Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, Sydney, New South Wales 2006, Australia.
Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark.
Nature. 2016 Jan 21;529(7586):364-7. doi: 10.1038/nature16171. Epub 2016 Jan 4.
Magnetic fields play a part in almost all stages of stellar evolution. Most low-mass stars, including the Sun, show surface fields that are generated by dynamo processes in their convective envelopes. Intermediate-mass stars do not have deep convective envelopes, although 10 per cent exhibit strong surface fields that are presumed to be residuals from the star formation process. These stars do have convective cores that might produce internal magnetic fields, and these fields might survive into later stages of stellar evolution, but information has been limited by our inability to measure the fields below the stellar surface. Here we report the strength of dipolar oscillation modes for a sample of 3,600 red giant stars. About 20 per cent of our sample show mode suppression, by strong magnetic fields in the cores, but this fraction is a strong function of mass. Strong core fields occur only in red giants heavier than 1.1 solar masses, and the occurrence rate is at least 50 per cent for intermediate-mass stars (1.6-2.0 solar masses), indicating that powerful dynamos were very common in the previously convective cores of these stars.
磁场在恒星演化的几乎所有阶段都起着作用。大多数低质量恒星，包括太阳，其表面磁场是由其对流包层中的发电机过程产生的。中等质量的恒星没有深对流包层，但有 10%的恒星表现出强烈的表面磁场，这些磁场被认为是恒星形成过程的残余。这些恒星确实有对流核心，可能产生内部磁场，这些磁场可能在恒星演化的后期存活下来，但由于我们无法测量恒星表面以下的磁场，信息受到限制。在这里，我们报告了一个包含 3600 颗红巨星的样本的偶极振荡模式的强度。我们的样本中约有 20%的样本显示出模式抑制，这是由于核心中的强磁场造成的，但这一分量强烈依赖于质量。强核心场仅出现在质量大于 1.1 个太阳质量的红巨星中，而对于中等质量恒星（1.6-2.0 个太阳质量），发生率至少为 50%，这表明在这些恒星以前的对流核心中，强大的发电机非常普遍。
