Fingering convection and cloudless models for cool brown dwarf atmospheres

This work aims to improve the current understanding of the atmospheres of brown dwarfs, especially cold ones with spectral type T and Y, whose modeling is a current challenge. Silicate and iron clouds are believed to disappear at the photosphere at the L/T transition, but cloudless models fail to reproduce correctly the spectra of T dwarfs, advocating for the addition of more physics, e.g. other types of clouds or internal energy transport mechanisms. We use a one-dimensional (1D) radiative/convective equilibrium code ATMO to investigate this issue. This code includes both equilibrium and out-of-equilibrium chemistry and solves consistently the PT structure. Included opacity sources are H2-H2, H2-He, H2O, CO, CO2, CH4, NH3, K, Na, and TiO, VO if they are present in the atmosphere. We show that the spectra of Y dwarfs can be accurately reproduced with a cloudless model if vertical mixing and NH3 quenching are taken into account. T dwarf spectra still have some reddening in e.g. J - H compared to cloudless models. This reddening can be reproduced by slightly reducing the temperature gradient in the atmosphere. We propose that this reduction of the stabilizing temperature gradient in these layers, leading to cooler structures, is due to the onset of fingering convection, triggered by the destabilizing impact of condensation of very thin dust.Comment: Accepted in ApJ

Transposable elements in cancer as a by-product of stress-induced evolvability

Transposable elements (TEs) are ubiquitous in eukaryotic genomes. Barbara McClintock's famous notion of TEs acting as controlling elements modifying the genetic response of an organism upon exposure to stressful environments has since been solidly supported in a series of model organisms. This requires the TE activity response to possess an element of specificity and be targeted towards certain parts of the genome. We propose that a similar TE response is present in human cells, and that this stress response may drive the onset of human cancers. As such, TE-driven cancers may be viewed as an evolutionary by-product of organisms' abilities to genetically adapt to environmental stress

An accreted continental terrane in Northwestern Peru

Cet article présente une étude paléomagnétique des échantillons de plusieurs formations du bassin de Lancones (province de Piura). Les auteurs formulent l'hypothèse de l'accrétion d'une terrane sur la marge péruvienne au cours du Néocomien. Un régime de cisaillement aurait également produit des rotations in situ. L'évolution géodynamique du nord du Pérou est donc comparable aux processus observés sur les Andes septentrionales, en Equateu

Citizen Science Time Domain Astronomy with Astro-COLIBRI

Astro-COLIBRI is an innovative tool designed for professional astronomers to facilitate the study of transient astronomical events. Transient events - such as supernovae, gamma-ray bursts and stellar mergers - are fleeting cataclysmic phenomena that can offer profound insights into the most violent processes in the universe. Revealing their secrets requires rapid and precise observations: Astro-COLIBRI alerts its users of new transient discoveries from observatories all over the world in real-time. The platform also provides observers the details they need to make follow-up observations. Some of the transient phenomena available through Astro-COLIBRI are accessible by amateur astronomers and citizen scientists. A subset of the features dedicated to this growing group of users are highlighted here. They include the possibility of receiving only alerts on very bright events, the possibility of defining custom observer locations, as well as the calculation of optimized observation plans for searches for optical counterparts to gravitational wave events.Comment: Proceedings Atelier Pro-AM Gemini, Journ\'ees SF2A 2023. arXiv admin note: text overlap with arXiv:2308.0704

The acceleration of superrotation in simulated hot Jupiter atmospheres

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordContext. Atmospheric superrotating flows at the equator are a nearly ubiquitous result when conducting simulations of hot Jupiters. One theory explaining how this zonally-coherent flow reaches equilibrium has already been developed in the literature. This understanding, however, relies on the existence of either an initial superrotating flow or a sheared flow, coupled with a slow evolution that permits a linear steady state to be reached. Aims. A consistent physical understanding of superrotation is needed for arbitrary drag and radiative timescales, along with the relevance of taking linear steady states into account, needs to be assessed. Methods. We obtained an analytical expression for the structure, frequency, and decay rate of propagating waves in hot Jupiter atmospheres around a state at rest in the 2D shallow-water β–plane limit. We solved this expression numerically and confirmed the robustness of our results with a 3D linear wave algorithm. We then compared it with 3D simulations of hot Jupiter atmospheres and studied the nonlinear momentum fluxes. Results. We show that under strong day-night heating, the dynamics do not transit through a linear steady state when starting from an initial atmosphere in solid body rotation. We further demonstrate that non–linear effects favor the initial spin-up of superrotation and that acceleration due to the vertical component of the eddy–momentum flux is critical to the initial development of superrotation . Conclusions. We describe the initial phases of the acceleration of superrotation, including the consideration of differing radiative and drag timescales, and we conclude that eddy-momentum-driven superrotating equatorial jets are robust, physical phenomena in simulations of hot Jupiter atmospheres.Leverhulme TrustScience and Technology Facilities Counci

Beam Dynamics and First Operation of the Sub-Harmonic Bunching System in the CTF3 Injector

The CLIC Test Facility 3 (CTF3), built at CERN by an international collaboration, aims at demonstrating the feasibility of the CLIC scheme by 2010. The CTF3 drive beam generation scheme relies on the use of a fast phase switch of a sub-harmonic bunching system in order to phase-code the bunches. The amount of charge in unwanted satellite bunches is an important quantity, which must be minimized. Beam dynamic simulations have been used to study the problem, showing the limitation of the present CTF3 design and the gain of potential upgrades. In this paper the results are discussed and compared with beam measurements taken during the first operation of the system

Probable Transmission of Coxsackie B3 Virus from Human to Chimpanzee, Denmark

In 2010, a chimpanzee died at Copenhagen Zoo following an outbreak of respiratory disease among chimpanzees in the zoo. Identification of coxsackie B3 virus, a common human pathogen, as the causative agent, and its severe manifestation, raise questions about pathogenicity and transmissibility among humans and other primates