The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations

The hot Jupiter HD189733b is the most extensively observed exoplanet. Its atmosphere has been detected and characterised in transmission and eclipse spectroscopy, and its phase curve measured at several wavelengths. This paper brings together results of our campaign to obtain the complete transmission spectrum of the atmosphere of this planet from UV to IR with HST, using STIS, ACS and WFC3. We provide a new tabulation of the transmission spectrum across the entire visible and IR range. The radius ratio in each wavelength band was rederived to ensure a consistent treatment of the bulk transit parameters and stellar limb-darkening. Special care was taken to correct for, and derive realistic estimates of the uncertainties due to, both occulted and unocculted star spots. The combined spectrum is very different from the predictions of cloud-free models: it is dominated by Rayleigh scattering over the whole visible and near infrared range, the only detected features being narrow Na and K lines. We interpret this as the signature of a haze of condensate grains extending over at least 5 scale heights. We show that a dust-dominated atmosphere could also explain several puzzling features of the emission spectrum and phase curves, including the large amplitude of the phase curve at 3.6um, the small hot-spot longitude shift and the hot mid-infrared emission spectrum. We discuss possible compositions and derive some first-order estimates for the properties of the putative condensate haze/clouds. We finish by speculating that the dichotomy between the two observationally defined classes of hot Jupiter atmospheres, of which HD189733b and HD209458b are the prototypes, might not be whether they possess a temperature inversion, but whether they are clear or dusty. We also consider the possibility of a continuum of cloud properties between hot Jupiters, young Jupiters and L-type brown dwarfs.Comment: Accepted for publication in MNRAS. 31 pages, 19 figures, 8 table

Integrating disciplinary-specific genre structure in discourse strategies to support disciplinary literacy

Classroom discourse plays an important role in shaping how students learn science in the classroom. Past research has examined how content area teachers use a variety of generic discourse strategies to foster classroom interaction and content mastery. However, few have focused on how teachers’ discourse strategy can be used in more specific ways to build subject-specialized genres of the discipline, such as scientific explanation. The purpose of this study is to examine how science teachers integrate disciplinary-specific genres in their discourse strategies to engage their students in thinking about the conceptual and epistemic aspects of the discipline. Through a three-year design research, four science teachers learned a genre-based instructional method designed to explicitly teach students how to construct scientific explanations. Lesson observations from these teachers before and after they learned the genre-based instruction were video-recorded and analyzed. It was found that with the incorporation of the genre-based instructional method, a discourse strategy that we call meta-discoursing was employed in ne w ways to facilitate the teaching of the explanation genre. Using multiple exemplars, we describe the ways in which this discourse strategy was enacted in tandem with the genre-based instructional method to facilitate disciplinary literacy through classroom talk

A new look at NICMOS transmission spectroscopy of HD189733, GJ-436 and XO-1: no conclusive evidence for molecular features

We present a re-analysis of archival HST/NICMOS transmission spectroscopy of three exoplanet systems; HD 189733, GJ-436 and XO-1. Detections of several molecules, including H20, CH4 and CO2, have been claimed for HD 189733 and XO-1, but similarly sized features are attributed to systematic noise for GJ-436. The data consist of time-series grism spectra covering a planetary transit. After extracting light curves in independent wavelength channels, we use a linear decorrelation technique account for instrumental systematics (which is becoming standard in the field), and measure the planet-to-star radius ratio as a function of wavelength. For HD 189733, the uncertainties in the transmission spectrum are significantly larger than those previously reported. We also find the transmission spectrum is considerably altered when using different out-of-transit orbits to remove the systematics, when some parameters are left out of the decorrelation procedure, or when we perform the decorrelation with quadratic functions rather than linear functions. Given that there is no physical reason to believe the baseline flux should be modelled as a linear function of any particular set of parameters, we interpret this as evidence that the linear decorrelation technique is not a robust method to remove systematic effects from the light curves for each wavelength channel. For XO-1, the parameters measured to decorrelate the light curves would require extrapolation to the in-transit orbit to remove the systematics, and we cannot reproduce the previously reported results. We conclude that the resulting NICMOS transmission spectra are too dependent on the method used to remove systematics to be considered robust detections of molecular species in planetary atmospheres, although the presence of these molecules is not ruled out.Comment: 17 pages, 28 figures, accepted in MNRA

Pressure-induced insulator-to-metal transition in low-dimensional TiOCl

We studied the transmittance and reflectance of the low-dimensional Mott-Hubbard insulator TiOCl in the infrared and visible frequency range as a function of pressure. The strong suppression of the transmittance and the abrupt increase of the near-infrared reflectance above 12 GPa suggest a pressure-induced insulator-to-metal transition. The pressure-dependent frequency shifts of the orbital excitations, as well as the pressure dependences of the charge gap and the spectral weight of the optical conductivity above the phase transition are presented.Comment: 4 pages, 6 figure

The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.The hot Jupiter HD 189733b is the most extensively observed exoplanet. Its atmosphere has been detected and characterized in transmission and eclipse spectroscopy, and its phase curve measured at several wavelengths. This paper brings together the results of our campaign to obtain the complete transmission spectrum of the atmosphere of this planet from UV to infrared with the Hubble Space Telescope, using the STIS, ACS and WFC3 instruments. We provide a new tabulation of the transmission spectrum across the entire visible and infrared range. The radius ratio in each wavelength band was re-derived, where necessary, to ensure a consistent treatment of the bulk transit parameters and stellar limb darkening. Special care was taken to correct for, and derive realistic estimates of the uncertainties due to, both occulted and unocculted star spots. The combined spectrum is very different from the predictions of cloud-free models for hot Jupiters: it is dominated by Rayleigh scattering over the whole visible and near-infrared range, the only detected features being narrow sodium and potassium lines. We interpret this as the signature of a haze of condensate grains extending over at least five scaleheights. We show that a dust-dominated atmosphere could also explain several puzzling features of the emission spectrum and phase curves, including the large amplitude of the phase curve at 3.6 μm, the small hotspot longitude shift and the hot mid-infrared emission spectrum. We discuss possible compositions and derive some first-order estimates for the properties of the putative condensate haze/clouds. We finish by speculating that the dichotomy between the two observationally defined classes of hot Jupiter atmospheres, of which HD 189733b and HD 209458b are the prototypes, might not be whether they possess a temperature inversion, but whether they are clear or dusty. We also consider the possibility of a continuum of cloud properties between hot Jupiters, young Jupiters and L-type brown dwarfs.Science and Technology Facilities Council (STFC)NASANSFTennessee State UniversityState of Tennesse

Contractors’ Attitude towards Enhancing Safety Performance: Case Study on Construction Firms in Penang

A qualitative study was conducted to investigate the contractors’ attitude towards enhancing the safety performance in construction site. Despite the fact that there are many safety initiatives established by the government, the rates of accidents are still in a critically high condition. Thus the purpose of this research is to study the contractors’ attitude towards enhancing the implementation of safety management system in construction site in order to increase the safety awareness of construction practitioners in construction site and improve the safety condition of construction sites. This study is conducted through oral interviews with the construction practitioners, and visual inspection of construction sites. The attitudes of contractors are evaluated from 3 aspects: Contractors’ efforts in implement and enforce the safety rules, Contractors efforts in overcoming the rate of accidents, and Reasons given by the contractors for not implement safety law

Influence of Anisotropy on Creep in a Whisker Reinforced MMC Rotating Disc

Whisker reinforced MMC may be employed in rotating disc , a common component in friction drives , turbines and a number of other machine components, often exposed to elevated temperatures . Creep characteristics of these composites have been studied analytically using von Mises flow rule and Norton 's steady state creep equations . The results for isotropic A16061 alloy and for isotropic composite containing 20 vol% SiCµ in a matrix of A16061 alloy have been compared with those obtained for anisotropic composites with characteristic parameters a = 0.7 and 1. 31, indicating respectively relative strengthening and weakening in the tangential direction presumably introduced by either processing or inhomogeneous distribution of reinforcement.The creep strain rates resulting in the isotropic rotating disc made of composite as well as the aluminum alloy, are tensile in the tangential direction but compressive in the axial and radial directions, also conforming to the condition of volume constancy.The creep rates in the composite are significantly reduced (by about three orders of magnitude) in all the directions compared to those observed in the base alloy. In case of anisotropy lowering the strength in the tangential direction (a> 1.0), the radial stresses in the region near inner periphery of the disc, increase while those near the outer periphery decrease in comparison to those for the isotropic composite . But the tangential stresses reduce in the middle region of the disc and enhances near the inner and the outer periphery, when compared to those for the isotropic composite . The magnitude of stress distribution , however, changes by a small extent due to ani sotropy in the disc introduced through processing or reinforcement distribution . The radial strain rate which always remained compressive for the isotropic composite and for a = 1.3,becomes tensile in the middle region of the disc when a = 0.7. If a is reduced from 1.3 to 0 . 7, the variation of tensile strain rate in the tangential direction remains similar but the magnitude reduces by five orders of magnitude . Anisotropy therefore, introduces significant change in the strain rates although its effect on the resulting stress distribution may be relatively small

VLT FORS2 comparative transmission spectroscopy: Detection of Na in the atmosphere of WASP-39b from the ground

We present transmission spectroscopy of the warm Saturn-mass exoplanet WASP-39b made with the Very Large Telescope FOcal Reducer and Spectrograph (FORS2) across the wavelength range 411–810 nm. The transit depth is measured with a typical precision of 240 parts per million (ppm) in wavelength bins of 10 nm on a V = 12.1 mag star. We detect the sodium absorption feature (3.2σ) and find evidence of potassium. The ground-based transmission spectrum is consistent with Hubble Space Telescope (HST) optical spectroscopy, supporting the interpretation that WASP-39b has a largely clear atmosphere. Our results demonstrate the great potential of the recently upgraded FORS2 spectrograph for optical transmission spectroscopy, with which we obtained HST-quality light curves from the ground

Direct k-space mapping of the electronic structure in an oxide-oxide interface

The interface between LaAlO3 and SrTiO3 hosts a two-dimensional electron system of itinerant carriers, although both oxides are band insulators. Interface ferromagnetism coexisting with superconductivity has been found and attributed to local moments. Experimentally, it has been established that Ti 3d electrons are confined to the interface. Using soft x-ray angle-resolved resonant photoelectron spectroscopy we have directly mapped the interface states in k-space. Our data demonstrate a charge dichotomy. A mobile fraction contributes to Fermi surface sheets, whereas a localized portion at higher binding energies is tentatively attributed to electrons trapped by O-vacancies in the SrTiO3. While photovoltage effects in the polar LaAlO3 layers cannot be excluded, the apparent absence of surface-related Fermi surface sheets could also be fully reconciled in a recently proposed electronic reconstruction picture where the built-in potential in the LaAlO3 is compensated by surface O-vacancies serving also as charge reservoir.Comment: 8 pages, 6 figures, incl. Supplemental Informatio