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On 15 February 2013, the asteroid 367943 Duende (2012 DA14) experienced anear-Earth encounter at an altitude of 27,700 km or 4.2 Earth radii. We presenthere the results of an extensive, multi-observatory campaign designed to probefor spectral and/or rotational changes to Duende due to gravitationalinteractions with the Earth during the flyby. Our spectral data reveal nochanges within the systematic uncertainties of the data. Post-flyby lightcurvephotometry places strong constraints on the rotation state of Duende, showingthat it is in non-principal axis rotation with fundamental periods of P_1 =8.71 +/- 0.03 and P_2 = 23.7 +/- 0.2 hours. Multiple lightcurve analysistechniques, coupled with theoretical considerations and delay-doppler radarimaging, allows us to assign these periods to specific rotational axes of thebody. In particular we suggest that Duende is now in a non-principal, shortaxis mode rotation state with a precessional period equal to P_1 andoscillation about the symmetry axis at a rate equal to P_2. Temporal andsignal-to-noise limitations inherent to the pre-flyby photometric dataset makeit difficult to definitively diagnose whether these periods represent a changeimparted due to gravitational torques during the flyby. However, based onmultiple analysis techniques and a number of plausibility arguments, we suggestthat Duende experienced a rotational change during the planetary encounter withan increase in its precessional rotation period. Our preferred interpretationof the available data is that the precession rate increased from 8.4 hoursprior to the flyby to 8.7 hours afterwards. A companion paper by Benson et al.(2019) provides a more detailed dynamical analysis of this event and comparesthe data to synthetic lightcurves computed from a simple shape model of Duende.(abbreviated abstract)

Observational Investigation of the 2013 Near-Earth Encounter by Asteroid (367943) Duende