Evolutions of CHCN abundance in molecular clumps  

作　　者：Zhen-Zhen He Guang-Xing Li Chao Zhang 

机构地区：[1]Department of Astronomy,Yunnan University,Kunming 650091,China [2]South-Western Institute For Astronomy Research,Yunnan University,Kunming 650091,China

出　　处：《Research in Astronomy and Astrophysics》2021年第8期245-252,共8页天文和天体物理学研究（英文版）

基　　金：support from the National Natural Science Foundation of China (Grant Nos.W820301904 and 12033005)。

摘　　要：To investigate the effects of massive star evolution on surrounding molecules,we select nine massive clumps previously observed with the Atacama Pathfinder Experiment(APEX) telescope and the Submillimeter Array(SMA) telescope.Based on the observations of APEX,we obtain luminosity to mass ratios Lclump/Mclump that range from 10 to 154 L_(⊙)/M_(⊙),where some of them embedded ultra compact(UC) H Ⅱ region.Using the SMA,CH3CN(12K-11K) transitions were observed toward nine massive starforming regions.We derive the CH3CN rotational temperature and column density using the XCLASS program,and calculate its fractional abundance.We find that CH3CN temperature seems to increase with the increase of Lclump/Mclump when the ratio is between 10 to 40 L_(⊙)/M_(⊙),then decrease when L_(clump)/M_(clump)≥ 40 L_(⊙)/M_(⊙).Assuming that the CH3CN gas is heated by radiation from the central star,the effective distance of CH3CN relative to the central star is estimated.The distance ranges from - 0.003 to - 0.083 pc,which accounts for - 1/100 to - 1/1000 of clump size.The effective distance increases slightly as Lclump/Mclump increases(Reff-(L_(clump)/M_(clump))0.5±0.2).Overall,the CH3 CN abundance is found to decrease as the clumps evolve,e.g.,XCH3CN -(L_(clump)/M_(clump))-1.0±0.7.The steady decline of CH3CN abundance as the clumps evolution can be interpreted as a result of photodissociation.

关 键 词：line:identification stars:evolution stars:formation ISM:molecules submillimeter:ISM 

分 类 号：P152[天文地球—天文学]