209 research outputs found
High Accuracy Molecular Line Lists for Studies of Exoplanets and Other Hot Atmospheres
The desire to characterize and model the atmospheres of the many extrasolar planets that have been discovered over the last three decades is a major driver of current astronomy. However, this goal is impacted by the lack of spectroscopic data on the molecules in question. As most atmospheres that can be studied are hot, some surprisingly so, this activity requires spectroscopic information not readily available from laboratory studies. This article will review the current status of available molecular spectroscopic data, usually presented as line lists, for studies of exoplanet atmospheres and, indeed, the atmospheres of other astronomical objects hotter than the Earth such as brown dwarfs, cool stars and even sunspots. Analysis of exoplanet transit spectra and the calculation of the relevant opacities often require huge datasets comprising billions of individual spectroscopic transitions. Conversely, the newly-developed high-resolution Doppler-shift spectroscopy technique has proved to be a powerful tool for detecting molecular species in exoplanet atmospheres, but relies on the use of smaller, highly accurate line lists. Methods of resolving issues arising from the competing demands of completeness versus accuracy for line lists are discussed
Blind extraction of an exoplanetary spectrum through Independent Component Analysis
Blind-source separation techniques are used to extract the transmission
spectrum of the hot-Jupiter HD189733b recorded by the Hubble/NICMOS instrument.
Such a 'blind' analysis of the data is based on the concept of independent
component analysis. The de-trending of Hubble/NICMOS data using the sole
assumption that nongaussian systematic noise is statistically independent from
the desired light-curve signals is presented. By not assuming any prior, nor
auxiliary information but the data themselves, it is shown that spectroscopic
errors only about 10 - 30% larger than parametric methods can be obtained for
11 spectral bins with bin sizes of ~0.09 microns. This represents a reasonable
trade-off between a higher degree of objectivity for the non-parametric methods
and smaller standard errors for the parametric de-trending. Results are
discussed in the light of previous analyses published in the literature. The
fact that three very different analysis techniques yield comparable spectra is
a strong indication of the stability of these results.Comment: ApJ accepte
Water vapour in the atmosphere of the habitable-zone eight Earth-mass planet K2-18 b
In the past decade, observations from space and ground have found HO to
be the most abundant molecular species, after hydrogen, in the atmospheres of
hot, gaseous, extrasolar planets. Being the main molecular carrier of oxygen,
HO is a tracer of the origin and the evolution mechanisms of planets. For
temperate, terrestrial planets, the presence of HO is of great significance
as an indicator of habitable conditions. Being small and relatively cold, these
planets and their atmospheres are the most challenging to observe, and
therefore no atmospheric spectral signatures have so far been detected.
Super-Earths -- planets lighter than ten M -- around later-type stars
may provide our first opportunity to study spectroscopically the
characteristics of such planets, as they are best suited for transit
observations. Here we report the detection of an HO spectroscopic signature
in the atmosphere of \planet\ -- an eight M planet in the
habitable-zone of an M-dwarf -- with high statistical confidence (ADI = 5.0,
3.6). In addition, the derived mean molecular weight suggests an
atmosphere still containing some hydrogen. The observations were recorded with
the Hubble Space Telescope/WFC3 camera, and analysed with our dedicated,
publicly available, algorithms. While the suitability of M-dwarfs to host
habitable worlds is still under discussion, \planet\ offers an unprecedented
opportunity to get insight into the composition and climate of habitable-zone
planets.Comment: Published in Nature Astronom
Remote ultra-wideband tomography of nonlinear electronic components
The efficiency of using ultra-wideband (UWB) signals for nonlinear radar is investigated. In the case at hand, it is necessary to see, based on scattered field disturbances, whether nonlinear inclusions are present in the field of view. The solution suggested is to compare the shapes of UWB signals reflected from the probe area under two conditions: an additional generator irradiating the probe area by intense monochromatic radiation is switched on and off. If a nonlinear electronic component is present in the probe area, the reflected UWB signals differ in shape. Thus, the difference in the shapes of the signals indicates the presence of a component with a nonlinear characteristic
Lightning chemistry on Earth-like exoplanets
AA, PBR and ChH gratefully acknowledge the support of the ERC Starting Grant no. 257431. IW, MR, SNY and JT also gratefully acknowledge the support of the STFC (ST/K502406/1), and the ERC projects ExoMol (26719) and ExoLights (617119).We present a model for lightning shock-induced chemistry that can be applied to atmospheres of arbitrary H/C/N/O chemistry, hence for extrasolar planets and brown dwarfs. The model couples hydrodynamics and the STAND2015 kinetic gas-phase chemistry. For an exoplanet analogue to the contemporary Earth, our model predicts NO and NO2 yields in agreement with observation. We predict height-dependent mixing ratios during a storm soon after a lightning shock of NO ≈ 10-3 at 40 km and NO2 ≈ 10-4 below 40 km, with O3 reduced to trace quantities (≪10-10). For an Earth-like exoplanet with a CO2/N2 dominated atmosphere and with an extremely intense lightning storm over its entire surface, we predict significant changes in the amount of NO, NO2, O3, H2O, H2 and predict a significant abundance of C2N. We find that, for the Early Earth, O2 is formed in large quantities by lightning but is rapidly processed by the photochemistry, consistent with previous work on lightning. The chemical effect of persistent global lightning storms are predicted to be significant, primarily due to NO2, with the largest spectral features present at ∼3.4 and ∼6.2 μm. The features within the transmission spectrum are on the order of 1 ppm and therefore are not likely detectable with the James Webb Space Telescope. Depending on its spectral properties, C2N could be a key tracer for lightning on Earth-like exoplanets with a N2/CO2 bulk atmosphere, unless destroyed by yet unknown chemical reactions.Publisher PDFPeer reviewe
HELIOS-K 2.0 Opacity Calculator and Open-source Opacity Database for Exoplanetary Atmospheres
Computing and using opacities is a key part of modeling and interpreting data of exoplanetary atmospheres. Since the underlying spectroscopic line lists are constantly expanding and currently include up to ∼1010–1011 transition lines, the opacity calculator codes need to become more powerful. Here we present major upgrades to the HELIOS-K GPU-accelerated opacity calculator and describe the necessary steps to process large line lists within a reasonable amount of time. Besides performance improvements, we include more capabilities and present a toolbox for handling different atomic and molecular data sets, from downloading and preprocessing the data to performing the opacity calculations in a user-friendly way. HELIOS-K supports line lists from ExoMol, HITRAN, HITEMP, NIST, Kurucz, and VALD3. By matching the resolution of 0.1 cm−1 and cutting length of 25 cm−1 used by the ExoCross code for timing performance (251 s excluding data read-in time), HELIOS-K can process the ExoMol BT2 water line list in 12.5 s. Using a resolution of 0.01 cm−1, it takes 45 s, equivalent to about 107 lines s−1. As a wavenumber resolution of 0.01 cm−1 suffices for most exoplanetary atmosphere spectroscopic calculations, we adopt this resolution in calculating opacity functions for several hundred atomic and molecular species and make them freely available on the open-access DACE database. For the opacity calculations of the database, we use a cutting length of 100 cm−1 for molecules and no cutting length for atoms. Our opacities are available for downloading from https://dace.unige.ch/opacityDatabase and may be visualized using https://dace.unige.ch/opacity
Probing the extreme planetary atmosphere of WASP-12b
We report near-infrared measurements of the terminator region transmission
spectrum and dayside emission spectrum of the exoplanet WASP-12b obtained using
the HST WFC3 instrument. The disk-average dayside brightness temperature
averages about 2900 K, peaking to 3200 K around 1.46 microns. We modeled a
range of atmospheric cases for both the emission and transmission spectrum and
confirm the recent finding by Crossfield et al. (2012b) that there is no
evidence for C/O >1 in the atmosphere of WASP-12b. Assuming a physically
plausible atmosphere, we find evidence that the presence of a number of
molecules is consistent with the data, but the justification for inclusion of
these opacity sources based on the Bayesian Information Criterion (BIC) is
marginal. We also find the near-infrared primary eclipse light curve is
consistent with small amounts of prolate distortion. As part of the calibration
effort for these data, we conducted a detailed study of instrument systematics
using 65 orbits of WFC3-IR grims observations. The instrument systematics are
dominated by detector-related affects, which vary significantly depending on
the detector readout mode. The 256x256 subarray observations of WASP 12
produced spectral measurements within 15% of the photon-noise limit using a
simple calibration approach. Residual systematics are estimated to be less than
70 parts per million.Comment: Accepted for publication in Icaru
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