98 research outputs found
A well-separated pairs decomposition algorithm for k-d trees implemented on multi-core architectures
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Variations of k-d trees represent a fundamental data structure used in Computational Geometry with numerous applications in science. For example particle track tting in the software of the LHC experiments, and in simulations of N-body systems in the study of dynamics of interacting galaxies, particle beam physics, and molecular dynamics in biochemistry. The many-body tree methods devised by Barnes and Hutt in the 1980s and the Fast Multipole Method introduced in 1987 by Greengard and Rokhlin use variants of k-d trees to reduce the computation time upper bounds to O(n log n) and even O(n) from O(n2). We present an algorithm that uses the principle of well-separated pairs decomposition to always produce compressed trees in O(n log n) work. We present and evaluate parallel implementations for the algorithm that can take advantage of multi-core architectures.The Science and Technology Facilities Council, UK
Inducing Probabilistic Grammars by Bayesian Model Merging
We describe a framework for inducing probabilistic grammars from corpora of
positive samples. First, samples are {\em incorporated} by adding ad-hoc rules
to a working grammar; subsequently, elements of the model (such as states or
nonterminals) are {\em merged} to achieve generalization and a more compact
representation. The choice of what to merge and when to stop is governed by the
Bayesian posterior probability of the grammar given the data, which formalizes
a trade-off between a close fit to the data and a default preference for
simpler models (`Occam's Razor'). The general scheme is illustrated using three
types of probabilistic grammars: Hidden Markov models, class-based -grams,
and stochastic context-free grammars.Comment: To appear in Grammatical Inference and Applications, Second
International Colloquium on Grammatical Inference; Springer Verlag, 1994. 13
page
Planet Hunters VII. Discovery of a New Low-Mass, Low-Density Planet (PH3 c) Orbiting Kepler-289 with Mass Measurements of Two Additional Planets (PH3 b and d)
We report the discovery of one newly confirmed planet ( days,
) and mass determinations of two previously
validated Kepler planets, Kepler-289 b ( days,
) and Kepler-289-c ( days,
), through their transit timing variations
(TTVs). We also exclude the possibility that these three planets reside in a
Laplace resonance. The outer planet has very deep (), high
signal-to-noise transits, which puts extremely tight constraints on its host
star's stellar properties via Kepler's Third Law. The star PH3 is a young
( Gyr as determined by isochrones and gyrochronology), Sun-like star
with , , and
K. The middle planet's large TTV amplitude (
hours) resulted either in non-detections or inaccurate detections in previous
searches. A strong chopping signal, a shorter period sinusoid in the TTVs,
allows us to break the mass-eccentricity degeneracy and uniquely determine the
masses of the inner, middle, and outer planets to be ,
, and , which we designate PH3 b, c, and
d, respectively. Furthermore, the middle planet, PH3 c, has a relatively low
density, g/cm for a planet of its mass, requiring a
substantial H/He atmosphere of by mass, and joins a
growing population of low-mass, low-density planets.Comment: 21 pages, 10 figures, 5 tables, accepted into Ap
Planet Hunters X: Searching for Nearby Neighbors of 75 Planet and Eclipsing Binary Candidates from the K2 Kepler Extended Mission
We present high-resolution observations of a sample of 75 K2 targets from
Campaigns 1-3 using speckle interferometry on the Southern Astrophysical
Research (SOAR) telescope and adaptive optics (AO) imaging at the Keck II
telescope. The median SOAR -band and Keck -band detection limits at 1"
were ~mag and ~mag, respectively. This
sample includes 37 stars likely to host planets, 32 targets likely to be
eclipsing binaries (EBs), and 6 other targets previously labeled as likely
planetary false positives. We find nine likely physically bound companion stars
within 3" of three candidate transiting exoplanet host stars and six likely
EBs. Six of the nine detected companions are new discoveries; one of the six,
EPIC 206061524, is associated with a planet candidate. Among the EB candidates,
companions were only found near the shortest period ones ( days), which is
in line with previous results showing high multiplicity near short-period
binary stars. This high-resolution data, including both the detected companions
and the limits on potential unseen companions, will be useful in future planet
vetting and stellar multiplicity rate studies for planets and binaries.Comment: Accepted in A
Facebook’s Cyber–Cyber and Cyber–Physical Digital Twins
A cyber-cyber digital twin is a simulation of a software system. By contrast, a cyber-physical digital twin is a simulation of a non-software (physical) system. Although cyber-physical digital twins have received a lot of recent attention, their cyber-cyber counterparts have been comparatively overlooked. In this paper we show how the unique properties of cyber-cyber digital twins open up exciting opportunities for research and development. Like all digital twins, the cyber-cyber digital twin is both informed by and informs the behaviour of the twin it simulates. It is therefore a software system that simulates another software system, making it conceptually truly a twin, blurring the distinction between the simulated and the simulator. Cyber-cyber digital twins can be twins of other cyber-cyber digital twins, leading to a hierarchy of twins. As we shall see, these apparently philosophical observations have practical ramifications for the design, implementation and deployment of digital twins at Facebook
Planet Hunters. VIII. Characterization of 41 Long-Period Exoplanet Candidates from Kepler Archival Data
The census of exoplanets is incomplete for orbital distances larger than 1
AU. Here, we present 41 long-period planet candidates in 38 systems identified
by Planet Hunters based on Kepler archival data (Q0-Q17). Among them, 17
exhibit only one transit, 14 have two visible transits and 10 have more than
three visible transits. For planet candidates with only one visible transit, we
estimate their orbital periods based on transit duration and host star
properties. The majority of the planet candidates in this work (75%) have
orbital periods that correspond to distances of 1-3 AU from their host stars.
We conduct follow-up imaging and spectroscopic observations to validate and
characterize planet host stars. In total, we obtain adaptive optics images for
33 stars to search for possible blending sources. Six stars have stellar
companions within 4". We obtain high-resolution spectra for 6 stars to
determine their physical properties. Stellar properties for other stars are
obtained from the NASA Exoplanet Archive and the Kepler Stellar Catalog by
Huber et al. (2014). We validate 7 planet candidates that have planet
confidence over 0.997 (3-{\sigma} level). These validated planets include 3
single-transit planets (KIC-3558849b, KIC-5951458b, and KIC-8540376c), 3
planets with double transits (KIC-8540376b, KIC-9663113b, and KIC-10525077b),
and 1 planet with 4 transits (KIC-5437945b). This work provides assessment
regarding the existence of planets at wide separations and the associated false
positive rate for transiting observation (17%-33%). More than half of the
long-period planets with at least three transits in this paper exhibit transit
timing variations up to 41 hours, which suggest additional components that
dynamically interact with the transiting planet candidates. The nature of these
components can be determined by follow-up radial velocity and transit
observations.Comment: Published on ApJ, 815, 127 Notations of validated planets are changed
in accordance with naming convention of NASA Exoplanet Archiv
Planet Hunters. VI: An Independent Characterization of KOI-351 and Several Long Period Planet Candidates from the Kepler Archival Data
We report the discovery of 14 new transiting planet candidates in the Kepler
field from the Planet Hunters citizen science program. None of these candidates
overlapped with Kepler Objects of Interest (KOIs) at the time of submission. We
report the discovery of one more addition to the six planet candidate system
around KOI-351, making it the only seven planet candidate system from Kepler.
Additionally, KOI-351 bears some resemblance to our own solar system, with the
inner five planets ranging from Earth to mini-Neptune radii and the outer
planets being gas giants; however, this system is very compact, with all seven
planet candidates orbiting AU from their host star. A Hill
stability test and an orbital integration of the system shows that the system
is stable. Furthermore, we significantly add to the population of long period
transiting planets; periods range from 124-904 days, eight of them more than
one Earth year long. Seven of these 14 candidates reside in their host star's
habitable zone.Comment: 27 pages, 6 figures, 5 tables, Accepted to AJ (in press) (updated
title from original astro-ph submission
A Population of Dipper Stars from the Transiting Exoplanet Survey Satellite Mission
Dipper stars are a classification of young stellar objects that exhibit
dimming variability in their light curves, dropping in brightness by 10-50%,
likely induced by occultations due to circumstellar disk material. This
variability can be periodic, quasi-periodic, or aperiodic. Dipper stars have
been discovered in young stellar associations via ground-based and space-based
photometric surveys. We present the detection and characterization of the
largest collection of dipper stars to date: 293 dipper stars, including 234 new
dipper candidates. We have produced a catalog of these targets, which also
includes young stellar variables that exhibit predominately bursting-like
variability and symmetric variability (equal parts bursting and dipping). The
total number of catalog sources is 414. These variable sources were found in a
visual survey of TESS light curves, where dipping-like variability was
observed. We found a typical age among our dipper sources of <5 Myr, with the
age distribution peaking at ~2 Myr, and a tail of the distribution extending to
ages older than 20 Myr. Regardless of the age, our dipper candidates tend to
exhibit infrared excess, which is indicative of the presence of disks. TESS is
now observing the ecliptic plane, which is rich in young stellar associations,
so we anticipate many more discoveries in the TESS dataset. A larger sample of
dipper stars would enhance the census statistics of light curve morphologies
and dipper ages.Comment: 19 pages, 11 figures, 1 table (included in latex source), accepted
for publication in ApJ
BG Ind: the nearest doubly eclipsing, compact hierarchical quadruple system
BG Ind is a well-studied, bright, nearby binary consisting of a pair of F stars in a 1.46-d orbit. We have discovered in the TESS light curve for TIC 229804573 (aka BG Ind), a second eclipsing binary in the system with a 0.53-d period. Our subsequent analyses of the recent TESS and archival ground-based photometric and radial velocity (RV) data reveal that the two binaries are gravitationally bound in a 721-d period, moderately eccentric orbit. We present the results of a joint spectro-photodynamical analysis of the eclipse timing variation curves of both binaries based on TESS and ground-based archival data, the TESS light curve, archival RV data, and the spectral energy distribution, coupled with the use of PARSEC stellar isochrones. We confirm prior studies of BG Ind that found that the brighter binary A consists of slightly evolved F-type stars with refined masses of 1.32 and 1.43 M-circle dot, and radii of 1.59 and 2.34 R-circle dot. The previously unknown binary B has two less massive stars of 0.69 and 0.64 M-circle dot and radii of 0.64 and 0.61 R-circle dot. Based on a number of different arguments that we discuss, we conclude that the three orbital planes are likely aligned to within 17 degrees
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