标题： 南天明亮恒星在百万分之一水平上的线偏振度 显示英文标题

标题： The linear polarisation of southern bright stars measured at the parts-per-million level

摘要： 我们报告了对50颗附近南天明亮恒星的线偏振观测，其中位灵敏度为$\sim$4.4 $\times 10^{-6}$。 我们发现的偏振度更大，并且有更多的高偏振恒星，这比之前的PlanetPol北天明亮恒星调查结果更高。 这是由于银河系中平面区域的星际介质更富含尘埃，同时存在更多B型恒星，导致更多固有偏振恒星，此外还使用了对固有偏振更敏感的波长，特别是在晚型巨星中。 在之前的调查组中，只有六颗恒星显示出显著的偏振，而我们现在能够推断出超过二十颗恒星的固有偏振机制。 样本中偏振度最高的四颗恒星是四颗经典的Be星（$\alpha$ Eri，$\alpha$ Col，$\eta$ Cen 和$\alpha$ Ara）。 对于其中三颗被干涉测量解析的天体，位置角与确定的原恒星盘方向一致。 我们在样本中的大多数B型恒星中发现了显著的固有偏振；其中包括一些密近双星和一个不寻常的双星碎片盘系统。 然而这些情况并不能解释样本中所有B型恒星的高偏振度，因此探索了其他偏振产生机制。 在几颗晚型巨星中也明显表现出固有偏振，这可以归因于接近的热原恒星尘埃或这些恒星光球中的亮点。 除了少数明显的碎片盘系统外，大多数A到K型恒星的偏振水平与星际偏振一致。 显示英文摘要

摘要： We report observations of the linear polarisation of a sample of 50 nearby southern bright stars measured to a median sensitivity of $\sim$4.4 $\times 10^{-6}$. We find larger polarisations and more highly polarised stars than in the previous PlanetPol survey of northern bright stars. This is attributed to a dustier interstellar medium in the mid-plane of the Galaxy, together with a population containing more B-type stars leading to more intrinsically polarised stars, as well as using a wavelength more sensitive to intrinsic polarisation in late-type giants. Significant polarisation had been identified for only six stars in the survey group previously, whereas we are now able to deduce intrinsic polarigenic mechanisms for more than twenty. The four most highly polarised stars in the sample are the four classical Be stars ($\alpha$ Eri, $\alpha$ Col, $\eta$ Cen and $\alpha$ Ara). For the three of these objects resolved by interferometry, the position angles are consistent with the orientation of the circumstellar disc determined. We find significant intrinsic polarisation in most B stars in the sample; amongst these are a number of close binaries and an unusual binary debris disk system. However these circumstances do not account for the high polarisations of all the B stars in the sample and other polarigenic mechanisms are explored. Intrinsic polarisation is also apparent in several late type giants which can be attributed to either close, hot circumstellar dust or bright spots in the photosphere of these stars. Aside from a handful of notable debris disk systems, the majority of A to K type stars show polarisation levels consistent with interstellar polarisation.