Thermohaline mixing in stars and the long-standing 3He problem

Thermohaline mixing has been recently identified as the dominating process that governs the photospheric composition of low-mass bright giant stars (Charbonnel & Zahn 2007). Here we present the predictions of stellar models computed with the code STAREVOL taking into account this mechanism together with rotational mixing and atomic diffusion. We compare our theorical predictions with recent observations and discuss how the corresponding yields for 3He are compatible with the observed behaviour of this light element in our Galax

Thermohaline mixing in stars: solving the long-standing 3He problem

Thermohaline mixing has been recently identified as the dominating process that governs the photospheric composition of low-mass bright giant stars (Charbonnel & Zahn 2007a). Here we present the predictions of stellar models computed with the code STAREVOL that takes into account this mechanism together with rotational mixing and atomic diffusion. We compare our theorical predictions with recent observations and discuss how the corresponding yields for 3He are compatible with the observed behaviour of this light element in our Galax

Testing the cores of first ascent red-giant stars using the period spacing of g modes

In the context of the determination of stellar properties using asteroseismology, we study the influence of rotation and convective-core overshooting on the properties of red-giant stars. We used models in order to investigate the effects of these mechanisms on the asymptotic period spacing of gravity modes ($\Delta \Pi_1$) of red-giant stars that ignite He burning in degenerate conditions (M$\lesssim$2.0 M$_{\odot}$). We also compare the predictions of these models with Kepler observations. For a given $\Delta\nu$, $\Delta \Pi_1$ depends not only on the stellar mass, but also on mixing processes that can affect the structure of the core. We find that in the case of more evolved red-giant-branch (RGB) stars and regardless of the transport processes occurring in their interiors, the observed $\Delta \Pi_1$ can provide information as to their stellar luminosity, within ~10-20%. In general, the trends of $\Delta \Pi_1$ with respect to mass and metallicity that are observed in Kepler red-giant stars are well reproduced by the models.Comment: 5pages, 6 figure

The thermohaline, Richardson, Rayleigh-Taylor, Solberg-Hoiland, and GSF criteria in rotating stars

Aims. We examine the interactions of various instabilities in rotating stars, which usually are considered as independent. Methods. An analytical study of the problem is performed, account is given to radiative losses, mu-gradients and horizontal turbulence. Results. The diffusion coefficient for an ensemble of instabilities is not given by the sum of the specific coefficients for each instability, but by the solution of a general equation. We find that thermohaline mixing is possible in low-mass red giants only if the horizontal turbulence is very weak. In rotating stars the Rayleigh-Taylor and the shear instabilities need simultaneous treating. This has for consequence that rotation laws of the form 1/r^(alpha) are predicted to be unstable for alpha > 1.6568, while the usual Rayleigh criterion predicts instability only for alpha > 2. Also, the shear instabilities are somehow reduced in Main Sequence stars by the effect of the Rayleigh-Taylor criterion. Various instability criteria should be expressed differently in rotating stars than in simplified geometries.Comment: accepted in A&

The Use of NTFPs in the Baka and Kounabembe Traditional Pharmacopoeia in the Northern Periphery of the Boumba-Bek National Park (Southeastern Cameroon)

Forest conservation around protected areas includes among others sustainable management of natural resources. This study was conducted in the area of the northern outskirts of the Boumba-Bek National Park in order to evaluate the potential use of plants in traditional medicine. Ethnobotanical surveys were conducted with local people using AFLORA survey forms. A total of 132 plant species used in traditional medicine for primary health care were identified. These plants belong to 109 genera and 45 families. 224 treatments for 101 disease symptoms were collected. These diseases include the nervous system, excretory system and nutritional function. The most recurrent diseases are cough, sexual weakness, back pain, abscess, general tiredness, malaria. Some plants such as Baillonella toxisperma, Alstonia boonei, Annonidium mannii, Ricinidendron heudelotii, Klainedoxa gabonensis, Scorodophloeus zenkeri, Swartzia sp. treat several diseases at once. The plant parts mostly used are stem bark, leaves, seeds, sap, the marrow of the bark, the pith of the stem. The main method of preparation of these recipes is decoction while the most common method of administration is oral administration. The plant resources of this village have a high potential in traditional medicine for primary health care. The importance index varied from plant to plant. Keywords: NTFPs, AFLORA, medicinal plants, traditional medicine, primary health care. DOI: 10.7176/JBAH/11-4-07 Publication date: February 28th 202

12C/13C isotopic ratios in red-giant stars of the open cluster NGC 6791

Carbon isotope ratios, along with carbon and nitrogen abundances, are derived in a sample of 11 red-giant members of one of the most metal-rich clusters in the Milky Way, NGC 6791. The selected red-giants have a mean metallicity and standard deviation of [Fe/H]=+0.39+-0.06 (Cunha et al. 2015). We used high resolution H-band spectra obtained by the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE). The advantage of using high-resolution spectra in the H-band is that lines of CO are well represented and their line profiles are sensitive to the variation of 12C/13C. Values of the 12C/13C ratio were obtained from a spectrum synthesis analysis. The derived 12C/13C ratios varied between 6.3 and 10.6 in NGC 6791, in agreement with the final isotopic ratios from thermohaline-induced mixing models. The ratios derived here are combined with those obtained for more metal poor red-giants from the literature to examine the correlation between 12C/13C, mass, metallicity and evolutionary status.Comment: Accepted for publication in MNRAS, 9 pages, 4 figures, 2 table

Heterosubtype Neutralizing Responses to Influenza A (H5N1) Viruses Are Mediated by Antibodies to Virus Haemagglutinin

Background: It is increasingly clear that influenza A infection induces cross-subtype neutralizing antibodies that may potentially confer protection against zoonotic infections. It is unclear whether this is mediated by antibodies to the neuraminidase (NA) or haemagglutinin (HA). We use pseudoviral particles (H5pp) coated with H5 haemagglutinin but not N1 neuraminidase to address this question. In this study, we investigate whether cross-neutralizing antibodies in persons unexposed to H5N1 is reactive to the H5 haemagglutinin. Methodology/Principal Findings: We measured H5-neutralization antibody titers pre- and post-vaccination using the H5N1 micro-neutralization test (MN) and H5pp tests in subjects given seasonal vaccines and in selected sera from European elderly volunteers in a H5N1 vaccine trial who had detectable pre-vaccination H5N1 MN antibody titers. We found detectable (titer ≥20) H5N1 neutralizing antibodies in a minority of pre-seasonal vaccine sera and evidence of a serological response to H5N1 in others after seasonal influenza vaccination. There was excellent correlation in the antibody titers between the H5N1 MN and H5pp tests. Similar correlations were found between MN and H5pp in the pre-vaccine sera from the cohort of H5N1 vaccine trial recipients. Conclusions/Significance: Heterosubtype neutralizing antibody to H5N1 in healthy volunteers unexposed to H5N1 is mediated by cross-reaction to the H5 haemagglutinin. Copyright: © 2009 Garcia et al.published_or_final_versio

Deciphering the evolution of the Milky Way discs: Gaia APOGEE Kepler giant stars and the Besançon Galaxy Model

[Context] Thanks to ongoing efforts to compute accurate stellar ages, we are able to characterise stars in different regions of the Milky Way. The Gaia and Kepler space-missions, along with ground-based spectroscopic surveys such as APOGEE, provide a unique way to study the chemo-kinematics relations as a function of age through the Galactic stellar populations and provide new constraints to Galactic evolution models. [Aims] We investigate the properties of the double sequences of the Milky Way discs visible in the [α/Fe] versus [Fe/H] diagram, which are usually associated to the chemical thin and thick discs at the solar circle. In the framework of Galactic formation and evolution, we discuss the complex relationships between age, metallicity, [α/Fe], and the radial, azimuthal, and vertical components of the space velocities. [Methods] We study stars with measured chemical and seismic properties from the APOGEE spectroscopic survey and the Kepler satellite, respectively. In addition, astrometry from the Gaia satellite is available for the majority of the sample. We separate the [α/Fe]-[Fe/H] diagram into three stellar populations: the thin disc, the high-α metal-poor thick disc, and the high-α metal-rich thick disc and characterise each of these in the age-chemo-kinematics parameter space. Because of the model-dependent nature of the ages inferred from asteroseismology, and because they depend on the quality of the input spectroscopic information, we compare results obtained from different APOGEE data releases (DR14 and DR16). We also use age determinations from two recent works in the literature. In addition, we use the Besançon stellar populations synthesis model to highlight selection biases and mechanisms (such as mergers and secular evolution) not included in the model. [Results] The thin disc exhibits a flat age-metallicity relation while [α/Fe] increases with stellar age. We confirm no correlation between radial and vertical velocities with [Fe/H], [α/Fe], and age for each stellar population. Considering both samples, Vφ decreases with age for the thin disc, while Vφ increases with age for the high-α metal-poor thick disc. We show that this difference is not due to sample selection. Although the age distribution of the high-α metal-rich thick disc is very close to that of the high-α metal-poor thick disc between 7 and 14 Gyr, its kinematics seems to follow that of the thin disc. This feature, not predicted by the hypotheses included in the Besançon Galaxy Model, suggests a different origin and history for this population. Finally, we show that there is a maximum dispersion of the vertical velocity, σZ, with age for the high-α metal-poor thick disc around 8 Gyr. The comparisons with the Besançon Galaxy Model simulations suggest a more complex chemo-dynamical scheme to explain this feature, most likely including mergers and radial migration effects.F.F., A.F., R.M., M.R., T.A. acknowledge support by the Spanish Ministry of Science, Innovation and University (MICIU/FEDER, UE) through grant RTI2018-095076-B-C21, the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia “María de Maeztu”) through grant CEX2019-000918-M, the Ramon y Cajal Fellowship RYC2018-025968-I. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 800502. AM acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 772293 – project ASTEROCHRONOMETRY, https://www.asterochronometry.eu

HAYDN: High-precision AsteroseismologY of DeNse stellar fields

In the last decade, the Kepler and CoRoT space-photometry missions have demonstrated the potential of asteroseismology as a novel, versatile and powerful tool to perform exquisite tests of stellar physics, and to enable precise and accurate characterisations of stellar properties, with impact on both exoplanetary and Galactic astrophysics. Based on our improved understanding of the strengths and limitations of such a tool, we argue for a new small/medium space mission dedicated to gathering high-precision, high-cadence, long photometric series in dense stellar fields. Such a mission will lead to breakthroughs in stellar astrophysics, especially in the metal poor regime, will elucidate the evolution and formation of open and globular clusters, and aid our understanding of the assembly history and chemodynamics of the Milky Way’s bulge and a few nearby dwarf galaxies