We present the first results of the MIRIAD (MIPS InfraRed Imaging of AGB Dust shells) project using the Spitzer Space Telescope. The primary aim of the project is to probe the material distribution in the extended
circumstellar envelopes (CSEs) of evolved stars and recover the fossil record of their mass-loss history. Hence, we must map the whole of the CSEs plus the surrounding sky for background subtraction while avoiding the
central star that is brighter than the detector saturation limit. With our unique mapping strategy, we have achieved better than 1 MJy sr 1 sensitivity in 3 hr of integration and successfully detected a faint (!5 MJy sr 1), extended (∼400 ) far-infrared nebula around the asymptotic giant branch (AGB) star R Hya. Based on the parabolic structure of the nebula, the direction of the space motion of the star with respect to the nebula shape, and the presence of extended Ha emission cospatial to the nebula, we suggest that the detected far-IR nebula is due to a bow shock at the interface of the interstellar medium and the AGB wind of this moving star. This is the first detection of the stellar-wind bow shock interaction for an AGB star and exemplifies the potential of Spitzer as a tool to examine the detailed structure of extended far-IR nebulae around bright central sources.This work is based on observations made with the Spitzer Space Telescope, which is operated by the JPL/Caltech under a contract with NASA. Support for this work was provided
by NASA through an award issued by JPL/Caltech. We also acknowledge additional support for the following individuals:
an NPP Research Fellowship Award to T. Ueta, NASA ADP grant NAG 5-12675 to A. K. Speck, the LDRD program (20060357ER) at LANL for F. Herwig, NASA contract 1215746 issued by JPL/Caltech to R. D. Gehrz, grant
2.P03D.017.25 to R. Szczerba, a Grant-in-Aid (C) from JSPS (17540221) to H. Izumiura, JSPS for M. Matsuura, and NSF grant AST 05-07421 to M. Elitzur. We thank C. J. Wareing for sharing his insights on the stellar-wind bow shocks with us
