. We find that the current distribution of extrasolar giant planet
masses implies that high mass (more than 1-2 Jupiter masses) giant planet
formation must be relatively rare. Finally, our simulations imply that the
efficiency of giant planet formation must be high: at least 10% and perhaps as
many as 80% of solar-type stars possess giant planets during their pre-main
sequence phase. These predictions, including those for pre-main sequence stars,
are testable with the next generation of ground- and space-based planet
detection techniquesComment: 25 pages, 5 figures. Double-space, single-column format to show long
equations. Accepted for publication in A&
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