496 research outputs found
Multimedia ontology matching by using visual and textual modalities
International audienceOntologies have been intensively applied for improving multimedia search and retrieval by providing explicit meaning to visual content. Several multimedia ontologies have been recently proposed as knowledge models suitable for narrowing the well known semantic gap and for enabling the semantic interpretation of images. Since these ontologies have been created in different application contexts, establishing links between them, a task known as ontology matching, promises to fully unlock their potential in support of multimedia search and retrieval. This paper proposes and compares empirically two extensional ontology matching techniques applied to an important semantic image retrieval issue: automatically associating common-sense knowledge to multimedia concepts. First, we extend a previously introduced textual concept matching approach to use both textual and visual representation of images. In addition, a novel matching technique based on a multi-modal graph is proposed. We argue that the textual and visual modalities have to be seen as complementary rather than as exclusive sources of extensional information in order to improve the efficiency of the application of an ontology matching approach in the multimedia domain. An experimental evaluation is included in the paper
Phase curves of WASP-33b and HD 149026b and a New Correlation Between Phase Curve Offset and Irradiation Temperature
We present new 3.6 and 4.5 Spitzer phase curves for the highly
irradiated hot Jupiter WASP-33b and the unusually dense Saturn-mass planet HD
149026b. As part of this analysis, we develop a new variant of pixel level
decorrelation that is effective at removing intrapixel sensitivity variations
for long observations (>10 hours) where the position of the star can vary by a
significant fraction of a pixel. Using this algorithm, we measure eclipse
depths, phase amplitudes, and phase offsets for both planets at 3.6 and
4.5 . We use a simple toy model to show that WASP-33b's phase offset,
albedo, and heat recirculation efficiency are largely similar to those of other
hot Jupiters despite its very high irradiation. On the other hand, our fits for
HD 149026b prefer a very high albedo and an unusually high recirculation
efficiency. We also compare our results to predictions from general circulation
models, and find that while neither are a good match to the data, the
discrepancies for HD 149026b are especially large. We speculate that this may
be related to its high bulk metallicity, which could lead to enhanced
atmospheric opacities and the formation of reflective cloud layers in localized
regions of the atmosphere. We then place these two planets in a broader context
by exploring relationships between the temperatures, albedos, heat transport
efficiencies, and phase offsets of all planets with published thermal phase
curves. We find a striking relationship between phase offset and irradiation
temperature--the former drops with increasing temperature until around 3400 K,
and rises thereafter. Although some aspects of this trend are mirrored in the
circulation models, there are notable differences that provide important clues
for future modeling efforts
Spitzer Secondary Eclipses of the Dense, Modestly-irradiated, Giant Exoplanet HAT-P-20b Using Pixel-Level Decorrelation
HAT-P-20b is a giant exoplanet that orbits a metal-rich star. The planet
itself has a high total density, suggesting that it may also have a high
metallicity in its atmosphere. We analyze two eclipses of the planet in each of
the 3.6- and 4.5 micron bands of Warm Spitzer. These data exhibit intra-pixel
detector sensitivity fluctuations that were resistant to traditional
decorrelation methods. We have developed a simple, powerful, and radically
different method to correct the intra-pixel effect for Warm Spitzer data, which
we call pixel-level decorrelation (PLD). PLD corrects the intra-pixel effect
very effectively, but without explicitly using - or even measuring - the
fluctuations in the apparent position of the stellar image. We illustrate and
validate PLD using synthetic and real data, and comparing the results to
previous analyses. PLD can significantly reduce or eliminate red noise in
Spitzer secondary eclipse photometry, even for eclipses that have proven to be
intractable using other methods. Our successful PLD analysis of four HAT-P-20b
eclipses shows a best-fit blackbody temperature of 1134 +/-29K, indicating
inefficient longitudinal transfer of heat, but lacking evidence for strong
molecular absorption. We find sufficient evidence for variability in the 4.5
micron band that the eclipses should be monitored at that wavelength by
Spitzer, and this planet should be a high priority for JWST spectroscopy. All
four eclipses occur about 35 minutes after orbital phase 0.5, indicating a
slightly eccentric orbit. A joint fit of the eclipse and transit times with
extant RV data yields e(cos{omega}) = 0.01352 (+0.00054, -0.00057), and
establishes the small eccentricity of the orbit to high statistical confidence.
Given the existence of a bound stellar companion, HAT-P-20b is another
excellent candidate for orbital evolution via Kozai migration or other
three-body mechanism.Comment: version published in ApJ, minor text and figure revision
Atmospheric Characterization of the Hot Jupiter Kepler-13Ab
Kepler-13Ab (= KOI-13.01) is a unique transiting hot Jupiter. It is one of
very few known short-period planets orbiting a hot A-type star, making it one
of the hottest planets currently known. The availability of Kepler data allows
us to measure the planet's occultation (secondary eclipse) and phase curve in
the optical, which we combine with occultations observed by warm Spitzer at 4.5
mic and 3.6 mic and a ground-based occultation observation in the Ks band (2.1
mic). We derive a day-side hemisphere temperature of 2,750 +- 160 K as the
effective temperature of a black body showing the same occultation depths.
Comparing the occultation depths with one-dimensional planetary atmosphere
models suggests the presence of an atmospheric temperature inversion. Our
analysis shows evidence for a relatively high geometric albedo, Ag= 0.33 +0.04
-0.06. While measured with a simplistic method, a high Ag is supported also by
the fact that the one-dimensional atmosphere models underestimate the
occultation depth in the optical. We use stellar spectra to determine the
dilution, in the four wide bands where occultation was measured, due to the
visual stellar binary companion 1.15 +- 0.05" away. The revised stellar
parameters measured using these spectra are combined with other measurements
leading to revised planetary mass and radius estimates of Mp = 4.94 - 8.09 Mjup
and Rp = 1.406 +- 0.038 Rjup. Finally, we measure a Kepler mid-occultation time
that is 34.0 +- 6.9 s earlier than expected based on the mid-transit time and
the delay due to light travel time, and discuss possible scenarios.Comment: V2: Accepted to ApJ on 2014 April 11. Spitzer photometry and model
fitting Matlab pipeline code is publicly available at:
http://gps.caltech.edu/~shporer/spitzerphot
Spitzer Secondary Eclipse Observations of Five Cool Gas Giant Planets and Empirical Trends in Cool Planet Emission Spectra
In this work we present Spitzer 3.6 and 4.5 micron secondary eclipse
observations of five new cool (<1200 K) transiting gas giant planets:
HAT-P-19b, WASP-6b, WASP-10b, WASP-39b, and WASP-67b. We compare our measured
eclipse depths to the predictions of a suite of atmosphere models and to
eclipse depths for planets with previously published observations in order to
constrain the temperature- and mass-dependent properties of gas giant planet
atmospheres. We find that the dayside emission spectra of planets less massive
than Jupiter require models with efficient circulation of energy to the night
side and/or increased albedos, while those with masses greater than that of
Jupiter are consistently best-matched by models with inefficient circulation
and low albedos. At these relatively low temperatures we expect the atmospheric
methane to CO ratio to vary as a function of metallicity, and we therefore use
our observations of these planets to constrain their atmospheric metallicities.
We find that the most massive planets have dayside emission spectra that are
best-matched by solar metallicity atmosphere models, but we are not able to
place strong constraints on metallicities of the smaller planets in our sample.
Interestingly, we find that the ratio of the 3.6 and 4.5 micron brightness
temperatures for these cool transiting planets is independent of planet
temperature, and instead exhibits a tentative correlation with planet mass. If
this trend can be confirmed, it would suggest that the shape of these planets'
emission spectra depends primarily on their masses, consistent with the
hypothesis that lower-mass planets are more likely to have metal-rich
atmospheres.Comment: 16 pages, 14 figures, accepted for publication in Ap
The Statistics of Albedo and Heat Recirculation on Hot Exoplanets
[Abridged] If both the day-side and night-side effective temperatures of a
planet can be measured, it is possible to estimate its Bond albedo, 0<A_B<1, as
well as its day-night heat redistribution efficiency, 0<epsilon<1. We attempt a
statistical analysis of the albedo and redistribution efficiency for 24
transiting exoplanets that have at least one published secondary eclipse. For
each planet, we show how to calculate a sub-stellar equilibrium temperature,
T_0, and associated uncertainty. We then use a simple model-independent
technique to estimate a planet's effective temperature from planet/star flux
ratios. We use thermal secondary eclipse measurements -those obtained at
lambda>0.8 micron- to estimate day-side effective temperatures, T_d, and
thermal phase variations -when available- to estimate night-side effective
temperature. We strongly rule out the "null hypothesis" of a single A_B and
epsilon for all 24 planets. If we allow each planet to have different
parameters, we find that low Bond albedos are favored (A_B<0.35 at 1 sigma
confidence), which is an independent confirmation of the low albedos inferred
from non-detection of reflected light. Our sample exhibits a wide variety of
redistribution efficiencies. When normalized by T_0, the day-side effective
temperatures of the 24 planets describe a uni-modal distribution. The
dimensionless quantity T_d/T_0 exhibits no trend with the presence or absence
of stratospheric inversions. There is also no clear trend between T_d/T_0 and
T_0. That said, the 6 planets with the greatest sub-stellar equilibrium
temperatures (T>2400 K) have low epsilon, as opposed to the 18 cooler planets,
which show a variety of recirculation efficiencies. This hints that the very
hottest transiting giant planets are qualitatively different from the merely
hot Jupiters.Comment: 12 pages, 7 figures, ApJ accepted. Substantial Changes: more planets
and data, refined analysis, different conclusion
The climate of HD 189733b from fourteen transits and eclipses measured by Spitzer
We present observations of seven transits and seven eclipses of the
transiting planet system HD 189733 taken with Spitzer IRAC at 8 microns. We use
a new correction for the detector ramp variation with a double-exponential
function. Our main findings are: (1) an upper limit on the variability of the
day-side planet flux of 2.7% (68% confidence); (2) the most precise set of
transit times measured for a transiting planet, with an average accuracy of 3
seconds; (3) a lack of transit-timing variations, excluding the presence of
second planets in this system above 20% of the mass of Mars in low-order
mean-motion resonance at 95% confidence; (4) a confirmation of the planet's
phase variation, finding the night side is 64% as bright as the day side, as
well as an upper limit on the night-side variability of 17% (68% confidence);
(5) a better correction for stellar variability at 8 micron causing the phase
function to peak 3.5 hrs before secondary eclipse, confirming that the
advection and radiation timescales are comparable at the 8 micron photosphere;
(6) variation in the depth of transit, which possibly implies variations in the
surface brightness of the portion of the star occulted by the planet, posing a
fundamental limit on non-simultaneous multi-wavelength transit absorption
measurements of planet atmospheres; (7) a measurement of the infrared
limb-darkening of the star, in agreement with stellar atmosphere models; (8) an
offset in the times of secondary eclipse of 69 sec, which is mostly accounted
for by a 31 sec light travel time delay and 33 sec delay due to the shift of
ingress and egress by the planet hot spot; this confirms that the phase
variation is due to an offset hot spot on the planet; (9) a retraction of the
claimed eccentricity of this system due to the offset of secondary eclipse; and
(10) high precision measurements of the parameters of this system.Comment: 18 pages, 19 figures, accepted for publication in the Astrophysical
Journa
Warm Spitzer Photometry of Three Hot Jupiters: HAT-P-3b, HAT-P-4b and HAT-P-12b
We present Warm Spitzer/IRAC secondary eclipse time series photometry of three short-period transiting exoplanets, HAT-P-3b, HAT-P-4b and HAT-P-12b, in both the available 3.6 and 4.5 μm bands. HAT-P-3b and HAT-P-4b are Jupiter-mass objects orbiting an early K and an early G dwarf star, respectively. For HAT-P-3b we find eclipse depths of 0.112^(+0.015)_(-0.030) (3.6 μm) and 0.094^(+0.016)_(-0.009)(4.5 μm). The HAT-P-4b values are 0.142^(+0.014)_(-0.016)(3.6 μm) and 0.122^(+0.012)_(-0.014)(4.5 μm). The two planets' photometry is consistent with inefficient heat redistribution from their day to night sides (and low albedos), but it is inconclusive about possible temperature inversions in their atmospheres. HAT-P-12b is a Saturn-mass planet and is one of the coolest planets ever observed during secondary eclipse, along with the hot Neptune GJ 436b and the hot Saturn WASP-29b. We are able to place 3σ upper limits on the secondary eclipse depth of HAT-P-12b in both wavelengths: <0.042% (3.6 μm) and <0.085% (4.5 μm). We discuss these results in the context of the Spitzer secondary eclipse measurements of GJ 436b and WASP-29b. It is possible that we do not detect the eclipses of HAT-P-12b due to high eccentricity, but find that weak planetary emission in these wavelengths is a more likely explanation. We place 3σ upper limits on the |e cos ω| quantity (where e is eccentricity and ω is the argument of periapsis) for HAT-P-3b (<0.0081) and HAT-P-4b (<0.0042), based on the secondary eclipse timings
Transiting Exoplanet Studies and Community Targets for JWST's Early Release Science Program
The James Webb Space Telescope will revolutionize transiting exoplanet
atmospheric science due to its capability for continuous, long-duration
observations and its larger collecting area, spectral coverage, and spectral
resolution compared to existing space-based facilities. However, it is unclear
precisely how well JWST will perform and which of its myriad instruments and
observing modes will be best suited for transiting exoplanet studies. In this
article, we describe a prefatory JWST Early Release Science (ERS) program that
focuses on testing specific observing modes to quickly give the community the
data and experience it needs to plan more efficient and successful future
transiting exoplanet characterization programs. We propose a multi-pronged
approach wherein one aspect of the program focuses on observing transits of a
single target with all of the recommended observing modes to identify and
understand potential systematics, compare transmission spectra at overlapping
and neighboring wavelength regions, confirm throughputs, and determine overall
performances. In our search for transiting exoplanets that are well suited to
achieving these goals, we identify 12 objects (dubbed "community targets") that
meet our defined criteria. Currently, the most favorable target is WASP-62b
because of its large predicted signal size, relatively bright host star, and
location in JWST's continuous viewing zone. Since most of the community targets
do not have well-characterized atmospheres, we recommend initiating preparatory
observing programs to determine the presence of obscuring clouds/hazes within
their atmospheres. Measurable spectroscopic features are needed to establish
the optimal resolution and wavelength regions for exoplanet characterization.
Other initiatives from our proposed ERS program include testing the instrument
brightness limits and performing phase-curve observations.(Abridged)Comment: This is a white paper that originated from an open discussion at the
Enabling Transiting Exoplanet Science with JWST workshop held November 16 -
18, 2015 at STScI (http://www.stsci.edu/jwst/science/exoplanets). Accepted
for publication in PAS
A Spitzer Transmission Spectrum for the Exoplanet GJ 436b, Evidence for Stellar Variability, and Constraints on Dayside Flux Variations
In this paper we describe a uniform analysis of eight transits and eleven
secondary eclipses of the extrasolar planet GJ 436b obtained in the 3.6, 4.5,
and 8.0 micron bands using the IRAC instrument on the Spitzer Space Telescope
between UT 2007 June 29 and UT 2009 Feb 4. We find that the best-fit transit
depths for visits in the same bandpass can vary by as much as 8% of the total
(4.7 sigma significance) from one epoch to the next. Although we cannot
entirely rule out residual detector effects or a time-varying, high-altitude
cloud layer in the planet's atmosphere as the cause of these variations, we
consider the occultation of active regions on the star in a subset of the
transit observations to be the most likely explanation. We reconcile the
presence of magnetically active regions with the lack of significant visible or
infrared flux variations from the star by proposing that the star's spin axis
is tilted with respect to our line of sight, and that the planet's orbit is
therefore likely to be misaligned. These observations serve to illustrate the
challenges associated with transmission spectroscopy of planets orbiting
late-type stars; we expect that other systems, such as GJ 1214, may display
comparably variable transit depths. Our measured 8 micron secondary eclipse
depths are consistent with a constant value, and we place a 1 sigma upper limit
of 17% on changes in the planet's dayside flux in this band. Averaging over the
eleven visits gives us an improved estimate of 0.0452% +/- 0.0027% for the
secondary eclipse depth. We combine timing information from our observations
with previously published data to produce a refined orbital ephemeris, and
determine that the best-fit transit and eclipse times are consistent with a
constant orbital period. [ABRIDGED]Comment: 26 pages, 18 figures, 7 tables in emulateapj format. Accepted for
publication in Ap
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