99 research outputs found
The La Silla - QUEST Kuiper Belt Survey
We describe the instrumentation and detection software and characterize the
detection efficiency of an automated, all-sky, southern-hemisphere search for
Kuiper Belt objects brighter than R mag 21.4. The search relies on Yale
University's 160-Megapixel QUEST camera, previously used for successful surveys
at Palomar that detected most of the distant dwarf planets, and now installed
on the ESO 1.0-m Schmidt telescope at La Silla, Chile. Extensive upgrades were
made to the telescope control system to support automation, and significant
improvements were made to the camera. To date, 63 new KBOs have been
discovered, including a new member of the Haumea collision family (2009 YE7)
and a new distant object with inclination exceeding 70 deg (2010 WG9). In a
survey covering ~7500 deg2, we have thus far detected 77 KBOs and Centaurs,
more than any other full-hemisphere search to date. Using a pattern of dithered
pointings, we demonstrate a search efficiency exceeding 80%. We are currently
on track to complete the southern-sky survey and detect any bright KBOs that
have eluded detection from the north.Comment: 20 pages, 2 tables, 7 figure
Planet Hunters: A Transiting Circumbinary Planet in a Quadruple Star System
We report the discovery and confirmation of a transiting circumbinary planet (PH1b) around KIC 4862625, an eclipsing binary in the Kepler field. The planet was discovered by volunteers searching the first six Quarters of publicly available Kepler data as part of the Planet Hunters citizen science project. Transits of the planet across the larger and brighter of the eclipsing stars are detectable by visual inspection every ~137 days, with seven transits identified in Quarters 1-11. The physical and orbital parameters of both the host stars and planet were obtained via a photometric-dynamical model, simultaneously fitting both the measured radial velocities and the Kepler light curve of KIC 4862625. The 6.18 ± 0.17 R_⊕ planet orbits outside the 20 day orbit of an eclipsing binary consisting of an F dwarf (1.734 ± 0.044 R_☉, 1.528 ± 0.087 M_☉) and M dwarf (0.378 ± 0.023 R_☉, 0.408 ± 0.024 M_☉). For the planet, we find an upper mass limit of 169 M_⊕ (0.531 Jupiter masses) at the 99.7% confidence level. With a radius and mass less than that of Jupiter, PH1b is well within the planetary regime. Outside the planet's orbit, at ~1000 AU, a previously unknown visual binary has been identified that is likely bound to the planetary system, making this the first known case of a quadruple star system with a transiting planet
Interpreting the densities of the Kuiper belt's dwarf planets
Kuiper Belt objects with absolute magnitude less than 3 (radius 500
km), the dwarf planets, have a range of different ice/rock ratios, and are more
rock-rich than their smaller counterparts. Many of these objects have moons,
which suggests that collisions may have played a role in modifying their
compositions. We show that the dwarf planets fall into two categories when
analysed by their mean densities and satellite-to-primary size ratio. Systems
with large moons, such as Pluto/Charon and Orcus/Vanth, can form in
low-velocity grazing collisions in which both bodies retain their compositions.
We propose that these systems retain a primordial composition, with a density
of about 1.8 g/cm. Triton, thought to be a captured KBO, could have lost
enough ice during its early orbital evolution to explain its rock-enrichment
relative to the primordial material. Systems with small moons, Eris, Haumea,
and Quaoar, formed from a different type of collision in which icy material,
perhaps a few tens of percent of the total colliding mass, is lost. The
fragments would not remain in physical or dynamical proximity to the parent
body. The ice loss process has not yet been demonstrated numerically, which
could be due to the paucity of KBO origin simulations, or missing physical
processes in the impact models. If our hypothesis is correct, we predict that
large KBOs with small moons should be denser than the primordial material, and
that the mean density of Orcus should be close to the primordial value.Comment: 8 pages, 2 figures. Accepted for publication in MNRA
The Peculiar Photometric Properties of 2010 WG9: A Slowly-Rotating Trans-Neptunian Object from the Oort Cloud
We present long-term BVRI observations of 2010 WG9, an ~100-km diameter
trans-Neptunian object (TNO) with an extremely high inclination of 70 deg
discovered by the La Silla - QUEST southern sky survey. Most of the
observations were obtained with ANDICAM on the SMARTS 1.3m at Cerro Tololo,
Chile from Dec 2010 to Nov 2012. Additional observations were made with EFOSC2
on the 3.5-m NTT telescope of the European Southern Observatory at La Silla,
Chile in Feb 2011. The observations reveal a sinusoidal light curve with
amplitude 0.14 mag and period 5.4955 +/- 0.0025d, which is likely half the true
rotation period. Such long rotation periods have previously been observed only
for tidally-evolved binary TNOs, suggesting that 2010 WG9 may be such a system.
We predict a nominal separation of at least 790 km, resolvable with HST and
ground-based systems. We measure B-R = 1.318 +/- 0.029 and V-R = 0.520 +/-
0.018, consistent with the colors of modestly red Centaurs and Damocloids. At
I-band wavelengths, we observe an unusually large variation of color with
rotational phase, with R-I ranging from 0.394 +/- 0.025 to 0.571 +/- 0.044. We
also measure an absolute R-band absolute magnitude of 7.93 +/- 0.05 and solar
phase coefficient 0.049 +/- 0.019 mag/deg.Comment: 17 pages, 5 figure
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
Planet Four: A Neural Network’s search for polar spring-time fans on Mars
Dark deposits visible from orbit appear in the Martian south polar region during the springtime. These are thought to form from explosive jets of carbon dioxide gas breaking through the thawing seasonal ice cap, carrying dust and dirt which is then deposited onto the ice as dark ‘blotches’, or blown by the surface winds into streaks or ‘fans’. We investigate machine learning (ML) methods for automatically identifying these seasonal features in High Resolution Imaging Science Experiment (HiRISE) satellite imagery. We designed deep Convolutional Neural Networks (CNNs) that were trained and tested using the catalog generated by Planet Four, an online citizen science project mapping the south polar seasonal deposits. We validated the CNNs by comparing their results with those of ISODATA (Iterative Self-Organizing Data Analysis Technique) clustering and as expected, the CNNs were significantly better at predicting the results found by Planet Four, in both the area of predicted seasonal deposits and in delineating their boundaries. We found neither the CNNs or ISODATA were suited to predicting the source point and directions of seasonal fans, which is a strength of the citizen science approach. The CNNs showed good agreement with Planet Four in cross-validation metrics and detected some seasonal deposits in the HiRISE images missed in the Planet Four catalog; the total area of seasonal deposits predicted by the CNNs was 27% larger than that of the Planet Four catalog, but this aspect varied considerably on a per-image basis
Unproceedings of the Fourth .Astronomy Conference (.Astronomy 4), Heidelberg, Germany, July 9-11 2012
The goal of the .Astronomy conference series is to bring together
astronomers, educators, developers and others interested in using the Internet
as a medium for astronomy. Attendance at the event is limited to approximately
50 participants, and days are split into mornings of scheduled talks, followed
by 'unconference' afternoons, where sessions are defined by participants during
the course of the event. Participants in unconference sessions are discouraged
from formal presentations, with discussion, workshop-style formats or informal
practical tutorials encouraged. The conference also designates one day as a
'hack day', in which attendees collaborate in groups on day-long projects for
presentation the following morning. These hacks are often a way of
concentrating effort, learning new skills, and exploring ideas in a practical
fashion. The emphasis on informal, focused interaction makes recording
proceedings more difficult than for a normal meeting. While the first
.Astronomy conference is preserved formally in a book, more recent iterations
are not documented. We therefore, in the spirit of .Astronomy, report
'unproceedings' from .Astronomy 4, which was held in Heidelberg in July 2012.Comment: 11 pages, 1 figure, .Astronomy 4, #dotastr
Planet Four: Terrains - Discovery of Araneiforms Outside of the South Polar Layered Deposits
We present the results of a systematic mapping of seasonally sculpted
terrains on the South Polar region of Mars with the Planet Four: Terrains (P4T)
online citizen science project. P4T enlists members of the general public to
visually identify features in the publicly released Mars Reconnaissance Orbiter
CTX images. In particular, P4T volunteers are asked to identify: 1) araneiforms
(including features with a central pit and radiating channels known as
'spiders'); 2) erosional depressions, troughs, mesas, ridges, and
quasi-circular pits characteristic of the South Polar Residual Cap (SPRC) which
we collectively refer to as 'Swiss cheese terrain', and 3) craters. In this
work we present the distributions of our high confidence classic spider
araneiforms and Swiss cheese terrain identifications. We find no locations
within our high confidence spider sample that also have confident Swiss cheese
terrain identifications. Previously spiders were reported as being confined to
the South Polar Layered Deposits (SPLD). Our work has provided the first
identification of spiders at locations outside of the SPLD, confirmed with high
resolution HiRISE imaging. We find araneiforms on the Amazonian and Hesperian
polar units and the Early Noachian highland units, with 75% of the identified
araneiform locations in our high confidence sample residing on the SPLD. With
our current coverage, we cannot confirm whether these are the only geologic
units conducive to araneiform formation on the Martian South Polar region. Our
results are consistent with the current CO2 jet formation scenario with the
process exploiting weaknesses in the surface below the seasonal CO2 ice sheet
to carve araneiform channels into the regolith over many seasons. These new
regions serve as additional probes of the conditions required for channel
creation in the CO2 jet process. (Abridged)Comment: accepted to Icarus - Supplemental data files are available at
https://www.zooniverse.org/projects/mschwamb/planet-four-terrains/about/results
- Icarus print version available at
http://www.sciencedirect.com/science/article/pii/S001910351730055
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