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The Dispersed Population of Dusty Young Stellar Objects in the Orion OB1 Association B. Mazur 1 , T. Megeath 1 , R. Gutermuth 2 , C. Briceno 3 , J. Hernandez 3 , J. Stauffer 4 1: U. of Toledo; 2: U. of Mass; 3: CIDA, Venezuela; 4: Spitzer Science Center Following the exhaustion of the cryogenic fluids, a `warm’ mission survey extended the of the off-cloud region in the Orion/OB1 association complex. These data supplement the existing surveys of the σ Orionis cluster and OB1b fields. Assemble a photometric catalogue of the extended region using Spitzer augmented with available 2MASS and WISE data. • Using only the three 2MASS bands and two IRAC bands at 3.6μm and 4.5μm, we estimate a recovered fraction of between 90 − 70%, when compared to the 3 + 4 band detections. • Using disc fractions measured by Hernandez et al. 2007, one can estimate a total off-cloud population, excluding the σ Orionis cluster, 3000 − 8500 young stars.
