Near-infrared colors of asteroid 2012 DA14 at its closest approach to Earth: Observations with the Nishiharima Infrared Camera (NIC)
We present the results of our JHKs photometry of asteroid 2012 DA14 at its closest approach to Earth on 2013 February 15. Possible spectral changes associated with resurfacing by planetary encounters are of great interest. The Earth flyby of 2012 DA14 provided a rare opportunity to investigate this effect. Our observations were conducted using the Nishiharima Infrared Camera (NIC) attached to the 2.0 m Nayuta telescope at the Nishi-Harima Astronomical Observatory. Despite the extraordinarily fast sky motion of up to near 50″ s-1, the telescope successfully tracked the asteroid. The NIC achievement of three-band simultaneous observations allowed us to reliably deduce the colors of this fast-moving object. The derived near-infrared relative reflectances are flat, which is consistent with the classification of the asteroid as L-type. The J - H and H - Ks colors at 0.5-1 hr after the closest approach are compared with those observed by de León (2013, A&A, 555, L2) at ∼ 10 hr after the closest time. We did not detect color changes significantly exceeding the photometric errors, which are ∼ 0.1 mag. This project has demonstrated the potential of the NIC as a three-band simultaneous imager, especially for observations of rapidly time-variable phenomena.