Wolf-Rayet star's winds can be so dense and so optically thick that the photosphere appears in the highly supersonic part of the outflow, veiling the underlying subsonic part of the star, and leaving the initial acceleration of the wind inaccessible to observations. We investigate the conditions and the structure of the subsonic part of the outflow of Galactic WR stars, in particular of the WNE subclass; our focus is on the conditions at the sonic point. We compute 1D hydrodynamic stellar structure models for massive helium stars adopting outer boundaries at the sonic point. We find that the outflows of our models are accelerated to supersonic velocities by the radiative force from opacity bumps either at temperatures of the order of 200kK by the Fe opacity bump or of the order of 50kK by the HeII opacity bump. For a given mass-loss rate, the conditions in the subsonic part of the outflow are independent from the detailed physical conditions in the supersonic part. The close proximity to the Eddington limit at the sonic point allows us to construct a Sonic HR diagram, relating the sonic point temperature to the L/M ratio and the stellar mass-loss rate, thereby constraining the sonic point conditions, the subsonic structure, and the stellar wind mass-loss rates from observations. The minimum mass-loss rate necessary to have the flow accelerated to supersonic velocities by the Fe opacity bump is derived. A comparison of the observed parameters of Galactic WNE stars to this minimum mass-loss rate indicates that their winds are launched to supersonic velocities by the radiation pressure arising from the Fe-bump. Conversely, models which do not show transonic flows from the Fe opacity bump form inflated envelopes. We derive an analytic criterion for the appearance of envelope inflation in the subphotospheric layers.
Fast rotating Wolf-Rayet stars are expected to be progenitors of long duration gamma-ray bursts. However, the observational test of this model is problematic. Spectral lines of Wolf-Rayet stars originate in expanding stellar wind, therefore a reliable spectroscopical determination of their rotational velocities is difficult. Intrinsic polarization of Wolf-Rayet stars due to the rotational modulation of the stellar wind may provide an indirect way to determine the rotational velocities of these stars. However, detailed wind models are required for this purpose. We determine the intrinsic polari…
The observed late-type WC Wolf-Rayet stars (WC7-9) with low luminosity below $\rm \log L/L_{\odot} < 5.4$ in the HR diagram cannot be reproduced satisfactorily by the evolutionary track of single stars. The mass transfer due to Roche lobe overflow drastically modifies the internal structure and surface compositions of two components. Therefore, binaries provide a very promising evolutionary channel to produce these WC stars.
The emission line spectra of WR stars are often formed completely in the optically thick stellar wind. Hence, any assumption on the wind velocity law in a spectral analysis has a profound impact on the determination of the stellar parameters. By comparing Potsdam Wolf-Rayet (PoWR) model spectra calculated with different $β$ laws, we show that the velocity field heavily influences the spectra: by using the appropriate $β$ laws, the entire range of late and early types can be covered with the same stellar model.
Wolf-Rayet stars are amongst the rarest but also most intriguing massive stars. Their extreme stellar winds induce famous multi-wavelength circumstellar gas nebulae of various morphologies, spanning from circles and rings to bipolar shapes. This study is devoted to the investigation of the formation of young, asymmetric Wolf-Rayet gas nebulae and we present a 2.5-dimensional magneto-hydrodynamical toy model for the simulation of Wolf-Rayet gas nebulae generated by wind-wind interaction. Our method accounts for stellar wind asymmetries, rotation, magnetisation, evolution and mixing of materials…
Mid-infrared photometry of the Wolf-Rayet star HD 38030 in the Large Magellanic Cloud from the NEOWISE-R mission show it to have undergone a dust-formation episode in 2018 and the dust to have cooled in 2019-20. New spectroscopy with the MagE spectrograph on the Magellan I Baade Telescope in 2019 and 2020 show absorption lines attributable to a companion of type near O9.7III-IV. We found a significant shift in the radial velocity of the C IV 5801-12 blend compared with the RVs measured in 1984 and 1993. The results combine to suggest that HD 38030 is a colliding-wind binary having short-lived …
A Study of Wolf-Rayet stars Formed via Chemically Homogeneous Evolution
利用恒星演化程序-恒星天体物理实验模块（MESA），研究了具有不同自转速度和金属丰度的大质量恒星向Wolf-Rayet星的演化.在我们的模拟中，初始旋转速度取为0，250，500和650 km s $^{-1}$，金属丰度等于0.02，0.014，0.008，0.006，0.004和0.002。我们在HR图中显示了我们的快速旋转模型与观测结果的比较。我们发现在高金属丰度时，旋转混合的效率较低，当中心的氦被点燃时，这些恒星成为Wolf-Rayet（WR）星。然而，快速旋转的低金属丰度大质量恒星很容易演化成WR星，因为旋转导致了化学均匀的演化。这可以解释低金属丰度星系中单个WR星的起源。在我们的模型中，观测到的SMC WR星与单星演化模型是一致的。然而，在更高的金属丰度，我们的单星演化模型只能解释发光，富氢的WN星和O星（以前被归类为WR星）。
It is now well established that the majority of massive stars reside in multiple systems. However, the effect of multiplicity is not sufficiently understood, resulting in a plethora of uncertainties about the end stages of massive-star evolution. In order to investigate these uncertainties, it is useful to study massive stars just before their demise. Classical Wolf-Rayet stars represent the final end stages of stars at the upper-mass end. The multiplicity fraction of these stars was reported to be ${\sim}0.4$ in the Galaxy but no correction for observational biases has been attempted. The aim…
Wolf-Rayet stars are advanced evolutionary stages of massive stars. Despite their large mass-loss rates and high wind velocities, none of them display a bow shock, although a fraction of them are classified as runaway. Our 2.5-D numerical simulations of circumstellar matter around a 60Mo runaway star show that the fast Wolf-Rayet stellar wind is released into a wind-blown cavity filled with various shocks and discontinuities generated throughout the precedent evolutionary phases. The resulting fast-wind slow-wind interaction leads to the formation of spherical shells of swept-up dusty material…
WR~102-1 was detected by Suzaku as a conspicuous point source in the 6.7 keV intensity map of the central region of the Milky Way. The source was suggested as a possible Wolf-Rayet binary based on its X-ray and infrared spectral characteristics. The iron line emission is expected to originate in the Wolf-Rayet star's dynamic stellar-wind when colliding the companion's mild stellar wind. Here, we report the result of a long-term X-ray monitoring of WR~102-1 since 1998 using archival data of ASCA, XMM-Newton, Chandra, Suzaku, and Swift to reveal variations of the iron K-emission line and the cir…
沃尔夫-拉叶星（WR）是大质量（$\geq$ 10 M $_{\odot}$）演化的恒星，在其核心经历高级核燃烧，迅速接近超新星生命的终点。它们强大的风使星际介质富含重元素，为未来的恒星提供原材料。我们简要总结了WR星的高能过程，主要集中在它们的X射线发射。我们提出了新的结果，从钱德拉观测的食WR+O二进制CQ Cep覆盖一个完整的轨道，严格测试X射线发射模型。
