752 research outputs found
A Temperature and Abundance Retrieval Method for Exoplanet Atmospheres
We present a new method to retrieve molecular abundances and temperature
profiles from exoplanet atmosphere photometry and spectroscopy. We run millions
of 1D atmosphere models in order to cover the large range of allowed parameter
space, and present error contours in the atmospheric properties, given the
data. In order to run such a large number of models, we have developed a
parametric pressure-temperature (P-T) profile coupled with line-by-line
radiative transfer, hydrostatic equilibrium, and energy balance, along with
prescriptions for non-equilibrium molecular composition and energy
redistribution. We apply our temperature and abundance retrieval method to the
atmospheres of two transiting exoplanets, HD 189733b and HD 209458b, which have
the best available Spitzer and HST observations. For HD 189733b, we find
efficient day-night redistribution of energy in the atmosphere, and molecular
abundance constraints confirming the presence of H2O, CO, CH4, and CO2. For HD
209458b, we confirm and constrain the day-side thermal inversion in an average
1D temperature profile. We also report independent detections of HO, CO,
CH and CO on the dayside of HD 209458b, based on six-channel Spitzer
photometry. We report constraints for HD 189733b due to individual data sets
separately; a few key observations are variable in different data sets at
similar wavelengths. Moreover, a noticeably strong carbon dioxide absorption in
one data set is significantly weaker in another. We must, therefore,
acknowledge the strong possibility that the atmosphere is variable, both in its
energy redistribution state and in the chemical abundances.Comment: 20 pages in emulateapj format, 11 figures. Final version, after proof
correction
A Search for Exotrojans in Transiting Exoplanetary systems
We present a search for Trojan companions to 25 transiting exoplanets. We use
the technique of Ford & Gaudi 2006, in which a difference is sought between the
observed transit time and the transit time that is calculated by fitting a
two-body Keplerian orbit to the radial-velocity data. This technique is
sensitive to the imbalance of mass at the L4/L5 points of the planet-star
orbit. No companions were detected. The median 2 upper limit is 60
Earth masses, and the most constraining limit is 2.5 Earth masses for the case
of GJ 436.Comment: To appear in Proceedings of the IAU Symposium No. 253, "Transiting
Planets", May 19 - May 23, 2008, Cambridge, M
JexoSim 2.0: End-to-end JWST simulator for exoplanet spectroscopy – implementation and case studies
The recently developed JWST Exoplanet Observation Simulator (JexoSim)
simulates transit spectroscopic observations of exoplanets by JWST with each of
its four instruments using a time-domain approach. Previously we reported the
validation of JexoSim against Pandexo and instrument team simulators. In the
present study, we report a substantially enhanced version, JexoSim 2.0, which
improves on the original version through incorporation of new noise sources,
enhanced treatment of stellar and planetary signals and instrumental effects,
as well as improved user-operability and optimisations for increased speed and
efficiency. A near complete set of instrument modes for exoplanet time-series
observations is now included. In this paper we report the implementation of
JexoSim 2.0 and assess performance metrics for JWST in end-member scenarios
using the hot Jupiter HD 209458 b and the mini-Neptune K2-18 b. We show how
JexoSim can be used to compare performance across the different JWST
instruments, selecting an optimal combination of instrument and subarray modes,
producing synthetic transmission spectra for each planet. These studies
indicate that the 1.4 {\mu}m water feature detected in the atmosphere of K2-18
b using the Hubble WFC3 might be observable in just one transit observation
with JWST with either NIRISS or NIRSpec. JexoSim 2.0 can be used to investigate
the impact of complex noise and systematic effects on the final spectrum, plan
observations and test the feasibility of novel science cases for JWST. It can
also be customised for other astrophysical applications beyond exoplanet
spectroscopy. JexoSim 2.0 is now available for use by the scientific community
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Search for radio emission from the exoplanets Qatar-1b and WASP-80b near 150 MHz using the giant metrewave radio telescope
We present radio observations made towards the exoplanets Qatar-1b and
WASP-80b near 150~MHz with the Giant Meterwave Radio Telescope. These targets
are relatively nearby irradiated giant exoplanets, a hot Jupiter and a hot
Saturn, with sizes comparable to Jupiter but different masses and lower
densities. Both the targets are expected to host extended H/He envelopes like
Jupiter, with comparable or larger magnetic moments. No radio emission was
detected from these exoplanets, with 3sigma limits of 5.9 and 5.2 mJy for
Qatar-1b and WASP-80b, respectively, from these targeted observations. These
are considerably deeper limits than those available for exoplanets from wide
field surveys at similar frequencies. We also present archival VLA observations
of a previously reported radio source close to Vir 61 (which has three
exoplanets). The VLA observations resolve the source, which we identify as an
extragalactic radio source, i.e. a chance association with Vir 61.
Additionally, we cross-match a recent exoplanet catalogue with the TIFR GMRT
Sky Survey ADR1 radio catalogue, but do not find any convincing associations
Dynamic Properties of Rubber Specimens
Resonant column and bender element tests were conducted on rubber specimens to study their dynamic properties, namely, shear modulus (G), damping ratio (D) and Poisson’s ratio (ν). It was found that similar to soil specimens, with an increase in strain level, the shear modulus of rubber decreases continuously whereas the damping ratio increases. The tests were also carried out to find the effect of confining pressures on the rubber specimens. It was observed that for the rubber with the lesser hardness, there was a slight increase in the shear modulus and a decrease in the damping ratio values as the confining pressures (σ3) was increased from 50 kPa to 500 kPa. This type of trend was, however, not observed for the rubber having greater hardness. Using bender and extender elements test, with the measurements of the travel times of the shear (S) and primary (P) waves, the variation of Poisson ratio (ν) was determined for the rubber specimens with respect to change in confining pressures (σ3). No significant change in the values of ν was found for both the rubber specimens with respect to change in σ3
Antioxidants in the Management of Fluoride Induced Neural Oxidative Stress in Developing Rats
Fluoride (F) is highly electronegative anion with cumulative toxic effects, from prolonged ingestion that can lead to the pathogenesis known as fluorosis, a condition especially persistent in third world countries, where populations have little choice as to the main source of F-contaminated drinking. In recent times many neurological problems among children are being addressed in endemic areas. Thereby reasons for the neurotoxicity have to be explicated thoroughly. In this study premated Wistar albino rats were exposed to 50 and 150 ppm fluoride in drinking water during gestation and pups born to them were used to analyze the extent of neurotoxicity imposed in discrete brain areas. Dose dependent toxicity was evident in different brain regions and fluoride exposure has significantly enhanced the levels of malondialdehyde (P>0.05), glutathione (P>0.05) and decreased the activities of superoxide dismutase (P>0.05), catalase (P>0.05), glutathione peroxidase (P>0.05) and glutathione- S-transferase (P>0.05). Alterations were region specific and oral supplementation of dietary antioxidants viz., vitamin-C (20mg), vitamin-E (400.g), zinc (200.g) and selenium (40.g) not only inhibited oxidative stress but also enhanced the activity of antioxidant enzymes. Thereby supplementation of antioxidants to toxicated animals significantly overcame toxic burden imposed by fluoride and therefore may be a therapeutic strategy for fluorotic victims
Efficiency of planetesimal ablation in giant planetary envelopes
Observations of exoplanetary spectra are leading to unprecedented constraints
on their atmospheric elemental abundances, particularly O/H, C/H, and C/O
ratios. Recent studies suggest that elemental ratios could provide important
constraints on formation and migration mechanisms of giant exoplanets. A
fundamental assumption in such studies is that the chemical composition of the
planetary envelope represents the sum-total of compositions of the accreted gas
and solids during the formation history of the planet. We investigate the
efficiency with which accreted planetesimals ablate in a giant planetary
envelope thereby contributing to its composition rather than sinking to the
core. From considerations of aerodynamic drag causing `frictional ablation' and
the envelope temperature structure causing `thermal ablation', we compute mass
ablations for impacting planetesimals of radii 30 m to 1 km for different
compositions (ice to iron) and a wide range of velocities and impact angles,
assuming spherical symmetry. Icy impactors are fully ablated in the outer
envelope for a wide range of parameters. Even for Fe impactors substantial
ablation occurs in the envelope for a wide range of sizes and velocities. For
example, iron impactors of sizes below ~0.5 km and velocities above ~30 km/s
are found to ablate by ~60-80% within the outer envelope at pressures below
10^3 bar due to frictional ablation alone. For deeper pressures (~10^7 bar),
substantial ablation happens over a wider range of parameters. Therefore, our
exploratory study suggests that atmospheric abundances of volatile elements in
giant planets reflect their accretion history during formation
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