A Program of High-Resolution Infrared Astronomical Spectroscopy

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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. ***