15,261 research outputs found
The bimodal color distribution of small Kuiper Belt objects
We conducted a two-night photometric survey of small Kuiper Belt objects
(KBOs) near opposition using the wide-field Hyper Suprime-Cam instrument on the
8.2 m Subaru Telescope. The survey covered about 90 deg^2 of sky, with each
field imaged in the g and i bands. We detected 356 KBOs, ranging in absolute
magnitude from 6.5 to 10.4. Filtering for high-inclination objects within the
hot KBO population, we show that the g-i color distribution is strongly
bimodal, indicative of two color classes - the red and very red subpopulations.
After categorizing objects into the two subpopulations by color, we present the
first dedicated analysis of the magnitude distributions of the individual color
subpopulations and demonstrate that the two distributions are roughly identical
in shape throughout the entire size range covered by our survey. Comparing the
color distribution of small hot KBOs with that of Centaurs, we find that they
have similar bimodal shapes, thereby providing strong confirmation of previous
explanations for the attested bimodality of Centaurs. We also show that the
magnitude distributions of the two KBO color subpopulations and the two color
subpopulations observed in the Jupiter Trojans are statistically
indistinguishable. Finally, we discuss a hypothesis describing the origin of
the KBO color bimodality based on our survey results.Comment: 9 pages, 6 figures, accepted for publication in AJ, supplemental
table accessible on online journa
Multiband photometry of a Patroclus-Menoetius mutual event: Constraints on surface heterogeneity
We present the first complete multiband observations of a binary asteroid
mutual event. We obtained high-cadence, high-signal-to-noise photometry of the
UT 2018 April 9 inferior shadowing event in the Jupiter Trojan binary system
Patroclus-Menoetius in four Sloan bands , , , and . We use
an eclipse lightcurve model to fit for a precise mid-eclipse time and estimate
the minimum separation of the two eclipsing components during the event. Our
best-fit mid-eclipse time of is 19
minutes later than the prediction of Grundy et al. (2018); the minimum
separation between the center of Menoetius' shadow and the center of Patroclus
is km slightly larger than the predicted 69.5 km. Using the
derived lightcurves, we find no evidence for significant albedo variations or
large-scale topographic features on the Earth-facing hemisphere and limb of
Patroclus. We also apply the technique of eclipse mapping to place an upper
bound of 0.15 mag on wide-scale surface color variability across
Patroclus.Comment: 5 pages, 3 figures, accepted for publication in A
A hypothesis for the color bimodality of Jupiter Trojans
One of the most enigmatic and hitherto unexplained properties of Jupiter
Trojans is their bimodal color distribution. This bimodality is indicative of
two sub-populations within the Trojans, which have distinct size distributions.
In this paper, we present a simple, plausible hypothesis for the origin and
evolution of the two Trojan color sub-populations. In the framework of
dynamical instability models of early Solar System evolution, which suggest a
common primordial progenitor population for both Trojans and Kuiper belt
objects, we use observational constraints to assert that the color bimodalities
evident in both minor body populations developed within the primordial
population prior to the onset of instability. We show that, beginning with an
initial composition of rock and ices, location-dependent volatile loss through
sublimation in this primordial population could have led to sharp changes in
the surface composition with heliocentric distance. We propose that the
depletion or retention of HS ice on the surface of these objects was the
key factor in creating an initial color bimodality. Objects that retained
HS on their surfaces developed characteristically redder colors upon
irradiation than those that did not. After the bodies from the primordial
population were scattered and emplaced into their current positions, they
preserved this primordial color bimodality to the present day. We explore
predictions of the volatile loss model - in particular, the effect of
collisions within the Trojan population on the size distributions of the two
sub-populations - and propose further experimental and observational tests of
our hypothesisComment: 8 pages, 3 figures, accepted for publication in A
Rapamycin attenuates acute seizure-induced astrocyte injury in mice in vivo
AbstractAstrocytes have been implicated in epileptogenesis and seizure-induced brain injury. Pathological studies reveal a variety of structural abnormalities in astrocytes, such as vacuolization and astrogliosis. While in vivo imaging methods have demonstrated rapid changes in astrocytes under a variety of physiological and pathological conditions, the acute effects of seizures on astrocyte morphology in vivo and corresponding mechanisms of seizure-induced astrocytic injury have not been documented. In this study, we utilized in vivo two-photon imaging to directly monitor the acute structural effects of kainate-induced seizures on cortical astrocytes. Kainate seizures cause an immediate, but transient, vacuolization of astrocytes, followed over several days by astrogliosis. These effects are prevented by pre- or post-treatment with rapamycin, indicating the mTOR pathway is involved in mediating seizure-induced astrocyte injury. These finding have clinical implications for mechanisms of seizure-induced astrocyte injury and potential therapeutic applications with mTOR inhibitors.</jats:p
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