The High Resolution Observations And Studies Of Massive Star-forming Region ”Orion KL”

The Orion KLeinmann-Low?Orion KL?nebula is the closest?414±7 pc?site of massive star formation.This region is complex with many remarkable objects?hot core,compact ridge,extended ridge and plateau?,and is a molecular line-rich object.As an ideal source for studies of the physical and chemical properties of high-mass star-forming regions,it has attracted considerable attention.But the heating source within the Orion KL hot core is uncertain.In this thesis,we present high spatial resolution AL-MA observations of vibrational transitions of HC₃N toward Orion KL in 214–247 GHz frequency band.41 transitions of HC₃N in 7 vibrationally excited states and 23 tran-sitions of¹³C isotopologues of HC₃N in two vibrational states are detected.The line images show that vibrationally excited HC₃N lines originate mainly from Orion hot core and IRc7.Based on multiple transitions of each vibrationally excited state,we per-formed local thermodynamic equilibrium calculations in XCLASS suite toward hot core and IRc7 positions.Generally,transitions in highly excited states have higher rotational temperatures and lower column densities.The rotational temperatures and column den-sities of the hot core range from 93 to 321 K,and from 1.0×10¹⁴to 4.9×10¹⁶cm^-2,respectively.Lower rotational temperatures ranging from 88 to 186 K and column den-sities from 1.0×10¹⁴to 3.2×10¹⁶cm^-2are obtained toward IRc7.The fact that the hot core emission peaks of vibrationally excited HC₃N lines move from south to northeast with increasing E_uand that higher energy HC₃N lines have higher rotational temper-atures and lower column densities,appears to support that the hot core is externally heated.The emission peaks are moving along the major axis of the SiO outflow,which may indicate that higher energy HC₃N transitions are excited by interaction between pre-existing dense medium and shocks generated by SiO outflows.Meanwhile,Orion KL is one of the prime templates of astrochemical and prebiotic chemical studies.We wish to explore more organic molecules with increasing com-plexity in this region.In particular,we have searched for one of the most complex organic molecules detected in space so far,ethyl formate?C₂H₅OCHO?.This species is the next step in chemical complexity after the simplest member of esters?methyl for-mate,CH₃OCHO?.The mechanisms leading to its formation are still poorly known.In large bandwidth from 214 to 247 GHz by using ALMA observations,we have detected111 unblended lines of C₂H₅OCHO?62 and 49 of the trans and gauche conformers,re-spectively?.The line images showed that C₂H₅OCHO arises mainly from the compact ridge and the hot core.The derived rotational temperatures and column densities are90±15 K,?2.2±0.6?×10¹⁶cm^-2for the hot core,and 78±22 K,?1.2±0.4?×10¹⁶cm^-2for the compact ridge.The comparison of spatial distribution and abundance ratios with chemically related molecules?methyl formate,ethanol and formic acid?indicates that C₂H₅OCHO is likely formed on the surface of dust grains by addition of CH₃to functional-group radicals?CH₂OCHO?derived from methyl formate?CH₃OCHO?.