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首页> 外文期刊>The Astrophysical journal >SEQUENTIAL STAR FORMATION IN OB ASSOCIATIONS: THE ROLE OF MOLECULAR CLOUD TURBULENCE
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SEQUENTIAL STAR FORMATION IN OB ASSOCIATIONS: THE ROLE OF MOLECULAR CLOUD TURBULENCE

机译：OB协会中的后续恒星形成：分子云湍流的作用

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摘要

Numerical simulations of shock propagation into a two-dimensional, clumpy, turbulent cloud suggest that the average shock speed, v_s, approximately equals the square root of the ratio of the external pressure to the average preshock density, ρ_0, and that the average shocked layer density, ρ_s, approximately equals the product of ρ_0 and the square of the velocity ratio, v_s/a_(turb), for postshock rms turbulent speed a_(turb). A comparison is made between seven theoretical formulations for the shock speed; all differ slightly from each other and from the measured shock speed, but usually not by more than a factor of 1.5. The maximum postshock density is much larger than the average postshock density because of the clumpy postshock structure; the maximum is comparable to ρ_0(v_s/a_(th))~2 for postshock thermal speed a_(th). These relations are useful for the interpretation of forced cloud motions and shock speeds in turbulent molecular clouds near H II regions. Preshock clumps form self-consistently by supersonic turbulence compression in the initial preshock gas. As the shock moves into the cloud, these clumps are squeezed and collected into the compressed layer, and they merge into a few massive, clumpy, postshock cores. The cores should produce bright rims in a real H II region because they protrude slightly into the ionized gas. The escape velocity in a typical model postshock core is larger than both the internal core velocity dispersion and the shock speed. Such a core would collapse gravita-tionally and ultimately form a star cluster. Stars could also form earlier when the preshock turbulent clumps collide with each other inside the postshock layer or when the clumps are squeezed by the high-pressure shock. Thus, there could be an age spread inside the triggered cluster equal to the entire age of the shock, although most of the stars will form when the massive postshock cores collapse. The separation between OB association subgroups should be related to the time for the embedded cluster to grow to such a large mass that the stellar pressures inside the core disperse the gas and halt further star formation.
机译：激波传播到二维的块状湍流云中的数值模拟表明，平均激波速度v_s近似等于外部压力与平均预激密度ρ_0之比的平方根，并且平均激波层对于震后rms湍流速度a_（turb），密度ρ_s近似等于ρ_0与速度比平方的乘积v_s / a_（turb）。对冲击速度的七个理论公式进行了比较。两者之间的差异与测得的震动速度略有不同，但通常相差不超过1.5。由于块状的余震结构，最大的余震密度比平均的余震密度大得多。震后热速度a_（th）的最大值相当于ρ_0（v_s / a_（th））〜2。这些关系对于解释H II区附近湍流分子云中的强迫云运动和激波速度很有用。预冲击团块在初始预冲击气体中通过超音速湍流压缩自洽地形成。当冲击波移入云层时，这些团块被压缩并收集到压缩层中，它们合并成几个大块的，团块状的震后岩心。磁芯应该在真实的H II区域中产生明亮的边缘，因为它们会稍微突出到离子化气体中。典型模型震后岩心中的逃逸速度大于内部岩心速度散布和冲击速度。这样的核心将引力坍塌，最终形成星团。当震前湍流团块在震后层内相互碰撞，或者当团块被高压激波挤压时，也可能形成恒星。因此，尽管大多数星将在巨大的震后岩心坍塌时形成，但在触发星团内部可能存在一个与电击整个年龄相等的时差。 OB关联子组之间的间隔应与嵌入星团生长到如此大质量的时间有关，以至于核心内部的恒星压力会分散气体并阻止进一步的恒星形成。

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