螺旋臂中的恒星复合体和超级云链
On the chains of star complexes and superclouds in spiral arms
摘要：
本文研究了螺旋臂中规则星簇链的出现与超级云的关系以及超级云的其它性质。一串规则的恒星复合体位于M31的西北臂;它们的大小大约相同，为0.6 kpc，间距为1.1 kpc。Beck等人（1989）在同一臂段内发现了波长为2.3kpc的规则磁场。我们注意到这个波长是复合体之间间距的两倍，并认为它们是由于沿着臂发展的磁引力不稳定性而形成的。在这个NW臂中，恒星复合体位于气体尘埃带内，而在M31的西南臂中，气体尘埃带位于明亮而均匀的恒星臂的上游。在西南旋臂中发现了年龄梯度的证据，所有这些都是螺旋激波的特征，这可能与西南旋臂段异常大的俯仰角（对于M31）有关。这样的冲击可能会阻止规则磁场的形成，这可能解释了那里没有恒星复合体的原因。在其他几个星系的旋臂中观察到了激波特征和恒星复合体存在之间的反相关。螺旋臂中的恒星复合体和超级云的规则链是罕见的，这可能意味着它们的形成涉及一个相当特定的机制，最有可能的是帕克-金斯不稳定性。本文简要讨论了银河系的旋涡结构，它的外围可能是M101型。在船底座臂和天鹅座（外）臂中发现了规则的HI超云双峰间距，这可能是这些臂上规则磁场的间接证据。
英文摘要：
The relation is studied between occurrence of a regular chain of star complexes and superclouds in a spiral arm, and other properties of the latter. A regular string of star complexes is located in the north-western arm of M31; they have about the same size 0.6 kpc with spacing of 1.1 kpc. Within the same arm segment the regular magnetic field with the wavelength of 2.3 kpc was found by Beck et al. (1989). We noted that this wavelength is twice as large as the spacing between complexes and suggested that they were formed in result of magneto-gravitational instability developed along the arm. In this NW arm, star complexes are located inside the gas-dust lane, whilst in the south-western arm of M31 the gas-dust lane is upstream of the bright and uniform stellar arm. Earlier, evidence for the age gradient has been found in the SW arm. All these are signatures of a spiral shock, which may be associated with unusually large (for M31) pitch-angle of this SW arm segment. Such a shock may prevent the formation of the regular magnetic field, which might explain the absence of star complexes there. Anti-correlation between shock wave signatures and presence of star complexes is observed in spiral arms of a few other galaxies. Regular chains of star complexes and superclouds in spiral arms are rare, which may imply that a rather specific mechanism is involved in their formation, and the most probable one is the Parker-Jeans instability. The spiral pattern of our Galaxy is briefly discussed; it may be of M101 type in the outer parts. The regular bi-modal spacing of HI superclouds is found in Carina and Cygnus (Outer) arms, which may be an indirect evidence for the regular magnetic field along these arms.
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