751 research outputs found
Descriptive Linear modeling of steady-state visual evoked response
A study is being conducted to explore use of the steady state visual-evoke electrocortical response as an indicator of cognitive task loading. Application of linear descriptive modeling to steady state Visual Evoked Response (VER) data is summarized. Two aspects of linear modeling are reviewed: (1) unwrapping the phase-shift portion of the frequency response, and (2) parsimonious characterization of task-loading effects in terms of changes in model parameters. Model-based phase unwrapping appears to be most reliable in applications, such as manual control, where theoretical models are available. Linear descriptive modeling of the VER has not yet been shown to provide consistent and readily interpretable results
A Method to Constrain the Size of the Protosolar Nebula
Observations indicate that the gaseous circumstellar disks around young stars
vary significantly in size, ranging from tens to thousands of AU. Models of
planet formation depend critically upon the properties of these primordial
disks, yet in general it is impossible to connect an existing planetary system
with an observed disk. We present a method by which we can constrain the size
of our own protosolar nebula using the properties of the small body reservoirs
in the solar system. In standard planet formation theory, after Jupiter and
Saturn formed they scattered a significant number of remnant planetesimals into
highly eccentric orbits. In this paper, we show that if there had been a
massive, extended protoplanetary disk at that time, then the disk would have
excited Kozai oscillations in some of the scattered objects, driving them into
high-inclination (i > 50 deg), low-eccentricity orbits (q > 30 AU). The
dissipation of the gaseous disk would strand a subset of objects in these
high-inclination orbits; orbits that are stable on Gyr time scales. To date,
surveys have not detected any Kuiper Belt Objects with orbits consistent with
this dynamical mechanism. Using these non-detections by the Deep Ecliptic
Survey (DES) and the Palomar Distant Solar System Survey we are able to rule
out an extended gaseous protoplanetary disk (R_D > 80 AU) in our solar system
at the time of Jupiter's formation. Future deep all sky surveys such as the
Large Synoptic Survey Telescope (LSST) will all us to further constrain the
size of the protoplanetary disk.Comment: 10 pages, Accepted to A
Discovery of a Binary Centaur
We have identified a binary companion to (42355) 2002 CR46 in our ongoing
deep survey using the Hubble Space Telescope's High Resolution Camera. It is
the first companion to be found around an object in a non-resonant orbit that
crosses the orbits of giant planets. Objects in orbits of this kind, the
Centaurs, have experienced repeated strong scattering with one or more giant
planets and therefore the survival of binaries in this transient population has
been in question. Monte Carlo simulations suggest, however, that binaries in
(42355) 2002 CR46 -like heliocentric orbits have a high probability of survival
for reasonable estimates of the binary's still-unknown system mass and
separation. Because Centaurs are thought to be precursors to short period
comets, the question of the existence of binary comets naturally arises; none
has yet been definitively identified. The discovery of one binary in a sample
of eight observed by HST suggests that binaries in this population may not be
uncommon.Comment: 20 pages, 4 figures, 1 table accepted for publication in Icaru
Constructing the secular architecture of the solar system II: The terrestrial planets
We investigate the dynamical evolution of the terrestrial planets during the
planetesimal-driven migration of the giant planets. A basic assumption of this
work is that giant planet migration occurred after the completion of
terrestrial planet formation, such as in the models that link the former to the
origin of the Late Heavy Bombardment. The divergent migration of Jupiter and
Saturn causes the g5 eigenfrequency to cross resonances of the form g5=gk with
k ranging from 1 to 4. Consequently these secular resonances cause
large-amplitude responses in the eccentricities of the terrestrial planets. We
show that the resonances g5=g_4 and g5=g3 do not pose a problem if Jupiter and
Saturn have a fast approach and departure from their mutual 2:1 mean motion
resonance. On the other hand, the resonance crossings g5=g2 and g5=g1 are more
of a concern as they tend to yield a terrestrial system incompatible with the
current one. We offer two solutions to this problem. The first uses the fact
that a secular resonance crossing can also damp the amplitude of a Fourier mode
if the latter is large originally. A second scenario involves a 'jumping
Jupiter' in which encounters between an ice giant and Jupiter, without ejection
of the former, cause the latter to migrate away from Saturn much faster than if
migration is driven solely by encounters with planetesimals. In this case, the
g5=g2 and g5=g1 resonances can be jumped over, or occur very briefly.Comment: Astronomy & Astrophysics (2009) in pres
Size determination of the Centaur Chariklo from millimeter-wavelength bolometer observations
Using the Max-Planck Millimeter Bolometer Array (MAMBO) at the IRAM 30m
telescope we detected emission at 250 GHz from the Centaur Chariklo (1997
CU26). The observed continuum flux density implies a photometric diameter of
273 km. The resulting geometric albedo is 0.055, somewhat higher than expected
from a comparison with most of the other few Centaurs and cometary nuclei for
which such data are available.Comment: 4 pages, 1 Postscript figure, to appear in Astronomy & Astrophysic
Polarimetry and photometry of the peculiar main-belt object 7968 = 133P/Elst-Pizarro
133P/Elst-Pizarro is an object that has been described as either an active
asteroid or a cometary object in the main asteroid belt. Here we present a
photometric and polarimetric study of this object in an attempt to infer
additional information about its origin.
With the FORS1 instrument of the ESO VLT, we have performed during the 2007
apparition of 133P/Elst-Pizarro quasi-simultaneous photometry and polarimetry
of its nucleus at nine epochs in the phase angle range 0 - 20 deg. For each
observing epoch, we also combined all available frames to obtain a deep image
of the object, to seek signatures of weak cometary activity. Polarimetric data
were analysed by means of a novel physical interference modelling.
The object brightness was found to be highly variable over timescales <1h, a
result fully consistent with previous studies. Using the albedo-polarization
relationships for asteroids and our photometric results, we found for our
target an albedo of about 0.06-0.07 and a mean radius of about 1.6 km.
Throughout the observing epochs, our deep imaging of the comet detects a tail
and an anti-tail. Their temporal variations are consistent with an activity
profile starting around mid May 2007 of minimum duration of four months. Our
images show marginal evidence of a coma around the nucleus. The overall light
scattering behaviour (photometry and polarimetry) resembles most closely that
of F-type asteroids.Comment: Accepted by Astronomy and Astrophysic
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