α\alpha Centauri A as a potential stellar model calibrator: establishing the nature of its core

Understanding the physical process responsible for the transport of energy in the core of $\alpha$ Centauri A is of the utmost importance if this star is to be used in the calibration of stellar model physics. Adoption of different parallax measurements available in the literature results in differences in the interferometric radius constraints used in stellar modelling. Further, this is at the origin of the different dynamical mass measurements reported for this star. With the goal of reproducing the revised dynamical mass derived by Pourbaix & Boffin, we modelled the star using two stellar grids varying in the adopted nuclear reaction rates. Asteroseismic and spectroscopic observables were complemented with different interferometric radius constraints during the optimisation procedure. Our findings show that best-fit models reproducing the revised dynamical mass favour the existence of a convective core ($\gtrsim$ 70% of best-fit models), a result that is robust against changes to the model physics. If this mass is accurate, then $\alpha$ Centauri A may be used to calibrate stellar model parameters in the presence of a convective core.Comment: 6 pages, 2 figures, 4 tables. Accepted for publication in Monthly Notices of the Royal Astronomical Society Letter

TESS asteroseismology of the known red-giant host stars HD 212771 and HD 203949

International audienc

Characteristics of rural chicken production in Apac and Kumi districts of Uganda

Across - sectional survey was conducted to establish the characteristics of rural chicken production in Apac and Kumi districts. This was necessary to establish a baseline benchmark against which the impact of the NARO/DFID chicken project could be gauged. Systematic sampling techniques were applied to 120 households to capture the necessary baseline data. The study revealed that farmers keep indigenous chickens mainly for food, cash and gifts and use eggs mainly for hatching chicks. Most people keep 2-10 hens and 1 breeding cock, and in a family, the majority of chickens are owned by the husband and w ife. The production indices obtained were typical of African rural chicken production systems and most chickens depended mainly on vending for themselves. Lack of proper housing and diseases were cited as major constraints and few farmers ever vaccinated their chickens. Traditional medicine is greatly used in disease control. Selection for genetic improvement is not commonly done although occasionally farmers buy new cocks. While women care for chickens, the decisions on sales and cash are jointly taken by the husband and wife. The results indicated that rural chicken production is still at subsistence level and the production indices still low, implying that the system is amenable to improvement in order to raise household incomes

The PLATO mission

PLATO (PLAnetary Transits and Oscillations of stars) is ESA’s M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2R ) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5%, 10%, 10% for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO‘s target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile towards the end of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases

MAISTEP: A new grid-based machine learning tool for inferring stellar parameters: I. Ages of giant planet host stars

Context. Our understanding of exoplanet demographics partly depends on their corresponding host star parameters. With the majority of exoplanet-host stars having only atmospheric constraints available, robust inference of their parameters (including ages) is susceptible to the approach used. Aims. The goal of this work is to develop a grid-based machine learning tool capable of determining the stellar radius, mass, and age using only atmospheric constraints. We also aim to analyse the age distribution of stars hosting giant planets. Methods. Our machine learning approach involves combining four tree-based machine learning algorithms (random forest, extra trees, extreme gradient boosting, and CatBoost) trained on a grid of stellar models to infer the stellar radius, mass, and age using effective temperatures, metallicities, and Gaia-based luminosities. We performed a detailed statistical analysis to compare the inferences of our tool with those based on seismic data from the APOKASC (with global oscillation parameters) and LEGACY (with individual oscillation frequencies) samples. Finally, we applied our tool to determine the ages of stars hosting giant planets. Results. Comparing the stellar parameter inferences from our machine learning tool with those from the APOKASC and LEGACY, we find a bias (and a scatter) of -0.5% (5%) and -0.2% (2%) in radius, 6% (5%) and -2% (3%) in mass, and -9% (16%) and 7% (23%) in age, respectively. Therefore, our machine learning predictions are commensurate with seismic inferences. When applying our model to a sample of stars hosting Jupiter-mass planets, we find the average age estimates for the hosts of hot Jupiters, warm Jupiters, and cold Jupiters to be 1.98 Gyr, 2.98 Gyr, and 3.51 Gyr, respectively. Conclusions. Our machine learning tool is robust and efficient in estimating the stellar radius, mass, and age when only atmospheric constraints are available. Furthermore, the inferred age distributions of giant planet host stars confirm previous predictions - based on stellar model ages for a relatively small number of hosts, as well as on the average age-velocity dispersion relation - that stars hosting hot Jupiters are statistically younger than those hosting warm and cold Jupiters

On the stellar core physics of the 16 Cyg binary system: constraining the central hydrogen abundance using asteroseismology

The unprecedented quality of the asteroseismic data of solar-type stars made available by space missions such as NASA’s Kepler telescope are making it possible to explore stellar interior structures. This offers possibilities of constraining stellar core properties (such as core sizes, abundances, and physics) paving the way for improving the precision of the inferred stellar ages. We employ 16 Cyg A and B as our benchmark stars for an asteroseismic study in which we present a novel approach aimed at selecting from a sample of acceptable stellar models returned from forward modelling techniques, down to the ones that better represent the core of each star. This is accomplished by comparing specific properties of the observed frequency ratios for each star to the ones derived from the acceptable stellar models. We demonstrate that in this way we are able to constrain further the hydrogen mass fraction in the core, establishing the stars’ precise evolutionary states and ages. The ranges of the derived core hydrogen mass fractions are [0.01–0.06] and [0.12–0.19] for 16 Cyg A and B, respectively, and, considering that the stars are coeval, the age and metal mass fraction parameters span the region [6.4–7.4] Gyr and [0.023–0.026], respectively. In addition, our findings show that using a single helium-to-heavy element enrichment ratio, (ΔY/ΔZ), when forward modelling the 16 Cyg binary system, may result in a sample of acceptable models that do not simultaneously fit the observed frequency ratios, further highlighting that such an approach to the definition of the helium content of the star may not be adequate in studies of individual stars

Asteroseismic modelling of solar-type stars: internal systematics from input physics and surface correction methods

International audienc