The celestial reference frame at K-band; imaging.I

Many of these sources are imaged with submilliarcsecond resolution for the first time at frequencies above X-band (8GHz). From each of the K-band images, we derive the following source properties: peak brightness, core and total flux density, the ratio of peak and core to total flux (compactness measure), radial source extent, structure index, source size, and jet direction.

The vast majority of sources are imaged at multiple epochs, providing insights into their temporal behavior. The use of K-band was motivated by the fact that the sources are generally intrinsically more compact at higher frequencies, as well as by the factor of 3 improvement in interferometer resolution relative to the historically standard S/X band (2.3/8.4GHz) used for a large amount of reference frame and calibrator work.