Assessing telluric correction methods for Na detections with high-resolution exoplanet transmission spectroscopy

ABSTRACT Using high-resolution ground-based transmission spectroscopy to probe exoplanetary atmospheres is difficult due to the inherent telluric contamination from absorption in Earth’s atmosphere. A variety of methods have previously been used to remove telluric features in the optical regime and calculate the planetary transmission spectrum. In this paper we present and compare two such methods, specifically focusing on Na detections using high-resolution optical transmission spectra: (1) calculating the telluric absorption empirically based on the airmass and (2) using a model of the Earth’s transmission spectrum. We test these methods on the transmission spectrum of the hot Jupiter HD 189733 b using archival data obtained with the HARPS spectrograph during three transits. Using models for Centre-to-Limb Variation and the Rossiter–McLaughlin effect, spurious signals which are imprinted within the transmission spectrum are reduced. We find that correcting tellurics with an atmospheric model of the Earth is more robust and produces consistent results when applied to data from different nights with changing atmospheric conditions. We confirm the detection of sodium in the atmosphere of HD 189733 b, with doublet line contrasts of $-0.64 \pm 0.07~{{\ \rm per\ cent}}$ (D2) and $-0.53 \pm 0.07~{{\ \rm per\ cent}}$ (D1). The average line contrast corresponds to an effective photosphere in the Na line located around 1.13 Rp. We also confirm an overall blueshift of the line centroids corresponding to net atmospheric eastward winds with a speed of 1.8 ± 1.2 km s−1. Our study highlights the importance of accurate telluric removal for consistent and reliable characterization of exoplanetary atmospheres using high-resolution transmission spectroscopy.

Observation of a Hydrogen Doublet Site in High Defect Density As-Grown a-Si:H by 1H NMR

Abstract1H NMR studies of hydrogenated amorphous silicon (a-Si:H) with ˜1017 cm-3 defects grown by PECVD with a rate of 5 Å/s show the existence of a hydrogen doublet for both asgrown and light-soaked samples. We observe the doublet over the temperature range from 5 to 20 K in a sample where no light soaking has occurred. The doublet line shapes display no narrowing over this temperature range. Vibrational modes characteristic of SiH2 wagging and scissor modes are seen from infrared spectroscopy. These results suggest that the doublet is due to SiH2 that occurs at a density of approximately 1 at. % in this sample. From line shape analysis, we estimate a lower limit of 1.8 ˜ for the hydrogen-to-hydrogen separation.

STUDY OF SITE GEOMETRY OF THE Sn CATIONS IN THE Sn-ADDED Tl-Pb(1223) SUPERCONDUCTING SYSTEM USING MÖSSBAUER AND AUGER EMISSION TECHNIQUES

The addition of Sn in Tl,Pb(1223) ( Tl 0.5 Pb 0.5 Sn x Sr 1.6 Ca 2.4 Cu 3 O y) has been investigated using AES and Mössbauer Emission techniques to probe the valence and site geometry of Sn cations. It was found that Sn is present in tetravalent state in the compound at two sites with differing weights. The major part of the tin resides inside the grain and a minor part (weak doublet line in Mossbauer spectra) represents the contribution from the tin at the grain boundary.

ESR in 13C Enriched a-Si1−xCx:H

ABSTRACTThe effect of using the 13C isotope on the ESR signal in a-Si1−x Cx:H is investigated. The ESR linewidth increases with increasing the C content for a-Si1−x Cx.:H with 12C, while it is almost unchanged for a-Si1−x Cx:H with 12C. However, a doublet line which is expected for a C dangling bond having the hyperfine interaction with the 13C nucleus was not detected. In the range of a small x, it is possible that Si dangling bonds with 13C at the back bonds are the origin of the wide ESR signal. In the range of a large x, 13C dangling bonds should exist, but they are in a clustered form, being observed as an exchange narrowed single line instead of the hyperfine split line.

Old Errors and New Corrections in X-Ray Line Profile Analysis

In recent years there has been an increasing awareness of the errors involved in X-Ray line profile analysis which is used to calculate coherently diffracting particle size, local strains and stacking fault probabilities in materials. Here a modified version of a Least Squares Analysis (L.S.A.) of the Fourier coefficients is presented. This method gives a possibility of making new corrections in a more natural and accurate way to the errors in the line profile analysis.The first error involves the fact that experimentally one accumulates data as a function of θ - the Bragg angle, whereas the Fourier analysis is made in terms of equidistant steps in sin θ, In the L.S.A. the data does not have to be given in equidistant steps of sin θ in order to be analyzed, so that this type of error does not exist at all.In the L.S.A. there is also no need for the explicit separation of the Kαl component from the total doublet line profile. This type of analysis is taken here one step further and it is shown that one can calculate the Fourier coefficients of each one of two merging lines. Each of these lines may be doublets in themselves and the two series of Fourier coefficients are calculated around the centers of gravity of their Kαl components respectively.The existence of an extra background which usually affects the Fourier coefficients when calculated by the Fourier transform method does not affect the L.S.A. except for a normalization factor. Here it is shown that this gives the possibility of calculating the strains without errors associated with the extra background.