低質量原恆星盤IRAS 16293-2422之溫度及含氘分子研究

A Study of the Temperature Profile and Deuterated Molecules in the Low-Mass Protostellar Sources IRAS 16293-2422

黃慧春(Hui-Chun Huang)

指導教授 ： 管一政

國立臺灣師範大學/理學院/地球科學系/博士(2009年)

摘要

我們使用SMA干涉儀陣列觀測到低質量年輕天體IRAS 16293-2422之CH3CN分子，並得知其原雙天體中I16293A之兩種速度分佈組成(1.1 km/s和5.2 km/s)。而另一天體I16293B因訊號較弱而無法量得較可信之動能溫度。天體I16293A所得到之藍移和紅移速度組成之動能溫度分別為165 K和711 K，而單一速度組成所對應之溫度為274 K。加上由CH3OH分子及HCOOCH3分子得到之轉動激發溫度分別為Trot > 250 K和Trot > 150 K，以及在此天體上觀測到之豐富有機分子，皆強烈支持此一接近重質量恆星形成區熱分子雲核之低質量熱核〝corinos〞的存在。我們並首次於此低質量天體I16293偵測到七種含氘分子的空間分佈。除CH3OD/CH3OH之分子比例為0.01 (I16293A)之外，其他分子所得之比例，如DCN /HCN (I16293A 為0.05)、D2CO/H2CO (I16293A為0.49; I16293B為1.04)、HDCS/H2CS (I16293A為0.014; I16293B為0.06)以及CH2CDCN/CH2CHCN (I16293A為0.07； I16293B為0.34)，多高於之前單一天線所得到之比值，此一結果暗示含氘分子的分佈較其氫飽和分子之分佈為密集。我們在此低質量原恆星核所得之含氘分子的高比值，與近來我們於長週期彗星C/2002 T7所得之HDCO/H2CO的高比值(~0.8)觀測結果一致。此結果強烈暗示星際中之重氫分子與低質量天體演化路徑接近之原太陽星雲有關聯。

關鍵字

低質量原恆星盤 ； 含氘分子 ； 動能溫度 ； 恆星形成

並列摘要

The solar-type source IRAS 16293-2422 were observed with methyl cyanide, and two velocity components C-v 1.1 and rv5.2 km S-l) were recognized in 116293A. The poor S/N ratios in 116293B make the temperature measurements unreliable. For 116293A, the kinetic temperatures are 165 K and 711 K for the blue and red velocity components, and 274 K for the combined single-component. Together with the high
rotational excitation temperatures inferred from CH30H (T叫> 250 K) and HCOOCH3 (T叫> 150 K) , and the rich organic inventory observed in 116293, the existence of low-mass hot cores "corinos鬥similar to the HMCs in massive star-forming regions is strongly supported. The spectral emission of 7 deuterated molecular species in 116293 is successfully imaged the first time. Except the CH30D/CH30H ratio (rvO.01 for 116293A), other fractionation ratios we derived, s叫1 as DCN /HCN (rvO.05 for 116293A), D2CO /H2CO (rv0.49 for 116293人 rv l.04 for 116293B), HDCS/H2CS (rvO.014 for 116293A, rvO.06 for 116293B) and CH2CDCN/CH2CHCN (rvO.07 for 116293人rvO.34 for 116293B), are mostly higher than those obtained from single-dish measurements implying the distribution of these deuterated species are spatially more compact than their corresponding abundant species. The extreme fractionation ratios found in solar-type protostellar cores are in good agreement with our recent finding ofhigh [HDCO]/[H2CO] ratio (rvO.8) in the long-period comet C/2002 T7. This s時gests strongly that interstellar deuteration may have a strong connection
to our presolar nebula, which may have gone through evolutionary stages similar to that of low-mass stellar objects!

並列關鍵字

low-mass protostellar disk ； deuterated molecule ； kinetic temperature ； star formation