ICE AND DUST IN THE PRESTELLAR DARK CLOUD LYNDS 183: PREPLANETARY MATTER AT THE LOWEST TEMPERATURES
ICE AND DUST IN THE PRESTELLAR DARK CLOUD LYNDS 183: PREPLANETARY MATTER AT THE LOWEST TEMPERATURES
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星前暗云中的冰和尘埃 LYNDS 183：最低温度下的行星前物质
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
A. Adamson
中科院分区：
文献类型：
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作者：
D. Whittet;C. Poteet;J. Chiar;L. Pagani;V. Bajaj;David Horne;Sachindev S. Shenoy;A. Adamson
尘埃颗粒是静止的星际云中冰盖生长的成核中心和催化剂，当新的恒星和太阳系在星云中形成时，其产物可能会积累成行星前物质。本文首次对L183(L134N)前恒星核附近的硅酸盐尘埃和分子冰H2O、CO和CO2进行了光谱探测。对该星云的红外光度测量被用来识别变红的背景恒星，我们给出了其中9颗恒星在2-20 μm波长范围内的固态吸收特征的光谱。在研究最深入的视线(朝向J15542044−0254073)，冰的平均组成为H2O：CO：CO2≈100：40：24。冰的结构是无定形的，表明它们自形成以来一直保持在低温(≲15K)。冰柱密度N(H2O)与尘埃变红有关，表现出一种阈值效应，对应于从云外层的无盖颗粒向内部有冰覆盖的颗粒的转变，类似于在其他暗云中观察到的情况。对L183和金牛座以及IC5146暗云的结果的比较表明了共同的行为，在每个例子中，地幔首先出现在与硅酸盐特征的峰值光学厚度τ9.7=0.15±0.03相对应的尘埃柱上。我们的结果支持了以前的结论，即颜色过剩EJ−K与截获稠密云的视线上的总尘埃柱并不服从简单的线性相关。最有可能的解释是，随着密度的增加，尘埃的光学性质发生了系统性的变化。
Dust grains are nucleation centers and catalysts for the growth of icy mantles in quiescent interstellar clouds, the products of which may accumulate into preplanetary matter when new stars and solar systems form within the clouds. In this paper, we present the first spectroscopic detections of silicate dust and the molecular ices H2O, CO, and CO2 in the vicinity of the prestellar core L183 (L134N). An infrared photometric survey of the cloud was used to identify reddened background stars, and we present spectra covering solid-state absorption features in the wavelength range 2–20 μm for nine of them. The mean composition of the ices in the best-studied line of sight (toward J15542044−0254073) is H2O:CO:CO2 ≈ 100:40:24. The ices are amorphous in structure, indicating that they have been maintained at low temperature (≲ 15 K) since formation. The ice column density N(H2O) correlates with reddening by dust, exhibiting a threshold effect that corresponds to the transition from unmantled grains in the outer layers of the cloud to ice-mantled grains within, analogous to that observed in other dark clouds. A comparison of results for L183 and the Taurus and IC 5146 dark clouds suggests common behavior, with mantles first appearing in each case at a dust column corresponding to a peak optical depth τ9.7 = 0.15 ± 0.03 in the silicate feature. Our results support a previous conclusion that the color excess EJ − K does not obey a simple linear correlation with the total dust column in lines of sight that intercept dense clouds. The most likely explanation is a systematic change in the optical properties of the dust as the density increases.