* Astronomy

Title: Spitzer IRAC observations of newly-discovered planetary nebulae from the Macquarie-AAO-Strasbourg H-alpha Planetary Nebula Project
Authors: Martin Cohen (1), Quentin A. Parker (2,3), Anne J. Green (4), Tara Murphy (4,5), Brent Miszalski (2,6), David J. Frew (2,7), Marilyn R. Meade (8), Brian Babler (8), Remy Indebetouw (9), Barbara A.Whitney (10), Christer Watson (11), Edward B. Churchwell (8), Douglas F. Watson (8) ((1) Radio Astronomy Lab., UC-Berkeley, CA, (2) Department of Physics, Macquarie University, Sydney, Australia, (3) Anglo- Australian Observatory, Epping, Australia, (4) School of Physics, University of Sydney, NSW, Australia, (5) School of Information Technologies, University of Sydney, NSW, Australia, (6) Observatoire Astronomique, Universite Louis Pasteur, Strasbourg, France, (7) Perth Observatory, Bickley, WA, Australia, (8) Dept. of Astronomy, University of Wisconsin, Madison, WI, (9) Astronomy Dept., University of Virginia, Charlottesville, VA, (10) Space Science Institute, Boulder, CO, (11) Dept. of Physics, Manchester College, North Manchester, IN)

We compare H-alpha, radio continuum, and Spitzer Space Telescope (SST) images of 58 planetary nebulae (PNe) recently discovered by the Macquarie-AAO-Strasbo- urg H-alpha PN Project (MASH) of the SuperCOSMOS H-alpha Survey. Using InfraRed Array Camera (IRAC) data we define the IR colours of PNe and demonstrate good isolation between these colours and those of many other types of astronomical object. The only substantive contamination of PNe in the colour-colour plane we illustrate is due to YSOs. However, this ambiguity is readily resolved by the unique optical characteristics of PNe and their environs. We also examine the relationships between optical and MIR morphologies from 3.6 to 8.0um and explore the ratio of mid-infrared (MIR) to radio nebular fluxes, which is a valuable discriminant between thermal and nonthermal emission. MASH emphasises late evolutionary stages of PNe compared with previous catalogues, enabling study of the changes in MIR and radio flux that attend the aging process. Spatially integrated MIR energy distributions were constructed for all MASH PNe observed by the GLIMPSE Legacy Project, using the H-alpha morphologies to establish the dimensions for the calculations of the Midcourse Space Experiment (MSX), IRAC, and radio continuum (from the Molonglo Observatory Synthesis Telescope and the Very Large Array) flux densities. The ratio of IRAC 8.0-um to MSX 8.3-um flux densities provides a measure of the absolute diffuse calibration of IRAC at 8.0 um. We independently confirm the aperture correction factor to be applied to IRAC at 8.0um to align it with the diffuse calibration of MSX. The result agrees with the recommendations of the Spitzer Science Centre and with results from a parallel study of HII regions. These PNe probe the diffuse calibration of IRAC on a spatial scale of 9-77 arcsec.

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