分析了近25年来Oe星HD 60848的光谱和光度变化。光谱显示经常性的，但不规则的周期增加拱星发射线。这些周期是高度不对称的，在大约6年内缓慢增加，然后在大约6个月内快速衰减。我们的分析侧重于最近的周期（2013 - 2020年）。发射峰的等效宽度和速度分离表明外盘半径的变化系数约为2.2，尽管这种变化比从光学薄开普勒盘的第一原理关系中预期的要复杂。我们观察到一方面He I 5876的强度变化与另一方面H-α和H-β的强度变化之间存在时间延迟。我们解释这种行为的两步磁盘增长的情况下，磁盘首先径向膨胀之前，其密度增加。在H-α和H I Paschen线之间也可以看到行为上的差异，后者显示出更对称的周期，类似于光度变化。在2001年、2009年和2018 - 2019年观测到的H-α发射的相当快的衰变表明，恒星的强辐射场和早期光谱类型导致盘的耗散比后期类型的Be星更快，正如理论预期的那样。我们讨论的X射线观测的恒星在高和低的发射状态。X射线光谱在两个时期都是软的，X射线通量只有轻微的不同，并且与O型星的正则Lx/Lbol关系保持一致。这些结果表明HD 60848的星周递减盘对恒星的X射线辐射基本上没有影响，后者很可能是在恒星风内部产生的。
英文摘要：
We analyse the spectroscopic and photometric variability of the Oe star HD 60848 over the last twenty five years. The spectra reveal recurrent, but irregular cycles of increased circumstellar emission lines. These cycles are highly asymmetric displaying a slow increase over about 6 years, followed by a fast decay within about 6 months. Our analysis focuses on the most recent cycle (2013 - 2020). The equivalent width and velocity separation of the emission peaks indicate variations of the outer disk radius by a factor ~ 2.2, although the variability appears more complex than expected from first principle relations for optically thin Keplerian disks. We observe a time delay between the variations of the strengths of He I 5876 on the one hand and H-alpha and H-beta on the other hand. We interpret this behaviour in a two-step disk growth scenario, where the disk first expands radially before its density increases. A difference in behaviour is also seen between H-alpha and the H I Paschen lines, with the latter displaying a more symmetric cycle, similar to the photometric variability. The rather fast decays of the H-alpha emission observed in 2001, 2009 and 2018 - 2019 suggest that the strong radiation field and early spectral type of the star lead to a faster dissipation of the disk than in later-type Be stars, as theoretically expected. We discuss X-ray observations of the star both during a high and a low-emission state. The X-ray spectrum is soft at both epochs, and the X-ray fluxes are only marginally different and remain consistent with the canonical Lx/Lbol relation of O-type stars. These results indicate that the circumstellar decretion disk of HD 60848 has essentially no impact on the star's X-ray emission, and that the latter most likely arises inside the stellar wind.
Exploring Polarized Millimeter Emission from Protoplanetary Disks with Irregular Dust Grains
Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México（墨西哥国立自治大学射电天文学与天体物理研究所）；Instituto de Astrofísica de Andalucía (IAA-CSIC)（安达卢西亚天体物理研究所）；European Southern Observatory（欧洲南方天文台）；Instituto de Astrofísica de Canarias（加那利天体物理研究所）；Nordic Optical Telescope（北欧光学望远镜）
