PI: Raghvendra Sahai, Jet Propulsion Laboratory, email@example.com
Address: Astrophysics and Space Sciences, 4800 Oak Grove Drive, Pasadena, CA 91109
CoI: Ken Hinkle, NOAO
CoI: Mark Morris, UCLA
Title: A Stellar Interloper Speeding through a Dense Interstellar Cloud
Abstract: We propose a high-spectral-resolution K-band study of I 18555, the prototype of a new class of serendipitously discovered stars interacting with the interstellar medium (``stellar interlopers"). These objects are likely runaway intermediate-mass stars with strong winds, which are moving through a locally dense ISM and forming bow-shocks and other shocked-gas structures. Optical HST images show highly-structured nebulosities associated with the interlopers. There has been little or no study of such objects as a class; the closest analogs are the far-IR bow-shocks seen associated with massive runaway stars. We have found many interlopers from our HST survey, and have begun a multiwavelength follow-up program to study this class. In I 18555, which shows a cometary-shaped head and a spiral-shaped wake (suggesting the presence of a wide binary companion), the star is obscured optically, most likely due to an edge-on accretion disk. We have found disk CO bandhead emission in I 18555 from hot (few\times1000 K) gas; such emission has been found in other young stellar objects. We propose to use Phoenix to obtain high spectral resolution observations of the CO bandhead emission; the data will enable us to distinguish between Keplerian disk emission and wind models. Observations of shocked H_2 2.1\micron lines will probe the detailed kinematics of the shocked gas in the tail, which is necessary to understand the presumably precessing, collimated outflow that has created its shape and structure.
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