大質量聯星系統可能形成自不同的機制，例如：盤面分裂、紊流分裂或其他情境，然而，一個系統真實的形成機制很難從為數不多的觀測資料中判斷出來。這邊我們從ALMA的資料庫中選定大質量原恆雙星系統IRAS17216-3801，發表波段位於350GHz的連續譜線和光譜。此資料無法解析雙星系統中由Kraus et al. 2017所發現的各個星體，位於東邊的團塊則是第一次被觀測到，其擁有的分子豐富度比主目標來的少。主目標的光譜主要由一氧化硫及二氧化硫所組成，另外也有甲醇、氰化氫、HCO+分子以及他們的類同位素分子，我們利用二氧化硫和甲醇計算了旋轉能階溫度約為25-178K。許多分子（特別是二氧化硫）都在主目標上呈現出旋轉結構，我們認為這些分子追蹤了圍繞在原恆雙星周圍的雙星周盤，我們利用多組不同能量躍遷的二氧化硫與克卜勒薄盤面模型進行資料擬合來限制雙星周盤的幾何與動態性質，得到盤面傾角37.8◦、盤內徑370-560 au、盤外徑750-1360 au以及位於參考半徑（0."1∼308 au）的盤面旋轉速度8.6 km/s。由此我們計算出系統的動態質量為25.8太陽質量，此數值小於先前Kraus et al. 2017所提出的38太陽質量。新的雙星周盤約束條件及未來雙星系統各個星體的觀測資料將給予我們機會探測IRAS17216-3801可能的形成機制。

High-mass multiple systems might form from different mechanisms such as disk fragmentation,turbulent fragmentation, or alternative scenarios. However, it is hard to tell the actual formationmechanism for a system with only few observational constraints. Here, we present the continuum andthe spectral emission of a high-mass protobinary system IRAS17216-3801 from ALMA archival dataat 350 GHz. The observation is unable to resolve each component discovered by Kraus et al. (2017).The east clump is first detected with fewer molecular lines than the main source. The spectrumof the main source is dominated by SO, SO2, and their isotopologues. CH3OH, HCN, HCO+, andtheir isotopologues are also detected from the main source. We calculate the rotation temperaturesof 22-298 K from SO2and CH3OH. We constrain the geometric and kinematic properties of thecircumbinary disk by fitting with a thin-disk Keplerian model from several SO2transitions. Theoptimized model gives the inclination angle (39.6◦), the inner (243 au) and outer radius (1232 au),and the rotation velocity of the disk (9.3 km/s at a reference radius of 0.1"∼308 au). The dynamicalmass of 30.3Mis calculated assuming Keplerian rotation, which is less than the previous study of 38M(Kraus et al. (2017)). The new constraints of the circumbinary disk with the future observationsof each component might allow us to probe the formation mechanism of IRAS17216-3801.

Abstract
List of Figures
List of Tables
1 Introduction--------------------------------------------1
1.1 Massive Star Formation-------------------------------1
1.2 The Formation of High-mass Multiple System-----------2
1.3 IRAS17216-3801---------------------------------------3
1.4 Astrophysical Radiative Processes--------------------3
1.4.1 Radiative Transfer Equation and Planck Function----3
1.5 Telescope Measurements-------------------------------4
2 Observations-------------------------------------------4
2.1 ALMA Observations------------------------------------4
2.2 Imaging----------------------------------------------5
3 Results------------------------------------------------6
3.1 Continuum Emission-----------------------------------6
3.2 Molecular Emission-----------------------------------8
3.2.1 Line Identification--------------------------------8
3.2.2 Channel Maps, Moment Maps and PV Diagrams----------9
4 Analysis-----------------------------------------------23
4.1 Rotation Diagrams------------------------------------23
4.2 The Thin Disk Model for the SO2 Emission-------------33
5 Discussion---------------------------------------------43
5.1 Dynamical Mass---------------------------------------43
5.2 Chemical Composition of the Circumbinary Disk around IRAS17216-3801------------------------------------------------------44
5.2.1 Isotope Ratio--------------------------------------44
5.2.2 The Origin of the Sulfurated Molecules-------------44
5.3 SiO outflows from IRAS17216-3801 B?------------------45
6 Conclusions--------------------------------------------47
A Appendix: Best-fit parameters with the different power-law index of intensity-------------------------------------------------48

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