11,749 research outputs found
The transiting multi-planet system HD3167: a 5.7 MEarth Super-Earth and a 8.3 MEarth mini-Neptune
HD3167 is a bright (V=8.9 mag) K0V star observed by the NASA's K2 space
mission during its Campaign 8. It has been recently found to host two small
transiting planets, namely, HD3167b, an ultra short period (0.96 d)
super-Earth, and HD3167c, a mini-Neptune on a relatively long-period orbit
(29.85 d). Here we present an intensive radial velocity follow-up of HD3167
performed with the FIES@NOT, [email protected], and HARPS-N@TNG spectrographs. We
revise the system parameters and determine radii, masses, and densities of the
two transiting planets by combining the K2 photometry with our spectroscopic
data. With a mass of 5.69+/-0.44 MEarth, radius of 1.574+/-0.054 REarth, and
mean density of 8.00(+1.0)(-0.98) g/cm^3, HD3167b joins the small group of
ultra-short period planets known to have a rocky terrestrial composition.
HD3167c has a mass of 8.33 (+1.79)(-1.85) MEarth and a radius of
2.740(+0.106)(-0.100) REarth, yielding a mean density of 2.21(+0.56)(-0.53)
g/cm^3, indicative of a planet with a composition comprising a solid core
surrounded by a thick atmospheric envelope. The rather large pressure scale
height (about 350 km) and the brightness of the host star make HD3167c an ideal
target for atmospheric characterization via transmission spectroscopy across a
broad range of wavelengths. We found evidence of additional signals in the
radial velocity measurements but the currently available data set does not
allow us to draw any firm conclusion on the origin of the observed variation.Comment: 18 pages, 11 figures, 5 table
How to Directly Image a Habitable Planet Around Alpha Centauri with a ~30-45cm Space Telescope
Several mission concepts are being studied to directly image planets around
nearby stars. It is commonly thought that directly imaging a potentially
habitable exoplanet around a Sun-like star requires space telescopes with
apertures of at least 1m. A notable exception to this is Alpha Centauri (A and
B), which is an extreme outlier among FGKM stars in terms of apparent habitable
zone size: the habitable zones are ~3x wider in apparent size than around any
other FGKM star. This enables a ~30-45cm visible light space telescope equipped
with a modern high performance coronagraph or starshade to resolve the
habitable zone at high contrast and directly image any potentially habitable
planet that may exist in the system. We presents a brief analysis of the
astrophysical and technical challenges involved with direct imaging of Alpha
Centauri with a small telescope and describe two new technologies that address
some of the key technical challenges. In particular, the raw contrast
requirements for such an instrument can be relaxed to 1e-8 if the mission
spends 2 years collecting tens of thousands of images on the same target,
enabling a factor of 500-1000 speckle suppression in post processing using a
new technique called Orbital Difference Imaging (ODI). The raw light leak from
both stars is controllable with a special wavefront control algorithm known as
Multi-Star Wavefront Control (MSWC), which independently suppresses diffraction
and aberrations from both stars using independent modes on the deformable
mirror. We also show an example of a small coronagraphic mission concept to
take advantage of this opportunity.Comment: 12 pages, 8 figures, 1 table, to appear in Proc. SPIE 9605. See other
ACESat papers by Bendek, Males, and Thoma
Decoding the Encoding of Functional Brain Networks: an fMRI Classification Comparison of Non-negative Matrix Factorization (NMF), Independent Component Analysis (ICA), and Sparse Coding Algorithms
Brain networks in fMRI are typically identified using spatial independent
component analysis (ICA), yet mathematical constraints such as sparse coding
and positivity both provide alternate biologically-plausible frameworks for
generating brain networks. Non-negative Matrix Factorization (NMF) would
suppress negative BOLD signal by enforcing positivity. Spatial sparse coding
algorithms ( Regularized Learning and K-SVD) would impose local
specialization and a discouragement of multitasking, where the total observed
activity in a single voxel originates from a restricted number of possible
brain networks.
The assumptions of independence, positivity, and sparsity to encode
task-related brain networks are compared; the resulting brain networks for
different constraints are used as basis functions to encode the observed
functional activity at a given time point. These encodings are decoded using
machine learning to compare both the algorithms and their assumptions, using
the time series weights to predict whether a subject is viewing a video,
listening to an audio cue, or at rest, in 304 fMRI scans from 51 subjects.
For classifying cognitive activity, the sparse coding algorithm of
Regularized Learning consistently outperformed 4 variations of ICA across
different numbers of networks and noise levels (p0.001). The NMF algorithms,
which suppressed negative BOLD signal, had the poorest accuracy. Within each
algorithm, encodings using sparser spatial networks (containing more
zero-valued voxels) had higher classification accuracy (p0.001). The success
of sparse coding algorithms may suggest that algorithms which enforce sparse
coding, discourage multitasking, and promote local specialization may capture
better the underlying source processes than those which allow inexhaustible
local processes such as ICA
Theoretical Reflectance Spectra of Earth-Like Planets through Their Evolutions: Impact of Clouds on the Detectability of Oxygen, Water, and Methane with Future Direct Imaging Missions
In the near-future, atmospheric characterization of Earth-like planets in the
habitable zone will become possible via reflectance spectroscopy with future
telescopes such as the proposed LUVOIR and HabEx missions. While previous
studies have considered the effect of clouds on the reflectance spectra of
Earth-like planets, the molecular detectability considering a wide range of
cloud properties has not been previously explored in detail. In this study, we
explore the effect of cloud altitude and coverage on the reflectance spectra of
Earth-like planets at different geological epochs and examine the detectability
of , , and with test parameters
for the future mission concept, LUVOIR, using a coronagraph noise simulator
previously designed for WFIRST-AFTA. Considering an Earth-like planet located
at 5 pc away, we have found that for the proposed LUVOIR telescope, the
detection of the A-band feature (0.76 m) will take
approximately 100, 30, and 10 hours for the majority of the cloud parameter
space modeled for the atmospheres with 10\%, 50\%, and 100\% of modern Earth
O abundances, respectively. Especially, for {the case of \%} of
modern Earth O abundance, the feature will be detectable with integration
time hours as long as there are lower altitude ( km)
clouds with a global coverage of . For the 1\% of modern Earth
abundance case, however, it will take more than 100 hours for
all the cloud parameters we modeled.Comment: 16 pages, 10 figures, accepted for publication in A
DeepCut: Joint Subset Partition and Labeling for Multi Person Pose Estimation
This paper considers the task of articulated human pose estimation of
multiple people in real world images. We propose an approach that jointly
solves the tasks of detection and pose estimation: it infers the number of
persons in a scene, identifies occluded body parts, and disambiguates body
parts between people in close proximity of each other. This joint formulation
is in contrast to previous strategies, that address the problem by first
detecting people and subsequently estimating their body pose. We propose a
partitioning and labeling formulation of a set of body-part hypotheses
generated with CNN-based part detectors. Our formulation, an instance of an
integer linear program, implicitly performs non-maximum suppression on the set
of part candidates and groups them to form configurations of body parts
respecting geometric and appearance constraints. Experiments on four different
datasets demonstrate state-of-the-art results for both single person and multi
person pose estimation. Models and code available at
http://pose.mpi-inf.mpg.de.Comment: Accepted at IEEE Conference on Computer Vision and Pattern
Recognition (CVPR 2016
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