Spectral Irradiance Calibration in the Infrared. XIV. The Absolute Calibration of 2MASS

Element-by-element we have combined the optical components in the three 2MASScameras, and incorporated detector quantum efficiency curves and site-specificatmospheric transmissions, to create three relative spectral response curves(RSRs). We provide absolute 2MASS attributes associated with "zero magnitude"in the JHKs bands so that these RSRs may be used for synthetic photometry. TheRSRs tie 2MASS to the Cohen-Walker-Witteborn framework of absolute photometryand spectra for the purpose of using 2MASS data to support the development ofabsolute calibrators for IRAC and pairwise cross-calibrators between all threeSIRTF instruments. We examine the robustness of these RSRs to changes in watervapor within a night. We compare the observed 2MASS magnitudes of 33 stars(converted from the precision optical calibrators of Landolt and Carter-Meadowsinto absolute infrared calibrators from 1.2-35 um with our predictions, therebyderiving 2MASS "zero point offsets" from the ensemble. These offsets are thefinal ingredients essential to merge 2MASS $JHK_{s}$ data with other absolutelycalibrated bands and stellar spectra, and to support the creation of faintcalibration stars for SIRTF.Comment: 25 pages, Latex, AASTEX5 macros. Revised Table 2 includes updated estimates of some uncertaintie