A simple representation of oscillation modes in stars: from mixed modes coupling to glitches

Analytical resonance conditions for oscillation modes in stars are very helpful both to predict and to examine their frequency spectra, as well as to make the link with their internal properties. In this short paper, we introduce a general quantization expression for oscillation modes accounting for the possible existence of a local sharp variation in the equilibrium structure, a so-called glitch. This representation is based on a direct adaptation of the progressive-wave picture of mixed modes proposed by Takata (2016b). In this formulation, a glitch turns out to be characterized by three parameters: its acoustic depth, the phase lags introduced after the wave reflection at the considered point, and a coupling factor. Such an expression has two main advantages. First, it can be easily applicable to a lot of different structural configurations. Second, it does not assume that the glitch is a small perturbation. Actually, we check that the obtained expression tends to the formulations previously derived when the glitch is weak. These research notes represent a preliminary step towards a more generalized description of multi-cavity oscillation modes, that was briefly addressed in the poster presented at the PHOST conference.Comment: Published 11 December 2018, 4 page

Generation of internal gravity waves by penetrative convection

The rich harvest of seismic observations over the past decade provides evidence of angular momentum redistribution in stellar interiors that is not reproduced by current evolution codes. In this context, transport by internal gravity waves can play a role and could explain discrepancies between theory and observations. The efficiency of the transport of angular momentum by waves depends on their driving mechanism. While excitation by turbulence throughout the convective zone has already been investigated, we know that penetrative convection into the stably stratified radiative zone can also generate internal gravity waves. Therefore, we aim at developing a semianalytical model to estimate the generation of IGW by penetrative plumes below an upper convective envelope. We derive the wave amplitude considering the pressure exerted by an ensemble of plumes on the interface between the radiative and convective zones as source term in the equation of momentum. We consider the effect of a thermal transition from a convective gradient to a radiative one on the transmission of the wave into the radiative zone. The plume-induced wave energy flux at the top of the radiative zone is computed for a solar model and is compared to the turbulence-induced one. We show that, for the solar case, penetrative convection generates waves more efficiently than turbulence and that plume-induced waves can modify the internal rotation rate on shorter time scales. We also show that a smooth thermal transition significatively enhances the wave transmission compared to the case of a steep transition. We conclude that driving by penetrative convection must be taken into account as much as turbulence-induced waves for the transport of internal angular momentum.Comment: Accepted for publication in A&A, 21 page

Amplitude of solar gravity modes generated by penetrative plumes

The detection of gravity modes is expected to give us unprecedented insights into the inner dynamics of the Sun. Within this framework, predicting their amplitudes is essential to guide future observational strategies and seismic studies. In this work, we predict the amplitude of low-frequency asymptotic gravity modes generated by penetrative convection at the top of the radiative zone. The result is found to depend critically on the time evolution of the plumes inside the generation region. Using a solar model, we compute the GOLF apparent surface radial velocity of low-degree gravity modes in the frequency range $10~\mu H_z\le \nu \le 100~\mu H_z$. In case of a Gaussian plume time evolution, gravity modes turn out to be undetectable because of too small surface amplitudes. This holds true despite a wide range of values considered for the parameters of the model. In the other limiting case of an exponential time evolution, plumes are expected to drive gravity modes in a much more efficient way because of a much higher temporal coupling between the plumes and the modes than in the Gaussian case. Using reasonable values for the plume parameters based on semi-analytical models, the apparent surface velocities in this case turn out to be one order of magnitude smaller than the 22-years GOLF detection threshold and than the previous estimates considering turbulent pressure as the driving mechanism, with a maximum value of $0.05$ cm s${}^{-1}$ for $\ell =1$ and $\nu\approx 100~\mu H_z$. When accounting for uncertainties on the plume parameters, the apparent surface velocities in the most favorable plausible case become comparable to those predicted with turbulent pressure, and the GOLF observation time required for a detection at $\nu \approx100~\mu H_z$ and $\ell=1$ is reduced to about 50 yrs.Comment: 18 pages, Accepted for publication in A&

Simplified open repair for anterior chest wall deformities. Analysis of results in 205 patients

SummaryIntroductionPectus deformities are the most frequently seen congenital thoracic wall anomalies. The cause of these conditions is thought to be abnormal elongation of the rib cartilages. We here report our clinical experience and the results of a sternochondroplasty procedure based on the subperichondrial resection of the elongated cartilages.HypothesisThis technique is a valuable surgical strategy to treat the wide variety of pectus deformities.Patients and methodsDuring the period from October 2001 through September 2009, 205 adult patients (171 men and 34 women) underwent pectus excavatum (181), carinatum (19) or arcuatum (5) repair. The patients’ pre and postoperative data were collected using a computerized database, and the results were assessed with a minimum 2-year follow-up.ResultsThe postoperative morbidity rate was minimal and the mortality was nil. The surgeon graded cosmetic results as excellent (72.5%), good (25%) or fair (2.5%), while patients reported better results. Patients with pectus excavatum were found to have much more patent foramen ovale (PFO) than the normal adult population, which occluded after the procedure in 61% of patients, and significant improvement was found in exercise cardiopulmonary function and exercise tolerance at the 1-year follow-up.DiscussionOur sternochondroplasty technique based on the subperichondrial resection of the elongated cartilages allows satisfactory repair of both pectus excavatum and sternal prominence. It is a safe procedure that might improve the effectiveness of surgical therapy in patients with pectus deformities.Level of evidenceLevel IV. Retrospective study

Coriolis darkening in late-type stars II. Effect of self-sustained magnetic fields in stratified convective envelope

Modeling the surface brightness distribution of stars is of prime importance to interpret observations. Nevertheless, this remains quite challenging for cool stars as it requires one to model the MHD turbulence that develops in their convective envelope. In Paper I, the effect of the Coriolis acceleration on the surface heat flux has been studied by means of hydrodynamic simulations. In this paper, we aim to investigate the additional effect of dynamo magnetic fields. We focus on an envelope thickness that is representative of either a $\sim0.35~M_\odot$ M dwarf, a young red giant star or a pre-main sequence star. We performed a parametric study using numerical MHD simulations of anelastic convection in thick rotating spherical shells. For each model, we computed the mean surface distribution of the heat flux, and examined the leading-order effect of the magnetic field on the obtained latitudinal luminosity profile. We identify three different regimes. Close to the onset of convection, while the first unstable modes tend to convey heat more efficiently near the equator, magnetic fields are shown to generally enhance the mean heat flux close to the polar regions (and the tangent cylinder). By progressively increasing the Rayleigh number, the development of a prograde equatorial jet was previously shown to make the equator darker when no magnetic field is taken into account. For moderate Rayleigh numbers, magnetic fields can instead inverse the mean pole-equator brightness contrast (which means going from a darker to a brighter equator when a dynamo sets in) and finally induce a similar regime to that found close to the onset of convection. For more turbulent models with larger Rayleigh numbers, magnetic fields alternatively tend to smooth out the brightness contrast. This general behavior is shown to be related to the quenching of the surface differential rotation by magnetic fields.Comment: Accepted in A&A - Acceptance date: 04/03/202

Thorough characterisation of the 16 Cygni system

Context. The advent of space-based photometry observations provided high-quality asteroseismic data for a large number of stars. These observations enabled the adaptation of advanced analyses techniques, until then restricted to the field of helioseismology, to study the best asteroseismic targets. Amongst these, the 16Cyg binary system holds a special place, as they are the brightest solar twins observed by the Kepler mission. For this specific system, modellers have access to high-quality asteroseismic, spectroscopic and interferometric data, making it the perfect testbed for the limitations of stellar models. Aims. We aim to further constrain the internal structure and fundamental parameters of 16CygA&B using linear seismic inversion techniques of both global indicators and localised corrections of the hydrostatic structure. Methods. We start from the models defined by detailed asteroseismic modelling in our previous paper and extend our analysis by applying variational inversions to our evolutionary models. We carried out inversions of so-called seismic indicators and attempted to provide local corrections of the internal structure of the two stars. Results. Our results indicate that linear seismic inversions alone are not able to discriminate between standard and non-standard models for 16CygA&B. We confirm the results of our previous studies that used linear inversion techniques, but consider that the observed differences could be linked to small fundamental parameters variations rather than to a missing process in the models. Conclusions. We confirm the robustness and reliability of the results of the modelling we performed in our previous paper. We conclude that non-linear inversions are likely required to further investigate the properties of 16CygA&B from a seismic point of view, but that these inversions have to be coupled to analyses of the depletion of light elements such as lithium and beryllium to constrain the macroscopic transport of chemicals in these stars and also to constrain potential non-standard evolutionary paths

Compton Large Area Silicon Timing Tracker for Cosmic Vision M3

International audienceProposed in response to the ESA call for the third Medium size mission (M3), CAPSiTT is a small mission designed for a 3-year survey of the non-thermal high energy sky from an equatorial LEO orbit. With a large effective area and a very wide field of view, its single instrument, a silicon tracker, provides good imaging, spectroscopic and polarimetric capabilities with a sensitivity 10-100 times better than COMPTEL. Nucleosynthesis and particle acceleration mechanisms in various sites are the main scientific topics addressed by CAPSiTT

Turbulence Heating ObserveR – satellite mission proposal

The Universe is permeated by hot, turbulent, magnetized plasmas. Turbulent plasma is a major constituent of active galactic nuclei, supernova remnants, the intergalactic and interstellar medium, the solar corona, the solar wind and the Earth’s magnetosphere, just to mention a few examples. Energy dissipation of turbulent fluctuations plays a key role in plasma heating and energization, yet we still do not understand the underlying physical mechanisms involved. THOR is a mission designed to answer the questions of how turbulent plasma is heated and particles accelerated, how the dissipated energy is partitioned and how dissipation operates in different regimes of turbulence. THOR is a single-spacecraft mission with an orbit tuned to maximize data return from regions in near-Earth space – magnetosheath, shock, foreshock and pristine solar wind – featuring different kinds of turbulence. Here we summarize the THOR proposal submitted on 15 January 2015 to the ‘Call for a Medium-size mission opportunity in ESAs Science Programme for a launch in 2025 (M4)’. THOR has been selected by European Space Agency (ESA) for the study phase

Identification and thermochemical analysis of high-lignin feedstocks for biofuel and biochemical production

Background - Lignin is a highly abundant biopolymer synthesized by plants as a complex component of plant secondary cell walls. Efforts to utilize lignin-based bioproducts are needed. Results - Herein we identify and characterize the composition and pyrolytic deconstruction characteristics of high-lignin feedstocks. Feedstocks displaying the highest levels of lignin were identified as drupe endocarp biomass arising as agricultural waste from horticultural crops. By performing pyrolysis coupled to gas chromatography-mass spectrometry, we characterized lignin-derived deconstruction products from endocarp biomass and compared these with switchgrass. By comparing individual pyrolytic products, we document higher amounts of acetic acid, 1-hydroxy-2-propanone, acetone and furfural in switchgrass compared to endocarp tissue, which is consistent with high holocellulose relative to lignin. By contrast, greater yields of lignin-based pyrolytic products such as phenol, 2-methoxyphenol, 2-methylphenol, 2-methoxy-4-methylphenol and 4-ethyl-2-methoxyphenol arising from drupe endocarp tissue are documented. Conclusions - Differences in product yield, thermal decomposition rates and molecular species distribution among the feedstocks illustrate the potential of high-lignin endocarp feedstocks to generate valuable chemicals by thermochemical deconstruction

Establishing causal order in longitudinal studies combining binary and continuous dependent variables

Longitudinal studies with a mix of binary outcomes and continuous variables are common in organizational research. Selecting the dependent variable is often difficult due to conflicting theories and contradictory empirical studies. In addition, organizational researchers are confronted with methodological challenges posed by latent variables relating to observed binary outcomes and within-subject correlation. We draw on Dueker’s (2005) qualitative vector autoregression (QVAR) and Lunn et al.’s (2014) multivariate probit model to develop a solution to these problems in the form of a qualitative short panel vector autoregression (QSP-VAR). The QSP-VAR combines binary and continuous variables into a single vector of dependent variables, making every variable endogenous a priori. The QSP-VAR identifies causal order, reveals within-subject correlation and accounts for latent variables. Using a Bayesian approach, the QSP-VAR provides reliable inference for short time dimension longitudinal research. This is demonstrated through analysis of the durability of elite corporate agents, social networks and firm performance in France. We provide our OpenBUGS code to enable implementation of the QSP-VAR by other researchers