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    题名: Millimeter and Submillimeter Observations of Barnard 1-bN and Barnard 1-bS
    作者: 劉芳君;Fang-Chun Liu
    贡献者: 天文研究所
    关键词: 恆星形成;原恆星;star formation;Class 0;protostar;prestellar core
    日期: 2009-05-26
    上传时间: 2009-09-22 10:13:51 (UTC+8)
    出版者: 國立中央大學圖書館
    摘要: 我們利用多波段觀測來研究兩個在巴納德星雲的毫米/次毫米天體,他們的名稱是Barnard 1-bN和Barnard 1-bS。從這兩個天體所發出的塵埃連續輻射訊號,我們發現他們物質分布很緻密,且物質本身相當低溫(塵埃溫度10-16 K)。Spitzer的MIPS望遠鏡所拍出的24和60微米波段影像裡,這兩個天體並沒有被偵測到,這表示他們還包裹在雲深處。由SMA觀測的CO(J=2-1)譜線資料顯現出Barnard 1-bS有噴流,Barnard 1-bN則是疑似有噴流。這些噴流都不是很大(大約2000 AU大小)。這個結果指出這兩個天體已經蘊含著Class 0原恆星。另一方面,這兩個天體的化學特性反而相似於前恆星核:N2D+(J=3-2)譜線訊號很強而且和塵埃連續輻射訊號的分布很一致。反之,H13CO+(J=1-0)譜線訊號則很微弱,甚至是沒有偵測到。這樣的化學特性可能是因為在低溫高密度環境中,H13CO+ 分子已經分解附著在塵粒上所導致。而這樣子的化學特性是相似於前恆星核的化學特性。因此,綜合我們所發現的這兩個天體的物理及化學特性,我們可以知道Barnard 1-bN和Barnard 1-bS是在恆星形成非常早期的天體,他們的演化時期可能正好落在前恆星核時期與Class 0原恆星時期中間。 The physical and chemical properties of two mm/sub-mm sources in Barnard cloud, Barnard 1-bN and Barnard 1-bS, are studied with multi-wavelength observations. The dust continuum from these two sources shows spatially compact distribution and very cold spectral energy distributions (T$_{dust}$=10--16 K). These two sources have no mid-IR counterpart in the Spitzer MIPS 24 and 60 micron bands, indicating that they are deeply embedded. The CO J=2--1 data obtained with the SMA suggest that B1-bS and probably B1-bN are associated with the compact ($sim$ 2000; AU size) molecular outflows. These results suggest that Barnard 1-bN and Barnard 1-bS are already harboring Class 0 protostars. On the other hand, the chemical properties of these two sources are similar to those of pre-stellar cores: the N$_2$D$^+$ J=3--2 emission is strong (0.3 K for B1-bN and 0.1 K for B1-bS) and clearly traces the two compact sources, while the H$^{13}$CO$^+$ J=1--0 emission is weak or barely detected near or at the continuum peaks. This lack of H$^{13}$CO$^+$ emission is probably due to the depletion of the H$^{13}$CO$^+$ molecule onto the grain under the condition of low temperature and high density, as in the case of pre-stellar cores. The observed physical and chemical properties suggest that B1-bN and B1-bS are in the very beginning stage of protostellar evolution, probably in the evolutionary stage between pre-stellar core and class 0 source.
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