51 research outputs found
TRIPPy: Trailed Image Photometry in Python
Photometry of moving sources typically suffers from reduced signal-to-noise
(SNR) or flux measurements biased to incorrect low values through the use of
circular apertures. To address this issue we present the software package,
TRIPPy: TRailed Image Photometry in Python. TRIPPy introduces the pill
aperture, which is the natural extension of the circular aperture appropriate
for linearly trailed sources. The pill shape is a rectangle with two
semicircular end-caps, and is described by three parameters, the trail length
and angle, and the radius. The TRIPPy software package also includes a new
technique to generate accurate model point-spread functions (PSF) and trailed
point-spread functions (TSF) from stationary background sources in sidereally
tracked images. The TSF is merely the convolution of the model PSF, which
consists of a moffat profile, and super sampled lookup table. From the TSF,
accurate pill aperture corrections can be estimated as a function of pill
radius with a accuracy of 10 millimags for highly trailed sources. Analogous to
the use of small circular apertures and associated aperture corrections, small
radius pill apertures can be used to preserve signal-to-noise of low flux
sources, with appropriate aperture correction applied to provide an accurate,
unbiased flux measurement at all SNR.Comment: 8 Figures, 11 Pages, Accepted to the Astronomical Journa
Col-OSSOS: Colors of the Interstellar Planetesimal 1I/`Oumuamua
The recent discovery by Pan-STARRS1 of 1I/2017 U1 (`Oumuamua), on an unbound
and hyperbolic orbit, offers a rare opportunity to explore the planetary
formation processes of other stars, and the effect of the interstellar
environment on a planetesimal surface. 1I/`Oumuamua's close encounter with the
inner Solar System in 2017 October was a unique chance to make observations
matching those used to characterize the small-body populations of our own Solar
System. We present near-simultaneous g, r, and J photometry
and colors of 1I/`Oumuamua from the 8.1-m Frederick C. Gillett Gemini North
Telescope, and photometry from the 4.2 m William Herschel Telescope. Our
grJ observations are directly comparable to those from the
high-precision Colours of the Outer Solar System Origins Survey (Col-OSSOS),
which offer unique diagnostic information for distinguishing between outer
Solar System surfaces. The J-band data also provide the highest signal-to-noise
measurements made of 1I/`Oumuamua in the near-infrared. Substantial, correlated
near-infrared and optical variability is present, with the same trend in both
near-infrared and optical. Our observations are consistent with 1I/`Oumuamua
rotating with a double-peaked period of hours and being a
highly elongated body with an axial ratio of at least 5.3:1, implying that it
has significant internal cohesion. The color of the first interstellar
planetesimal is at the neutral end of the range of Solar System and
solar-reflectance colors: it is like that of some dynamically excited objects
in the Kuiper belt and the less-red Jupiter Trojans.Comment: Accepted to ApJ
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
Col-OSSOS: The Distribution of Surface Classes in Neptune's Resonances
The distribution of surface classes of resonant trans-Neptunian objects
(TNOs) provides constraints on the protoplanetesimal disk and giant planet
migration. To better understand the surfaces of TNOs, the Colours of the Outer
Solar System Origins Survey (Col-OSSOS) acquired multi-band photometry of 102
TNOs, and found that the surfaces of TNOs can be well described by two surface
classifications, BrightIR and FaintIR. These classifications both include
optically red members and are differentiated predominantly based on whether
their near-infrared spectral slope is similar to their optical spectral slope.
The vast majority of cold classical TNOs, with dynamically quiescent orbits,
have the FaintIR surface classification, and we infer that TNOs in other
dynamical classifications with FaintIR surfaces share a common origin with the
cold classical TNOs. Comparison between the resonant populations and the
possible parent populations of cold classical and dynamically excited TNOs
reveal that the 3:2 has minimal contributions from the FaintIR class, which
could be explained by the secular resonance clearing the region near
the 3:2 before any sweeping capture occurred. Conversely, the fraction of
FaintIR objects in the 4:3 resonance, 2:1 resonance, and the resonances within
the cold classical belt, suggest that the FaintIR surface formed in the
protoplanetary disk between 34.6 and 47 au, though the outer bound depends on
the degree of resonance sweeping during migration. The presence and absence of
the FaintIR surfaces in Neptune's resonances provides critical constraints for
the history of Neptune's migration, the evolution of the , and the
surface class distribution in the initial planetesimal diskComment: 19 pages, 8 figures. in Press at PS
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]
Col-OSSOS: Z-Band Photometry Reveals Three Distinct TNO Surface Types
Several different classes of trans-Neptunian objects (TNOs) have been
identified based on their optical and near-infrared colors. As part of the
Colours of the Outer Solar System Origins Survey, we have obtained , ,
and band photometry of 26 TNOs using Subaru and Gemini Observatories.
Previous color surveys have not utilized band reflectance, and the
inclusion of this band reveals significant surface reflectance variations
between sub-populations. The colors of TNOs in and show obvious
structure, and appear consistent with the previously measured bi-modality in
. The distribution of colors of the two dynamically excited surface types
can be modeled using the two-component mixing models from Fraser \& Brown
(2012). With the combination of and , the dynamically excited
classes can be separated cleanly into red and neutral surface classes. In and , the two dynamically excited surface groups are also clearly
distinct from the cold classical TNO surfaces, which are red, with
0.85 and 0.6, while all dynamically excited objects
with similar colors exhibit redder colors. The band photometry
makes it possible for the first time to differentiate the red excited TNO
surfaces from the red cold classical TNO surfaces. The discovery of different
colors for these cold classical TNOs makes it possible to search for cold
classical surfaces in other regions of the Kuiper belt and to completely
separate cold classical TNOs from the dynamically excited population, which
overlaps in orbital parameter space.Comment: 11 pages, 2 figures, Accepted to A
OSSOS. IV. DISCOVERY OF A DWARF PLANET CANDIDATE IN THE 9 : 2 RESONANCE WITH NEPTUNE
We report the discovery and orbit of a new dwarf planet candidate, 2015 RR245, by the Outer Solar System Origins Survey (OSSOS). The orbit of 2015 RR245 is eccentric (e = 0.586), with a semimajor axis near 82 au, yielding a perihelion distance of 34 au. 2015 RR245 has g - r = 0.59 +/- 0.11 and absolute magnitude H-r = 3.6 +/- 0.1; for an assumed albedo of p(V) = 12%, the object has a diameter of similar to 670. km. Based on astrometric measurements from OSSOS and Pan-STARRS1, we find that 2015 RR245 is securely trapped on ten-megayear timescales in the 9: 2 mean-motion resonance with Neptune. It is the first trans-Neptunian object (TNO) identified in this resonance. On hundred-megayear. timescales, particles in 2015 RR245-like orbits depart and sometimes return to the resonance, indicating that 2015 RR245 likely forms part of the long-lived metastable population of distant TNOs that drift between resonance sticking and actively scattering via gravitational encounters with Neptune. The discovery of a 9: 2 TNO stresses the role of resonances in the long-term evolution of objects in the scattering disk. and reinforces the view that distant resonances are heavily populated in the current solar system. This object further motivates detailed modeling of the transient sticking population.Peer reviewe
Dynamic contrast-enhanced CT compared with positron emission tomography CT to characterise solitary pulmonary nodules: the SPUtNIk diagnostic accuracy study and economic modelling
BACKGROUND: Current pathways recommend positron emission tomography-computerised tomography for the characterisation of solitary pulmonary nodules. Dynamic contrast-enhanced computerised tomography may be a more cost-effective approach.
OBJECTIVES: To determine the diagnostic performances of dynamic contrast-enhanced computerised tomography and positron emission tomography-computerised tomography in the NHS for solitary pulmonary nodules. Systematic reviews and a health economic evaluation contributed to the decision-analytic modelling to assess the likely costs and health outcomes resulting from incorporation of dynamic contrast-enhanced computerised tomography into management strategies.
DESIGN: Multicentre comparative accuracy trial.
SETTING: Secondary or tertiary outpatient settings at 16 hospitals in the UK.
PARTICIPANTS: Participants with solitary pulmonary nodules of ≥ 8 mm and of ≤ 30 mm in size with no malignancy in the previous 2 years were included.
INTERVENTIONS: Baseline positron emission tomography-computerised tomography and dynamic contrast-enhanced computer tomography with 2 years' follow-up.
MAIN OUTCOME MEASURES: Primary outcome measures were sensitivity, specificity and diagnostic accuracy for positron emission tomography-computerised tomography and dynamic contrast-enhanced computerised tomography. Incremental cost-effectiveness ratios compared management strategies that used dynamic contrast-enhanced computerised tomography with management strategies that did not use dynamic contrast-enhanced computerised tomography.
RESULTS: A total of 380 patients were recruited (median age 69 years). Of 312 patients with matched dynamic contrast-enhanced computer tomography and positron emission tomography-computerised tomography examinations, 191 (61%) were cancer patients. The sensitivity, specificity and diagnostic accuracy for positron emission tomography-computerised tomography and dynamic contrast-enhanced computer tomography were 72.8% (95% confidence interval 66.1% to 78.6%), 81.8% (95% confidence interval 74.0% to 87.7%), 76.3% (95% confidence interval 71.3% to 80.7%) and 95.3% (95% confidence interval 91.3% to 97.5%), 29.8% (95% confidence interval 22.3% to 38.4%) and 69.9% (95% confidence interval 64.6% to 74.7%), respectively. Exploratory modelling showed that maximum standardised uptake values had the best diagnostic accuracy, with an area under the curve of 0.87, which increased to 0.90 if combined with dynamic contrast-enhanced computerised tomography peak enhancement. The economic analysis showed that, over 24 months, dynamic contrast-enhanced computerised tomography was less costly (£3305, 95% confidence interval £2952 to £3746) than positron emission tomography-computerised tomography (£4013, 95% confidence interval £3673 to £4498) or a strategy combining the two tests (£4058, 95% confidence interval £3702 to £4547). Positron emission tomography-computerised tomography led to more patients with malignant nodules being correctly managed, 0.44 on average (95% confidence interval 0.39 to 0.49), compared with 0.40 (95% confidence interval 0.35 to 0.45); using both tests further increased this (0.47, 95% confidence interval 0.42 to 0.51).
LIMITATIONS: The high prevalence of malignancy in nodules observed in this trial, compared with that observed in nodules identified within screening programmes, limits the generalisation of the current results to nodules identified by screening. CONCLUSIONS: Findings from this research indicate that positron emission tomography-computerised tomography is more accurate than dynamic contrast-enhanced computerised tomography for the characterisation of solitary pulmonary nodules. A combination of maximum standardised uptake value and peak enhancement had the highest accuracy with a small increase in costs. Findings from this research also indicate that a combined positron emission tomography-dynamic contrast-enhanced computerised tomography approach with a slightly higher willingness to pay to avoid missing small cancers or to avoid a 'watch and wait' policy may be an approach to consider.
FUTURE WORK: Integration of the dynamic contrast-enhanced component into the positron emission tomography-computerised tomography examination and the feasibility of dynamic contrast-enhanced computerised tomography at lung screening for the characterisation of solitary pulmonary nodules should be explored, together with a lower radiation dose protocol
OSSOS. VII. 800+Trans-Neptunian Objects-The Complete Data Release
The Outer Solar System Origins Survey (OSSOS), a wide-field imaging program in 2013-2017 with the Canada-France-Hawaii Telescope, surveyed 155 deg(2) of sky to depths of m(r) = 24.1-25.2. We present 838 outer solar system discoveries that are entirely free of ephemeris bias. This increases the inventory of trans-Neptunian objects (TNOs) with accurately known orbits by nearly 50%. Each minor planet has 20-60 Gaia/Pan-STARRS-calibrated astrometric measurements made over 2-5 oppositions, which allows accurate classification of their orbits within the trans-Neptunian dynamical populations. The populations orbiting in mean-motion resonance with Neptune are key to understanding Neptune's early migration. Our 313 resonant TNOs, including 132 plutinos, triple the available characterized sample and include new occupancy of distant resonances out to semimajor axis a similar to 130 au. OSSOS doubles the known population of the nonresonant Kuiper Belt, providing 436 TNOs in this region, all with exceptionally high-quality orbits of a uncertainty sigma(a)Peer reviewe
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