Disks and winds around hot stars: new insights from multi-wavelength spectroscopy and interferometry
E. S. G. de Almeida
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PhD Thesis, Université Côte d'Azur, Observatoire de la Côte d'Azur, 2020, 300 pages, in English. Abstract shortened to fit within arXiv character limit
Hot stars are the main source of ionization of the interstellar medium and its enrichment due to heavy elements. Constraining the physical conditions of their environments is crucial to understand how these stars evolve and their impact on the evolution of galaxies. The objective of my thesis was to investigate the physical properties of the photosphere and circumstellar environment of massive hot stars confronting multi-band spectroscopic or spectro-interferometric observations and sophisticated non-LTE radiative transfer codes. My work was focused on two main lines of research. The first concerns radiative line-driven winds. Using UV and visible spectroscopic data and the radiative transfer code CMFGEN, I investigated the weak wind phenomenon on a sample of nine Galactic O stars. This study shows for the first time that the weak wind phenomenon, originally found for O dwarfs, also exists on more evolved O stars and that future studies must evaluate its impact on the evolution of massive stars. My other line of research concerns the study of classical Be stars, the fastest rotators among the non-degenerated stars, and which are surrounded by rotating equatorial disks. I studied the Be star $ο$ Aquarii using H$α$ (CHARA/VEGA) and Br$γ$ (VLTI/AMBER) spectro-interferometric observations, the radiative transfer code HDUST, and developing new automatic procedures to better constrain the kinematics of the disk. This multi-band study allowed to draw the most detailed picture of this object and its environment, to test the limits of the current generation of radiative transfer models, and paved the way to my future work on a large samples of Be stars observed with VEGA, AMBER, and the newly available VLTI mid-infrared combiner MATISSE.
Red supergiants (RSGs) are evolved massive stars in a stage preceding core-collapse supernova. Understanding evolved-phases of these cool stars is key to understanding the cosmic matter cycle of our Universe, since they enrich the cosmos with newly formed elements. However, the physical processes that trigger mass loss in their atmospheres are still not fully understood, and remain one of the key questions in stellar astrophysics. We use a new method to study the extended atmospheres of these cold stars, exploring the effect of a stellar wind for both a simple radiative equilibrium model and a…
The winds of hot, massive stars are variable from processes happening on both large and small spatial scales. A particular case of such wind variability is 'discrete-absorption components' (DACs) that manifest themselves as outward moving density features in UV resonance line spectra. Such DACs are believed to be caused by large-scale spiral-shaped density structures in the stellar wind. We consider novel 3-D radiation-hydrodynamic models of rotating hot star winds and study the emergence of co-rotating spiral structures due to a local (pseudo-)magnetic spot on the stellar surface. Subsequentl…
Line-driven winds of hot, luminous stars are intrinsically unstable due to the line-deshadowing instability (LDI). In non-magnetic hot stars, the LDI leads to the formation of an inhomogeneous wind consisting of small-scale, spatially separated clumps that can have great effects on observational diagnostics. However, for magnetic hot stars the LDI generated structures, wind dynamics, and effects on observational diagnostics have not been directly investigated so far. We investigated the non-linear development of LDI generated structures and dynamics in a magnetic line-driven wind of a typical …
3-D Radiative Transfer Modeling of Structured Winds in Massive Hot Stars with Wind3D
利用Wind3D辐射转移（RT）程序，我们建立了大质量热星结构风的三维模型。我们研究了在B型超巨星HD 64760的风中观测到的大尺度结构的物理性质，并对Si IV λ1395中的离散吸收分量（DAC）和转动调制进行了详细的线轮廓拟合。我们开发参数化输入模型Wind3D与大规模的赤道风密度和速度结构，或所谓的“同向旋转相互作用区”（CIR）和“旋转调制区”（RMR）。参数化模型提供了高性能RT计算从头算流体动力学输入模型的重要优势。输入模型计算的加速使我们能够模拟和研究大质量热恒星扩展风中的各种物理条件。新的建模方法是非常灵活的约束HD 64760中的RMR的动态和几何风特性。我们计算的调制产生的径向密度增强，几乎线性地突出到赤道风的规则模式。我们发现，调制所造成的狭窄的“辐条状”风区。我们提出的流体动力学模型表明，线性形状的径向风图案可以引起的机械波作用在底部的恒星风从蓝超巨星。
Mapping Wolf-Rayet winds with spectro-interferometry I. Detection of multiple co-rotating interaction regions in WR 6
KU Leuven（荷语鲁汶大学）；NSF NOIRLab（美国国家光学-红外天文研究实验室）；European Southern Observatory（欧洲南方天文台）；Macquarie University（麦考瑞大学）；Université de Montréal（蒙特利尔大学）；Zentrum für Astronomie der Universität Heidelberg（海德堡大学天文学中心）；Embry-Riddle Aeronautical University（埃姆布里-里德尔航空大学）
Models for Weak Wind and Momentum Problems in the Winds of Hot Stars
我们提出了热星风超音速部分的速度结构模型，以估计密度和速度聚集的影响。使用XSTAR（Kallman，2018）计算Sobolev近似下谱线（力倍增器FM）中的辐射压力（Castor等人，1975 CAK; Stevens和Kallman，1990）。FM计算为两个参数的函数：Xi和t。线力包含在动量方程和质量守恒中。这些被集成在超音速部分的风的一个样本的OB-和WR-明星。用速度定律进行拟合，得到质量损失率和流出速度作为输出。亚音速部分的边界条件和速度定律用β定律公式（β = 0.6，Vin = 10 km/s）近似。据发现，WR-星，由于其大的吸收，已经在r/Rstar = 1.01辐射光谱缺乏软X射线低于230埃（氦II电离）。这一关键事实将力乘数提高了10倍，使其能够在CAK框架中加速风。因此，动量问题是一个不透明度问题（Gayley et al.，1995）。OB-stars的结果指向中等密度的聚集（Fvol=0.13）。此外，主序星OB需要速度聚集（Fvel=0.1，Sundqvist et al 2014）。这可以解释弱风的问题。
In the regime of hot stars, winds were not seen as a common thing until the era of UV astronomy. Since we have access to the UV wavelength range, it has become clear that winds are not an exotic phenomenon limited to some special objects, but actually ubiquitous among hot and massive stars. The opacities due to spectral lines are the decisive ingredient that allows hot, massive stars to launch powerful winds. While the fundamental principles of these so-called line-driven winds have been realized decades ago, their proper quantitative prediction is still a major challenge today. Established th…
Atmospheric escape of close-in exoplanets can be driven by high energy radiation from the host star. The planetary outflows interacting with the stellar wind may generate observable transit signals that depend on the strength of the stellar wind. We perform detailed radiation-hydrodynamics simulations of the atmospheric escape of hot Jupiters with including the wind from the host star in a self-consistent, dynamically coupled manner. We show that the planetary outflow is shaped by the balance between its thermal pressure and the ram pressure of the stellar wind. We use the simulation outputs t…
We present an analysis of Chandra grating spectra of key helium-like line complexes to put constraints on the location with respect to the photosphere of the hottest ($T \gtrsim{6 \times 10^6}$ K) plasma in the wind of the O supergiant zeta Pup and to explore changes in the 18 years between two sets of observations of this star. We fit two models -- one empirical and one wind-shock-based -- to the S XV, Si XIII, and Mg XI line complexes and show that an origin in the wind flow, above $r \approx 1.5$ R$_{\ast}$, is strongly favored over an origin less than 0.3 R$_{\ast}$ above the photosphere (…
