Science observations with the Keck Interferometer Nuller

The Keck Interferometer Nuller (KIN) is now largely in place at the Keck Observatory, and functionalities and performance are increasing with time. The main goal of the KIN is to examine nearby stars for the presence of exozodiacal emission, but other sources of circumstellar emission, such as disks around young stars, and hot exoplanets are also potential targets. To observe with the KIN in nulling mode, knowledge of the intrinsic source spectrum is essential, because of the wide variety of wavelengths involved in the various control loops - the AO system operates at visible wavelengths, the pointing loops use the J-band, the high-speed fringe tracker operates in the K-band, and the nulling observations take place in the N-band. Thus, brightness constraints apply at all of these wavelengths. In addition, source structure plays a role at both K-band and N-band, through the visibility. In this talk, the operation of the KIN is first briefly described, and then the sensitivity and performance of the KIN is summarized, with the aim of presenting an overview of the parameter space accessible to the nuller. Finally, some of the initial observations obtained with the KIN are described.