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A distance scale of planetary nebulae based on mid-infrared data

Some of the most successful statistical methods for obtaining distances of planetary nebulae (PNe) are based on their apparent sizes and radio emission intensities. These methods have the advantage of being "extinction-free" and are especially suited to be applied to PNe situated at large distances. A similar method, based on the mid-infrared (MIR) emission of PNe, would have the advantage of being applicable to the large databases created after the various all-sky or Galactic plane infrared surveys, such as IRAS, MSX, ISOGAL, GLIMPSE, etc. In this work we propose a statistical method to calculate the distance of PNe based on the apparent nebular radius and the MIR flux densities. We show that the specific intensity between 8 and 21 micron is proportional to the brightness temperature T_b at 5 GHz. Using MIR flux densities at 8, 12, 15 and 21 microns from the MSX survey, we calibrate the distance scale with a statistical method by Stanghellini et al. 2008 (SSV). The database used in the calibration consisted of 67 Galactic PNe with MSX counterparts and distances determined by SSV. We apply the method to a sample of PNe detected at 8 microns in the GLIMPSE infrared survey, and determine the distance of a sample of PNe located along the Galactic plane and bulge.