Aims . HD 96446 is a magnetic B2p He-strong star that has been reported to be a β Cep pulsator. We present a detailed spectroscopic analysis of this object based on an intensive observational data set obtained in a multisite campaign with the spectrographs CORALIE, FEROS, and HARPS (La Silla); UVES (Paranal); HERCULES (Mt. John Observatory); and GIRAFFE (SAAO). Methods . Radial velocities were measured by cross-correlations and analysed to detect periodic variations. On the other hand, the mean spectrum was fit with spectral synthesis to derive atmospheric parameters and chemical abundances. Results . From the analysis of radial velocities, HD 96446 was found to be a spectroscopic binary with a period of 799 days. The stellar companion, which contributes only ∼5% of the total flux, is an A0-type star. A frequency analysis of the radial velocities allowed us to detect two pulsational modes with periods 2.23 h and 2.66 h. The main mode is most probably a low-inclination, dipole mode ( l , m ) = (1, 0), and the second pulsation mode corresponds to ( l , m ) = (2, 2) or to a pole-on ( l , m ) = (3, 2) configuration. In addition to radial velocities, the main pulsation mode is evidenced through small variations in the spectral morphology (temperature variations) and the light flux. The rotation period of 23.4 d, was detected through the variation in line intensities. Chemical abundances are unevenly distributed over the stellar surface, with helium concentrated at the negative magnetic pole and most metals strengthened at lower latitudes. The mean chemical abundance of helium is strongly abnormal, reaching a value of 0.60 (number fraction).
This file contains the python scripts needed to re-produce figures 2-11 in our paper. It also contains the information to re-run our 22Ne tests and other WD mass models. The README.md file contains a more detailed description of the data.
We update the capabilities of the open-knowledge software instrument Modules for Experiments in Stellar Astrophysics (MESA). The new auto_diff module implements automatic differentiation in MESA, an enabling capability that alleviates the need for hard-coded analytic expressions or finite difference approximations. We significantly enhance the treatment of the growth and decay of convection in MESA with a new model for time-dependent convection, which is particularly important during late-stage nuclear burning in massive stars and electron degenerate ignition events. We strengthen MESA's implementation of the equation of state, and we quantify continued improvements to energy accounting and solver accuracy through a discussion of different energy equation features and enhancements. To improve the modeling of stars in MESA we describe key updates to the treatment of stellar atmospheres, molecular opacities, Compton opacities, conductive opacities, element diffusion coefficients, and nuclear reaction rates. We introduce treatments of starspots, an important consideration for low-mass stars, and modifications for superadiabatic convection in radiation-dominated regions. We describe new approaches for increasing the efficiency of calculating monochromatic opacities and radiative levitation, and for increasing the efficiency of evolving the late stages of massive stars with a new operator split nuclear burning mode. We close by discussing major updates to MESA's software infrastructure that enhance source code development and community engagement.
view Abstract Citations (121) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hydrodynamic Simulations of Galaxy Formation. I. Dissipation and the Maximum Mass of Galaxies Thoul, Anne A. ; Weinberg, David H. Abstract We describe an accurate, one-dimensional, spherically symmetric Lagrangian hydrodynamics/gravity code, designed to study the effects of radiative cooling and photoionization on the formation of protogalaxies. The code can treat an arbitrary number of fluid shells (representing baryons) and collisionless shells (representing cold dark matter). As a test of the code, we reproduce analytic solutions for the pulsation behavior of a polytrope and for the self-similar collapse of a spherically symmetric, cosmological perturbation. In this paper we concentrate on the effects of radiative cooling, examining the ability of collapsing perturbations to cool within the age of the universe. In contrast to, some studies based on order-of-magnitude estimates, we find that cooling arguments alone cannot explain the sharp upper cutoff observed in the galaxy luminosity function. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175455 arXiv: arXiv:astro-ph/9410009 Bibcode: 1995ApJ...442..480T Keywords: Astronomical Models; Energy Dissipation; Galactic Evolution; Galactic Mass; Gravitation; Hydrodynamics; Computerized Simulation; Finite Difference Theory; Luminosity; Mathematical Models; Photoionization; Polytopes; Radiative Heat Transfer; Astrophysics; GALAXIES: FORMATION; HYDRODYNAMICS; METHODS: NUMERICAL; Astrophysics E-Print: 33 pages, uuencoded compressed postscript with figures, Ap.J. (in press), corrections to axes in Fig 1 full text sources arXiv | ADS | Related Materials (1) Part 2: 1996ApJ...465..608T
The information on stellar parameters and on the stellar interior we can get by studying pulsating stars depends crucially on the available observational constraints: both seismic constraints precision and number of detected modes, identification, nature of the modes) and "classical" observations (photospheric abundances, effective temperature, luminosity, surface gravity). We consider the case of beta Cephei pulsators and, with the aim of estimating quantitatively how the available observational constraints determine the type and precision of our inferences, we set the stage for Hare&Hound exercises. In this contribution we present preliminary results for one simple case, where we assume as "observed" frequencies a subset of frequencies of a model and then evaluate a seismic merit function on a dense and extensive grid of models of B-type stars. We also compare the behaviour of chi^2 surfaces obtained with and without mode identification.
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