2,938 research outputs found
The Influence of Host Star Spectral Type on Ultra-Hot Jupiter Atmospheres
Ultra-hot Jupiters are the most highly irradiated gas giant planets, with
equilibrium temperatures from 2000 to over 4000 K. Ultra-hot Jupiters are
amenable to characterization due to their high temperatures, inflated radii,
and short periods, but their atmospheres are atypical for planets in that the
photosphere possesses large concentrations of atoms and ions relative to
molecules. Here we evaluate how the atmospheres of these planets respond to
irradiation by stars of different spectral type. We find that ultra-hot
Jupiters exhibit temperature inversions that are sensitive to the spectral type
of the host star. The slope and temperature range across the inversion both
increase as the host star effective temperature increases due to enhanced
absorption at short wavelengths and low pressures. The steep temperature
inversions in ultra-hot Jupiters around hot stars result in increased thermal
dissociation and ionization compared to similar planets around cooler stars.
The resulting increase in H opacity leads to a transit spectrum that has
muted absorption features. The emission spectrum, however, exhibits a large
contrast in brightness temperature, a signature that will be detectable with
both secondary eclipse observations and high-dispersion spectroscopy. We also
find that the departures from local thermodynamic equilibrium in the stellar
atmosphere can affect the degree of heating caused by atomic metals in the
planet's upper atmosphere. Additionally, we further quantify the significance
of heating by different opacity sources in ultra-hot Jupiter atmospheres.Comment: 13 pages, 9 figures, 2 tables. Accepted for publication in Ap
The PHOENIX Exoplanet Retrieval Algorithm and Using H Opacity as a Probe in Ultra-hot Jupiters
Atmospheric retrievals are now a standard tool to analyze observations of
exoplanet atmospheres. This data-driven approach quantitatively compares
atmospheric models to observations in order to estimate atmospheric properties
and their uncertainties. In this paper, we introduce a new retrieval package,
the PHOENIX Exoplanet Retrieval Analysis (PETRA). PETRA places the PHOENIX
atmosphere model in a retrieval framework, allowing us to combine the strengths
of a well-tested and widely-used atmosphere model with the advantages of
retrieval algorithms. We validate PETRA by retrieving on simulated data for
which the true atmospheric state is known. We also show that PETRA can
successfully reproduce results from previously published retrievals of WASP-43b
and HD 209458b. For the WASP-43b results, we show the effect that different
line lists and line profile treatments have on the retrieved atmospheric
properties. Lastly, we describe a novel technique for retrieving the
temperature structure and density in ultra-hot Jupiters using H
opacity, allowing us to probe atmospheres devoid of most molecular features
with JWST.Comment: 17 pages, 18 figures. Accepted for publication in A
Extremely Irradiated Hot Jupiters: Non-Oxide Inversions, H- Opacity, and Thermal Dissociation of Molecules
Extremely irradiated hot Jupiters, exoplanets reaching dayside temperatures
2000 K, stretch our understanding of planetary atmospheres and the models
we use to interpret observations. While these objects are planets in every
other sense, their atmospheres reach temperatures at low pressures comparable
only to stellar atmospheres. In order to understand our \textit{a priori}
theoretical expectations for the nature of these objects, we self-consistently
model a number of extreme hot Jupiter scenarios with the PHOENIX model
atmosphere code. PHOENIX is well-tested on objects from cool brown dwarfs to
expanding supernovae shells and its expansive opacity database from the UV to
far-IR make PHOENIX well-suited for understanding extremely irradiated hot
Jupiters. We find several fundamental differences between hot Jupiters at
temperatures 2500 K and their cooler counterparts. First, absorption by
atomic metals like Fe and Mg, molecules including SiO and metal hydrides, and
continuous opacity sources like H all combined with the short-wavelength
output of early-type host stars result in strong thermal inversions, without
the need for TiO or VO. Second, many molecular species, including HO, TiO,
and VO are thermally dissociated at pressures probed by eclipse observations,
biasing retrieval algorithms that assume uniform vertical abundances. We
discuss other interesting properties of these objects, as well as future
prospects and predictions for observing and characterizing this unique class of
astrophysical object, including the first self-consistent model of the hottest
known jovian planet, KELT-9b.Comment: 23 pages, 16 figures, 1 table. Submitted to Ap
Evolution of photoemission spectral functions in doped transition metal oxides
We discuss the experimental photoemission and inverse photoemission of early
transition metal oxides, in the light of the dynamical mean field theory of
correlated electrons which becomes exact in the limit of infinite dimensions.
We argue that a comprehensive description of the experimental data requires
spatial inhomogeneities and present a calculation of the evolution of the
spectral function in an inhomogenous system with various degrees of
inhomogeneity. We also point out that comparaison of experimental results and
large d calculations require that the degree of correlation and disorder is
larger in the surface than in the bulk
Spectral functions in doped transition metal oxides
We present experimental photoemission and inverse photoemission spectra of
SrTiO representing electron doped systems. Photoemission
spectra in presence of electron doping exhibit prominent features arising from
electron correlation effects, while the inverse photoemssion spectra are
dominated by spectral features explainable within single-particle approaches.
We show that such a spectral evolution in chemically doped correlated systems
is not compatible with expectations based on Hubbard or any other similar
model. We present a new theoretical approach taking into account the
inhomogeneity of the `real' system which gives qualitatively different results
compared to standard `homogeneous' models and is in quantitative agreement with
experiments.Comment: 10 pages; 1 tex file+4 postscript files (to appear in Europhysics
Letters
Fixed-range optimum trajectories for short-haul aircraft
An algorithm, based on the energy-state method, is derived for calculating optimum trajectories with a range constraint. The basis of the algorithm is the assumption that optimum trajectories consist of, at most, three segments: an increasing energy segment (climb); a constant energy segment (cruise); and a decreasing energy segment (descent). This assumption allows energy to be used as the independent variable in the increasing and decreasing energy segments, thereby eliminating the integration of a separate adjoint differential equation and simplifying the calculus of variations problem to one requiring only pointwise extremization of algebraic functions. The algorithm is used to compute minimum fuel, minimum time, and minimum direct-operating-cost trajectories, with range as a parameter, for an in-service CTOL aircraft and for an advanced STOL aircraft. For the CTOL aircraft and the minimum-fuel performance function, the optimum controls, consisting of air-speed and engine power setting, are continuous functions of the energy in both climb and descent as well as near the maximum or cruise energy. This is also true for the STOL aircraft except in the descent where at one energy level a nearly constant energy dive segment occurs, yielding a discontinuity in the airspeed at that energy. The reason for this segment appears to be the relatively high fuel flow at idle power of the engines used by this STOL aircraft. Use of a simplified trajectory which eliminates the dive increases the fuel consumption of the total descent trajectory by about 10 percent and the time to fly the descent by about 19 percent compared to the optimum
Access and barriers to immunization in West Bengal, India: quality matters
While many studies attempted to evaluate performance of immunization programmes in developing countries by full coverage, there is a growing awareness about the limitations of such evaluation, irrespective of the overall quality of performance. Availability of human resources, equipment, supporting drugs, and training of personnel are considered to be crucial indicators of the quality of immunization programme. Also, maintenance of time schedule has been considered crucial in the context of the quality of immunization. In addition to overall coverage of vaccination, the coverage of immunization given at right time (month-specific) is to be considered with utmost importance. In this paper, District Level Household and Facility Survey-3 (DLHS-3) 2007-2008 data have been used in exploring the quality of immunization in terms of month-specific vaccine coverage and barriers to access in West Bengal, India. In West Bengal, the month-specific coverage stands badly below 20% but the simple non-month-specific coverage is as high as 75%. Among the demand-side factors, birthplace of the child and religion of the household heads came out as significant predictors while, from the supply-side, availability of male health workers and equipment at the subcentres, were the important determinants for month-specific vaccine coverage. Hence, there should be a vigorous attempt to make more focused planning, keeping in mind the nature of the barriers, for improvement of the month-specific coverage in West Bengal.ICDDR,B; DFI
Ground-based detections of thermal emission from CoRoT-1b and WASP-12b
We report a new detection of the H-band thermal emission of CoRoT-1b and two
confirmation detections of the Ks-band thermal emission of WASP-12b at
secondary eclipses. The H-band measurement of CoRoT-1b shows an eclipse depth
of 0.145%\pm0.049% with a 3-{\sigma} percentile between 0.033% - 0.235%. This
depth is consistent with the previous conclusions that the planet has an
isother- mal region with inefficient heat transport from dayside to nightside,
and has a dayside thermal inversion layer at high altitude. The two Ks band
detections of WASP-12b show a joint eclipse depth of 0.299%\pm0.065%. This
result agrees with the measurement of Croll & collaborators, providing
independent confirmation of their measurement. The repeatability of the
WASP-12b measurements also validates our data analysis method. Our
measurements, in addition to a number of previous results made with other
telescopes, demonstrate that ground-based observations are becoming widely
available for characterization of atmospheres of hot Jupiters.Comment: 20 pages, including 8 figures and 1 table. Accepted for publication
in Ap
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