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 H$_2$O, CO, CH$_4$ and CO$_2$ 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$\sigma$ 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

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

On the Inference of Thermal Inversions in Hot Jupiter Atmospheres

Several studies in the recent past have inferred the existence of thermal inversions in some transiting hot Jupiter atmospheres. Given the limited data available, the inference of a thermal inversion depends critically on the chemical composition assumed for the atmosphere. In this study, we explore the degeneracies between thermal inversions and molecular abundances in four highly irradiated hot Jupiter atmospheres, day-side observations of which were previously reported to be consistent with thermal inversions based on Spitzer photometry. The four systems are: HD 209458b, HAT-P-7b, TrES-4, and TrES-2. For each system, we explore the model parameter space with ~ 10^6 models using a Markov chain Monte Carlo routine. Our results primarily suggest that a thorough exploration of the model parameter space is necessary to identify thermal inversions in hot Jupiter atmospheres. We find that existing observations of TrES-4 and TrES-2 can both be fit very precisely with models with and without thermal inversions, and with a wide range in chemical composition. On the other hand, observations of HD 209458b and HAT-P-7b are better fit with thermal inversions than without, as has been reported before. We do not see a correlation between irradiation levels and thermal inversions, given current data. Before JWST becomes available, near-IR observations from ground and with HST, along with existing Spitzer observations, can potentially resolve thermal inversions in some systems.Comment: 16 pages in emulate ApJ format, 6 figures, 3 tables (Accepted in ApJ