标题： 分辨率和氦丰度对A型恒星表面对流模拟的影响 显示英文标题

标题： Effects of resolution and helium abundance in A star surface convection simulations

摘要： 我们展示了使用ANTARES代码对A型恒星表面层全可压缩对流的二维辐射流体动力学模拟结果。 光谱指示剂显示，在Teff ~8000 K附近速度达到最大值。在这个范围内，Am星子类中的测量值最大。 迄今为止，无论是理论模型还是数值模型，都无法精确再现这个温度范围内尖线A型星和Am型星的线轮廓。 一般来说，A型星的氦丰度无法从观测中得知。 因此，我们在模拟中考虑了两种极端情况：以太阳氦丰度为上限，零氦丰度为下限。 发现无氦情况下模拟的结果与太阳氦丰度情况相比，具有更大的速度、更大的流动结构，并且氢电离区内的动能能量流出现符号反转。 这两种模拟都显示出从光学表面延伸出的激波前沿，以及远低于氢部分电离区域的混合现象，并且在初始扰动被抑制后出现垂直振荡。 我们讨论了A型恒星表面快速辐射冷却相关的问题，如分辨率和有效弛豫。 目前的工作被视为对A至F型恒星对流系统研究的一个步骤，受到来自脉动变星探测任务和高分辨率光谱学为这些天体提供新数据的推动。 显示英文摘要

摘要： We present results from 2D radiation-hydrodynamical simulations of fully compressible convection for the surface layers of A-type stars with the ANTARES code. Spectroscopic indicators for photospheric convective velocity fields show a maximum of velocities near Teff ~8000 K. In that range the largest values are measured for the subgroup of Am stars. Thus far, no prognostic model, neither theoretical nor numerical, is able to exactly reproduce the line profiles of sharp line A and Am stars in that temperature range. In general, the helium abundance of A stars is not known from observations. Hence, we have considered two extreme cases for our simulations: a solar helium abundance as an upper limit and zero helium abundance as a lower limit. The simulation for the helium free case is found to differ from the case with solar helium abundance by larger velocities, larger flow structures, and by a sign reversal of the flux of kinetic energy inside the hydrogen ionisation zone. Both simulations show extended shock fronts emerging from the optical surface, as well as mixing far below the region of partial ionisation of hydrogen, and vertical oscillations emerging after initial perturbations have been damped. We discuss problems related to the rapid radiative cooling at the surface of A-type stars such as resolution and efficient relaxation. The present work is considered as a step towards a systematic study of convection in A- to F-type stars, encouraged by the new data becoming available for these objects from both asteroseismological missions and from high resolution spectroscopy.