Magnetic configurations, stable on the long term, appear to exist in various evolutionary phases, from Main-Sequence stars to white dwarfs and neutron stars. The large scale ordered nature of these fields, often approximately dipolar, and their scaling according to the flux conservation scenario favor the model of a fossil field (Duez et al. 2010). We make some first estimates of the magnetic coupling between the stellar cores and the outer layers in red giants and supergiants. Analytical expressions of the truncation radius of the field coupling are established for a convective envelope and for a rotating radiative zone with horizontal turbulence. The timescales of the internal exchanges of angular momentum are considered.
Numerical estimates are made on the basis of recent model grids. The direct magnetic coupling of the core to the extended convective envelope of red giants and supergiants appears unlikely. However, we find that the intermediate radiative zone is fully coupled to the core during the He-burning and later phases. This coupling is able to produce a strong spin down of the core of red giants and supergiants, also leading to relatively slowly rotating stellar remnants, like white dwarfs and pulsars. Some angular momentum is also transferred to the outer convective envelope of red giants and supergiants during the He-burning phase and later.
The red hypergiant VY CMa and the more typical red supergiant Betelgeuse provide clear observational evidence for discrete, directed gaseous outflows in their optical and infrared imaging, spectra, and light curves. In the very luminous VY CMa, mass loss estimates from the infrared bright knots and clumps, not only dominate its measured overall mass loss, but explain it. In the lower luminosity Betelgeuse, similar mass estimates of its circumstellar condensations show that they contribute significantly to its measured mass loss rate. We present new measurements for both stars and discuss addit…
Context. Red supergiants are observed to undergo vigorous mass-loss. However, to date, no theoretical model has succeeded in explaining the origins of these objects' winds. This strongly limits our understanding of red supergiant evolution and Type II-P and II-L supernova progenitor properties. Aims. We examine the role that vigorous atmospheric turbulence may play in initiating and determining the mass-loss rates of red supergiant stars. Methods. We analytically and numerically solve the equations of conservation of mass and momentum, which we later couple to an atmospheric temperature struct…
在一些早期类型的恒星表面的磁场已被直接检测到。这些场的量值在几百G到几kG之间。我们研究了磁制动对自转（$\upsilon_{\rm ini}$ =200 km s $^{-1}$）10 M $_\odot$恒星模型在主序相太阳金属丰度演化的影响.根据ud-Doula等人对磁风约束的二维MHD模拟推导出的形式，磁制动过程被包含在我们的恒星模型中。关于恒星内部的磁场大小和角动量输运机制的效率，我们做了各种各样的假设。当磁制动发生在模型与差动旋转，强烈和快速的混合是在表面获得伴随着在表面速度的快速降低。这样的过程可以解释一些MS星表现出强烈的混合和低表面速度。当固体旋转被施加在内部时，恒星被如此迅速地减速，以至于表面富集比没有磁制动的类似模型要小。在这两种模型（差分或均匀旋转），磁制动由于几个100 G的字段显着降低了角动量的核心在MS阶段。这种减少在固体旋转模型中要大得多。
Fast yellow pulsating supergiants (FYPS) are a recently-discovered class of evolved massive pulsator. As candidate post-red supergiant objects, and one of the few classes of pulsating evolved massive stars, these objects have incredible potential to change our understanding of the structure and evolution of massive stars. Here we examine the lightcurves of a sample of 126 cool supergiants in the Magellanic Clouds observed by the Transiting Exoplanet Survey Satellite (\tess~) in order to identify pulsating stars. After making quality cuts and filtering out contaminant objects, we examine the di…
Yellow supergiants as supernova progenitors: an indication of strong mass loss for red supergiants?
观测到的超新星事件越来越多，这使得在存档图像中更频繁地发现祖星成为可能。在少数情况下，祖先恒星是黄超巨星。这些恒星在赫罗图中的估计位置与经典单星模型的理论轨道不相容。根据几位作者的说法，红超巨星阶段的质量损失率可能被低估了。我们研究了这些质量损失率的增加对12至15 M \odot恒星在其核生命结束时的位置的影响，以调和理论轨道与观察到的黄超巨星祖先。我们使用Geneva恒星演化程序对12 ~ 15 M \odot旋转恒星模型进行了计算。为了说明在RSG阶段的质量损失率的不确定性，我们增加了质量损失率的恒星（3和10倍之间的标准）在该阶段和比较恒星的演化经历这样高的质量损失率与模型计算的标准质量损失处方。我们表明，在赫兹-罗素图的模型的最终位置取决于他们在红超巨星阶段经历的质量损失。随着质量损失率的增加，我们发现一些模型在与观察到的几个超新星祖先的位置相一致的位置结束了它们的核生命。我们的结论是，增加的质量损失率（其中的物理机制仍需要澄清）允许单星模型，以再现同时估计的位置在HRD的YSG SN祖，以及SN类型。
Excitation of radial oscillations in population I (X=0.7, Z=0.02) red supergiants is investigated using the solution of the equations of radiation hydrodynamics and turbulent convection. The core helium burning stars with masses 8M_odot <= M <= 20M_odot end effective temperatures T_eff < 4000K are shown to be unstable against radial pulsations in the fundamental mode. The oscillation periods range between 45 and 1180 days. The pulsational instability is due to the kappa-mechanism in the hydrogen and helium ionization zones. Radial pulsations of stars with mass M < 15M_odot are strictly periodi…
Large scale surface convection on red supergiants (RSGs) can lead to shifts in the photocenter of the star which might be measured by Gaia and used as a new probe of the surface dynamics of these rare but important stars. Unlike brightness variations, photocenter motions would provide information on the physical scale of the convective cells. The signal would be that RSGs show an excess astrometric noise at the level of a few percent of the stellar radius. Unfortunately, we find that the excess astrometric noise level of Gaia EDR3 is roughly an order of magnitude too large to detect the predic…
Wind-fed high-mass X-ray binaries are powered by accretion of the radiatively driven wind on the compact star. Accretion-generated X-rays alter the ionization state of the wind. Because higher ionization states drive the wind less effectively, X-ray ionization may brake acceleration of the wind. This causes a decrease in the wind terminal velocity and mass flux in the direction toward the X-ray source. We study the effect of X-ray ionization on the stellar wind of B supergiants. We determine the binary parameters for which the X-ray irradiation significantly influences the stellar wind. This c…
A modest change in magnetic braking at the fully convective boundary explains cataclysmic variable evolution
Universidad Técnica Federico Santa María (UTFSM)（费德里科·圣玛丽亚技术大学）；Pontificia Universidad Católica de Valparaíso (PUCV)（瓦尔帕莱索天主教 Pontificia 大学）；University of Sheffield（谢菲尔德大学）；Yunnan Observatories, CAS（中国科学院云南天文台）；Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦阿基米德天体物理研究所）
由于红超巨星（RSG）被预测将以IIP型核心坍缩超新星（CCSN）的形式结束生命，因此需要充分了解它们在爆炸前的行为。质量损失率控制RSG向SN的演变，并对由此产生的爆炸的外观有很强的影响。为了研究质量损失率如何随恒星演化而变化，我们测量了一个同时代星团中19个RSG周围的星周物质。我们的研究表明，在RSG的整个生命周期中，质量损失率都会上升，更进化的恒星的质量损失率比早期的RSG高出40倍。有趣的是，我们还发现了在整个RSG生命周期中星周灭绝增加的证据，这意味着最进化的恒星受到的影响最严重。我们发现，如果NGC2100中最进化的RSG进入SN，这种额外的灭绝将导致祖先的初始质量被低估高达9 M $_\odot$。
Aims. We seek to understand convection in red supergiants and the mechanisms that trigger the mass loss from cool evolved stars. Methods. Linear spectropolarimetry of the atomic lines of the spectrum of $μ$ Cep reveals information well outside the wavelength range expected from previous models. This is interpreted as structures in expansion that are visible in the front hemisphere and sometimes also in the back hemisphere. We model the plasma distribution together with its associated velocities through an inversion algorithm to fit the observed linear polarization. Results. We find that suppos…
ALMA detection of CO rotational line emission in red supergiant stars of the massive young star cluster RSGC1 -- Determination of a new mass-loss rate prescription for red supergiants
