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arXiv 0804.2491astro-ph
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前主序星双星系统HD 155555的两个分量的差旋

Differential rotation on both components of the pre main-sequence binary system HD 155555

N. J. Dunstone, G. A. J. Hussain, A. Collier Cameron, S. C. Marsden, M. Jardine, J. R. Barnes, J. C. Ramirez Vlex, J. -F. Donati

摘要:

本文首次测量了一个前主序星双星系统的表面差异自转。使用强度(斯托克斯I)和圆偏振(斯托克斯V)时间序列光谱,在英澳望远镜(AAT)的11个晚上,我们将太阳般的微分旋转定律的表面成像过程。我们发现年轻的1800万年前的HD 155555(V824 Ara,G5IV + K0IV)双星系统的两个组成部分都表现出显著的差旋。根据强度谱确定的赤道极圈时间,主星为80天,主星为163天。同样的磁谱,我们得到的44和71天的赤道极laptimes分别,表明剪切的磁性区域的时间尺度大约是一半的恒星斑点。因此,这两个组成部分被发现有类似于那些相同的光谱类型的主序星的差分旋转率。因此,HD 155555的结果与其他更演化的双星系统中发现的结果形成对比,这些双星系统中发现的差异旋转可以忽略不计或很弱。我们讨论了两种可能的解释,首先,在年龄的HD 155555二进制潮汐力还没有时间来抑制差分旋转,其次,弱差分旋转以前观察到的演化双星是一个后果,其大对流区深度。我们认为,后者是更可能的解决方案,并表明温度和对流区深度(从演化模型)是很好的预测差分旋转强度。最后,我们还研究了双星日冕相互作用的测量差异旋转的可能后果。

英文摘要:

We present the first measurements of surface differential rotation on a pre-main sequence binary system. Using intensity (Stokes I) and circularly polarised (Stokes V) timeseries spectra, taken over eleven nights at the Anglo-Australian Telescope (AAT), we incorporate a solar-like differential rotation law into the surface imaging process. We find that both components of the young, 18 Myr, HD 155555 (V824 Ara, G5IV + K0IV) binary system show significant differential rotation. The equator-pole laptimes as determined from the intensity spectra are 80 days for the primary star and 163 days for the secondary. Similarly for the magnetic spectra we obtain equator-pole laptimes of 44 and 71 days respectively, showing that the shearing timescale of magnetic regions is approximately half that found for stellar spots. Both components are therefore found to have rates of differential rotation similar to those of the same spectral type main sequence single stars. The results for HD 155555 are therefore in contrast to those found in other, more evolved, binary systems where negligible or weak differential rotation has been discovered. We discuss two possible explanations for this; firstly that at the age of HD 155555 binary tidal forces have not yet had time to suppress differential rotation, secondly that the weak differential rotation previously observed on evolved binaries is a consequence of their large convection zone depths. We suggest that the latter is the more likely solution and show that both temperature and convection zone depth (from evolutionary models) are good predictors of differential rotation strength. Finally, we also examine the possible consequences of the measured differential rotation on the interaction of binary star coronae.

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