An Extremely Red Nucleus in an Absorbed QSO at z = 0 . 65

The results of K-band-imaging observations of a candidate of an absorbed QSO at z = 0.653, AX J131831+3341, are presented. The B − K color of the object is 4.85 mag, which is much redder than optically-selected QSOs. The K-band image shows nuclear and extended components, the same as in the optical V -, R-, and I-band images. The nuclear component (I −K = 4.29 mag) is much redder than the power-law models with energy indices of 0 to −1.0, which well reproduce the V −R and R− I optical colors of the nuclear component. A heavily absorbed (AV ∼ 3 mag) nucleus may emerge in the K-band, while optical light may originate from scattered nuclear light. The I −K color of the extended component is 2.2 mag, which is consistent with the post-starburst nature of the host galaxy, which is also suggested from the V −R and R− I colors of the extended component.