61,805 research outputs found
Secondary Eclipse Photometry of WASP-4b with Warm Spitzer
We present photometry of the giant extrasolar planet WASP-4b at 3.6 and 4.5
micron taken with the Infrared Array Camera on board the Spitzer Space
Telescope as part of Spitzer's extended warm mission. We find secondary eclipse
depths of 0.319+/-0.031% and 0.343+/-0.027% for the 3.6 and 4.5 micron bands,
respectively and show model emission spectra and pressure-temperature profiles
for the planetary atmosphere. These eclipse depths are well fit by model
emission spectra with water and other molecules in absorption, similar to those
used for TrES-3 and HD 189733b. Depending on our choice of model, these results
indicate that this planet has either a weak dayside temperature inversion or no
inversion at all. The absence of a strong thermal inversion on this highly
irradiated planet is contrary to the idea that highly irradiated planets are
expected to have inversions, perhaps due the presence of an unknown absorber in
the upper atmosphere. This result might be explained by the modestly enhanced
activity level of WASP-4b's G7V host star, which could increase the amount of
UV flux received by the planet, therefore reducing the abundance of the unknown
stratospheric absorber in the planetary atmosphere as suggested in Knutson et
al. (2010). We also find no evidence for an offset in the timing of the
secondary eclipse and place a 2 sigma upper limit on |ecos(omega)| of 0.0024,
which constrains the range of tidal heating models that could explain this
planet's inflated radius.Comment: 8 pages, 7 figures (some in color), accepted for publication in Ap
Detection of Planetary Emission from the Exoplanet TrES-2 using Spitzer /IRAC
We present here the results of our observations of TrES-2 using the Infrared
Array Camera on Spitzer. We monitored this transiting system during two
secondary eclipses, when the planetary emission is blocked by the star. The
resulting decrease in flux is 0.127%+-0.021%, 0.230%+-0.024%, 0.199%+-0.054%,
and 0.359%+-0.060%, at 3.6 microns, 4.5 microns, 5.8 microns, and 8.0 microns,
respectively. We show that three of these flux contrasts are well fit by a
black body spectrum with T_{eff}=1500 K, as well as by a more detailed model
spectrum of a planetary atmosphere. The observed planet-to-star flux ratios in
all four IRAC channels can be explained by models with and without a thermal
inversion in the atmosphere of TrES-2, although with different atmospheric
chemistry. Based on the assumption of thermochemical equilibrium, the chemical
composition of the inversion model seems more plausible, making it a more
favorable scenario. TrES-2 also falls in the category of highly irradiated
planets which have been theoretically predicted to exhibit thermal inversions.
However, more observations at infrared and visible wavelengths would be needed
to confirm a thermal inversion in this system. Furthermore, we find that the
times of the secondary eclipses are consistent with previously published times
of transit and the expectation from a circular orbit. This implies that TrES-2
most likely has a circular orbit, and thus does not obtain additional thermal
energy from tidal dissipation of a non-zero orbital eccentricity, a proposed
explanation for the large radius of this planet.Comment: 8 pages, 4 figures, 2 tables. Accepted for publication in the
Astrophysical Journal. V2: New figure added ; other minor changes throughou
Fast and Accurate Camera Covariance Computation for Large 3D Reconstruction
Estimating uncertainty of camera parameters computed in Structure from Motion
(SfM) is an important tool for evaluating the quality of the reconstruction and
guiding the reconstruction process. Yet, the quality of the estimated
parameters of large reconstructions has been rarely evaluated due to the
computational challenges. We present a new algorithm which employs the sparsity
of the uncertainty propagation and speeds the computation up about ten times
\wrt previous approaches. Our computation is accurate and does not use any
approximations. We can compute uncertainties of thousands of cameras in tens of
seconds on a standard PC. We also demonstrate that our approach can be
effectively used for reconstructions of any size by applying it to smaller
sub-reconstructions.Comment: ECCV 201
Distortion Estimation Through Explicit Modeling of the Refractive Surface
Precise calibration is a must for high reliance 3D computer vision
algorithms. A challenging case is when the camera is behind a protective glass
or transparent object: due to refraction, the image is heavily distorted; the
pinhole camera model alone can not be used and a distortion correction step is
required. By directly modeling the geometry of the refractive media, we build
the image generation process by tracing individual light rays from the camera
to a target. Comparing the generated images to their distorted - observed -
counterparts, we estimate the geometry parameters of the refractive surface via
model inversion by employing an RBF neural network. We present an image
collection methodology that produces data suited for finding the distortion
parameters and test our algorithm on synthetic and real-world data. We analyze
the results of the algorithm.Comment: Accepted to ICANN 201
Low-Cost Compressive Sensing for Color Video and Depth
A simple and inexpensive (low-power and low-bandwidth) modification is made
to a conventional off-the-shelf color video camera, from which we recover
{multiple} color frames for each of the original measured frames, and each of
the recovered frames can be focused at a different depth. The recovery of
multiple frames for each measured frame is made possible via high-speed coding,
manifested via translation of a single coded aperture; the inexpensive
translation is constituted by mounting the binary code on a piezoelectric
device. To simultaneously recover depth information, a {liquid} lens is
modulated at high speed, via a variable voltage. Consequently, during the
aforementioned coding process, the liquid lens allows the camera to sweep the
focus through multiple depths. In addition to designing and implementing the
camera, fast recovery is achieved by an anytime algorithm exploiting the
group-sparsity of wavelet/DCT coefficients.Comment: 8 pages, CVPR 201
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