Optical properties of potential condensates in exoplanetary atmospheres

The prevalence of clouds in currently observable exoplanetary atmospheres motivates the compilation and calculation of their optical properties. First, we present a new open-source Mie scattering code known as LX-MIE, which is able to consider large size parameters ($\sim 10^7$) using a single computational treatment. We validate LX-MIE against the classical MIEV0 code as well as previous studies. Second, we embark on an expanded survey of the published literature for both the real and imaginary components of the refractive indices of 32 condensate species. As much as possible, we rely on experimental measurements of the refractive indices and resort to obtaining the real from the imaginary component (or vice versa), via the Kramers-Kronig relation, only in the absence of data. We use these refractive indices as input for LX-MIE to compute the absorption, scattering and extinction efficiencies of all 32 condensate species. Finally, we use a three-parameter function to provide convenient fits to the shape of the extinction efficiency curve. We show that the errors associated with these simple fits in the Wide Field Camera 3 (WFC3), J, H and K wavebands are $\sim 10\%$. These fits allow for the extinction cross section or opacity of the condensate species to be easily included in retrieval analyses of transmission spectra. We discuss prospects for future experimental work. The compilation of the optical constants and LX-MIE are publicly available as part of the open-source Exoclime Simulation Platform (http://www.exoclime.org).Comment: accepted version; 15 pages, 5 figures, 3 table

Analytical Models of Exoplanetary Atmospheres. IV. Improved Two-stream Radiative Transfer for the Treatment of Aerosols

We present a novel generalization of the two-stream method of radiative transfer, which allows for the accurate treatment of radiative transfer in the presence of strong infrared scattering by aerosols. We prove that this generalization involves only a simple modification of the coupling coefficients and transmission functions in the hemispheric two-stream method. This modification originates from allowing the ratio of the first Eddington coefficients to depart from unity. At the heart of the method is the fact that this ratio may be computed once and for all over the entire range of values of the single-scattering albedo and scattering asymmetry factor. We benchmark our improved two-stream method by calculating the fraction of flux reflected by a single atmospheric layer (the reflectivity) and comparing these calculations to those performed using a 32-stream discrete-ordinates method. We further compare our improved two-stream method to the two-stream source function (16 streams) and delta-Eddington methods, demonstrating that it is often more accurate at the order-of-magnitude level. Finally, we illustrate its accuracy using a toy model of the early Martian atmosphere hosting a cloud layer composed of carbon-dioxide ice particles. The simplicity of implementation and accuracy of our improved two-stream method renders it suitable for implementation in three-dimensional general circulation models. In other words, our improved two-stream method has the ease of implementation of a standard two-stream method, but the accuracy of a 32-stream method.Comment: Accepted by ApJS. 7 pages, 5 figure

Exoplanet Characterization by Multi-Observatory Transit Photometry with TESS and CHEOPS

Space-based photometric surveys have discovered large numbers of planets transiting other stars, but these observe in a single band-pass and yield only the planet radius, orbital period, and transit duration. Information on the masses, compositions, and any atmospheres of these planets requires additional observations from the ground or space. The Transiting Exoplanet Survey Satellite (TESS) will yield thousands of planets around bright stars suitable for such follow-up. In the absence of spectroscopy or spectrophotometry from space, observations through the different pass-bands of multiple space telescopes provide some spectral information useful for identifying false positive signals, distinguishing between reflected light and thermal emission from hot Jupiters, and detecting Rayleigh scattering by planetary atmospheres. We calculated the expected difference in transit depths measured by the TESS and Characterizing Exoplanets Satellites (CHEOPS) missions, which will be more sensitive to redder and bluer optical wavelengths, respectively. The difference due to companion or background stars is small (<3% for main sequence companions) and likely to be negligible and undetectable. For only a few "hot" Jupiters, can combined photometry disambiguate between the reflected and thermal signals from planets. However, Rayleigh scattering by hazy atmospheres with particles sizes near 0.04 $\mu$m and at pressure altitudes above ~1 mbar can be detected for ~100 transiting planets, assuming every planet has such an atmosphere. Hazes with this characteristic particle size do not obscure observations at longer (near-infrared) wavelengths; CHEOPS follow-up of TESS-detected planets could thus identify candidates suitable for further study with the James Webb Space Telescope.Comment: MNRAS, in pres

Clouds in the atmospheres of extrasolar planets. IV. On the scattering greenhouse effect of CO2 ice particles: Numerical radiative transfer studies

Owing to their wavelengths dependent absorption and scattering properties, clouds have a strong impact on the climate of planetary atmospheres. Especially, the potential greenhouse effect of CO2 ice clouds in the atmospheres of terrestrial extrasolar planets is of particular interest because it might influence the position and thus the extension of the outer boundary of the classic habitable zone around main sequence stars. We study the radiative effects of CO2 ice particles obtained by different numerical treatments to solve the radiative transfer equation. The comparison between the results of a high-order discrete ordinate method and simpler two-stream approaches reveals large deviations in terms of a potential scattering efficiency of the greenhouse effect. The two-stream methods overestimate the transmitted and reflected radiation, thereby yielding a higher scattering greenhouse effect. For the particular case of a cool M-type dwarf the CO2 ice particles show no strong effective scattering greenhouse effect by using the high-order discrete ordinate method, whereas a positive net greenhouse effect was found in case of the two-stream radiative transfer schemes. As a result, previous studies on the effects of CO2 ice clouds using two-stream approximations overrated the atmospheric warming caused by the scattering greenhouse effect. Consequently, the scattering greenhouse effect of CO2 ice particles seems to be less effective than previously estimated. In general, higher order radiative transfer methods are necessary to describe the effects of CO2 ice clouds accurately as indicated by our numerical radiative transfer studies.Comment: accepted for publication in A&

Musil, Robert: Immobiliengeographie. : Märkte, Akteure, Politik

No abstract necessaryNo abstract necessar

Strategies for genetic transfer of an allele for resistance to Phytophthora megasperma f. sp. glycinea Kuan and Erwin in soybean [Glycine max (L.) Merr.]

The efficiency of backcrossing to transfer major genes for resistance to phytophthora stem and root rot, caused by Phytophthora megasperma f. sp. glycinea Kuan and Erwin, into susceptible soybean Glycine max (L.) Merr. cultivars is dependent on the number of backcrosses required to recover the desirable agronomic characteristics of the recurrent parent. The objective of this study was to determine in which backcross generation individual lines with Phytophthora resistance and yield equivalent to that of the recurrent parent can be selected, and in which backcross generation a group of random lines from the population have an average yield equivalent to that of the recurrent parent. The allele Rps(,1)(\u27k), for resistance to Phytophthora, was transferred from the cultivar Williams 82 to two susceptible recurrent parents, Cumberland and A78-123018. Thirty-six random resistant lines from each of five backcross generations were evaluated individually for agronomic traits. Bulks of the 36 lines of each backcross generation also were tested. The results indicated that, if the donor and recurrent parents differ in yield by 10% or less, a single cross is sufficient to develop a population from which a homozygous resistant line with a yield equal to that of the recurrent parent can be selected. Alternatively, the recurrent parent can be replaced by a bulk of random homozygous resistant lines after one backcross