Millimeter Observations of Vibrationally Excited CS toward IRC +10216: A New Circumstellar Maser?
Millimeter Observations of Vibrationally Excited CS toward IRC +10216: A New Circumstellar Maser?
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IRC 10216 振动激发 CS 的毫米级观测：一种新的环星微波激射器？
DOI：
10.1086/317242
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发表时间：
2000
期刊：
影响因子：
--
通讯作者：
J. Mangum
中科院分区：
文献类型：
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作者：
Circumstellar Maser;J. L. Highberger;J. Bieging;L. Ziurys;J. Mangum
利用NRAO 12 m望远镜和CSO对IRC +10216星周壳层进行了振动激发CS的新观测。在146、292和340 GHz的v = 1能级上检测到J = 3 → 2、6 → 5和7 → 6跃迁，并再次观察到J = 2 → 1和5 → 4谱线。在考虑了来自其他物质的污染后，这些CS跃迁都表现出比IRC +10216中大多数分子更窄的谱线轮廓（ΔV1/2 ~ 10 km s-1），表明起源于内部恒星包层。J = 3 → 2线特别窄（ΔV1/2 ~ 1-2 km s-1），由VLSR ~ -26和-22 km s-1处的两个独立速度分量组成。这些特征表明在这次转变中微波激射作用较弱。在其他跃迁中观察到的窄线宽表明源尺寸为100.“5，这意味着在v = 1状态下CS列密度约为2-6 × 1016 cm-2。因此，当Tvib = 500 K时，基态（v = 0）柱密度约为0.8-2 × 1018 cm-2。因此，在~ 14 R* 下，CS相对于H2的丰度分数为f ~ 3-7 × 10-5。在恒星光球层附近有如此高的丰度，是强有力的证据，证明CS是IRC +10216的“母”分子，这是由v = 0 → 1振动跃迁的红外研究和干涉观测所提出的。
New observations of vibrationally excited CS in its v = 1 state have been conducted toward the circumstellar shell of IRC +10216 using the NRAO 12 m telescope and the CSO. The J = 3 → 2, 6 → 5, and 7 → 6 transitions in the v = 1 level at 146, 292, and 340 GHz have been detected toward this object, and the J = 2 → 1 and 5 → 4 lines were also reobserved. After accounting for contamination from other species, these CS transitions all exhibit line profiles that are narrower (ΔV1/2 ~ 10 km s-1) than those displayed by most molecules in IRC +10216, indicating an origin in the inner stellar envelope. The J = 3 → 2 line is particularly narrow (ΔV1/2 ~ 1-2 km s-1), and consists of two separate velocity components at VLSR ~ -26 and -22 km s-1. These characteristics are suggestive of weak maser action in this transition. The narrow line widths observed in the other transitions indicate a source size ≲ 0.″5, which implies a CS column density in the v = 1 state of ~ 2-6 × 1016 cm-2. The ground-state (v = 0) column density is therefore on the order of 0.8-2 × 1018 cm-2 for Tvib = 500 K. The fractional abundance of CS relative to H2 is consequently f ~ 3-7 × 10-5 at ~ 14 R*. Such a high abundance close to the stellar photosphere is strong evidence that CS is a "parent" molecule in IRC +10216, as suggested by infrared studies of the v = 0 → 1 vibrational transition and interferometric observations.