2,089 research outputs found
1I/2017 U1 (`Oumuamua) is Hot: Imaging, Spectroscopy and Search of Meteor Activity
1I/2017 U1 (`Oumuamua), a recently discovered asteroid in a hyperbolic orbit,
is likely the first macroscopic object of extrasolar origin identified in the
solar system. Here, we present imaging and spectroscopic observations of
\textquoteleft Oumuamua using the Palomar Hale Telescope as well as a search of
meteor activity potentially linked to this object using the Canadian Meteor
Orbit Radar. We find that \textquoteleft Oumuamua exhibits a moderate spectral
gradient of , a value significantly lower
than that of outer solar system bodies, indicative of a formation and/or
previous residence in a warmer environment. Imaging observation and spectral
line analysis show no evidence that \textquoteleft Oumuamua is presently
active. Negative meteor observation is as expected, since ejection driven by
sublimation of commonly-known cometary species such as CO requires an extreme
ejection speed of m s at au in order to reach the
Earth. No obvious candidate stars are proposed as the point of origin for
\textquoteleft Oumuamua. Given a mean free path of ly in the solar
neighborhood, \textquoteleft Oumuamua has likely spent a very long time in the
interstellar space before encountering the solar system.Comment: ApJL in pres
Near-UV OH Prompt Emission in the Innermost Coma of 103P/Hartley 2
The Deep Impact spacecraft fly-by of comet 103P/Hartley 2 occurred on 2010
November 4, one week after perihelion with a closest approach (CA) distance of
about 700 km. We used narrowband images obtained by the Medium Resolution
Imager (MRI) onboard the spacecraft to study the gas and dust in the innermost
coma. We derived an overall dust reddening of 15\%/100 nm between 345 and 749
nm and identified a blue enhancement in the dust coma in the sunward direction
within 5 km from the nucleus, which we interpret as a localized enrichment in
water ice. OH column density maps show an anti-sunward enhancement throughout
the encounter except for the highest resolution images, acquired at CA, where a
radial jet becomes visible in the innermost coma, extending up to 12 km from
the nucleus. The OH distribution in the inner coma is very different from that
expected for a fragment species. Instead, it correlates well with the water
vapor map derived by the HRI-IR instrument onboard Deep Impact
\citep{AHearn2011}. Radial profiles of the OH column density and derived water
production rates show an excess of OH emission during CA that cannot be
explained with pure fluorescence. We attribute this excess to a prompt emission
process where photodissociation of HO directly produces excited
OH*() radicals. Our observations provide the first direct
imaging of Near-UV prompt emission of OH. We therefore suggest the use of a
dedicated filter centered at 318.8 nm to directly trace the water in the coma
of comets.Comment: 21 page
Forward Modeling of Double Neutron Stars: Insights from Highly-Offset Short Gamma-Ray Bursts
We present a detailed analysis of two well-localized, highly offset short
gamma-ray bursts---GRB~070809 and GRB~090515---investigating the kinematic
evolution of their progenitors from compact object formation until merger.
Calibrating to observations of their most probable host galaxies, we construct
semi-analytic galactic models that account for star formation history and
galaxy growth over time. We pair detailed kinematic evolution with compact
binary population modeling to infer viable post-supernova velocities and
inspiral times. By populating binary tracers according to the star formation
history of the host and kinematically evolving their post-supernova
trajectories through the time-dependent galactic potential, we find that
systems matching the observed offsets of the bursts require post-supernova
systemic velocities of hundreds of kilometers per second. Marginalizing over
uncertainties in the stellar mass--halo mass relation, we find that the
second-born neutron star in the GRB~070809 and GRB~090515 progenitor systems
received a natal kick of at the 78\% and 91\%
credible levels, respectively. Applying our analysis to the full catalog of
localized short gamma-ray bursts will provide unique constraints on their
progenitors and help unravel the selection effects inherent to observing
transients that are highly offset with respect to their hosts.Comment: 18 pages, 7 figures, 1 table. ApJ, in pres
Urinary ATP and visualization of intracellular bacteria: a superior diagnostic marker for recurrent UTI in renal transplant recipients?
Renal transplant recipients (RTR) are highly susceptible to urinary tract infections (UTIs) with over 50% of patients having at least one UTI within the first year. Yet it is generally acknowledged that there is considerable insensitivity and inaccuracy in routine urinalysis when screening for UTIs. Thus a large number of transplant patients with genuine urine infections may go undiagnosed and develop chronic recalcitrant infections, which can be associated with graft loss and morbidity. Given a recent study demonstrating ATP is released by urothelial cells in response to bacteria exposure, possibly acting at metabotropic P2Y receptors mediating a proinflammatory response, we have investigated alternative, and possibly more appropriate, urinalysis techniques in a cohort of RTRs.Mid-stream urine (MSU) samples were collected from 53 outpatient RTRs. Conventional leukocyte esterase and nitrite dipstick tests, and microscopic pyuria counts (in 1 ?l), ATP concentration measurements, and identification of intracellular bacteria in shed urothelial cells, were performed on fresh unspun samples and compared to ‘gold-standard’ bacterial culture results.Of the 53 RTRs, 22% were deemed to have a UTI by ‘gold-standard’ conventional bacteria culture, whereas 87%, 8% and 4% showed evidence of UTIs according to leukocyte esterase dipstick, nitrite dipstick, and a combination of both dipsticks, respectively. Intracellular bacteria were visualized in shed urothelial cells of 44% of RTRs, however only 1 of the 23 RTRs (44%) was deemed to have a UTI by conventional bacteria culture. A significant association of the ‘gold-standard’ test with urinary ATP concentration combined with visualization of intracellular bacteria in shed urothelial cells was determined using the Fisher’s exact test.It is apparent that standard bedside tests for UTIs give variable results and that seemingly quiescent bacteria in urothelial cells are very common in RTRs and may represent a focus of subclinical infection. Furthermore, our results suggest urinary ATP concentration combined with detection of intracellular bacteria in shed urinary epithelial cells may be a sensitive means by which to detect ‘occult’ infection in RTRs
Dust Emission and Dynamics
When viewed from Earth, most of what we observe of a comet is dust. The
influence of solar radiation pressure on the trajectories of dust particles
depends on their cross-section to mass ratio. Hence solar radiation pressure
acts like a mass spectrometer inside a cometary tail. The appearances of
cometary dust tails have long been studied to obtain information on the dust
properties, such as characteristic particle size and initial velocity when
entering the tail. Over the past two decades, several spacecraft missions to
comets have enabled us to study the dust activity of their targets at much
greater resolution than is possible with a telescope on Earth or in near-Earth
space, and added detail to the results obtained by the spacecraft visiting
comet 1P/Halley in 1986. We now know that the dynamics of dust in the inner
cometary coma is complex and includes a significant fraction of particles that
will eventually fall back to the surface. The filamented structure of the
near-surface coma is thought to result from a combination of topographic
focussing of the gas flow, inhomogeneous distribution of activity across the
surface, and projection effects. It is possible that some
larger-than-centimetre debris contains ice when lifted from the surface, which
can affect its motion. Open questions remain regarding the microphysics of the
process that leads to the detachment and lifting of dust from the surface, the
evolution of the dust while travelling away from the nucleus, and the extent to
which information on the nucleus activity can be retrieved from remote
observations of the outer coma and tail.Comment: Chapter in press for the book Comets III, edited by K. Meech and M.
Combi, University of Arizona Pres
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