Abstract
We have found that positions in the 2MASS All-sky Catalog of Point Sources show local systematic differences with characteristic length-scales of ∼ 5 to ∼ 8 arcminutes when compared with several catalogs. We have observed that when 2MASS positions are used in the computation of proper motions, the mentioned systematic differences cause systematic errors in the resulting proper motions. We have developed a method to locally rectify 2MASS with respect to UCAC4 in order to diminish the systematic differences between these catalogs. The rectified 2MASS catalog with the proposed method can be regarded as an extension of UCAC4 for astrometry with accuracy ∼ 90 mas in its positions, with negligible systematic errors. Also we show that the use of these rectified positions removes the observed systematic pattern in proper motions derived from original 2MASS positions.
