6,672 research outputs found
Cue combination for 3D location judgements
Cue combination rules have often been applied to the perception of surface shape but not to judgements of object location. Here, we used immersive virtual reality to explore the relationship between different cues to distance. Participants viewed a virtual scene and judged the change in distance of an object presented in two intervals, where the scene changed in size between intervals (by a factor of between 0.25 and 4). We measured thresholds for detecting a change in object distance when there were only 'physical' (stereo and motion parallax) or 'texture-based' cues (independent of the scale of the scene) and used these to predict biases in a distance matching task. Under a range of conditions, in which the viewing distance and position of the tarte relative to other objects was varied, the ration of 'physical' to 'texture-based' thresholds was a good predictor of biases in the distance matching task. The cue combination approach, which successfully accounts for our data, relies on quite different principles from those underlying geometric reconstruction
Hubble Space Telescope astrometry of the closest brown dwarf binary system -- I. Overview and improved orbit
Located at ~2pc, the L7.5+T0.5 dwarfs system WISE J104915.57-531906.1
(Luhman16AB) is the third closest system known to Earth, making it a key
benchmark for detailed investigation of brown dwarf atmospheric properties,
thermal evolution, multiplicity, and planet-hosting frequency. In the first
study of this series -- based on a multi-cycle Hubble Space Telescope (HST)
program -- we provide an overview of the project and present improved estimates
of positions, proper motions, annual parallax, mass ratio, and the current best
assessment of the orbital parameters of the A-B pair. Our HST observations
encompass the apparent periastron of the binary at 220.5+/-0.2 mas at epoch
2016.402. Although our data seem to be inconsistent with recent ground-based
astrometric measurements, we also exclude the presence of third bodies down to
Neptune masses and periods longer than a year.Comment: 19 pages, 9 figures, 9 tables. Accepted for publication in MNRAS on
2017 May
Reducing "Structure From Motion": a General Framework for Dynamic Vision - Part 1: Modeling
The literature on recursive estimation of structure and motion from monocular image sequences comprises a large number of different models and estimation techniques. We propose a framework that allows us to derive and compare all models by following the idea of dynamical system reduction.
The "natural" dynamic model, derived by the rigidity constraint and the perspective projection, is first reduced by explicitly decoupling structure (depth) from motion. Then implicit decoupling techniques are explored, which consist of imposing that some function of the unknown parameters is held constant. By appropriately choosing such a function, not only can we account for all models seen so far in the literature, but we can also derive novel ones
Reducing “Structure from Motion”: a general framework for dynamic vision. 1. Modeling
The literature on recursive estimation of structure and motion from monocular image sequences comprises a large number of apparently unrelated models and estimation techniques. We propose a framework that allows us to derive and compare all models by following the idea of dynamical system reduction. The “natural” dynamic model, derived from the rigidity constraint and the projection model, is first reduced by explicitly decoupling structure (depth) from motion. Then, implicit decoupling techniques are explored, which consist of imposing that some function of the unknown parameters is held constant. By appropriately choosing such a function, not only can we account for models seen so far in the literature, but we can also derive novel ones
Depth Perception in Driving: Alcohol Intoxication, Eye Movement Changes, and the Disruption of Motion Parallax
Motion parallax, the ability to recover depth from retinal motion, is acrucial part of the visual information needed for driving. Recent work indicatesthat the perception of depth from motion parallax relies on the slow eyemovement system. It is well known that that alcohol intoxication reduces the gainof this slow eye movement system, the basis for the horizontal gaze nystagmus field sobriety test. The current study shows that alcohol intoxication also impairsthe perception of depth from motion parallax due to its influence on the slow eyemovement system. Observer thresholds in both active and passive motion parallaxtasks are significantly increased by acute alcohol intoxication. Perhaps such afailure of motion parallax plays a role when intoxicated drivers must make quickjudgements with what could be inaccurate or missing perceptual information aboutthe location of obstacles around them
Local kinematics of K and M giants from Coravel/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue triggered many kinematic and
dynamical studies of the solar neighbourhood. Nevertheless, those studies
generally lacked the third component of the space velocities, i.e., the radial
velocities. This work presents the kinematic analysis of 5952 K and 739 M
giants in the solar neighbourhood which includes for the first time radial
velocity data from a large survey performed with the CORAVEL
spectrovelocimeter. It also uses proper motions from the Tycho-2 catalogue,
which are expected to be more accurate than the Hipparcos ones. The UV-plane
constructed from these data for the stars with precise parallaxes reveals a
rich small-scale structure, with several clumps corresponding to the Hercules
stream, the Sirius moving group, and the Hyades and Pleiades superclusters. A
maximum-likelihood method, based on a bayesian approach, has been applied to
the data, in order to make full use of all the available stars and to derive
the kinematic properties of these subgroups. Isochrones in the
Hertzsprung-Russell diagram reveal a very wide range of ages for stars
belonging to these groups. These groups are most probably related to the
dynamical perturbation by transient spiral waves rather than to cluster
remnants. A possible explanation for the presence of young clusters in the same
area of the UV-plane is that they have been put there by the spiral wave
associated with their formation, while the kinematics of the older stars of our
sample has also been disturbed by the same wave. The term "dynamical stream"
for the kinematic groups is thus more appropriate than the traditional term
"supercluster" since it involves stars of different ages, not born at the same
place nor at the same time.Comment: 22 pages, 16 figures, accepted for publication in A&
Spectra disentangling applied to the Hyades binary Theta^2 Tau AB: new orbit, orbital parallax and component properties
Theta^2 Tauri is a detached and single-lined interferometric-spectroscopic
binary as well as the most massive binary system of the Hyades cluster. The
system revolves in an eccentric orbit with a periodicity of 140.7 days. The
secondary has a similar temperature but is less evolved and fainter than the
primary. It is also rotating more rapidly. Since the composite spectra are
heavily blended, the direct extraction of radial velocities over the orbit of
component B was hitherto unsuccessful. Using high-resolution spectroscopic data
recently obtained with the Elodie (OHP, France) and Hermes (ORM, La Palma,
Spain) spectrographs, and applying a spectra disentangling algorithm to three
independent data sets including spectra from the Oak Ridge Observatory (USA),
we derived an improved spectroscopic orbit and refined the solution by
performing a combined astrometric-spectroscopic analysis based on the new
spectroscopy and the long-baseline data from the Mark III optical
interferometer. As a result, the velocity amplitude of the fainter component is
obtained in a direct and objective way. Major progress based on this new
determination includes an improved computation of the orbital parallax. Our
mass ratio is in good agreement with the older estimates of Peterson et al.
(1991, 1993), but the mass of the primary is 15-25% higher than the more recent
estimates by Torres et al. (1997) and Armstrong et al. (2006). Due to the
strategic position of the components in the turnoff region of the cluster,
these new determinations imply stricter constraints for the age and the
metallicity of the Hyades cluster. The location of component B can be explained
by current evolutionary models, but the location of the more evolved component
A is not trivially explained and requires a detailed abundance analysis of its
disentangled spectrum.Comment: in press, 13 pages, 10 Postscript figures, 5 tables. Table~4 is
available as online material. Keywords: astrometry - techniques: high angular
resolution - stars: binaries: visual - stars: binaries: spectroscopic -
stars: fundamental parameter
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