Examinando por Autor "Sundqvist, J. O."

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Acceso Abierto
Atmospheric NLTE models for the spectroscopic analysis of blue stars with winds V. Complete comoving frame transfer, and updated modeling of X-ray emission
(EDP Sciences, 2020-10-19) Puls, J.; Najarro, F.; Sundqvist, J. O.; Sen, K.; Agencia Estatal de Investigación (AEI); Research Foundation Flanders (FWO); 0000-0002-0874-1669; 0000-0002-9124-0039; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. Obtaining precise stellar and wind properties and abundance patterns of massive stars is crucial to understanding their nature and interactions with their environments, as well as to constrain their evolutionary paths and end-products. Aims. To enable higher versatility and precision of the complete ultraviolet (UV) to optical range, we improve our high-performance, unified, NLTE atmosphere and spectrum synthesis code FASTWIND. Moreover, we aim to obtain an advanced description of X-ray emission from wind-embedded shocks, consistent with alternative modeling approaches. Methods. We include a detailed comoving frame radiative transfer for the essential frequency range, but still apply methods that enable low turnaround times. We compare the results of our updated computations with those from the alternative code CMFGEN, and our previous FASTWIND version, for a representative model grid. Results. In most cases, our new results agree excellently with those from CMFGEN, both regarding the total radiative acceleration, strategic optical lines, and the UV-range. Moderate differences concern He II λλ4200-4541 and N V λλ4603-4619. The agreement regarding N III λλ4634−4640−4642 has improved, though there are still certain discrepancies, mostly related to line overlap effects in the extreme ultraviolet, depending on abundances and micro-turbulence. In the UV range of our coolest models, we find differences in the predicted depression of the pseudo-continuum, which is most pronounced around Lyα. This depression is larger in CMFGEN, and related to different Fe IV atomic data. The comparison between our new and previous FASTWIND version reveals an almost perfect agreement, except again for N V λλ4603-4619. Using an improved, depth-dependent description for the filling factors of hot, X-ray emitting material, we confirm previous analytic scaling relations with our numerical models. Conclusions. We warn against uncritically relying on transitions, which are strongly affected by direct or indirect line-overlap effects. The predicted UV-continuum depression for the coolest grid-models needs to be checked, both observationally, and regarding the underlying atomic data. Wind lines from “super-ionized” ions such as O VI can, in principle, be used to constrain the distribution of wind-embedded shocks. The new FASTWIND version v11 is now ready to be used.
Acceso Abierto
New predictions for radiation-driven, steady-state mass-loss and wind-momentum from hot, massive stars II. A grid of O-type stars in the Galaxy and the Magellanic Clouds
(EDP Sciences, 2021-04-08) Björklund, R.; Sundqvist, J. O.; Puls, J.; Najarro, F.; Agencia Estatal de Investigación (AEI); Sundqvist, J. O. [0000-0003-1729-1273]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. Reliable predictions of mass-loss rates are important for massive-star evolution computations. Aims. We aim to provide predictions for mass-loss rates and wind-momentum rates of O-type stars, while carefully studying the behaviour of these winds as functions of stellar parameters, such as luminosity and metallicity. Methods. We used newly developed steady-state models of radiation-driven winds to compute the global properties of a grid of O-stars. The self-consistent models were calculated by means of an iterative solution to the equation of motion using full non-local thermodynamic equilibrium radiative transfer in the co-moving frame to compute the radiative acceleration. In order to study winds in different galactic environments, the grid covers main-sequence stars, giants, and supergiants in the Galaxy and both Magellanic Clouds. Results. We find a strong dependence of mass-loss on both luminosity and metallicity. Mean values across the grid are Ṁ~L*2.2 and Ṁ~L*0.95; however, we also find a somewhat stronger dependence on metallicity for lower luminosities. Similarly, the mass loss-luminosity relation is somewhat steeper for the Small Magellanic Cloud (SMC) than for the Galaxy. In addition, the computed rates are systematically lower (by a factor 2 and more) than those commonly used in stellar-evolution calculations. Overall, our results are in good agreement with observations in the Galaxy that properly account for wind-clumping, with empirical Ṁ versus Z* scaling relations and with observations of O-dwarfs in the SMC. Conclusions. Our results provide simple fit relations for mass-loss rates and wind momenta of massive O-stars stars as functions of luminosity and metallicity, which are valid in the range Teff = 28 000–45 000 K. Due to the systematically lower values for Ṁ, our new models suggest that new rates might be needed in evolution simulations of massive stars.