3个典型恒星形成区的气尘比

发布时间：2018-05-06 21:17

本文选题：恒星 + 形成　；参考：《天文学报》2017年02期

【摘要】："气尘比"(Gas to Dust Ratio,GDR)是星际气体与星际尘埃的质量之比.广泛认同的银河系气尘比值是100-150.气尘比值的大小不仅取决于星际环境,也与所考虑的尘埃成分相关.恒星形成区是恒星形成的致密分子云区域,不同的分子云,其GDR也可能不同于普遍采用的数值.此工作选择3个典型的恒星形成区进行气尘比的研究,它们分别是:大质量恒星形成活跃的猎户座(Orion)分子云,小质量恒星形成区的代表金牛座(Taurus)分子云,极少或者无恒星形成活动的Polaris分子云,对这3个天区的研究有利于了解不同辐射环境恒星形成区的气尘比变化.在此对CO谱线积分强度与氢分子柱密度之间的转换系数X_(CO)取常数,以统计的方法计算了3个分子云的气尘比N(H)/A_V,其值在Orion天区、Taurus天区和Polaris天区分别为25、38和55(单位:10~(20)cm~(-2).mag~(-1)),明显高于之前人们给出的银河系平均值.根据星际尘埃模型,将N(H)/A_v转换成气体尘埃的质量比.采用被广泛接受的WD01尘埃模型(V波段的选择性消光比R_v=3.1的情况),得到3个恒星形成区的气尘比分别为:160(Orion分子云)、243(Taurus分子云)、354(Polaris分子云),显著高于普遍采用的弥漫星际介质中100-150的取值范围.恒星形成区的N(H)/A_v值高于平均值的另外一个可能的原因是,恒星形成区的尘埃由于吸积或者碰撞增长变大,降低了V波段的单位质量消光效率,而不是气尘质量比本身的增加.
[Abstract]:Gas to Dust GDR is the mass ratio of interstellar gas to interstellar dust. The widely accepted Milky way Gas-Dust ratio is 100-150. The ratio of gas to dust depends not only on the interstellar environment, but also on the dust composition considered. Star forming region is the dense molecular cloud region of star formation. The GDR of different molecular clouds may be different from the commonly used values. Three typical star forming regions were selected to study the gas-dust ratio: the active Orion molecular cloud for massive star formation and the Taurus molecular cloud for the small mass star formation region. For the Polaris molecular clouds with little or no star formation activity, the study of these three regions is helpful to understand the variation of the gas-dust ratio in the star forming regions in different radiation environments. In this paper, the conversion coefficient between the integral intensity of CO line and the density of hydrogen molecular column is taken as the constant. The gas / dust ratios of three molecular clouds are calculated by statistical method. The values of the gas / dust ratios of the three molecular clouds are 25 ~ 38 in the Orion sky region and 55 in the Polaris sky region, respectively, which are obviously higher than the Milky way average values given before. According to interstellar dust model, N(H)/A_v is converted to mass ratio of gas and dust. Using the widely accepted WD01 dust model, the selective extinction ratio (R_v=3.1) in V band is obtained. The ratio of gas to dust in three star forming regions is: 1: 160? O? O? Range of 100-150 values in the medium. Another possible reason that the N(H)/A_v value of the star forming region is higher than the average is that the dust in the star forming region increases due to accretion or collision, which reduces the extinction efficiency per unit mass in V band, rather than the increase of the gas-dust mass ratio itself.
【作者单位】：北京师范大学天文系;
【基金】：国家自然科学基金项目(11373015,11533002) 973项目(2014CB845702) 中央高校基本科研业务费专项资助
【分类号】：P152

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