Solving non-LTE problems in rotational transitions using the Gauss–Seidel method and its implementation in the Atmospheric Radiative Transfer Simulator

This article presents our implementation of a non-LTE solver in spherical symmetry for molecular rotational transition in static or expanding atmospheres. The new open-source code relies on the Gauss–Seidel Accelerated Lambda Iteration methodology that provides a rapid and accurate convergence of the non-LTE problems, which is now routinely used in astrophysical and planetary research. The non-LTE code is interfaced with the widely used package, the Atmospheric Radiative Transfer Simulator (ARTS), to facilitate spectral line simulations for various viewing geometries. In this paper we describe the numerical implementation, provide the first validation results for the populations against two other non-LTE codes, and then discuss the possible application. The quantitative comparisons are performed using an established ortho-water non-LTE model applied to cases of optical thick and thin conditions of Ganymede’s atmosphere. The differences in populations expressed as excitation temperatures show very good agreement in both cases. Finally, we also apply this model to a sample of data from the Microwave Instrument for the Rosetta Orbiter (MIRO) instrument. The new non-LTE package is demonstrated to be fast and accurate, and we hope that it will be a useful addition to the planetary community. In addition, being open source and part of the ARTS, it will be further improved and developed.

Line profiles of OB star winds using a Monte Carlo method

The solution of the radiative transfer in an expanding atmospheres using the Monte Carlo method is presented. We applied our method to winds of several OB stars. In our calculation, the velocity and density structure is assumed to be given. Selected line profiles are shown.

On the ionizing populations in GEHRs: unveiling integrated properties from the analysis of the Wolf-Rayet population

In recent years, the detection of Wolf-Rayet stars in Giant Extragalactic H ii Regions (GEHRs) has yielded several questions about our current understanding of massive stars evolution and hot expanding atmospheres, the age of the ionizing populations and their impact onto the physical properties of GEHRs. Here, we present spectrophotometric observations of four extragalactic GEHRs which show WR features in their spectra. Our goal is to reproduce simultaneously the observed WR properties and the emission-line spectra with the help of current evolutionary synthesis models.

Hydrodynamic model atmospheres for hot stars

Recent non-LTE models for expanding atmospheres, accounting for iron group line-blanketing and clumping, show a radiative acceleration which supplies a large part of the driving force of WR and O star winds. Aiming at the calculation of fully consistent wind models, we developed a method to include the solution of the hydrodynamic equations into our atmosphere code, taking into account the radiation pressure from the CMF radiation transport. In the present work we discuss the resulting wind acceleration for ‘standard’ WR and O-type star model atmospheres, and present a hydrodynamically consistent non-LTE model for the O4I(n)f star ζ Pup. In addition we demonstrate the effect of clumping on the radiative acceleration.

Spectral Analysis of the LMC [WC] Star SMP 61

HST UV and optical spectra of the early-type [WC] star SMP 61 in the LMC are analyzed by means of line blanketed non-LTE models for expanding atmospheres. The known distance to the LMC allows a reliable determination of the stellar parameters. The low iron surface abundance of the object possibly indicates a preceding evolution through a very late thermal pulse (VLTP).