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arXiv 1610.00543astro-ph.SR
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磁化介质中热大质量恒星的弓形激波星云

Bow shock nebulae of hot massive stars in a magnetized medium

D. M. -A. Meyer, A. Mignone, R. Kuiper, A. Raga, W. Kley

摘要:

相当一部分的OB型主序星被归类为逃逸恒星,并以超音速运动通过星际介质(ISM)。它们强烈的恒星风与周围环境相互作用,在那里,局部ISM磁场的典型强度约为3.5-7微G,这可能导致弓形激波星云的形成。我们调查这样的磁场的影响,与流动的运动,对这些拱星结构的形成和发射特性。我们的轴对称,磁流体动力学模拟与光学薄辐射冷却,加热和各向异性热传导表明,背景ISM磁场的存在下,影响我们的弓冲击在哈和[OIII] lambda 5007,分别成为约1-2个数量级的微弱的投影光发射。对尘埃不透明度的辐射转移计算表明,磁场稍微减少了它们投射的红外辐射,我们的弓形激波在60微米处发出明亮的辐射。这也许可以解释为什么电离逃逸的大质量恒星产生的弓形激波通常很难被识别。最后,我们讨论了我们的研究结果的背景下的弓激波的Zeta蛇夫座,我们支持解释其不完美的形态作为证据的存在的ISM磁场不对齐的运动,其驱动星。

英文摘要:

A significant fraction of OB-type, main-sequence massive stars are classified as runaway and move supersonically through the interstellar medium (ISM). Their strong stellar winds interact with their surroundings where the typical strength of the local ISM magnetic field is about 3.5-7 micro-G, which can result in the formation of bow shock nebulae. We investigate the effects of such magnetic fields, aligned with the motion of the flow, on the formation and emission properties of these circumstellar structures. Our axisymmetric, magneto-hydrodynamical simulations with optically-thin radiative cooling, heating and anisotropic thermal conduction show that the presence of the background ISM magnetic field affects the projected optical emission our bow shocks at Ha and [OIII] lambda 5007 which become fainter by about 1-2 orders of magnitude, respectively. Radiative transfer calculations against dust opacity indicate that the magnetic field slightly diminishes their projected infrared emission and that our bow shocks emit brightly at 60 micron. This may explain why the bow shocks generated by ionizing runaway massive stars are often difficult to identify. Finally, we discuss our results in the context of the bow shock of Zeta Ophiuchi and we support the interpretation of its imperfect morphology as an evidence of the presence of an ISM magnetic field not aligned with the motion of its driving star.

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