A Program of High-Resolution Infrared Astronomical Spectroscopy

在美国国家科学基金会的支持下，德克萨斯大学的John Lacy博士开发了德克萨斯梯队交叉梯队光谱仪（TEXES）。TEXES可用于几种模式：高分辨率交叉分散，中低分辨率长缝和源采集成像。它工作在5-25微米光谱区域。TEXES的高分辨率能力是独一无二的。没有其他中红外天文光谱仪具有类似的分辨率和灵敏度的组合。TEXES由仪器小组操作，但对天文学界的所有成员开放。Lacy博士及其同事将进行的观测项目包括研究恒星形成区域的分子气体、超紧凑HII区域的电离气体、原行星盘中的分子和行星大气中的分子。红外光谱提供了几种独特的星际分子探测，特别是研究像C2H2和CH4这样没有永久偶极矩的分子的能力。对猎户座KL恒星形成区C2H2和HCN的TEXES初步观测显示，这些线条由多个窄组分组成，表明气体的精细尺度聚集。进一步的观测将提供有关原恒星风与周围气体相互作用的信息，以及对几种分子丰度的测量，这些分子丰度显示了恒星形成对分子云化学的影响。高质量恒星形成的六个区域将被研究。超紧凑的HII区域是年轻的大质量恒星的显著标志，但它们的结构，特别是它们的寿命还没有得到很好的理解。红外离子精细结构线比其他探测这种被遮蔽的电离气体的探针有显著的优势，因为它们提供了丰度、物理条件和运动学的信息，而没有氢谱线的大热增宽。对各种形态的超压缩H II区域进行调查，目的是区分这些对象的不同模型。与近红外和毫米观测相比，年轻恒星周围的气体盘的中红外光谱探测了1-10 AU的行星形成区域。用TEXES应该可以观测到H2， H2O，可能还有C2H2和NH3的谱线，尽管最初的观测结果似乎与ISO卫星获得的光谱结论相矛盾。如果可以测量多普勒谱线，它们将提供圆盘中半径分子分布的信息，也许会显示形成行星的特征。中红外光谱可能是探测巨行星大气最重要的方法。它们发射的大部分辐射是中红外的，它们的分子成分在中红外有它们的光谱特征。TEXES将用于各种行星研究，目前的计划集中在平流层分子和卫星大气上。＊＊＊

AST-0205518LacyWith previous NSF support, Dr. John Lacy, at the University of Texas, developed the Texas Echelon Cross Echelle Spectrograph (TEXES). TEXES can be used in several modes: high resolution cross-dispersed, low to medium resolution long-slit, and source-acquisition imaging. It operates in the 5-25 micrometer spectral region. TEXES's high resolution capabilities are unique. No other mid-infrared astronomical spectrograph has a comparable combination of resolution and sensitivity. TEXES is operated by the instrument team, but is available to all members of the astronomical community. Observational projects to be carried out by Dr. Lacy and colleagues with this award include studies of molecular gas in star-formation regions, ionized gas in ultracompact HII regions, molecules in protoplanetary disks, and molecules in planetary atmospheres. Infrared spectroscopy provides several unique probes of interstellar molecules, notably the abilityto study molecules like C2H2 and CH4 without permanent dipole moments. Initial observationswith TEXES of C2H2 and HCN in the KL star-formation region in Orion show the lines to consistof multiple narrow components indicative of fine-scale clumping of the gas. Further observationswill provide information about the interaction of a protostellar wind with surrounding gas, as wellas measurements of the abundances of several molecules showing the influence of star formation onmolecular cloud chemistry. Six regions of high-mass star formation will be studied. Ultracompact HII regions are prominent sign-posts of young, very massive stars, but their structure and especially their longevity is not well understood. Infrared ionic fine-structure lines have significant advantages over other probes of such obscured ionized gas in that they provide information about abundances, physical conditions, and kinematics without the large thermal broadening of hydrogen lines. A survey of ultracompact H II regions of various morphologies will be carried out with the goal of distinguishing among different models of these objects. In contrast to near-infrared and millimeter observations, mid-infrared spectroscopy of gas disks around young stars probes the 1-10 AU planet-forming region. Lines of H2, H2O, and possibly C2H2 and NH3 should be observable with TEXES, although initial observations appear to contradict conclusions from spectra taken with the ISO satellite. If line Doppler profiles can be measured, they will provide information on the distribution of molecules with radius in the disks, perhaps showing the signature of forming planets. Mid-infrared spectroscopy is probably the most important probe of the atmospheres of the giant planets. Most of their emitted radiation is in the mid-infrared, and their molecular constituents have their spectral signatures in the mid-infrared. TEXES will be used for a variety of planetary studies, with current plans concentrating on stratospheric molecules and atmospheres of moons. ***