木星族彗星 73P/Schwassmann-Wachmann 3 及歐特雲族彗星 C/2007 W1 Boattini 之毫米波段觀測

Abstract

彗星，保存最原始的物質，也被認為是保留早期太陽系形成過程中產生的分子。因此，對於我們對太陽系形成的理解，包括太陽型的低質量恆星的形成和觀測彗星的分子都相當重要。我們在2006年5月利用兩座位於亞利桑那州的電波天文台: 基特峰12米望遠鏡（KP12M）和次毫米波望遠鏡（SMT），來觀測木星族彗星73P/Schwassmann-Wachmann（73P-B）和C（73P-C），和2008年6月歐特雲族彗星（OCCs）C/2007 W1（Boattini），。 我們尋找彗星的CS，氰化氫，H2CO分子，c-C3H2，甲醇和一些氘分子的分子以及最簡單的環分子cyclopropenylidene，c-C3H2，這是一種廣泛分佈在星際介質中的分子。我們也期待觀測到彗星C/2007 W1（Boattini）中的CS、HCN、H2CO與HDCO。和其他已知的彗星相比，73P-B、73P-C的發現HCN相對於水的比值為0.10％和0.11％。我們得出這樣的結論：這兩個彗星碎片是類似的化學成分和他們分裂以來，已通過了類似的化學演化，這樣的結果可能暗示，木星族彗星形成類似太陽的距離。 彗星C/2007 W1（Boattini）被觀察到有大量的CS，但很少HCN。此外，觀測到的CS 為0.35％，和海爾－波普彗星相比(0.40％); 我們認為Boattini為迄今觀察到彗星中非常特殊的一顆。

Comets, the most pristine deposits of ice, are thought to preserve molecules produced during the formation of early Solar System. Thus, knowledge of solar-type low-mass star formation and observations of cometary molecules are both important to our understanding of Solar System formation. To reveal the chemical evolution of Solar Nebula, we observed the break-up of Jupiter Family comet (JFCs) 73P/Schwassmann- Wachmann fragments B (73P-B) and C (73P-C) in 2006 May, and the Oort Cloud comet (OCCs) C/2007 W1 (Boattini) in 2008 June, by using the Kitt Peak 12m telescope (KP12M) and the Submillimeter Telescope (SMT) of Arizona Radio Observatory. We searched for cometary molecular species CS, HCN, H2CO, c-C3H2, CH3OH and some deuterated molecules toward 73P-B and 73P-C. We have HCN clearly detected with production rates of 1.92×1025 sec-1 for 73P-B and 1.40–4.26×1025 sec-1 for 73P-C. The simplest ring molecule cyclopropenylidene, c-C3H2, which is widely distributed in the interstellar medium was tentatively detected in 73P-C. We also looked for CS, HCN, H2CO and HDCO toward Comet C/2007 W1 (Boattini) and had a clear detection of CS at a production rate of 4.30×1025 sec-1, plus a tentative detection of HCN. Compared to other known comets, 73P-B and 73P-C showed similar HCN abundances of 0.10% and 0.11%, typical to JFCs, to each other. With no detection of CS in 73P, and with HCN the only molecule detected securely of similar abundances in both Fragments B and C of 73P, we conclude that these two cometary fragments are of similar chemical compositions and have gone through similar chemical evolution since their breakup; our results may simply imply that most JFCs were formed in regions at similar distances from the Sun. Comet C/2007 W1 (Boattini) was observed to have a large quantity of CS molecules presented but with very few HCN molecules. Furthermore, the observed CS mixing ratio of 0.35% relative to water was found close to that of Comet Hale–Bopp, 0.40%; our finding made Boattini a very special comet among all comets observed to date.