Rotation- and temperature-dependence of stellar latitudinal differential rotation
Rotation- and temperature-dependence of stellar latitudinal differential rotation
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恒星纬度差自转的旋转和温度依赖性
DOI：
10.1051/0004-6361:20053911
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发表时间：
2005
影响因子：
6.5
通讯作者：
A. Reiners
中科院分区：
文献类型：
--
作者：
A. Reiners
获得了 600 多个光谱类型 F 及以后的恒星的高分辨率光谱，以便寻找线剖面中微分旋转的特征。可以测量 147 颗恒星的自转规律，其中 28 颗恒星被发现存在差异自转。与光谱类型 A 的恒星的旋转定律进行比较表明，差分旋转在 HR 图中的对流边界处开始；没有比对流边界热得多的恒星表现出差分旋转的特征。四颗靠近对流边界且位于 $v\,\sin{i} \约 100$ km s -1 的晚期 A/早期 F 型恒星在一天左右的短自转周期内显示出异常强烈的绝对切变。这表明这是由于它们的对流区深度较小并且与表面速度的狭窄范围有关；这四颗星的 T eff 和 $v\,\sin{i}$ 非常相似。分析了不同温度和旋转速度的恒星中差分旋转的检测频率 $\alpha = \Delta\Omega/\Omega > 0$。可测量的差动旋转在晚型恒星和慢速旋转体中更为常见。绝对剪切强度、$\Delta\Omega$ 和微分旋转 α 被检查为恒星有效温度和旋转周期的函数。 $\Delta\Omega$ 的最高值出现在两到三天之间的轮换周期内。在较慢的旋转器中，给定旋转速率 $\Delta\Omega_{\rm max}$ 下的最强绝对剪切大约由 $\Delta\Omega_{\rm max} \propto P^{-1}$ 给出，即 $\alpha_{\rm max} \approx$ const。在更快的旋转器中，$\alpha_{\rm max}$ 和 $\Delta\Omega_{\rm max}$ 减小得较慢。与后来光谱类型恒星的差分旋转测量的比较表明，F星比较冷的恒星表现出更强的剪切力，并且绝对剪切力$\Delta\Omega$随温度的上限与多普勒成像测量中发现的温度缩放定律一致。
More than 600 high resolution spectra of stars with spectral type F and later were obtained in order to search for signatures of differential rotation in line profiles. In 147 stars the rotation law could be measured, with 28 of them found to be differentially rotating. Comparison to rotation laws in stars of spectral type A reveals that differential rotation sets in at the convection boundary in the HR-diagram; no star that is significantly hotter than the convection boundary exhibits the signatures of differential rotation. Four late A-/early F-type stars close to the convection boundary and at $v\,\sin{i} \approx 100$ km s -1 show extraordinarily strong absolute shear at short rotation periods around one day. It is suggested that this is due to their small convection zone depth and that it is connected to a narrow range in surface velocity; the four stars are very similar in T eff and $v\,\sin{i}$. Detection frequencies of differential rotation $\alpha = \Delta\Omega/\Omega > 0$ were analyzed in stars with varying temperature and rotation velocity. Measurable differential rotation is more frequent in late-type stars and slow rotators. The strength of absolute shear, $\Delta\Omega$, and differential rotation α are examined as functions of the stellar effective temperature and rotation period. The highest values of $\Delta\Omega$ are found at rotation periods between two and three days. In slower rotators, the strongest absolute shear at a given rotation rate $\Delta\Omega_{\rm max}$ is given approximately by $\Delta\Omega_{\rm max} \propto P^{-1}$, i.e., $\alpha_{\rm max} \approx$ const. In faster rotators, both $\alpha_{\rm max}$ and $\Delta\Omega_{\rm max}$ diminish less rapidly. A comparison with differential rotation measurements in stars of later spectral type shows that F-stars exhibit stronger shear than cooler stars do and the upper boundary in absolute shear $\Delta\Omega$ with temperature is consistent with the temperature-scaling law found in Doppler Imaging measurements.