85 research outputs found
Implementing State Health Reform: Lessons for Policymakers
Drawing on five states' experiences, discusses questions and considerations, including the need to coordinate state agencies' work and share data, simplify eligibility and enrollment procedures, and involve community groups and businesses in outreach
Global and Episodic Bundling: An Overview and Considerations for Medicaid
Examines implementation issues for two payment strategies under which a group of providers receives a single payment per patient for a predefined time period for a predefined set of services and which involve risk adjustment and quality measurement
OSSOS VI. Striking Biases in the detection of large semimajor axis Trans-Neptunian Objects
The accumulating, but small, set of large semi-major axis trans-Neptunian
objects (TNOs) shows an apparent clustering in the orientations of their
orbits. This clustering must either be representative of the intrinsic
distribution of these TNOs, or else arise as a result of observation biases
and/or statistically expected variations for such a small set of detected
objects. The clustered TNOs were detected across different and independent
surveys, which has led to claims that the detections are therefore free of
observational bias. This apparent clustering has led to the so-called "Planet
9" hypothesis that a super-Earth currently resides in the distant solar system
and causes this clustering. The Outer Solar System Origins Survey (OSSOS) is a
large program that ran on the Canada-France-Hawaii Telescope from 2013--2017,
discovering more than 800 new TNOs. One of the primary design goals of OSSOS
was the careful determination of observational biases that would manifest
within the detected sample. We demonstrate the striking and non-intuitive
biases that exist for the detection of TNOs with large semi-major axes. The
eight large semi-major axis OSSOS detections are an independent dataset, of
comparable size to the conglomerate samples used in previous studies. We
conclude that the orbital distribution of the OSSOS sample is consistent with
being detected from a uniform underlying angular distribution.Comment: Accepted for publicatio
OSSOS III - Resonant Trans-Neptunian Populations: Constraints from the first quarter of the Outer Solar System Origins Survey
The first two observational sky "blocks" of the Outer Solar System Origins
Survey (OSSOS) have significantly increased the number of well-characterized
observed trans-Neptunian objects (TNOs) in Neptune's mean motion resonances. We
describe the 31 securely resonant TNOs detected by OSSOS so far, and we use
them to independently verify the resonant population models from the
Canada-France Ecliptic Plane Survey (CFEPS; Gladman et al. 2012), with which we
find broad agreement. We confirm that the 5:2 resonance is more populated than
models of the outer Solar System's dynamical history predict; our minimum
population estimate shows that the high eccentricity (e>0.35) portion of the
resonance is at least as populous as the 2:1 and possibly as populated as the
3:2 resonance. One OSSOS block was well-suited to detecting objects trapped at
low libration amplitudes in Neptune's 3:2 resonance, a population of interest
in testing the origins of resonant TNOs. We detected three 3:2 objects with
libration amplitudes below the cutoff modeled by CFEPS; OSSOS thus offers new
constraints on this distribution. The OSSOS detections confirm that the 2:1
resonance has a dynamically colder inclination distribution than either the 3:2
or 5:2 resonances. Using the combined OSSOS and CFEPS 2:1 detections, we
constrain the fraction of 2:1 objects in the symmetric mode of libration to be
0.2-0.85; we also constrain the fraction of leading vs. trailing asymmetric
librators, which has been theoretically predicted to vary depending on
Neptune's migration history, to be 0.05-0.8. Future OSSOS blocks will improve
these constraints.Comment: Accepted for publication in A
Col-OSSOS: The Colours of the Outer Solar System Origins Survey
The Colours of the Outer Solar System Origins Survey (Col-OSSOS) is acquiring
near-simultaneous , , and photometry of unprecedented precision with
the Gemini North Telescope, targeting nearly a hundred trans-Neptunian objects
(TNOs) brighter than mag discovered in the Outer Solar System
Origins Survey. Combining the optical and near-infrared photometry with the
well-characterized detection efficiency of the Col-OSSOS target sample will
provide the first flux-limited compositional dynamical map of the outer Solar
System. In this paper, we describe our observing strategy and detail the data
reduction processes we employ, including techniques to mitigate the impact of
rotational variability. We present optical and near-infrared colors for 35
TNOs. We find two taxonomic groups for the dynamically excited TNOs, the
neutral and red classes, which divide at . Based on simple
albedo and orbital distribution assumptions, we find that the neutral class
outnumbers the red class, with a ratio of 4:1 and potentially as high as 11:1.
Including in our analysis constraints from the cold classical objects, which
are known to exhibit unique albedos and colors, we find that within our
measurement uncertainty, our observations are consistent with the primordial
Solar System protoplanetesimal disk being neutral-class-dominated, with two
major compositional divisions in color space.Comment: Accepted to ApJS; on-line supplemental files will be available with
the AJS published version of the pape
OSSOS: XIII. Fossilized Resonant Dropouts Tentatively Confirm Neptune's Migration was Grainy and Slow
The migration of Neptune's resonances through the proto-Kuiper belt has been
imprinted in the distribution of small bodies in the outer Solar System. Here
we analyze five published Neptune migration models in detail, focusing on the
high pericenter distance (high-q) trans-Neptunian Objects (TNOs) near Neptune's
5:2 and 3:1 mean-motion resonances, because they have large resonant
populations, are outside the main classical belt, and are relatively isolated
from other strong resonances. We compare the observationally biased output from
these dynamical models with the detected TNOs from the Outer Solar System
Origins Survey, via its Survey Simulator. All of the four new OSSOS detections
of high-q non-resonant TNOs are on the Sunward side of the 5:2 and 3:1
resonances. We show that even after accounting for observation biases, this
asymmetric distribution cannot be drawn from a uniform distribution of TNOs at
2sigma confidence. As shown by previous work, our analysis here tentatively
confirms that the dynamical model that uses grainy slow Neptune migration
provides the best match to the real high-q TNO orbital data. However, due to
extreme observational biases, we have very few high-q TNO discoveries with
which to statistically constrain the models. Thus, this analysis provides a
framework for future comparison between the output from detailed, dynamically
classified Neptune migration simulations and the TNO discoveries from future
well-characterized surveys. We show that a deeper survey (to a limiting
r-magnitude of 26.0) with a similar survey area to OSSOS could statistically
distinguish between these five Neptune migration models.Comment: Accepted for publication in the Astronomical Journa
OSSOS XXV: Large Populations and Scattering-Sticking in the Distant Transneptunian Resonances
There have been 77 TNOs discovered to be librating in the distant
transneptunian resonances (beyond the 2:1 resonance, at semimajor axes greater
than 47.7~AU) in four well-characterized surveys: the Outer Solar System
Origins Survey (OSSOS) and three similar prior surveys. Here we use the OSSOS
Survey Simulator to measure their intrinsic orbital distributions using an
empirical parameterized model. Because many of the resonances had only one or
very few detections, : resonant objects were grouped by in order to
have a better basis for comparison between models and reality. We also use the
Survey Simulator to constrain their absolute populations, finding that they are
much larger than predicted by any published Neptune migration model to date; we
also find population ratios that are inconsistent with published models,
presenting a challenge for future Kuiper Belt emplacement models. The estimated
population ratios between these resonances are largely consistent with
scattering-sticking predictions, though further discoveries of resonant TNOs
with high-precision orbits will be needed to determine whether
scattering-sticking can explain the entire distant resonant population or not.Comment: Accepted for publication in Planetary Sciences Journal (PSJ
A dearth of small members in the Haumea family revealed by OSSOS
An extensive survey to search for members of the only known Kuiper belt family, named after the parent body Haumea, found no family members fainter than absolute magnitude H-r = 7.9, significantly brighter than the detection limit (H-r = 9.5). This lack of small members is inconsistent with a catastrophic disruption as the origin of the Haumea family. While collisional families are common in the asteroid belt, only one is known in the Kuiper belt, linked to the dwarf planet Haumea. The characterization of Haumea's family helps to constrain its origin and, more generally, the collisional history of the Kuiper belt. However, the size distribution of the Haumea family is difficult to constrain from the known sample, which is affected by discovery biases. Here, we use the Outer Solar System Origins Survey (OSSOS) Ensemble to look for Haumea family members. In this OSSOS XVI study we report the detection of three candidates with small ejection velocities relative to the family formation centre. The largest discovery, 2013 UQ(15), is conclusively a Haumea family member, with a low ejection velocity and neutral surface colours. Although the OSSOS Ensemble is sensitive to Haumea family members to a limiting absolute magnitude (H-r) of 9.5 (inferred diameter of ~90 km), the smallest candidate is significantly larger, H-r = 7.9. The Haumea family members larger than similar or equal to 20 km in diameter must be characterized by a shallow H-distribution slope in order to produce only these three large detections. This shallow size distribution suggests that the family formed in a graze-and-merge scenario, not a catastrophic collision.6 month embargo; published online: 26 August 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
OSSOS. V. Diffusion in the Orbit of a High-perihelion Distant Solar System Object
We report the discovery of the minor planet 2013 SY, on an
exceptionally distant, highly eccentric orbit. With a perihelion of 50.0 au,
2013 SY's orbit has a semi-major axis of au, the largest
known for a high-perihelion trans-Neptunian object (TNO), well beyond those of
(90377) Sedna and 2012 VP. Yet, with an aphelion of au,
2013 SY's orbit is interior to the region influenced by Galactic tides.
Such TNOs are not thought to be produced in the current known planetary
architecture of the Solar System, and they have informed the recent debate on
the existence of a distant giant planet. Photometry from the
Canada-France-Hawaii Telescope, Gemini North and Subaru indicate 2013 SY
is km in diameter and moderately red in colour, similar to other
dynamically excited TNOs. Our dynamical simulations show that Neptune's weak
influence during 2013 SY's perihelia encounters drives diffusion in its
semi-major axis of hundreds of astronomical units over 4 Gyr. The overall
symmetry of random walks in semi-major axis allow diffusion to populate 2013
SY's orbital parameter space from the 1000-2000 au inner fringe of the
Oort cloud. Diffusion affects other known TNOs on orbits with perihelia of 45
to 49 au and semi-major axes beyond 250 au, providing a formation mechanism
that implies an extended population, gently cycling into and returning from the
inner fringe of the Oort cloud.Comment: First reviewer report comments incorporated. Comments welcom
OSSOS. IX. Two Objects in Neptune's 9: 1 Resonance - Implications for Resonance Sticking in the Scattering Population
We discuss the detection in the Outer Solar System Origins Survey (OSSOS) of
two objects in Neptune's distant 9:1 mean motion resonance at semimajor axis
~au. Both objects are securely resonant on 10~Myr timescales,
with one securely in the 9:1 resonance's leading asymmetric libration island
and the other in either the symmetric or trailing asymmetric island. These
objects are the largest semimajor axis objects with secure resonant
classifications, and their detection in a carefully characterized survey allows
for the first robust resonance population estimate beyond 100~au. The detection
of these objects implies a 9:1 resonance population of objects
with (~km) on similar orbits (95\% confidence range
of ). Integrations over 4~Gyr of an ensemble of clones
spanning these objects' orbit fit uncertainties reveal that they both have
median resonance occupation timescales of ~Gyr. These timescales are
consistent with the hypothesis that these objects originate in the scattering
population but became transiently stuck to Neptune's 9:1 resonance within the
last ~Gyr of solar system evolution. Based on simulations of a model of
the current scattering population, we estimate the expected resonance sticking
population in the 9:1 resonance to be 1000-4500 objects with ; this
is marginally consistent with the OSSOS 9:1 population estimate. We conclude
that resonance sticking is a plausible explanation for the observed 9:1
population, but we also discuss the possibility of a primordial 9:1 population,
which would have interesting implications for the Kuiper belt's dynamical
history.Comment: accepted for publication in A
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